III - Biochemical Aspects

Effect of Prosopis species on properties of arid zone soils - R.K. Aggarwal

Central Arid Zone Research Institute, Jodhpur 342003, India

Introduction

Tree vegetation during the course of its establishment initiates a series of changes in ecological and soil physico-chemical characteristics, these changes dependent upon the type of vegetation. The rooting pattern, canopy architecture, type and quantity of litter fall and nitrogen fixing ability of arboreal vegetation have a great influence on the fertility and moisture status of the soil.

Nair (1984, 1987) documented the effects of trees on soils in different parts of the world and showed that different mechanisms operate in assessing the role of trees in soil productivity. The magnitude of the beneficial or adverse effects that could be experienced will depend upon a number of site specific factors. Moreover, many of the attributes of trees, as compared with annual crops, can only be realised over long periods of time. In arid regions of western Rajasthan, two species of Prosopis dominate the landscape, the indigenous P. cineraria and P. juliflora, an exotic species of wide ecological amplitude. Both of these are multi-purpose tree species (MPTS) and are an intricate part of life for desert dwellers. The present paper summarises the relative effects of these species on soil productivity parameters in the arid ecosystems of western Rajasthan.

Amelioration of soil fertility

One of the advantages commonly attributed to MPTS in agroforestry is the potential for soil fertility improvement through more efficient cycling of nutrients, a better soil moisture regime and a higher activity of soil micro-organisms. In general, in arid and semi-arid lands, improvement in inherent soil fertility is a slow process. Aggarwal et al. (1976) studied soil fertility changes under a 15 year old stand of Prosopis (Table 1). The results showed the highest levels of organic matter and macro and micro nutrients under P. cineraria, rather than under P. juliflora, with only levels of iron reduced. This could be related to the correlation with higher populations of micro-organisms under these species rather than in the open field situation (Table 2). Soils from below the leaf litter of the two species did not differ in nutritional status.

Singh and Lal (1969) also reported a significant improvement in the fertility status of soils under P. cineraria over P. juliflora in arid regions, and attributed this effect to variations in litter fall, ground flora and the root systems of these tree species. Aggarwal and Kumar (1990) studied the relative availability of nutrients from soil beneath P. cineraria over open field conditions and showed that the relative yield of pearl millet was 2-3 times higher than in the open field soil. The efficiency of applied nitrogen increased from 27% in the open field to 46% in soil under P. cineraria. The gradual accumulation of mineral nutrients by this slow growing tree, and the incorporation of these into an enlarged plant-litter-soil nutrient cycle seems to be the mechanism responsible for this soil enrichment.

The higher content of nitrogen in relation to organic carbon seems due partly to the nitrogen fixed by P. cineraria during the course of its growth (Virginia, 1986) and also due to the higher content of nitrogen in P. cineraria leaf litter over that of P. juliflora. Reviewing the role of nitrogen fixation in MPTS, Dommergues (1987) concluded that the potential direct and ancillary benefits from nitrogen fixing trees vary greatly depending on the species, climate, soil and management practices, and suggested selection of tree species which have high nitrogen fixing potential which are also adapted to the site conditions.

Table 1. Soil fertility under mature stands of P. cineraria and P. juliflora and under adjacent open field, on an arid sandy soil.

Table 2. Microbial population (total numbers per g dry surface soil) under 2 Prosopis species in an arid sandy soil.

The review of Singh and Das (1984) indicated that under the semi-arid conditions of Hyderabad, Leucaena leucocephala can yield foliage containing 500-600 kg N/ha, and after 6 years of alley cropping with L. leucocephala on a pH 6 entisol soil, plots receiving prunings had a higher nutritional status and twice the organic matter content of plots not receiving prunings. Juo and Lal (1977) also compared the effects of a Leucaena fallow versus a bush fallow on selected soil chemical properties on alfisols in western Nigeria, and found a significant increase in the cation exchange capacity and levels of exchangeable calcium and potassium under Leucaena. Some tree and shrub species can selectively accumulate certain nutrients, even in soils containing very low amounts of these nutrients, and such species have therefore an important role to play in agroforestry systems.

Improvement in soil physical conditions

Over time, the growth of MPTS can also lead to improvements in physical attributes of soil such as infiltration rate, water holding capacity, and moisture availability through the indirect effects of litter fall, understory growth and root distribution, depending on the species and site conditions. Aggarwal et al. (1976) and Gupta and Saxena (1978), studied the effects of trees on soil physical characteristics after 15 years growth and observed higher moisture content in soils under the canopy of P. cineraria than under P. juliflora. This was attributed to a relatively higher organic matter content, litter fall and a deeper root distribution, confirmed by a higher depletion of moisture from deeper layers under P. cineraria, compared to the surface spread of lateral roots of P. juliflora which depleted moisture from shallow soil layers. Hazra (1989) also reported an increase in field capacity from 14.1% to 16.2% and a decrease in bulk density from 1.58 to 1.37 g/cm³ in soil under the canopy of Albizia lebbek as compared to the open field.

Soil conservation

Along with the improvement in soil fertility, soil physical and micro-climatic conditions, the trees play an important role in soil binding processes and the reduction in the eroding action of both water and wind. Gupta et al. (1984) observed a 36% reduction in the magnitude of wind erosion behind a P. juliflora shelterbelt in western Rajasthan. In a 3 month period from April to June, mean soil loss over a 2 year period (1979-80) was 351.2 kg/ha on leeward of the shelterbelt and 546.8 kg/ha in adjacent unprotected soil.

Conclusion

The comparison of the two widespread Prosopis species in arid environments reveals the differential behaviour in soil amelioration effects, which can be a better index for their utilisation in different land use systems. P. cineraria, with a taproot system having the potential of improving soil fertility, can be more suitable for agroforestry land use systems, tree density varying with rainfall. P. juliflora however, having a lower potential in improving soil conditions and a spreading lateral root system, would be more suitable for the revegetation of wastelands and sand dunes, and for use in shelterbelts for arresting sand and soil movement.

References

Aggarwal, R.K., J.P. Gupta, S.K. Saxena and K.D. Muthana, 1976. Studies on soil physico-chemical and ecological changes under 12 year old five desert tree species of western Rajasthan. Indian Forester 102: 863-872.

Aggarwal, R.K. and P. Kumar, 1990. Nitrogen response to pearl millet (Pennisetum typhoides S&H) grown on soil underneath P. cineraria and adjacent open site in an arid environment. Annals of the Arid Zone 29: 289-293.

Dommergues, Y.R., 1987. The role of biological nitrogen fixation in agroforestry. In: H.A. Steppter and P.K.R. Nair (eds.), Agroforestry: A Decade of Development. ICRAF, Nairobi.

Gupta, J.P., G.G.S.N. Rao, Y.D. Rama Krishna and B.B. Ramana Rao, 1984. Role of shelterbelts in arid zone. Indian Farming 34: 29-38.

Gupta, J.P. and S.K. Saxena, 1978. Studies on the monitoring of dynamics of moisture in the soil and the performance of ground flora under desertic communities of trees. Indian Journal of Ecology 5: 30-36.

Hazra, C.R., 1989. Forage productivity under agro-forestry production system. In: Proceedings of an International Symposium on Managing Sandy Soils. Vol II. CAZRI, Jodhpur. pp602-606.

Juo, A.S.R. and R. Lal, 1977. The effect of fallow and continuous cultivation on the chemical and physical properties of an alfisols in western Nigeria. Plant and Soil 47: 567-584.

Nair, P.K.R., 1984. Soil Productivity Aspects of Agroforestry. ICRAF, Nairobi.

Nair, P.K.R., 1987. Soil productivity under agroforestry. In: H. Gholz (ed.), Agroforestry: Realities, Potentials and Possibilities. Martinus Nijhoff, The Hague. pp21-30.

Singh, S.K. and P. Lal, 1969. Effect of Khejri (Prosopis specigera Linn) and Babool (Acacia arabica) trees on the soil fertility and profile characteristics. Annals of the Arid Zone 8: 33-36.

Singh, R.P. and S.K. Das, 1984. Nutrient management in drylands with special reference to cropping systems and semi-arid red soils. All India Coordinated Research Project for Dryland Agriculture, Bulletin No. 8. Hyderabad, India. 55p.

Virginia, R.A., 1986. Soil development under legume tree canopies. Forest Ecology and Management 16: 69-79.

Amino acids in seeds and seedlings of P. cineraria and P. Juliflora - V.K. Khandelwal and D.N. Sen

Ecology Laboratory, Botany Department, J.N.V. University, Jodhpur 342001, India

Introduction

Prosopis species are of great importance in arid and semi-arid regions of the world and are classified as life supporting species (Shankar, 1987). Similar plant morphology makes species identification difficult, but the use of chemical characters would make species differentiation more objective. Modern methods of chemical analyses, such as chromatography and electrophoresis are relatively cheap, and rapid to assess using relatively small quantities of material. A paper chromatographic analysis is useful in determining if biochemical methods can be used to detect differences between species and possible pathways of speciation.

Materials and methods

From mature seeds and seedlings of the two common Prosopis species of the Indian arid zone, P. cineraria and P. juliflora, 1 g of material was extracted separately in 5 ml of 90% ethanol. This extraction was allowed to continue for 24 h. Of this extract, 1 ml was spotted on Whatman No. 1 chromatographic paper. A mixture of N-butanol, acetic acid, and water (4:1:5) was used as the solvent for chromatography (Block et al., 1958). The separation was carried out in an ascending manner for 12 h. The paper was dried and then sprayed with 0.25% ninhydrin. For identification of amino acids, Rf values were calculated and compared with those of known amino acids obtained under identical conditions.

Table 1. Comparative account of amino acids separation in seeds and seedlings of P. cineraria and P. juliflora by paper chromatography (+ = present; - = not detected).

Results

The seeds and seedlings of both the species contained varying numbers of amino acids (Table 1). Seven amino acids were detected from the seed extract of P. cineraria, with 8 from P. juliflora. Seedling extracts of both species contained 8 amino acids each. In seeds, arginine monohydroxychloride, nor-leucine and methionine were present in both species. In the seeds of P. cineraria, alanine, amino-n-butyric acid, cystine hydrochloride and cystine were also present, while in P. juliflora, aspartic acid, dihydroxyphenylalanine, iso-leucine, tryptophan and tyrosine were also detected. In seedlings, iso-leucine was common in both species.

Seedlings of P. cineraria exhibited the presence of aspartic acid, glycine, histidine monohydroxychloride, leucine, ornithine monohydroxychloride, threonine and tryptophan, none of which were found in P. juliflora. Instead of these amino acids, P. juliflora seedlings had amino-n-butyric acid, glutamic acid, nor-leucine, methionine, phenylalanine, serine and valine. Nor-leucine, iso-leucine and methionine were found to be common in both seeds and seedlings of P. juliflora, although no amino acid was common in seeds and seedlings of P. cineraria.

Discussion

Chromatographic techniques have shown that chemical criteria can be reliable taxonomic guides for speciation. Ashraf and Sen (1978) observed variations in free amino acid contents in the leaves and seeds of two forms of Celosia argentea and Khandelwal and Sen (1993) observed the same in Eragrostis spp. Bhatnagar et al. (1977) reported 2-7 free amino acids in different plant parts of various species growing in the Indian desert. However, a large variation in the free amino acid pool was not found in these studies but several qualitative differences were noted. Hungs and Villanueva (1993) determined amino acid, polyamine and protein concentration in seeds, and their evolution during the germination of two species of Dipterocarpaceae, which showed further support for the present work.

References

Ashraf, N. and D.N. Sen, 1978. Differentiation of amino acids in two forms of Celosia argentea. Linn. Biol. Comtemp 5: 89-90.

Bhatnagar, R., R. Bhusan, S.P. Garg and R.C. Kapoor, 1977. Protein and free amino acid composition of certain Indian desert plants. Trans. Isdt. and Ucds 2: 13-16.

Block, R.J., E.L. Durrum, and G.A. Zweig, 1958. A Manual on Paper Chromatography and Paper Electrophoresis. Academic Press, New York.

Hungs, H. and R.V. Villanueva, 1993. Amino acids, polyamines and protein during seed germination of two species of Dipterocarpaceae. Trees 7: 189-193.

Khandelwal, V.K. and D.N. Sen, 1993. Amino acid differentiation in two species of Eragrostis. Geobios 20: 113-114.

Shankar, V. 1987. Life support species in the Indian Thar desert. In: Life Support Species. Seminar Proceedings. Commonwealth Science Foundation and NBPGR Publishers. IARI, New Delhi. pp37-41.

A plant growth regulator from Prosopis cineraria and Prosopis juliflora - H.A. Khan

Central Arid Zone Research Institute, Jodhpur 342003, India

Introduction

Prosopis cineraria, commonly known as ‘Khejri’, is well known for its economic and medicinal value (Kirtikar and Basu, 1935), and is frequently used as a remedy for rheumatism and as a safeguard against miscarriages in the indigenous systems of medicine (Chopra et al., 1956). A number of compounds have also been reported from P. juliflora, an exotic species now naturalised in most of arid and semi-arid India, the most common of these being steroids, tannins, leucoanthocyanidin and ellagic acid glycosides (Malhotra and Misra, 1983).

Chemical investigations of the waxy part of plant extracts led to the isolation of triacontanol from the galls of P. cineraria (Khan et al., 1987), and from the leaves of both P. cineraria and P. juliflora (Khan et al., 1992). Triacontanol was found to be effective in increasing growth and water uptake of rice seedlings (Reis et al., 1977), and also to promote germination, growth and stubble sprouting in corn and barley. The present paper reports the variation in triacontanol content in different plant parts of P. cineraria and P. juliflora.

Materials and methods

Samples of leaves, pods, galls and bark from P. cineraria and P. juliflora were collected, dried and crushed, and an extract of each was made using petroleum ether (60-80°). The TLC of the extract indicated the presence of triacontanol. Triacontanol (0.01%) was then isolated by preparative TLC and recrystallised from chloroform. The identity of triacontanol was confirmed by m.p., m.m.p. and co-TLC.

Table 1. Triacontanol content in different parts of P. cineraria and P. juliflora.

Results and discussion

The triacontanol contents from the various parts of the two tree species are given in Table 1. The highest levels were recorded in the leaves for both species, with greatly enhanced levels in the leaves of P. juliflora. The presence of such a plant growth promoting substance in the leaves of these Prosopis species may increase the growth of plants under the canopy of trees, that are affected by leaf litter fall. Such increases in the yields of grass under P. cineraria (Shankar et al., 1976) and under P. juliflora (J.C. Tewari, pers. comm.) were postulated to be due to the increased soil fertility around the trees. However, the effects of plant growth substances on the growth of understory vegetation cannot now be discounted.

References

Chopra, R.N., S.L. Nayar and I.C. Chopra, 1956. Glossary of Indian Medicinal Plants. CSIR, New Delhi. 204p.

Khan, H.A., V. Lodha and A. Ghanim, 1987. Plant growth regulator from the galls of Prosopis cineraria. Trans ISDT 12: 149-151.

Khan, H.A., V. Lodha and A. Ghanim, 1987. Triacontanol from the leaves of Prosopis cineraria and Prosopis juliflora. Trans ISDT 17: 29-32.

Kirtikar, K.R. and B.D. Basu, 1935. Indian Medicinal Plants. Volume III. Bishan Singh Maharastra Pal Singh, Dehra Dun, India. 910p.

Malhotra, S. and K. Misra, 1983. Polyphenols from Prosopis juliflora pods. Indian Journal of Chemistry 22: 936-938.

Reis, S.K., C.C. Sweeley and R.A. Leavit, 1977. Triacontanol: a new naturally occurring plant growth regulator. Science 195: 1339.Shankar, V., N.K. Dadhich and S.K. Saxena, 1976. Effect of Khejri Prosopis cineraria MacBride) on the productivity of range grasses growing in its vicinity. Forage Research 2: 91-96.

Seasonal Variations of Metabolic Status of Prosopis juliflora - D.N. Sen and M. Mehta

Ecology Laboratory, Botany Department, J.N.V. University, Jodhpur 342001, India

Introduction

Prosopis juliflora is native to Central and South America, from where the tree has spread to other arid and semi-arid parts of the world, particularly India, where it has been planted on a large scale. The species can thrive on a variety of soils, from sandy to rocky, in regions with 150-750 mm annual precipitation. The roots penetrate deep groundwater to draw moisture and survive extreme drought situations.

In arid conditions, the main factors influencing plant metabolism besides scarcity of water and other soil factors are extremes of temperature, intense solar radiation and high wind velocity. To cope with these stresses, plants possess organised control mechanisms which enable them to grow and survive. Sharples and Burkhart (1954) found that levels of carbohydrates were influenced by various environmental factors and the growth activity of plants. Plants that drastically reduce their metabolic activities below their compensation point will have low carbohydrate requirements, and therefore a greater tolerance to lower assimilation rates than plants without this mechanism (Singh, 1966).

Proteins are substrates of the first order in the metabolism of every organism. It has been reported that considerable hydrolysis of proteins occurs in water stressed plants, and is accompanied by an increase in amino acid content (Chibnall, 1954; Barnett and Naylor, 1966). Proline (pyrrolidine-2-carboxylic acid) is an amino acid which has gained prominence in recent years, due to its phenomenal accumulation in plants subjected to various stress conditions such as water, osmotic, salt and low temperature stress (Dashek and Erickson, 1981; Mohammed and Sen, 1987).

Materials and methods

To understand the metabolic responses of P. juliflora to arid conditions, juvenile and mature leaves were analysed for sugar, crude protein and proline contents. For sugar and crude protein, dry materials were used, and sugars were estimated using Anthrone reagent (Plummer, 1971) and crude protein by the micro-Kjeldahl method (Peach and Tracey, 1955). For free proline, fresh leaves were fixed in a standard volume of 3% sulphosalicylic acid in the field, and quantitatively assessed using the method of Bates et al. (1973).

Results and discussion

Table 1 shows the seasonal variation with regards to sugar, crude protein and free proline. In mature as well as juvenile leaves, more sugar was found in the summer, with 38.61 and 45.55 mg/g dry weight (DW) respectively, and less in the rainy season, with 22.72 and 24.94 mg/g DW respectively. Young leaves were found to have a higher sugar content than mature ones. Crude protein showed little variation between the three seasons in mature leaves, while it was higher throughout in juvenile leaves, reaching a maximum of 29.37% in the rainy season. Proline was higher in the summer in both mature leaves, with 5.18 mg/g fresh weight (FW), as well as young leaves, with 6.28 mg/g FW.

In the Indian arid zone where the climate is hot and dry for most of the year, soil water potentials are often sub-optimal. Excess water loss from the plant body often results in dehydration, which in turn leads to an increase in the concentration of cell sap and intercellular fluid. This causes stress on the protoplasm and most biochemical processes are adversely affected because of the water imbalance.

In the present investigation, sugar was found to be maximum in the summer in P. juliflora leaves, both juvenile and mature. Lekhak (1983) also observed higher sugar values during the summer in P. chilensis and P. cineraria. Mohammed (1988) recorded higher values for sugar content during the rainy season in some saline plants. It has been noted that plant leaves subjected to water stress often show decreases in sugar content (Levitt, 1956), however the sugar content does not increase with all species.

Soluble nitrogenous compounds play essential roles in plant metabolism, being the primary products of inorganic nitrogen assimilation and precursors of proteins and nucleic acids. In this investigation, crude protein was observed to be variable in P. juliflora throughout the year. Nutrient quality of the current year’s growth varies with the growth stage (Blair and Hall, 1968) and similarly, foliar nutrient content varies with leaf age (Blair and Epps, 1967). Protein content is usually highest in the plant parts which are growing rapidly (Hall, 1966). Juvenile leaves of P. juliflora had more protein than mature leaves.

Table 1. Seasonal variation in sugar, crude protein and proline in young and mature leaves of P. juliflora.

The occurrence of a derangement in protein metabolism is a common feature of water stress. Decreases in protein content can be attributed to the enhancement of proteolytic activity resulting in the accumulation of amino acids (Rao et al., 1981). Of all the amino acids, proline is the most stable, least toxic for cell growth and the most resistant to oxidative acid hydrolysis in water stressed plants (Palfi et al., 1974). Accumulation of free proline in leaves has been shown to be an adaptive mechanism for resistance to stress, with accumulation seen in leaves when plants are subjected to low temperature or starvation (Aspinall et al., 1973; Bawa and Sen, 1991). Mohammed and Sen (1987) recorded up to 2,000% increases in proline concentrations in some desert species under water stress compared with well watered (control) plants.

In the present investigation, leaves of P. juliflora had higher proline contents during the summer (i.e., in water stress conditions) and less in the rainy season. The young leaves of P. juliflora had higher values of proline and sugar than the mature leaves which indicate that they are more prone to fluctuating climatic conditions. The overall metabolic changes during conditions of water stress help the plant to survive the harsh climatic conditions of the desert. This along with other adaptive mechanisms, ensures the perpetuation of the species.

References

Aspinall, D., T.N. Singh and L.G. Paleg, 1973. Stress metabolism V. Abscisic acid nitrogen metabolism in barley and Lolium temulentum L. Australian Journal of Biological Science 26: 319-327.

Barnett, N.M. and A.W. Naylor, 1966. Amino acid and protein metabolism in Bermuda grass during water stress. Plant Physiology 41: 1222-1230.

Bates, L.S., R.P. Walden and I.D. Teare, 1973. Rapid determination of free proline for water stress studies. Plant and Soil 39: 205-207.

Bawa, A.K. and D.N. Sen, 1991. Note on proline accumulation in some annual desert grasses as a response to moisture stress. Current Agriculture 15: 85-86.

Blair, R.M. and E.A. Epps, 1967. Distribution of protein and phosphorus in spring growth of rushy blackhaw. Journal of Wildlife Management 31: 188-190.

Blair, R.M. and L.K. Hall, 1968. Growth and forage quality of four southern browse species. Southern Association of Game and Fish Comm., 21st Annual Conference Proceedings. pp57-62.

Chibnall, A.C., 1954. Protein metabolism in rooted runner bean leaves. New Physiology 53: 31-38.

Dashek, W.V. and S.S. Erickson, 1981. Isolation, assay, biosynthesis, metabolism, translocation and functions of proline in plant cells and tissues. Botany Review 47: 349-385.

Hall, L.K., 1966. Seasonal growth of deer browse plants. Proceedings of the 10th International Grassland Congress, Helsinki, Finland. pp987-990.

Lekhak, H.D., 1983. Plant life with special reference to leaf and stomatal behaviour in Indian desert. Ph.D. Thesis, University of Jodhpur, India. (unpublished).

Levitt, J., 1956. The Hardiness of Plants. Academic Press Inc., New York.

Mohammed, S., 1988. Comparative studies of saline and nonsaline vegetation in Indian arid zone. Ph.D. Thesis, University of Jodhpur, India. (unpublished).

Mohammed, S. and D.N. Sen, 1987. Proline accumulation in arid zone plants. Journal of Arid Environments 13: 231-236.

Palfi, G., M. Bito, R. Nehez and R. Schastian, 1974. A rapid production of protein-forming amino acids with the aid of water stress and photosynthesis. Acta Biology 20: 95-106.

Peach, K. and H.V. Tracey, 1955. Modern Methods of Plant Analysis. Springer Verlag, Berlin.

Plummer, D.T., 1971. An Introduction to Practical Biochemistry. Tata McGraw Hill Publishing Co. Ltd., New Delhi.

Rao, G.C., R.K.V. Ramana and G.R. Rao, 1981. Studies on salt tolerance of pigeon pea cultivars. 1. Germination, seedling growth and some physiological changes. Proceedings of Indian Academic Science 90: 555-559.

Sharples, G.E. and L. Burkhart, 1954. Seasonal changes in march grape fruit trees in Arizona. Proceedings of the American Society of Horticulture 63: 74-80.

Singh, P.N., 1966. Studies into the metabolism of crop plants. D.Phil. Thesis, University of Allahabad, India. (unpublished).

Pretreatments to enhance germination of Prosopis juliflora seed - J.C. Tewari, M.D. Bohra, N.K. Sharma, U. Burman and L.N. Harsh

Central Arid Zone Research Institute, Jodhpur 342003, India

Introduction

Prosopis juliflora has proved to be versatile for the afforestation of shifting sand dunes, coastal sands, eroded hills, river beds, saline areas, dry degraded grasslands and wastelands with low and variable rainfall (Muthana, 1988). For the large scale plantation of this species, the raising of nursery grown seedlings is the only practical propagative technique, which requires the use of seed for germination. Repeated attempts to germinate Prosopis seeds inside their endocarps has yielded less than 5% germination (Ffolliot and Thames, 1983). The present investigation reports the effects of different methods of scarification on the germination percentage of P. juliflora, along with describing the phenology of flowering and fruiting, and morphology of the seed.

Materials and methods

Seeds collected from Pali, Falna and Jodhpur, Rajasthan, were removed from the ripe dry pods, air-dried and kept in air-tight containers. One hundred randomly selected pods were measured for their size and then opened to calculate the seed distribution per pod. Seed size, shape, volume and percentage moisture content was determined after Pandeya et al. (1968). Seeds were surface sterilised with 0.1% mercuric chloride for 1 min and rinsed with distilled water. Different pretreatments were then applied; incubation at various temperatures, boiling water, mechanical scarification with sandpaper, a pointed knife and a hot needle burn, and chemical scarification with concentrated sulphuric acid. For determining the response of seeds to electrical shock of different voltages, seeds were immersed in distilled water, acidified with 2 drops of hydrochloric acid, and an electric current of 1.0 A, 1.5 A and 2.0 A was passed through 2 copper plate electrodes for 15 min. All seeds were thoroughly washed with distilled water before being germinated. Each treatment was represented by 3 replicates of 10 seeds, each being placed on moist filter paper in Petri dishes. Germination of untreated seeds at room temperature (28 ^oC ± 2^oC) formed the control for each experiment.

Results and discussion

Some important phenological observations and seed and pod characteristics of P.juliflora are given in Table 1. Early stages of germination comprised of a swelling of the seed, followed by the emergence of the radicle, the whole germination process taking 2-15 days. No further increases in total germination were seen after 14 days in any experiment. The germination of control seeds never exceeded 13%. The incubation of seeds at 60^oC for 12-24 h improved the germination percentage (Table 2). The maximum germination of 50% was recorded with seeds incubated for 24 h at 60^oC, with the onset of the germination process beginning much earlier with 60^oC incubation in the 6, 12 and 24 h duration treatments.

Table 1. Certain phenological attributes, and pod and seed characteristics of P. juliflora.

Seeds undergoing boiling water treatments from 1 to 6 min all exhibited improved germination over the control (Table 3). However, boiling the seeds for more than 1 min resulted in a gradual decline in germination. The boiling of seeds for 1 min gave 27% germination, whereas the corresponding values for 3 min and 6 min boiling water treatments were 20% and 13% respectively. Such responses to boiling water treatments over time has also been reported by Anonymous (1948), Oseni (1979) and Gill et al. (1986) in other leguminous genera. Germination was also improved following electric shock treatment (Table 3). Maximum germination (63%) was recorded with an electric shock of 2.0 A for 15 min. Pandeya et al. (1968) also reported that seeds of many species responded to electric shocks of different voltages. Nelson et al. (1978) found similar results with electric shock pretreatments on P. juliflora seed.

Concentrated sulphuric acid treated seeds exhibited higher germination than boiling water treated seeds (Table 4). Seed soaked for 20 min gave 47% germination, but soaking for 10 min and 15 min gave only 26% and 23% germination respectively. This result with acid scarified seeds of P. juliflora was lower than results seen with seed of other arid zone trees such as Acacia tortilis, A. nilotica and A. senegal which always give more than 70% germination with acid pretreatment. Mechanical scarification of seeds with sand paper, puncturing the seed coat with a pointed knife, and burning the seed coat at one point of its flat surface by a red hot iron needle, all resulted in 90% germination or more after 14 days (Table 4). With the hot needle treatment, 100% germination was observed after 12 days. Ffolliot and Thames (1983) also observed that mechanical scarification is the most effective method of achieving very high germination of Prosopis seeds.

Table 2. Percentage germination of P. juliflora seeds incubated for 30^oC, 40^oC, 50^oC and 60^oC.

Table 3. Percentage germination of P. juliflora seeds following 3 boiling water treatments, and electrical treatment at 3 different currents.

Table 4. Percentage germination of P. juliflora seeds following chemical scarification with concentrated sulphuric acid (H₂SO₄) for 3 time intervals, and mechanical scarification with 3 different methods.

The general concept behind all the pretreatments is to facilitate improved and more rapid water imbibition and gaseous exchange through the seed coat. The hard P. juliflora seed testa causes inhibition via impermeability to water and oxygen and a mechanical barrier to radicle emergence. With mechanical scarification, the seed testa is relatively more weakened than with other treatments. Therefore all the above mentioned processes are initiated quickly, which ultimately results in a higher germination percentage. Mechanical scarification is the recommended method for the pretreatment of Prosopis seed for large scale plantation programmes.

References

Anonymous, 1948. Seed and its development. Wood Plant Seed Manual. Miscellaneous Publication No. 645, USDA, U.S.A.

Ffolliot, P.F. and J.L. Thames, 1983. Collection, handling, storage and pre-treatment of Prosopis seeds in Latin America. FAO, Rome. 45p.

Gill, L.S., R.O. Jagede and S.W.H. Husaini, 1986. Studies on the seed germination of Acacia farnesiana (L.) Wild. Journal of Tree Science 5: 92-97.

Muthana, K.D., 1988. Prosopis juliflora (SW) DC, a fast growing tree to blossom the desert. In: Habit, M.A. and Saavedra, J.C. (eds.), The Current State of Knowledge on Prosopis juliflora. FAO, Rome. pp133-143.

Nelson, S.O., R.W. Bovey and L.E. Stepon, 1978. Germination response of some woody plant seeds to electrical treatment. Weed Science 26: 286-291.

Oseni, C.E., 1979. Hardening treatment of seeds and the effect on their germination and growth. B.Sc. Thesis, University of Benin, Nigeria, 54p (unpublished).

Pandeya, S.C., G.S. Puri and J.S. Singh, 1968. Methods in Plant Ecology. Asia House, Bombay. 272p.

Effect of seed weight and sowing depth on germination and seedling quality of Prosopis juliflora - Neeta Mutha and U. Burman

Central Arid Zone Research Institute, Jodhpur 342002, India

Introduction

Seedling vigour and seed weight have been found to be positively correlated in some tree species (Gonzalez, 1993; Ponnamal et al., 1993). Along with seed weight, sowing at an optimum depth is an important aspect, to obtain higher germination and good quality seedlings (Singh et al., 1973; Chandra and Atma Ram, 1980). This research aims to identify the effect of seed weight and sowing depth on germination and seedling vigour of P. juliflora, an important multi-purpose tree species of arid regions.

Materials and methods

Seeds of P. juliflora were collected from Mandvi region of Kutch, Gujarat, by the Gujarat Development Corporation. These were classified into seven groups of 100 seed each (A to G), based on the mean seed weight, being 1.07, 1.46, 1.93, 2.64, 3.21, 3.44 and 4.00 g respectively. Three seeds were sown in each polythene bag, filled with farm yard manure, soil and sand (1:1:2), each replicate comprising of 35 bags. Watering was carried out when necessary to maintain soil moisture. Germination was recorded daily until no further increase was observed. Germination value (GV) was calculated following Czabator (1962).

For the effects of seed weight on seedling quality, the height and stem diameter of five randomly selected seedlings from each group was measured 15 days after sowing. The shoot and root were separated, and oven dried at 80-85^oC for 72 h. The quality of seedlings obtained from each group of seed was described on the basis of data collected 36 days after sowing, following the Dickson Quality Index (DQI) (Dickson et al., 1960), shown below;

DQI = Total Dry Weight (DW)/

Simultaneously, only the largest seeds from group G were sown at 5 different depths (10-50 mm) in three replicates of 100 seed as above to assess the impact of sowing depth, on seed germination and seedling quality. The quality of seedlings was assessed using the sturdiness quotient (SQ), being the ratio of height in cm to collar diameter in mm (Thompson, 1985).

Results and discussion

Large and heavy seeds showed earlier and higher percentage germination, germination values and mean daily germination (Table 1). The values of these parameters were lowest in group A, significantly different from all other groups, and maximum in group G, though there was no significance difference between the largest 5 groups of seeds (C to G). Seedling quality obtained from seeds of A, B and C groups was relatively poor (DQI <4.0), with groups B and C being significantly so, compared with the seedlings obtained from D, E, F and G groups (DQI >4.0). Seeds with higher 100-seed weights, produced seedlings with more shoot and root dry weight (data not presented), which may be due to greater nutrient reserves in large seeds (Kathju et al., 1978). Dry weights increased positively with the increase in seed weight.

Table 1: Effect of seed weight on percentage germination (and angular transformed data, A.T.V.), mean daily germination (MDG), germination value (GV) and Dickson quality index (DQI) of P. juliflora. Means in the same column followed by a different letter, differ significantly at the 5% level.

Seedlings from seeds of A, B and C groups were weak and had much reduced shoot and root dry weight respectively, compared with seedlings produced by seeds of G group. A similar trend was also reported for Virola koschnyi (Gonzalez 1993) and H. binata (Ponnamal et al., 1993).

In the second experiment, maximum germination was recorded at the shallowest depth (10 mm), and with increasing depth the germination percentage and mean daily germination (MDG) values significantly decreased. Germination ranged from 2.5% (at 50 mm) to 80% (at 10 mm), MDG values were 0.25 and 8.0 respectively and germination values were 0.08 and 166.60 respectively (Table 2). A strong negative correlation existed between sowing depth and germination percentage (r = -0.80), with the linear relationship between them expressed as Y = 76.2275 - 1.4544 Y, with X = sowing depth and Y = germination %. The results concur with earlier reports of lower and slower germination in deodar (Chandra and Atma Ram, 1980) and kail pine (Singh et al., 1973) when seeds are deep sown. The seedlings of each sowing depth were grouped into 3 categories based on their decreasing sturdiness quotient i.e., >6 (I), >4<6 (II) and <4 (III) (Table 3). Within groups I and II, the highest percentage of seedlings were from seeds sown at 10 mm depth. However, in the weakest category (III), a higher proportion of seeds were from the 20 and 30 mm sowing depths. Sowing at less than 10 mm depth is harmful to the seedlings, allowing for excessive seed desiccation and losses from rodents and birds. It can be concluded that by rejecting smaller seeds, with a 100 seed weight of below 2 g (i.e. groups A, B and C) at the time of sowing, and also by sowing seeds at a depth of 10 mm, this will not only give early and improved germination, but also an improved quality of seedlings.

Table 2. Effect of sowing depth on germination percentage (G%), mean daily germination (MDG) and germination value (GV) of P. juliflora seed.

Table 3. Percentage distribution of P. juliflora seedlings in different sturdiness quotient categories in relation to different sowing depths.

References

Chandra, J.P. and Atma Ram, 1980. Studies on depth of sowing deodar seed. Indian Forester 106: 852-855.

Czabator, F.J., 1962. Germination value - an index combining speed and completeness of pine seed germination. Forest Science 8: 386-393.

Dickson, A., A.L. Leaf and J.F. Hosner, 1960. Quality appraisal of white spruce and white pine seedling stock in nurseries. Forestry Chronicle 36: 10-13.

Gonzalez, J.F., 1993. Effect of seed size on germination and seedling vigour of Virola koschnyi Warb. Forest Ecology and Management 57: 275-281.

Kathju, S., A.N. Lahiri and K.A. Shankarnarayan, 1978. Influence of seed size and composition on dry matter yield of Cenchrus ciliaris. Experentia 34: 848-849.

Ponnamal, N.R., M.C. Arjunan and K.A. Antony, 1993. Seedling growth and biomass production in H. binata Roxb. as affected by seed size. Indian Forester 119: 59-62.

Singh, R.V., J.P. Chandra and S.N. Sharma, 1973. Effect of depth of sowing on germination of kail seeds. Indian Forester 99: 367-371.

Thompson, B.E., 1985. Seedlings’ morphological evaluation - on what you can tell by looking. In: Durea, M.L. (ed.), Evaluating Seedling Quality. Corvallis, U.S.A. pp59-71.

Possibilities of manipulating mycorrhizal associations for higher production in Prosopis juliflora - J.C. Tarafdar and A.V. Rao

Central Arid Zone Research Institute, Jodhpur 342003, India

Introduction

Mycorrhizal fungi occur widely in various environmental conditions, and are found in association with a number of leguminous trees. Mycorrhizal fungi are a group of important soil micro-organisms, ubiquitous throughout the world. They are known to improve plant growth by increasing nutrient uptake, increasing the absorbing surface area, mobilising sparingly available nutrient sources, or by excretion of chelating compounds or ectoenzymes. Mycorrhizal infection may also protect roots from soil pathogens (Perrin, 1990), thereby increasing root growth and nutrient acquisition by the host root. They also improve the activity of nitrogen fixing organisms in the root zone (Mosse et al., 1976).

Most studies on vesicular-arbuscular mycorrhiza (VAM) - Rhizobium interactions suggest that colonisation with efficient endophytes significantly improves phosphorus nutrition and consequently nodulation and nitrogen fixation (Hayman, 1986). While the principal effect of mycorrhiza on nodulation is undoubtedly phosphate mediated, mycorrhiza may have other secondary effects. Potentially limiting factors may include the supply of photosynthates, trace elements or plant hormones. This report brings together results and experiences obtained by the authors during the phase of a mycorrhiza project, on the practical possibilities of utilising mycorrhiza in Prosopis juliflora production systems.

Survey

A survey was conducted to screen the VAM infected root material of P. juliflora in 9 environmentally harsh sites in Rajasthan under natural conditions. The data indicated that P. juliflora plants growing at different locations carry VAM infections in their roots, although the intensity of infection varies. For example, VAM infection of 3-12 month old P. juliflora plants in Khyasaria was >25% with 89 viable VAM spores/kg of rhizosphere soil, whereas VAM infection in Lathi was >95% with 553 viable VAM spores/kg of rhizosphere soil. However, the percentage of VAM infections did not vary with plant age. Samples collected from different locations showed that the infection of plants 3-12 months old varied by only 5-10%. The density of infection did not vary with plant age, but young roots carried mostly mycelia with a small number of vesicles, with spores and vesicles found in roots from mature trees. P. juliflora were mostly infected by VAM fungi belonging to the genus Glomus spp.

Nursery trial

The build up of VAM spores, and the consequent effect on plant height and dry matter yield after inoculation with Glomus mosseae and G. fasciculatum on P. juliflora under nursery conditions was investigated. A 2-fold increase in spore number, 1.5-fold increase in plant height and up to a 3-fold increase in dry matter yield were noticed 5 months after inoculation, compared with the uninoculated control. A similar experiment was conducted after inoculating P. juliflora seedlings with ectomycorrhiza (Pisolitus tinctorius) under nursery conditions. After 4 months, the inoculated seedlings exhibited 26% and 37% increases in plant height and dry matter yield respectively, but after this initial growth stage, the effect was much reduced, up to 9 months. In general, the effect of VAM fungi was greater than that of ectomycorrhizal fungi under nursery conditions at similar plant ages.

Field trial

A field experiment was conducted with P. juliflora seedlings inoculated with G. mosseae and G. fasciculatum. After two years growth, a significant improvement in plant height, dry matter yield, bacteria and actinomycete population, VAM spore development, alkaline phosphatase activity, percentage root infection and organic matter content in the rhizosphere soil was observed (Table 1). Beside this, a significant increase in the population of nitrifying bacteria and a significant decrease in the fungal population was observed following inoculation with G. mosseae, and a significant increase in acid phosphatase activity with the inoculation of G. fasciculatum was noticed. In general, the maximum positive effect on all the parameters tested was seen with G. fasciculatum. These field results support the results obtained from nursery conditions and clearly demonstrates that G. fasciculatum is the most suitable VAM fungus for enhancing growth and productivity of P. juliflora under arid conditions.

Table 1. Influence of different vesicular-arbuscular mycorrhiza fungi on plant height, dry matter yield and biochemical parameters in the rhizosphere of P. juliflora grown under field conditions after 2 years. (Significance of difference: *p<0.05; **p<0.01; ***p<0.001).

Conclusions

It is found that simultaneous inoculation of legumes with Rhizobium and VAM causes synergistic beneficial effects (Bagyaraj et al., 1979). The effects of inoculating seeds of P. juliflora with different Rhizobium spp. and inoculating soil with VAM fungi singly or in combination appear promising, although not always uniform. It should not be forgotten however, that the rhizosphere is a complex region in the soil-plant interface, with high microbial activity. However, results obtained from biological interaction studies between VAM fungi and other beneficial soil organisms are encouraging, and indicate the need for strengthening research in this area.

References

Bagyaraj, D.J., A. Manjunath and R.B. Patel, 1979. Interaction between VAM mycorrhizae and Rhizobium and their effects on soyabean in the field. New Phytologist 82: 141-145.

Hayman, D.S., 1986. Mycorrhizae of nitrogen fixing legumes. MIRCEN Journal of Applied Microbiological Biotechnology 2: 121-145.

Mosse, B., C.L. Powell and D.S.Hayman, 1976. Plant growth responses to vesicular-arbuscular mycorrhiza. IX. Interactions between VA mycorrhiza, rock phosphate and symbiotic nitrogen fixation. New Phytologist 76: 331-342.

Perrin, R., 1990. Interactions between mycorrhizae and diseases caused by soil borne fungi. Soil Use and Management 6: 189-195.

Studies on vesicular-arbuscular mycorrhiza in association with Prosopis juliflora - V. Mohan, K.K. Srivastava and Neelam Verma

Arid Forest Research Institute, Jodhpur 342003, India

Introduction

Vesicular-arbuscular mycorrhiza (VAM) fungi are found in many regions including arid and semi-arid tracts. Among the different types of associations between non-parasitic fungi and plant roots, mycorrhizal association is considered as the most important in the forestry sector. It has been demonstrated that the VAM fungal mycelia help in binding sand grains, thereby arresting their movement, and also in the establishment, survival and growth of sand-dune colonising plant species (Nicolson, 1960; Koske et al., 1975; Koske and Polson, 1984). Prosopis juliflora is used for afforestation programmes particularly in sand-dunes, coastal sands, eroded hills, riverbeds and waste lands. In view of the limited studies available on VAM association with P. juliflora, the present investigation was undertaken to study the VAM fungal association with P. juliflora plants grown in various nurseries and plantations at different locations around Jodhpur, Rajasthan.

Materials and methods

Root and rhizosphere soil samples from P. juliflora plants were collected from 4 nurseries (AFRI, Lokswell, Osian and Phalodi) and 5 plantations (Chopasni, Chaukha, Devlia, Jhalamand and Mandore) in and around Jodhpur. The soil surrounding the root zone of P. juliflora plants was screened for different VAM fungal propagules. The roots were washed gently in tap water and immediately fixed in formalin-acetic acid-alcohol (FAA) (13 ml formalin + 5 ml glacial acetic acid + 200 ml 50% ethyl alcohol) for further studies. The method of Phillips and Hayman (1970) was followed for cleaning and staining the roots for the rapid assay of endomycorrhizal colonisation. Percentage VAM infection was calculated, and the fungal propagules were isolated from the rhizosphere soil samples by using the wet-sieving and decanting technique (Gerdemann and Nicolson, 1963) and identified following Schenck and Perez (1987).

Results and discussion

The roots of all the nursery samples had both vesicular and arbuscular structures, but only vesicular structures and spores were seen in the roots from natural plantation samples. Table 1 shows the percentage colonisation of VAM in root samples of P. juliflora collected from the different nursery and plantation stands.

The following VAM fungal species were identified based on spore characters; Glomus fasciculatum, G. fulvus, G. intraradices and G. macrocarpum. Of these, G. fasciculatum was found to be very common in the rhizosphere soil samples of both nursery and natural plantation sites. It was also observed that the VAM fungal species G. fasciculatum and G. intraradices were found to be very common in the rhizosphere soils collected from the nursery sites (Table 2).

Table 1. Type of, and percentage colonisation of vesicular-arbuscular mycorrhiza in root samples of P. juliflora collected from various nurseries and natural plantation stands.

Table 2. Distribution of VAM fungal (Glomus spp.) species in the rhizosphere soils of P. juliflora seedlings and mature trees in natural plantation stands (+ = present; - = absent).

The VAM fungal spores isolated from the rhizosphere soils of the 5 natural plantation stands showed the presence of G. fasciculatum and G. macrocarpum (Table 2). The occurrence of other species varied place to place. This study corroborates with the findings of Mukerji and Kapoor (1986). Similar observations were made on the occurrence of VAM fungal species G. fasciculatum, G. macrocarpum and G. microcarpum in the sodic soil samples collected under the root zone of P. juliflora by Tharpar et al. (1991). Thus the prevalence of VAM fungi in both nursery and plantation samples indicated that mycorrhiza appeared to be of great importance for the growth of P. juliflora in arid and semi-arid zones.

References

Gerdemann, J.W. and T.H. Nicolson, 1963. Spores of mycorrhizal Endogone species extracted from soil by wet-sieving and decanting. Transactions of the British Mycology Society 46: 235-244.

Koske, R.E., J.C. Sutton and B.R. Sheppard, 1975. Ecology of Endogone in Lake Huron sand dunes. Canadian Journal of Botany 53: 87-93.

Koske, R.E. and W.R. Polson, 1984. Are VA-mycorrhizae required for sand dune stabilization? Bio Science 34: 420-424.

Mukerji, K.B. and Anita Kapoor, 1986. Occurrence and importance of vesicular-arbuscular mycorrhizal fungi in semi-arid regions of India. Forest Ecology and Management 16: 117-126.

Nicolson, T.H., 1960. Mycorrhiza in the Graminae. II. Development in different habitats, particularly sand dunes. Transactions of the British Mycology Society 43: 132-145.

Phillips, J.M. and D.S. Hayman, 1970. Improved procedures for clearing roots and staining parasitic and vesicular-arbuscular mycorrhizal fungi for rapid assessment of infection. Transactions of the British Mycology Society 55: 158-161.

Schenck, N.C. and Y. Perez, 1987. Manual for the Identification of VA-Mycorrhizal Fungi. University of Florida, Gainesville, Florida, USA.

Tharpar, H.S., K. Uniyal and R.K. Verma, 1991. Survey of native VAM fungi of sodic soils of Haryana State. Indian Forester 117: 1059-1069.