S. R. Gupta

PLANT DECOMPOSITION AND SOIL RESPIRATION IN TERRESTRIAL ECOSYSTEMS

SummaryThis review deals with methodological approaches, measured rates, and environmental control of two major interdependent processes regulating the structure and function of terrestrial ecosystems, viz., plant decomposition and soil respiration.Both these processes have been evaluated through indirect assessments as well as through direct measurements under the field conditions. The techniques used suffer in general from difficulties in creating conditions of natural environment during the process of measurement. Generalizations regarding the magnitude of rates in different ecosystems are difficult because of limited results or non-comparability of results from different methods.Temperature and moisture and their interactions markedly influence both the processes. The surface feeders and soil animals have a marked influence on the decomposition. Partitioning of soil respiration into components due to live roots, microbes, and soil fauna has eluded a satisfactory solution so far.SommaireCette revue traite des approches méthodologiques, des vitesses mesurées et du contrôle des environs de deux procédés interdépendants principaux qui règlent la structure et la fonction des écosystèmes terrestes, viz, la décomposition des plantes et de la respiration du sol.Ces deux procédés ont été évalués par des méthodes indirectes aussi bien que par des mesures directes sous le terrain. Les techniques employées souffrent en géneral des difficultés dans la création des conditions de l’environnement naturel pendant mesure. Des généralisations en ce qui concerne la grandeur des vitesses dans les différents écosystèmes sont difficiles parce que les différentes méthodes ne peuvent pas être comparées que d’une façon limitée ou non-comparable.La température et l’humidité et leurs interactions ont une très grande influence sur les deux procédés. Les animaux et les plantes qui se nourrissent sur la surface et les animaux dans la terre ont une très grande influence sur la décomposition. La séparation de la respiration du sol en composantes causée par des microbes des racines vivantes et de la faune du sol a echappé à une solution satisfaite jusqu’à présent.

The effect of plant species, weather variables and chemical composition of plant material on decomposition in a tropical grassland

SummaryThe decomposition of litter and roots ofChenopodium album, Desmostachya bipinnata and mixed grass samples for a period of 402 days and ofDichanthium annulatum andSesbania bispinosa for a period of 278 days was studied in a tropical grassland. Litter bags positioned at midcanopy height, soil surface and at five cm depth below the soil surface and root bags placed at 5, 15, 25 and 35 cm depths belowground were used. For the total study period, the cumulative weight loss in litter bags was: Chenopodium=76–100%; Desmostachya=33–98%; Dichanthium=26–96%; mixed grass=43–99% and Sesbania=25–99%. The weight loss in root bags was: Chenopodium=93–100%; Desmostachya=47–56%; Dichanthium=71–87%; mixed grass=61–82%; Sesbania=87–100%. The nature of plant species affected decomposition rates. The position of litter/root bags also affected the decomposition rates. The mean relative decomposition rates of litter as well as of root material were found to be highest in rainy season and lowest in winter months. Rainfall, particularly the frequency of rainfall, was an important factor affecting decomposition rates. The litter species characterized by highest concentration of nitrogen, ash, acid detergent cell wall component and lowest concentration of carbon, cellulose and lignin, decomposed rapidly. In the case of roots, the material having high nitrogen, carbon, cellulose and ash content and low C/N ratio and lignin content decomposed rapidly.

Effect of soil salinity and soil water availability on growth and chemical composition ofSorghum halepense L.

SummaryEffects of soil salinity and soil water regime on growth and chemical composition ofSorghum halepense L. was studied with a view to evaluating its potential as a forage crop in saline soils. The experiment was conducted under controlled conditions using pot-culture with three levels of soil salinity (ECe 0.5, 5.0, 10.0 ds/m) and three soil water regimes (60%, 40% and 20% of water holding capacity of the soil). High soil salinity and low soil water combiningly had an adverse effect on plant growth but the biomass production was appreciably high (57 to 75% of control) even under high soil salinity (ECe 10 ds/m) when sufficient water was available. Belowground plant parts were relatively more salt-tolerant than shoots. There occurred an increase in the concentration of certain nutrients (N, Ca, Mg, TNC) in the plants in response to salinity, which along with increased root: shoot ratios was inferred as an adaptive feature of the plant for persistence under saline conditions.

Effects of osmotic tension and salt stress on germination of three grass species

Effects of osmotic tension, salinity and alkalinity were studied on seed germination of three grasses of Karnal-Kurukshetra region with a view to evaluating their capacity to establish through seeds in saline and alkaline environments. Experiments were conducted under controlled conditions in petri dishes lined with blotting papers that were wetted with non-ionic osmotic solutions of mannitol (−2.5 to −15 bars); salinized solutions of NaCl, Na2SO4, MgCl2 and CaSO4 (Electrical conductivity, EC, ranging from 4 to 16 dS/m), alkaline solutions of Na2CO3 (pH 9 to 10) and also in dishes filled with alkali soil grades of the same pH range. Seed germination of all the three grasses was observed to be delayed and finally suppressed by the stress conditions, magnitude of reduction being related to the kind and level of stress as well as to the species. WhileSorghum halepense showed a strikingly superior stress-resistance,Panicum miliare did not appear to be suited to establishment through seeds.Diplachne fusca, on the other hand, was found to be remarkably adapted to alkalinity.