Growth, biomass production and photosynthesis of Cenchrus ciliaris L. under Acacia tortilis (Forssk.) Hayne based silvopastoral systems in semi arid tropics.

The growth, biomass production and photosynthesis of Cenchrus ciliaris was studied under the canopies of 17 yr old Acacia tortilis trees in semi arid tropical environment. On an average the full grown canopy of A. tortilis at the spacing of 4x4 m allowed 55% of total Photosynthetically Active Radiation (PAR) which in turn increased Relative Humidity (RH) and reduced under canopy temperature to -1.75oC over the open air temperature. C. ciliaris attained higher height under the shade of A. tortilis. The tiller production and leaf area index decreased marginally under the shade of tree canopies as compared to the open grown grasses. C. ciliaris accumulated higher chlorophyll a and b under the shade of tree canopies indicating its shade adaptation potential. The assimilatory functions such as rate of photosynthesis, transpiration, stomatal conductance, photosynthetic water use efficiency (PN/TR) and carboxylation efficiency (PN/CINT) decreased under the tree canopies due to low availability of PAR. The total biomass production in term of fresh and dry weight decreased under the tree canopies. On average of 2 yr C. ciliaris had produced 12.78 t ha-1 green and 3.72 t ha-1 dry biomass under the tree canopies of A. tortilis. The dry matter yield reduced to 38% under the tree canopies over the open grown grasses. The A. tortilis + C. ciliaris maintained higher soil moisture, organic carbon content and available N P K for sustainable biomass production for the longer period. The higher accumulation of crude protein, starch, sugar and nitrogen in leaves and stem of C. ciliaris indicates that this grass species also maintained its quality under A. tortilis based silvopastoral system. The photosynthesis and dry matter accumulation are closely associated with available PAR indicating that for sustainable production of this grass species in the silvopasture systems for longer period about 55% or more PAR is required.

Elevated CO2 influences photosynthetic characteristics of Avena sativa L cultivars.

The impact of elevated CO2 concentration on the growth, photosynthesis and biomass production was investigated in three oat (Avena sativa L) cultivars viz. Kent, JHO-822 and JHO-851 by growing under three environmental conditions i.e. elevated CO2 at 600 ± 50 μ mol mol-1 (C600), OTC with ambient CO2 (COTC) and under open field condition (Ca). Plant height and leaf area increased in the elevated CO2 grown plants. JHO-822 attained maximum height under C600 followed by Kent and JHO-851. The specific leaf mass (SLM) and specific leaf area (SLA) were also influenced significantly when the plants were grown under C600. Kent showed highest SLM under C600 corresponding lower value of SLA. The accumulation of soluble protein in the oat leaves decreased under C600 except JHO-822 where marginal increase in soluble protein was recorded under C600. JHO-822 showed an increase in Chl orophyll a, b and total in C600 over Ca, whereas other two cultivars did not follow any specific trend in the pigment accumulation. Our results confirmed that the net phosynthetic rate (PN) increased by 37% in Kent followed by JHO 822 under elevated CO2 over the control. This strong association of PN with gs was evidenced by a positive significant correlation (r=0.885**). A clear stimulatory effect at elevated CO2 was detected in all the cultivars in term of green and dry matter production than at ambient CO2 and COTC. A large increase in PN in the present investigation was accompanied by relatively small decrease in gs, which limits the water loss through transpiration rate. The elevated CO2 induced changes in gs and reduction in transpiration.

Growth, yield and photosynthesis of Panicum maximum and Stylosanthes hamata under elevated CO2.

Plant height, biomass production, assimilatory functions and chlorophyll accumulation of Panicum maximum and Stylosanthes hamata in intercropping systems was influenced significantly under elevated CO2 (600 ±50 ppm) in open top chambers (OTCs). The plant height increased by 32.0 and 49.0% over the control in P. maximum and S. hamata respectively in intercropping system under elevated CO2 over open field grown crops (Ca). P. maximum and S. hamata produced 67 and 85% higher fresh and dry biomass respectively under elevated CO2. Rates of photosynthesis and stomatal conductance increased in both the crop species in intercropping systems under elevated CO2. The canopy photosynthesis (photosynthesis x leaf area index) of these crop species increased significantly under elevated CO2 over the open grown crops. The chlorophyll a and b accumulation were also higher in the leaves of both the crop species as grown in OTC with elevated CO2. The increased chlorophyll content, leaf area index and canopy photosynthesis led to higher growth and biomass production in these crop species under elevated CO2. The total carbon sequestration in crop biomass and soils during the three years was 21.53 Mg C/ha under elevated CO2. The data revealed that P. maximum and S. hamata intercropping system is the potential as a sink for the increasing level of CO2 in the atmosphere in the semi-arid tropics.