ABSTRACT
Seasonal changes in soil respiration (SR), soil temperature (ST) and soil moisture (SM) were compared between a barren land with no vegetation (control) and grassland dominated by Heteropogon contortus (L.) of a semi-arid eco-system during 2005-2006. A statistically significant (p<0.001) seasonal change in SR was observed between the two sites. The variation characteristics of soil CO2 efflux rates were observed during wet periods along precipitation gradients and it was consistently higher in grasslands than in control. A maximum soil CO2 efflux of 13.35 ± 0.33 Amol m-2 s-1 in grassland and 7.33 ± 0.8 Amol m-2 s-1 in control was observed during rainy season-II, i.e., from October to December, a minimum of 1.27 ± 0.2 Amol m-2 s-1 in grassland and 0.67 ± 0.5 Amol m-2 s-1 in control during summer season, i.e., from March to June. A positive significant relation observed between soil respiration and soil moisture (r2 above 0.8) and no significant relation was observed between soil CO2 efflux and soil temperature (r2 below 0.3). In water-limited semi-arid ecosystem, rewetting of the soil due to precipitation events triggered the increased pulses of soil respiration especially in grassland when compared to the barren land. The observed soil respiration rates during summer and after the subsequent precipitation events strongly indicated that the soil water-deficit conditions reduce the efflux both in barren land (control) and in grassland of semi-arid eco-system.
ABSTRACT
Diurnal trends in net photosynthesis rate (PN ), stomatal conductance (gs ), water use efficiency (WUE) and biomass were compared in six-month-old seedlings of Albizia lebbeck and Cassia siamea, under different levels of drought stress. The potted plants were subjected to four varying drought treatment by withholding watering for 7 (D1), 14 (D2) and 25 (D3) days. The fourth group (C) was watered daily and treated as unstressed (control). Species differed significantly (p<0.001) in their physiological performance under varying stress conditions. Higher PN of 11.6 ± 0.05 in control followed by 4.35 ± 0.4 in D1 and 2.83 ± 0.18 @mol m-2 s-1 in D2 was observed in A. lebbeck. A significant (p<0.001) reduction in PN was observed in C. siamea ( C 7.65 ± 0.5 @mol m-2 s-1, D1, 2.56 ± 0.33 @mol m-2 s-1 and D2, 1.4 ± 0.01 @mol m-2 s-1 ) at 9 hr. A positive correlation was seen between PN and gs (A. lebbeck, r2= 0.84; C. siamea, r2= 0.82). Higher WUE was observed in C. siamea (D2, 7.1± 0.18 @mol m-2 s-1; D3, 8.39 ± 0.11 @mol m-2 s-1) than A. lebbeck, (control, 7.58 ± 0.3 @mol m-2 s-1 and D3, 8.12 ± 0.15 @mol m-2 s-1). The chlorophyll and relative water content (RWC) was more in A. lebbeck than C. siamea. Maximum biomass was produced by A. lebbeck than C. siamea. From the study, one could conclude that A. lebbeck is better than C. siamea in adopting suitable resource management strategy and be best suited for the plantation programs in the semi-arid dry lands.