Abstract:
Forests play a vital role in regulating the greenhouse gases, particularly the level of atmospheric CO2; hence planting forests has been identified as one of the main options available to mitigate the effects of climate change. Rubber (Hevea brasiliensis), being a multipurpose tree which provides an economically viable (in terms of both latex and timber production) and socially acceptable system, can be effectively used in participatory tree planting programmes. Although the availability of carbon in rubber trees has been assessed before, the potential capacity of sequestering atmospheric CO2 in mature rubber trees has not been quantified. Therefore the present study was geared towards this whilst characterizing the genotypic differences in CO2 sequestration. Two promising genotypes viz. RRIC121 and RRIC100, were selected for the study. CO2 assimilation rates of rubber leaves in three canopy strata under varying light levels were measured and parameters of photosynthetic light response curves (LRC) were estimated. Leaf area distribution and light attenuation within the canopy were also measured. With previous weather records on incident light, its availability at different canopy levels was estimated using existing ecophysiological models and then the photosynthetic rates at canopy level were estimated. Maximum rate of photosynthesis and quantum yield (photosynthetic efficiency) decreased with the increase in depth of the canopy whilst it was vice versa for the convexity of light response curve. In general, parameters of LRC were superior in RRIC 121 to RRIC 100. Irrespective of the clone, a greater proportion of leaves was found in the top than in the lowest stratum. Leaf area index in RRIC 121 was greater than RRIC 100 with values of 5.88 and 3.47, respectively. Light extinction coefficient was less in RRIC 121 allowing more light to penetrate through the canopy than in RRIC 100. The capability of sequestering atmospheric CO2 was greater in RRIC 121 than that in RRIC 100 with annual rates of 117 and 45 MTha-1, respectively. On average, mature rubber is capable of sequestering 81 MT of CO2 per hectare annually and, within the 24 years of mature phase, 1,296 MT of CO2 would be sequestered in a hectare of rubber.
