CARBON SEQUESTERING THROUGH THE PHOTOSYNTHESIS IN RUBBER PLANTATIONS; A COMPARISON BETWEEN GENOTYPES

Abstract

Being an industrial crop, rubber (Hevea brasilensis) is having a consistentdemand and grown in smallholdings under different environmental conditionsproviding an economically viable (in terms of both latex and timberproduction) and socially acceptable system. Also in terms of theenvironmental benefits, rubber helps to mitigate climate change through thefixing of atmospheric carbon and reducing the carbon emission formnonrenewable resources. Therefore, the present study aimed to assess thegenotypic differences in carbon fixing capability of field grown maturerubber cultivations with two specific objectives, 1) to quantify the potentialcarbon fixation of the mature rubber plantations through the CO2 assimilationand 2) to establish the genotypic differences of rubber in fixing atmosphericcarbon.

The experiment was' conducted in the Dartonfield estate of the RubberResearch Institute at Agalawatte. Two promising genotypes i.e. RRIC 100and RRIC 121 at maximum productivity (i.e. in mature stage; 12 years old)were selected for the study. The assessment of the carbon fixation capabilityof rubber tree was based on measurements on leaf level photosynthesis, leafarea distribution and light attenuation of the rubber canopy. CO2 assimilationrates in rubber leaves under varying light levels were monitored with aportable infra red gas analyzer after dividing the canopy into three strata andthen, the parameters of light response curve of photosynthesis were estimatedusing a quadratic function. Leaf area distribution was assessed by physicalcounting with point quadrats and the available light for the photosynthesis indifferent canopy levels was estimated using existing ecophysiological modelsand then, canopy photosynthetic rates were calculated.

In general, mature rubber was capable of sequestering 22 MT of carbon perhectare annually. Monthly values of carbon fixed differed according to thenumber of sunny and dull days. The highest rate of carbon sequestering wasgiven in the month of March, whilst November has shown the lowest rate.The value estimated for the whole economic lifecycle of rubber was 660MT/ha. The genotype, RRIC 121 was superior (160% greater) to RRIC 100 in fixing atmospheric carbon with annual rates of 31.8 and 12.2 MTha-1,respectively. Differences in the capacity of photosynthetic apparatus andcanopy architecture were identified as the reasons for the genotypicdifferences in carbon sequestering.