Changes in organic carbon pool in a tropical soil planted to rice in relation to photosynthetic carbon fixation

Abstract

Information on the fate of photosynthesized carbon (C) in plant soil system is essential for understanding the soil organic carbon pool and carbon dynamics in agricultural ecosystem. Our objectives in the present study were to quantify the photosynthetic carbon fixation by high yielding rice genotypes and contribution of rice ecosystem to soil organic carbon pool in a tropical rice soil. A field experiment was conducted during 3 consecutive monsoon rice season (July – December) of 2012, 2013 and 2014 in a randomized block design (RBD). A portable photosynthesis system was used for measurement of flag leaf photosynthesis. Stomatal frequency of the flag leaves were studied by scanning electron microscopy (SEM). Soil organic carbon storage was estimated by a total organic carbon (TOC) analyzer. Differences in flag leaf photosynthetic carbon fixation amongst the varieties were significant. Differential ability for carbon partitioning in terms of biomass accumulation were also noteworthy (p = 0.000). Flag leaf photosynthetic rate observed in the study showed a good correlation (r = 0.486, p ≤ 0.05) with the stomatal frequency of the flag leaves. The leaf stomatal frequency ranged from 605 to 783 mm -2 of leaf area with a high in the rice variety, Swarnamahsuri and low in Gitesh. There were significant differences in cumulative methane (CH4) emission amongst the four rice varieties. The grain productivity in retaliation to genetic differences of the rice varieties highly favored their correlations with flag leaf photosynthesis (r = 0.999, p ≤ 0.01) and leaf area index (r = 0.961, p ≤ 0.01). Above ground and below ground dry matter of the plants were found to influence the quantity of soil organic carbon and soil C storage. Our results also clearly bespoke that a rice ecosystem can effectively sequester carbon (0.338 Mg C ha -1 yr -1 ) at 0 - 15cm depth of soil. The results led us to conclude that lowland rice ecosystem is a good sink of carbon dioxide (CO2).