[MIS25-P10] Variation among carbon isotopes of plants growing in mixed evergreen-deciduous ecosystem.
The variation of leaf bulk carbon isotope values C3 plants (δ13Cbulk) at a global scale displays strongest dependence on mean annual precipitation (MAP) among all climate variables. However, the MAP-δ13Cbulk relation in regional scale studies displays varying correlation among the two variables. Such studies are conducted across a precipitation gradient, leading to differences in both environmetal factors (soil moisture, topography etc.) as well as species assemblage. Additionally, the observed MAP-δ13Cbulk relation may be a one-time occurrence and not remain constant over time. To understand the MAP-δ13Cbulk relation temporally and minimize environmental variations, 18 naturally occurring plant species were sampled from a single location over a period of six years (2012-18). The study region (22°57’N, 88°31’E) lies in the lower Gangetic floodplain experiencing sub-tropical monsoonal climate which supports mixed deciduous-evergreen vegetation. Among the two plant functional types (deciduous and evergreen), lower δ13Cbulk values were observed in evergreen species at an annual timescale with a difference of 0.9‰ to 1.5 ‰. The dataset compiled in this study shows no correlation among δ13Cbulk and rainfall amount in the months of June, July and August which is the period when maximum rainfall intensity occurs. However, a strong correlation is seen when δ13Cbulk values are correlated with MAP. Deciduous species exhibit a stronger correlation with MAP (r2=0.55) compared to evergreen (r2=0.20). The observations can be explained through the difference in leaf growth strategies between deciduous and evergreen species. The higher δ13Cbulk values in deciduous trees indicate a higher water use efficiency leading to lower carbon assimilation. Their dependency on MAP is a result of shorter leaf life-span compared to evergreen trees. In the context of changing climate with predictions of varying precipitation regime, a potential shift in plant community composition can alter the carbon assimilation at a global scale and tend to have an adverse effect on growth of deciduous species.