# Climatic implications of $\delta^{13}C$ and $\delta^{18}O$ ratios from C3 and C4 plants growing in a tropical montane habitat in southern India

Rajagopalan, Geeta and Ramesh, R and Sukumar, R (1999) Climatic implications of $\delta^{13}C$ and $\delta^{18}O$ ratios from C3 and C4 plants growing in a tropical montane habitat in southern India. In: Journal of Biosciences, 24 (4). pp. 491-498.

The stable carbon and oxygen isotope ratios in cellulose of C3 and C4 plants growing on the surface of a montane peat bog in the Nilgiri hills, southern India, were measured. The mean monthly $\delta^{13}C$ values in cellulose of both C3 and C4 plants are found to be significantly related to rainfall, while the $\delta^{18}O$ values are sensitive to changes in maximum temperature and relative humidity of the region. Further, higher $\delta^{18}O$ values were observed in C4 plants compared to C3 plants, suggesting that C4 plants are probably less sensitive to relative humidity as compared to C3 plants and are able to photosynthesize even during drier conditions. The plant isotope-climate correlations thus established can be used for reconstructing the past temperature and rainfall conditions of the tropics from the isotopic ratios of peat deposits, derived from a mixture of C3 and C4 plants in the region.