Control of regional climate on carbon and nitrogen turnover and their stable isotopic compositions in Indian soils

Stable isotopic analysis of carbon (C) and nitrogen (N) has helped to predict climate specific response of biological mediators of C and N cycles, and thus, turnover and availability of these elements in soils. However, application of general isotopic trends to soils of different ecosystems remains undetermined pertaining to inadequate data from vast eco-regions, including the Indian subcontinent. The present study focuses on filling this data gap through isotopic analysis of soils from the arid, humid, and montane regions of India to understand the distribution and availability of total organic carbon (TOC) and total nitrogen (TN) under different temperature and precipitation conditions in an understudied tropical region. Our results for arid soils showed low TOC and TN contents with high 613C and 615N indicating active mineralization under limited organic matter supply. Contrarily, humid soils showed high concentrations of TOC and TN with low 613C and 615N indicating conservative N cycle. Isotopic signatures of montane soils showed spread over both arid and humid soils signifying higher control of edaphic factors over climate in the organic matter turnover in montane soils. Absence of climate specific isotopic pattern in the montane soils suggests careful application and interpretation of stable isotopic techniques in such regions. In our results, we find partial confirmation that climate is a prominent control of C and N turnover but also evidence for the importance of edaphic and other local factors, especially in the montane region. This work fills the knowledge gap in an understudied region and confirms that even within a larger tropical setting, the regional climate regulates the elemental biogeochemistry and organic matter dynamics of soils.