What controls carbon and nitrogen allocation in montane vegetation: A case study from the Himalayas

Plants play a critical role in the surficial environment, influencing energy transfer, the global carbon (C) and nitrogen (N) cycles, and climate change. Knowledge of botanical and climatic controls on terrestrial C and N-cycling within and across ecosystems is central to understanding plant ecophysiology. In this study, we examined the effects of climate and forest composition on plant C and N, and systematically measured foliar δ¹³C and δ¹⁵N along an altitudinal gradient ranging 1900 to 5200 m, across three transects spanning west to east Himalayas. Total C and N content in plants significantly decreased with altitude, except for TOC in central and western Himalayan gymnosperms. Precipitation and temperature gradients differentiated 76% of the variation in TN and δ¹⁵N, and only 2.5% in TOC and δ¹³C stocks in the Himalayan plants. We report a complex climatic and topographic control on the C and N allocation in montane ecosystems, quantified via isotopic signature and abundance, linking plant ecophysiology with resource availability. C and N being complementary in several foliar biochemical processes, their mutual abundance was realised, examined and inferred in previously unexplored montane ecosystems and climate. In addition, the spatial distribution of foliar-isotope-abundance helped cluster plant responses, eventually leading to the construction of a spatially comprehensive map known as a dual isoscape.