Carbon and Nitrogen Metabolism in Leaves and Roots of Dwarf Bamboo (Fargesia denudata Yi) Subjected to Drought for Two Consecutive Years During Sprouting Period

Abstract

Dwarf bamboo is an ecologically and economically important forest resource that is widespread in mountainous regions of eastern Asia and southern America. Fargesia denudata, one of the most important dwarf bamboos, is a staple food of the giant panda, but our knowledge about how F. denudata copes with drought stress is very limited. The objective of this study was to determine the responses of carbon (C) and nitrogen (N) metabolism to drought in leaves and roots of F. denudata plants. Plants were subjected to three water treatments, well-watered [WW, 85 % relative soil water content (RSWC)], moderate drought (MD, 50 % RSWC), and severe drought (SD, 30 % RSWC), for two consecutive years during the sprouting period. Plant growth parameters, levels of carbohydrates and N compounds, and activities of key enzymes involved in C and N metabolism were analyzed. In young leaves, C metabolism was in balance after drought stress, but nitrate (NO3−) reduction and ammonium (NH4+) assimilation were accelerated. In old leaves, drought stress decreased carbohydrate contents by spurring the activities of the main enzymes that participate in C metabolism, whereas N metabolism was enhanced only under SD. Roots showed unchanged C metabolism parameters under MD, together with stable NO3− reduction and the key enzymes related to NH4+ assimilation, whereas they were stimulated by SD. Hydrolysates of carbohydrates in old leaves could be transferred into roots, but only to meet MD. Meanwhile, roots could allocate more N nutrition to young leaves and less to old leaves. These changes regulated the overall metabolic balance of F. denudata. Consequently, the results indicate that different organs with various response strategies will be well adapted to different drought intensities for ensuring regular growth of F. denudata plants at the whole-plant level.