Whole plant water status and non‐structural carbohydrates under progressive drought in a Caatinga deciduous woody species

Progressive drought induced a gradual increase in non-structural carbohydrates in roots and leaves, slowing the drop in water status. The roots had an increase of 95 % compared to well-watered plants, while the leaves only increased by 21 %. Since Cenostigma pyramidale is a deciduous species, the non-structural carbohydrates are mainly found in the roots, which helps the plant survive the intense drought period. The ability to produce and control the distribution of non-structural carbohydrates (NSC) may be critical to the success of deciduous woody plants from seasonally dry tropical forests. Thus, our aim was to investigate how carbohydrate allocation occurs and the dynamics of water status during the pre-senescence leaf period. We performed a controlled experiment on progressive drought stress using Cenostigma pyramidale, and found that leaf relative water content decreased only under severe drought conditions (SVD), when soil water content was approximately 5%, three times less than well-hydrated plants, and foliar relative water content (RWC) was close to 35%. Gas exchange was maintained at a high level until the moderate drought stage (MD), with soil water content and RWC of 8% and 75%, respectively. Prior to leaf senescence, C. pyramidale maintained the net CO2 assimilation and intense production of NSC, which were stored mainly in the leaves (45%), and roots (44%), with only 11% in the stems. This increase in root NSC content during progressive drought levels suggests that this tissue may be the main storage site for NSC, which could allow the plant to survive the dry season, and also have reserves for leaf sprouting at the beginning of the next rainy season. The results suggest that studies involving carbon metabolism in woody species under stress should consider root tissue, as this is an important source of NSC during drought.