Understanding the relationship between biomass production and water use of Populus tomentosa trees throughout an entire short-rotation

Understanding the relationship between tree production and water use, as well as the main environmental and plant-related drivers of water use, is crucial for the establishment of production prediction models and reliable water management under current and future climatic conditions. However, the relation between tree water use and biomass production has never been assessed throughout the entire life-cycle of a poplar rotation; nor have detailed investigations been reported on how poplar transpiration and its regulation change inter-annually. Therefore, we studied the relationship between transpiration ( E ) and aboveground biomass (ABM), as well as the main drivers of E , in a plantation established on the North China Plain, with 2- to 5-year-old (2016 to 2019) Populus tomentosa trees under three water treatments. Our results indicated that ABM increase depended on annually accumulated E and that their relationship can be fitted with a logistic curve for the entire life cycle ( R 2 > 0.89). Throughout the whole rotation period, compared with non-irrigated trees, full irrigation trees produced 59% more biomass with only 12% more E , while deficit irrigation trees attained 46% more biomass with 32% more E . The daily E had a strong exponential relationship with vapor pressure deficit ( D ) during years 3-5 of their growth cycle, which the asymptote of this relationship increasing with tree age (1.6 kPa (2017), 2 kPa (2018), 2.5 kPa (2019)). The E was also strongly linearly correlated to solar radiation ( R s ) for each year although with slightly weaker relationships than for D . Similar to other poplar clones, P. tomentosa showed effective stomatal control on E . However, soil water content had almost no effect, for all treatments, no matter which soil layer was considered. Finally, our research quantified the relationship between tree production and water use throughout the rotation. We also confirmed that D and R s are indeed the major drivers of transpiration during the growing season as well as during drought in this semi-humid boreal region. Our findings should enable a better understanding of the water-use strategies of poplars in the North China Plain and will help sustainably manage plantations in water-scarce regions around the world under changing environmental conditions.