Higher canopy transpiration rates induced dieback in poplar (Populus × xiaozhuanica) plantations in a semiarid sandy region of Northeast China

Lining Song, Jiaojun Zhu, Ting Zhang, Kai Wang, Guochen Wang and Jianhua Liu

Agricultural Water Management, 2021, vol. 243, issue C

Abstract: Poplar (Populus × xiaozhuanica) plantations play an important role in controlling desertification in semiarid sandy regions of Northeast China, but their dieback occurs frequently in extreme drought years due to greater water loss by transpiration than water uptake. However, little is known about dynamics of canopy transpiration in poplar plantations, which limits our understanding of dieback mechanisms and proper management of these poplar plantations. Here, canopy transpiration and canopy conductance in 18-year-old poplar plantations were quantified by sap flow measurements in combination with monitoring of concurrent environmental variables during two consecutive growing seasons in normal and wet years (2018 and 2019). Results showed that daily canopy transpiration averaged 1.2 mm d−1 (between 0.3 and 1.9 mm d−1) and 1.5 mm d−1 (between 0.2 and 2.4 mm d−1) in 2018 and 2019, respectively. Solar radiation explained more variability of daily canopy transpiration than vapor pressure deficit (VPD) in both years, indicating that canopy transpiration was more controlled by radiation than by VPD. Total canopy transpiration during the growing seasons in 2018 and 2019 was 184.1 mm and 235.9 mm, respectively, accounting for 47.1 % and 44.2 % of precipitation over the same period. Sum of canopy transpiration, soil evaporation and change in soil water storage was higher than precipitation in most months, indicating that trees took up water from deep soil layer (>1.0 m) and groundwater. Additionally, canopy conductance averaged 1.4 m s−1 and 1.9 m s−1 in 2018 and 2019, respectively, and decreased significantly with increasing VPD. However, sensitivity of canopy conductance to VPD decreased from 0.62 in 2018 to 0.27 in 2019, indicating a shift from more to less strict stomatal regulation. These findings indicate that poplar plantations are vulnerable to dieback during extreme drought years with decline in groundwater level due to utilization of groundwater for higher canopy transpiration rate.

Keywords: Sap flow; Solar radiation; Vapor pressure deficit; Groundwater; Canopy conductance (search for similar items in EconPapers)
Date: 2021
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Citations: View citations in EconPapers (3)

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Persistent link: https://EconPapers.repec.org/RePEc:eee:agiwat:v:243:y:2021:i:c:s0378377420304078

DOI: 10.1016/j.agwat.2020.106414

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