Variations in sap flow of Zenia insignis under different rock bareness rate in North Guangdong, China.

Understanding the impact of rock bareness on the transpiration in karst plants is essential to karst rocky desertification control and sustainable management of plantation in karst area. This study focused on the variations in sap flow of Zenia insignis caused by different rock bareness rate, and the impact of climate factors, soil water content (SWC) and leaf area index (LAI) on transpiration in karst plants, by continuously measuring sap flux densities (Fd) of 12 sample trees using thermal dissipation probes and monitoring micrometeorology and SWC on a typical karst hill in north Guangdong of China during the year of 2016. Results show that: (1) the maximum hourly sap flux density occurred at 11:00–14:00 and the peak daily sap flux density occurred in September. (2) Sap flow density of Zenia insignis increased with rock bareness rate at all hourly, daily and monthly scales, with the sequence of extremely severe > severe > moderate > mild rock bareness. (3) The transpiration of Zenia insignis is controlled by different factors at different temporal scales. At hourly scale, transpiration was highly (n=144, R²>0.72) correlated to Solar radiation (R_s), Air temperature (T_a), relative humidity (RH), and water vapor pressure deficit (VPD). At daily scale, transpiration was greatly (77=366, R²>0.31) affected by Solar radiation (Rs), Air temperature (T_a), and water vapor pressure deficit (VPD). While at monthly scale, transpiration was mainly (n=12, R²=0.8s) controlled by LAI. Our study proved that Zenia insignis has a good physiecological adaption to fragile karst environment, and Zenia insignis plantation has long-term sustainability even in extremely rocky landscapes. The results may provide scientific basis for plantation management and ecological restoration in karst area. [ABSTRACT FROM AUTHOR]