Estimation of water use of Pinus tabulaeformis Carr. in Loess Plateau of Northwest China

Abstract

Tree transpiration plays a determining role in the water balance of forest stands and in seepage water yields from forested catchments, especially in arid and semiarid regions where climatic conditions are dry with severe water shortage, forestry development is limited by water availability. To clarify the response of water use to climatic conditions, sap flow was monitored by heat pulse velocity method from May to September, 2014, in a 40–year–old Pinus tabulaeformis Carr. plantation forest stands in the semiarid Loess Plateau region of Northwest China. We extrapolated the measurements of water use by individual plants to determine the area–averaged transpiration of the woodlands. The method used for the extrapolation assumes that the transpiration of a tree was proportional to its sapwood area. Stand transpiration was mainly controlled by photosynthetically active radiation and vapor pressure deficit, whereas soil moisture had more influence on monthly change in stand transpiration. The mean sap flow rates for individual P. tabulaeformis trees ranged from 9 to 54 L d−1. During the study period, the mean daily stand transpiration was 1.9 mm day−1 (maximum 2.9 and minimum 0.8 mm day−1) and total stand transpiration from May to September was 294.1 mm, representing 76% of the incoming precipitation over this period. Similar results were found when comparing transpiration estimated with sap flow measurements to the Penman–Monteith method (relative error: 16%), indicating that the scaling procedure can be used to provide reliable estimates of stand transpiration. These results suggested that P. tabulaeformis is highly effective at utilizing scarce water resources in semiarid environments.

Using microdialysis to assess soil diffusive P and translocated sap flow P concentrations in Southern Pinus taeda plantations

“…Sap ow P was initially analyzed with atmospheric conditions as a random effect, but adjustments were made due to the high variance between sunny and cloudy conditions. Sap ow P collected during cloudy conditions were increased by 100% based on ndings from previous studies (Xia et al 2008;Jian et al 2019) that reported similar increases during overcast conditions for translocated P. Differences between carryover treatments from Year 0 to Year 1 were analyzed using a two-way ANOVA with P fertilization treatment and treatment year as xed effects. Carryover treatments were separately analyzed within each treatment year and site using one-way ANOVA.…”