Effect of changing precipitation in different periods on precipitation use efficiency in a semi-arid grassland

Climate change intensifies global and regional water cycles, leading to changes in both the magnitude and timing of precipitation. Precipitation use efficiency (PUE) plays a crucial role in measuring the response of above-ground net primary productivity (ANPP) to precipitation changes. However, little is known about how changes in precipitation during different periods affect PUE. Using a manipulation precipitation experiment in a semi-arid steppe, we simulated a 60% increase and decrease in precipitation during the early (April-June), late (July-September), and entire (April-September) growing seasons across 2015-2021 to examine the effects of changes in precipitation timing on PUE. The results showed that: (1) decreased precipitation in the late growing season (DLP) and whole growing season (DWP) stimulated PUE by an average of 0.14 and 0.12 g m-2 mm-1 yr-1, respectively, whereas increased precipitation in the late growing season (ILP) and whole growing season (IWP) suppressed PUE by ..., The experiment was conducted on April 15th of 2015 with a completely randomized block design. The experiment had seven treatments, including control (C), a 60% decrease in precipitation during the early growing season (from April to June, DEP), late growing season (from July to September, DLP), and whole growing season (from April to September, DWP), a 60% increase in precipitation during the early growing season (from April to June, IEP), late growing season (from July to September, ILP), and whole growing season (from April to September, IWP)., , We classified the plants by species and then dried them at 65°C until they reached a constant weight. We chose 34 common species, which accounted for more than 95% of the above-ground biomass, for trait measurements at the flowering time from July 1st first to August 20th in 2018 to measure plant functional trait. There were three replicates per species. Evapotranspiration was measured using LI-6400 Portable Photosynthesis System (Li-Cor Inc, Lincoln, NE, USA), which connected to a transparent chamber (0.5m x 0.5m x 0.5 m) three times a month. The transparent chamber was placed on a permanent aluminum frame (0.5 m x 0.5 m), which inserted into the soil with a depth of 3 cm. There were two fans inside the chamber running continuously to mix the air during measurements. The water flux was recorded every 10 seconds during 90 seconds. ET was calculated based on the time courses of water flux. In mid-September of each year, two 20 cm soil cores were drilled using a 7cm soil auger, and the so...