Small rainfall pulses affected leaf photosynthesis rather than biomass production of dominant species in semiarid grassland community on Loess Plateau of China

In the semiarid region Loess Plateau of China, rainfall events, typically characterised as pulses, affect photosynthesis and plant community characteristics. The response of dominant species and grassland community to rainfall pulses was evaluated through a simulation experiment with five pulse sizes (0, 5, 10, 20 and 30 mm) in the semiarid Loess Plateau of China in June and August of 2013. The study was conducted in a natural grassland community dominated by Bothrichloa ischaemum (L.) Keng and Lespedeza davurica (Lax.) Schindl. In June, the leaf photosynthetic rate (P-n), transpiration rate, stomatal conductance, intercellular CO2 concentration of both species and soil water content increased rapidly after rainfall pulses. B. ischaemum was more sensitive to the pulses and responded significantly to 5 mm rainfall, whereas L. davurica responded significantly only to rainfall events greater than 5 mm. The magnitude and duration of the photosynthetic responses of the two species to rainfall pulse gradually increased with rainfall sizes. The maximum P-n of B. ischaemum appeared on the third day under 30 mm rainfall, whereas for L. davurica it appeared on the second day under 20 mm rainfall. Soil water storage (0-50 cm) was significantly affected under 10, 20 and 30 mm rainfall. Only large pulses (20, 30 mm) increased community biomass production by 21.3 and 27.6% respectively. In August, the effect of rainfall on the maximum P-n and community characteristics was generally not significant. Rainfall pulses affected leaf photosynthesis because of a complex interplay between rainfall size, species and season, but might not induce a positive community-level feedback under changing rainfall patterns.