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 (Pn), 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 Pn 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 Pn 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.

Leaf wettability, adhesion or repulsion of water drops, varies greatly among species and plays an important role in plant-soil hydrological relations. This study aimed to examine the variability in leaf wettability among species in different habitats and growth periods, and their relationships with plant surface water retention in the semiarid Loess Plateau of China. The leaf adaxial and abaxial contact angles, the surface water retention of leaves and individual plants, and general plant traits of 68 species belonging to 28 families were examined from May to August in 2017. Results showed that leaf water contact angles ranged from 27.3°to 133.4°and leaves with higher contact angles normally had lower variation coefficients. Leaf wettability was affected by internal properties (including leaf side, family, and leaf age) and external conditions (growth period), whereas the life form and slope aspect did not show significant effects. There were 47 species having higher contact angles on adaxial than abaxial surfaces, and the differences were significant in 23 species. Gramineous and leguminous species were more unwettable than compositae and rosaceous species. New leaves were more unwettable than old leaves. Surface wettability increased from May-June to July-August period. Leaf wettability was positively correlated with leaf surface water retention and was the best predictor of individual plant surface water retention compared with other plant traits. Leaf wettability showed interspecific differences associated with family and growth stage and can be a considerable variable in predicting canopy interception and evaluating vegetation hydrological function in drought environments.

Rainfall is the main resource of soil moisture in the semiarid areas, and the altered rainfall pattern would greatly affect plant growth and development. Root morphological traits are critical for plant adaptation to changeable soil moisture. This study aimed to clarify how root morphological traits of Bothriochloa ischaemum (a C4 herbaceous species) and Lespedeza davurica (a C3 leguminous species) in response to variable soil moisture in their mixtures. The two species were co-cultivated in pots at seven mixture ratios under three soil water regimes [80% (HW), 60% (MW), and 40% (LW) of soil moisture field capacity (FC)]. At the jointing, flowering, and filling stages of B. ischaemum, the LW and MW treatments were rewatered to MW or HW, respectively. At the end of growth season, root morphological traits of two species were evaluated. Results showed that the root morphological response of B. ischaemum was more sensitive than that of L. davurica under rewatering. The total root length (TRL) and root surface area (RSA) of both species increased as their mixture ratio decreased, which suggested that mixed plantation of the two species would be beneficial for their own root growth. Among all treatments, the increase of root biomass (RB), TRL, and RSA reached the highest levels when soil water content increased from 40 to 80% FC at the jointing stage. Our results implied that species-specific response in root morphological traits to alternated rainfall pattern would greatly affect community structure, and large rainfall occurring at early growth stages would greatly increase their root growth in the semiarid environments.

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Climate change is increasing the extreme precipitation depth and frequency, which may cause a strong response of ecological processes in drought regions. To investigate how rainfall depth and frequency alter soil respiration (SR), a rainfall simulation experiment was conducted in grassland communities dominated by Artemisia gmelinii and Lespedeza davurica in Loess Plateau of China. SR rate (R s ), soil temperature (T s ) and soil volumetric water content (S v ) were monitored before and after the rainfall treatments, that is, four depths (5, 10, 20 and 40 mm) and three frequencies (40 mm  1, 20 mm  2 and 10 mm  4) during the growing season (June to September). Results indicated that the response magnitude of R s increased with rainfall depths, reaching the maximum under 40 mm, and the increments were tightly related to rainfall frequency and community type. The increase and mean value of R s in A. gmelinii community were significantly higher than those in L. davurica and bare land under same rainfall depth. L. davurica community was more sensitive to rainfall lower than 10 mm, whereas it had weaker but longer response under rainfall larger than 10 mm compared with A. gmelinii community. Successive rainfall events dampened the pulse effect of R s but generated more cumulative CO 2 emission in vegetation communities. T s and S v varied significantly with rainfall depth and co-regulated SR. These findings implied more CO 2 will be released from soil in the semiarid grasslands under extreme and successive rainfalls and emphasized the importance of species impact on SR for soil carbon evaluation under future rainfall regimes.