Altered precipitation regimes significantly affect ecosystem structure and function in arid and semi-arid regions. In order to investigate effects of precipitation changes on natural grassland community in the semi-arid Loess Plateau, the current research examined eco-physiological characteristics of two co-dominant species (i.e., Bothriochloa ischaemum and Lespedeza davurica) and community composition following two watering instances (i.e., precipitation pulses, July and August, 2011, respectively) in a natural grassland community. Results showed that the photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO2 concentration rapidly increased on the first to third day following watering in both species, and both months. Under watering treatments, the maximum net photosynthetic rates appeared on the second to third day after watering, which increased 30–80% in B. ischaemum and 40–50% in L. davurica compared with non-watering treatments, respectively. Leaf water use efficiency kept stable or initially decreased in both species under watering treatments. Watering in July produced more promoting effects on grass photosynthesis than in August, particularly in B. ischaemum. Community above-ground biomass at the end of the growing season increased after watering, although no significant changes in species diversity were observed. Our results indicated that timing and magnitude of watering could significantly affect plant eco-physiological processes, and there were species-specific responses in B. ischaemum and L. davurica. Pulsed watering increased community productivity, while did not significantly alter community composition after one growing season. The outcomes of this study highlight eco-physiological traits in dominant species may playing important roles in reshaping community composition under altered precipitation regimes.

Plant surface water storage greatly affects rainfall interception in water-limited environments. The storage characteristics of 55 common herbaceous species and their relationships with plant morphology, biomass-related traits, and leaf wettability were examined using artificial wetting method in semiarid Loess Plateau. Results indicated that plant mass storage ranged from 0.12-1.26 g g −1 , and Glycyrrhiza uralensis and Leymus secalinus had the highest and lowest values, respectively. Leaf storage ratio ranged from 40.2-93.2%, with the highest value in G. uralensis and the lowest in Chenopodium album. Fifty-two species had higher storage capacities in leaves than that in stems. Gramineous and leguminous species had relatively lower mass storage and leaf storage ratio than compositae and rosaceae. Plant and leaf mass storage were negatively correlated with leaf adaxial/abaxial contact angles, and stem mass storage was negatively correlated with plant height. Storage capacities were closely related to morphological and biomass-related traits, and leaf area was a better predictor of plant and leaf storage capacities, and stem fresh weight was a better predictor at the stem level. Path analysis revealed that leaf area and adaxial contact angle were two independent variables directly affecting plant and leaf storage capacities. Their ratio (i.e., wettability index) had higher correlations with storage capacities than other single trait and multiple regression models of these traits. Our results implied that high proportions of gramineous and leguminous species in grassland community would favour reducing interception loss, and wettability index can be an effective indicator for evaluating rainfall interception and vegetation hydrological benefits. KEYWORDSleaf area, leaf contact angle, leaf storage ratio, species family, surface water storage, wettability index

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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.

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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.

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Understanding the ecophysiological and nutrient-use strategies of dominant species is important for clarifying plant growth and an ecological process in their community under unbalanced N and P inputs. This study investigated effects of N and P addition [main plot: 0, 25, 50, and 100 kg(N) ha −1 year −1 ; subplot: 0, 20, 40, and 80 kg(P) ha -1 year -1 ] on leaf N and P contents (LNCa and LPCa), photosynthetic capacity (PNmax) and photosynthetic N-and P-use efficiencies (PNUE and PPUE) in three species (Stipa bungeana, Bothriochloa ischaemum, and Lespedeza davurica) in a semiarid grassland in China. At the assessing time, N addition alone significantly increased LNCa and LNCa/LPCa ratio of Stipa bungeana (C3 grass) only, while PNmax increased significantly in all three species. Under N addition, P addition caused significantly lower LNCa, but higher PNUE and PNmax in Bothriochloa ischaemum (C4 grass) and Stipa bungeana. The LNCa, PNmax, and PNUE of Lespedeza davurica (C3 legume) increased significantly after P addition regardless of N application. The LNCa/LPCa for optimum PNUE changed with species. The PNmax and PNUE of Bothriochloa ischaemum and Stipa bungeana had a peak when LNCa/LPCa attained ~ 11 and ~ 20. Lespedeza davurica tended to retain greater PNmax and PNUE at lower LNCa/LPCa. Our results indicated that the C3 grass was more sensitive to N and P addition than the C4 grass and the C3 legume in terms of leaf N and P contents and PNmax. Such interspecific variations of nutrient use in response to N and/or P addition are favorable for maintaining the diversity and the stability of the grassland community.