Canopy Rainfall Interception Characteristics Of Grassland Community In Loess Hilly-Gully Region And Its Dominant Species In Response To Simulated Rainfall

Rainfall,the only source of soil moisture,is a key factor in controlling plant growth and distribution in the semiarid loess-hilly region.Vegetation canopy interception is the primary link of rainfall redistribution,which directly affects land surface eco-hydrological processes and the water availability of plant.Quantifying rainfall interception and utilization characteristics of grassland communities and their dominant species is helpful to understand the internal influencing mechanism of canopy interception and the eco-hydrological effects of vegetation restoration.In this study,the abandoned grassland communities and their main species were selected.We systematically measured the seasonal changes of canopy storage capacity and community characteristics,the surface storage characteristics and morphological traits of main species,and leaf photosynthesis and water potential responses of dominant species to simulated rainfall.The main results are as follows:?1?Leaf wettability had obvious inter-species differences and was an important indicator in affecting leaf and plant surface storage.A total of 68 common species in grassland communities were investigated.Leaf contact angles were between 27.3°and 133.4°,and the variation coefficient was negatively correlated with contact angle?r=-0.56;p<0.001?.Leaf wettability was affected by leaf side,family,leaf age and growth period,whereas the life form and slope aspect did not show significant effects.There were 47 species having higher wettability in adaxial surface than the abaxial,and the differences were significant in 23 species?p<0.05?.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 surface storage was negatively correlated with adaxial?r=-0.42?and abaxial contact angles?r=-0.43?.Plant surface storage was negatively correlated with adaxial contact angle?r=-0.42?,whereas it had approximate correlation with abaxial contact angle?r=-0.35;p=0.073?.Leaf wettability is an important plant trait for comparing species differences in rainfall interception performance.The species and seasonal variations of leaf wettability should be taken into account when accurately predicting rainfall interception.?2?Leaf area and wettability index were suitable indicators for judging plant storage capacity.A total of 55 common species in grassland communities were investigated.Plant surface storage ranged from 0.12?1.26 g g^-1,and Glycyrrhiza uralensis and Leymus secalinus had the highest and lowest values,respectively.Rosaceous species had the highest surface storage,followed by leguminous and compositae species,and the gramineous species were the lowest.Leaf storage ratio ranged from 40.2?93.2%,and Glycyrrhiza uralensis and Chenopodium album had the highest and lowest values,respectively.There were 52 species having higher water storage in leaves than that in stems.Among all morphological traits,plant and leaf surface storage were only significantly correlated with leaf adaxial and abaxial contact angles?p<0.05?,same as stem surface storage to stem fresh weight.Storage capacities were closely related to morphological and biomass-related traits,as leaf area had the highest correlations with plant and leaf storage capacities.Path analysis showed that leaf area and adaxial contact angle were two independent variables,directly affecting plant and leaf storage capacities.The ratio of leaf area to adaxial contact angle?i.e.wettability index?had higher correlations with storage capacities than other single trait and multiple regression models of these traits.High proportions of gramineous and leguminous species in grassland community would favor reducing interception loss,increasing soil moisture input,and wettability index can be an effective indicator for predicting plant storage capacity.?3?Canopy storage capacity of abandoned grassland community was closely related to coverage and aboveground biomass.The 2,7,15 and 30-years abandoned grasslands were investigated.From May to September,the community coverage and aboveground biomass increased firstly and then decreased,reaching the maximum in August,whereas there were no significant differences in litter and species richness.The diversity indexes increased firstly and then stabilized in 2-years abandoned grassland.In 7-years abandoned grassland,they increased firstly and then decreased.In 15 and 30-years,they decreased firstly and then increased.With the increase of abandoned years,the coverage,biomass and litter all increased.The species diversity increased firstly and then decreased,reaching the maximum in 15-years abandoned grassland.Canopy,living plants,litter and standing litter storage capacities ranged from 0.11?0.56,0.03?0.51,0.027?0.21 and 0.044?0.17 mm,respectively.The first three reached the maximum in July or August?rainy season?,and the latter did not differ significantly during the month.All of them showed an increasing trend with the increase of restoration years.Canopy storage capacity was positively correlated with the total coverage of each species,fresh biomass,dry biomass,standing litter and litter,and the correlation was decreasing.No significant correlation was found between storage capacity and species diversity.The high storage capacities in 15-and 30-years abandoned grasslands were not only attributed to the high coverage and biomass,but also the surface storage of dominant species?Artemisia gmelinii,Lespedeza davurica?was higher than that in 2-and 7-years abandoned grasslands?Artemisia capillaris,Setaria viridis?.Canopy storage capacitiy increased with the years of vegetation restoration,reaching the maximum in the rainy season.The coverage and biomass were the most suitable variables to explain the change,and the dominant species type had more contribution to storage capacitiy than the diversity of species.Therefore,evaluating vegetation hydrological function requires a comprehensive consideration of vegetation cover and dominant species types,so as to adopt appropriate vegetation restoration strategies.?4?The physiological responses of dominant species in grassland community to rainfall depended on rainfall,species type and growing season.After simulated rainfall in June and August,the net photosynthetic rate?P_n?,transpiration rate?T_r?,stomatal conductance?G_s?and leaf water potential of Bothrichloa ischaemum and Lespedeza davurica and surface soil water content were significantly increased.The peak values appeared in 2?3 days for P_n,T_r and G_s,and 1?2 days for leaf water potential and soil water content.The response magnitude gradually increased with rainfall size.Photosynthetic parameters and leaf water potential of B.ischaemum were more sensitive to simulated rainfall than that of L.davurica,which mainly reflected in the higher increased values under the same rainfall.The increase of photosynthetic parameters and leaf water potential in June was less than that in August.Altered rainfall patterns can cause leaf-level eco-physiological responses of dominant species,which may result in changes in community structure and function.