| Rainfall is the main factor that affect the development and succession of naturalgrassland community in loess hilly-gully region and rainfall pattern change will haveprofound effect on its community structure under the background of global climate change.Understanding its rainfall redistribution characteristics and response of dominant species willcontribute to accurately assess the impact of climate change on grassland ecosystem, andprovide theoretical basis for vegetation construction and recovery. Six different artificialprecipitation events (0mm,3mm,5mm,10mm,20mm,30mm) were applied to natural grasslandcommunity, which was dominated by Bothrichloa ischaemum(C4grass) and Lespedezadavurica (C3subshrub), before the rainy season (in June) and during the rainy season (inAugust) in loess hilly-gully region. The rainfall redistribution characteristics, photosyntheticphysiological indexes of the species, soil moisture content were measured, and The mainresults were as follows:1. Canopy interception capacity had a quadratic polynomial relationship with rainfallamount, while the ratio of canopy interception capacity to rainfall had a negative indexequation relationship with rainfall amount in two months. The redistribution of30mm rainfallin June and August were mainly lost by runoff (45.0%) and infiltration (47.4%) respectively.Canopy interception and rainfall infiltration capacity in August were higher than in June.2. Rall pulse in June significantly affected soil moisture beween0-50cm layers. Both B.ischaemum and L. davurica showed significant increase in photosynthetic rate, transpirationrate, intercellular CO2concentrations and stomatal conductance after rain pulses. Theminimum threshold of rainfall that caused B. ischaemum and L. davurica photosyntheticresponse were5and10mm, respectively. The level and duration of B. ischaemum response torain pulse increased gradually with rainfall size while L. davurica decreased when rainfallreached30mm. 3. Soil moisture content and pofile distribution did not change obviously after rain pulsesin August beween0-120cm layers, because sufficient natural rainfall before treaments,saturated soil in the profile, and no obvious changes in photosynthetic performance of B.ischaemum and L. davurica were observed either.4. Only20mm and30mm rain pulses in June significant improved community biomassproduction by11.6%and16.8%respectively, but had no effects on soil moisture storagecapacity.3mm5mm and10mm rainfall in June and all the rain treatments in August had noeffects on biomass production and soil moisture in community. Results suggest that singlelarge rain event in special time could significantly affect grassland community netproductivity in semiarid regions, but short-term physiological responses are not completelyconsistent with community productivity. |
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