In May to August of 2011, we assessed the effects of extreme rainfall （quantity and intensity） events on the carbon release from soils covered by different types of biological soil crusts （BSCs） in fixed sand dunes in the Tengger Desert, northern China. A Li-6400-09 Soil Chamber was used to measure the respiration rates of the BSCs immediately after the rainfall stopped, and continued until the respiration rates of the BSCs returned to the pre-rainfall basal rate. Our results showed that almost immediately after extreme rainfall events the respiration rates of algae crust and mixed crust were significantly inhibited, but moss crust was not significantly affected. The respiration rates of algae crust, mixed crust, and moss crust in extreme rainfall quantity and intensity events were, respectively, 0.12 and 0.41 μmolCO2/（m2.s）, 0.10 and 0.45 gmolCO2/（m2·s）, 0.83 and 1.69 gmolCO2/（m2.s）. Our study indicated that moss crust in the advanced succession stage can well adaot to extreme rainfall events in the short term.
Yang ZhaoXinRong LiZhiShan ZhangRongLiang JiaYiGang HuPeng Zhang
Fencing is the most common land-management practice to protect grassland degradation from livestock overgrazing on the Tibetan Plateau. However, it is unclear whether fencing reduces CO_2, CH_4, and N_2O emission. Here, we selected four vegetation types of alpine meadow(graminoid, shrub, forb, and sparse vegetation) to determine fencing effects on ecosystem respiration(Re), CH_4, and N_2O fluxes during the growing season. Despite increased average monthly ecosystem respiration(Re) for fenced graminoid vegetation at the end of the growing season, there was no significant difference between grazing and fencing across all vegetation types. Fencing significantly reduced average CH_4 uptake by about 50% in 2008 only for forb vegetation and increased average N_2O release for graminoid vegetation by 38% and 48% in 2008 and 2009,respectively. Temperature, moisture, total organic carbon, C/N, nitrate, ammonia, and/or bulk density of soil, as well as above-and belowground biomass, explained 19%~71% and 6%~33% of variation in daily and average Re and CH_4 fluxes across all vegetation types, while soil-bulk density explained 27% of variation in average N_2O fluxes. Stepwise regression showed that soil temperature and soil moisture controlled average Re, while soil moisture and bulk density controlled average CH_4 fluxes. These results indicate that abiotic factors control Re, CH_4, and N_2O fluxes; and grazing exclusion has little effect on reducing their emission—implying that climatic change rather than grazing may have a more important influence on the budgets of Re and CH_4 for the Tibetan alpine meadow during the growing season.
YiGang HuZhenHua ZhangShiPing WangZhiShan ZhangYang ZhaoZengRu Wang
