Effects Of Precipitation Change On Soil Labile N Pools And Net N Mineralization In Semiarid Grassland Of Inner Mongolia

Currently, it's not certain to make sure that how the precipitation change affects the semiarid steppe ecosystem.To study the impact of changes in precipitation quantity and precipitation pattern on ecosystem functions in Inner Mongolian semiarid grassland, we set two different manually controlled experiments about different patterns of precipitation quantity and precipitation distribution in Xilinhot, Inner Mongolia, including rainout shelters to manipulate precipitation experiment platform in Xiwuqi?reduced 30%?P-30%? and 60%?P-60%? growing precipitation, control ?CK? and increased 30%?P+30%? and 60% ?P+60%? growing precipitation and increased 30%?P+30%? and 60%?P+60%? growing precipitation once in the beginning of every month? and rainout shelters controlling growing season precipitation quantity and patterns experiment platform in Inner Mongolia Grassland Ecosystems Research Station, Chinese Academy of Science ?precipitation quantity experiments:100 mm?150 mm?200 mm?300 mm? 350 mm?400 mm?450 mm?500 mm growing precipitation; precipitation patterns experiments:275 mm growing precipitation distribution at the amount for early-to middle-growing season was 1:1?1:2?1:4? 1:8; extreme precipitation patterns experiments:100 mm and 500 mm growing precipitation distribution at the amount for early-to middle-growing season was 1:1 and 1:8?. During the growing season we controlled the precipitation quantity and precipitation patterns to study the variation of soil water content, grassland productivity, soil labile N pools and soil net N mineralization rate of semiarid steppe ecosystem in Inner Mongolia.?1? The main conclusions of precipitation quantity control experiments were as follows:? Soil moisture content significantly increased with increasing precipitation quantity, while it significantly decreased with reduced precipitation quantity. The effect of changes precipitation distribution treatments on soil moisture content was significantly higher than that in increasing precipitation quantity treatments.? Aboveground and belowground net primary productivity ?ANPP and BNPP? significantly increased with precipitation quantity increasing and changes in precipitation quantity distribution treatments, which were higher than that in other treatments. There were significantly relationship between ANPP and BNPP and soil moisture content.? Increased precipitation quantity reduced soil ammonium ?NH₄⁺-N?, nitrate ?NO₃^--N? and inorganic nitrogen ?NH₄⁺-N+NO₃^--N? concentration, while reduced precipitation quantity has significantly increased the concentration of NH₄⁺-N, but significantly decreased the concentration of NO₃^--N and NH₄⁺-N+NO₃^--N; With changes in precipitation quantity, soils NH₄⁺-N concentration was negatively related to soil moisture content, NO₃^--N and NH₄⁺-N+NO₃^--N concentration were significantly related to soil moisture content.? Increased precipitation quantity and changed precipitation quantity distribution treatments had no effect on soil microbial biomass carbon ?MBC?. MBC decreased with precipitation decreasing, while no effects were found in increased precipitation on soil microbial biomass nitrogen ?MBN?. However, MBN was significantly decreased with precipitation quantity reduced. Soil MBN significantly increased with changes in precipitation quantity distribution. Increased precipitation quantity and changed precipitation quantity distribution treatments had no effect on soil microbial biomass carbon to nitrogen ratio ?MBC/MBN?, but the ratio of MBC/MBN significantly increased with precipitation quantity decreasing. No significant correlation was found between MBC and soil water content across all precipitation quantity treatments; a significant negative correlation had found between MBC/MBN and soil water content.?2? The main conclusions of precipitation patterns control experiments were as follows:? Soil water content increased with quantity of growing season precipitation increasing, Changes in precipitation patterns did not significantly alter the soil water content. Effects of extreme drought and extreme precipitation on soil water content were not significantly.? ANPP and BNPP significantly increased with quantity of growing season precipitation increasing, and had a significant positive correlation with soil water content. Precipitation quantity and precipitation patterns in the pattern of had no significant effects on belowground biomass. Extreme precipitation treatment of ANPP and BNPP were significantly higher than treatments of extreme drought treatment. It had no significant correlation between belowground net primary productivity and soil water content under treatments of precipitation patterns, soil water content were significantly related with ANPP and BNPP under treatments of precipitation quantity and precipitation patterns changes.? Soils NH₄⁺-N concentration were increased with precipitation quantity increasing in middle and late of growing season in 2014. Effects of precipitation changes on soil NO₃^--N and NH₄⁺-N+NO₃^--N concentrations in middle and late of growing season in 2014 and the growing season in 2015 on soil NH₄⁺-N, NO₃^--N and NH₄⁺-N+NO₃^--N concentrations was not significant. There were no significant effect were found in precipitation patterns and extreme precipitation patterns ?extreme droughts and extreme precipitation treatments? on the soil of NH₄⁺-N, NO₃^--N, NH₄⁺-N+NO₃^--N concentrations. Soil water content was positively related with soil inorganic N concentrations under precipitation quantity and precipitation pattern treatments.? Precipitation quantity changes had no effect on soil microbial biomass in 2015, the ratio of MBC/MBN was significantly lower than other four treatments under the 500 mm precipitation quantity treatments of growing season in 2015.No effect were found in changes in precipitation pattern and extreme precipitation patterns on soil microbial biomass. MBC and MBN under treatment of precipitation quantity, and MBC and MBC/MBN under treatment of precipitation patterns were positively correlated with soil water content.? No significant effects were found in precipitation quantity, precipitation patterns and extreme precipitation patterns ?extremes of drought and extreme precipitation patterns? on the soil net ammonification, nitrification and N mineralization rates. Net ammonification, nitrification and N mineralization rates were not significant related with soil water content under precipitation quantity and precipitation pattern treatments.In summary, the precipitation change under the background of grassland of inorganic nitrogen and the change of the net nitrogen mineralization rate could be a litter, plant and soil environment and the result of many factors such as soil microbial interactions. For ecosystems change slowly, but will have a profound impact on the process, long-term manipulation experiment is also vital necessary.