Responses Of Soil Respiration To Rain Additions In A Nitraria Sphaerocarpa Community In Hvperarid Area

Soil respiration is the main components of terrestrial ecosystem carbon cycle and in a verykey process of positive feedback between climate warming and global carbon cycle.In order toevaluate the uncertainty of forecast global climate change, we need to understand urgently theresponse of soil respiration to global warming. As one of the main features of global climatechange, change of rainfall patterns may have alterated global carbon cycle. The effect ofrainfall on the ecological system carbon cycle is more important in arid region, which have thecharacteristic of vast area and easy to effected by water. Climate models predict that moreextreme precipitation events will occur in the arid regions in China. To discuss the potentialeffects of rain addition on the soil respiration in arid region, Manipulative rain additionexperiment with diffetent treatments was conducted in Dun huang during the growing seasonin form2010to2011. With Li-8100automated soil CO2flux system, Soil water content,surface temperature and soil respiration rates were measured in both bare and vegetated soilsbefore and after the rain addition for each rain treatment. The main results and conclusionsfrom this study included:(1) The rain enrichment could increased bare and vegetated soils respiration rate. Themore the rainfall enrichment, the greater the increment and the longer duration time effect tosoil respiration rate.200%(16mm) and300%(24mm) of the rain enrichment couldsignificantly increased bare soil respiration rate90%and106%(P<0.01), respectively. Bycontrast, Soil respiration rate in shrubs areas with100%(8mm),200%(16mm) and300%(24mm) of the rain enrichment could significantly increased68%,157%and205%(P<0.01),respectively. The response time of bare and vegetated soil respiration to rainfall enrichment isasynchronous. Response variable of soil respiration in vegetated soil is higher118%than soilrespiration in bare soil. For every1mm increment of precipitation, the soil respiration rateincreased by0.01and0.04μmol·m^-2·s^-1respectively in vegetated soil and bare soil. (2) There was significant positive correlation between soil respiration rate and soil watercontent during the growing season (P<0.01), but there was no significant positive correlationbetween soil respiration rate and soil water temperature. The relationship between soil watercontant, soil temperature and soil respiration suggested that soil respiration rate remainunchanged with soil temperature increased if the soil water contant was smaller and soilrespiration rate was increased with soil temperature increased if the soil water contant waslarger. When the temperature unchanged, soil respiration rate was increased with increased ofsoil water content. This suggested that soil water availability determines the carbon balance inhyperarid area with the increased rainfall in future.(3) The seasonal variation of soil respiration in bare and vegetated soils present a singlepeak curve under all rain addition treatments. Rain addition treatments increased diurnal meanvalues of relative change of soil CO2efflux in both vegetation cover types of this desertecosystem. Rain addition increased the basal rate soil CO2efflux in the vegetated soils, but hadno effect on basal rate soil CO2efflux in the bare soil. The sensitivity soil CO2efflux totemperature (Q10) was enhanced with the increase in rain addition size in the bare soils, butthere was no such relationship between Q10and rain addition size in the vegetated soils. Bycontrast, with200%(16mm) of the rain enrichment could significantly increased Q10of baresoils.(P<0.01). but there was no obvious influence to Q10of vegetated soils.(4) Increasing rain was able to accelerate the vegetated and bare soil respiration in theplots. Increasing rainfall1mm, the soil carbon emissions in vegetated and bare soil increased1.12g·m^-2and0.27g·m^-2, respectively. Given the community cover, every increase of1mmrainfall could increase0.69g·m^-2of soil carbon emissions compared with the control treatment.Soil carbon emissions will increased in hyperarid area on the condition that moreprecipitation in future. There was more significant influence on carbon emissions of vegetatedsoil than carbon emissions of bare soil.(5) Under the same condition of rain addition, the mean of soil respiration rate of4×4mmand2×8mm rain addition treatments was significantly higher than that of the1×16mm, but nosignificant changes in vegetated soil(p>0.05). It is indicated that several times of small rainfall event could lead to more larger carbon loss than a larger rainfall events in monthlyscale.Altered rainfall timing (100%increase in length of dry intervals between events) couldnot significantly increased or reduced soil respiration rate in both bare and vegetatedsoils(p>0.05).