Soil Respiration Characteristics And Its Influencing Factors Of Desert Steppe With Different Closure Years In NingXia

Soil respiration (Rs) is an important source of atmospheric CO2. Soil respiration is an important component of an ecosystem’s carbon cycle and the main pathway for carbon moving from the ecosystem to the atmosphere. It is essential to global-scale carbon cycle regulation. Grassland ecosystem has become one of the most important carbon stocks of terrestrial, and it is significant in the global carbon cycle. Therefore, study the mechanism of grassland ecosystem carbon cycle, estimate the grassland ecosystem carbon storage, and estimate the value of grassland ecosystems in global change and ecological, these are significant. In this study, we used desert steppe with different closure years in Ningxia as the research object. Combined with dynamic chamber method and statistical analysis method. In order to explore soil respiration characteristics and influencing factors of the different fenced years in arid desert grassland, we continuously observed Rs rate and environmental factors on 2014 to 2015 of fenced enclosure 11a,7a and no fenced (CK) desert steppe in Ningxia. Systematic study of diurnal, seasonal, annual dynamic variation of Rs, analyze the relationship between Rs rate and soil temperature, humidity and other factors,The main results of the study were as follows:(1) On the seasonal scale,, Total nitrogen, Alkali solution nitrogen, available phosphorus, soil organic carbon, soil organic carbon density, soil urease activity, alkaline phosphatase activity were showed as the enclosure> no enclosure, Available potassium, pH value, total phosphorus, soil catalase activity, invertase activity were showed as the enclosure<no enclosure. Soil nutrients, organic carbon and enzyme activity maximum in 0-40 cm soil layer. According to statistical analysis, it indicated that soil organic carbon had a significant positive relationship with Total nitrogen, soil organic matter, organic carbon density, soil catalase activity, urease activity, invertase activity, alkaline phosphatase activity in fenced enclosure of 11 years,7 years, CK desert steppe (P<0.01).Soil enzyme activity had a positive relationship with soil organic matter, soil organic carbon, and other enzyme activity (P<0.05). Soil quality index SQI in 2014 to 2015 were showed as 11 a> 7a> CK.(2) On different time scales, R, rate had a obvious single peak curve variation in fenced closure of 11 years, 7 years, CK desert steppe. On the daily scale, the maximum and minimum values of Rs rate were found in 12:00-16:00 and 00:00-06:00, respectiveiy. On the month scale, month maximum is in August and September, the minimum is in January. And all were expressed as the enclosure> No fencing. Rs rate were expressed as 11a> 7a> CK in two growth stages. The annual average Rs rate of two years were showed as lla [0.089 g·(m2·h)-1]>7a [0.081 g·(m2·h)-1]>CK [0.079 g·(m2·h)-1]. On the interannual variability it showed as 2014> 2015.(3) On different time scales, soil profile CO2 concentration in 5 cm to 20 cm has obvious single peak curve variation in fenced closure of 11 years,7 years, CK desert steppe. With the increasing of soil depth, CO2 concentration in soil profile increased. The CO2 concentration in soil profile was first increased and then decreased in the growing season, was showed firstly decrease and then increased in the non growing season. Treatments showed 7a> 11a> CK. On the annual scale, month maximum is in July, the minimum is in January. On the interannual variability it showed as 2014> 2015. By mathematical statistical analysis, on the day, month, year scale, CO2 concentration in soil profile had a significant positive correlation with soil temperature, rainfall (P<0.05).(4) On different time scales, it indicated that Rs rate had a significant exponential positive relationship with air and soil temperature in fenced enclosure of 11 years,7 years,CK desert steppe (P< 0.01). The temperature sensitivity coefficient Q10 increased gradually with the soil depth, and 0-20cm mean value of Q10 in different fenced enclosure years was showed as 11a>7a>CK. On the day scale, A significant quadratic function model was observed for the relationship between Rs rate and relative air humidity, soil moisture content of fenced enclosure 11a,7a and CK desert steppe in whole growing season(P<0.05). On the day, month, year scale, A extremely significant quadratic model was observed for the relationship between Rs rate and rainfall of fenced enclosure 11a,7a and CK desert steppe in whole growing season(P<0.01). It showed a significant quadratic regression model between Rs rate and air CO2 concentration,5-20cm CO2 concentration in soil profile on the monthly and yearly scale (P <0.05). By principal component analysis the present study meteorological environmental factors,0-20 cm soil temperature and moisture were the main influencing factors of soil respiration of arid desert steppe.(5) The aboveground biomass and underground biomass showed a single peak curve of fenced enclosure 11a,7a and CK desert steppe in whole growing season. On the annual scale, month maximum is in August. Treatments showed 11 a>7a>CK. There was a significant linear positive correlation between Rs rate and aboveground biomass, underground biomass, aboveground and underground biomass of different closure years desert steppe (P<0.05). The relationship between Rs rate and soil pH value, soil organic matter, soil organic carbon, soil organic carbon density and soil catalase activity was negatively correlated of different closure years desert steppe (P<0.05).(6) Net ecosystem productivity NEP of desert steppe were showed as 11 a> 7a> CK, and NEP>0 in fenced closure of 11 years,7 years, CK desert steppe. It indicated that carbon balance of desert steppe ecosystem expressed as carbon sinks. And after enclosure recovery, net ecosystem productivity of desert steppe was higher than the grazing desert steppe.In summary, forbidding grazing enclosure measures in a certain extent could improve soil organic carbon content and soil enzyme activity in desert steppe, it effectively improved the soil quality index. Forbidding grazing enclosure measures play a certain role in degraded grassland vegetation restoration and improvement of soil nutrients. With enclosure-year increasd, soil respiration increased. With the increase of soil depth, the temperature sensitivity coefficient increased gradually. Soil respiration of fenced enclosure 11a,7a was showed better than grazing without enclosure. Sureface soil water and thermal conditions were the main influencing factors of soil respiration of arid desert steppe. Desert steppe ecosystem performance "carbon sink" in the carbon cycle. This study has important implications to understand the role that different fenced enclosure years play in carbon emission. Such information will lay a foundation for assessing carbon source or carbon sequestration of different fenced enclosure years in desert steppe. Therefore, our research results have important function for better managing grassland in desert steppe in Ningxia and other arid and semiarid areas of North China. In conclusion fenced enclosure measures can effectively improve the arid desert grassland soil respiration, It has some important implications for global climate change.