Research Of Soil Respiration In Different Ecosystems Of Ebinur Lake Area

Arid and semi-arid land area account for about 1 / 3 of the whole land area, whose soil inorganic carbon is the third largest carbon pool in the earth, which inferiors to the oceans and soil organic carbon pool and plays an important role in the global carbon cycle and climate system. Ebinur Lake Basin locates in arid areas, whose ecological environment is fragile, affected by climate greatly, and contrary to other areas, there are extreme weather conditions. Soil respiration rate of Ebinur Lake area is measured from Nov. in 2009 to Sep. in 2010 under the outdoors using an automated CO₂ efflux system(LI-8100), samples are located in farmland ecosystem (cotton fields are 50a and 9a, abandoned lands are 7a and 3a.), solonchalk desert ecosystems(Communities of Populus euphratica and Phragmites australis), sandy desert ecosystem (desert). At the same time, we observe the soil respiration rate and main environmental factors, and then analyze the spatial and temporal variation law of soil respiration rate and its main impact factors, discussing the differences and reasons of soil respiration rate in different ecosystem types, in order to supply basis for revealing the regulation of soil respiration and quantitative description of the Ebinur "carbon sink" effect size. The results show that:1,In farmland ecosystem , soil respiration rate of 50a cotton field shows 2 or 3 peaks in winter, while 9a cotton field shows a single peak. Generally, peaks appear in 13:00 15:00, valley appear time is uncertain, diurnal variation of soil respiration of 50a cotton fields in growing season is little. 9a cotton fields showed a weak bimodal curve in July , 2010 , peak appear in 15:00 and 19:00,showing a strong single peak curve in late growing season (September ,2010), peak at 13:00 in the next day and 4:00 to reach the minimum. 7a abandoned land in March 2010 showed a single valley curve (amount to in 15:00), showing a single peak curve in other months, and whose peak is in the 11:00 15:00. 3a abandoned land in non-growing season is similar to the sine curve, and the peak time of day varies with the seasons, but usually in the 4:00 at night reach the maximum, in the growing season which shows a single peak curve. Only in the growth stage, there is synchronization in trends of farmland ecosystem soil respiration rate and near-surface temperature.2,In solonchalk desert ecosystems, the diurnal variation of soil respiration in Populus euphratica community shows more than 2 to 3 peaks, which inconsistent with the near-surface air temperature trends; soil respiration rate in Phragmites australis community showed a single peak or single valley curve, there is Synchronization in near surface air temperature and soil respiration rate, except for March.3,Sandy desert ecosystem shows a single peak curve in Apr. and Sep. in 2010, and whose peak at 13:00 to 15:00; other months shows 2 or 3 peaks, generally one peak reaches to 11:00 ¹3:00. Soil respiration rate shows more consistent with the diurnal temperature trend.4,All the ecological systems have obvious seasonal changes. Farmland ecosystem is "∽" type, in January or March to reach the minimum, July is maximum, seasonal variation of soil respiration rate is more consistent with the trend of temperature changes; in Solonchalk desert ecosystems , Populus euphratica community in the early winter (Nov.) to reach the minimum, in April and September up to the maximum, Phragmites australis community reaches the minimum value in January, in September reached the maximum; seasonal variation of soil respiration rate and temperature trends are not consistent in those two solonchalk desert communities. Seasonal changes in desert soil respiration showed a single peak, in Nov. to reach the minimum, July is maximum, seasonal changes in desert soil respiration and temperature trends are inconsistent.5,There is no significant relationship between soil moisture of all layers and soil respiration rate in different ecosystems in growing season; in winter, except that there is no significant relationship in soil moisture of 15 30cm and soil respiration rate, there was significant or highly significant relationship in soil moisture of other layers and soil respiration rate, which shows that soil water content is the major factor in soil respiration rate in winter. Relative humidity and soil respiration rate show the negative relevance in the whole year, indicate that air moisture affect soil respiration rate in arid area. There was higher correlation in soil respiration rate and air temperature, near-surface air temperature, soil temperature in 5cm and 10cm depth in all the ecosystems. The range of Q10 values are -0.141 25.765, -0.294 18.265 and 0.176 8.637 in the farmland ecosystems, sandy desert ecosystem, and solonchalk desert ecosystem respectively. Q10 values in all ecosystems are the largest in non-growing season, and the Q10 value of the amplitude in non-growing season higher than in the growing season. Water-temperature and soil respiration in two-factor fitting model could simulate the change of soil respiration rate (R2 = 0.9195～0.9998) in each ecosystem.6,There is the significant and highly significant correlation in both soil respiration rate and wind speed in the growing season, while there is not a significant correlation in non-growing season. There was no significant correlation between soil respiration rate and soil pH, soil microbe in farmland ecosystem; showing significantly negative correlation and positive correlation in 15～30cm and 30～50cm layers'soil porosity, respectively, and shows a cubic equation; and soil respiration rate significantly correlate with soil organic matter content in 30～50cm layer, while shows no significant correlation in others. In winter, there is the significant and highly significant positive correlation in soil respiration rate and 15～30cm and 30～50cm soil total nitrogen content, respectively while showed no significant correlation in the growing season. In farmland ecosystem, soil conductivity and soil respiration shows significant or highly significant positive correlation. In solonchalk desert ecosystem and sandy desert ecosystem, there is no significant relation ship between soil respiration and soil porosity, total nitrogen, organic matter, microorganisms, soil pH, and conductivity. There are no relevance between biomass and soil respiration rate in the same period - different samples and in the same sample -different periods.7,The correlation between snow thickness and 5cm, 10cm ground temperature is higher than between the snow density and 5cm, 10cm ground temperature, and in arid areas when there is snow on the surface, the soil respiration and 5cm soil temperature showed correlation ship (R = 0.383～0.836). However, there is no significant relationship between soil respiration rate and snow depth, snow density.8,In solonchalk desert ecosystem and sandy desert ecosystem of study area, Water - temperature two-factor fitting model could simulate soil respiration rate, but it is not suitable for the farmland ecosystem. This study suggests that it is more reasonable to estimate contribution of winter soil respiration to the whole year soil respiration using the measuring value in the soil respiration in study area.9,For the farmland ecosystem, average annual rate of soil respiration were 3a abandoned land(2.52μmol·m^-2·s^-1)>50a cotton field(2.385μmol·m^-2·s^-1)>9a cotton field(2.024μmol·m^-2·s^-1) >7a abandoned land (0.880μmol·m^-2·s^-1)>Populus euphratica(0.746μmol·m^-2·s^-1)>desert(0.360μmol·m^-2·s^-1)>Phragmites australis(0.127μmol·m^-2·s^-1). Can be seen from the soil reclaimed to abandoned, soil respiration rate shows a decreasing trend after the first growth, showing that solonchalk desert would increase soil carbon release when it is reclaimed, however, when land is abandoned for a certain time, which would become soil carbon sequestration.10,In non-growing season, orders of soil respiration rates of all the ecosystems are: farmland ecosystem(0.564μmol·m^-2·s^-1)> solonchalk desert ecosystems(0.308μmol·m^-2·s^-1)>sandy desert ecosystem(0.212μmol·m^-2·s^-1).In growing season, the orders were: farmland ecosystem(4.728μmol·m^-2·s^-1)> solonchalk desert ecosystems(0.703μmol·m^-2·s^-1)>sandy desert ecosystem(0.658μmol·m^-2·s^-1). In growing season soil respiration rate of all the ecosystems are higher than in non-growing season, showing that: the ratio of former and latter in farmland ecosystem is 11.926,solonchalk desert ecosystems is 3.172, sandy desert ecosystem is 3.104. The biomass, soil properties, litter and other factors impact jointly the differences of soil respiration in different ecosystems.11,Soil CO₂ emission in growing season was higher than non-growing season. Soil CO₂ emission was the largest in 9a cotton field in non-growing season, and minimum of soil CO₂ emission existed in Phragmites australis communis community. Soil CO₂ emission was the largest in 3a abandon field in growing season, and minimum of soil CO₂ emission existed in Phragmites communis community. The winter soil CO₂ efflux is from 8.072 to116.378 gC·m^-2, average is 77.242 gC·m^-2; In all the samples, the contributions of winter soil CO₂ efflux to annual soil respiration were 4.82%～33.34% and 23.52%～81.58%.12,Sensitivity of seasonal frozen soil thickness in arid area to the soil temperature than air temperature; In arid seasonal frozen soil area, with the climate warming, large ecosystem of human disturbance had higher sensitivity on external thermal disturbances; in frozen area, soil temperature is the most important factor of seasonal frozen soil thickness while it was not influenced by environmental factor during frost free period; there were different degrees of impact on depth of frozen earth to soil respiration rate in different periods, showed that there was significant positive correlation between soil respiration rate and depth of frozen earth during the freezing period (R2=0.782, P<0.05), while there was no correlation during the initial stage of freezing period(P>0.5); there was no significant difference of soil respiration rate between the freezing period and the initial stage of freezing period, while soil respiration rate significantly increased with the temperature increased until soil unfrozen completely(D-value is 0.140～0.370μmol·m^-2·s^-1).13,Soil respiration rates of 3a abandoned land in March and April are negative, which may be due to melting snow and rainfall making microbial respiration inhibited; the whole year, soil respiration rates of Phragmites australis community are negative, except Nov. in 2009, and shows weak carbon sink about -0.014 gC·m^-2 in January to Feb., whose reason may be that ice coverage, water in atmospheric and soil surface and CO₂ in atmospheric generate carbonate, depositing in the soil. Characteristics of different plant species and other reasons which interact together.14,Fertilization and irrigation would not increase soil respiration rate directly, while increase indirectly the soil respiration rate through increasing the supply capacity of soil nutrients and plant biomass.