Effect of Multiple Wet-Dry Cycles on Soil Carbon Cycling in Farmland
|Keywords||wet-dry cycles soil organic carbon Birch effect CO2 dissolved organiccarbon microbial biomass carbon microbial biomass soil enzyme soil aggregate|
Global warming is the main symbol of climate change, which caused by the temperature and humidity changes in soil organic carbon will also have an important impact. Farmland soil organic carbon change has been well recognized is land ecological system for carbon source and sink effect the important basis. And in recent years appear constantly extreme climate also warned it is necessary for us to study and predict these might occur during the process of change, one of the very important aspect is heated water cycle (evaporation and precipitation). These changes will affect the intensity and frequency of the alternating wet and dry seasons, thus affecting the farmland soil microbial community and their participation in the all physiological and biochemical process.In order to research the multiple alternating wet and dry seasons pattern and soil aggregate size on soil carbon cycle, the influence mechanism, this paper through the indoor incubation test, including a test in three different aggregate size surface soil (0-20cm) for the tested soil, from respiratory rate, soluble organic carbon release and microbial biomass change of key research the multiple dry-wet circulation and soil aggregate grain size of the effect of Birch. The results show that after water promoted the soil respiration, increased the soil microbial biomass, but to microbial quantity and breathing produce surge effect did not last long. After water3h respiratory rate peak, and along with the dry and wet cycle reduce with the increase of the frequency, including soil particles through the four wet cycle to reduce. Different soil aggregate grain size of Birch effect of strength different, but both and is not a simple linear relationship. Soil aggregate can protect part of the organic matter is not microbial decomposition mineralization, multiple alternating wet and dry seasons interference the protection function, improve the organic carbon biocompatibility. Birch effect in mineralization of organic carbon is more from the new organic matter of exposure, part of the drought period from microbial cells accumulation of solute. It is important to note that with the increase of the number of dry-wet circulation, be exposed new organic matter in mineralization decomposition may before there is still other intermediate process.Test two simulated natural dry-wet cycle, at the same time set constant water content control test, focus on the slow drought and fast after water treatment methods on soil organic carbon change trend, the influence mechanism. The results show that with the constant water content than control group, multiple alternating wet and dry seasons treatment can improve soil mineralization, the soil microorganisms in multiple water within24hours of rapid increase, four wet and dry period makes the total microbial biomass carbon grew by an average of45%. The soil organic carbon of solubility in water is complex microbial utilization, reduce the rate of10%～20%. But there is no foreign carbon supply situation, four alternating wet and dry seasons make soil total organic carbon is the original level was reduced by21%.To sum up, the soil drought experience after water, soil respiration and microbial biomass in a few hours increased significantly. Soil aggregate to the organic carbon decomposition mineralization have certain protective effect, to mobilize soil organic carbon have important influence. But multiple dry-wet cycle will destroy soil aggregate structure, be exposed organic matter is further microbial decomposition mineralization, thus increasing inert organic carbon biological availability. Soluble organic carbon in the complex water increased, this may come from microbial cell after water release of osmotic regulation substances, these carbon is then surviving microorganisms rapid decomposition, release a large amount of CO2. After multiple dry-wet cycles, drive soil respiration release CO2power is more from the physical and chemical process, but is not strictly physiological process.