Effects Of Rice Cultivation On Peatland Soil Enzyme Activities

Peatlands store nearly one third of terrestrial soil organic carbon,and their slight changes will affect the concentration of greenhouse gases in the atmosphere,so they occupy an important position in the global carbon cycle and global climate change.Due to the increased pressure from population,large areas of peatland have been reclaimed into cultivated land.In the process of peatland reclamation,human activities(fertilization,drainage,tillage,etc.)interfered and the natural evolution of the ecosystem was destroyed,which changed the process of original material cycle in peatland.So the reclamation of peatland may lead to the transformation of soil carbon “source” and “sink” functions and produce significant ecological and environmental effects.Therefore,it is necessary to strengthen the study of peatland carbon cycle for global carbon cycle and response to global climate change.Soil enzymes participate in the biochemical processes such as the decomposition of organic matter,nutrient cycle,and energy transfer in soil.And the decomposition of soil enzymes restricts the process of soil material and energy cycle,so their activities are often used as an indicator of microbial activity,nutrient status and the decomposition and synthesis rate of humus and various organic matter in soil,which play an important role in revealing the cycle process and the related relationships of soil carbon,nitrogen,phosphorus and other substances in the ecosystem.In this study,in order to investigate the effect of rice cultivation on soil physical,chemical properties,soil enzyme activities and relationships of them in peatland,we collected soil samplings in spring,summer and autumn from Jinchuan peatland,and the soil cores were collected at depths 0~60 cm in the stratigraphic profile.The main results were as follows:(1)Rice cultivation significantly increased soil pH,the content of ammonium nitrogen,total phosphorus and available phosphorus in upper soil layer,but significantly reduced the content of soluble organic carbon,total phenol and soil organic carbon and total nitrogen in the middle and upper soil layer.In the vertical profile,the soil pH and the content of ammonium nitrogen in paddy-peatland decreased with the increase of depth,but the content of the total nitrogen and phenol increased with the increase of depth,while other physical and chemical properties were similar to those in the natural peatland.In seasonal variations,the content of organic carbon and total nitrogen in upper soil of paddy-peatland had significant variations,but not on ammonium nitrogen.Besides,other soil physical and chemical properties in paddy-peatland and natural peatland were with similar seasonal change.(2)Rice cultivation significantly increased the activities of ?-1,4-glucosidase(?G),phenol oxidase(PPO)and peroxidase(PER),but inhibited the activities of ?-1,4-N-acetylglucosaminidase(NAG)and acid phosphatase(AP).In the vertical profile,rice cultivation had a significant effect on ?-1,4-N-acetylglucosaminidase(NAG)and acid phosphatase(AP)in spring.In seasonal changes,the soil enzyme activities of paddy-peatland and natural peatland generally showed a consistent pattern,the maximum activities of enzymes occurred in spring,and the minimum were in autumn.(3)The ?-1,4-glucosidase(?G)related to carbon cycle was significantly correlated with soil pH,the content of ammonium nitrogen,nitrate nitrogen,total phosphorus and total phenol.?-1,4-N-acetylglucosaminidase(NAG)related to nitrogen cycle was significantly correlated with the content of total nitrogen,ammonium nitrogen and nitrate nitrogen.Acid phosphatase(AP)related to phosphorus cycle was significantly correlated with the content of total nitrogen and total phosphorus.Two oxidase activities were significantly correlated with soil physical and chemical properties.It can be seen that soil pH and the content of nitrogen and phosphorus had more significant effects on soil enzyme activities.(4)Rice cultivation increased the enzyme activities related to soil carbon cycle,and accelerated the degradation of soil organic carbon,so it is not conducive to the accumulation of organic carbon in peatland,affecting its carbon sink function.