Study On Soil Enzyme Activity And Dynamic Characteristics Of Orchard In Loess Plateau Under Mulching Mode

The Loess Plateau is the main production area of high-quality apples in China,and the apple industry has become a pillar industry to promote regional economic development and improve the ecological environment.In recent years,orchard mulching,especially orchard grass mulching,has been promoted as a soil management mode for sustainable development of orchard in apple producing areas on the Loess Plateau.The research on the mechanism of soil quality improvement of orchard by different mulching modes has an important role in optimizing the orchard mulching technology and promoting the promotion of mulching in apple orchard on the Loess Plateau.Soil enzyme is an important indicator of soil quality.Revealing the evolution characteristics of soil enzyme activity in orchard under different mulching modes can provide a basis for further revealing the mechanism of soil quality improvement in orchard under mulching mode.This study was based on the mulching and positioning experiment of apple orchards in weibei Loess Plateau.The soil physical and chemical properties,microbial biomass,soil absolute enzyme activity,soil specific enzyme activity,soil enzyme kinetic parameters and catalytic efficiency of orchard under different mulching treatments were measured,to clarify the change characteristics and influencing factors of soil absolute and specific enzyme activities in orchard under different mulching modes and long-term grass mulching,to reveal the dynamic characteristics and influencing factors of soil enzyme in orchard under long-term grass growing,and to provide a basis for further revealing the mechanism of soil quality improvement in orchard under mulching mode.The main results obtained are as follows:（1）The change characteristics and influencing factors of absolute and specific enzyme activities of orchard soil under different mulching measures were revealed.Straw mulching（CS）,ryegrass mulching（RE）and white clover mulching（WC）increased the absolute and specific enzyme activities of 0-40cm soil layer in different degrees.The activities ofα-glucosidase（AG）,β-glucosidase（BG）,β-xylosidase（BXYL）,cellobiosidase（CBH）,β-N-acetylglucosaminidase（NAG）and alkaline phosphatase（ALP）in 0-40 cm soil layer showed the following pattern:CS>RE>WC>CT.The results of L-leucine aminopeptidase（LAP）showed WC>CS>RE>CT.The changes of soil specific enzyme activities per unit of organic carbon and soil microbial biomass carbon were basically consistent with soil absolute enzyme activity under different mulching treatments.The results of redundancy analysis showed that soil enzyme activity was positively correlated with soil organic carbon,total nitrogen,total phosphorus and other physical and chemical properties,but negatively correlated with p H and bulk density.Organic carbon,total nitrogen,dissolved organic carbon,nitrate nitrogen,ammonium nitrogen and available potassium were the main environmental factors affecting soil enzyme activities.（2）The characteristics and influencing factors of soil absolute enzyme activity and specific enzyme activity in orchard with different grass species were analyzed.The absolute enzyme activities in 0-40 cm soil layer were increased by different types of long-term grass,and BG,NAG and ALP activities were the highest under the treatment of orchard grass（OG）,while LAP showed white clover treatment（WC）>crown vetch treatment（CV）>Orchard grass treatment（OG）>conventional tillage treatment（CT）.Grass mulching increased the activities of soil specific enzyme activities per unit of organic carbon and microbial biomass carbon in 0-40 cm soil layer,and the activities of soilβ-glucosidase per unit of organic carbon（BG/SOC）,β-N-acetylglucosaminidase per unit of organic carbon（NAG/SOC）and alkaline phosphatase per unit of organic carbon（ALP/SOC）were the highest in OG treatment.The activity of soil specific enzyme activities per unit of microbial biomass carbon was different with different grass species.Correlation analysis showed that soil enzyme activity was positively correlated with organic carbon,total nitrogen,microbial biomass carbon and microbial biomass phosphorus,and negatively correlated with p H.Redundancy analysis showed that organic carbon and ammonium nitrogen were common driving factors affecting soil absolute and specific enzyme activities under long-term grassy treatment.（3）The characteristics and influencing factors of soil enzyme dynamics in orchard planted with different perennial grasses were clarified.The maximum reaction rates(V_max)of BG,NAG,LAP and ALP in the 0-40cm soil layer of the orchard were increased by planting long-term grass with different grass species,and the V_maxvalue was greater under OG.The K_mvalue of soil enzyme affinity to substrate under CV and OG was higher than that under CT,while the K_mvalue under WC had little difference with CT.Grass can improve the catalytic efficiency K_catof BG,NAG and LAP,while the K_catof ALP has little difference under different grass treatments.The results of redundancy analysis showed that soil V_max,K_mand K_catwere closely correlated with organic carbon,total nitrogen,total phosphorus,dissolved organic carbon,nitrate nitrogen and available phosphorus,and nitrate nitrogen was the common driving factor of soil dynamic parameters and catalytic efficiency.