Effects Of Orchard Litter Decomposition On The Stoichiometry Characteristics Of Soil Eco-Enzymes

Orchard is an important part of ecological agriculture construction,and it is the basic unit of?soil and water conservation type?ecological agriculture,?pig-marsh-fruit?recycling agriculture,?sightseeing orchard?tourism agriculture.It can not only improve the economic income of rural residents,but also beautify the village appearance.It is an important part of building beautiful countryside and beautiful economy.But,orchard management may strongly affect microbial metabolism and soil nutrients cycling due to human disturbance.However,current researches rarely explore the impact of economic forests on soil nutrients cycling and microbial metabolic functions from an ecological perspective.In this study,the effects of three different land use types on soil nutrients,microbial biomass and enzyme activities were studied from the perspective of soil microbial metabolism function.The effects of decomposition of three kinds of litter?peach leaves?P?,citrus leaves?C?,and alfalfa?A??on soil nutrients,microbial biomass,and extracellular enzyme activities related to carbon,nitrogen and phosphorus cycles were studied by laboratory simulation experiments.And use enzyme stoichiometry to reveal its effects on microbial metabolic function.The main results of the study are as follows:?1?Land use patterns have great impacts on soil chemical properties.The SOC from 0-20 cm soil followed the order:cropland(7.62 g·kg^-1)>peach orchard(7.15g·kg^-1)>citrus orchard(6.83 g·kg^-1).Compared with cropland,the organic carbon content of citrus orchard and peach orchard decreased by 6.2%and 10.4%,respectively,indicated that human disturbance in the orchard,such as long-term clearing and weeding,was not conducive to the maintenance of surface soil organic carbon.The contents of total nitrogen and total phosphorus in soil under different land use patterns were about1.00 g·kg^-1 and 0.29 g·kg^-1,respectively,and the difference was not significant.The content of soluble organic carbon?DOC?in citrus orchard was significantly lower than that in cropland(136.0 g·kg^-1)and peach orchard(123.4 g·kg^-1),the soil available nitrogen and available phosphorus in cropland were significantly higher than that in orchards,which indicated that orchard management had great impacts on soil nutrient availability.?2?The soil enzyme vector angles of the cropland,peach and citrus orchard in the sampling area were 67.9°,70.4°and 78.9°,respectively,indicated that the soil microbes were restricted by different degrees of phosphorus under all the three lands,compared with the cropland and the peach orchard.The citrus orchard'may lead to more severe phosphorus restrictions.The soil enzyme vector length of cropland was 0.90,significantly higher than peach and citrus orchard?0.74 and 0.79,respectively?,indicated that although the SOC and DOC content were higher in the cropland when compared with the orchards,soil microbes in cropland were subject to stronger carbon restrictions.?3?During litter decomposition,soil nutrient availability was gradually reduced.DOC and NH₄⁺-N decreased from 108.3 mg·kg^-1,15.1 mg·kg^-1 to 52.8 mg·kg^-1 and 7.9mg·kg^-1,respectively,indicated that the bio-immobilization of inorganic nutrients was caused by the priming effect in the early stage of decomposition,which reduced the availability of soil nutrients;NO₃^--N gradually decreased at 0-21 d,and slowly increased at 21-65 d,indicated that nitrogen mineralization occurred in the late stage of decomposition;while Olsen-P content did not change significantly with time.Litter type and decomposition time were the main factors affecting soil nutrients availability.Litter type could explain the variation of DOC,NH₄⁺-N,NO₃^--N,Olsen-P content by 45.5%,5.25%,10.5%,37.9%,and decomposition time could explain 45.1%,88.9%,69.1%,2.0%respectively.Among them,compared with peach and citrus leaves,alfalfa decomposition could input more carbon and nitrogen into the soil.?4?During litter decomposition,soil respiration rate,microbial biomass and enzyme activity all increased first and then decreased.Soil respiration rate and microbial biomass peaked on 3 d.The peak respiration rate of 3 d was as follows:PA>A>CA>P>C.During litter decomposition,the overall order of soil enzyme activity was:AP>BG>?NAG+LAP?,BG enzyme activity was between 105.91-475.34 nmol·g^-1·h^-1,?NAG+LAP?enzyme activity was between 39.24-236.10 nmol·g^-1·h^-1,and the AP enzyme activity was between 173.52-801.52 nmol·g^-1·h^-1.Compared with respiration rate and microbial biomass dynamics,soil enzyme activity dynamics had a significant hysteresis:BG and acid AP activity gradually increased from 0-7 d,while NAG and LAP gradually increased from 0 to 14 d and decreased from 14 to 65 d.?5?During litter decomposition,the enzyme vector angle gradually decreased,and enzyme vector length gradually increased,indicated that the soil microbial nutrient limitation was gradually weakened,and the energy limitation was gradually increased,which indicated that the litter decomposition helped to alleviate the nutrient limitation of microorganisms,but may exacerbate the limits of energy to microorganisms,therefore soil microbes were gradually strengthened by carbon limitation.Litter type and decomposition time were the main factors affecting the enzyme vector characteristics,which could explain the variation of the enzyme vector length of 42.47%and 21.97%,respectively,explain the variation of the enzyme vector angle of 81.28%and 7.52%.Specifically,the alfalfa decomposition caused a higher energy limitation,the peach and citrus leaves decomposition caused larger nutrients limitation,and the mixed decomposition of peach and citrus leaves with alfalfa could alleviate the nutrients limitation to microbial while causing less energy limitation.