Ecological Stoichiometric Analysis Based On Natural Grass Growing Technology In Apple Orchard

The Loess Plateau is one of the largest apple producing areas in the world,and it is also the excellent growth area of apple in China.The apple industry greatly promotes the economic development and ecological environment construction in this region.As a soil management model for sustainable development of orchards,grass growing in orchards is an important way to improve soil quality and promote green development of orchards.Natural grass has been paid more and more attention because of its advantages of improving orchard ecological environment and saving weeding labor.In this study,natural grasses(NG)and rapeseed +natural grasses(NGR)in apple orchards on Weibei Loess Plateau were taken as research objects,and white clover(WC),ryegrass(RE)and clear cultivation(CT)were taken as controls.To analyze the relationship between microbial biomass,enzyme activity and stoichiometric characteristics of carbon,nitrogen,phosphorus and phosphorus,extracellular enzyme activity and enzyme stoichiometric characteristics of carbon,nitrogen,phosphorus and phosphorus in soil,carbon,nitrogen,phosphorus and potassium contents in above-ground and underground parts of plants and their stoichiometric ratios,and explore the relationship between microbial biomass,enzyme activity,soil carbon,nitrogen and phosphorus,plant carbon,nitrogen and phosphorus and stoichiometric characteristics.In order to provide theoretical basis for technology optimization and effect evaluation of natural grass in apple orchard.The main research results are as follows:(1)The two natural grass treatments increased soil microbial biomass carbon,nitrogen and phosphorus,microbial entropy,and changed microbial quantification stoichiometry,among which NGR had a more prominent effect.Compared with CT,NG and NGR treatments increased soil microbial biomass carbon(MBC),microbial biomass nitrogen(MBN)and microbial biomass phosphorus(MBP),and NG and NGR treatments significantly increased microbial biomass carbon,nitrogen and phosphorus(MBP)in 0-10 cm soil layer than RE treatments.In 0-20 cm soil layer,the microbial biomass carbon,nitrogen and phosphorus of NGR treatment was higher than that of NG treatment.The effect of natural grasses on quantified microbiological econometric was mainly manifested in 0-10 cm soil layer.Compared with CT treatment,NG and NGR treatment significantly increased soil MBC:MBN and MBC:MBP,while decreased soil MBN:MBP.Compared with CT,natural grass treatment significantly increased microbial carbon entropy.In the 0-10 cm soil layer,the microbial nitrogen entropy of NG and NGR treatments was significantly higher than that of RE and CT treatments,but significantly lower than that of WC treatments.The effect of natural grasses on microbial phosphorus entropy was mainly manifested in 0-20 cm soil layer.NG and NGR treatments were significantly higher than CT treatments,but significantly lower than WC treatments.In 0-20 cm soil layer,microbial biomass entropy of NGR treatment was higher than that of NG treatment.The microorganisms showed strong homeostasis after the natural growth of grass.The results of redundancy analysis showed that soil microbial biomass and microbial entropy were positively correlated with soil nutrients such as dissolved organic carbon,ammonium nitrogen and available phosphorus,and negatively correlated with bulk density and p H.Microbial quantization stoichiometry showed opposite changes,which was negatively correlated with soil available nutrients and total nutrients,and positively correlated with soil bulk density and p H.The results of Monte Carlo test showed that dissolved organic carbon was the common driving factor of soil microbial biomass,microbial entropy and microbial quantization stoichiometry.(2)The two natural grass treatments increased the enzyme activity and changed the enzyme stoichiometry in the orchard soil,and NGR had a more prominent effect on the enzyme activity.The effect of natural grass on enzyme activity was mainly manifested in 0-40 cm soil layer.The activity of carbon,nitrogen and phosphorus cycling enzyme in natural grass treatment was significantly higher than that in clear tillage treatment.The β-glucosidase(BG),fibrodisaccharide hydrolase(CBH),β-xylosidase(BX),acetylglucosidase(NAG)and alkaline phosphatase(ALP)of NG and NGR treatments were higher than those of RE treatments.The activities of carbon,nitrogen and phosphorus cycling enzymes in 0-20 cm soil layer treated by NGR were higher than those treated by NG.The effect of natural grass on carbon enzyme activity per unit microbial biomass was mainly in 0-20 cm soil layer.Compared with CT,NG and NGR significantly increased BG/MBC and ALP/MBC in 0-20 cm soil layer.In the 0-10 cm soil layer,CBH/MBC and BX/MBC of NG and NGR treatment were significantly lower than those of WC treatment,but higher than those of RE treatment.The unit organic carbon enzyme activity under NG and NGR treatment was higher than that under CT treatment.In the 0-20 cm soil layer,the two natural grasses significantly increased the stoichiometry of carbonitrogenase and carbophosphogenase,while decreased the stoichiometry of nitrophosphogenase.Soil microorganisms were limited by phosphorus after natural grassing,and increased with the increase of soil depth.Compared with clear tillage,natural grass treatment increased microbial carbon limitation.However,the microbial carbon limit of natural grass treatment was lower than that of leguminous WC treatment.The results of redundancy analysis showed that the enzyme activity was positively correlated with the physicochemical properties of dissolved organic carbon,total nitrogen and organic carbon,and negatively correlated with bulk density and p H.Monte Carlo test was performed on the influencing factors of enzyme activity.The results showed that total nitrogen,nitrate nitrogen and dissolved organic carbon were the key driving factors regulating the change of enzyme activity.(3)Natural grass treatment had different effects on soil stoichiometry and plant-like stoichiometry,and there was a coupling relationship between microbial biomass,enzymes,soil nutrients and their stoichiometry.Compared with clear tillage,the effect of natural grass treatment on soil C/N ratio was mainly in the range of 10-20 cm,and NG treatment was higher than CT and WC treatment.In the soil surface 0-10 cm,the natural grasses NG increased the soil C/P ratio and N/P ratio.The content of carbon,nitrogen,phosphorus and potassium in above-ground parts of plant samples is higher than that in underground parts.In the aboveground part,the contents of total carbon and total nitrogen under NG and NGR treatment were lower than those under WC treatment,but the contents of total phosphorus and total potassium under RE and WC treatment were higher.The correlation analysis showed that the enzyme activity was positively correlated with the microbial biomass,the soluble organic carbon and ammonium nitrogen were significantly positively correlated with the enzyme activity and microbial biomass,and the total carbon content of underground plant samples was significantly correlated with the microbial biomass.Soil-and plant-like C-P ratios were negatively correlated with carbophosphorase stoichiometry.Structural equation model showed that soil C,N,P and soil C,N,P stoichiometry changed enzyme activity and enzyme stoichiometry mainly by influencing microbial biomass and microbial quantization stoichiometry.