Effects Of Mulching Measures On Soil Carbon, Nitrogen And Phosphorus Components And Enzyme Kinetics In Apple Orchard

The Loess Plateau is one of the main apple producing areas in China.However,due to natural factors and long-term unreasonable land use,the soil quality in the Loess Plateau declined day by day,which greatly restricted the local apple production.Therefore,how to improve soil quality in the Loess Plateau to improve apple yield has become a key problem to be solved.Studies have proved that soil cover in apple orchard is one of the effective ways to solve the decline of soil quality and improve apple yield.At present,the mechanism of how different mulching measures in apple orchard affect the stability of soil nutrient cycle is not clear,which restricts people’s understanding of conservation tillage in agroecosystem.Taking the apple orchard soil ecosystem in the Loess Plateau as the research object and the clearing treatment（CT）as the control treatment,this study studied the response of Soil carbon,nitrogen and phosphorus components,soil enzyme dynamics and soil element cycle function genes in the soil ecosystem to different kinds of ground cover measures（RE、CS、BF）,different years of grass mulching（6a WC、15a WC）and different grass species of grass mulching（WC、OG、CV）.The results show that:（1）The effect of grass mulching on improving the stability of soil carbon,nitrogen and phosphorus nutrients was better than other mulching measures,and the stability was stronger with the increase of years.Orchard ground cover measures significantly increased the content of soil nutrients.Among different kinds of ground cover measures,CS had the best effect on increasing the content of soil carbon,nitrogen and phosphorus nutrients.Compared with CT,CS increased SOC 191%,TN 91%and TP 270%.The contents of SOC,TN and TP in RE,CS and BF were much higher than those in CT.Grass mulching measures have the best effect on improving the quality of soil nutrient elements.Under grass mulching measures,the proportion of soil stable carbon and stable nitrogen is higher（IOC 84%;SN 86.4%）,which is conducive to improving the stability of carbon and nitrogen nutrients.CS and BF improved the proportion of phosphorus components,and the stability of phosphorus was higher.Among different grass cover species,WC improved the stability of soil carbon and nitrogen nutrients and increased the proportion of stable carbon and nitrogen components（IOC 85%;SN 90%）;OG and CV increased the proportion of more stable phosphorus components（92.7%;92.9%）.Compared with short-term grass mulching,long-term grass mulching increased the content of soil nutrients.Compared with6a WC,15a WC increased the contents of SOC and TN by 26.9%and 33.6%.The stability of soil carbon,nitrogen and phosphorus nutrients increased with the increase of grass years.CS is more conducive to the improvement of soil nutrient content.Long term grass mulching measures can not only improve soil nutrient content,but also improve soil nutrient quality and increase nutrient stability（2）Among all ground cover measures,organic ground cover measures CS,RE and long-term grass mulching increased the activity of more soil enzyme systems,and the stability of enzyme systems under BF and short-term grass mulching was higher.The temperature sensitivity of the semi saturation constant(K_m-Q₁₀)had little difference under different measures.The temperature sensitivity of the maximum enzymatic reaction rate(V_max-Q₁₀)was the main factor affected the temperature sensitivity of the soil enzyme system.Among different ground cover measures,RE and CS increased V_max and K_cat of BG,NAG and ALP,and improved the ability of soil enzyme system to decompose substrates and the efficiency of substrate utilization.BF reduced the temperature sensitivity of the enzyme system by reducing Vmax and kcat,and BF improved the stability of the enzyme system.Among different grass mulching,legume CV mulching had the best effect on the promotion of V_max.Under the optimum temperature of enzymatic reaction at 25℃,the V_max of CV was the highest,which was significantly higher than that of CT.Three kinds of grass mulching increased the K_cat of three enzymes.Among them,the K_cat of BG and NAG was the highest under CV mulching,and the K_cat of ALP was the highest under OG mulching.Among the three grass mulching,the V_max-Q₁₀ of the three enzymes under WC was the lowest and the enzyme system was the most stable.Long-term grass mulching 15a WC increased the V_max and K_cat of the three enzymes compared with short-term grass mulching6a WC,and 6a WC decreased V_max-Q₁₀ compared with 15a WC,which improved the stability of the enzyme system.The soil temperature sensitivity under short-term WC and inorganic cover BF was lower,and the soil enzyme system was more stable;Under long-term grass mulching and straw mulching,the ability of enzyme system to decompose substrate and the efficiency of substrate utilization were higher;CV had the best effect on improving V_max and K_cat.（3）Ground cover measures had different effects on the abundance of functional genes related to soil element cycle.In general,the functional genes in soil microbial community are carbon-cycle>nitrogen-cycle>phosphorus-cycle.Among different kinds of ground cover measures,grass mulching RE had the best effect on improving the gene abundance of soil element cycling function.At the level of functional subclasses,grass mulching improved the abundance of carbon and nitrogen fixation functional genes,so it had the effect of improving nutrient quality.The overall trend of each ground cover measure was as follows:15a grass mulching improved the abundance of SOC decomposition function genes,CS and BF reduced the abundance of SOC decomposition function genes,and short-term grass mulching had little effect on SOC decomposition function.Therefore,the accumulation of SOC under CS and BF was higher.Among the three kinds of grass mulching,CV had the best effect on improving the gene abundance of nitrogen cycle function,OG had the best effect on improving the gene abundance of carbon cycle and phosphorus cycle function,and CV had the best effect on improving the diversity of gene functional communities related to carbon,nitrogen and phosphorus cycle.Short-term grass mulching decreased the abundance of functional genes but increased the H and E of gene functional community.Long-term grass mulching increased the abundance of functional genes but decreased the H and E of gene functional community.The years of grass growth had little effect on the abundance of functional genes of carbon,nitrogen and phosphorus cycle,and the abundance of functional genes under long-term grass cover was greater than that under short-term grass cover.15a mulching measures had the best effect on improving soil functional communities in apple orchards,and different grass species have different effects on functional communities.It is suggested to take perennial grass mulching measures in orchard production.To sum up,corn straw mulching（CS）was the most effective ground cover measure to improve soil nutrient content,while grass mulching was a ground cover measure to increase nutrient content and improve nutrient quality.And long-term grass mulching had a better effect on improving nutrient quality and improving the ability of soil enzyme system to use nutrients.The improvement effect of each nutrient element component varies with the grass species covered with grass.Therefore,it is suggested to select suitable grass species for long-term mulching cultivation according to the actual demand for nutrients in future production activities.