Effects Of Carbon And Nitrogen Regulation On Grassland Biological Characteristics And Comprehensive Evaluation Of Soil Fertility

Grassland,as the largest terrestrial ecosystem in China,plays a very important role in water conservation,climate regulation,and soil and water conservation.In the context of global change,nitrogen deposition has become an important factor affecting grassland ecosystems.Excessive nitrogen deposition may have a negative impact on soil properties,plant growth,and microbial community structure.Will simultaneous carbon addition affect The buffering effect of nitrogen deposition remains unclear.Therefore,it is important to evaluate the effects of nitrogen deposition and carbon addition on soil chemical properties,microbial biomass quantity and activity,and enzyme activity.In this paper,the carbon(glucose)and nitrogen(urea)addition plots set up in the Erguna Forest Steppe Ecosystem in the Shenyang Institute of Applied Ecology,Chinese Academy of Sciences are used as experimental platforms.The test is based on the set of 0,25,50,100,200 kg N ha-1year-15 nitrogen addition treatments(N0,N25,N50,N100,N200);0,250,500 kg C ha-1year-1)3 carbon addition treatments(C0,C250,C500).The effects of carbon and nitrogen additions on soil chemical properties,microbial biomass and activity,enzyme activity,and changes in soil quality were investigated.The results of this study are as follows:(1)In grassland ecosystems,long-term excessive nitrogen addition significantly reduces soil p H,leading to soil acidification.Appropriate addition of nitrogen(N25,N50,N100)at the same carbon level can increase the TN content of the soil.The addition of carbon changed the soil C: N,and the trend of soil C: N at the same nitrogen level was C0> C500> C250.Appropriate carbon addition increased soil SOC content,the highest soil SOC content was at medium carbon(C250)level,and decreased soil SOC content at high carbon(C500)level.(2)As the amount of nitrogen increases,soil microbial biomass carbon and nitrogen(MBC,MBN)content shows a downward trend,while MBC: MBN tends to increase.High nitrogen(N200)significantly reduced MBC,MBN,and increased MBC: MBN;at the N100 and N200 levels,soil MBC: MBN was higher,and soildehydrogenase(DHA)activity increased first and then decreased with nitrogen The soil dehydrogenase activity is highest under the nitrogen addition level of N25,and high nitrogen(N200)significantly inhibits soil dehydrogenase activity.The reason may be that the soil p H is reduced due to excessive nitrogen input and the growth of microorganisms is inhibited;the addition of a carbon source increases soil dehydrogenase activity and alleviates the decrease in soil p H.(3)With the increase of the amount of nitrogen added,the phenol oxidase activity of the soil showed a trend of first increase and then decrease.The phenol oxidase activity increased significantly under the conditions of nitrogen addition of N25 and N50,but under the conditions of nitrogen addition of N100 and N200 Significantly lower phenol oxidase activity.Soil phenol oxidase activity at C500 compared to C0 and C250 levels.Soil phenol oxidase activity decreased significantly.At C0 and C250 levels,soil cellobiose hydrolase activity showed an increasing trend with the increase of nitrogen addition.The reason may be that the addition of nitrogen reduced the microorganism's demand for nitrogen,and in turn increased the carbon demand,which increased the cellobiose hydrolase(CBH)activity;at the C500 level,the cellobiohydrolase activity increased first and then decreased The application of carbon at the same nitrogen level significantly increased ?-glucosidase activity;The addition of carbon and nitrogen had no significant effect on peroxidase,?-glucosidase and ?-xylosidase;the relationship between soil properties and soil enzyme activity was significantly different at the three levels of carbon addition.Soil p H,MBC,and MBN were significantly related to enzyme activity at C0,C250,and C500 levels,and p H was the main factor limiting enzyme activity.(4)Through the principal component analysis of soil quality indicators,the changes in soil quality after the simulated nitrogen deposition test were evaluated.C250N25,C250N50,C250N100,C250N0 soil comprehensive quality indexes were larger,C500N200,C0N100,C0N200 soil comprehensive quality index was smaller,The overall soil quality showed good fertility in the low and medium nitrogen application groups(N0,N25,N50),and the worst soil quality in the high nitrogen group(N200).This indicates that proper nitrogen addition can promote soil quality,and excessive nitrogen application is Inhibitory.When the carbon content was C250,the soil quality was significantly higher than the C0 and C500 levels.It shows that the addition of carbon will alleviate the negative effects brought by high nitrogen input,and the synergistic addition of carbon and nitrogen will help improve the soil quality of grassland.