Effect Of Nitrogen And Phosphorus Additions And Resin Tapping On Soil Enzyme Activity And Microbial Nutrient Limitation Of Pinus Elliottii Plantation

Slash pine（Pinus elliottii）is native to the southeastern United States.It was introduced to China for cultivation in the 1930s.It has a history of more than 80 years and combines many advantages such as papermaking,timber and high-yield grease.As one of the main measures for the intensive management of plantation forests and the improvement of forest soil nutrients,fertilization（addition of nitrogen and phosphorus）is of great significance for the efficient cultivation of slash pine wood forest.However,the nutrient requirements and proportions of the various growth stages of the trees are different,and the research on the availability of forest soil nutrients and the maintenance of the long-term soil fertility,so the specific types and proportions of fertilizers required at each stage are also different.In addition,China currently implements the project of restricting timber logging and building national reserve forests,and resin production has become the main means for forest farmers to obtain economic benefits.However,resin tapping will hinder the growth and development of trees,and it is very important to carry out scientific and reasonable forest management research on slash pine wood forest.However,the current researches on pine tree plantation for tallowing are mostly focused on the study of tree growth,and there is no research on pine tallowing for soil nutrients and soil enzyme activity related indicators.As the most active biologically active substance in the process of energy flow exchange and material circulation in the ecosystem,soil enzymes participate in a variety of biochemical reactions in the soil to promote the mineralization,homogenization of nutrients and the conversion of organic matter.Therefore,soil enzyme activity can be used as an important indicator of soil quality evaluation to a large extent,and can reflect the status of material transformation in the soil.Moreover,compared with chemical indicators,soil enzymes,as biological indicators for soil quality evaluation,are more sensitive to environmental changes than other chemical indicators.Therefore,soil enzymes can more sensitively reflect soil nutrient status and evaluate soil quality.In this paper,28-year-old slash pine resin tapped and untapped forests were used as the research object to carry out five levels CK(0 kg N·hm^-2·a^-1+0 kg P·hm^-2·a^-1)、LN(50 kg N·hm^-2·a^-1+0 kg P·hm^-2·a^-1)、HN(100 kg N·hm^-2·a^-1+0 kg P·hm^-2·a^-1)、HN+LP(100 kg N·hm^-2·a^-1+50 kg P·hm^-2·a^-1)and HN+HP(100 kg N·hm^-2·a^-1+100 kg P·hm^-2·a^-1)of nitrogen and phosphorus addition experiments to determine soil nutrients and soil enzyme activities under different treatments,and use enzyme stoichiometry and vector analysis to study microbial nutrient distribution situation.The results are as follows:Resin tapping reduced the soil p H,TP,SOC,TN,K,Ca,Mg content to a certain extent,increased the soil DOC,NH₄⁺-N content,and had no obvious influence on the soil DON and NO₃^--N content.Increased soil MBC and MBN,significantly increased the activity of S-ACP（p<0.05）,increased the activity of S-SC and S-CAT,and had no significant effect on the activity of S-URE.The stoichiometric ratio of soil nutrient in the harvested forest was higher than that in the unpicked forest,and the stoichiometric ratio of soil enzyme activity was lower than that in the unpicked forest.The addition of nitrogen and phosphorus at all levels reduced the soil p H,DOC,MBC,and MBN content,and increased the soil NH₄⁺-N,SOC,K,and TN content.The addition of nitrogen and phosphorus increased the soil TP content and The TP content of the soil is reduced under the fat-harvesting forest stand.The addition of nitrogen alone and the combined addition of nitrogen and phosphorus both reduced the activity of S-URE and increased the activity of S-SC,S-CAT and soil E_C/N;addition of nitrogen alone increased the activity of S-ACP and reduced soil EC/P,nitrogen The co-addition of phosphorus reduced the activity of S-ACP and increased soil E_C/P,and the HN+HP treatment significantly reduced the activity of S-ACP compared with HN and CK under tallow and non-tucked stands（p<0.05）.The addition of nitrogen and phosphorus under non-greased forests reduced soil EN/P.Addition of nitrogen alone lowered soil E_N/Punder fat-harvesting stands,while adding nitrogen and phosphorus together increased soil EN/P.According to the RDA analysis,the soil carbon nutrient correlation index is the key factor of soil enzyme activity and microbial nutrient acquisition strategy in this experimental area.In addition,microorganisms are mainly limited by soil carbon and phosphorus.In the future,topdressing phosphate fertilizers and increasing soil carbon sources can be used to improve soil fertility in slash pine plantations in this area.