| China is the third largest nitrogen deposition area in the world.The continuous nitrogen deposition has caused a series of complex ecological effects on the function and structure of forest ecosystems.Nitrogen deposition and litter changes are the main factors causing changes in soil carbon and nitrogen input in forest ecosystems;soil enzymes are important players in soil carbon and nitrogen cycles.Therefore,studying the combined effects of nitrogen fertilization and litter on the enzyme activities of forest soils is of great significance for understanding the impacts of soil carbon and nitrogen cycles in forest ecosystems in the context of global climate change.Pinus elliottii is one of the main quality tree species of coniferous tree protection forests in southern China.In this study,field simulation experiments were conducted to study the effects of nitrogen deposition and litter composition on soil physical and chemical properties and soil enzyme activities in Pinus elliottii plantations.The main results are as follows:?1?Nitrogen fertilization significantly increased soil polyphenol oxidase and catalase activity?P<0.05?,increased soil pH and soil nutrient contents such as total nitrogen,ammonium nitrogen and nitrate nitrogen,total phosphorus,available phosphorus,available potassium,organic carbon content of Pinus elliottii plantation?p<0.05?;significantly reduced soil cellulase,urease and sucrase activity?p<0.05?,reduced soil C/N.It indicated that proper nitrogen application was beneficial to increase the decomposition rate of lignin in soil of Pinus elliottii plantation and improve soil nutrient status,but inhibited the decomposition rate of cellulose in soil.?2?All litter treatments significantly reduced soil urease activity?p<0.05?;The composition of litter composition SA?Pinus elliottii litter mixed with Eucalyptus grandis at a ratio of 1:1?and SX?Pinus elliottii litter mixed with Acacia crassicarpa at a ratio of 1:1?significantly increased the soil polyphenol oxidase activity of Pinus elliottii plantation?P<0.05?;SA?Pinus elliottii litter mixed with Eucalyptus grandis at a ratio of 1:1?increased soil cellulase?p<0.05?;had no significant effect on soil urease and invertase activity.The soil pH was increased,and the organic carbon was significantly increased in the later stage of the experiment?p<0.05?.The decomposition cycle was short and did not have a significant effect on the remaining soil indicators.?3?SALN?Pinus elliottii litter mixed with Eucalyptus grandis at a ratio of 1:1+Low N?promoted the soil polysucrose oxidase activity,but SALN?Pinus elliottii litter mixed with Eucalyptus grandis at a ratio of1:1+Low N?and SMLN?Pinus elliottii litter mixed with Casuarina equisetifolia at a ratio of 1:1+Low N?in the soil of Pinus elliottii plantation inhibitde soil invertase activity;under the same litter SM treatment?Pinus elliottii litter mixed with Casuarina equisetifolia at a ratio of 1:1?,soil urease and catalase activity increased with nitrogen deposition concentration.The increase of soil polyphenol oxidase,cellulase and catalase activity was highest in SA treatment under the same nitrogen deposition HN treatment(High N,160 kg·hm-2·a-1).Under the same litter treatment,the soil pH,ammonia nitrogen,nitrate nitrogen and available potassium increased with the increase of nitrogen deposition concentration,and the available phosphorus and soil C/N decreased with the increase of nitrogen deposition concentration;Under treatment,soil pH and nitrate nitrogen were treated with higher SM?Pinus elliottii litter mixed with Casuarina equisetifolia at a ratio of 1:1?,and soil total pHosphorus and total potassium were higher with SA treatment(Pinus elliottii litter mixed with Eucalyptus grandis at a ratio of 1:1.It is indicated that in the background of nitrogen deposition,SA treatment?Pinus elliottii litter mixed with Eucalyptus grandis at a ratio of 1:1?is more conducive to the improvement of soil properties of Pinus elliottii plantation than other litter treatments;?4?Two-way analysis of variance showed that nitrogen deposition treatment significantly affected soil catalase and urease activity of Pinus elliottii plantation?P<0.01?,only significantly affected soil polyphenol oxidase and cellulase activity in the early stage?p<0.05?,significantly affected soil invertase activity in the middle only period?p<0.05?.Litter composition treatment significantly affected soil urease activity of Pinus elliottii plantation?p<0.05?;only in the early stage,soil cellulase activity was significantly affected?p<0.01?.Polyphenol oxidase,sucrase and catalase activity were significantly affected in the middle and late stages of the experiment?p<0.05?.The interaction between nitrogen deposition and litter composition treatment significantly affected soil urease and catalase activity of Pinus elliottii plantation?p<0.01?in the experimental period;it was only significant in the early stage.The soil polyphenol oxidase activity?p<0.01?was significantly affected in the middle and late stages?p<0.05?,and had no significant effect on soil cellulase activity. |
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