Effects Of Nitrogen Addition On Litter Decomposition Of Three Mixed Plantations In Rainy Area Of West China

Litter decomposition and its related biological processes are of great significance in geographic maintenance and bio-element cycling,which can be affected by various biological and abiotic factors.Moreover,many reserches suggest that atmospheric nitrogen deposition may directly or indirectly affect plantation litter decomposition and its related biological processes.However,the results of relevant studies still remain uncertain,which may be caused by the differences in existing experimental methods.Therefore,in this study,a Phoebe zhennan and Camptotheca acuminata mixed plantation,a Quercus acutissima and Camptotheca acuminata mixed plantation and a multi-species mixed plantation in Rainy Area of West China were selected as the research objects.The effects of different dose of nitrogen addition(CK:0 kg·N·hm^-2·a^-1;LN:20 kg·N·hm^-2·a^-1;HN:kg·N·hm^-2·a^-1)on litter quality,litter decomposition,soil microbial community structure and enzyme activities of three typical mixed plantations were studied to understand the response of different mixed plantations to atmospheric nitrogen deposition,so as to provide basic data for sustainable development and management of plantations in Rainy Area of West China.Academic basis.The results:?1?The nitrogen addition significantly affected the litter quality,and the changes of litter quality varied with the mixed plantation type.In the Phoebe zhennan and Camptotheca acuminata mixed plantation,the LN and HN treatments significantly increased the litter P and N concentrations and the HN treatment reduced the litter C concentration,which may premote the litter decomposition in the early stage.In the Quercus acutissima and Camptotheca acuminata mixed plantation,the LN treatment renduced the litter P concentration and increased the lignin concetration,which may inhibit the litter decomposition.In the multi-species mixed plantation,both the LN and HN treatments increased the litter lignin concentration,which may inhibit the litter decomposition.?2?The effect of nitrogen addition on litter decomposition rate varied with the type of mixed plantation and the type of litter.The LN and HN treatments promoted the decomposition of litter in the Quercus acutissima and Camptotheca acuminata mixed plantation and the multi-species mixed plantation,respectively.?3?The effect of nitrogen addition on litter nutrient release varied with the type of mixed plantation and the type of litter.The LN and HN treatments promoted the N release of litter in the Quercus acutissima and Camptotheca acuminata mixed plantation and the N release of abnormal litter in the Phoebe zhennan and Camptotheca acuminata mixed plantation,respectively.The LN treatment promted the P release of litter in the multi-species mixed plantation,and both the LN and the HN treatments promted the P release of abnormal litter in the Phoebe zhennan and Camptotheca acuminata mixed plantation.?4?The effect of nitrogen addition on the decomposition of lignin and cellulose in litter was complex.The LN treatment promoted the lignin degeneration of litter in multi-species mixed plantation.Both the LN and HN treatments promoted the cellulose degeneration of abnormal litter in the Phoebe zhennan and Camptotheca acuminata mixed plantation.The LN treatment inhibited the cellulose degeneration of litter in the Quercus acutissima and Camptotheca acuminata mixed plantation.?5?The nitrogen addition showed neither significant effect on the?Logk and E4/E6values of litter humus in three mixed plantations nor on?Logk values of abnormal litter in three mixed plantations.However,both the LN and HN treatments reduced the E4/E6 values of abnormal litter humus in three mixed plantations,which indicated that the nitrogen addition might promote the humification process of the abnormal litter.?6?The variation of soil enzyme activity values with time were different between treatments in three mixed plantations.Except for that the change of leucine aminopeptidase activity value with time was not obivious,the other enzyme activity values all showed a trend of decreasing with time.The enzyme activity values were found jenerally higher from April to July and lower in January.In three kinds of mixed plantations,both the LN and HN treatments increased the?-glucosidase activity value but decreased the peroxidase activity value,the LN treatment increased the cellobiohydrolase activity value,and the HN treatment decreased the leucine oxidase activity value.However,these changes did not reach significant levels.?7?The content of soil bacteria,Gram-positive bacteria,Gram-negative bacteria and total microorganisms were all increased first and then decreased with time.Their values of average content in three mixed plantations were all found to be the highest in October and the lowest in January.In the three mixed plantations,the LN treatment reduced the total microbial,bacterial and fungal content and G+/G-value.However,these changes did not reach significant levels.In summary,the effects of nitrogen addition on litter quality,decomposition,nutrient release,lignocellulose degradation and humification process of mixed forest in Rainscreen Area of West China were more complex.The results varied with the types of mixed forest,litter types and nitrogen addition dosage.The effects of nitrogen addition on soil enzyme activities and microorganisms in different mixed forests shared some commonalities,however,their changes did not reach a significant level,which might be due to the insufficient experiment time.Based on the above studies,basic data were provided for the response of litter decomposition to nitrogen deposition in artificial mixed forests in rainscreen area of West China,which further indicated that the response of litter decomposition to nitrogen deposition was affected by mixed forests and litter types.