Effects Of Different Thinning Methods On The Soil Nutrient Dynamics And Tree Growth Of Mixed Cunninghamia Lanceolata And MangLietia Yuyuanensis Plantation

The thinning of plantations involves not only the tree growth and harvest of forest products,but also the maintenance of soil fertility of plantations.How to maintain the soil fertility of plantations and manage forests sustainably has attracted concerns from many scholars.In this study,the mixed plantation of Cunninghamia lanceolata and Manglietia yuyuanensis was used as the research object.Three different ratios of Cunninghamia lanceolata to Manglietia yuyuanensis?1:1/Control treatment,2:1 and 3:1?were set by thinning.The soil temperatures and moisture,nitrogen mineralization,soil microbial community and tree growth were investigated after thinning.The main findings are as follows:?1?The daily soil temperature reaches the maximum value?18.94²0.10°C?at 18:00and reaches the minimum value?17.54¹8.74°C?at 08:00.The trend was 3:1>2:1>1:1.The daily soil moisutre reaches its maximum value?90.91⁹5.40%?at 02:00 and reached the minimum?89.68⁹4.32%?at 18:00.The opposite trend was shown between soil temperature and moisture.The seasonal variation of soil temperature and moisture under each treatments was as follows:summer>spring>autumn>winter.There was a significantly positive correlation between soil temperature and soil moisture in spring,summer and autumn.In winter,soil temperature and soil moisture showed a significantly negative correlation.?2?Soil water contents was 26.77⁴0.94%.Soil inorganic nitrogen contents was dominated by the ammonium nitrogen,and the average value of ammonium nitrogen content in each treatment showed as spring>autumn>winter>summer,the spring ammonium nitrogen content was 1:1>3:1.While nitrate nitrogen contents showed the opposite trend,i.e.summer>winter>autumn>spring.There was no significant difference in nitrate nitrogen contents between treatments in different seasons.Soil available P contents in spring and winter was significantly higher than in summer and autumn.In spring,the available P contents was 1:1 treatment and the 2:1 treatment is significantly larger than 3:1 treatment.?3?The results showed that 2:1 treatment and 3:1 treatment significantlyincreased soil nitrogen mineralization and annual nitrification,which could improve soil nitrogen supply.To improve the supply of nutrients to soil microbes and forests,but it should also be noted that soil nitrogen leaching would be increased.?4?The amount of bacterial PLFAs accounted for 43.62⁴8.21%of the total PLFAs,followed by fungal PLFAs and actinomycetes PLFAs(5.74⁶.69nmol·g^-1).Treatments with 3:1 ratio significantly increased soil microbial biomass,which would increase soil nitrification rate and mineralization rate,and accelerate nitrogen cycling in the study area,Treatment with 2:1 ratio had not significantly changed soil microbial biomassand community structure.RDA analysis showed that soil nitrate nitrogen content was positively correlated with PLFAs community,and available P showed negative correlation with PLFAs community.?5?After 44 months of thinning,the average diameter at breast height?DBH?of the Manglietia yuyuanensis was 15.82¹7.19cm,and the average DBH of the Cunninghamia lanceolata was 13.37¹3.67cm.The annual DBH growth of the Manglietia yuyuanensis was greater than that of Cunninghamia lanceolata.It indicated that Manglietia yuyuanensis have stronger competition compared with Cunninghamia lanceolata.In addition,Treatments with 3:1 and 2:1 ratios a can significantly increase the annual DBH growth of Cunninghamia lanceolata and Manglietia yuyuanensis.In conclusion,treatments with 3:1 and 2:1 ratios can significantly increase soil temperature and humidity,soil annual nitrogen mineralization and forest DBH compared with control treatment?1:1 ratio?in the mixture of Cunninghamia lanceolata and Manglietia yuyuanensis plantation after thinning.Treatment with 3:1 ratio can significantly increase the amount of total PLFAs,which would be the main driver of soil mineralization.The risk of soil nutrient leaching was also enhanced after the thinning of the plot,where soil and water conservation managements should be taken to prevent or reduce soil erosion and maintain the soil fertility.To reduce the soil.