| High-density pure forest planting patterns and biological characteristics of Chinese fir(Cunninghamia lanceolate)caused the worsening soil degradation and the decrease in forest productivity.Mixed planting of Chinese fir and broad-leaved trees contributes to the restoration of soil fertility.In this study,soil samples of pure Chinese fir plantations(PCP)and mixed-species plantations of Chinese fir and Schima Schima plantations(MCP)at different stand ages were collected.Soil physical and chemical properties,enzyme activities,and microbial communities were analyzed to evaluate the effects of mixed planting on soil fertility and provide a scientific basis for the maintenance and sustainable management of Chinese fir plantation soil fertility.The main results are as follows:(1)Mixed planting significantly improved soil structure and soil water status.The effects of mixed planting on the surface soil layer were significant.Compared with PCP,the minimum and maximum soil water holding capacity of MCP increased by 25.2% and 23.55%,respectively.Soil moisture content increased with soil depth,while soil bulk density was the opposite.Soil moisture content,bulk density,and minimum water holding capacity initially increased and then decreased with the increase of the shand age,and reached the highest value in the middle stand age.The opposite results were observed in soil maximum water holding capacity.(2)Mixed planting significantly increase soil nutrients and p H,soil p H,total potassium(TK),total nitrogen(TN),and available potassium(AK)increased by 10.35%,7.59%,46.99%,and 144.14%,respectively.Surface soil p H,organic carbon(SOC),TN,and AK were significantly higher than those in the deep soil and decreased with the increase of soil depth.Moreover,with the increase of soil depth,SOC and TN decrease significantly,while soil total phosphorus(TP)decreased less.SOC,TN,and ammonium nitrogen of MCP initially decreased and then increased with the increase of stand age.With the increase of soil depth,soil TP,p H,and TK of MCP initially increased and then decreased.(3)Mixed planting significantly improves soil enzyme activity of different soil layers,especially the surface soil.Compared with PCP,in young stand age,soil catalase and sucrase activities of MCP were significantly higher,increased by 101.89% and 0.89%,respectively;in mature stand age,soil catalase activity of MCP was significantly higher than that of PCP,which increased by 88.24%.The soil enzyme activity of MCP decreased with the increase in soil depth,and the enzyme activity of surface soil was significantly higher than that of deep soil.With the increase of the stand age,the soil enzyme activity of the MCP initially decreased and then increased,and was the lowest in the age of the forest.(4)The Alpha diversity of soil bacterial and fungal communities was significantly increased by mixed planting.Compared with PCP,soil microbial community Alpha diversity of MCP in young and mature stand age was higher,but there was no difference between PCP and MCP in middle-aged forests.With the increase of stand age,the Alpha diversity of soil bacterial and fungal communities of MCP at different ages initially decreased first and then increased,and reached the lowest value in the middle-aged.The Alpha diversity of soil bacteria and fungi community was decreased with increasing soil depth.(5)Mixed planting significantly changed the composition and relative abundance of soil microbial communities.Mixed planting increased the relative abundance of Basidiomycetes,but decreased the relative abundance of Ascomycetes.In both young and mature stand ages,the relative abundances of Chloromycetes,Proteobacteria,and Actinomycetes were higher in MCP than those in PCP,but the opposite was observed in middle-aged.The composition of the soil microbial community was different between surface and deep soil layers and stand ages.Compared with the PCP,the composition of the soil bacterial community of MCP in the middle-aged and mature stand age was similar.(6)The correlation between soil environmental factors and microbial communities was significant,especially on the surface soil.Soil TN,p H SOC,AK,and ammonium nitrogen were the main factors that affected soil bacterial and fungal communities,and soil AK significantly affected soil fungal communities.In conclusion,mixed planting can improve soil fertility by improving soil p H,AK,enzyme activity,and microbial community diversity.This study is of great significance in guiding the restoration of degraded forests and provides a theoretical basis for the sustainable development of Chinese fir plantations. |
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