Study On Soil Rhizosphere Effect Of Cunninghamia Lanceolata-Phoebe Bournei Mixed Plantation

Cunninghamia lanceolata,a unique and excellent fast-growing timber tree species native to China,is widely cultivated and utilized.However,single plantation patterns and long-term continuous planting severely affect the sustainable management of Cunninghamia lanceolata artificial forests.The establishment of mixed needle-broadleaf forests can improve the instability of stand structure and the decline of forest land productivity caused by large-scale cultivation of Cunninghamia lanceolata pure forests,and enrich species diversity to enhance the resistance of trees to various hazards.Phoebe bournei,a class Ⅱ rare and endangered tree species in China,has extremely high economic and ecological value.Studying the effects of Cunninghamia lanceolata-Phoebe bournei mixed plantation on soil nutrients,enzyme activity,and microbial biomass can provide a scientific basis for the nutrient management and sustainable operation of Cunninghamia lanceolata and Phoebe bournei.Therefore,this study used 10-year-old pure Cunninghamia lanceolata,pure Phoebe bournei,and mixed Cunninghamia lanceolata-Phoebe bournei forests as research subjects.During dry and rainy seasons,the shaking root method was used to collect rhizosphere and non-rhizosphere soil and fine root samples in different stands,and soil samples of different soil layers in each stand were collected to determine soil nutrient content,enzyme activity,microbial biomass,and fine root nutrients.This study investigated the seasonal and stand variations in different soil layers’ soil properties,soil rhizosphere effects,and fine root nutrient changes,and used correlation analysis and principal component analysis to explore the relationships between soil indicator content and rhizosphere effects.Additionally,it further analyzed the impact of plant fine roots on soil using correlation analysis and partial least squares path analysis.The main results were as follows:(1)The soil nutrient content and enzyme activity generally decreased with the increase of soil layer depth in both dry and rainy seasons.Trace elements were significantly affected by seasonal changes,mostly showing higher levels in the dry season than the rainy season.Except for sucrase activity,other enzyme activities were stronger in the rainy season than in the dry season.The soil nutrient content in mixed forests was generally lower than that in pure forests.(2)The total content of mineral elements such as calcium,magnesium,iron,and aluminum in the rhizosphere soil of mixed dry and wet season forests was generally higher than that of pure forests.The highest total calcium content was found in the mixed dry and wet season Cunninghamia lanceolata soil,at 0.35 and 0.45 g·kg-1,respectively.The total content of magnesium and manganese in the soil was relatively low,with little difference between different forest types.However,nutrient elements in the soil were mostly higher in pure forests.The correlation between nutrient content,enzyme activity,and microbial biomass in rhizosphere and non-rhizosphere soil differed in different seasons,with stronger correlations between various indices in the wet season compared to the dry season.Soil nutrient elements exhibited a positive rhizosphere effect in both dry and wet seasons.The strongest rhizosphere effect for soil organic carbon was found in pure Cunninghamia lanceolata forests,at 0.61 and 0.80 in the dry and wet seasons,respectively.The strongest rhizosphere effect for total nitrogen and phosphorus in the dry season was found in mixed Cunninghamia lanceolata forests,at 0.78 and 0.94,respectively.In both dry and wet seasons,the strongest rhizosphere effect for total magnesium and aluminum was found in Phoebe bournei pure forests,at 0.37 and 0.53,respectively.Soil aluminum,iron,and manganese elements mostly exhibited a negative rhizosphere effect.Microbial biomass carbon,nitrogen,and phosphorus mostly exhibited a positive rhizosphere effect.In the wet season,the rhizosphere effect values for microbial biomass phosphorus in pure Cunninghamia lanceolata and Phoebe bournei forests reached up to 6.16 and 3.03,respectively.Soil enzyme activity mostly exhibited a positive rhizosphere effect,with higher enrichment of acid phosphatase and peroxidase in the rhizosphere.The correlation between rhizosphere effects of microbial biomass and enzyme activities was weak in drought and rainy season,and the rhizosphere effects of various nutrient elements were mostly negative correlation,and the rhizosphere abundance of nutrient elements inhibited the supplement of other nutrient elements.Overall,the rhizosphere effects of nutrients and enzymes in different forest types were stronger in the wet season than in the dry season,while microbial biomass exhibits the opposite trend.The rhizosphere effect values of soil elements,microbial biomass and enzyme activities in pure forest were generally higher than those in mixed forest.The correlation between soil nutrient,enzyme,and microbial biomass rhizosphere effects was stronger in the wet season than in the dry season.(3)Significant differences existed in the fine root nutrient content among different forest types.The nutrient content of fine roots in pure forests was mostly lower than that in mixed forests,and the nutrient content of fine roots in the wet season was higher than that in the dry season.In both dry and wet seasons,the highest fine root carbon content was found in pure fir forests,at 227.17 and 374.16 g·kg-1,respectively.In the dry season,the highest fine root nitrogen and phosphorus content was found in Phoebe bournei pure forests,at 6.49 and 0.18 g·kg-1,respectively.In the wet season,the highest fine root nitrogen and phosphorus content was also found in Phoebe bournei pure forests,at 10.64 and 0.32 g·kg-1,respectively.Among the mineral elements in plant fine roots,potassium,calcium,and magnesium were mostly found in higher concentrations in mixed forests compared to pure forests.The correlation between fine root nutrients and soil nutrients,and acid phosphatase was relatively strong,while the correlation with soil microbial biomass was relatively weak.Partial least squares path analysis shows that soil nutrients in the dry season and soil enzyme activity in the wet season played a dominant role in the interaction between plant fine roots and soil,exerting significant effects on plant nutrient changes.In conclusion,this study investigated plant fine roots and soil in different forest types to explore the changing patterns and correlations among soil conditions and nutrient indices in each forest type.The preliminary results indicated that the mixed Cunninghamia lanceolata-Phoebe bournei forest utilized the rhizosphere enrichment effect to drive soil microbes and various enzymes,rationally allocate soil nutrient content around the plant root system,and promote or inhibit the absorption and utilization of different nutrients by plants.This,in turn,affected plant growth and development,contributing to further research on mixed Cunninghamia lanceolata afforestation models.