| Soil aggregate is a crucial component of soil that affect soil nutrients,soil organic carbon and microbial activity.High-quality soil aggregate play an essential role in maintaining soil quality by improving soil productivity and soil corrosion resistance and reducing the risk of soil erosion.Subtropical forests play an important role as carbon sinks in addressing climate change and nutrient cycle processes.With different degree of disturbance and restoration,subtropical forests in China are in different stages of restoration,which provides an ideal platform for the study of soil aggregate stability and its influencing factors in vegetation restoration.It is of great significance to understand the formation process of soil aggregates,soil carbon sequestration,nutrient maintenance and soil and water conservation in subtropical secondary forests by identifying the factors affecting the particle size,nutrient distribution and accumulation characteristics of soil aggregates and their stability in different secondary forests during vegetation restoration.Therefore,three types of secondary forests in different restoration stages of subtropical region(Pinus massoniana-Lithocarpus glaber,Choerospondias axillaris,L.glaber-Cyclobalanopsis glauca)were selected as research objects in this study.Using dry and wet sieve experiments to examine particle size distribution,stability,nutrient content and storage,stoichiometric ratio of soil aggregates across different soil layers.The findings were then combined with vegetation community characteristics and soil physicochemical properties to analyze the influence of soil aggregate stability.The primary results of this research are summarized as follows:(1)In the secondary forest at different recovery stages,the mechanical and water stability aggregates increased first and then decreased.In the middle restoration stage of Choerospondias axillaris had the highest soil aggregate stability.The highest proportion of all kinds of sample plot aggregates was the size>2 mm,the proportion of mechanically stable aggregates ranged from 64.8%-70.1%,and the proportion of waterstable aggregates ranged from 59.8%-69.9%,the proportion of 0.25-2.0 mm aggregates is the second,and the proportion of<0.25 mm aggregates is the least.The proportion of aggregates>0.25mm was more than 90%,with the trend of middle>early>late restoration stage observed with vegetation restoration.At different recovery stages,the soil mechanical-stable and water-stable aggregate decreased as particle size decreased,and the difference was significant(P<0.05).Across different soil layers,the content of water-stable aggregate was highest in the 0-10cm layer compared to the 10-20cm layer.Additionally,the stability indexes mean weight diameter(MWD)and geometric mean diameter(GMD)were consistent with the proportion of water-stable large aggregate content.With vegetation restoration,the trend of middle>early>late restoration stage was also observed for MWD values in different soil layers,with all MWD values higher than 2.(2)The organic carbon content,total nitrogen and total phosphorus content in the early restoration(P.massoniana forest),middle restoration(C.axillaris forest)and late restoration(Q.glauca)first increased and then decreased with the restoration stage.The content of carbon,nitrogen and phosphorus in different soil layers at different restoration stages was higher in 0-10 cm soil layer than in 10-20 cm soil layer.The results showed that the improvement of aggregate nutrients in the vegetation restoration processes was mainly concentrated in the surface soil.Soil aggregate C/N shows the P.massoniana forest>Q.glauca>C.axillaris forest.Soil aggregate C/P shows Q.glauca>C.axillaris>P.massoniana forest.Soil aggregate N/P is largely consistent with C/P trends.Soil aggregate carbon stock increased gradually with vegetation restoration,especially from the early to the middle restoration stage.The nitrogen stock of soil aggregates first increased and then decreased with vegetation restoration in the order of middle restoration stage>late restoration stage>early restoration stage.Phosphorus stock in soil aggregates decreased gradually with vegetation restoration.At different vegetation restoration stages,the aggregate carbon stock and nitrogen stock in 0-10 cm soil layer was higher than that of 10-20 cm soil layer.There was no significant difference in phosphorus stock of soil aggregate between different soil layers(P>0.05).(3)The soil organic carbon content and total nitrogen content of soil aggregate are positively correlated(P<0.01)with the stability of soil aggregate in different secondary forests,which indicate that the stability of aggregates is effective for carbon and nitrogen protection.There was no significant correlation between the total phosphorus content of the soil aggregate and the stability of the soil aggregate in each forest(P>0.05).There was a significant positive correlation between the aggregate stability and the soil aggregate C/N,C/P and N/P in the middle restoration stage dominated by C.axillaris forest(P<0.05).Except for the carbon stock in Pinus massoniana forest in the early stage of recovery,there was a significant positive correlation between aggregate stability and nutrient stock of aggregates(P<0.05).(4)The redundancy analysis of soil aggregate stability with soil physicochemical properties and vegetation community characteristics showed that soil organic carbon,total phosphorus,pH,bulk density and silt content were significantly correlated with soil aggregates(P<0.05).Soil organic carbon is the most important factor driving soil aggregate stability variation with highest correlation with aggregate stability.The stand density,proportion of deciduous species,amount of litter and tree species diversity are significantly correlated with the stability of soil aggregate(P<0.05).Among them,stand density has the highest explanation rate for aggregate stability,which is the most critical plant community factor driving soil aggregate stability variation. |
PDF Full Text Request