| Soil carbon,nitrogen,and phosphorus stoichiometric characteristics(soil carbon,nitrogen,and phosphorus stoichiometric ratio)are important indicators of the coupling cycle of soil carbon,nitrogen,and phosphorus.Although large number of studies about soil C-N-P stoichiometry and their influence factors reported,these studies pay more attention to the influence of single factor,lacking for the analysis of the multiple factors(soil,biology,and topography).Besides,these studies also ignore the soil depth as an important influence factor for soil C-N-P stoichiometry in both regional and global scales.As an important global carbon sink region,the response of soil C-N-P stoichiometry in the subtropical forest of China to climate change(e.g.N addition and Warming)is attracting more attention in recent years.The research focusing on the present situation of soil CN-P stoichiometry and the influencing factors in the subtropical forest area helps us to understand the change processes of soil C-N-P stoichiometry.On this basis,the study on the stoichiometric characteristics and influence factors of soil C-N-P stoichiometry under both the addition of nitrogen and phosphorus and the modification of the estimation formula of the carbon use efficiency of soil microbes are beneficial to more accurately simulate of soil C-N-P stoichiometry under the changing climate in the future in subtropical areas.First of all,this study analyzed the change trends and the influence factors of soil C-N-P stoichiometry in multi-site subtropical forests.Secondly,this study analyzed the driving factors of the spatial variation of soil C-N-P stoichiometry under the multiple factors(biological factors,soil factors,and topographic factors)at a single site(Tiantong subtropical evergreen forest site).Thirdly,both the response of soil C-N-P stoichiometry with nitrogen and phosphorus addition and its influence factors were analyzed in the subtropical evergreen forest(Tiantong subtropical evergreen forest site).Finally,this study constructed the global database of soil microbial carbon use efficiency,and the relationship of soil microbial carbon use efficiency with soil carbon content and nitrogen content were analyzed.The main results are as follows:(1)To improve the understanding of the soil C-N-P stoichiometry in subtropical evergreen broad-leaved forest area,we studied the changing trend of soil C-N-P stoichiometry and the influence factors in three subtropical evergreen forest sites.The results showed that with the positive development of succession stage,soil organic carbon(SOC)concentration,total nitrogen(TN)concentration and total phosphorus(TP)concentration increased significantly,whereas soil C:N ratio,N:P ratio,and C:P ratio decreased,but the decreasing trend was not significant.SOC,TN,TP and their stoichiometric ratios decreased with the increase of soil depth.The factors such as elevation,mean annual temperature(MAT),mean annual precipitation(MAP)and biomass(NPP)were strongly correlated with the surface(0-30cm)and middle(30-60cm)soil C-N-P stoichiometry.The correlation between soil C-N-P stoichiometry and the environmental factors(such as elevation,MAT,MAP,and NPP)decreased with the increase of soil depth,especially for SOC.(2)To better reveal the impact factor of soil C-N-P stoichiometry,especially for deep soil,this study used multiple factors(soil,biology,and topography)to explore the different driving factors of soil C,N,and P concentrations at the landscape scale of subtropical forest(Tiantong subtropical evergreen forest site).The results showed that the SOC,TN and TP and their stoichiometric ratios decreased significantly with the increase of soil depths.There were significant correlations between SOC,TN,and TP in each soil layer,among which the correlation between SOC and TN was the strongest.The correlation between SOC and TN decreased with the increase of soil depths.The correlation between TP and SOC and TN increased with the increase of soil depths.Soil p H was the main influence factor of SOC and TN,while TP was jointly affected by the topographic factors(convexity and slope),biological factors(litter N:P ratio)and soil factors(soil p H).(3)To explore the effect of N and P addition on the soil C-N-P stoichiometry in subtropical evergreen forest,this study analyzed the changes of soil C-N-P stoichiometry,the correlation of soil carbon,nitrogen and phosphorus,and the causes of the changes under the addition of N and P.The results showed that the addition of N promoted an increase in SOC.The addition of N and P promoted an increase in TP.The addition of P promoted an increase in SOC,TN,and TP at the same time.The P addition also enhanced the correlation of soil carbon and nitrogen,especially for deep soil.The C-N correlation of surface soil increased from 0.84 to 0.93,and that of bottom soil increased from 0.77 to 0.98.The P addition promoted the increase of sucrase and cellulase in soil.Besides,the P addition also promoted the simultaneous increase of microbial carbon,microbial nitrogen,SOC and TP in the soil.We believe that the increase in the content of saccharide decomposing enzyme under the P addition treatment may promote the decomposition of organic matter in soil and the growth of microbes,and thus promote the increase in the content of carbon and nitrogen in both soil and microbes,which leads to the enhanced correlation of soil carbon and nitrogen elements.(4)This study also studied the correlation between soil microbial carbon use efficiency and soil carbon,nitrogen content and soil nutrient status based on the global database of soil microbial carbon use efficiency.The frequency distribution of soil microbial carbon use efficiency and its influencing factors were further analyzed.The main results were as follows: soil microbial carbon use efficiency significantly affected soil carbon and soil nitrogen content.Soil carbon and nitrogen content significantly increased with the increase of microbial carbon use efficiency.The frequency distribution of global soil microbial carbon use efficiency is relatively discrete(0.01-0.99).The carbon use efficiency of soil microbes was affected by the environmental temperature,substrate type and substrate reduction degree.The carbon use efficiency of soil microbes decreases gradually with the increase of temperature.The carbon use efficiency of soil microbes was highest when the substrate type was glucose.The effect of nitrogen addition on the carbon use efficiency of soil microbes varies with different substrates. |
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