| Soil organic carbon（SOC）mineralization is one of the important processes of carbon cycle in terrestrial ecosystems,and its response to global climate change is closely related to soil carbon dioxide emissions.Soil nitrogen mineralization,as one of the important links of nitrogen internal circulation,significantly affects the structure and function of ecosystem.Walnut is an important economic forest tree species in C hina,which has high nutritional value.In recent years,the state has vigorously supported the economic development in Q inba Mountain area,cultivated walnuts as the main local economic forest tree species,and actively promoted the planting of walnuts under the forest.Planting walnuts under the forest is helpful to improve economic benefits,but the mineralization of carbon and nitrogen in the soil planted under the walnut forest remains to be studied.Therefore,it is of great significance to understand the SOC mineralizatio n dynamics of different planting patterns in walnut forest and the response law of soil nitrogen mineralization to hydrothermal changes and litter addition for evaluating soil ecological benefits and nitrogen supply capacity.Based on this,this study used soil samples of eluvial layer（0～20 cm）and sedimentary layer（20～40 cm）in 12 plots of walnut planted under different forests in Q inba Mountain area as experimental materials,and studied the SOC mineralization rate and mineralization amount in each plot by indoor constant temperature cultivation method,and analyzed the soil SOC mineralization dynamics.The effects of different humidity and temperature gradients on soil nitrogen mineralization were studied by two-factor experimental design.The humid ity gradients were 20%,40%,60%and 80%of field water capacity（FWC）,and the temperature gradients were 5℃,15℃,25℃and35℃,respectively.The relationship between humidity and temperature and soil nitrogen mineralization and the optimum humidity te mperature for soil nitrogen mineralization were analyzed and discussed.The difference of soil nitrogen mineralization ability under the conditions of 25℃,natural water content and adding different litter was analyzed by indoor culture.The results of this study are as follows:（1）During the 28-day culture,the SOC rate and SOC cumulative mineralization in 0～20 cm soil layer were significantly higher than those in 20～40 cm soil layer.The cumulative mineralization of SOC decreased rapidly in the ear ly stage of culture and gradually showed a stable trend in the later stage.Ammonium nitrogen showed an upward trend before and after SOC carbon mineralization,and soil nitrate nitrogen content in other planting patterns also showed an upward trend except walnut+Paeonia lactiflora and walnut+motherwort.Sucrase and urease did not change significantly before and after SOC carbon mineralization.Mineralization of soil organic carbon was significantly correlated with soil organic carbon content,sucrase activity and nitrate nitrogen content（P<0.05）.The mineralization process of SOC was independently fitted by the first-order kinetic equation,and the order of SOC mineralization capacity was walnut+Paeonia lactiflora>grassland>walnut+potato>wa lnut+soybean>tea forest>walnut forest>walnut+motherwort>walnut+sweet potato>walnut+Polygonatum>walnut+Atractylodes macrocephala>walnut+ginger>Pinus massoniana forest.（2）The net mineralization rate of soil nitrogen was significantly affected by water and temperature,and the net mineralization rate of soil nitrogen showed the maximum at 60%FWC and 25℃.With the increase of water content and temperature,the net mineralization rate of soil nitrogen increased first and then decreased.The effects of moisture and temperature on the net ammoniation rate,net nitrification rate and net nitrogen mineralization rate of soil were extremely significant（P<0.01）,and the interaction between them had significant effects on the net ammo niation rate and net nitrogen mineralization rate of soil.By fitting the binary quadratic regression equation of soil nitrogen net mineralization rate（y3）with soil moisture content（x1）and temperature（x2）in various plots,it can be calculated that the net nitrogen mineralization rate is the largest in walnut forest under the optimum hydrothermal combination,and it is significantly higher than that in Pinus massoniana forest and tea forest.（3）The addition of litter can significantly improve the net ammoniation rate,net nitrification rate and net nitrogen mineralization rate.The effects of litter addition of different tree species on the net nitrogen mineralization rate are significantly different,and increase with the increase of litter concentration.Under the same concentration gradient,tea tree>walnut>Pinus massoniana.Pearson correlation analysis showed that the net mineralization rate of soil nitrogen was positively correlated with the total N added by litter,and negatively correlated with cellulose,C/N and lignin/N（P<0.05）.To sum up,the SOC mineralization ability of walnut+Paeonia lactiflora is the strongest,and that of walnut+ginger is the weakest among different planting patterns under walnut forest.The soil of walnut forest land has the strongest nitrogen supply capacity,so the planting mode of walnut and ginger can be adopted,and the tea tree litter can be properly added to the forest,which can not only improve the economic benefit but also improve the soil fertility,and also help to reduce the carbon loss of forest soil and achieve the effect of ecological protection. |
