Dynamic Change Of Soil Soluble Organic Nitrogen And Nitrogen Mineralization In Artificial Forest And Grassland In The Loess Plateau

Soil nitrogen plays an indispensable role in plant growth.As a relatively active part of soil nitrogen,soil soluble organic nitrogen?SON?can be directly or indirectly transformed,absorbed and utilized by plants.It is of great value in the nitrogen cycle.In this study,the forest of Prunus armeniaca,Hipppophae rhamnoides,Robinia pseudoacacia,Pinus tabuliformis and grassland in the vegetation restoration area of the Loess Plateau in northern Shaanxi?in Zhidan county,Yan'an city?were taken as the research object.To study the distribution characteristics and correlation of soil soluble organic nitrogen,soil free amino acid,soil enzyme activity and soil physical and chemical properties under different vegetation restoration types,soil layers,slope directions and seasons were studied.The main results are as follows:?1?Vegetation restoration significantly increased the content of SON in soil,and Hipophae rhamnoides forest was better than almond forest and grassland in increasing the content of SON in soil,while Robinia pseudoacacia forest and Pinus tabuliformis forest did not increase the annual average effect.Season and soil depth and their interactions have a significant impact on SON content in soil.With the change of season,SON content in soil first decreases and then increases,and SON content in spring and winter is significantly higher than that in summer and autumn.There were significant differences in soil SON between different slopes,and the variation trend was different.?2?Vegetation restoration significantly increased soil water content,soil nutrients and soil enzyme activities,and the increase effect of Hipophae rhamnoides forest,Prunus armeniaca forest and grassland was the most significant,planting Hipophae rhamnoides forest is more conducive to the accumulation of nutrients.In addition to EC,pH,catalase activity,the other indicators showed significant seasonal variation characteristics.Soil nutrients,sucrase activity and urease activity decreased with soil layer deepening,and soil water content increased with soil layer deepening.The effect of slope direction on soil water content,soil nutrients and enzyme activities was different,but the overall content was higher on the sunny slope of Prunus armeniaca forest than on the sunny slope,and higher on the sunny slope of Hipophae rhamnoides forest than on the sunny slope.?3?The correlation between soil SON and soil physical and chemical properties varies with the seasons.Among them,there was no significant correlation between SON and physical and chemical properties in spring and autumn.In summer,there was a significant negative correlation between the content of SON in soil and available potassium in soil,and a significant positive correlation between SON content and soil catalase activity.In winter,the content of SON in soil was negatively correlated with available nitrogen,available phosphorus,sucrase activity and water content,and positively correlated with soil pH.?4?In the soil layer of 10-20 cm,vegetation restoration has no significant effect on soil nitrogen mineralization and mineralization rate,and N₀ has no significant effect on soil nitrogen mineralization either.The accumulation of soil nutrients after vegetation restoration does not affect the mineralization potential and mineralization rate of soil layer of 10-20 cm.It can be seen that vegetation restoration has a limited effect on soil nitrogen mineralization in the soil layer of 10-20 cm.Planted the forest of Pinus tabuliformis is not conducive to the accumulation of soil nitrogen and has no effect on soil nitrogen supply capacity.