The Ecological Stoichiometry Characteristics And Nutrient Storage In Fine Roots And Soil Of Typical Plantations In The Loess Alpine Region

To explore the carbon（C）,nitrogen（N）,and phosphorus（P）contents and their ecological stoichiometry characteristics of the fine root and soil of typical plantations in the Loess alpine region,as well as to understand the status of underground C,N,and P storage of vegetation after returning farmland to forests,soil coring method was used to sample the fine roots and soil of four typical plantations in this region,contained Betula platyphylla Suk,Populus cathayana Rehd,Larix principis-rupperchii and Picaea crassifolia.The seasonal dynamics and vertical variation of C,N and P ecological stoichiometry characteristics and nutrient storage in fine root and soil were studied.At the same time,we explored the relationship between soil and fine root stoichiometric characteristics.The results can provide theoretical basis and technical guidance for vegetation restoration and management in the Loess alpine region.The main research conclusions of this paper are as follows:1.Fine root C,N and P content and stoichiometric ratio variation characteristicsDuring the growing season,the content of C and N in the fine root of Populus cathayana Rehd was higher,while the P content of fine roots varied little among plantation types.The C content of fine roots gradually increased form the initial growth stage to the end of growth stage,and the N and P contents in the vigorous growth stage were significantly lower than other growth stages（P<0.05）.The content of C and N in fine roots showed a decreasing trend with the increase of soil depth,and the distribution of P content was relatively uniform.The C/N and C/P of fine roots in the vigorous growth stage were the highest.The N/P of fine roots in 4 plantations were all less than 14,indicating that vegetation growth was restricted by N.Meanwhile,the growth of coniferous forests was restricted by N more severely.The fine root C/N of coniferous forests was significantly higher than that of broad-leaved forests（P<0.05）while the fine root of Populus cathayana Rehd was highest among all plantations.With the increase of soil depth,the C/N of fine roots increased.The C/P and N/P of fine roots in broad-leaved forests decreased with the increase of the soil depth,while the C/P and N/P of fine roots in coniferous forests had no obvious changes in soil layers.2.Soil C,N and P contents and stoichiometric ratio variation characteristicsThe soil C,N and P contents in the end of growth stage were highest during the growing season.The vertical distribution of soil C and N contents showed a obvious property of surface-aggregation.The soil P content in the 0-10 cm soil layer was significantly higher than other soil layers（P<0.05）.The soil C and N contents of Populus cathayana Rehd were the highest among different plantations,while the soil P content varied little among plantation types.The variation degrees of soil C/N in plantations types,seasons and soil layers were small,and its temporal and spatial variation was relatively stable.The soil C/P of the Populus cathayana Rehd was significantly higher than that of other plantations,showing that its P absorption capacity was higher.With the deepening of soil depth,the soil C/P gradually decreased and the soil N/P of the broad-leaved forest decreased while the soil N/P of coniferous forests decreased in the order of 0-10cm>20-40cm>10-20cm>40-60cm.3.The correlation of fine roots and soil stoichiometric characteristics and their influencing factorsThere was a extremely significant correlation between fine root N/P and soil N/P（P<0.01）,indicating that their N/P could collectively reflect the elemental limitation of forest growth.Fine roots C,N,P and their stoichiometric ratios had a significantly positive correlation.RDA analysis showed that the nutrient contents of fine roots were mainly affected by soil C,soil ammonia nitrogen,plantation type,soil nitrate nitrogen,and soil bulk density.The main influencing factors of stoichiometric ratios of fine root C,N,P were fine root P,fine root N,fine root C,soil nitrate nitrogen,soil ammonia nitrogen,and soil available phosphorus.There was a significantly positive correlation between soil C,N and P（P<0.01）.Soil available potassium,fine root C,soil nitrate nitrogen,and soil ammonia nitrogen were the main influencing factors of soil C,N,and P contents.There was a significantly positive correlation between soil C/P and N/P（P<0.01）.Soil C/N had no significant correlation with soil physical and chemical properties and fine root characteristics.RDA analysis showed that the stoichiometric ratios of soil C,N,and P were mainly affected by soil C,soil N,and soil P.4.Stoichiometric homeostasis of fine root C,N and PDifferent plantations had different stoichiometric homeostasis indexes,indicating that plantation types had an impact on the elemental utilization and accumulation of fine root C,N,and P.The H_N and H_P of fine roots in each plantation were lower than H_N/P,indicating the synergy of N and P variation in the fine roots.The H_C/N and H_C/P of fine roots in the coniferous forests were negative numbers,indicating that the C/N and C/P of fine roots in the coniferous forests had low stability.5.Fine root-soil C,N and P storage variation characteristics and their influencing factorsThe fine root C,N and P storages in the end of growth stage were significantly higher than other growth stages（P<0.05）,and their vertical distribution showed a obvious property of surface-aggregation.Soil C,N,and P storages had no obvious seasonal variation characteristic.The soil C and N storages of Populus cathayana Rehd were the highest,and the soil P storage of Larix principis-rupperchii was higher than other plantations.The soil C and N storages of broad-leaved forest had a obvious property of surface-aggregation,while the soil C and N storage of coniferous forest were more evenly distributed among soil layers.The soil P storage showed an increasing trend with the deepening of the soil depth.There was a significantly positive correlation between soil C and N storage（P<0.01）,while soil P storage had no significant correlation with soil C and N storages.Soil layer,soil C,soil N,soil P,soil water content,and soil available potassium were the mainly influencing factors of soil C,N and P storages.Soil P storage and fine root C,N and P storages had a significantly negative correlation（P<0.01）.