| The contents and cycles of soil carbon(C),nitrogen(N)and phosphorus(P)are important indicators for ecosystem function and services,especially for the assessment of ecosystem health.Researchers have been chronically concentrating on the distribution,storage and cycle of soil C with anabatic global climate change and frequent human activities.However,at large scale,past studies less focused on soil N and P,especially in dryland ecosystem.In this paper,we further explored the spatial distribution patterns and driving factors of soil N and P based on our team’s research on soil C content in arid and semiarid zones of China.Specifically,we concentrated on soil in arid and semiarid zones covering about 52.5% of China’s land surface,by systematically investigating soil total nitrogen(STN)and total phosphorus(STP)contents of different layers(0-10 cm,10-20 cm,20-40 cm,40-60 cm,60-80 cm,80-100cm)from 177 sites.We explored soil N and P in arid and semiarid zones of China from three perspectives,including spatial distribution characteristics and their driving factors,spatial variability and their driving factors and coupling interrelation between N and P and its driving mechanism.This will reveal the spatial distribution regulation of soil N and P in arid and semiarid ecosystem of China,and it will provide the basis data and scientific basis for further exploring the structure and function of this ecosystem.The results are as follows:1.Spatial distribution characteristics and driving factors of soil N and P(1)Generally,contents of STN and STP decrease when soil depth becomes deeper,and contents of STN are more obvious than those of STP;contents of STN of different layers all decrease from east to west in the study area,but those of STP show an increase tendency,and the distribution characteristics of STP are different among different layers.(2)Contents of STN are significantly different between under canopy and bare area,while those of STP are not significant;contents of STN under canopy obviously decrease with soil depth.(3)Contents of STN among different vegetation types followed the rule as: cropland > grassland >> shrubland > barren(>> represents significantly high),and contents of STN in cropland and grassland obviously decrease with soil depth;there is no significant difference for contents of STP among different vegetation types at topsoil of 0-20 cm depth,but that of STP in cropland is significantly the lowest at deep soil below 20 cm depth,and content of STP in cropland obviously decreases with soil depth.(4)Contents of STN among different climate types followed the rule as: sub-humid area > semiarid area >> arid area > hyper-arid,and content of STN in sub-humid area obviously decreases with soil depth;content of STP in sub-humid area is the highest at topsoil of 0-20 cm depth,but that in hyper-arid is the highest at deep soil below 20 cm depth,and content of STP in semiarid area is the lowest at the deep soil.(5)Spatial variation of STN:STP is mediated by the variation of STN content,and the spatial variation characteristic of STN:STP is similar to that of STN content.(6)By analyzing the relationship between STN(STP)and the factors of climate,geography and biology,this study shows that the distribution of STN content at the topsoil is significantly driven by latitude,mean annual temperature,EVI,pH and sand content,and the distribution of STN content at the deep soil is significantly driven by latitude,mean annual temperature and sand content.The distribution of STP content is significantly driven by longitude,mean annual temperature and sand content.2.Spatial variability and driving factors of soil N and P(1)With the method of spatial interpolation for the variation coefficients of the STN,STP content and STN:STP at 0-10 cm layer in the study area(i.e.the horizontal direction)and profile layers of all sampling point(i.e.the vertical direction),it was found that the variability of STN content in the west of Yinshan mountains is significantly higher than that in the east of Yinshan mountains in both horizontal and vertical directions,and the variability of STN:STP is consistent with the variation of STN content,but the variability of STP content in the west of Yinshan mountains is significantly lower than that in the east of Yinshan mountains.(2)At horizontal direction,the variability of STN is significantly driven by aridity,and the variability of STP is significantly driven by latitude,longitude,wind speed and nitrogen deposition.In addition,the variability of STN:STP is significantly driven by latitude,aridity and human footprint camp of cumulative pressures on the environment.At vertical direction,the variability of STN is significantly driven by latitude,aridity and human footprint camp of cumulative pressures on the environment,and the variability of STP is significantly driven by longitude,aridity,pH and precipitation of driest month.In addition,the variability of STN:STP is significantly driven by aridity and human footprint camp of cumulative pressures on the environment.3.Coupling relationship between N and P and its driving mechanism(1)STN is significantly and positively related to STP,while climate can indirectly affect EVI and further affect the coupling relationship between STN and STP.Meanwhile,climate can directly affect the relationship between STN and STP,which would lead to the decoupling of soil N and P cycle.(2)In arid and semiarid zones of China,N is the obvious restrictive nutrient;climate change would make soil be alkaline,and human activities(including nitrogen deposition and human footprint)do not significantly affect the coupling relationship between STN and STP.The results of this study will play a positive role in revealing the spatial distribution of soil nutrients in arid and semi-arid ecosystems of China,and provide valuable basic information for further exploration of the functions and services of the ecosystem.Furthermore,it will provide basic data for relevant managers to make plans in the process of ecological environment restoration and protection in this research area. |
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