Soil Ecological Stoichiometry Characteristics Of Biological Soil Crusts And Its Response To Disturbance In The Hilly Loess Plateau Region,China

The biological soil crust?biocrusts?is widely developed in the loess hilly area and becomes the main ground cover of the area.It is an important factor affecting the soil nutrient and circulation of the cultivated land.At present,the research on soil nutrients of biocrusts mainly focuses on the elements themselves,and rarely involves the coupling synergy between elements.Ecological chemometrics is a discipline that studies ecological processes and ecological functions based on element ratios,but it has some studies have insufficient research on the chemometric characteristics of biocrusts soil,and the relationship between the chemometric characteristics of biocrusts and its type and seasonal dynamics is still unclear.disturbance is a common natural phenomenon,which often leads to great changes in the coverage and composition of biocrusts.However,little research has focused on the effects of disturbance on the biochemimetric characteristics of biocrusts.To this end,the study focused on the development of stable biocrusts in the loess hilly region,and analyzed the differences in the stoichiometry of different types of biocrust soil and their seasonal dynamics through field investigation and sampling.On this basis,the effects of different intensity disturbances on the chemometric characteristics of biocrusts were studied by using simulated grazing disturbance tests.The main conclusions are as follows:?1?The ecological stoichiometry characteristics of different types of biocrusts were significantly different,and the stoichiometric ratio of the biocrustal layer was significantly higher than that of the lower soil.The effect of biocrusts on soil nutrients is mainly concentrated in the biocrustal layer and below 0² cm.In the biocrustal layer,the organic carbon content of light cyanobacterial crust,dark cyanobacterial crust,mixed crusts,and moss crust is13.49²7.07 g·kg^-1,and the total nitrogen content is 1.47².42 g·kg^-1.The total phosphorus content is 0.56⁰.67 g·kg^-1,C/N is 9.52¹2.63,C/P is 22.25⁴1.29,N/P is 2.41³.84;C,N,C/P,N/P The soil layer is deepened and reduced,and the size is moss crust>mixed crusts>dark cyanobacterial crust>light cyanobacterial crust,C/N and P are less affected by soil depth,although there are significant differences between the types,but The difference is lower;in 0² cm soil layer,the organic carbon content of soil under light-colored cyanobacterial crust,dark cyanobacterial crust,mixed crust,moss crust,Diploschistes spp.crust and Nostoc commune crust is 5.29¹8.96 g·kg^-1,total nitrogen content is 0.62¹.68 g·kg^-1,total phosphorus content is 0.52⁰.63 g·kg^-1,C/N is8.41¹1.49,C/P is 9.45³0.78,N/P is 1.17².64,C,N,P,C/N,C/P,N/P of Nostoc commune crust were significantly higher than other types of biocrusts.?2?The ecological stoichiometry characteristics of biocrusts soil are affected by the season,but the biocrusts type affects it more than the season.In the biocrustal layer,the average content of organic carbon,total nitrogen and total phosphorus in the light cyanobacterial crust,dark cyanobacterial crust,mixed crusts and moss crust is 9.63²6.60,1.10².15,0.57⁰.66 g·kg^-1,C/N,C/P,and N/P were 9.35¹3.21,16.94⁴0.66,and 1.89³.34,respectively;N and N/P were the lowest in the rainy season,and were significantly different from other seasons.Before the rainy season,the decline was 20.8⁴5.3%and 18.0⁴4.6%.The total phosphorus content was stable and affected by the season.In different seasons,C,N,C/P and N/P all showed moss crust>mixed crusts>dark cyanobacterial crust>light cyanobacterial crust,and the coefficient of variation of these four types of biocrusts?C,N,P,C/N,C/P,N/P?were 3.23¹1.76,0.93¹8.20,3.81²0.83 and 4.73³7.33,the coefficient of variation of crust and crust is the smallest.The 0² cm soil layers C,N,P,C/N,C/P,and N/P are affected by the season,but the change is small.?3?The biocrustal layer C,N,C/P,and N/P with significantly reduced disturbance are related to the disturbance intensity,soil depth and disturbance duration,and the disturbance has little effect on P and C/N.After six months of disturbance,under different treatments?no disturbance,20%,40%,60%,80%,100%?,the effects of biocrustal layer and 0² cm soil layer on disturbance are inconsistent.In the biocrustal layer,C,N,C/P,and N/P under different disturbance treatments were all reduced,with 20%disturbance processing having the largest reduction,and C,N,C/P,and N/P decreasing by 3.55 g·kg^-1,0.36 g·kg^-1,7.12,0.71,the reductions were 25.6%,26.9%,29.0%,30.0%,respectively,and the difference was not significantly different from the disturbance treatment,and the difference from other disturbance treatment was not significant.In the 0² cm soil layer,C,N content increased under 40%,60%and 80%disturbance treatment,and C/P and N/P increased under 60%and 80%disturbance treatment.The difference was not significant.Similar to the biocrustal layer,the 20%disturbance treatment decreased the most,and the decreases of C,N,C/P,and N/P were 7.6%,17.6%,9.4%,and 19.1%,respectively.The changes in P and C/N were small,and the differences between treatments were not significant.After 3 years of disturbance,under the respective treatments?no disturbance,20%,40%?,the biocrustal layers C,N,C/P,and N/P were 15.29¹9.82 g·kg^-1,1.24¹.68 g·kg^-1.26.03³2.14,2.12².73;with the increase of years,C,N,C/P,N/P showed an increasing trend without disturbance and 20%disturbance treatment,and decreased under 40%disturbance treatment,C,N The C/P and N/P variations are-5.39⁷.34 g·kg^-1,-0.23⁰.54g·kg^-1,-11.22¹0.11,-0.46⁰.14,respectively;less disturbance,20%and 40%of the treatments reduced C,N,C/P,and N/P,and the amount of change showed no disturbance of>20%disturbance>40%disturbance.The effect of different disturbance degrees on the stoichiometric ratio of 0² cm soil layer is similar to that of the biocrustal layer.?4?The disturbance changed the coverage of the biocrusts,the composition,the soil hydrothermal condition,and reduced the fixation of C and N by the biocrusts,which in turn affected the soil ecological stoichiometric ratio.After 3 years of disturbance,without disturbance,20%disturbance and 40%disturbance intensity,the cyanobacterial crust decreased by 24.2%,18.8%and 41.3%,and the moss crusts decreased by 39.1%,51.6%and 83.1%.The amplitude is higher than the cyanobacterial crust.The biomass of cyanobacterial under 20%and 40%disturbance was5.93 and 11.67 mg·g^-1 lower than that of non-disturbance treatment,and the biomass ratio was 0.73 and 0.80 g·dm^-2.After 3 years of disturbance,the soil moisture content of the biocrusts increased by 6.8%,5.3%and 5.4%,respectively,without disturbance,20%and40%disturbance,less disturbance,20%and 40%disturbance reduced the surface of the biocrusts Soil water content.After 3 years of disturbance,the temperature of the biocrustal layer under no disturbance,20%and 40%disturbance treatment was higher than that of the lower 5 cm soil at 2.27°C,1.12°C and 0.73°C,of which 20%and 40%interfered with the temperature of the biocrustal layer.The disturbance is 1.28°C and 1.69°C.The disturbance of the biocrusts cover component?especially the moss crust cover?and the change of soil hydrothermal condition are the most important factors affecting the soil C and N fixation,which leads to the change of soil ecological stoichiometric ratio?interpretation rate 95.6%?.