Effects Of Tan-sheep Grazing On C:N:P Stoichiometry And Multifunctionality Of Typical Steppe

Grazing is one of the main ways of grassland management.Previous studies have focused on the integrated effect of grazing,while the individual and interactive effects of feeding,excretion and trampling on grassland were still lacking,which hampered the understanding of grazing effects and their mechanisms.Although nitrogen(N)deposition is a global process,its effects interacted with grazing need to be studied quantitatively.Therefore,the effects of feeding,excretion and trampling of Tan-sheep on plant and soil carbon:nitrogen:phosphorus(C:N:P)stoichiometry,as well as the interaction effects of stocking rate and nitrogen addition level were studied to analyze the responses of ecosystem multifunctionality in a long-term rotational grazing systems,which was located in Huanxian Grassland Agriculture Trial Station of Lanzhou University in Huan County.The results were as follows:1 Grazing sheep feeding affects plant and soil C:N:P stoichiometry and multifunctionality of typical steppeSheep feeding intake was significantly negatively correlated with soil organic carbon(OC)and total phosphorus(TP)concentrations,significantly positively correlated with plant C and N concentrations,and insignificantly correlated with soil total nitrogen(TN)concentrations and C:N:P stoichiometric ratios,and plant TP concentration and C:N:P stoichiometric ratios.The aboveground biomass and species richness of typical steppe increased with feed intake.The ecosystem multifunctionality index showed a‘hump'curve with feed intake,and reached a peak when the dry matter intake was 1.66 kg head^-1 d^-1,corresponding to a stocking rate of 4.60 sheep ha^-1.With the increase of precipitation,feeding accelerated N limitation in typical steppe.2 Grazing sheep excrement affects plant and soil C:N:P stoichiometry and multifunctionality of typical steppeDuring two years(2016 and 2017),sheep excrement promoted the accumulation of C,N and P in soil and soil microorganisms.The soil TP concentration under the mixed of dung and urine was significantly higher than that in dung or urine,while the variance of soil TN concentration was on the contrary.Urine had no significant effect on soil C:N,but dung and their mixtures increased soil C:N.Urine and dung increased soil C:P and N:P,while the mixtures(urine 1.5 L m^-2 and dung 14.2 g m^-2;simulated a stocking rate of 8.7 sheep ha^-1)significantly decreased soil C:P and N:P,and increased plant P concentration.Both dung and urine increased plant N concentrations,reaching a peak at 1.0 L m^-2 urine.Sheep excrement did not significantly affect plant C concentration,C:N,C:P and N:P.Dung and urine had no effect on plant N:P,but the mixtures resulted in the decreases of plant C:P and N:P,which aggravated the N limitation of typical steppe.Sheep excrement increased aboveground biomass and ecosystem multifunctionality index,with the highest values at simulated 8.7 sheep ha^-1and 9.4 g m^-2 dung,respectively.Sheep excrement exacerbated the P limitation of the typical steppe as precipitation increased.Two years later,sheep excrement had legacy effects on the increases of C,N and P concentrations in soil and soil microorganisms.The continuous effects of excrement still increased ecosystem multifunctionality index,peaked at urine 1.0 L m^-2and dung9.4 g m^-2(simulated a stocking rate of 5.3 sheep ha^-1).3 Simulated sheep trampling affects plant and soil C:N:P stoichiometry and multifunctionality of typical steppeThe effect of simulated trampling on soil C:N and N:P was not significant for two years.In 2016,trampling had no significant effect on soil C:P.In 2017,trampling at120 footsteps m^-2 increased soil C:P.Plant C,N and P concentrations showed‘hump'curves with trampling intensity,increasing by 15.8%,14.0%and 27.6%,respectively,corresponding to 40,80 and 80 footsteps m^-2.Trampling significantly reduced the plant C:N and C:P.In 2016,trampling decreased plant N:P,but increased it in 2017.Precipitation amplified trampling-induced P limitation in typical steppe.Simulated trampling increased aboveground biomass in 2016 and vice versa in 2017.Trampling reduced Shannon-Wiener index,while increased ecosystem multifunctionality index.Two years after simulated trampling stopped,trampling still significantly increased soil OC and TP concentrations,peaking at 40 or 80 footsteps m^-2.Trampling significantly reduced plant C:N and C:P,species richness and Shannon-Wiener index.The results showed that the grassland management was suitable when the trampling intensity was 2.7-5.3 sheep ha^-1(corresponding to 40-80 footsteps m^-2).4 Sheep grazing affects plant and soil C:N:P stoichiometry and multifunctionality of typical steppeIn Tan-sheep rotational grazing paddocks in the warm season,among the three pathways of grazing on grasslands,feeding had the highest contributions to soil TN concentration,C:N and N:P,plant C and P concentration,and C:P,and species richness;excrement had the greatest effects on soil TP concentration,soil C:P and plant N:P.Trampling played the most important role in soil OC concentration,plant N concentration and C:N,aboveground biomass,Shannon-Wiener index,and ecosystem multifunctionality index.The negative effects of feeding on soil and vegetation function reduced the ecosystem multifunctionality index;excrement had a neutral effect on ecosystem multifunctionality index due to conflict effects of urine or dung.Trampling increased C,N and P sequestration to improve the ecosystem multifunctionality index.Grazing at 2.7 and 5.3 sheep ha^-1 decreased soil OC,TN and TP concentrations,C:N and C:P,and increased soil N:P.Grazing significantly increased N and P concentrations,but decreased C:N and C:P concentrations.In 2016,grazing increased plant N:P,but vice versa in 2017.The species richness and Shannon-Wiener index,ecosystem multifunctionality index decreased with the increases of stocking rate,with non-significant difference among four stocking rates.Sheep grazing exacerbated the N limitation of the typical steppe with an increase in annual precipitation.5 Nitrogen addition level and stocking rate affect plant and soil C:N:P stoichiometry and multifunctionality of typical steppeThere were no interaction effects of N addition level and stocking rate on soil OC and C:N,while their interacted effects significantly influenced other soil and plant stoichiometric characteristics.In 2017,N addition significantly reduced soil TN concentration at 2.7 sheep ha^-1,while increased it at 8.7 sheep ha^-1.Nitrogen addition significantly increased soil TP concentration.Nitrogen addition levels did not significantly impact soil OC concentration,C:N,C:P and N:P.Nitrogen addition significantly increased plant N concentration and decreased plant C:N.Nitrogen addition under grazing significantly decreased plant P concentration.Nitrogen addition under 2.7 and 8.7 sheep ha^-1 significantly increased plant C concentration and C:P,while Nitrogen addition decreased plant C concentration and C:P at 5.3 sheep ha^-1.Nitrogen addition significantly increased plant N:P at 2.7 and 8.7 sheep ha^-1,while decreased plant N:P at 5.3 sheep ha^-1.Soil TP concentration showed a‘saddle'curve with the increase of stocking rate.The soil TN concentration significantly increased at 8.7 sheep ha^-1.Grazing had no significant effect on soil OC,C:N,C:P and N:P.Grazing significantly reduced plant C concentration,plant C:N and C:P,while increased plant N and P concentrations.In 2016,grazing at 8.7 sheep ha^-1 significantly reduced plant N:P.In 2017,plant N:P showed a‘hump'curve with the increase of stocking rate,with the highest values at 2.7 sheep ha^-1The negative effects of N addition on aboveground biomass and Shannon-Wiener index were amplified with increasing stocking rates.In 2016,grazing at 2.7 and 5.3sheep ha^-1 weakened the positive effect of N addition on ecosystem multifunctionality index at 10 g N m^-2yr^-1.In 2017,when N addition was higher than 10 g N m^-2yr^-1,grazing at 2.7 and 5.3 sheep ha^-1 weakened the N addition-induced positive effects on the ecosystem multifunctionality index.N addition exacerbated P limitation induced by grazing in wet year in the typical steppe.In summary,sheep feeding,excrement and trampling had antagonistic and synergistic effects on ecosystem multifunctionality of typical steppe via regulating plant and soil C:N:P stoichiometry,which depends on stocking rate and precipitation.The legacy effects of sheep excrement and trampling increased the ecosystem multifunctionality of typical steppe.The low level of nitrogen addition weakened the negative effect of grazing on the multifunctionality of typical steppe.