Responses Of The Structure And Function Of Alpine Ecosystem To Plant-livestock Interactions

The interactions of soil,plant,animal and human grazing management affect the production and stability of grassland ecosystems,and also provide the driving force for the functions and services of that.Most of experimental studies are essential to disentangle the response of plant productivity to grazing,but such researches to study the effects of plant and livestock,and their interactions on ecosystem coupling and material cycle are currently lacking.Here,we conducted the experiments in the pastoral areas of the Qinghai-Tibetan Plateau.Our objectives were to estimate the effects of livestock-rodent interactions on the ecosystem structure and functions,and to investigate the mechanism driving the process of litter decomposition response to livestock excrement and plant composition.The main results are as follows:1.Response of ecosystem coupling of alpine meadow to livestock-rodent interactionsSpecies richness under warm season grazing treatment was significantly higher than that under No grazing treatment.The increase was 19.8%.The same trends also occurred at ecosystem coupling,ecosystem multifunctionality and their relationships.There were no significant effects for plant and soil properties between cold season grazing treatment and no grazing treatment.Live weights of livestock were lost when biomass of standing crop were less than 3000 kg/ha and 1000 kg/ha under rotational grazing and continuous grazing,respectively.Live weight of livestock was lost when month average temperature was less than-2.5?.Live weight of livestock was increased rapidly when month precipitation was between 20-80mm.Live weight of livestock was increased steadily when month precipitation was more than 80 mm.With rotational grazing in warm season,CO₂ efflux were the lowest when the densities were 100 burrows/ha and 210 mounds/ha for Pikas and Zokors,respectively;CH₄ efflux were the lowest when the densities were 110 burrows/ha and 600 mounds/ha for Pikas and Zokors,respectively.With rotational grazing in cold season,CO₂ efflux were the lowest when the densities were 100 burrows/ha and 600 mounds/ha for Pikas and Zokors,respectively;CH₄ efflux were the lowest when the densities were 95burrows/ha and 500 mounds/ha for Pikas and Zokors,respectively.With rotational grazing at 24 SM/ha,live weight gain peaked at 100 burrows/ha and 470 mounds/ha for Pikas and Zokors,respectively.With rotational grazing at 48 SM/ha,live weight gain was significantly decreased with rodent density was increased.2.Removing plant functional groups,adding yak excrement and their interactions affects litter decomposition and nutrient turnover in an alpine meadowCompared to whole-mixed plant litter?P1?,sedges functional group?FG?removal?P2?led a significant increase for litter decomposition constants?37.2%?,release rates of nitrogen?3.5%?,phosphorus?6.9%?and sulfur?4.4%?;grasses FG removal?P4?also led a significant increase for litter decomposition constants?28.1%?,release rates of nitrogen?3.8%?,phosphorus?3.5%?and sulfur?1.1%?.Compared to whole-mixed plant litter?P1?,legumes FG removal?P3?led a significant decrease for litter decomposition constants?14.9%?,release rates of nitrogen?2.4%?,phosphorus?0.4%?and sulfur?0.9%?;forbs FG removal?P5?also led a significant decrease for litter decomposition constants?22.6%?,release rates of nitrogen?4.6%?,phosphorus?0.4%?and sulfur?0.5%?.The explained mechanism was that initial nitrogen and phosphorus content were significantly increased under P2 and P4 litter types.Initial lignin content and Lignin/N and Lignin/P values are significantly increased under P3 and P5 litter types and further affected the non-additive synergistic effect among different litter species.Compared to no adding excrement treatment?CK?,adding dung treatment?D?led a significant increase for litter decomposition constants?80%?,release rates of nitrogen?24.5%?,phosphorus?20.2%?and sulfur?19.1%?;adding dung and urine treatment?DU?also led a significant increase for litter decomposition constants?70.1%?,release rates of nitrogen?21.3%?,phosphorus?18.4?and sulfur?16.7%?.Compared to no adding excrement treatment?CK?,adding Urine treatment?U?led a significant increase for litter decomposition constants?22.6%?,release rates of phosphorus?21.6%?and sulfur?9.1%?in the first 60 incubation days.There were significant relationships between litter decomposition constants?K?,nutrient release rate and soil properties.Structural equation model showed that adding excrement promote litter decomposition through significantly increasing soil moisture,and soil TN,soil TP and soil microbial activities.3.Plant litter type,yak excrement adding and their interactions affects litter decomposition and nutrient turnover in an alpine shrubland.Compared to alpine meadow,alpine shrubland significantly decreased litter decomposition constants?6.1%?,release rates of nitrogen?2.3%?,phosphorus?5.2%?and sulfur?3.4%?by reducing soil temperature,soil pH and soil moisture.Soil TC,TN,MBC and MBN contents in alpine shrubland were significantly higher than that in alpine meadow.The effects of soil nutrients from“fertility islands effects”was significantly higher than that from the show decomposition caused by shrubs as above.In shrubland,compared to whole-mixed plant litter?L'?,mixed plant litter and shrub leaves?L1?led a significant increase for litter decomposition constants?10.3%?,release rates of nitrogen?2.5%?,phosphorus?3.9%?and sulfur?2.5%?;mixed plant litter,shrub leaves and shrub stem?L2?led a significant decrease for litter decomposition constants?20.5%?,release rates of nitrogen?15.2%?,phosphorus?16.1%?and sulfur?6.0%?.Shrub leaves have higher initial nitrogen and phosphorus content.Shrub stems have higher initial lignin content,C/N,C/P,and Lignin/N values.In conclusion,ecosystem coupling and material cycle of alpine meadow are significantly affected by plant and livestock,and their interactions.Warm season grazing promotes species diversity,and cold season grazing has no significant effects on plant and soil properties.A appreciate density of rodent are benefited for promoting livestock productivity and reducing GHG emissions.Grazing can change grassland vegetation composition and soil nutrients,and further affect the turnover of carbon and nutrient in litter decomposition.This research provides a theoretical understanding and experimental evidence for sustainable grazing management,and also has an important ecological significance for species diversity protection in alpine ecosystem.