Effects Of Plateau Pika Disturbances On Soil Nutrient Concentrations Of Alpine Meadow At Three Spatial Scales

Plateau pika?Ochotona curzoniae?is a mainly small endemic and common soil bioturbator of the alpine meadow ecosystem in the Qinghai-Tibetan Plateau?QTP?,which can affect the ecosystem functions of alpine meadow by changing soil properties through multiple behaviors.At present,the study on the effects of plateau pika disturbances on soil nutrients is either soil sampling at one site or ignored the changes of dominant plant species in regard to different disturbance intensity areas across different grassland types,resulting in very different results between different studies.Therefore,it is an alternative way to elucidate the effects of plateau pika disturbances on soil nutrients in alpine meadow by carrying out multi-point sampling,confining the disturbed areas and undisturbed areas to the same meadow type,and dividing the disturbed area into the bare land and the adjacent vegetated land to soil sampling.This study investigated the effects of the presence and intensity of plateau pika disturbances on the soil nutrient concentrations of the Kobresia pygmaea meadow at three different spatial scales across three study site?Luqu,Maqu and Gonghe County?in the QTP.For analyses,vegetated/bare land?micro-scale?were nested within different disturbance intensity areas?intermediate scale?,which were nested within presence/absence of plateau pika in view of overall scale across three study sites?large-scale?.This study will be beneficial for obtaining the common regularity of the influence of plateau pika disturbances on the soil nutrients of the alpine meadow,and to providing scientific basis for the comprehensively assessment of the role of plateau pika,and a theoretical basis for the ecological prevention and control of plateau pika in the alpine meadows in the QTP.The main conclusions are as follows:1.In large-scale,the disturbance of plateau pika significantly increased the soil total nitrogen?TN?,soil organic carbon?SOC?and total phosphorus?TP?concentrations,and was beneficial to the storage of soil carbon and nitrogen in the alpine meadow of the QTP.The soil TN,SOC and TP concentrations in disturbed areas were significantly higher relative to the areas devoid of plateau pika,while the available phosphorus?AP?concentrations significantly decreased in undisturbed areas across all three study sites.So,in large-scale,the plateau pika disturbances significantly increased the soil total nutrients concentrations,and it was beneficial to the soil carbon and nitrogen fixation in the alpine meadow of the QTP.The effects of plateau pika disturbances on the available nutrients concentrations were related to the type of available nutrients.2.In intermediate scale,these soil nutrient changes induced by plateau pika disturbances intensity are related to a threshold,and that the most appropriate disturbance intensity of plateau pika was most beneficial to increase the soil nutrients in the alpine meadow.The soil total nutrients?TN,SOC and TP?concentrations and available nutrients?NO₃^--N,NH₄⁺-N and AP?concentrations of disturbed areas showed significant unimodal curvilinearity as the intensity of the plateau pika disturbances increased.However,the TN,SOC and TP concentrations of vegetated land significantly increased at first and later decreased notably,while NO₃^--N,NH₄⁺-N and AP concentrations of vegetated land dropped significantly at first and later increased rapidly,and the all soil nutrients of bare land slightly increased at first and subsequently sharply declined as the disturbance intensity of plateau pika increased.The threshold of disturbance intensities was 443?443±50?burrow entrances per ha and 327?327±144?burrow entrances per ha for vegetated land and bare land,respectively.Therefore,the response of soil nutrients concentrations to the disturbance intensities between vegetated land and bare land are inconsistent.3.In micro-scale,the appropriate disturbance of plateau pika caused the formation of bare land relatively high in available nitrogen concentrations,mitigated the competing effects of plants in soil nutrients and space.The plateau pika disturbances significantly decreased the SOC,TN and TP concentrations,and increased the AP,NO₃^--N and NH₄⁺-N concentrations of bare land.Therefore,disturbance within the threshold disturbance intensities of plateau pika is accumulate higher soil available nutrient concentrations in the topsoil.The increase of soil available soil nitrogen?NO₃^--N,NH₄⁺-N?concentrations in the QTP will optimize the grazing quality and keep high plant diversity of alpine meadow by providing good habitats for some rare plants and supplying nutrients for the nitrophilous graminoid plants to grow well in bare land of the QTP.4.The disturbance of plateau pika changed the coupling relationships of soil nutrients,and influenced the soil nutrients cycle.Under the plateau pika's disturbance,soil total nutrients was in negative relationships with available nutrients in the disturbed areas and vegetated land,but in positive relationships in the undisturbed areas and bare lands.Specially,SOC was in significantly negative relationships with available nitrogen,NO₃^--N,NH₄⁺-N and AP in the vegetated land,but in significantly positive relationships in the bare lands.It indicates that the disturbance of plateau pika changed the coupling relationships and cyclic process of soil C and N.