Spatial Heterogeneity Of Above-ground Primary Productivity And Soil Nutrients In Hequ Grassland

Grassland primary productivity is an important indicator of grassland service function,and is affected by natural factors and human activities.The Hequ grassland in the source area of the Yellow River was taken as the object in this study.The grassland above-ground primary productivity was measured and soil nutrients were analyzed,and the relationship between soil nutrients and plant above-ground primary productivity was explored.By analyzing the sulfur,phosphorus,carbon,nitrogen contents in soil,plant and yak muscles and isotope abundance of ?13C and ?15N,the distribution characteristics of these indicators in different grassland types and spatial types were studied,and the relationship between soil nutrients and grassland above-ground primary productivity and grassland degradation in Hequ grassland was discussed.A total of 127 soil samples,86 plant samples,8 yak muscle samples and 26 yak dung samples were collected from 6 townships in Henan Mongolian Autonomous County,Huangnan Tibetan Autonomous Prefecture,Qinghai Province.The contents of soil total nitrogen,total phosphorus,total potassium,available nitrogen,available phosphorus,available potassium and organic matter content and p H were determined by routine analysis of soil nutrients.The contents of phosphorus in different type of samples were measured with i CAP Qc.The contents of sulfur in different type of samples were measured with i CAP 6300.The carbon and nitrogen and their stable isotope abundance of different samples were analyzed with Isoprime100.The following results and conclusions were obtained:(1)The above-ground primary productivity of grassland in Hequ was as follows: flat land > slope;shrub meadow > typical meadow > marsh meadow(wetland);shady slope > flat land > sunny slope.The above-ground primary productivity difference between degraded grassland and non-degraded grassland was not significant(P>0.05).(2)The soil p H of Hequ grassland ranged from 5.31 to 7.91,belonging to neutral soil.Soil total nitrogen content was between2.24g/kg~14.89g/kg,total phosphorus content between 0.93g/kg~2.86g/kg,total potassium content between 15.32g/kg~27.39g/kg,soil sulfur content between 41.95mg/kg~475.55mg/kg;soil available nitrogen content between 173mg/kg~764 mg/kg,available phosphorus content between 6.7mg/kg~41.6 mg/kg,available potassium content between 51mg/kg~584 mg/kg,soil organic matter content between 13.97g/kg~318.79g/kg,soil carbon content between 3.40%~20.24%.The soil carbon to nitrogen ratio was 11.77:1.The distribution pattern of total nitrogen content in soil was: shrub > wetland > meadow;shady slope > sunny slope > flat land.Soil total potassium content in soil followed the order of meadow > shrub > wetland.Soil available nutrients generally showed shady slope > flat land > sunny slope.The degradation of Hequ grassland did not cause soil nutrients loss.(3)There was a significant negative correlation between the above-ground primary productivity of wetland and soil total nitrogen,available nitrogen,available potassium and organic matter content(P<0.05).The relationship between above-ground primary productivity of shrubs and meadows and soil nutrient content was not significant(P>0.05).(4)The carbon contents of the soil,plants,yak muscle and yak dung of Hequ grassland were: 7.38±3.26%,41.09±3.17%,45.65±0.62% and 32.73±5.48%;the ?13C abundance was-25.82±1.41‰,-27.27±0.39‰,-28.50±0.40‰ and-24.62±0.20‰,respectively.The difference between the different sample types was more than 1 thousand points.The nitrogen contents were: 0.63±0.25%,1.99±0.39%,1.91±0.49% and 13.23±0.39%,respectively.The nitrogen content of the plants and yak muscles was equivalent;the ?15N values were 3.23±1.33‰,-0.44±1.83‰,4.50±1.17‰ and 4.00±0.38‰,respectively.?15N was higher in soil,yak muscle and cow dung.(5)The phosphorus contents of the soil,plants,yak muscles and yak dung of the Hequ grassland were 0.76±0.23mg/kg,0.85±0.30mg/kg,4.42±0.25mg/kg and 1.07±0.93mg/kg,respectively.Except for the plants and soil,the phosphorus content difference of other samples was significantly different(P<0.05).The sulfur content was 117.43±55.46mg/kg,171.93±37.59mg/kg,748.67±37.07mg/kg and 234.16±39.10mg/kg,and was significantly different between different types of samples(P<0.05).The above-ground primary productivity and soil nutrient of different types of grassland,degradation degree,topography and aspect in the study area were moderately variable.The relationship between above-ground primary productivity and soil nutrient index was not significant except for marsh meadow(wetland).Grassland degradation in the study area was slight,and soil nutrients were not lost.The ?13C in soil,plants,yak muscle and yak dung presented consistency,but carbon,nitrogen,phosphorus,sulfur content and ?15N abundance showed great differences.