不同放牧强度上内蒙古短花针茅草原植物功能群水分和氮素利用效率相关分析

Integration of Water and Nitrogen Use Efficiency of Plant Function Groups in the Stipa breviflora Grassland of Inner Mongolia along Grazing Gradients

以内蒙古短花针茅(Stipa breviflora)草原为研究对象,设置4个不同的放牧梯度:无牧区、轻度放牧、中度放牧、重度放牧,载畜率依次为0、0.91、1.82和2.71 sheep·hm^(-2)·0.5 a^(-1);根据生活型划分植物功能群(多年生杂类草,多年生禾草,一年生草本,小半灌木),利用稳定性碳同位素测定植物叶片的碳同位素值,结合植物叶片C/N,探讨放牧对植物功能群水分及氮素利用效率的影响,分析不同植物功能群面对干扰时的生理生态应对策略,为放牧条件下荒漠草原植物资源利用对策的选择提供参考。结果表明:(1)随着放牧强度的增大,一年生草本植物的水分利用效率增大(P=0.000 7),而多年生杂草和多年生禾草水分利用效率降低(P=0.000 9,P=0.000 02),小半灌木的水分利用效率没有显著差异(P>0.05);(2)随放牧强度的增大,植物功能群的N素含量普遍增大,而C/N普遍降低,植物的资源利用效率降低;(3)在一年生草本植物中,δ^(13)C与C/N呈极显著负相关(r=-0.865,P<0.01),而在多年生禾草、杂类草和半灌木中,二者呈显著正相关(r=0.699,r=0.593,r=0.642,P<0.05);δ^(13)C与C/N之间的关系因植物体内N的分配而异,不同植物具有不同的资源利用策略。

Desert steppe of Stipa breviflora in Inner Mongolia was taken as the object,and randomized block experiment was set based on4grazing gradients,represented by control(0sheep·hm-2),light grazing(0.91sheep·hm-2),moderate grazing(1.82sheep·hm-2)and heavy grazing(2.71sheep·hm-2),respectively,as well as plant functional groups were divided according to different life forms(perennial grasses,perennial forbs,annual herbs,half-subshrubs).Furthermore,the carbon isotope values of plant leaves were determined by stable carbon isotope,the C/N was used to analyze the nitrogen use efficiency.This paper intends to study the effects of different grazing gradients on water and nitrogen use efficiency,to analyze the physiological and ecological strategies of different plant functional groups in the face of disturbance,and to provide a reference for the selection of plant resources in the desert grassland under grazing conditions.The results showed that:(1)The water use efficiency of annual herbs increased(P=0.0007)as grazing gradients increased,the perennial grass and forbs decreased with the increase of the grazing gradients(P=0.0009,P=0.00002),whereas the half-subshrub were not observed differences(P>0.05).(2)With increasing grazing gradients,The N percent of the plant functional groups elevated,while the C/N decreased(P<0.05),so the efficiency of plant resource utilization reduced.(3)Theδ13C were negatively associated with C/N in annual herbs(r=-0.865,P<0.01),while in perennial grass,perennial forbs and half-subshrub,there were significantly positive relationship(r=0.699,r=0.593,r=0.642,P<0.05).The different relationship betweenδ13C and C/N was due to the distribution of N elements in the plant,different plants have different resource utilization strategies.