放牧对内蒙古典型草原生态系统植物及土壤δ^(15)N的影响  

Effects of grazing on the δ^(15)N values of foliage and soil in a typical steppe ecosystem in Inner Mongolia,China

作　　者：吴田乡[1,2] 黄建辉[1] 

机构地区：[1]中国科学院植物研究所植被与环境变化国家重点实验室,北京100093 [2]中国科学院研究生院,北京100049

出　　处：《植物生态学报》2010年第2期160-169,共10页Chinese Journal of Plant Ecology

基　　金：中国科学院西部行动计划(二期)(KZCX2-XB2-01-04)

摘　　要：植物和土壤中的15N自然丰度值(δ15N)是评价生态系统N循环的一个重要指标,而放牧是草原生态系统的主要土地利用方式,对草原生态系统的N循环过程的改变起着重要作用。该研究测定了内蒙古锡林河流域放牧和围封条件下草原群落主要优势植物和土壤的δ15N值,探讨放牧对草原N循环的影响。研究中所测定的8种植物叶片δ15N变化很大(-4.04‰-4.34‰),但与植物功能型有一定的相关性。放牧显著降低了大针茅(Stipa grandis)、杂类草和小半灌木木地肤(Kochia prostrata)的δ15N值。具有潜在共生固氮能力的豆科植物δ15N偏低负值(-4.04‰--1.90‰),但在放牧和围封条件下无显著差异;而被认为具有联合固氮能力的羊草(Leymus chinensis),放牧后δ15N显著增加,一定程度上表明了豆科植物和羊草生物固氮能力的存在。所有植物中,除无菌根侵染的木地肤外,其他有丛枝菌根真菌侵染记录的物种δ15N值较低,通常接近0或为负值,说明在N限制的内蒙古草原,菌根转运N可能也是一种重要的N源途径。放牧显著降低了0-20cm土壤δ15N值,这也与过去的研究结果不同。δ15N的测定为生态系统提供了一个整合时空N循环过程的综合指标,反映出放牧改变了草原生态系统的N循环。Aims Stable N isotope signature （δ^15N） in both plant and soil is potentially an important parameter to evaluate N cycling in grassland ecosystems. Grazing is a dominant land use in northern China grasslands and might have greatly changed N cycling. Our objective was to determine the ^15N signature of leaves and soils in grazed and fenced plots of a typical steppe to investigate how δ^15N values in an ecosystem are affected by grazing. Methods We collected foliar and soil samples in a nearly 20 years fenced plot and an adjacent freely grazed plot. The foliar samples came from eight dominant species, including three perennial legumes （Caragana microphylla, Astragalus galactites and Melilotoides ruthenica）, two grasses （Leymus chinensis and Stipa grandis）, two forbs （Heteropappus altaicus and Potentilla acaulis） and a semi-shrub （Kochia prostrata）. We also sampled 0-10 and 10-20 cm rhizosphere soils of C. microphylla and K. prostrata. Nitrogen isotope ratios were determined with a Thermal Finnigan MAT Deltaplus XP isotope-ratio mass spectrometer （IRMS）. Important findings Although the δ^15N value of leaves of different plant species varied greatly, the observed pattern of variability is consistent in both grazed and fenced plots, i.e., semi-shrub 〉 forbs and grasses 〉 legumes. Long-term grazing reduced foliar δ^15N values of forbs, semi-shrub and S. grandis significantly while changing little or even increasing that of potential biological N fixers （legumes and L. chinensis）. As the only arbuscular mycorrhizae non-infected plant species, K. prostrata is enriched in ^15N （with δ^15N values of 4.34‰± 0.35‰ and 2.04‰ ± 0.20‰ in fenced and grazed plots, respectively） compared with the depletion of other species. Mycorrhizal association may be considered to play an important role in plant nutrient transfer in those N-limited grassland ecosystems. In contrast to results of previous studies, soil δ^15N values decreased significantly with grazing.

关 键 词：δ~15N 草原生态系统 放牧 氮循环 

分 类 号：S812[农业科学—草业科学]