植物生态学报 ›› 2010, Vol. 34 ›› Issue (2): 160-169.DOI: 10.3773/j.issn.1005-264x.2010.02.007

所属专题: 稳定同位素生态学

• 稳定同位素生态学专题论文 • 上一篇    下一篇

放牧对内蒙古典型草原生态系统植物及土壤δ15N的影响

吴田乡1,2, 黄建辉1,*()   

  1. 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
  • 收稿日期:2009-01-21 接受日期:2009-05-06 出版日期:2010-01-21 发布日期:2010-02-01
  • 通讯作者: 黄建辉
  • 作者简介:* E-mail: jhhuang@ibcas.ac.cn

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

WU Tian-Xiang1,2, HUANG Jian-Hui1,*()   

  1. 1State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
    2Graduate University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2009-01-21 Accepted:2009-05-06 Online:2010-01-21 Published:2010-02-01
  • Contact: HUANG Jian-Hui

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0-20 cm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。

关键词: δ15N, 草原生态系统, 放牧, 氮循环

Abstract:

Aims Stable N isotope signature (δ15N) 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 the15N signature of leaves and soils in grazed and fenced plots of a typical steppe to investigate how δ15N 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 δ15N 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 δ15N 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 in15N (with δ15N 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 δ15N values decreased significantly with grazing.

Key words: 15N signature, grassland ecosystems, grazing, N cycling