CAJ | 학술논문

植物和土壤中的~(15)N自然丰度值(δ~(15)N)足评价生态系统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δ~(15)N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δ~(15)N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δ~(15)N值.具有潜在共生固氮能力的豆科植物δ~(15)N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δ~(15)N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δ~(15)N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δ~(15)N值,这也与过去的研究结果不同.δ~(15)N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.
식물화토양중적~(15)N자연봉도치(δ~(15)N)족평개생태계통N순배적일개중요지표,이방목시초원생태계통적주요토지이용방식,대초원생태계통적N순배과정적개변기착중요작용.해연구측정료내몽고석림하류역방목화위봉조건하초원군락주요우세식물화토양적δ~(15)N치,탐토방목대초원N순배적영향.연구중소측정적8충식물협편δ~(15)N변화흔대(4.04‰_4.34‰),단여식물공능형유일정적상관성.방목현저강저료대침모(Stipa grandis)、잡류초화소반관목목지부(Kochia prostrata)적δ~(15)N치.구유잠재공생고담능력적두과식물δ~(15)N편저부치(-4.04‰--1.90‰),단재방목화위봉조건하무현저차이;이피인위구유연합고담능력적양초(Leymus chinensis),방목후δ~(15)N현저증가,일정정도상표명료두과식물화양초생물고담능력적존재.소유식물중,제무균근침염적목지부외,기타유총지균근진균침염기록적물충δ~(15)N치교저,통상접근0혹위부치,설명재N한제적내몽고초원,균근전운N가능야시일충중요적N원도경.방목현저강저료0-20 cm토양δ~(15)N치,저야여과거적연구결과불동.δ~(15)N적측정위생태계통제공료일개정합시공N순배과정적종합지표,반영출방목개변료초원생태계통적N순배.
Aims Stable N isotope signature δ~(15)N)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 δ~(15)N signature of leaves and soils in grazed and fenced plots of a typical steppe to investigate how δ~(15)N 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 Delta~(plus) XP isotope-ratio mass spectrometer (IRMS).Important findings Although the δ~(15)N 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~(15)>N 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 myeorrhizae non-infected plant species, K. Prostrata is enriched in ~(15)N (with δ~(15)N values of 4.34‰ ± 0.35‰ and 2.04‰ ± 0.20‰ in fenced and grazed plots, respectively)compared with the depletion of other species. My-corrhizai 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~(15)N values decreased significantly with grazing.