以广东连州自然分布的3种国家重点保护野生植物南方红豆杉〔Taxus chinensis var. mairei （Lemée et Lévl.） Cheng et L. K. Fu〕、半枫荷（Semiliquidambar cathayensis Chang）和金荞麦〔Fagopyrum dibotrys （D. Don） Hara〕为研究对象，分析了根、茎和叶片及根际土壤和岩石的C、N含量和C∶N比以及δ13C和δ15N值的差异；在此基础上，通过δ13C和δ15N值的散点图比较了3种植物生态位的差异。结果表明：在同种植物中，根、茎和叶片的C和N含量及C∶N比总体高于根际土壤和岩石，其中，叶片中C和N含量均最高，茎的C∶N比最高；而根际土壤和岩石的δ_¹³C和δ_¹⁵N值总体高于根、茎和叶片。在供试的3种植物间，根际土壤和岩石中C和N含量总体上无明显差异，但根、茎和叶片中C和N含量以及根、茎和叶片及根际土壤和岩石的C∶N比、δ13C和δ15N值均有一定差异；其中，金荞麦根中C含量显著（P＜0.05）低于南方红豆杉和半枫荷，其根、茎和叶片中N含量和δ15N值均极显著（P＜0.01）高于后二者，其根、茎和叶片的C∶N比和δ13C值均极显著低于后二者，其根际土壤和岩石的C∶N比和δ13C值总体上也低于后二者；南方红豆杉和半枫荷的叶片中C和N含量以及茎和叶片的δ13C值、根际土壤和岩石的δ13C和δ15N值均存在显著差异，但二者的整体差异相对较小。从散点图上看，金荞麦的生态位远离南方红豆杉和半枫荷，而后二者的生态位有交集。综合分析结果显示：草本植物金荞麦与木本植物南方红豆杉和半枫荷的C和N含量以及δ13C和δ15N值的差异不仅与植物自身的生活型有关，而且与各自生境中的光照和土壤因子等相关。另外，供试3种植物的根、茎和叶片的δ13C值变幅为-31.69‰～-26.46‰，符合C3植物的δ13C值范畴。

Taking three national key preserved wild plants of Taxus chinensis  var. mairei （Lemée et Lévl.） Cheng et L. K. Fu， Semiliquidambar cathayensis Chang and Fagopyrum dibotrys （D. Don） Hara naturally distributed in Lianzhou of Guangdong as research objects， differences in C and N contents， C∶N ratio， and δ13C and δ15N values of their root， stem and blade， and rhizosphere soil and rock were analyzed； on the basis， ecological niche differences in three plants were analyzed by using scatter diagram of δ13C and δ15N values. The results show that C and N contents and C∶N ratio of root， stem and blade are generally higher than those of rhizosphere soil and rock in the same plant， in which， C and N contents in blade are the highest， C∶N ratio of stem is the highest； while δ13C and δ15N values of rhizosphere soil and rock are generally higher than those of root， stem and blade. Among three tested plants， there is no significant difference in C and N contents in rhizosphere soil and rock in general， while there are some differences in C and N contents in root， stem and blade， as well as in C∶N ratio， δ13C and δ15N values of root， stem and blade， and rhizosphere soil and rock； in which， C content in root of F. dibotrys is significantly （P＜0.05） lower than that of T. chinensis var. mairei and S. cathayensis， while its N content and δ15N value， and C∶N ratio and δ13C value of root， stem and blade are extremely significantly （P＜0.01） higher and extremely significantly lower than those of the latter two， respectively， and its C∶N ratio and δ13C value of rhizosphere soil and rock are lower than those of the latter two in general； there are significant differences in C and N contents in blade， δ13C value of stem and blade， and δ13C and δ15N values of rhizosphere soil and rock between T. chinensis var. mairei and S. cathayensis， but the overall differences are relatively small. Ecological niche of F. dibotrys is far from that of T. chinensis var. mairei and S. cathayensis in the scatter diagram， while there is intersection of ecological niche between the latter two. The comprehensive analysis results show that the differences in C and N contents and δ13C and δ15N values between herbaceous plant F. dibotrys and woody plant T. chinensis var. mairei and S. cathayensis are not only related with their life forms， but also with light, soil factors, etc. in their respective habitats. In addition， variation range of δ13C value of root， stem and blade of three plants tested is -31.69‰--26.46‰， which is in accord with δ13C value range of C3 plant.