氮素利用效率（NUE）是植物养分策略研究中的一项重要内容。该文利用Berendse和Aerts提出的氮素利用效率概念和原理研究了高密度的藜(Chenopodium album)种群中不同植物个体在种内竞争条件下的氮素利用效率。结果表明，由于植株的氮素吸收速率与其个体大小成非线性关系，说明不同植株个体对氮素的竞争属于非对称竞争。个体较大的植株氮素输入较高，而个体较小的植株氮素输出较高，因而较大个体植株的氮素净增加也较高。植株的氮素损失随着个体大小的增加而增加，较大植株个体的氮素浓度随着生长而下降，而较小植株个体的氮素浓度随时间的变化不大，说明个体较小的植株的生长受光照的限制比受氮素的限制更大，而对较大的植株个体而言，它们的生长受氮素的限制更大。高密度藜种群中的不同植物个体具有不同的养分策略，氮素利用效率及其组成部分氮素生产力（NP）和氮素滞留时间（MRT）均不同。植株的NP和MRT与其个体大小正相关，较大的植物个体具有较高的NP和较长的MRT，因而氮素利用效率也高于个体较小的植株。在个体水平上，种内不同植株的NP与MRT不存在权衡关系（Trade-off）。因此，Berendse和Aerts提出的氮素利用效率概念不仅适用于研究种间的养分策略，对于研究种内不同植株的养分策略也同样适用。
The concept of nitrogen use efficiency (NUE) offers a powerful tool to study plant strategies with respect to nutrient limitation. We studied the NUE of an annual herb, Chenopodium album, in a dense monospecific stand using the concept introduced by Berendse and Aerts. Larger individuals absorbed more N in greater proportions relative to their size, suggesting that the competition for soil nitrogen was asymmetric (one-sided) among individual plants in the stand. Nitrogen loss from individuals also increased with plant size. Nitrogen influx (rin, the rate of N uptake per unit aboveground N) was greater in larger individuals while nitrogen outflux (rout, the rate of N loss per unit aboveground N) was the reverse. Therefore, the relative rate of nitrogen increment (rin-rout) was greater in larger individuals whereas it was around zero in the smallest plants. Larger individuals decreased their N concentration with time while smaller individuals showed little change in N concentration. These results suggested that the growth of smaller individuals was limited by light availability rather than by N availability, and N limitations were greater in larger individuals. Individual plants in this dense stand of C. album differed in their N economy. NUE and its components, i.e., MRT and NP, were different among individuals in the stand. Both NP and MRT were positively related to plant size. Larger individuals had longer MRT and higher NP, both of which contributed to higher NUE, than the smaller individuals. No trade-off relationship between NP and MRT was found at the intraspecific level. This study showed that the concept of NUE defined by Berendse and Aerts offered a powerful tool in studing plant strategies within species as well as among species.