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杨树刺槐混交林是我国北方地区沿河及滨海沙地上成功的固氮树种和非固氮树种人工混交林。本文在简单介绍混交林生长情况的基础上，主要对林地土壤养分改良及其种间Ｎ、Ｐ养分互补关系进行了阐述。指出杨树刺槐混交林生产力提高主要是因为林地土壤养分（特别是Ｎ素养分）的极大改善及树种间Ｎ、Ｐ养分的互补。混交林土壤Ｎ素养分水平提高的根本原因是林地土壤微生物活性高，加快了含Ｎ较高枯落物分解速度，增强了土壤氨化及硝化强度。而杨树刺槐种间的Ｎ、Ｐ养分互补则主要表现在混交林中杨树可将吸收入体内的Ｐ素通过根系接触转移给相邻的刺槐，而刺槐则可将固定的Ｎ素通过根系接触转移给杨树，而且Ｎ、Ｐ转移的强度很大。这种奇妙的树种间养分互补机制对杨树刺槐混交林幼林期生产力提高是有重大意义的。
The mixed forest of poplar and black locust is a kind of mixed plantation of nitrogen-fixing and non-nitrogen-fixing species successfully along the river and coastal sandy land in northern China. Based on the brief introduction of the growth of mixed forest, this paper describes the improvement of soil nutrient and the complementary relationship of N and P nutrients in forest. The results showed that the productivity of poplar and black locust was mainly due to the great improvement of soil nutrients (especially N-nutrients) and the complementation of N and P nutrients among species in forest. The basic reason for the increase of N-nutrient in soils is that the activity of soil microorganisms in forestland is high, the decomposition rate of higher N-containing litter is accelerated, and the soil ammonification and nitrification intensity are enhanced. Poplar Acacia species N, P nutrients complement each other mainly in the mixed forest poplar can be absorbed into the body of P through the root contact transfer to the adjacent acacia, while Locust can be fixed N through the root system Contact transfer to poplar, and N, P transfer intensity. This wonderful mechanism of nutrient complementarity between tree species in poplar and black locust hybrid forest increased productivity is of great significance.