Abstract:

The mixed plantation of poplar (Populus spp.) and Black Locust (Robinia pseudoacacia) is one of the typical mixed stands with nitrogen-fixing and nonnitrogen-fixing species. The interaction between two species in the mixed stand is harmonious and its productivity is high, so this kind of mixed plantations has become the very successful pattern on poor sandy sites in north of China. In this paper, fine-root decomposition of two species was studied in the mixed plantation of Canadian Poplar(P. canadansis)(27 a) and Black Locust (22 a) on sandy sites along the Chaobai River in Beijing. Mechanism of harmonious interaction between two species was found out in the view of the nutrient recycle of fine-roots. The result shows: (1) fine-root decomposition of Canadian poplar and black locust trees was different. The concentration of N, Ca and Mg was gradually increased and P, K was gradually decreased in poplar fine roots during the early period of decomposition. The concentration of N, P and K was gradually decreased in Black Locust fine roots during decomposition. The nutrient decomposition speed of mixed fine roots of two species during decomposition was between speeds of two pure samples. (2) the return amount of N, K and Mg in 1 a Black Locust fine roots was the biggest, mixed fine roots was the second and poplar fine roots was the smallest. (3) the increased N return amount of mixed fine roots could improve N nutrient condition of poplar trees. P return amount of poplar fine roots was more than Black Locust, which could improve the P nutrient condition of Black Locust trees. The interaction of mutual supplement of N and P nutrient recycle of fine roots between tree species was formed.

Key words: Fine roots, Nutrient, Poplar, Black Locust, The mixed plantation