Net nitrogen mineralisation characteristics of Citrus reticulate and Conyza canadensis in ecological barrier area of Danjiangkou Reservoir

Two typical species (Citrus reticulate and Conyza canadensis) from riparian buffer strips in the Danjiangkou Reservoir were selected to evaluate the soil nitrogen mineralisation characteristics of single leaf and/or root treatments and to examine whether the interactive effects between leaves and root mixed treatments existed under laboratory incubation conditions. We measured the rate of nitrogen mineralisation of the plants on days 1, 3, 7, 14, 21, 31, 41, 51, and 61. The main results were summarised as follows:1) the laboratory incubation experiment had three stages, the first (1-7 days) comprised soil microbial adaptation, the content of mineral nitrogen was markedly increased in the second stage (7-41 days), and became steady in the final stage (41-61 days); 2) ANOVA strongly indicated that C. reticulate leaf treatment (GL) was correlated to C. canadensis leaf treatment (PL) in the whole incubation (P<0.05), but C. reticulate root treatment (GR) was not correlated to C. canadensis root treatment (PR) in the second and third stages (P>0.05). There was a strong correlation between GL and GR and PL and PR (except at day 41) in the plants; 3) For single treatments, only GL promoted soil net N mineralisation, and GL+PL and GL+PR in mixed treatments, whereas others had no effect; and 4) the Pearson method and PCA demonstrated the total N of plant was the most important plant chemical property. In conclusion, the plant chemical properties played a key role in the net N mineralisation and the existence of interactive effects between mixed treatments depended on the plant chemical properties and incubation conditions.