[Responses of marsh wetland plant Calamagrostis angustifolia to exogenous nitrogen input]

Taking the typical marsh wetland plant Calamagrostis angustifolia in Sanjiang Plain of Northeast China as test material, a field control experiment was conducted to study its leaf morphological characters, chlorophyll content, and aboveground biomass under effects of different levels of exogenous nitrogen input in 2004-2007. Four nitrogen (N) fertilization treatments, i.e., 0 (CK), 6 g x m(-2) x a(-1) (N6), 12 g x m(-2) x a(-1) (N12) and 24 g x m(-2) x a(-1) (N24), were installed. The results showed that there were no significant differences in the leaf length and width among different N fertilization treatments, but the specific leaf area was the smallest (149.54 +/- 18.27 cm2 x g(-1)) under N12, which indicated that the leaves of C. angustifolia were thicker under this N treatment. The leaf chlorophyll content showed a unimodal distribution over the growth season, which increased with the amount of N input before the peak. The peak occurred earlier under N12 and N24 than under N6 and CK. After the peak, the chlorophyll content declined sharply under N24 but slowly under N6, indicating that moderate N input could delay leaf senescence. Continuous high N (N24) input might advance plant growth, while leaf senescence would occur earlier. By the end of growth season both in 2005 and in 2007, the aboveground biomass of C. angustifolia increased with increasing N input, but declined by 53.72% after 4 years continuous high N (N24) input (in 2007), compared with that after 2 years treatment (in 2005).