Abstract: From May to October in 2004, the characteristics of nitrogen (N) accumula tion and allocation in Calamagrostis angustifolia, the dominant species in t he typical meadow and marsh meadow communities of Sanjiang Plain, were studied. The results showed that the total nitrogen (TN) content in the aboveground organ s and litters of typical meadow C. angustifolia (TMC) and marsh meadow C. angustifolia (MMC) decreased during growth season, which could be described by exponential decay model (TN=Aexp(-t/B1)+B2,R2≥094). The TN content in TMC and MMC roots fluctuated greatly, and a significant N accumula tion period (15〖KG-*2〗-〖KG-*7〗30 d) was observed before the coming of growth midseason. The N accumulation amount and rate of different organs and litters h ad obvious seasonal changes, and their values of the aboveground organs were muc h higher for TMC than for MMC， while the values of the roots were in adverse. The N allocation ratio of different parts of TMC and MMC also had significant diffe rences. Root was the important N storage, and the root N allocation ratio of TMC and MMC was (5938±1286)% and (8458±338)%, respectively. Among the abo veground parts, leaf had the highest N allocation ratio, being (2428±1209)% for TMC and (818±332)% for MMC. The change patterns of the N allocation ra tio of aboveground and underground parts were just in adverse, which reflected t he osculation contact in N supplement aspect. The annual N absorption amount and maximum standing crop of TMC and MMC were 2302， 3630 g·m-2,and 2818， 5143 g·m-2, respectively. The N absorption coefficient and ut ilization coefficient of TMC were much higher than those of MMC (0017 and 0634 relative to 0015 and 0548, respectively), illustrating that TMC had higher capability of N absorption and utilization than MMC.

Key words: nematode, community structure, biological diversity, Tibet.