三江平原不同群落小叶章氮素的累积与分配

2004年5—10月，对三江平原典型小叶章草甸和小叶章-苔草沼泽化草甸群落优势植物小叶章的氮素累积与分配特征进行了研究.结果表明：典型草甸和沼泽化草甸小叶章地上器官及枯落物的全氮含量在生长季均呈递减变化，符合指数衰减模型(T_N=Aexp(-t/B₁)+B₂,R²≥0.94)，二者根的全氮含量波动较大，且在生长高峰期前的15～30 d存在一个明显的养分蓄积时期.不同器官和枯落物的氮累积量和累积速率(V_N)季节变化明显，且典型草甸小叶章地上部分的氮累积量和V_N明显高于沼泽化草甸，而地下部分则相反.两个群落小叶章不同部位的氮分配比差异明显，其中根分配比高达(59.38±12.86)%和(84.58±3.38)%，地上部分的氮分配比以叶最高，为(24.28±12.09)%和(8.18±3.32)%，其他部分较低.二者地上与地下部分的氮分配比呈相反规律变化，反映了其在氮供给方面的密切联系.典型草甸和沼泽化草甸小叶章氮的年吸收量和最大现存量分别为23.02、36.30 g·m^-2和28.18、51.43 g·m^-2，前者的氮吸收系数(0.017)和利用系数(0.634)明显高于后者(0.015和0.548)，说明典型草甸在氮的吸收与利用方面强于沼泽化草甸.

Community structure of soil mesofauna under different land use patterns in purple soil hilly area of Sichuan Basin.

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.