不同供氮水平对水曲柳苗木生物量、氮分配及其季节变化的影响

在温室内以水曲柳苗木为材料进行砂培试验，探讨了4种不同氮素浓度处理(1、4、8和16mmol·L^-1)下的水曲柳苗木根系和叶片内氮分配以及对苗木生物量的影响．结果表明，氮素供给浓度显著影响苗木根系氮浓度和叶片氮浓度．随着供氮水平提高，苗木体内根系和叶片氮浓度明显提高．在生长初期(6月)和中期(7、8月)，叶片中氮浓度分别高于根系9．40、9．55和4．21mg·g^-1，而在生长末期(9月)叶片中氮浓度低于根系；随着水曲柳幼苗生长发展，体内氮贮量呈明显上升趋势．9月份全株氮贮量比6月份平均增加了4倍．不同氮处理下水曲柳体内氮贮量明显不同．高氮处理下氮贮量平均为N1处理下4倍．氮贮量分配在不同部位有很大不同．分配到叶片中的比例在6月份最高，平均为43％．分配到根系中氮贮量比例随生长而增加，9月份根系氮贮量相对值最高，为81％．如果不考虑氮浓度和季节的作用，根系中分配的氮最多，其次为叶片，茎中最少．

Effect of different nitrogen supply on Fraxinus mandshurica seedling's biomass,N partitioning and their seasonal variation

Nitrogen is one of the most important limiting nutrients for tree growth in temperature forest ecosystems. In this paper, the effects of nitrogen treatments on nitrogen partition and biomass allocation in roots and leaves of one-year-old Fraxinus mandshurica seedlings were studied during a five-month period. The plants were sand-cultured in pots supplied with various concentrations of N (1, 4, 8, 16 mmol x L(-1)). The results suggested that N supply could significantly increase the N concentration in roots and leaves. In the initial (June) and middle growth stage (July and August), the N concentration in leaves was over 9.40, 9.55 and 4.21 mg x g(-1) respectively, which was higher than that in roots, but in the latter growth stage (September), it was lower than that in roots. From June to September, the N content of whole plant increased markedly, and was 4 times more in September than in June. The N content in Ash seedlings varied with N supply. It increased by 5.5 times in 16 mmol x L(-1) N treatment, in comparing with 1 mmol x L(-1) N treatment in September. The N allocation also varied in leaf, stem, and root. The proportion of N allocation in leaf was the highest in June (43% in average), and the lowest in September (9% in average). The proportion of N allocation to root increased with plant growth, which was the highest in September (81% in average). Regardless N treatments and tree growth stages, the proportion of N allocation to root was the highest, followed by to leaf, and the lowest was to stem. These results provided the theoretical foundation for the further studies of nitrogen absorption and carbon allocation mechanism in root system of Manchurian ash.