Response of biological nitrogen fixation and nitrogen distribution of Alhagi Spacifolia Shap seedlings to different water conditions

在塔克拉玛干沙漠南缘荒漠-绿洲过渡带上有一定面积的骆驼刺植被分布，这种豆科植物不仅是当地重要的防风固沙植物，而且是当地重要的优质牧草。但是，由于人类活动的影响，植被退化严重，严重影响了当地的生态环境和人民的生产生活，对骆驼刺的保护与恢复重建已经得到当地政府高度重视。当地极端干旱，可利用的养分极少，生物固氮是很重要的氮素来源，生物固氮占总氮素（根、茎、叶中氮素含量之和）比例，既生物固氮对氮素来源的贡献，对骆驼刺的生存至关重要，因此，研究骆驼刺生物固氮和氮素分配对于揭示荒漠植物对极端干旱环境的适应策略有重要的生态学意义。本研究依托中科院策勒站，在两个生长季内，以一年龄骆驼刺幼苗为研究对象，通过不同灌溉（0、0.1m3/m2、0.2m3/m2）处理，以生物固氮、氮素分配、氮素利用效率、氮素转移对灌溉的响应特征为研究内容，采用15N稳定同位素法研究了生物固氮对一年龄骆驼刺幼苗氮素来源的贡献，通过进行根、茎、叶氮素浓度的测定，计算出分配到根、茎、叶的氮素比例和质量。最后，得出生物固氮、氮素分配、氮素利用效率、氮素转移的季节变化规律。此外，在进行该项实验时，作为对比试验，对不同灌溉处理（0、0.1m3/m2、0.2m3/m2）的二年龄骆驼刺幼苗生物固氮能力也进行了测定；对不同潜水埋深深度（0.7m、1.5m、2.0m、2.5m）的一年龄和两年龄骆驼刺幼苗也进行了生物固氮能力的测定；对荒漠区天然骆驼刺的生物固氮能力也进行了一次测定。在试验观测、测定分析和数据处理的基础上，得出如下结论： ⑴ 骆驼刺生物固氮对不同水分条件的响应特征： ① 骆驼刺幼苗生物固氮对不同灌溉的响应特征：从整个生长季来看，灌溉促进骆驼刺幼苗生物固氮的增加，但是，灌水量过多会抑制生物固氮。对于一年龄骆驼刺幼苗而言，在生长季末，0.1m3/m2水分灌溉下，生物固氮能力最大，为0.836g/株，其次是0.2m3/m2水分灌溉下，为0.433g/株，灌水量为0时生物固氮能力最小，仅为0.182g/株。二年龄骆驼刺幼苗生物固氮能力比一年龄骆驼刺要强，在0.2m3/m2水分灌溉下，仍对氮素来源保持较高的贡献。在相同潜水埋深条件下，不同年龄的骆驼刺的生物固氮能力有较大的差异。随着年龄的增大，生物固氮能力显著增强。灌水量为0时，一年龄的骆驼刺幼苗生物固氮占总氮的比例只有14.85%，到了二年龄，则达到了40.02%，荒漠区天然多年龄高达89.93%。 ② 骆驼刺幼苗生物固氮对不同潜水埋深的响应特征：潜水埋深的深浅，与骆驼刺幼苗生物固氮占总氮素的比例成反比，一年龄和二年龄的骆驼刺幼苗对此反应都是如此。二年龄骆驼刺幼苗生物固氮占总氮素的比例显著高于一年龄骆驼刺幼苗生物固氮占总氮素的比例。 ⑵ 骆驼刺幼苗氮素分配对不同水分条件的响应特征灌溉使得氮素分配到骆驼刺幼苗茎、叶中的比例、质量增加，分配到表层根系(0-60cm)中的氮素质量增加。随着灌水量的增加，叶、茎中氮素质量之比增大，叶、根中氮素质量之比先增大后减小，这说明灌溉有利于氮素分配到叶中，但是，灌水量过多则不利于氮素分配到叶中。 ⑶ 骆驼刺幼苗氮素利用效率对不同水分条件的响应特征从整个生长季来看，灌溉有利于增加氮素利用效率，但是，灌水量过多会抑制氮素利用效率。在生长季末，三种水分灌溉梯度 (0、0.1m3/m2、0.2m3/m2) 下氮素利用效率分别是：77.91、104.33、84.54。 ⑷ 骆驼刺幼苗氮素转移对不同水分条件的响应特征骆驼刺幼苗茎、叶中的氮素在生长季末向根系中转移。到了9月底至10月底间，三种水分灌溉梯度 (0、0.1m3/m2、0.2m3/m2) 下，茎中的氮素向根中转移的质量分别为： 0.084g、0.088g、0.108g，叶中的氮素向根中转移的质量分别为0.308g、0.282g、0.151g。The research on plant biological fixation of nitrogen and the nitrogen assignment is important for revealing the eremophytes ecology adaptation strategy significance in extreme arid environment. There are some Alhagi.sparsifolia Shap grow in the oasis-desert transition in south fringe of Taklamakan desert in Xinjiang. This kind of leguminous plant is not only the local important sandstorm defending plants, but also a local important high quality pasturage grass. This research take one-year-old、two-year-old、perennial Alhagi.sparsifolia seedlings, study on its biological fixation of nitrogen、the nitrogen assignment、the nitrogen using the efficiency and the nitrogen transfer under the simulation of flood irrigation and the groundwater depth controlled. From April 2007 to October 2008, two plant vegetal periods, we used the 15N stable isotope method to study biological fixation of nitrogen and the nitrogen assignment. During the trial observation, measurement and analysis and data processing on the basis of the experiment, conclusions are as follows: Response of biological nitrogen fixation and nitrogen distribution of Alhagi Spacifolia Shap seedlings to different water conditions ⑴ Response of biological nitrogen fixation to different irrigation: ① Biological fixation of nitrogen irrigation: Judging from the entire growth season, the irrigation is conducive to the promotion of biological fixation of nitrogen, but excessive irrigation will suppress the biological fixation of nitrogen. For one-year-old Alhagi.sparsifolia seedlings, at the end of growth season, the ability biological fixation of nitrogen is biggest under the irrigation of 0.1m3/m2, is 0.836g per plant, next is the irrigation of 0.2m3/m2, is 0.433g per plant, under the anhydrous irrigation, the ability biological fixation of nitrogen is smallest, is only 0.182g per plant. The ability of one-year-old biological fixation of nitrogen is much better than the two-year-old. The ability of biological nitrogen fixation has larger difference with different year old Alhagi.sparsifolia, and the ability of biological nitrogen fixation was significantly enhanced with age. The proportion of one-year-old Alhagi.sparsifolia for biological nitrogen fixation accounted fototal nitrogen is only 14.85%t, by two-year-old, it is up to 40.02%, by multi-ages, it reaches as high as to 89.93%. ②Biological fixation of nitrogen under groundwater table: The ability of biological fixation of nitrogen is inversely proportional to the groundwater depth. The response of biological fixation of nitrogen for one-year-old is the same with two-year-old. Two-year-old Alhagi.sparsifolia seedlings’ biological fixation of nitrogen occupies the total nitrogen the proportion obviously to be higher than one-year-old Alhagi.sparsifolia seedlings’ biological fixation of nitrogen to occupy the total nitrogen proportion. ⑵Nitrogen distribution under different water treatment: The moisture content processes to the nitrogen assignment to the stem, leave, and increases nitrogen distribution s to the surface layer root system (0-60cm). With irrigation increase, in the leaf、the stem ratio of the nitrogen quality increases, in after the leaf、the root ratio of the nitrogen quality increases, indicating water in favor of nitrogen to the leaves, but water not conducive to leaves under excessive irrigation. ⑶ Nitrogen use efficiency under different water treatment: Judging from the entire growing season, irrigation is conducive to the promotion of nitrogen use efficiency. But excessive irrigation measures many will inhibit the nitrogen use efficiency. In the growth end of season, under three kind of moisture content irrigation gradient (0、0.1m3/m2、0.2m3/m2), the nitrogen use efficiency respectively is: 77.91、104.33、84.54. ⑷ Nitrogen transfer under different water treatment: Judging from the entire growing season, the nitrogen transfer from stem and leaves to root. Under three irrigation(0、0.1m3/m2、0.2m3/m2). By the end of September to the end of October, the quality of nitrogen transferred from stem and leaves to root is: 0.308g、0.282g、0.151