Effect of irrigation on nitrogen characteristics of Alhagi sparsifolia seedlings
骆驼刺幼苗氮素特征对不同灌溉量的响应

We investigated the effect of different irrigation levels on nitrogen characteristics of Alhagi sparsifolia Shap. seedlings to study the ecological adaptation strategy of the eremophytes in Qira oasis in the extremely arid southern margin of the Taklamakan desert. We used stable isotope 15N labeling and stratified root excavation methods to investigate the biological fixation of nitrogen, nitrogen allocation and nitrogen use efficiency of a month old A. sparsifolia seedlings under three different irrigation regimes (CK, 0.1 m3/m2, 0.2 m3/m2) during the growing season (March-October) in 2008. The results indicate that irrigation influenced all studied nitrogen characteristics of A. sparsifolia seedings. (1) Irrigation promoted biological fixation of nitrogen compared to control, but decreased at higher irrigation rates (0.2m3/m2). The biological fixation of nitrogen was greatest under 0.1m3/m2 irrigation with 0.8g per plant or 42.8% and lowest under control (0.2 g per plant, 11.3%). Intermediate nitrogen fixation rates were observed under the greatest irrigation rates (0.4 g per plant, 30%). (2) Irrigation initially increased the nitrogen allocation in the stem, leaves, and the quantity of nitrogen in the surface layer of root system (0-60cm). In the beginning of the growing season, leaves had the largest proportion of nitrogen and roots had the smallest. At the end of the growing season, the proportion of nitrogen in root system under the three different irrigation regimes were 49.2% (control), 44.5% (0.1 m3/m2), and 55.0% (0.2 m3/m2). Over the course of the entire growing season, irrigation promoted the nitrogen use efficiency compared to control, but decreased under large amounts of irrigation. At the end of growing season we observed a nitrogen use efficiency of 77.9 for the control, 104.3 for the 0.1 m3/m2 irrigation and 84.5 for the 0.1 m3/m2 irrigation. (3) In this experiment, we compared the influence of different irrigation on the characteristic of nitrogen of Alhagi sparsifolia Shap. Seedlings. The result indicate that the irrigation of 0.1m3/m2 is the better. In summary, irrigation of 0.1m3/m2 had the most stimulating effect on A. sparsifolia seedlings. The plants had the greatest biological nitrogen fixation, greatest nitrogen use efficiency and allocated most of the nitrogen to the root system.