对毛乌素沙地自然生境中油蒿(Artemisia ordosica Krasch.)不同生长期(6 月份至9 月份)的气体交换参数和枝条水势日变化特征进行了比较研究,并探讨了环境因子对油蒿气体交换参数及枝条水势的影响作用。结果表明:6 月份至9 月份油蒿的净光合速率日均值波动幅度不大,其大小与当月的土壤含水量不对应,其中8 月份的净光合速率日均值最大(13. 16 μmol·m^-2 ·s^-1 );各月份间油蒿的蒸腾速率日均值差异较大,最大值出现在7 月份(7. 93 mmol·m^-2 ·s^-1 ),与土壤含水量的变化相对应;7 月份油蒿的水分利用效率最低,但枝条水势日均值最大,其余3 个月水分利用效率波动幅度不大,各月间枝条水势日均值差异也不大且变化幅度较小。在6 月份和7 月份,油蒿净光合速率的日变化呈双峰型曲线,6 月份的峰值出现在8:00 和14:00,7 月份的峰值出现在10:00 和14:00,谷值都出现在12:00;在8 月份和9 月份则呈单峰型曲线,峰值分别出现在10:00 和12:00。在6 月份和7 月份,油蒿蒸腾速率的日变化均呈双峰型曲线,峰值分别出现在10:00 和14:00;在8 月份和9 月份则呈单峰型曲线,最大值均出现在12:00。在这4 个月中,油蒿枝条水势的日变化与大气水势的日变化一致,均在12:00 达到最低;油蒿的水分利用效率日变化有着较好的规律性,均为早上最高,然后降低,但总体上变化幅度平缓,表明生长在毛乌素沙地自然生境中的油蒿对环境的适应能力较强。

The branch water potential and gas exchange parameters of Artemisia ordosica Krasch. in natural habitat of Mu Us sandland were comparatively studied, and the effect of environmental factors on them was also discussed at the same time. The results show that the fluctuation range of daily average value of net photosynthetic rate (Pn ) of A. ordosica is small from June to September, and the daily average value of Pn is not corresponding to soil water content in the same month, with a biggest daily average value of Pn of 13. 16 μmol·m^-2 ·s^-1 in August. The daily average value of transpiration rate (Tr) appears a great difference from June to September with a maximum daily average value of Tr of 7. 93 mmol·m^-2 ·s^-1 in July, which is corresponding to change of soil water content. In July, the daily average value of water use efficiency (WUE) is the smallest and its fluctuation range is small in other three months, while the daily average value of branch water potential is the biggest in July with a little difference and a small fluctuation range among four months. The daily change trend of Pn displays two-peak pattern in June and July, and the peak value appears at 8:00 and 14:00 in June and at 10:00 and 14:00 in July, respectively, while all the valley values appear at 12:00. And it displays one-peak pattern in August and September and the peak value appears at 10:00 and 12:00, respectively. The daily change trend of Tr displays two-peak pattern in June and July with a peak value at 10:00 and 14:00, respectively, and does one-peak pattern in August and September with a peak value at 12:00. During four months, the daily change trend of branch water potential is in agreement with that of atmosphere water potential, and both reach the minimum at 12:00. The daily change trend of WUE appears a better regularity with the highest in the morning and then decreasing, but generally having a smoothly daily variety, showing that A. ordosica growing in natural habitat of Mu Us sandland possesses a stronger adaptability to changes of environmental factors.