关键词: 三叶草, 分枝杆菌, 根系分泌物, 多环芳烃, 加氧酶, 降解

Abstract: Based on the 1960-2010 daily precipitation data from 26 meteorological stations in Gansu Province of Northwest China, and by using standardized precipitation index (SPI) and Z index, this paper analyzed the variation characteristics of the annual and spring drought in different climate regions of the Province in recent 51 years. Overall, the annual SPI and Z index in the Province presented an increasing trend in the cool and warm climate regions of Hexi and in the Qilian Mountains, with the greatest increment in the arid areas of western warm temperate zone in Hexi, and the change tendency rate of both SPI and Z index being 0.13·(10a)^-1, and a decreasing trend in the semi-humid region of southern cold temperate zone of Longzhong, semi-arid region of northern cold temperate zone of Longzhong, and humid region of alpine Gannan, with the greatest decrement in the semihumid region of southern cold temperate zone of Longzhong, and the change tendency rate of SPI and Z being -0.13·(10a)^-1 and -0.14·(10a)^-1, respectively. The drought degree in early spring showed a decreasing trend, with the greatest decrement in the semihumid region of southern cold temperate zone of Longzhong, and the change tendency rate of SPI and Z being -0.12·(10a)^-1 and -0.06·(10a)^-1, respectively. The annual and spring SPI and Z index had the same variation trends. Severe drought occurred in Hexi in the 1960s and in Hedong in the 1990s. In the cool and warm climate regions of Hexi and in the Qilian Mountains, the change rate of drought index was positive, the drought degree decreased, and the change degree of spring drought was smaller than that of annual drought; whereas in the semi-humid region of southern cold temperate zone of Longzhong, semiarid region of northern cold temperate zone of Longzhong, and humid region of alpine Gannan, the change rate of drought index was negative, the drought degree exacerbated, and the change degree of spring drought was greater than that of annual drought. In the Province, there was an obvious difference in the spatial distribution of drought, with an increasing trend from northwest to southeast.

Key words: clover (Trifolium repens), Mycobacterium, root exudates, polycyclic aromatic hydrocarbons (PAHs), dioxygenase, degradation.