Response to climate changes in radial growth of Picea crassifolia in the Qilian mountains of northwestern China

In order to investigate the response to climate changes in radial growth of Picea crassifolia at the lower tree line in the middle Qilian mountains in northwestern China, relationships of standardized chronologies of annual ring, earlywood and latewood widths with mean monthly temperature and total monthly precipitation were analyzed by ways of correlation and pointer year analyses. The results show that annual ring, earlywood and latewood widths are significantly negatively correlated with mean monthly temperature in June and July. Annual ring and earlywood widths are significantly and positively correlated with total monthly precipitation in March, May and June and negatively correlated with total monthly precipitation in September. Latewood width is less sensitive to climate changes than the width of earlywood and insignificantly sensitive to precipitation. The results of pointer year analysis revealed that when summer temperatures are higher than the mean summer temperature synchronization and the summer precipitation lower than mean summer precipitation synchronization, narrow annual rings are formed. Wide annual rings are formed when summer temperatures are lower than the mean summer temperature synchronization and summer precipitation higher than mean summer precipitation synchronization. The results indicate that more precipitation in the spring and summer is helpful for radial growth while warmer summer restricts radial growth of P. crassifolia at the lower tree line in the middle Qilian mountains.

Comparison of Differentially Expressed Genes Involved in Drought Response between Two Elite Rice Varieties

Dear Editor, Drought is the most devastating factor limiting the pro- ductivity and geographical distribution of rice （Oryza sativa）. Several drought-tolerant varieties have been developed from drought-tolerant germplasm. These varieties make it imper- ative to clarity the mechanism of drought responses at the genomic level, which will provide a foundation for future breeding and genetic engineering efforts （Zhou et al., 2007）. Yangdao6 （YD6） was used to breed many elite varieties in China, which was developed from Yangdao2 （YD2） through a series of crosses （Supplemental Figure 1）. Here, we veri- fied that YD6 seedlings showed better drought tolerance than YD2, Yangdao4 （YD4）, and 3021 seedlings （Figure 1A）. After drought treatment for 8 d, over 81.9% of YD2 plants were rolled, which is about three times that of YD6 plants. Recovering normal growth with water, the survival rates of YD6 and YD2 seedlings were 92.2% and 65.6%, respectively.