Xylem formation of and its response to water-heat factors in the lower reaches of Tarim River, China.

To deeply understand the effects of water and temperature factors on the xylem formation of , taking the Yingsu section in the lower reaches of Tarim River as an example, we selected micro-coring samples of around monitoring wells F and F in the 100 and 1500 m distance from the channel of Tarim River. We used wood anatomy method to analyze the xylem anatomy of and its response to water and temperature factors. The results showed that the changes of the total anatomical vessel area and the vessel number of in the two plots were basically consistent during the whole growing season. The vessel number of xylem conduits of increased slowly with the increases of groundwater depth, while the total conduit area increased firstly and then decreased. The total vessel area, minimum vessel area, average vessel area, and maximum vessel area of xylem increased significantly with the increases of temperature in the growing season. The contribution of groundwater depth and air temperature to xylem varied among different growth stages. In the early growing season, air temperature had the largest contribution to the number and total area of xylem conduits of . During the middle growing season, air temperature and groundwater depth jointly affected the parameters of each conduit. During the later growing season, groundwater depth had the largest contribution to the number and total area of conduits. Results of the sensitivity analysis indicated that the groundwater depth sensitive to xylem vessel number change of was 5.2 m and that to the change in the total conduit area was 5.9 m. The temperature sensitive to total vessel area of xylem was 22.0 ℃, and that to average vessel area was 18.5 ℃. Therefore, the sensitive groundwater depth affecting xylem growth was at the range of 5.2-5.9 m, and the sensitive temperature was at the range of 18.5-22 ℃. This study could provide scientific basis for the restoration and protection of forest in the lower reaches of Tarim River.