Intrinsic water use efficiency in wet and dry years at young and old plantations of Pinus sylvestris var. mongolica in semiarid China

摘要

Rainfall is the most important factor influencing the growth and survival of Mongolian pine (Pinus sylvestris var. mongolica), but the responses of these trees to extremes of rainfall are still poorly understood. Intrinsic water use efficiency (iWUE, as proxied by delta C-13), specific leaf area, dry matter content, soil water content and groundwater level were measured in 18-year-old and 38-year-old Mongolian pine stands (young and old) during two conservative years with extreme rainfalls (280 mm, 2009; and 580 mm, 2010). The results indicated that young trees displayed higher delta C-13 values of current-year-old needles in 2009 than in 2010, but no difference was detected in old trees. For both age groups of trees, no significant differences were observed in the specific leaf area and dry matter content of current-year-old needles between the two years. These results suggested that the iWUE of young trees was more sensitive to the extreme rainfall than that of the old trees. The groundwater level remained within vertical root distributions for old trees. In 2009, the mean delta C-13 value of the current-year-old needles was higher in young trees than in old trees, but this pattern was reversed in 2010. In conclusion, young trees improved iWUE to acclimate to extremely low rainfall, whereas old trees maintained a lower iWUE, possibly because of the uptake of groundwater.