海拔对高山栎光合气体交换和叶性状的影响

理解影响植物分布的式样及过程是生态学研究的中心内容之一，但对许多物种而言，限制其分布的原因还不清楚。为了认识高山栎分布与生理生态特性的关系，我们在不同海拔的4个观测点研究了帽斗栎的光合气体交换、叶氮含量、叶绿素含量和比叶重。由于高的水气压亏缺和气温，帽斗栎的光合作用和蒸腾作用在午间表现出明显的降低现象。帽斗栎的饱和光合速率、水分利用效率、最大羧化速率、最大电子传递速率和氮利用效率在海拔中部比低海拔或高海拔处的为高。不同海拔的叶氮含量在5月份有差异，8月份则没有明显不同。叶片厚度随海拔增加，但叶绿素含量及光合最适温度随海拔升高而降低。帽斗栎光合作用的海拔变化与叶片的生化效率和氮含量有关，而与比叶重无关。研究结果说明，温度的海拔变化对高山栎的光合作用和叶性状有明显影响，最适宜帽斗栎光合碳获取及生长的海拔范围是3180～3610m。

Effects of Altitude on Photosynthetic Gas Exchange and the Associated Leaf Trait in an Alpine Oak, Quercus guyavifolia (Fagaceae)

Understanding the pattern and process governing the distribution is a central goal of ecology, yet for many species the causes of distribution limit are unknown. To understand the relationship between altitudinal distribution of alpine oak and ecophysiological trait, leaf nitrogen content, chlorophyll content, leaf mass per unit area and photosynthetic gas exchange of Quercus guyavifolia were investigated at four sites along an altitudinal gradient from 2 650 to 3 920 m in the Hengduan Mountains. Q. guyavifolia showed a significant midday depression in photosynthesis and transpiration at all sites due to high vapour pressure deficit and temperature. Both in May and August, this species had higher light-saturated photosynthesis, water use efficiency, maximum RuBP rate of carboxylation, light saturated rate of electron transport and photosynthetic nitrogen use efficiency at the middle altitude than at the lowest or highest location. Leaf nitrogen content was different in May among altitudes, but remained relatively constant in August.Leaf thickness increased with altitude while chlorophyll content and photosynthetic optimum temperature decreased.The altitudinal trend in photosynthesis of Q. guyavifolia could be linked to leaf biochemical efficiency and nitrogen content, but not leaf mass per unit area. The variation in temperature along the altitudinal gradient imposed a constraint on photosynthesis and leaf trait. The altitudinal range from 3 180 m to 3 610 m would be optimal for the photosynthetic carbon gain and growth of Q. guyavifolia.