Altitudinal Change in the Photosynthetic Capacity of Tropical Trees: A Case Study from Ecuador and a Pantropical Literature Analysis

作者：Wittich Baerbel; Horna Viviana; Homeier Juergen; Leuschner Christoph^*

来源：Ecosystems, 2012, 15(6): 958-973.

DOI：10.1007/s10021-012-9556-9

• altitudinal gradient
• foliar N
• foliar P
• leaf dark respiration
• light-saturated net photosynthesis
• tropical lowland forests
• mature trees
• C source limitation
• tropical montane forests

In tropical mountains, trees are the dominant life form from sea level to above 4,000-m altitude under highly variable thermal conditions (range of mean annual temperatures: %26lt; 8 to %26gt; 28A degrees C). How light-saturated net photosynthesis of tropical trees adapts to variation in temperature, atmospheric CO2 concentration, and further environmental factors, that change along elevation gradients, is not precisely known. With gas exchange measurements in mature trees, we determined light-saturated net photosynthesis at ambient temperature (T) and [CO2] (A (sat)) of 40 tree species from 21 families in tropical mountain forests at 1000-, 2000-, and 3000-m elevation in southern Ecuador. We tested the hypothesis that stand-level averages of A (sat) and leaf dark respiration (R (D)) per leaf area remain constant with elevation. Stand-level means of A (sat) were 8.8, 11.3, and 7.2 mu mol CO2 m(-2) s(-1); those of R (D) 0.8, 0.6, and 0.7 mu mol CO2 m(-2) s(-1) at 1000-, 2000-, and 3000-m elevation, respectively, with no significant altitudinal trend. We obtained coefficients of among-species variation in A (sat) and R (D) of 20-53% (n = 10-16 tree species per stand). Examining our data in the context of a pan-tropical A (sat) data base for mature tropical trees (c. 170 species from 18 sites at variable elevation) revealed that area-based A (sat) decreases in tropical mountains by, on average, 1.3 mu mol CO2 m(-2) s(-1) per km altitude increase (or by 0.2 mu mol CO2 m(-2) s(-1) per K temperature decrease). The A (sat) decrease occurred despite an increase in leaf mass per area with altitude. Local geological and soil fertility conditions and related foliar N and P concentrations considerably influenced the altitudinal A (sat) patterns. We conclude that elevation is an important influencing factor of the photosynthetic activity of tropical trees. Lowered A (sat) together with a reduced stand leaf area decrease canopy C gain with elevation in tropical mountains.

• 出版日期2012-9