Leaf functional trait responses of Quercus aquifolioides to high elevations

Investigations about phenotypic plasticity and adaptive traits of species facing rapidly changing stressful conditions are particularly relevant in context of rapid climate change. Morphological and physiological traits of Quercus aquifolioides plants growing at 2600 m and 3500 m above sea level (in the vicinity of the tree line) were studied. Leaf mesophyll conductance (g(m)) and stomatal conductance (g(s)) decreased, whereas carbon isotope composition (delta C-13), nitrogen concentration and dark respiration increased with elevation. The specific leaf area (SLA) did not change, whereas photosynthetic capacity was dramatically inhibited at higher elevation. Differences in decline of photosynthesis (similar to 64%) and g(m) (similar to 80%) at elevations were reflected by similar chloroplast (P-c) to atmospheric (P-a) CO2 partial pressure ratio between the two populations. Therefore, delta C-13 changes were not associated to either SLA or P-c/P-a, delta C-13 furnished an estimation of long-term P-c/P-a and, in turn, of long-term water use efficiency. Air temperature, which decreased consistently with altitude, significantly affected the long-term P-c/P-a. Plausibly, low temperature is the main determinant affecting delta C-13 at high altitude. In conclusion, phenotypic plasticity enabled Q. aquifolioides to maintain a positive carbon balance in response to dramatic environmental changes.