Associations between leaf form and ecophysiology in alpine, desert, and forest plants.

摘要

The objective of this research was to quantify leaf structural characteristics to determine their functional significance associated with habitat stress, leaf light reflectance, and gas exchange. First, models were tested relating leaf form to habitat and relating leaf characteristics to each other, based on potential photosynthetic significance. Measurements were made for 50 species at three alpine sites in Wyoming with varying soil water content. Leaves from the lowest water site were more steeply inclined (>50°), more amphistomatous, and had less mesophyll cell surface area exposed to air spaces per unit leaf area (Ames/A < 12). These data suggest a previous model, relating leaf form to photosynthesis, also operates on a finer spatial scale. Next, relationships between characteristics of leaf anatomy were examined among 56 alpine, forest, and desert species. The most important variable predicting Ames/ A was the percent of mesophyll volume occupied by air space ( P = 0.00). Ames/A estimations based on geometric conversions were found to overestimate by up to 24 fold.;Leaf gas exchange, structure, and nitrogen were measured in Aquilegia caerulea and Raphanus sativa grown under two CO2 levels. Photosynthesis was enhanced in plants grown under elevated CO2, although photosynthetic down-regulation may have occurred. Leaf N content was positively associated with mesophyll conductance and stomatal conductance was correlated to %pore area (P < 0.05). The effects of elevated CO2 on leaf structure were also examined in 28 species grown in either chambers or FACE facilities in Wyoming, Nevada, North Carolina, and Wisconsin. Nine species had more mesophyll volume per unit leaf area (P < 0.1) at elevated CO 2. The maximum amount of leaf surface occupied by stomatal pores increased by up to 118% in many species, but was reduced in others. These results indicate elevated CO2 experiments may provide insight into leaf form/function mechanisms. Finally, associations between leaf near-infrared reflectance (NIRR) and leaf structure were investigated. A quantitative model was first constructed for six alpine species, correlating measured NIRR with A mes/A, and the presence of leaf bicoloration and of a thick leaf cuticle (r2 = 0.93). This model predicted NIRR accurately for 48 species.