Field Measurements of Photosynthesis and Leaf Growth Rates of Three Alpine Plant Species

Leaf photosynthetic measurements using a portable 14Co2 field system were carried out and correlative leaf relative growth rates, RGR, were determined at different leaf positions of three alpine plant species throughout the growing season. Initially there was a period of high leaf RGR associated with a period of increasing photosynthetic activity. Following this stage was a long period of no net change in length of the living leaf. During this period, photosynthetic activity generally increased to a maximum level and then decreased steadily. The final ontogenetic stage was a period of negative leaf RGR denoting leaf senescence which was associated with a marked decline in leaf Co2 uptake. Ontogenetic timing of these alpine species is geared with the surge and decline of individual leaf photosynthetic activity so that one to several leaves operating at near maximal photosynthetic capacity are always maintained during the growing season for each plant. These findings are discussed in relation to their adaptive significance for these species.