The Effects of Leaf Age on Plant Nitrogen Distribution, Photosynthesis and Spectral Reflectance

Many wild and cultivated plant species distribute nutrients such as nitrogen (in chlorophyll and photosynthetic enzymes) according to the vertical gradient of light passing through the canopy to maximize photosynthesis. Leaf age and light microenvironments are key factors in this distribution process. Near and air/space-borne optical remote sensing of leaves and canopies have been well correlated with foliage nutrient levels and, in combination with characterizing canopy light and nitrogen gradients, have been used to measure canopy nitrogen content and photosynthetic rates over regions that are impractical or costly to monitor otherwise.  Foliage nutrient levels and their impact on photosynthesis are important parameters in predicting ecological processes and for precision agriculture. In many studies, leaves are sampled randomly, or only fresh young leaves are sampled from the bottom and top of canopies when characterizing vertical nitrogen gradients. To develop improved methods for estimating leaf and canopy N-content, the effects of leaf age on nitrogen distribution will be investigated by manipulating the light microenvironments on stems of potted peppermint (Mentha piperita) to control for leaf age. Leaf and canopy nitrogen content and rates of photosynthesis will be measured and related to leaf and canopy-level spectra.