Document: JOS-3-29-10

The relationship between leaf nitrogen and radiation absorption in New Zealand indigenous forests.

WHITE, J.D.* ¹ and N.A.SCOTT ²

Baylor University, Waco, TX 76798 ¹
Landcare Research, Palmerston North, New Zealand ²

Abstract:

Forests along an environmental gradient across the South Island of New Zealand were studied to determine whether the distribution of leaves in the canopy and leaf nitrogen corresponded with climate. Vertical profiles of leaf nitrogen, specific leaf area (SLA), leaf area index (LAI) were measured in indigenous New Zealand forest canopies with varying radiation, temperature, and precipitation. We found positive correlation between LAI and canopy average nitrogen concentration (g N g^-1 dry weight) which were comparable to data published in other studies. However, when the nitrogen data were expressed on a leaf area basis (g N m^-2 leaf area) the canopy average values were not predicted by site LAI. Comparison of leaf nitrogen to fraction of intercepted photosynthetic active radiation (fIPAR) illustrated that leaf nitrogen is a function of a) distribution of leaves in the canopy and b) direct versus diffuse radiation. In general, the relationship between average canopy nitrogen and fIPAR is more predictable under direct beam, high intensity light environments. Leaf nitrogen measured in the top portion of the canopy were highly correlated with total annual radiation (r²=0.97). Within the canopy, leaf nitrogen and cumulative LAI were negatively correlated while SLA and LAI were positively correlated. A value of 0.82 was estimated for the nitrogen distribution coefficient (k_N) from all forest data which changed with temperature, precipitation, and radiation when estimated from local samples. The conservative relationships found between radiation, canopy structure and nitrogen distribution provided the means for predicting nitrogen spatially. Regional estimates of canopy nitrogen were produced by utilizing climate surfaces of radiation to predict top of the canopy nitrogen coupled with satellite data to determine LAI from the general k_N value. Spatial estimates of average canopy nitrogen and from climate and remote sensing data were improved over simple prediction from satellite vegetation indices

Keywords: canopy nitrogen, radiation, leaf area, specific leaf area, fIPAR

This abstract is being presented at: 10:30 AM in session:
Poster Session #1: Light Relations.