Nutrient availability constraints on the hydraulic architecture and water relations of savanna tree

BUCCI S. J., SCHOLZ FG, GOLDSTEIN G., MEINZER FC. VILLALOBOS R., FRANCO AC.

Miami

Simposio; Asociation for Tropical Biology and Conservation, Conference 2004; 2004

The investment in plant parts that acquire the limiting nutrient is usually favored at the expense of allocation to plant parts that have a large requirement for the limiting resource. Plants will allocate relatively more biomass to their roots to enhance nutrient uptake if the soils are, for example, N limited. If N limitations are relief, the pattern of biomass allocation may change favoring the expansion of the leaf surface area, to enhance CO2 capture, at the expenses of underground plant parts. The objective of this study was to remove some of the nutrient limitations of Brazilian savanna (Cerrado) soils by long term fertilizations (six years of continuous fertilization with N, P and N+P) and to explore the consequences that potential changes in the pattern of carbon allocation may have on the hydraulic architecture and water relations of five dominant tree species. Addition of N and N+P increased the total number of leaves per tree, total surface area per tree, and the leaf area per unit of sapwood area, which is a morphological index of water transport efficiency. On the other hand, leaf size decreased significantly in all species with P fertilizations. Daily sap flow per individuals tended to be higher with N and N+P additions despite a substantial decrease in daily transpiration rates. The largest physiological effect of fertilizations with N and N+P was a large decrease in midday leaf water potential (e.g. 1 MPa). Apparent soil to leaf hydraulic conductance at midday tended to be lower in the fertilized plots across all species. Overall, the results suggest that fertilization with N, resulting in an increase in the total leaf surface area per tree, is not compensated by an increase in the hydraulic capacity of the water conductive tissues.