Foliar nutrient dynamics, growth, and nutrient use efficiency ofHamamelis virginianain three forest microsites

摘要

To determine the relative importance of soil moisture and soil nutrient availability in determining levels of nutrient use efficiency, seasonal nutrient dynamics and growth rates were determined for individuals ofHamamelis virginianaL., an understory tree, in three forest microsites. The mixed oak site had the lowest levels of soil nutrients and moisture, the mixed mesophytic site the highest nutrient availability, and the valley bottom the highest moisture levels. Foliar nitrogen and phosphorus levels declined over the season in all trees, while calcium levels increased with time. Relative growth rates did not differ significantly among sites, though growth varied inversely with tree mass. Proportional nitrogen resorption was highest in trees at the fertile mesophytic site. Phosphorus and calcium use efficiency were higher at the infertile mixed oak site than the others, and phosphorus resorption was highest in trees from the mixed oak site. Projected nitrogen uptake needs for the next growing season were least at the mixed mesophytic site, while projected phosphorus uptake needs were least at the mixed oak site. Within the ranges of moisture and soil pH ndash; nutrient availability present, growth and nitrogen dynamics seemed most closely correlated to soil moisture, and phosphorus dynamics to phosphorus availability. This differential dependence among elements on moisture levels is suggested to be the underlying reason for differences in the form of the relationship between proportional resorption and soil availability of N and P for a variety of woody species.