Vernal ecophysiology of understory vegetation and soil microbes in a second-growth northern hardwood forest of the Catskill Mountains, New York

I investigated parameters related to vernal functioning of understory plant species and soil microbes in a northern hardwood forest of the Catskill Mountains, New York. Specifically, I measured photosynthesis in the dominant fern species and assessed, through experimental and descriptive studies, the ability of plants and soil microbes to serve as nutrient sources and sinks.; Results of a pair of experimental nutrient availability studies indicate that understory plants from the Catskills can serve as N and P sinks when both are applied at high levels. However, when applied separately, understory plants were only sinks for P, suggesting that they are P- and not N-limited. A comparison of N:P ratios in these plants with published thresholds indicative of N- and P-limitation supports this interpretation. Phosphorus limitation in these understory plants indicates that this Catskill northern hardwood forest is advancing in N saturation.; I assessed vernal photosynthetic rates and N and P retranslocation in Dryopteris intermedia to determine the importance of maintaining wintergreen fronds. This fern photosynthesizes during spring but does not retranslocate N and P from old fronds during senescence. These results reveal that old fronds provide an energetic benefit to the plant during spring.; I monitored N and P pool sizes in understory plants and soil microbes through three successive springs to document net nutrient uptake and release. In two out of three springs, plants served as a nutrient sink. Soil microbes, while having a higher nutrient content than plants, were a source of N in one spring and neither a source nor sink for nutrients in any other spring. These results demonstrate that understory plants are a variable yet greater potential net sink for vernal nutrients than are soil microbes in this Catskill northern hardwood forest. Plant species differed in timing and quantity of their nutrient sink size and strength. There was spatial complementarity in nutrient sink size among understory species and both temporal overlap and complementarity in nutrient sink size and strength. These results disclose that the presence of multiple species with vernal nutrient sink potential increased the net retention of nutrients within the understory plant community.