Department Chair

Dr. Gregory Wadsworth

Date of Award

12-2012

Access Control

Open Access

Degree Name

Biology, M.A.

Department

Biology Department

Advisor

Dr. Daniel L. Potts

Department Home page

http://biology.buffalostate.edu/

First Reader

Dr. Christopher Pennuto

Second Reader

Dr. Edward Standora

Abstract

Nitrogen (N) and phosphorus (P) affect the structure and function of grasslands by altering plant competitive interactions, shifting patterns of above- and belowground biomass allocation, and by increasing net primary production. However, the influence of N and P on net ecosystem productivity is poorly understood. In the context of a field-based factorial N- and P-addition experiment, I measured soil moisture, leaf area index and component fluxes of ecosystem CO2 exchange throughout the growing season in a restored temperate grassland near Buffalo, New York. I predicted that N-addition would enhance ecosystem CO2 uptake (GEE) while P-addition would stimulate ecosystem respiration (Re). As predicted, N-addition increased GEE and correspondingly amplified net ecosystem CO2 exchange (NEE) to increase ecosystem CO2 uptake. In contrast, P-addition did not significantly increase Re. However, N- and P-addition interacted to significantly reduce NEE in comparison with plots that received N alone. Moreover, water limitation and phenological constraints during the middle and late growing season appear to limit autotrophic responses to nutrient addition. These results suggest that influences of N- and P-addition on ecosystem processes are seasonally dynamic and that the availability of N and P in soils may interact to weaken the strength of the terrestrial carbon sink.

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