The effects of changing precipitation patterns on soil microbial communities and nitrogen cycling in the New Jersey Pinelands:

I studied the potential effects of a change in the amount, frequency and timing of precipitation on soil microbes and nitrogen cycling in the New Jersey Pinelands. I performed a two year field manipulation of precipitation amount and measured the response of the microbial community, potential net nitrogen mineralization and amino acid production. I found that soil microbes were not affected by rain exclusion or a doubling of rainfall. Nematode densities, but not community composition, were sensitive to precipitation amount. A large accumulation of ammonium in drought plots suggested sustained microbial activity under extreme drought conditions. I observed small changes in potential net nitrogen mineralization due to the effects of soil moisture on diffusion and immobilization. I measured the short-term response of the microbial community to a rewetting of dry soil and found a very rapid (three hour) change in the microbial community. The accumulation of ammonium within drought plots appears to have suppressed fungal biomass following the rewetting event. In a two year winter study, I found no long-term effect of supplemental winter rainfall on the soil microbial community. Elevated winter precipitation prevented ammonium accumulation, presumably by protecting plant roots from freeze damage. I found that supplemental watering insulates soil microbes from cold stress over the short-term (days), but that mid-winter declines in biomass due to cold soil. These experiments demonstrate that soil microbial communities in Pinelands soils are highly tolerant of abiotic stressors such as drought, upshock stress and soil freezing. Recovery from these disturbances is extremely rapid, occurring on the scale of hours to days. I conclude that changing precipitation patterns will not have a direct, long-term effect on soil microbial communities. Changes in precipitation patterns are more likely to alter nitrogen cycling rates via the influence on nitrogen diffusion and plant and microbial uptake. Furthermore, precipitation-induced changes in nematode densities may have important implications for nitrogen cycling in the New Jersey Pinelands.Ph.D.Includes bibliographical referencesby William Joel Landesma