| Long-term irrigation (9-years) of annually-burned tallgrass could result in increases in soil C inputs. Soil water content and C availability are two primary controls of tallgrass prairie ecosystem function, affecting organic matter storage, nutrient dynamics, and microbial ecology. Three primary questions were the catalyst for the work described in this dissertation: (1) Can greater plant productivity and soil C inputs in irrigated soil be maintained in a system where plant available nutrients are primarily controlled by the soil microbiota? (2) Will changes in the microbial community significantly alter ecosystem function, and hence long-term ecosystem response to irrigation? (3) Will C accrual occur due to greater C inputs despite the potential for greater C losses in irrigated soil? Results suggest that the xeric upland was much more responsive to water addition than the mesic lowland site. In the upland site, water addition resulted in a 53% increase in root productivity. Since C losses from microbial activity and turnover were unaffected by water addition, the 25% increase in potentially-mineralizable soil C was probably the result of greater soil C inputs. Addition of water to dry soil resulted in a 25 to 350% increase in CO2 production, indicating that wetting of dry soil may, at times, have a greater effect on soil C losses than overall soil water potential. No change in the size of the potentially-mineralizable N pool despite the possibility of greater N losses due to irrigation suggests that plant available N pools were maintained. Alterations in microbial communities suggest that fungi became more dominant, and that microbial stress was reduced with irrigation. These alterations may be responsible for the greater carbon-utilization efficiency of the soil microbial community in water-amended irrigated compared to un-irrigated soils. Physiological and organismal changes in the microbial community, in turn, may be partially responsible for C accrual due to irrigation. Results suggest that tallgrass prairie net ecosystem productivity was positively influenced by increased water availability. The maintenance of soil and plant N pools after 10-years of irrigation further indicates that, with time, tallgrass prairie net ecosystem productivity will continue to respond positively to irrigation. |
