Numerous studies have indicated that increases in atmospheric CO2 have the potential to decrease nitrogen availability through the process of progressive nitrogen limitation (PNL). The timing and magnitude of PNL in field experiments is varied due to numerous ecosystem processes. Here we examined the responsiveness of nutrient dynamics to changes in atmospheric CO2 in prairie monoliths from three soil types. The three soil types include a clay vertisol, a sandy-clay loam alfisol, and a silty-clay mollisol. We hypothesized that nutrient dynamics would be most responsive to CO2 in the high-clay vertisol because it had the lowest soil water potential, which can influence nutrient mineralization. We used in situ ion exchange resins, gross flux measures, and enzyme activity assays to characterize soil nutrient dynamics.
Results/Conclusions
Our four years of data indicate that the vertisol monoliths show a decrease in mid-growing season N and P availability from low to high CO2. In the fourth year of the experiment, the alfisol also showed a decrease in N availability mid-summer. Accompanying the decrease in N-availability is a decrease in the magnitude of the CO2 effect on aboveground Net Primary Production in the vertisol monoliths. In the mollisol monoliths, there were no significant relationships between CO2 and nutrient availability. Aminopeptidase activity was positively correlated with N availability in vertisol monoliths. These data indicate that soil type influences the magnitude and timing of ecosystem responses to changes in atmospheric CO2. Regional responsiveness to changes in atmospheric CO2 may be heterogeneous depending on the diversity of soil types within an area.
