Climate change in changing landscapes: Dynamic controls on soil moisture and nutrient cycling

Background/Question/Methods

Changing climate and altered land cover or land use represent the largest threats to ecosystem function worldwide. Yet few studies have experimentally examined the impact of long-term shifts in those factors on ecosystem function. Especially rare are studies in dryland ecosystems, which cover over a third of the terrestrial land surface. We examine how long-term experimental shifts in precipitation seasonality and vegetation types, mediated by variability in antecedent soil moisture, change nutrient pools and process rates, and the potential for nutrient losses in dryland ecosystems. Our objectives were, 1) how do persistent shifts in precipitation magnitude and seasonality, or changes in vegetation type alter soil water and nutrient partitioning in the biologically active surface horizons, and 2) how do annual fluctuations in antecedent soil moisture patterns (i.e. wet vs. dry periods) modulate ecosystem controls on N partitioning?

Results/Conclusions

Our results indicate that belowground processes that modulate inorganic nitrogen availability are differentially controlled by climate and vegetation under contrasting soil moisture regimes. Precipitation additions induced changes in nutrient pools and process rates only in the dry year, showing little variability between the control and treatments during the wet year, stressing the importance of antecedent moisture despite persistent long-term shifts in precipitation. In contrast to precipitation shifts, vegetation treatments had a larger impact on nutrient pools and process rates during the wet year vs. the dry year, modulating ecosystem processes when water was not limiting. Although we observed only small difference in soil moisture between under-plant and inter-plant spaces, differences in nutrient dynamics were significant in both wet and dry years.  This study demonstrates a strong hierarchical control of ecosystem processes by pulses of water availability within the context of changing hydroclimate and land cover.