The objectives of this study are as follows:
- Determine response of vegetation to timing of irrigation and soil depth, and conversely the influence of plant communities and vegetation type on deep soil water infiltration
- Investigate microbial communities of plots to assess whether fundamental ecosystem changes to treatments are occurring and could feed back on water flow patterns
- Investigate changes in soil carbon pools due to vegetation and precipitation differences.
Other biogeochemical and soil physical aspects of plots, such as stable isotope compositions that can reveal changes in water patterns and plant water use among plots, also are being evaluated. The ultimate objective is to determine how plot responses to the treatments feed back on water infiltration, availability and use.
Researchers are evaluating long-term impacts of different plant communities commonly found throughout Idaho subject to different precipitation regimes and to different soil depths. These treatments allow researchers to investigate how vegetation, precipitation and soil interact to influence patterns of water infi ltration, uptake, and storage. This information will be used to improve a variety of models, as well as provide data for these models.
The researchers observed no differences in rates of photosynthesis, plant water potential, leaf chlorophyll fluorescence, or specific leaf area among the treatments. However, differences in carbon isotopes suggested that shrubs in the ambient moisture plots used water more efficiently than did shrubs on the plots winter irrigation plots. Vegetation cover was greatest on the winter irrigation plots and least on the ambient plots. Shrub cover was greatest on the winter irrigation plots with deeper soil. Shrub cover was reduced on winter irrigated plots that had shallow soils.
Soil microbial studies suggested that winter precipitation may promote storage of soil carbon deeper in the soil profile while summer precipitation may promote greater carbon inputs from the overlying plants at shallower soil depths. Higher heterotrophic soil respiration was observed in summer irrigated plots. These higher rates of soil carbon mineralization and lower carbon storage could be a climate change feedback process in semi-arid ecosystems