Control of Nitrogen Mineralization a Sagebrush Steppe Landscape

Factors controlling N turnover in sagebrush ecocystems are separable into two groups. The first group consists of properties that exhibit strong spatial patterning at a landscape scale but are temporally static at time scales of years or tens of years. These static properties include plant species assemblages, total soil nutrient pools, and soil texture. A second group includes properties that vary across the landscape over shorter time scales, i.e., annually, seasonally, and diurnally. These dynamic properties include soil moisture, temperature, and amount of available nutrients. This paper evaluates the landscape variability of properties in both of these groups, and examines the extent to which these factors control N turnover. Static ecosystem properties were entered into a principle components analysis resulting in four axes of landscape variability. A statistical analysis of the relationship of net N mineralization with the principal components and with soil temperature and moisture suggested that soil microclimate and organic matter quality both control in situ N turnover. Soil microclimate limited N mineralization to a short season in early spring and summer; only during this time did soil organic matter exert control. In landscape positions where soil organic matter pools were low, improved soil microclimate conditions did not increase N mineralization rates. A similar approach may be useful in evaluating control over ecosystem processes in other systems that are characterized by strong seasonal and spatial variability.