Restoration of Nitrogen Cycling in a Degraded Shrubland Ecosystem
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Effects on native ecosystems caused by human disturbance or non-native species invasions can persist far longer than the initial activity, particularly if soil properties such as nutrients are altered. Soil legacy effects present a complex challenge for restoration, because both plants and microbes play important roles in soil biogeochemical cycling. We examined whether nitrogen cycling could be restored by removing non-native vegetation and inoculating degraded sites with native soil microbial communities. These strategies were applied in degraded Florida shrublands that were mildly disturbed or entirely converted to pasture, or undisturbed native control sites. We measured inorganic nitrogen pools, gross rates of nitrogen mineralization, and gross rates of nitrogen consumption 2 years after the treatments were implemented. Gross rates were quantified using the pool dilution technique. We found that gross N mineralization rates, gross N consumption rates, and N pool sizes increased with increasing disturbance. In disturbed sites, non-native vegetation removal and microbial addition individually decreased gross rates, and effectively restored native N conditions. In pastures, the combination of both treatments was most effective, but resulted in an elevated inorganic nitrate pool. Disturbance compounded by non-native invasion increases soil legacy effects by altering soil nutrient dynamics, but responds proportionally to a restoration scheme to reapproximate native N cycling rates.