Technical Abstract: 1. Increased soil nitrogen (N) availability may often facilitate plant invasions. Therefore, lowering N availability might be expected to reduce those invasions and favor native species. Numerous studies have examined effects of low N availability on specific invaders, but a synthesis of these studies is needed to evaluate this hypothesis more fully. 2. Here, we examine effects of lowering soil N availability on invasion by reviewing 47 experiments that measured plant responses to soil carbon (C) addition, which stimulates microbial N immobilization and thus lowers N availability. 3. Together, these experiments suggest that lowering soil N availability often favors native or late-successional species over invasive or early-successional species, especially when the invasive or early-successional species are annuals or grasses. In most experiments, C addition lowered N availability, lowered plant growth, and increased growth of native, late-successional species relative to weedy, early-successional species. Variation in results among experiments was not consistently related to species traits, environmental conditions or methods. 4. Lowering N availability at relevant scales for ecological management often will require methods that are less expensive than C addition. We discuss the potential utility of several alternative methods for lowering N availability, including revegetation, burning, grazing, topsoil removal and biomass removal. We conclude that these approaches may be promising for lowering N availability by stimulating N immobilization, even though most of them are relatively ineffective for removing N from ecosystems. Specifically, revegetation, burning, grazing and mowing all may increase N immobilization if they favor late-successional plant species that produce high C:N tissue and thus slow N cycling. 5. Synthesis and applications. C addition studies suggest that lowering N availability can reduce invasion. Further, a variety of management approaches may be effective for lowering N availability by stimulating N immobilization. Still, lowering N availability sufficiently to reduce invasion may be difficult, particularly in sites with high atmospheric N deposition or agricultural runoff. Therefore, reducing the disturbances that increase N availability often may be necessary to reduce populations of nitrophilic weeds.