Our previous work in California annual grasslands indicates that nitrogen released from seedling thinning accounts for 37-63% of annual internal N cycling, suggesting that seed densities could have profound effects on plant N supply. Restoration seeding rates are often orders of magnitude lower than natural densities, which could be detrimental to plant establishment if seedling thinning is a significant source of plant N. In order to test the impact of seedling thinning on stand biomass and N uptake, we grew
Results/Conclusions
Regardless of species composition, higher seed densities doubled end-of-season stand biomass and N content. These patterns were seen at a whole-plant level, as well as individually for shoots, roots, and seeds. These patterns suggest that plant N limitation may be diminished by the N released from dying seedlings in high-density neighborhoods. Density treatments did not impact end-of-season live tissue C/N ratios, but significantly decreased litter C/N values in monocultures. Together, these results suggest that increased planting density not only increases the current season’s N availability and plant productivity, but will also likely enhance plant biomass and N content in subsequent growing seasons through two different pathways. Seedling thinning inputs are likely to be higher in the 2nd growing season due to higher seed density and N content, and litter decomposition inputs should also increase due to both doubled litter N content, and higher litter quality. While increasing seed densities would substantially increase restoration costs, it would likely yield long-term benefits in plant establishment.