PARENT SESSION
Oral Session 3: Biogeochemistry I: Litter and Decomposition.
Presiding: J Dilustro
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room A 107.
Seedling thinning contributes as much to internal N cycling as does decomposition of senesced litter.
Eviner, Valerie*,1, Vaughn, Charles2, 1 Institute of Ecosystem Studies, Millbrook, NY, USA2 Hopland Research and Extension Center, Hopland, CA, USA
ABSTRACT- In most terrestrial ecosystems, litter senesced at the end of the growing season is assumed to be the main internal source of carbon and nutrients. We demonstrate the importance of a previously overlooked input of labile C and nutrients, self-thinning of grass seedlings. In California annual grasslands, 70% of aboveground plant N is retranslocated from senescing litter to seeds. Over 90% of these seeds germinate the following fall. Intense seedling competition through the growing season results in mortality of 75% of the seedlings. These young seedlings have a low proportion of structural compounds, and thus are highly labile, releasing their C and N quickly. The timing of peak self-thinning leads to the release of readily-mineralizable N precisely at the time of peak plant competition, when only relatively recalcitrant, low N litter remains. Thus, it appears that thinning seedlings are a major source of nutrients for growing plants. Over the growing season, the cumulative inputs of N from seedling thinning are equivalent to the amount of N released from litter that senesces at the end of the growing season.
Key words: self-thinning, nitrogen retention, nitrogen cycling, plant nitrogen supply