Effects of self-thinning of shoots on the nutrient budgets of Zizania latifolia

This experimental study focused on the seasonal changes and mobilization of nutrients between plant parts to understand the implications of self-thinning in the ecology of Zizania latifolia (Griseb.) Turcz. ex Stapf. The observations of shoot density, above- and belowground biomass, and total nitrogen and total phosphorus concentrations were conducted from February 2002 to August 2003. The biomass of shoots that died during the period and daily uptake of nutrients were determined. The shoot density sharply increased until mid-April and thereafter decreased significantly due to self-thinning of shoots. Total nitrogen and phosphorus concentrations of rhizomes decreased initially due to translocation to new shoots; however, the nutrients of rhizomes were slightly replenished from dead shoots during self-thinning. In contrast to other species, self-thinning of Z. latifolia shoots reallocates some of the minerals contained in the dead shoots back to the rhizomes, which can be regarded as a strategy to replenish the reduced resources of the rhizomes. The initial intensive growth of shoots can be regarded as a strategy to maintain resource competition.