Nitrogen, phosphorus, and light effects on reproduction and fitness of wild rice

Abstract

Plant fitness is typically correlated with total seed biomass or the number of seeds produced per plant, but the connection from seed production to seedlings the following year is seldom made. Seedling production in grasses, including wild rice ( Zizania palustris L.) is determined by the number of inflorescences produced, the number of seeds per inflorescence, the mean mass per seed, proportion of seeds that are filled, predation on seeds, and germination rates. Previous studies have shown that wild rice biomass production is limited primarily by nitrogen and secondarily by phosphorus and light. To test how nitrogen, phosphorus, and light modulate plant fitness, we evaluated the effects of nitrogen, phosphorus, and light on the above parameters. Nitrogen addition increased number of inflorescences, seeds per inflorescence, and mean seed mass, resulting in more seedlings produced, hence greater fitness, despite increased rice worm predation and lower germination rates of seeds compared to seeds from plants grown without nitrogen addition. Phosphorus additions and full sunlight also increased the number of seedlings per plant, mainly after nitrogen was added. Therefore, the maternal environment not only affects seed production but the number of seedlings that emerge the following year, especially with respect to nitrogen.