PLASTICITY OF SEED NUMBER, MASS, AND ALLOCATION IN CLONES OF THE PERENNIAL GRASS AMPHIBROMUS-SCABRIVALVIS

Phenotypic variation in seed traits was investigated in cloned genotypes of the perennial grass Amphibromus scabrivalvis to explore the degree to which individuals alter reproductive traits in response to enhanced soil resources. The seeds of this species matured in cleistogamous spikelets on panicles enclosed within leaf sheaths along each tiller. Ten clones, each a genotype from one seed, were separated into 48 ramets and planted in the greenhouse. One-half of all ramets received 20%-20%-20% (N-P-K) fertilizer every 2 wk, while the other half were not fertilized. For each clone, 24 ramets were harvested after 20 and 26 wk. Seed number and dry mass were recorded; seed allocation was expressed as a percentage of total dry mass. To visualize the relation of genotype to phenotype, reaction norms were plotted. Plasticity was expressed as an index that measured the percentage change in a trait from the fertilized to the unfertilized environment. There were significant differences among clones in seed number and total seed mass at both 20 and 26 wk, and in seed allocation at 20 wk. Most seed traits were increased by nutrient addition. Crossing of reaction norms and some significant treatment by clone interactions revealed that clones varied in the extent to which they responded to elevated nutrients. For both harvests, seed number and total seed mass were significantly more plastic than seed allocation and mean seed mass; however, variation in plasticity among clones was significantly greater for the latter two traits. This species mostly changes seed number in response to enhanced soil resources rather than mean seed mass or seed allocation. The marked genotypic variation in the plasticity of mean seed mass and allocation indicates that selection could alter the relative abundance of genotypes if the phenotypic responses of these traits to the availability of soil resources enhances reproductive fitness.