Colonizing ability in the Echinochloa crus-galli complex (barnyard grass). I. Variation in life history

Abstract

A comparison of life history traits in four taxa of the Echinochloa crus-galli complex (barnyard grass) which differ in colonizing ability and weediness was made under various environmental conditions. The taxa were the alien var. crus-galli, a cosmopolitan weed; var. oryzicola, a crop-mimic restricted to rice fields; var. frumentacea, a crop domesticate; and E. muricata, a native of wetland habitats. Populations studied were from the Central Valley of California where the four taxa are sympatric but ecologically differentiated. All comparisons were made under uniform glasshouse conditions to isolate the genetic component of life history variation. Measurements of the patterns of dry weight allocation, time to flowering, reproductive effort, and seed production were made on individuals grown during different periods of the year under "stress" and "nonstress" conditions utilizing randomized multi-harvest designs.Developmental plasticity in allocation patterns and reproductive phenology occurred in all taxa in response to seasonality and nutrient stress although there were significant differences among taxa in the form of the response. Individuals germinating in August yielded less total biomass and allocated a smaller proportion to roots and a larger proportion to secondary tillers and seed than individuals germinating in April. In all taxa, except E. crus-galli var. frumentacea, a delay in flowering under long days resulted in larger vegetative biomass, lower reproductive effort, and where nutrients were limiting, inhibition of secondary tillers. Nutrient stress resulted in a delay in flowering, increased senescence rates, and a reduction in total biomass and reproductive effort. Although each taxon displayed a wide range of tactics, certain differences in life history strategy among the taxa were maintained. In all regimes E. crus-galli var. crus-galli flowered earlier, and exhibited a greater seed production and reproductive effort than var. oryzicola. In general, E. crus-galli var. frumentacea and E. muricata were intermediate in behaviour.Interpopulation variability in the life history traits of E. crus-galli var. crus-galli and E. muricata was measured in a single-harvest, completely randomized design using 10 populations of each taxon. Significant interpopulation variation was recorded within taxa in tiller height and number, aboveground vegetative biomass, time to anthesis, reproductive biomass, harvest index, seed production, and seed weight. Averaged over 10 populations, E. crus-galli var. crus-galli was taller during vegetative growth, flowered more rapidly, allocated a greater proportion of aboveground biomass to reproduction, and produced a greater number of seeds than E. muricata.Variation in life history parameters among barnyard grass taxa may explain differences in colonizing potential. In particular, the failure of E. muricata and E. crus-galli var. oryzicola to colonize open, seasonally moist sites in California where E. crus-galli var. crus-galli flourishes, may be due to their inability to reach reproductive maturity before the onset of summer drought.