The Land Institute is developing perennial grains to be grown in prairie-like mixtures. One approach involves the development of a perennial grain sorghum by crossing tetraploid Sorghum bicolor with wild S. halepense to combine high seed yield with overwintering ability via rhizome production. We grew tetraploid S. bicolor, F1 hybrid (BC0), and two backcross generations (BC1 and BC2) in a randomized block design to examine total biomass, seed yield, and allocation to plant parts within and across generations. Root, rhizome, stem and leaf, and total biomass decreased from the BC0 to BC2 to S. bicolor generations, whereas panicle mass, seed mass, and reproductive allocation were lowest in the BC0 generation (p < 0.05, ANOVA). Mean seed mass (g ∙ plant−1) was 39.1 in the BC0, 107.3 in the BC1, 84.1 in the BC2, and 92.7 for the S. bicolor parent, which translated into yields of 171.9, 471.6, 396.7, and 407.5 g ∙ m−2, respectively. Reproductive allocation varied from 14.7% in BC0 to 28.9% in BC2 compared with 33.5% in S. bicolor. Mean allocation to rhizomes was 2.71% in BC0 but negligible in BC1 and BC2. There was no relationship between rhizome mass and seed mass within any generation, but there was a positive correlation between total plant mass and rhizome mass in BC0. We divided the BC0 population into four groups with respect to rhizome production and found no significant differences among the groups in plant size or seed yield. Within each generation, reproductive allocation was inversely related to culm mass. The lack of an apparent trade-off between allocation to rhizome versus allocation to seed within any generation supports the possibility of combining within a population high seed yield and production of perennating belowground organs. Key words: backcross, hybrid, perennial grains, reproductive allocation, rhizome, seed mass, Sorghum bicolor, Sorghum halepense.

No abstract

The ecological role of biodiversity in achieving successful restoration has been little explored in restoration ecology. We tested the prediction that we are more likely to create persistent, species-rich plant communities by increasing the number of species sown, and, to some degree, by varying functional group representation, in experimental prairie plantings. There were 12 treatments consisting of 1-, 2-, 3-, 4-, 8-, 12-, and 16-species mixtures of native perennials representing four functional groups (C 4 grasses, C 3 grasses, nitrogen-fixing species, and late-flowering composites) that predominate within Central Plains tallgrass prairies. In 2000, species were seeded into square plots (6 3 6 m), with five replicates per treatment, on former agricultural land. Annually, we measured total species richness and evenness, target species richness and cover, and richness and cover of resident species (i.e., those emerging from the seed bank). Both target species richness and rate of establishment of target communities were highest in the most speciesrich mixtures, but there was no additional benefit for treatments that contained more than eight species. Richness of resident species did not vary with target species richness; however, cover by resident species was lower in the higher target species treatments. Our results, indicating that establishment of species-rich prairie mimics can be enhanced by starting with larger numbers of species at the outset, have implications for grassland restoration in which community biodiversity creation and maintenance are key goals.

No abstract

A natural productivity gradient was used to test questions about plant species composition, diversity, and sensitivity to environmental change of prairie vegetation within the tallgrass region. From 1986 to 1992 I monitored seasonal net aboveground production and species composition at four sites with soils that differed in texture and percent organic matter, pH, and concentrations of NH4, total N, K, Ca, Mg, and SO4. Four years of the survey featured above normal precipitation and 3 were drought years. August standing crop averaged 566 ± 307, 419 ± 143, 268 ± 158, and 232 ± 148 g ∙ m−2 at the four sites. Production generally increased with soil fertility (i.e., percent organic matter, total N, and K) and precipitation. The two more productive sites featured higher percentages of grass biomass, but legumes were rare. The site with the lowest soil N supported the consistently highest legume biomass and lowest grass biomass among sites. The least productive site displayed the highest percentage of composites. Species evenness, but not richness, was inversely related to August biomass for all sites. There were significant differences in production across years, as well as in percentages of grass, legume, and composite biomass. Total plot richness ranged from 24 to 40 species sampled per year at site 2 to 51 –53 species at site 4, and tended to decline in the dry year 1989. Poor soils, although less productive overall, appear to prevent dominance by tall grasses and thereby maintain relatively more diverse spring and summer floras. Increased light availability near the soil surface probably enables the persistence of low-growing plants. Evenness, but not richness, varied among sites. The patterns of plant community composition have implications for restoration ecology as well as the design of prairielike perennial grain mixtures. Key words: diversity, evenness, plant community, prairie, soil type, variability.