Biomass allocation of wet-mesic prairie species through destructive harvest

Background/Question/Methods

In prairie ecosystems, total biomass production and allocation between aboveground vs. belowground pools influence how different species interact, especially in urban ecosystems. However, plant-specific data are lacking for many species of prairie commonly used by bioretention. Our first objective was to quantify the aboveground and belowground pools of biomass for thirteen species of wet-mesic flowering forbs, with the expectation that biomass allocation would vary by species. Our second objective was to assess whether species with similar morphology and phenology would share similar patterns in biomass allocation. We categorized each species based on its aboveground morphology (unbranched stems, branched stems, or basal rosette with flowering stalks) and the month it typically begins to flower. Monocultures of each species were grown in plastic cylinders (area 0.10 m², height 0.92 m) for two years in Madison, WI. At the beginning of seed set, we harvested whole plants to quantify total dry biomass and biomass allocation. We tested whether non-destructive measurements such as canopy size, specific leaf area, and leaf area index could predict differences in biomass allocation.

Results/Conclusions

As expected, individual species varied in total biomass and in their root to shoot ratio of biomass (R:S). Grouping species based on aboveground morphology and month of flowering strengthened the differences in R:S allocation, but not in total biomass production. The three morphological groupings did not differ in total biomass (p = 0.1797), but these groups did differ in their R:S (p < 0.01). Species with unbranched stems had nearly twice the R:S (0.69) compared to species with branched stems and basal rosette growth (0.38 and 0.39, respectively). The three flowering groups displayed similar total biomass (p < 0.10), yet had very different R:S ratios (p < 0.001). Species that typically began flowering in July had approximately twice the R:S (0.69) compared to species that began flowering earlier in the growing season (0.35) and species that began flowering in August or later (0.32). These results suggest that morphological and phenotypic groups may be valuable tools for non-destructive estimation of biomass allocation within urban settings.