Fine‐scale dynamics of rhizomes in a grassland community

Abstract

Spatial dynamics in grassland communities are constrained by the belowground spatial distribution of roots and rhizomes. Their dynamics are difficult to measure as underground data collection tends to be destructive and cannot be repeated at the same plot over time. We investigated rhizome dynamics indirectly by examining rhizome spatial structure on long‐term grassland study plots where aboveground shoot counts have been recorded using a fine‐scale grid over nine years. Number of rhizome apical ends, basal ends and total rhizome length of both live and dead rhizomes were obtained from the data by scanning rhizomes and processing them by GIS vectorization. These rhizome variables were correlated with the above‐ground shoot counts in grid cells over varying temporal lags. There was a general decrease in the intensity of correlation between live rhizomes and shoot counts with increasing time lags. Correlation of dead rhizomes increased with increasing time lag, reaching a maximum after several years, and then declined. Species differed strongly in the change of rhizome‐shoot counts correlation over varying time lags. These differences were used to infer rhizome growth dynamics, namely rhizome growth rate and lifespan, and rhizome mean decomposition time. The species involved differed in all these traits. Mean rhizome growth rate ranged from 0.2 (Polygonum bistorta) to 3.3 cm ur−1 (Deschampsia flexuosa); mean rhizome lifespan ranged from 5 yr (Anthoxanthum alpinum) to over 8 yr (Nardus stricta) and mean decomposition time from one growing season (Anthoxanthum) to 7 yr (Polygonum). Presence of dead rhizomes below living rhizomes or aboveground shoots was taken as an indication of fine‐scale replacements between species. These were highly non‐random, with some species pairs replacing significantly more frequently. These differences in rhizome growth parameters underlie different strategies of horizontal growth and dieback between species. These can serve as one of the mechanisms of species replacements and contribute to the fine‐scale coexistence of species.