Root survival of six cool-temperate wetland graminoids in autumn and early winter

Abstract

Background: Timing of leaf senescence is an important ecological trait of species in cool-temperate climates. In contrast to above-ground biomass, not much is known about timing and extent of root mortality of herbaceous perennials at the end of the growing season. Aims: We undertook to assess patterns of end-of-season root mortality in species of temperate wetlands, investigate if the interspecific variation in the pattern of leaf senescence in autumn is reflected in patterns of root mortality, and determine if coarse axile roots and fine lateral roots differ in their autumn mortality pattern in wetland graminoids. Methods: For six cool-temperate perennial wetland graminoids, we assessed whether their roots die back for the winter, if the species-specific timing of senescence corresponds to interspecific variation in leaf senescence, and if fine lateral roots and axile roots differ in their mortality pattern. Survival and mortality of lateral and axile roots, and above-ground senescence was assessed in Sudbury, Ontario, Canada, from 11 September to 11 December, 2007, a period during which most of the above-ground biomass died. Root mortality was assessed using 2,3,5-triphenyltetrazolium chloride. Results: In Carex oligosperma, Carex stricta, Phalaris arundinacea and Scirpus microcarpus the majority of lateral and axile roots showed little mortality until mid-December. Axile roots of Dulichium arundinaceum showed little mortality, but its lateral roots died in October. Both lateral and axile roots of Sparganium androcladum died in October. Conclusions: These results indicate that fine roots of many species do not senesce along with the leaves for winter in cool-temperate climates. In some species, however, all roots senesce in autumn.