Plant rhizome positioning in the soil and under litter: Trade-offs of frost avoidance versus growth

Abstract

Herbaceous plants can avoid frost stress by positioning their rhizomes deep in the soil or under plant litter, but this insulation may come at a cost of delayed emergence and reduced growth, particularly if frost stress is absent. We explored the strength of this trade-off for a range of rhizomatous plant species by conducting a suite of experiments to disentangle the direct effects of soil depth and litter cover on plant growth and survival from the effects of variation in frost exposure. Rhizome fragments were planted in the fall to experience winter conditions in the field at one of two depths with one of three litter treatments, and the latter treatments were combined with snow removal to increase frost intensity. For comparison, a second set of rhizome fragments that were overwintered in a growth chamber under mild conditions were exposed to the same soil depth and litter treatments in the spring. A third set of rhizomes was subjected to one of six freezing temperatures under controlled conditions then planted at a common depth in the spring. At the end of summer, all plants were harvested, and height and dry biomass were measured. For half the species studied, the depth and litter treatments reduced the severity of the snow removal effects on plant growth or survival, and the results of the controlled condition freezing experiment provided additional support for reduced freezing damage being the main driver of this response. However, deep soil positioning and litter cover were a cost for most species when they were planted in the spring. Overall, these results demonstrated that the benefits of soil and litter cover can outweigh the costs when frost is present; the balance of this trade-off could shift further with climate change and the resulting increase in soil frost caused by reduced snow cover in some regions.