Variation in the location and timing of experimental severing demonstrates that the persistent rhizome serves multiple functions in a clonal forest understory herb

1. In clonal plants, persistent rhizomes can serve multiple purposes, including resource storage, modulation of heterogenous resource distributions, maintenance of bud banks and promotion of recovery from disturbance. Clonal plants are commonly long-lived and, in temperate zones, often exhibit organ preformation. Thus, investigations of how the timing of disturbance to the rhizome affects plant performance must occur over multiple growing seasons, but these types of studies are rare.

2. We conducted a field experiment to examine how the persistent rhizome supports the existing shoot, new ramet production, and recovery from damage using mayapple (Podophyllum peltatum; Berberidaceae), a common herbaceous perennial of low-light forest understories in Eastern North America. Mayapple maintains a long-lived rhizome and exhibits a developmentally-programmed seasonal pattern of resource transport and new ramet initiation. We varied both the position and timing of rhizome severing in rhizome systems with terminal sexual or vegetative shoots, and tracked plants for two years following severing.

3. The location and timing of severing affected both plant persistence (production of new shoots) and performance (leaf area), with effects differing for new shoots at the front vs. the back of the rhizome system. Across years, severing location and past years' shoot size influenced plant persistence and performance, while the effect of timing of severing diminished; initial sexual status had little effect on rhizome system response that was not accounted for by initial leaf area. Severing generally led to the establishment of two independent rhizome systems. Relative to unmanipulated control systems, these two systems had more total leaf area, but less average leaf area per system.

4. Synthesis. Our results point to the rhizome as a resource integrator that affects plant responses to disturbance immediately following damage and in subsequent growing seasons. Rhizome bud age and/or subtending rhizome size, and developmental program influence responses to disturbance. While the effects of experimental disturbance on plant performance decreased two years after disturbance, further long-term investigation is needed to fully understand the demographic consequences of damage to persistent rhizomes.