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Little is known about how carbon integration and storage dynamics affect and are affected by demography in field populations. We sought to elucidate this link by examining dynamic patterns of carbon integration relative to the timing of demographically significant developmental decisions regarding shoot type determination in mayapple, Podophyllum peltatum, a clonal plant with large and persistent rhizomes. Individual rhizome systems growing in natural populations were fed 14CO2 either in late-April, early-May, or mid-June, then harvested at intervals throughout the current season and into the next. When distribution of label was examined we found that carbon fixed at different times in the growing season is used differently: April-fixed assimilate remained in the labeled shoot or was moved into the old rhizome, May-fixed assimilate was found predominantly in the old rhizome, while early-June fixed assimilate moved into the old rhizome and the extending new ramet. Movement of assimilate into the old rhizome appeared to have precedence over formation of additional new ramets. Despite significant within season changes in location of dominant sinks within rhizome systems, there was little redistribution of labeled assimilate: early fixed assimilate was not used to fuel later within season growth, however, assimilate was redistributed between seasons. Vegetative and sexual systems differed in the distribution only of April-fixed assimilate. This was observed even though early labeling occurred prior to anthesis. Sexual systems retained a greater proportion of assimilate in the stem than did vegetative ones, which exported more to the old rhizome. 14C-distribution patterns did not vary between systems differing in future demographic status suggesting that the developmental decision regarding shoot type is based on resources acquired in prior years. We explore the hypothesis that preformation and storage are functionally linked traits that permit plants to coordinate the developmental determination of structures differing in cost and demographic function with known resource status. We conclude that demography influences and is influenced by integrative physiology and that physiological restrictions on within season redistribution of assimilates constrain plants' capacities to respond to short-term environmental variation. Such constraints may affect plants' abilities to respond to rapid environmental change in the Anthropocene. [ABSTRACT FROM AUTHOR]

In clonal plants, persistent rhizomes can serve multiple purposes, including resource storage, modulation of heterogeneous 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.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 2 years following severing.The location and timing of severing affected both plant persistence (production of new shoots) and performance (leaf area), with effects differing for new shoots that developed at the front versus 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.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 programme influence responses to disturbance. While the effects of experimental disturbance on plant performance decreased 2 years after disturbance, further long‐term investigation is needed to fully understand the demographic consequences of damage to persistent rhizomes. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Plants' programs of development can be considered evolved traits. If this is correct, then we should be able to detect variation among clones in developmental traits and demonstrate that this variation leads to fitness differences. Here we report variation in three developmental traits: timing of shoot emergence and senescence and the timing of shoot type determination. We demonstrate significant variation among colonies for all three traits. A reciprocal transplant experiment in the field goes on to demonstrate that the timing of emergence and senescence has both a genetic and environmental component. Variation in emergence and senescence date should effect clonal resource dynamics while variation in the timing of shoot type determination should effect how both short and long term environmental variation influences the demographic trajectory and, hence, fitness of different clones. Further reciprocal transplant experiments are needed to demonstrate genetic variation in the timing of shoot type determination.

Plant-mycorrhizal interactions are generally considered to be examples of a mutualism in which both plant and mycorrhizal fungi benefit. Plants gain increased access to soil nutrients, particularly phosphorus, while mycorrhizal fungi gain access to the carbon fixed by plants. However, there are exceptions to this pattern. Numerous workers have noted that some plants shed mycorrhizal fungi when soil nutrients are supplemented, suggesting that under nutrient rich conditions, the costs to the plant of maintaining the symbiosis outweigh the benefits. In such systems the symbiosis is facultative. Much less is known about plant-mycorrhizal fungi interactions in woodland as opposed to grassland, prairie or agricultural systems. Here we report the nature and properties of the symbiosis in mayapple, Podophyllum pelatum L. (Berberidaceae), a long-lived perennial of the eastern deciduous forest floor. Our data indicate that the mayapple-fungal interaction is facultative; addition of soil phosphorous reduces the intensity of colonization of mayapple roots by mycorrhizal fungi. Of greater interest, we find that not all roots are equally colonized. Roots at young rhizome nodes contain few if any mycorrhizal fungi. Fungal loads increase to their highest level at two to four year old nodes before dropping again. The pattern of soil phosphate depletion mirrors the pattern of mycorrhizal fungi distribution, with the greatest depletion of soil P observed under the most heavily colonized nodes. Hypotheses relating to the regulation of plant-mycorrhizal fungal interactions will be discussed.

Mutualisms, beneficial interactions between species, are expected to be unstable because delivery of benefit likely involves fitness costs and selection should favour partners that deliver less benefit. Yet, mutualisms are common and persistent, even in the largely promiscuous associations between plants and soil microorganisms such as arbuscular mycorrhizal fungi. In two different systems, we demonstrate preferential allocation of photosynthate by host plants to the more beneficial of two AM fungal symbionts. This preferential allocation could allow the persistence of the mutualism if it confers sufficient advantage to the beneficial symbiont that it overcomes the cost of mutualism. We find that the beneficial fungus does increase in biomass when the fungi are spatially separated within the root system. However, in well-mixed fungal communities, non-beneficial fungi proliferate as expected from their reduced cost of mutualism. Our findings suggest that preferential allocation within spatially structured microbial communities can stabilize mutualisms between plants and root symbionts. [ABSTRACT FROM AUTHOR]