Summary1. Most studies of soil heterogeneity have focused on underlying abiotic factors such as soil nutrients. However, increasing recognition of plant-soil feedback (PSF) effects on plant growth, combined with the observation that PSFs operate at small spatial scales, suggests that heterogeneity due to PSF could affect plant population and community dynamics. The consequences of PSF-generated heterogeneity for coexistence depend on heterogeneity's effects on vital rates and how those vital rates influence population-level recruitment dynamics. 2. We measured vital rates and recruitment dynamics of three congeneric pairs of introduced perennial plants grown as monocultures in experimental PSF-generated soil environments. Field soils collected from conspecifics and congeners were alternated in patches or mixed together to produce heterogeneous and homogeneous soils, respectively. 3. We quantified the effects of PSF-generated heterogeneity on germination and establishment and determined how these vital rates affected recruitment. We calculated net pairwise interaction coefficients to predict whether PSFs could mediate coexistence between congeners. 4. Soil heterogeneity altered the relationship of vital rates to recruitment dynamics for some species. For example, Solanum dulcamara recruited later into heterogeneous than homogeneous soils, and germination was a stronger predictor of the timing of recruitment in heterogeneous soil, while mortality was a stronger predictor in homogeneous soil. Contrasts between soils of different origin suggest that mixing soils had non-additive effects on vital rates (e.g. Rumex crispus mortality was higher in homogeneous than in conspecific or congener soil). Interaction coefficients predicted that PSFs in heterogeneous soils might mediate stable coexistence only of Rumex congeners. 5. Synthesis. Heterogeneity generated by PSFs had species-specific effects on vital rates, with consequences for recruitment dynamics. Mixing soils of different origin often resulted in non-additive effects, which may indicate an interaction between soil abiotic and/or biotic properties and could predict non-additive responses to soil disturbance. Finally, quantifying the reciprocal effects of PSFs on congeners suggests that PSF-generated heterogeneity may promote coexistence of certain species, which was not evident from individual PSF responses. Future studies should determine whether such mechanisms might operate for more distantly related species.

Summary Plant radiations are widespread but their influence on community assembly has rarely been investigated. Theory and some evidence suggest that radiations can allow lineages to monopolize niche space when founding species arrive early into new bioclimatic regions and exploit ecological opportunities. These early radiations may subsequently reduce niche availability and dampen diversification of later arrivals. We tested this hypothesis of time‐dependent lineage diversification and community dominance using the alpine flora of New Zealand. We estimated ages of 16 genera from published phylogenies and determined their relative occurrence across climatic and physical gradients in the alpine zone. We used these data to reconstruct occupancy of environmental space through time, integrating palaeoclimatic and palaeogeological changes. Our analysis suggested that earlier‐colonizing lineages encountered a greater availability of environmental space, which promoted greater species diversity and occupancy of niche space. Genera that occupied broader niches were subsequently more dominant in local communities. An earlier time of arrival also contributed to greater diversity independently of its influence in accessing niche space. We suggest that plant radiations influence community assembly when they arise early in the occupancy of environmental space, allowing them to exclude later‐arriving colonists from ecological communities by niche preemption.

1. Biological invasions are a major driver of ecosystem change but causes of variation in their environmental impacts over space and time remain poorly understood. Most approaches used to quantify the impacts of non-native species assume there are interactions among per capita (i.e. individual level) effects, species abundance and the area occupied by the species. However, studies rarely evaluate these factors and their interactions and often fail to recognize that the magnitude of impacts can be highly context dependent. Understanding what drives the context dependence of non-native species impacts can improve our understanding and predictions of ecosystem change and better inform options for mitigation.2. Conifers, especially pines, are among the most problematic non-native plant species globally. We use Pinaceae to illustrate how context dependence in biodiversity and environmental impacts of non-native plant species can be generated by at least four processes: nonlinear density effects; intraspecific variation in functional traits; shifts in impacts over time; and persistence of impacts as biological or ecosystem legacies following non-native species removal. Using this understanding, we develop a framework to better quantify interactions of impacts along environmental gradients (e.g. soil fertility, climate, ecosystem age).3. We demonstrate how impacts of non-native species can occur at both low and high density, and that failing to account for intraspecific variation in effect traits can lead to significant errors in the prediction of impacts. By incorporating context dependence in regard to density and functional traits, we can measure how the interaction of this context dependence will shift along environmental gradients. | 945Functional Ecology SAPSFORD et Al.

Plant-soil feedbacks can affect plant community dynamics by influencing processes of coexistence or invasion, or by maintaining alternate stable states. Darwin's naturalization hypothesis suggests that phylogenetic relatedness should be a critical factor governing such feedbacks in invaded communities but is rarely considered in soil feedback studies. We investigated the effects of soil biota from experimentally established native and invaded California grassland communities on resource capture and allocation of three native and three exotic grass species, comprising three tribes, grown in the laboratory. Phylogeny was the single greatest determinant of grass biomass, root:shoot ratio, and growth rate, with presence of soil biota explaining the second greatest proportion of variance in total grass biomass. Similar trends were observed in soil collected from naturally occurring stands of native perennial and exotic annual grasses. Species of similar life history/provenance exhibited similar biomass responses to the same soil community, while more closely related species exhibited similar root:shoot ratio responses to the same soil community. Relationships between the plant community composition of a field plot and species responses to soil inoculum collected from that field plot were idiosyncratic, with many aspects of plant community structure potentially contributing to soil feedbacks. Thus, future studies should explicitly consider both phylogeny and provenance and evaluate soil feedbacks in a community setting.

Summary1. Understanding the mechanisms governing coexistence is a central goal in ecology and has implications for conserving and restoring communities, yet the high diversity in many plant communities is difficult to explain. Theory suggests that plant-soil feedbacks (PSF) can lead to frequency-dependent coexistence by suppressing conspecifics more than heterospecifics, potentially helping to explain high-diversity plant communities. In addition, species-specific population dynamics, including the rate at which individuals are replaced in a population or population turnover rate, may influence coexistence outcomes. 2. We have created a rigorous test of the coexistence predictions of theory by generating a soil heterogeneity experiment in the field and testing for mutual invasibility by establishing resident populations, then experimentally invading them. Experimental tests of mutual invasibility can demonstrate coexistence because, if species are able to invade one another's populations when at low density, they should exhibit long-term coexistence. We use pairs of congeners in this experiment that coexist at small spatial scales, sometimes within cm, at our field site. 3. We demonstrate that invader individuals established better in congener's soils than in conspecific soils, consistent with plant-soil feedback mediated coexistence. This effect was often mediated by competition with established resident plants. 4. Further, we show that soil heterogeneity interacted with the population turnover rate of the resident population to influence invasibility (P < 0.10), consistent with the theoretical prediction that a plant's population dynamics will interact with heterogeneity to influence coexistence. 5. Synthesis. Plant-soil feedbacks (PSF) can in theory lead to frequency-dependent coexistence, and reciprocally, negative feedback effects in glasshouse experiments are often consistent with this prediction. We provide the first field test of mutual invasibility structured by PSF, demonstrating that PSF can lead to coexistence when they create a patchy, or heterogeneous, soil environment. This work suggests that understanding the influence of PSF on diversity necessitates understanding the spatial scale at which soil heterogeneity emerges in the field. Thus, high diversity might be maintained in plant communities by heterogeneity created by plants' influence on the soil, and this outcome depends strongly on population dynamics.