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Creators/Authors contains: "Segnitz, R. Max"

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  1. Abstract

    Seedling recruitment can be strongly affected by the composition of nearby plant species. At the neighborhood scale (on the order of tens of meters), adult conspecifics can modify soil chemistry and the presence of host microbes (pathogens and mutualists) across their combined canopy area or rooting zones. At local or small spatial scales (on the order of one to few meters), conspecific seed or seedling density can influence the strength of intraspecific light and resource competition and also modify the density‐dependent spread of natural enemies such as pathogens or invertebrate predators. Intrinsic correlation between proximity to adult conspecifics (i.e., recruitment neighborhood) and local seedling density, arising from dispersal, makes it difficult to separate the independent and interactive factors that contribute to recruitment success. Here, we present a field experiment in which we manipulated both the recruitment neighborhood and seedling density to explore how they interact to influence the growth and survival ofDryobalanops aromatica, a dominant ectomycorrhizal tree species in a Bornean tropical rainforest. First, we found that both local seedling density and recruitment neighborhood had effects on performance ofDaromaticaseedlings, though the nature of these impacts varied between growth and survival. Second, we did not find strong evidence that the effect of density on seedling survival is dependent on the presence of conspecific adult trees. However, accumulation of mutualistic fungi beneath conspecifics adults does facilitate establishment ofDaromaticaseedlings. In total, our results suggest that recruitment near adult conspecifics was not associated with a performance cost and may have weakly benefitted recruiting seedlings. Positive effects of conspecifics may be a factor facilitating the regional hyperabundance of this species. Synthesis: Our results provide support for the idea that dominant species in diverse forests may escape the localized recruitment suppression that limits abundance in rarer species.

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  2. Abstract

    While work in temperate forests suggests that there are consistent differences in plant–soil feedback (PSF) between plants with arbuscular and ectomycorrhizal associations, it is unclear whether these differences exist in tropical rainforests. We tested the effects of mycorrhizal type, phylogenetic relationships to overstory species, and soil fertility on the growth of tree seedlings in a tropical Bornean rainforest with a high diversity of both ectomycorrhizal and arbuscular mycorrhizal trees. We found that ectomycorrhizal tree seedlings had higher growth in soils conditioned by close relatives and that this was associated with higher mycorrhizal colonization. By contrast, arbuscular mycorrhizal tree seedlings generally grew more poorly in soils conditioned by close relatives. For ectomycorrhizal species, the phylogenetic trend was insensitive to soil fertility. For arbuscular mycorrhizal seedlings, however, the effect of growing in soils conditioned by close relatives became increasingly negative as soil fertility increased. Our results demonstrate consistent effects of mycorrhizal type on plant–soil feedbacks across forest biomes. The positive effects of ectomycorrhizal symbiosis may help explain biogeographic variation across tropical forests, such as familial dominance of the Dipterocarpaceae in southeast Asia. However, positive feedbacks also raise questions about the role of PSFs in maintaining tropical diversity.

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