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Abstract Plant‐microbial‐herbivore interactions play a crucial role in the structuring and maintenance of plant communities and biodiversity, yet these relationships are complex. In grassland ecosystems, herbivores have the potential to greatly influence the survival, growth and reproduction of plants. However, few studies examine interactions of above‐ and below‐ground grazing and arbuscular mycorrhizal (AM) mycorrhizal symbiosis on plant community structure.We established experimental mesocosms containing an assemblage of eight tallgrass prairie grass and forb species in native prairie soil, maintained under mycorrhizal and nonmycorrhizal conditions, with and without native herbivorous soil nematodes, and with and without grasshopper herbivory. Using factorial analysis of variance and principal component analysis, we examined: (a) the independent and interacting effects of above‐ and below‐ground herbivores on AM symbiosis in tallgrass prairie mesocosms, (b) independent and interacting effects of above‐ and below‐ground herbivores and mycorrhizal fungi on plant community structure and (c) potential influences of mycorrhizal responsiveness of host plants on herbivory tolerance and concomitant shifts in plant community composition.Treatment effects were characterized by interactions between AM fungi and both above‐ground and below‐ground herbivores, while herbivore effects were additive. The dominance of mycorrhizal‐dependent C4grasses in the presence of AM symbiosis was increased (p < 0.0001) by grasshopper herbivory but reduced (p < 0.0001) by nematode herbivory. Cool‐season C3grasses exhibited a competitive release in the absence of AM symbiosis but this effect was largely reversed in the presence of grasshopper herbivory. Forbs showed species‐specific responses to both AM fungal inoculation and the addition of herbivores. Biomass of the grazing‐avoidant, facultatively mycotrophic forbBrickellia eupatorioidesincreased (p < 0.0001) in the absence of AM symbiosis and with grasshopper herbivory, while AM‐related increases in the above‐ground biomass of mycorrhizal‐dependent forbsRudbeckia hirtaandSalvia azureawere eradicated (p < 0.0001) by grasshopper herbivory. In contrast, nematode herbivory enhanced (p = 0.001) the contribution ofSalvia azureato total biomass.Synthesis. Our research indicates that arbuscular mycorrhizal symbiosis is the key driver of dominance of C4grasses in the tallgrass prairie, with foliar and root herbivory being two mechanisms for maintenance of plant diversity.
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Root herbivory controls the effects of water availability on the partitioning between above‐ and below‐ground grass biomass
Abstract The fraction of primary productivity allocated below‐ground accounts for a larger flow of carbon than above‐ground productivity in most grassland ecosystems. Here, we addressed the question of how root herbivory affects below‐ground allocation of a dominant shortgrass prairie grass in response to water availability. We predicted that high levels of root herbivory by nematodes, as seen under extreme drought in sub‐humid grasslands, would prevent the high allocation to root biomass normally expected in response to low water availability.We exposed blue gramaBouteloua gracilis, which accounts for most of the net primary productivity in the shortgrass steppe of the central and southern Great Plains, to three levels of water availability from extreme low to intermediate and extreme high crossed with a gradient of rootherbivore per cent abundance relative to the total nematode community in soil microcosms.As hypothesized, the effect of water availability on below‐ground biomass allocation was contingent on the proportion of root herbivores in the nematode community. The relationship between below‐ground biomass allocation and water availability was negative in the absence of root herbivory, but tended to reverse with increasing abundance of root feeders. Increasing abundance of root‐feeding nematodes prevented grasses from adjusting their allocation patterns towards root mass that would, in turn, increase water uptake under dry conditions. Therefore, below‐ground trophic interactions weakened plant responses and increased the negative effects of drought on plants.Our work suggests that plant responses to changes in precipitation result from complex interactions between the direct effect of precipitation and indirect effects through changes in the below‐ground trophic web. Such complex responses challenge current predictions of increasing plant biomass allocation below‐ground in water‐stressed grasslands, and deserve further investigation across ecosystems and in field conditions. A freePlain Language Summarycan be found within the Supporting Information of this article.
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- Award ID(s):
- 1832194
- PAR ID:
- 10452068
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Functional Ecology
- Volume:
- 34
- Issue:
- 11
- ISSN:
- 0269-8463
- Format(s):
- Medium: X Size: p. 2403-2410
- Size(s):
- p. 2403-2410
- Sponsoring Org:
- National Science Foundation
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