Lekberg, Y. | bioRxiv Science

bioRxiv2020

Divergence in bidirectional plant-soil feedbacks between montane annual and coastal perennial ecotypes of yellow monkeyflower (Mimulus guttatus)

O_LIUnderstanding the physiological and genetic mechanisms underlying plant variation in interactions with root-associated biota (RAB) requires a micro-evolutionary approach. We use locally adapted montane annual and coastal perennial ecotypes of Mimulus guttatus (yellow monkeyflower) to examine population-scale differences in plant-RAB-soil feedbacks. C_LIO_LIWe characterized fungal communities for the two ecotypes in-situ and used a full-factorial greenhouse experiment to investigate the effects of plant ecotype, RAB source, and soil origin on plant performance and endophytic root fungal communities. C_LIO_LIThe two ecotypes harbored different fungal communities and responsiveness to soil biota was highly context-dependent. Soil origin, RAB source, and plant ecotype all affected the intensity of biotic feedbacks on plant performance. Feedbacks were primarily negative, and we saw little evidence of local adaptation to either soils or RAB. Both RAB source and soil origin significantly shaped fungal communities in roots of experimental plants. Further, the perennial ecotype was more colonized by arbuscular mycorrhizal fungi (AMF) than the montane ecotype, and preferentially recruited home AMF taxa. C_LIO_LIOur results suggest life history divergence and distinct edaphic habitats shape plant responsiveness to RAB and influence specific associations with potentially mutualistic root endophytic fungi. Our results advance the mechanistic study of intraspecific variation in plant-soil-RAB interactions. C_LI

ecology↗

bioRxiv2020

Plant carbohydrate depletion spreads via ectomycorrhizal networks impairing plant water relations

Carbon and water relations are fundamental to plant life and strongly interact. Under drought, the ability of plants to assimilate carbon is reduced, which increases their consumption of stored labile carbon in the form of non-structural carbohydrates (NSC). This process may impair plant water relations, but mechanisms are not clear, and we do not know if their effects are independent of water deficit. If so, carbon costs of fungal symbionts could also indirectly influence drought tolerance of plants through stored NSC depletion. We connected well-watered Pinus ponderosa seedling pairs via ectomycorrhizal (EM) networks where one seedling was shaded and the other experienced full light and compared responses to seedling pairs in the light. We measured plant water relations and traced carbon movements using 13CO2 to explore the mechanisms linking stored NSC to water relations, and to identify potential tradeoffs between drought tolerance and maintaining EM fungi under carbon-limiting conditions. We found that even in the absence of drought, mild NSC depletion decreased plant drought tolerance by indirectly impairing osmoregulation capacity and turgor maintenance. This demonstrates that NSC storage influences plant drought tolerance independently of plant water status. We also found that EM networks propagated NSC depletion and its negative effects on drought tolerance from carbon stressed hosts to non-stressed hosts. These results highlight carbon allocation tradeoffs between supporting fungal symbionts and retaining water via stored NSC and have implications for biotic interactions and forest drought responses. Significance StatementThe potential effects of future drought on global carbon cycles, vegetation-climate feedbacks, species distributions and their ecological impacts, urgently call for a clear understanding of factors influencing vegetation tolerance to drought. Key to this is the understanding of mechanisms and processes by which plants tolerate drought and how prevalent plant-fungal interactions may influence these processes. We demonstrate that even mild depletion of plant non-structural carbohydrate (NSC) storage readily decreases plant water retention capacity, therefore decreasing tolerance to drought. Because plant-fungal interactions depend on NSC exchange, plants face carbon-allocation tradeoffs between maintaining drought tolerance and feeding fungal symbionts. The impacts of these tradeoffs extend across plants connected via ectomycorrhizal networks as fungi propagate NSC depletion from NSC-limited plants to non-stressed individuals.

plant biology↗