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Dawson, Hilary Rose [1], Maxwell, Toby M. [2], Shek, Katherine L. [1], Bomfim, Barbara [3], Reed, Paul B. [1], Bridgham, Scott [1], Silva, Lucas C.R. [1].

Carbon and nitrogen transfer in root-mycorrhizal networks vary with species traits and community composition in Pacific Northwest grasslands.

Introduction: Plant rhizospheres are connected by common mycorrhizal networks (CMNs) that transfer carbon and nutrients between individual plants, shaping community structure and function. It is unclear how climate change may alter these networks, or how these networks support plant ecophysiological performance under climatic stress. We hypothesize that diverse prairie communities would have greater carbon and nutrient transfer compared to pasture grass communities, and that experimental drought would decrease this transfer in both systems.
Methods: We established experimental plots at three sites spanning a 520 km climate gradient in Oregon and Washington. At each site, we restored plots to mixed prairie communities and compared them to adjoining established pasture grass communities. We placed rainout shelters over half the plots to simulated 40% drought. Using enclosed chambers, we labeled 57 donor plants from four species (9 Agrostis capillaris [Poaceae], 10 Alopecurus pratensis [Poaceae], 10 Schedonorus arundinaceus [Poaceae], 28 Sidalcea malviflora [Malvaceae]) with isotopically labeled gases (ammonia and carbon dioxide; 99% enriched, 15NH3 and 13CO2). To determine transfer between 20 plant species, we measured how surrounding plants’ leaf isotopic signature changed at 4, 11, 21, and 65 days after labeling at multiple distances from the donor species. As explanatory variables for variation in transfer, we measured specific leaf area (SLA), intrinsic water-use efficiency (iWUE), and changes in elemental concentration. Finally, we explored the effects of drought and mean phylogenetic pairwise distance (MPD) to identify potential mechanisms driving variation in C and N transfer.
Results: Our preliminary data suggest that a) although applied simultaneously, C and N showed different patterns of retention and distribution over time and space, a response that co-varied with species traits and community composition; b) we found no clear response to experimental drought but form-function relationships (e.g. SLA-iWUE) correlated strongly with the amounts of N transferred; c) donor individuals in diverse communities shared the most N and pasture communities retained most of the N applied across treatments; d) C shows limited enrichment that follows an expected relationship with iWUE, SLA, and MPD.
Conclusion: Our data support the hypothesis that diverse communities have greater C and N transfer compared to pastures, but we found no evidence that drought would decrease C and N transfer. Our next steps will include characterization of the fungal community in each plot and DNA stable isotope probing to determine if the resilience-building power of certain strains can be used to C and N retention in CMNs.

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1 - University of Oregon, Eugene, OR, USA
2 - Boise State University, Boise, ID, USA
3 - Lawrence Berkeley National Laboratory, Berkeley, CA, USA

climate change
stable isotope
plant community ecology
plant-fungal interactions
common mycorrhizal networks
carbon dioxide
leaf traits

Presentation Type: Poster
Session: P2, Ecophysiology Posters
Location: Virtual/Virtual
Date: Tuesday, July 20th, 2021
Time: 5:00 PM(EDT)
Number: P2PE001
Abstract ID:89
Candidate for Awards:None

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