Research

"Plasticity and adaptation of northern California eelgrass in response to sediment conditions" (Zabinski et al., in review)

Considerable research describes the interactions between seagrasses and their sedimentary environment, but there is little information on how populations differ in their innate versus plastic responses to these differences. Here, we test whether sediment contributes to eelgrass population differentiation and the nature of plastic responses to different sediment environments. We do this via a 15-week, fully crossed common garden experiment with two populations and their native sediment types. Plants from the warmer-temperature, clay-dominated site (90% silt + clay, 10% sand) consistently maintained greater biomass than plants from the cooler, sand-dominated site (60% sand, 40% silt + clay). Plants from both populations were highly plastic for root length and clonal shoot size, with both increasing when planted in clay-dominated compared to sand-dominated sediment. Plants from the clay-dominated site grew longer rhizomes in foreign sediment while plants from the sand-dominated site had no change in this plant trait, indicating some measure of home site advantage with respect to sediment conditions. Porewater sulfide also exhibited this pattern where concentrations were very low in clay-dominated sediment for all plants, but in the sand-dominated treatment, only plants native to sand-dominated sediment maintained porewater sulfide concentrations below toxic levels. These patterns may be mediated by microbiome differences between populations as roots from plants native to clay-dominated sediment had more fixed microbiomes between treatments compared to plants native to sand-dominated sediment. These results support that sediment type partially mediates home site advantage in eelgrass populations and suggest differential population responses may be mediated by the associated microbiome.

Collaborators: Claire Murphy (UC Davis), Katherine DuBois (Bangor University), and Jay Stachowicz (UC Davis)

Related publications: Estuaries and Coasts

"Transgenerational effects on plant traits, but not microbiomes, differentiate eelgrass populations in response to thermal stress" (Zabinski et al., in prep)

Phenotypic plasticity, both within (WGP) and transgenerational (TGP), and the microbiome are mechanisms organisms can use to rapidly respond to changing environments. However, intraspecific variation in plasticity can complicate predicting the relative importance of adaptation versus plasticity in response to environmental change. Additionally, the fitness consequences of plasticity often fail to account for its influence on an organism’s extended phenotype, like its microbiome. We assessed how populations of seagrass, Zostera marina, with different thermal histories vary in their ability to adjust plant and microbiome phenotypes within and across generations. We hypothesized the population with historically high exposure to extreme temperatures (exposed population) would more frequently exhibit patterns of adaptive TGP or positive carryover effects than the population with rare historical exposure (unexposed population) and that these trends would extend to the microbiome. We conducted a split-brood experiment, exposing parental shoots (F0) to either ambient temperatures or a simulated marine heat wave of 5 weeks. Afterwards, we harvested one offspring from each individual (F1) and propagated them at ambient temperatures for one year before exposing F1 shoots to either the same or opposite treatment as their parent. At the end of the second generation (F1 + F2), we measured plant fitness-related traits and characterized endophytic root and rhizosphere microbiomes, along with bare sediment controls. Warming drove strong WGP in both populations’ F1 and F2 above ground biomass, F1 productivity, F2 size, and only affected rhizome biomass in the unexposed population. The exposed population expressed adaptive TGP and positive carryover effects in F1 biomass, F1 productivity, F2 size, below ground biomass and rhizome biomass, and had the highest performance when re-exposed to warming. Conversely, the unexposed population only exhibited positive carryover effects for belowground as well as rhizome biomass and exhibited negative carryover effects for F2 size. These results suggest that individuals from the historically exposed site may mediate repeated warming events through epigenetic, transgenerational modifications. Despite plant trait plasticity, we found no evidence for WGP or TGP in microbial assembly between populations. Root microbiomes were consistently dominated by Methylophagaceae and Prolixibacteraceae, while rhizosphere microbiomes reflected the same dominant families as sediment-only controls. This lack of plasticity and high selectivity suggests a potential role of a consistent microbiome in plant health. Together, these results indicate that TGP may be a locally adapted trait mediated by environmental exposure history, and that plants may retain certain microbial taxa regardless of environmental conditions. 

Collaborators: Brooke Benson (UC Davis), Katie DuBois (Bangor University), Rachael Bay (UC Davis), Jay Stachowicz (UC Davis)

As a member of the MSCollaboratory, a Moore Foundation Initiative to characterize marine symbioses, we use solid-phase extraction and LC-MS/MS to isolate and characterize eelgrass-microbiome rhizosphere metabolites. This project is being conducted in collaboration with the Stachowicz, Sogin (UC Merced), and Dorrestein (UC San Diego) labs exploring the effects of eelgrass genotypic diversity on rhizosphere exometabolome production under marine heat wave versus ambient conditions. Here, we conducted a fully factorial marine heat wave (MHW) experiment on individuals from three locally adapted eelgrass populations along the central California coast: a cold-adapted population (Bodega Harbor, BH; 10-13˚C, N=480), a cool-adapted population (Blake’s Landing, BL; 15-18˚C N=480), and a warm-adapted population (Millerton Point, MP; 18-21˚C, N=480). We grew plants in mesocosms at equal densities in either population mono or polycultures under marine heat wave or ambient conditions in mesocosm. After simulating a 15 week marine heat wave, we sampled for each culture type-treatment combination’s rhizosphere metabolome and used non-targeted LC-MS/MS to examine how root exudates at the culture-level interact with genotypic diversity and temperature stress in a marine habitat forming species. In addition to the metabolome, we also measured eelgrass performance traits and sampled for eelgrass wasting disease severity and prevalence (caused by the pathogen Labyrinthula zosterae) as well as the rhizosphere microbiome for metagenomics analyses. Stay tuned for more!

Collaborators: Zach Quinlan (University of Hawai'i), Gina Chaput (UC Davis), Pieter Dorrestein & the MSCollaboratory (UCSD), Maggie Sogin (UC Merced), and Jay Stachowicz (UC Davis)

Related publications: protocols.io