Potential effects of sea-level rise on plant productivity: species-specific responses in northeast Pacific tidal marshes

Abstract

Coastal wetland plants are adapted to varying degrees of inundation. However, functional relationships between inundation and productivity are poorly characterized for most species. Determining species-specific tolerances to inundation is necessary to evaluate sea-level rise (SLR) effects on future marsh plant community composition, quantify organic matter inputs to marsh accretion, and inform predictive modeling of tidal wetland persistence. In 2 macrotidal estuaries in the northeast Pacific we grew 5 common species in experimental mesocosms across a gradient of tidal elevations to assess effects on growth. We also tested whether species abundance distributions along elevation gradients in adjacent marshes matched productivity profiles in the mesocosms. We found parabolic relationships between inundation and total plant biomass and shoot counts in Spartina foliosa and Bolboschoenus maritimus in California, USA, and in Carex lyngbyei in Oregon, USA, with maximum total plant biomass occurring at 38, 28, and 15% time submerged, respectively. However, biomass of Salicornia pacifica and Juncus balticus declined monotonically with increasing inundation. Inundation effects on the ratio of belowground to aboveground biomass varied inconsistently among species. In comparisons of field distributions with mesocosm results, B. maritimus, C. lyngbyei and J. balticus were abundant in marshes at or above elevations corresponding with their maximum productivity; however, S. foliosa and S. pacifica were frequently abundant at lower elevations corresponding with sub-optimal productivity. Our findings show species-level differences in how marsh plant growth may respond to future SLR and highlight the sensitivity of high marsh species such as S. pacifica and J. balticus to increases in flooding.

Flooding Alters Plant‐Mediated Carbon Cycling Independently of Elevated Atmospheric CO2 Concentrations

“…We observed a marginal increase in belowground root production and no response in total belowground production in response to greater average flooding depth; this is in contrast to previous studies that have shown decreases in S. alterniflora belowground biomass in response to increased flooding (Snedden et al, ; Voss et al, ; Watson et al, ). Other marsh species also typically respond strongly to flooding in biomass production above‐ and belowground (e.g., Janousek et al, ; Kirwan & Guntenspergen, ). We are confident that our 20‐cm soil depth captured realistic belowground responses in this species, especially for live roots (Darby & Turner, ).…”

The role of changing climate in driving the shift from perennial grasses to annual succulents in a Mediterranean saltmarsh

“…accelerated rates of relative sea level rise due to subsidence), and/or reductions in sediment supply, plants often cannot maintain their intertidal position (Janousek et al . ; Kirwan et al . ).…”

“…; Janousek et al . ; Kirwan et al . ), and because coastal squeeze largely prevents landward migration of the plants to higher elevation (Cencini ).…”

“…In contrast, with rapid increases in inundation (e.g. accelerated rates of relative sea level rise due to subsidence), and/or reductions in sediment supply, plants often cannot maintain their intertidal position (Janousek et al 2016;Kirwan et al 2016). This results in widespread losses of plants at the lower edge of their range but can be compensated for by shoreward expansion at the upper edges, when space permits Moffett et al 2015;Osland et al 2016).…”

“…This results in widespread losses of plants at the lower edge of their range but can be compensated for by shoreward expansion at the upper edges, when space permits Moffett et al 2015;Osland et al 2016). These problems are often exacerbated in systems with a microtidal range and irregular fluctuations in water levels (Wigand et al 2015;Janousek et al 2016).…”