Abstract
Climate change impacts, such as accelerated sea‐level rise, will affect stress gradients, yet impacts on competition/stress tolerance trade‐offs and shifts in distributions are unclear. Ecosystems with strong stress gradients, such as estuaries, allow for space‐for‐time substitutions of stress factors and can give insight into future climate‐related shifts in both resource and nonresource stresses. We tested the stress gradient hypothesis and examined the effect of increased inundation stress and biotic interactions on growth and survival of two congeneric wetland sedges, Schoenoplectus acutus and Schoenoplectus americanus. We simulated sea‐level rise across existing marsh elevations and those not currently found to reflect potential future sea‐level rise conditions in two tidal wetlands differing in salinity. Plants were grown individually and together at five tidal elevations, the lowest simulating an 80‐cm increase in sea level, and harvested to assess differences in biomass after one growing season. Inundation time, salinity, sulfides, and redox potential were measured concurrently. As predicted, increasing inundation reduced biomass of the species commonly found at higher marsh elevations, with little effect on the species found along channel margins. The presence of neighbors reduced total biomass of both species, particularly at the highest elevation; facilitation did not occur at any elevation. Contrary to predictions, we documented the competitive superiority of the stress tolerator under increased inundation, which was not predicted by the stress gradient hypothesis. Multifactor manipulation experiments addressing plant response to accelerated climate change are integral to creating a more realistic, valuable, and needed assessment of potential ecosystem response. Our results point to the important and unpredicted synergies between physical stressors, which are predicted to increase in intensity with climate change, and competitive forces on biomass as stresses increase.
Highlights
Climate change will influence plant communities through shifts in temperature, carbon dioxide concentrations, precipitation, nitrogen, and sea level, among other abiotic factors, and shifts are apparent already in plant distribution, productivity, and phenology (Dieleman et al, 2012; Garcia, Cabeza, Rahbek, & Araújo, 2014; Jump & Peñuelas, 2005; Parmesan & Yohe, 2003; Sproull, Quigley, Sher, & González, 2015; Zavaleta, Shaw, Chiariello, Mooney, & Field, 2003)
The critical abiotic factors affecting plant distributions are anaerobic conditions created through inundation duration and depth and salinity (Howard, Biagas, & Allain, 2016; McKee, Cahoon, & Feller, 2007; McKee & Mendelssohn, 1989; Mendelssohn, McKee, & Patrick, 1981), and these factors are likely to be highly affected by climate change (Kirwan & Megonigal, 2013)
While the impact and interactions of abiotic and biotic stresses are likely to shift with climate change (Brooker, 1996; Suttle, Thomsen, & Power, 2007), little is known about the role of accelerated climate change in the context of trade-offs among stress tolerance, competition, and facilitation (Adler, Dalgleish, & Ellner, 2012; Gilman, Urban, Tewksbury, Gilchrist, & Holt, 2010; Maestre et al, 2010)
Summary
Climate change will influence plant communities through shifts in temperature, carbon dioxide concentrations, precipitation, nitrogen, and sea level, among other abiotic factors, and shifts are apparent already in plant distribution, productivity, and phenology (Dieleman et al, 2012; Garcia, Cabeza, Rahbek, & Araújo, 2014; Jump & Peñuelas, 2005; Parmesan & Yohe, 2003; Sproull, Quigley, Sher, & González, 2015; Zavaleta, Shaw, Chiariello, Mooney, & Field, 2003). With facilitation, inundation-tolerant species possess a high proportion of aerenchymatous tissue, which increases oxygen flow to belowground organs and subsequently can oxygenate soil, increase soil redox potential, and enable growth of species less tolerant of anoxic conditions (Hacker & Bertness 1995; Kludze & DeLaune, 1995; Callaway & King, 1996a,b; Jackson & Armstrong, 1999). Examining whether these processes can occur within this relatively simple system could give insight into similar dynamics in other ecosystems with strong stress gradients such as chaparral, deserts, and the rocky intertidal. Based on current marsh distributions, we hypothesized that: (1) without competition, S. acutus would perform better than its congener, S. americanus, under increased inundation stress; (2) S. americanus would have a competitive advantage under conditions of lower inundation stress; and (3) when grown together, S. acutus would facilitate the growth of its congener under the greatest inundation stress (increased facilitation via the alleviation of anaerobic conditions) owing to its potential to aerate anoxic soil through its rich aerenchymatous tissue (Sloey, Howard, & Hester, 2016)
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