Latitudinal trends in Spartina alterniflora productivity and the response of coastal marshes to global change

Abstract

Marshes worldwide are actively degrading in response to increased sea level rise rates and reduced sediment delivery, though the growth rate of vegetation plays a critical role in determining their stability. We have compiled 56 measurements of aboveground annual productivity for Spartina alterniflora, the dominant macrophyte in North American coastal wetlands. Our compilation indicates a significant latitudinal gradient in productivity, which we interpret to be determined primarily by temperature and/or the length of growing season. Simple linear regression yields a 27 g m À2 yr À1 increase in productivity with an increase of mean annual temperature by 1 1C. If temperatures warm 2-4 1C over the next century, then marsh productivity may increase by 10-40%, though physiological research suggests that increases in the north could potentially be offset by some decreases in the south. This increase in productivity is roughly equivalent to estimates of marsh lost due to future sea level change. If a warming-induced stimulation of vegetation growth will enhance vertical accretion and limit erosion, then the combined effects of global change may be to increase the total productivity and ecosystem services of tidal wetlands, at least in northern latitudes.

Cordgrass Biomass in Salt Marshes

“…600 g DW m -2 yr -1 following Castillo et al, 2008a) than North American marshes of S. alterniflora (Craft et al, 1999(Craft et al, , 2002(Craft et al, , 2003Edwards & Mills, 2005), which seems to be related to warmer winters in Iberian salt marshes. Thus, S. alterniflora productivity decreases with latitude and air temperature along the western Atlantic coast of North America (Kirwan et al, 2009). Other climatic factors such as rainfall that determinates erosion, salinity and flooding may also limit cordgrasses biomass accumulation (Gonzalez Trilla et al, 2009).…”

“…More complete sampling would result from recording biomass variations throughout the year. However, recording maximum biomass accumulation at the end of the growing season seems to be a good method for comparing studies (Kirwan et al, 2009). The above-ground biomass of cordgrasses may also be estimated by allometric relationships relating biomass with shoot density and shoot height (Castillo et al, 2008a;Tyrrell et al, 2008;Gonzalez Trilla et al, 2009).…”

Temperature sensitivity of organic-matter decay in tidal marshes

“…Long-term elevated CO 2 experiments demonstrate a sustained increase in belowground organic-matter production (Erickson et al, 2007), and an increase in the rate of marsh-elevation gain that can counteract the effects of sea-level rise in brackish marshes dominated by C 3 plants (Langley et al, 2009). Warming may have a similar impact on salt marshes dominated by C 4 plants, where enhanced above-ground productivity would presumably lead to enhanced mineral sediment deposition (Charles and Dukes, 2009;Kirwan et al, 2009;Gedan et al, 2011;Mudd et al, 2010). Moderate increases in flooding frequency associated with sea-level rise may increase rates of above and below-ground productivity in both salt and brackish marshes (Morris et al, 2002; without altering decomposition rates (Blum and Christian, 2004;Kirwan et al, 2013).…”

“…Complex interactions between soil elevation relative to sea level and vegetation characteristics control the response of coastal carbon pools to climate change (Kirwan and Mudd, 2012;Langley and Megonigal, 2010). Long-term elevated CO 2 experiments demonstrate a sustained increase in belowground organic-matter production (Erickson et al, 2007), and an increase in the rate of marsh-elevation gain that can counteract the effects of sea-level rise in brackish marshes dominated by C 3 plants (Langley et al, 2009).…”

Global change effects on decomposition processes in tidal wetlands: implications from a global survey using standardized litter

“…Indeed, Chmura and colleagues hypothesized stimulated microbial decomposition at higher temperatures to 340 be the responsible driver for this relationship. Plant production and thus OM input is known to increase with latitude and temperature in tidal wetlands (Charles & Dukes, 2009;Gedan & Bertness, 2009;Kirwan et al, 2009;Baldwin et al, 2014), but this increase seems to be more than compensated by higher microbial decomposition. Working on the same spatial scale as Chmura et al (2003), our study strongly supports this hypothesis and provides the mechanistic insight into the 345 temperature control of OM decomposition as an important driver of C sequestration tidal wetlands.…”