Nitrogen further promotes a dominant salt marsh plant in an increasingly saline environment

Abstract

Aims Human alterations of the environment are combining in unprecedented ways, making predictions of alterations to natural communities a difficult and pressing challenge. Estuarine systems have been subject to a high degree of modification, including increased nitrogen (N) inputs and altered salinity, factors important in shaping estuarine plant communities. As human populations increase and the climate changes, both N and salinity levels are likely to increase in these coastal marshes. Our objective was to evaluate the interactive effects of N and salinity on US West Coast salt marsh species; in particular, the performance of the dominant species Sarcocornia pacifica (pickleweed) alone and in mixed species assemblages. We expected increased salinity to favor S. pacifica but that N enrichment could help maintain greater species richness through use of N in salinity tolerance mechanisms. Methods We crossed treatments of N (added or not) and salinity (salt added or not) in a field experiment at a salt marsh in the San Francisco Estuary, California, USA, in each of three habitats: (i) monotypic pickleweed on the marsh plain, (ii) monotypic pickleweed along channels and (iii) mixed assemblages along channels. In a greenhouse experiment, we crossed treatments of N (added or not) and salinity (at three levels to simulate brackish to saline conditions) in (i) pots of pickleweed only and (ii) the same species mix as in the field. Important Findings N addition doubled S. pacifica biomass and branching in both channel and marsh plain habitats regardless of salinity and greatly increased its dominance over Distichlis spicata and Jaumea carnosa in mixed assemblages along channels. In the greenhouse, S. pacifica biomass increased 6-to 10-fold with N addition over the range of salinities, while D. spicata and J. carnosa biomass increased with N addition only at lower salinity levels. Thus, while localized management could influence outcomes, expected overall increases in both N and salinity with human population growth and climate change are likely to enhance the production of S. pacifica in US West Coast marshes while reducing the diversity of mixed species assemblages. This decline in diversity may have implications for the resilience of marshes already subject to multiple stressors as the climate changes.

Distribution and Invasion Potential of Limonium ramosissimum subsp. provinciale in San Francisco Estuary Salt Marshes

“…Below MHHW, higher salinity and inundation likely limit the size and reproductive output of LIRA. This fits with prior studies of Limonium species (e.g., Boorman 1971) and with upper salt marsh species in general (e.g., Cooper 1982;Seliskar 1985;Schile et al 2011;Ryan and Boyer 2012). Since LIRA grows largest in low stress conditions, we suspect it may compete most aggressively within the transition zone.…”

“…Where abiotic stress is high (e.g., via hypersalinity, anaerobic conditions or extreme desiccation), plant species able to tolerate harsh environmental conditions succeed. But where abiotic stress is low (e.g., conditions of low salinity or moderate moisture), marsh halophytes often grow taller, and/or produce more seed (Seliskar 1985;Schile et al 2011;Ryan and Boyer 2012) and interspecific competition may become a more important factor structuring marsh communities (Pennings and Callaway 1992;Crain et al 2004). …”

Effects of climate change on tidal marshes along a latitudinal gradient in California

“…Tidal marshes on the outer coast of California are dominated by perennial pickleweed, Sarcocornia pacifica, a highly salt-tolerant species (Pennings and Callaway, 1992;Ryan and Boyer, 2012). This species occurred across most elevation zones at most of the sites in the study, implying that it has some tolerance of variation in flooding as well.…”

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

“…Rising salinity may favor more salt tolerant species (Ryan & Boyer 2012, Snedden et al 2015, decrease productivity (Pearcy & Ustin 1984, Hester et al 2001, and reduce plant diversity in marsh assemblages (Engels & Jensen 2009). Increasing inundation may also be associated with lower soil redox potential (Bertness & Ellison 1987), which in turn may correspond with differences in marsh species composition (Sánchez et al 1998).…”