Nitrogen loading leads to increased carbon accretion in both invaded and uninvaded coastal wetlands

Abstract

. 2016. Nitrogen loading leads to increased carbon accretion in both invaded and uninvaded coastal wetlands. Ecosphere 7(9):e01459. 10. 1002/ecs2.1459 Abstract. Gaining a better understanding of carbon (C) dynamics across the terrestrial and aquatic landscapes has become a major research initiative in ecosystem ecology. Wetlands store a large portion of the global soil C, but are also highly dynamic ecosystems in terms of hydrology and N cycling, and are one of the most invaded habitats worldwide. The interactions between these factors are likely to determine wetland C cycling, and specifically C accretion rates. We investigated these interactions using MONDRIAN, an individual-based model simulating plant growth and competition and linking these processes to N and C cycling. We simulated the effects of different levels of (1) N loading, (2) hydroperiod, and (3) plant community (natives only vs. invasion scenarios) and their interactions on C accretion outcomes in freshwater coastal wetlands of the Great Lakes region of North America. Results showed that N loading contributed to substantial rates of C accretion by increasing NPP (net primary productivity). By mediating anaerobic conditions and slowing decomposition, hydroperiod also exerted considerable control on C accretion. Invasion success occurred with higher N loading and contributed to higher NPP, while also interacting with hydroperiod via ecosystem-internal N cycling. Invasion success by both Typha × glauca and Phragmites australis showed a strong nonlinear relationship with N loading in which an invasion threshold occurred at moderate N inputs. This threshold was in turn influenced by duration of flooding, which reduced invasion success for P. australis but not for T. × glauca. The greatest simulated C accretion rates occurred in wetlands invaded by P. australis at the highest N loading in constant anaerobic conditions. These model results suggest that while plant invasion may increase C storage in freshwater coastal wetlands, increased plant productivity (both native and invasive) due to increased N loading is the main driver of increased C accretion.

Effectiveness of cattail (Typha spp.) management techniques depends on exogenous nitrogen inputs

“…Mondrian is an individual-based model that spans several major levels of ecological organization, from individual plant physiology to ecosystem function, and is formulated through a set of algorithms in an object-oriented programming language (Visual Basic.Net). Mondrian was fully described by Currie et al (2014), with additional code development described in Martina et al (2016). Here we briefly describe the previously published model followed by more detail on additions made for the research described here.…”

“…Plants can scavenge for N by growing clonally across grid cells. Additionally, light competition occurs from shading from neighboring plants and species-specific light extinction curves that reduces the growth rate of each ramet using a Michaelis-Menten equation of relative growth rate as a function of light availability (Martina et al 2016). C and N demand to create a daughter ramet from rhizomes during clonal reproduction connects resource competition among individuals to population dynamics in a heterogeneous environment.…”

“…For a further description of C and N cycling in Mondrian, including controls on decomposition, decomposition feedbacks on N mineralization, and plant growth and uptake of N see Currie et al (2014). For a description of hydrology and anaerobic zonation and their effects on C and N cycling, see Martina et al (2016).…”

“…Because wetlands are often tightly connected to the surrounding landscape, invasive plant propagule pressure is high, resulting in higher invasion rates in wetlands and riparian areas than neighboring uplands (Brown & Peet 2003). Invasion reduces native plant diversity and some wetland ecosystem functions (Moreno-Mateos et al 2012), although community and ecosystem responses to invasion are not necessarily linear , Eviner et al 2012, Currie et al 2014, Martina et al 2016.…”

“…Once established, Typha creates a thick accumulation of litter that reduces light at the soil surface and ramps up internal nitrogen cycling (Currie et al 2014). Typha also increases carbon storage and nutrient retention in eutrophic wetlands (Martina et al 2014, Martina et al 2016. These changes in wetland ecosystem function promote the growth of Typha, making the restoration of ecosystem function vital to the longterm success of a Typha management program.…”