An invasive wetland grass primes deep soil carbon pools

Abstract

Understanding the processes that control deep soil carbon (C) dynamics and accumulation is of key importance, given the relevance of soil organic matter (SOM) as a vast C pool and climate change buffer. Methodological constraints of measuring SOM decomposition in the field prevent the addressing of real-time rhizosphere effects that regulate nutrient cycling and SOM decomposition. An invasive lineage of Phragmites australis roots deeper than native vegetation (Schoenoplectus americanus and Spartina patens) in coastal marshes of North America and has potential to dramatically alter C cycling and accumulation in these ecosystems. To evaluate the effect of deep rooting on SOM decomposition we designed a mesocosm experiment that differentiates between plant-derived, surface SOM-derived (0-40 cm, active root zone of native marsh vegetation), and deep SOM-derived mineralization (40-80 cm, below active root zone of native vegetation). We found invasive P. australis allocated the highest proportion of roots in deeper soils, differing significantly from the native vegetation in root : shoot ratio and belowground biomass allocation. About half of the CO produced came from plant tissue mineralization in invasive and native communities; the rest of the CO was produced from SOM mineralization (priming). Under P. australis, 35% of the CO was produced from deep SOM priming and 9% from surface SOM. In the native community, 9% was produced from deep SOM priming and 44% from surface SOM. SOM priming in the native community was proportional to belowground biomass, while P. australis showed much higher priming with less belowground biomass. If P. australis deep rooting favors the decomposition of deep-buried SOM accumulated under native vegetation, P. australis invasion into a wetland could fundamentally change SOM dynamics and lead to the loss of the C pool that was previously sequestered at depth under the native vegetation, thereby altering the function of a wetland as a long-term C sink.

Complementary responses of morphology and physiology enhance the stand‐scale production of a model invasive species under elevated CO2 and nitrogen

“…stem height and leaf area). In addition, P. australis invasions are not likely to be limited by N availability once established given the lineage's ability to root deeply (Mozdzer, Langley, Mueller, & Megonigal, 2016) and increase N availability by priming the microbial decomposition of organic matter (Bernal, Megonigal, & Mozdzer, 2017).…”

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

“…We therefore conclude that other parameters exerted overriding influence on k, mainly masking temperature effects and have not been captured by our experimental design. For instance, we do not have data on plant-biomass parameters that are thought to exert strong control on decomposition in tidal wetlands through priming effects (Wolf et 325 al., 2007;Mueller et al, 2016;Bernal et al, 2017). Likewise, large differences in site elevation and hydrology could have induced high variability in k across sites and masked potential temperature effects.…”

“…Curiel Yuste et al, 2007), and S should at least not expected to be high in the top-soil environment of tidal wetlands. Potentially, moisture and nutrient supply are even high enough to allow for considerable break down of non-hydrolysable compounds within three months of deployment, such as lignin (Berg & McClaugherty, 2003;Knorr et al, 2005;Feng et al, 440 2010; Duboc et al, 2014). Second, different protocols and methods to determine hydrolysable and non-hydrolysable fractions of plant materials exist and lead to variable results.…”

Drivers and Mechanisms of Peat Collapse in Coastal Wetlands

“…Wetlands, although occupying only ~5-8% of the earth's surface, store 20-30% of soil carbon (C) because of their high productivity and low decomposition rate Gosselink 2007, Nahlik and). Yet wetlands are highly susceptible to ecosystem fluctuations such as changes in hydrology, water chemistry, and vegetation regime , Bernal et al 2017. Coastal wetlands are particularly vulnerable to saltwater intrusion.…”