Contrasting Photosynthetic Responses of Two Dominant Macrophyte Species to Seasonal Inundation in an Everglades Freshwater Prairie

Malone

Oberbauer

et al. 2019

Global Change Biology

Self Cite

Climate change has altered global precipitation patterns and has led to greater variation in hydrological conditions. Wetlands are important globally for their soil carbon storage. Given that wetland carbon processes are primarily driven by hydrology, a comprehensive understanding of the effect of inundation is needed.In this study, we evaluated the effect of water level (WL) and inundation duration (ID) on carbon dioxide (CO 2 ) fluxes by analysing a 10-year (2008-2017) eddy covariance dataset from a seasonally inundated freshwater marl prairie in the Everglades National Park. Both gross primary production (GPP) and ecosystem respiration (ER) rates showed declines under inundation. While GPP rates decreased almost linearly as WL and ID increased, ER rates were less responsive to WL increase beyond 30 cm and extended inundation periods. The unequal responses between GPP and ER caused a weaker net ecosystem CO 2 sink strength as inundation intensity increased. Eventually, the ecosystem tended to become a net CO 2 source on a daily basis when either WL exceeded 46 cm or inundation lasted longer than 7 months. Particularly, with an extended period of high-WLs in 2016 (i.e., WL remained >40 cm for >9 months), the ecosystem became a CO 2 source, as opposed to being a sink or neutral for CO 2 in other years. Furthermore, the extreme inundation in 2016 was followed by a 4-month postinundation period with lower net ecosystem CO 2 uptake compared to other years. Given that inundation plays a key role in controlling ecosystem CO 2 balance, we suggest that a future with more intensive inundation caused by climate change or water management activities can weaken the CO 2 sink strength of the Everglades freshwater marl prairies and similar wetlands globally, creating a positive feedback to climate change. K E Y W O R D Secosystem respiration, flooding, gross primary production, hydrology, net ecosystem CO 2 exchange, wetland

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Intensified inundation shifts a freshwater wetland from a CO₂ sink to a source

Malone

Oberbauer

et al. 2019

Global Change Biology

Self Cite

“…Light conditions within the chamber were controlled by the internal LED light and set to levels equivalent to photosynthetically active radiation (PAR) of 2000 and 0 µmol m −2 s −1 to measure net photosynthesis ( A ) and dark respiration ( R d ) rates, respectively. Since photosynthesis of the two study species saturates below a PAR of 2000 µmol m −2 s −1 (Zhao et al, 2018), the measured net photosynthetic rate is referred to as the photosynthetic capacity ( A max ). After switching PAR from 2000 to 0 µmol m −2 s −1 , we allowed R d to stabilize for at least 30 s before the value was recorded.…”

Section: Methodsmentioning

confidence: 99%

“…Muhly grass has rolled leaf blades and fibrous roots. In a field study, we previously found that inundation caused greater stress on photosynthesis in muhly grass than in sawgrass (Zhao et al, 2018).…”

mentioning

confidence: 97%

Freshwater wetland plants respond nonlinearly to inundation over a sustained period

Malone

Staudhammer

et al. 2021

American J of Botany

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Premise: Wetland plants regularly experience physiological stresses resulting from inundation; however, plant responses to the interacting effects of water level and inundation duration are not fully understood. Methods: We conducted a mesocosm experiment on two wetland species, sawgrass (Cladium jamaicense) and muhly grass (Muhlenbergia filipes), that co-dominate many freshwater wetlands in the Florida Everglades. We tracked photosynthesis, respiration, and growth at water levels of −10 (control), 10 (shallow), and 35 cm (deep) with reference to soil surface over 6 months. Results: The response of photosynthesis to inundation was nonlinear. Specifically, photosynthetic capacity (A max ) declined by 25% in sawgrass and by 70% in muhly grass after 1-2 months of inundation. After 4 months, A max of muhly grass in the deep-water treatment declined to near zero. Inundated sawgrass maintained similar leaf respiration and growth rates as the control, whereas inundated muhly grass suppressed both respiration and growth. At the end of the experiment, sawgrass had similar nonstructural carbohydrate pools in all treatments. By contrast, muhly grass in the deep-water treatment had largely depleted sugar reserves but maintained a similar starch pool as the control, which is critical for post-stress recovery. Conclusions: Overall, the two species exhibited nonlinear and contrasting patterns of carbon uptake and use under inundation stress, which ultimately defines their strategies of surviving regularly flooded habitats. The results suggest that a future scenario with more intensive inundation, due to the water management and climate change, may weaken the dominance of muhly grass in many freshwater wetlands of the Everglades.

“…Inundation creates anaerobic conditions in the flooded soil that exert a physiological stress on wetland plants depending on the inundation-tolerance of a species (Liu et al 2018;Zhao et al 2018). For less inundation-tolerant plants, this stress limits photosynthetic leaf area due to partial submergence of shoots and leaves (Schedlbauer et al 2010;Jimenez et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Inundation depth affects ecosystem CO2 and CH4 exchange by changing plant productivity in a freshwater wetland in the Yellow River Estuary

Song

et al. 2020

Plant Soil

Aims Climate change (extreme rainfall) and water management activities have led to variation in hydrological regimes, especially inundation, which may alter the function and structure of wetlands as well as wetlandatmosphere carbon (C) exchange. However, the degree to which different inundation depths (standing water depth above the soil surface) affect ecosystem CH 4 fluxes, ecosystem respiration (R eco ) and net ecosystem CO 2 exchange (NEE) remains uncertain in wetland ecosystems.Methods We conducted a field inundation depth manipulation experiment (no inundation, i.e. only natural precipitation; 0, water-saturated; 5, 10, 20, 30 and 40 cm inundation depth) in a freshwater wetland of the Yellow River Delta, China. The CH 4 fluxes, R eco and NEE were measured with a static chamber technique during the growing seasons (May-October) of 2018 and 2019. Results Inundation depth significantly increased plant shoot density, above-water level leaf area index (WLAI), above-water level plant shoot height (WHeight), aboveground and belowground biomass of