Freshwater wetland plants respond nonlinearly to inundation over a sustained period.

Junbin Zhao,Gregory Starr,Sparkle L. Malone,Henrik Hartmann,Christina L. Staudhammer,Steven F. Oberbauer

doi:10.1002/ajb2.1746

Abstract

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. 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. The response of photosynthesis to inundation was nonlinear. Specifically, photosynthetic capacity (Amax ) declined by 25% in sawgrass and by 70% in muhly grass after 1-2 months of inundation. After 4 months, Amax 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. 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.

Highlights

RESPONSES OF WETLAND PLANTS TO INUNDATION limit photosynthesis under inundation stress
Given that nonstructural carbohydrate (NSC) reserves are critical for plant survival under environmental stresses (Ram et al, 2002; Hartmann and Trumbore, 2016), further investigation of plant NSC storage under different levels of inundation stress could be very important for understanding different plant responses to inundation
Sawgrass is generally distributed in areas with higher water levels and longer hydroperiods compared to muhly grass, habitats of the two species overlap in large areas of short‐hydroperiod freshwater marshes and prairies in the Everglades (Todd et al, 2010)

Summary

Introduction

RESPONSES OF WETLAND PLANTS TO INUNDATION (e.g., carboxylation, electron transport) limit photosynthesis under inundation stress. Since oxygen availability generally decreases with increases in water depth (e.g., Rose and Crumpton, 1996), high water levels might intensify the anoxic stress to plants and induce earlier and greater physiological responses by plants To investigate these relationships, one needs to measure changes in physiological processes over a substantial period of inundation at different water levels. Sawgrass is generally distributed in areas with higher water levels and longer hydroperiods compared to muhly grass, habitats of the two species overlap in large areas of short‐hydroperiod freshwater marshes and prairies in the Everglades (Todd et al, 2010). We previously found that inundation caused greater stress on photosynthesis in muhly grass than in sawgrass (Zhao et al, 2018)

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Conclusion