Photosynthetic variation and carbon isotope discrimination in invasive wetland grasses in response to flooding

Abstract

Ecological success is dependent on physiological tolerance to abiotic stress. This is particularly meaningful when considering the success of invasive plants in wetland systems. In this study, physiological flooding tolerance was measured in invasive Phragmites australis, Phalaris arundinacea, Sorghum halepense, and native Spartina pectinata. Plants were maintained at deep flooding, medium flooding, low flooding, and dry conditions in a greenhouse, and their responses were measured at 7 and 28 days of treatment. Photosynthetic rates in Sorghum were maximized at deep flooding conditions at 7 days, but at 28 days all deep and medium flooded Sorghum were dead or dying. Photosynthesis in Phragmites and Spartina were saturated at deep flooding conditions whereas photosynthesis was saturated in Phalaris under medium flooding at 28 days. Increased flooding caused higher stomatal conductance and lower δ 13C in Phragmites, but the opposite occurred in Phalaris. As flooding increased for Sorghum and Spartina, δ 13C remained unchanged. Activities of the anaerobic respiration enzyme alcohol dehydrogenase in roots suggested invasive Phragmites was the most tolerant of flooding. Spartina was the next most flood tolerant of the four species, slightly less tolerant compared to Phragmites. Phalaris was moderately flood tolerant and Sorghum was flood sensitive. Invasion of grasses in wetlands might be helped by increased photosynthesis in short-term flooding.