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Strong leaf surface basification and CO 2 limitation of seagrass induced by epiphytic biofilm microenvironments
Author(s) -
Brodersen Kasper Elgetti,
Koren Klaus,
Revsbech Niels Peter,
Kühl Michael
Publication year - 2020
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/pce.13645
Subject(s) - epiphyte , seagrass , phyllosphere , zostera marina , botany , photosynthesis , biogeochemical cycle , biology , environmental chemistry , eutrophication , ecology , chemistry , ecosystem , nutrient , genetics , bacteria
Coastal eutrophication is a growing problem worldwide, leading to increased epiphyte overgrowth of seagrass leaves. Yet little is known about how epiphytes affect key biogeochemical conditions and processes in the seagrass phyllosphere. We used electrochemical microsensors to measure microgradients of O 2 , pH, and CO 2 at the bare and epiphyte‐covered leaf surface of seagrass ( Zostera marina L.) to determine effects of epiphytes on the leaf chemical microenvironment. Epiphytes result in extreme daily fluctuations in pH, O 2 , and inorganic carbon concentrations at the seagrass leaf surface severely hampering the plant's performance. In light, leaf epiphyte biofilms and their diffusive boundary layer lead to strong basification, markedly reducing the CO 2 and HCO 3 ‐ availability at the leaf surface, leading to reduced photosynthetic efficiency as a result of carbon limitation and enhanced photorespiration. With epiphytes, leaf surface pH increased to >10, thereby exceeding final pH levels (~9.62) and CO 2 compensation points for active photosynthesis. In darkness, epiphyte biofilms resulted in increased CO 2 and hypoxia at the leaf surface. Epiphytes can lead to severe carbon limitation in seagrasses owing to strong phyllosphere basification leading to CO 2 depletion and costly, yet limiting, HCO 3 ‐ utilization, increasing the risk of plant starvation.