Fire can lead to transitions between forest and grassland ecosystems and trigger positive feedbacks to climate warming by releasing CO2into the atmosphere. Climate change is projected to increase the prevalence and severity of wildfires. However, fire effects on the fate and impact of terrestrial organic matter (i.e., terrestrial subsidies) in aquatic ecosystems are unclear. Here, we performed a gradient design experiment in freshwater pond mesocosms adding 15 different amounts of burned or unburned plant detritus and tracking the chronology of detritus effects at 10, 31, 59, and 89 days. We show terrestrial subsidies had time‐ and mass‐dependent, non‐linear impacts on ecosystem function that influenced dissolved organic carbon (DOC), ecosystem metabolism (net primary production and respiration), greenhouse gas concentrations (carbon dioxide [CO2], methane [CH4]), and trophic transfer. These impacts were shifted by fire treatment. Burning increased the elemental concentration of detritus (increasing %N, %P, %K), with cascading effects on ecosystem function. Mesocosms receiving burned detritus had lower [DOC] and [CO2] and higher dissolved oxygen (DO) through Day 59. Fire magnified the effects of plant detritus on aquatic ecosystem metabolism by stimulating photosynthesis and respiration at intermediate detritus‐loading through Day 89. The effect of loading on DO was similar for burned and unburned treatments (Day 10); however, burned‐detritus in the highest loading treatments led to sustained hypoxia (through Day 31), and long‐term destabilization of ecosystem metabolism through Day 89. In addition, fire affected trophic transfer by increasing autochthonous nitrogen source utilization and reducing the incorporation of15N‐labeled detritus into plankton biomass, thereby reducing the flux of terrestrial subsidies to higher trophic levels. Our results indicate fire chemically transforms plant detritus and alters the role of aquatic ecosystems in processing and storing carbon. Wildfire may therefore induce shifts in ecosystem functions that cross the boundary between aquatic and terrestrial habitats.
Coral reefs are naturally exposed to daily and seasonal variations in environmental oxygen levels, which can be exacerbated in intensity and duration by anthropogenic activities. However, coral’s diel oxygen dynamics and fermentative pathways remain poorly understood. Here, continuous oxygen microelectrode recordings in the coral diffusive boundary layer revealed hyperoxia during daytime and hypoxia at nighttime resulting from net photosynthesis and net respiration, respectively. The activities of the metabolic enzymes citrate synthase (CS), malate dehydrogenase, and strombine dehydrogenase remained constant throughout the day/night cycle, suggesting that energy metabolism was regulated through adjustments in metabolite fluxes and not through changes in enzyme abundance. Liquid chromatography-mass spectrometry analyses identified strombine as coral’s main fermentative end product. Strombine levels peaked as oxygen became depleted at dusk, indicating increased fermentation rates at the onset of nightly hypoxia, and again at dawn as photosynthesis restored oxygen and photosynthate supply. When these peaks were excluded from the analyses, average strombine levels during the day were nearly double those at night, indicating sifnificant fermentation rates even during aerobic conditions. These results highlight the dynamic changes in oxygen levels in the coral diffusive boundary layer, and the importance of fermentative metabolism for coral biology.
more » « less- NSF-PAR ID:
- 10201854
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 10
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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