Global synthesis of the temperature sensitivity of leaf litter breakdown in streams and rivers

• Published in: Global change biology 2017-08, Vol.23 (8), p.3064-3075
• Main Authors: Follstad Shah, Jennifer J., Kominoski, John S., Ardón, Marcelo, Dodds, Walter K., Gessner, Mark O., Griffiths, Natalie A., Hawkins, Charles P., Johnson, Sherri L., Lecerf, Antoine, LeRoy, Carri J., Manning, David W. P., Rosemond, Amy D., Sinsabaugh, Robert L., Swan, Christopher M., Webster, Jackson R., Zeglin, Lydia H.
• Format: Article
• Language: English
• Subjects: Activation energy; Alnus; Atmosphere; Availability; Breakdown; Carbon; Carbon - chemistry; carbon cycling; Categories; Chemistry; Climate; climate chagne; Climate Change; Conduits; Correlation; Creeks & streams; detritivore; Detritivores; Downstream; Ecosystem; Energy; Energy measurement; ENVIRONMENTAL SCIENCES; Genera; leaf chemistry; Leaf litter; Leaves; Litter; Marine environment; Mathematical analysis; metabolic theory; Metabolism; microbe; Microorganisms; Organic matter; Plant Leaves; Reservoirs; Rivers; Sensitivity; Streams; Synthesis; Temperature; Temperature effects; temperature sensitivity; Tropical climate; Water availability; Water temperature
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.13609

Streams and rivers are important conduits of terrestrially derived carbon (C) to atmospheric and marine reservoirs. Leaf litter breakdown rates are expected to increase as water temperatures rise in response to climate change. The magnitude of increase in breakdown rates is uncertain, given differences in litter quality and microbial and detritivore community responses to temperature, factors that can influence the apparent temperature sensitivity of breakdown and the relative proportion of C lost to the atmosphere vs. stored or transported downstream. Here, we synthesized 1025 records of litter breakdown in streams and rivers to quantify its temperature sensitivity, as measured by the activation energy (Ea, in eV). Temperature sensitivity of litter breakdown varied among twelve plant genera for which Ea could be calculated. Higher values of Ea were correlated with lower‐quality litter, but these correlations were influenced by a single, N‐fixing genus (Alnus). Ea values converged when genera were classified into three breakdown rate categories, potentially due to continual water availability in streams and rivers modulating the influence of leaf chemistry on breakdown. Across all data representing 85 plant genera, the Ea was 0.34 ± 0.04 eV, or approximately half the value (0.65 eV) predicted by metabolic theory. Our results indicate that average breakdown rates may increase by 5–21% with a 1–4 °C rise in water temperature, rather than a 10–45% increase expected, according to metabolic theory. Differential warming of tropical and temperate biomes could result in a similar proportional increase in breakdown rates, despite variation in Ea values for these regions (0.75 ± 0.13 eV and 0.27 ± 0.05 eV, respectively). The relative proportions of gaseous C loss and organic matter transport downstream should not change with rising temperature given that Ea values for breakdown mediated by microbes alone and microbes plus detritivores were similar at the global scale. Warmer water enhances decomposition of organic matter in streams and rivers, but it is unclear if climate change will result in more carbon emitted to the atmosphere or transported to the ocean. We assembled over 1000 published data points on leaf litter breakdown in streams and rivers globally to assess how rates of breakdown will change with elevated temperature. Across 85 plant genera, we found that rates may increase only half as much as expected should water temperature rise by 1–4 °C. Among 12 pl