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ArticleImplications of improved representations of plant respiration in a changing climate(Nature Publishing Group, 2017-11-17) Huntingford, Chris ; Atkin, Owen K. ; Martinez-de la Torre, Alberto ; Mercado, Lina M. ; Heskel, Mary ; Harper, Anna B. ; Bloomfield, Keith J. ; O'Sullivan, Odhran S. ; Reich, Peter B. ; Wythers, Kirk R. ; Butler, Ethan E. ; Chen, Ming ; Griffin, Kevin L. ; Meir, Patrick ; Tjoelker, Mark ; Turnbull, Matthew H. ; Sitch, Stephen ; Wiltshire, Andrew J. ; Malhi, YadvinderLand-atmosphere exchanges influence atmospheric CO2. Emphasis has been on describing photosynthetic CO2 uptake, but less on respiration losses. New global datasets describe upper canopy dark respiration (Rd) and temperature dependencies. This allows characterisation of baseline Rd, instantaneous temperature responses and longer-term thermal acclimation effects. Here we show the global implications of these parameterisations with a global gridded land model. This model aggregates Rd to whole-plant respiration Rp, driven with meteorological forcings spanning uncertainty across climate change models. For pre-industrial estimates, new baseline Rd increases Rp and especially in the tropics. Compared to new baseline, revised instantaneous response decreases Rp for mid-latitudes, while acclimation lowers this for the tropics with increases elsewhere. Under global warming, new Rd estimates amplify modelled respiration increases, although partially lowered by acclimation. Future measurements will refine how Rd aggregates to whole-plant respiration. Our analysis suggests Rp could be around 30% higher than existing estimates.
ArticleSource to sink : evolution of lignin composition in the Madre de Dios River system with connection to the Amazon basin and offshore(John Wiley & Sons, 2016-05-21) Feng, Xiaojuan ; Feakins, Sarah J. ; Liu, Zongguang ; Ponton, Camilo ; Wang, Renée Z. ; Karkabi, Elias ; Galy, Valier ; Berelson, William M. ; Nottingham, Andrew T. ; Meir, Patrick ; West, A. JoshuaWhile lignin geochemistry has been extensively investigated in the Amazon River, little is known about lignin distribution and dynamics within deep, stratified river channels or its transformations within soils prior to delivery to rivers. We characterized lignin phenols in soils, river particulate organic matter (POM), and dissolved organic matter (DOM) across a 4 km elevation gradient in the Madre de Dios River system, Peru, as well as in marine sediments to investigate the source-to-sink evolution of lignin. In soils, we found more oxidized lignin in organic horizons relative to mineral horizons. The oxidized lignin signature was maintained during transfer into rivers, and lignin was a relatively constant fraction of bulk organic carbon in soils and riverine POM. Lignin in DOM became increasingly oxidized downstream, indicating active transformation of dissolved lignin during transport, especially in the dry season. In contrast, POM accumulated undegraded lignin downstream during the wet season, suggesting that terrestrial input exceeded in-river degradation. We discovered high concentrations of relatively undegraded lignin in POM at depth in the lower Madre de Dios River in both seasons, revealing a woody undercurrent for its transfer within these deep rivers. Our study of lignin evolution in the soil-river-ocean continuum highlights important seasonal and depth variations of river carbon components and their connection to soil carbon pools, providing new insights into fluvial carbon dynamics associated with the transfer of lignin biomarkers from source to sink.