The fate of C₄ and C₃ macrophyte carbon in central Amazon floodplain waters: Insights from a batch experiment

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• 作者：J.M. Mortillaro^a ; ⁱ ; ^{jean-michel.mortillaro@cirad.fr" class="auth_mail" title="E-mail the corresponding author} ; C. Passarelli^a ; G. Abril^b ; ^c ; C. Hubas^a ; P. Alberic^d ; L.F. Artigas^e ; M.F. Benedetti^f ; N. Thiney^a ; P. Moreira-Turcq^g ; M.A.P. Perez^c ; ^f ; L.O. Vidal^h ; T. Meziane^a
• 关键词：Central amazon ; Floodplains ; Fatty acids ; Stables isotopes ; Macrophytes ; Degradation
• 刊名：Limnologica - Ecology and Management of Inland Waters
• 出版年：2016
• 出版时间：July 2016
• 年：2016
• 卷：59
• 期：Complete
• 页码：90-98
• 全文大小：1846 K

文摘

The central Amazon floodplains are particularly productive ecosystems, where a large diversity of organic carbon sources are available for aquatic organisms. Despite the fact that C₄ macrophytes generally produce larger biomasses than C₃ macrophytes, food webs in the central Amazon floodplains appear dominantly based on a C₃ carbon source.

In order to investigate the respective fate and degradation patterns of C₄ and C₃ aquatic plant-derived material in central Amazon floodplains, we developed a 23-days batch experiment. Fatty acid and carbon concentrations as well as stable isotope compositions were monitored over time in 60 L tanks. These tanks contained Amazon water, with different biomasses of C₃ and C₄ macrophyte, representative of in situ densities occurring in central Amazon floodplains.

In the C₄Paspalum repens treatments, organic (POC, DOC) and inorganic carbon (DIC) got rapidly enriched in ¹³C, whereas in the C₃Salvinia auriculata treatments, POC and DOC showed little change in concentration and isotopic composition, and DIC got depleted in ¹³C. The contribution of P. repens to POC and DOC was estimated to reach up to 94.2 and 70.7%, respectively. In contrast, no differences were reported between the C₃S. auriculata and control treatments, an observation attributed to the lower C₃ biomass encountered in the field, to a slower degradation rate of C₃ compared to C₄ compounds, and to similar isotopic compositions for river POC and DOC, and C₃ compounds.

The ¹³C enrichments of POC, DOC, and DIC from P. repens treatments were attributed to an enhanced bacterially-mediated hydrolysis and mineralization of C₄ material. Evolutions of bacterial abundance and branched fatty acid concentrations confirmed the role of heterotrophic microbial communities in the high P. repens decomposition rate. Our experiment highlights the predominant role of C₄ aquatic plants, as a large source of almost entirely biodegradable organic matter available for heterotrophic activity and CO₂ outgassing to the atmosphere.