Experimental warming promotes phytoplankton species sorting towards cyanobacterial blooms and leads to potential changes in ecosystem functioning

• Published in: The Science of the total environment Vol. 924; p. 171621
• Main Authors: Moresco, Geovani Arnhold, Dias, Juliana Déo, Cabrera-Lamanna, Lucía, Baladán, Claudia, Bizic, Mina, Rodrigues, Luzia Cleide, Meerhoff, Mariana
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 10.05.2024
• Subjects: CO2 flux; Cyanobacterial blooms; Eutrophication; Heating experiment; Resource use efficiency; Heating experiment; Cyanobacterial blooms; CO2 flux; Resource use efficiency; Eutrophication; CO flux
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2024.171621

A positive feedback loop where climate warming enhances eutrophication and its manifestations (e.g., cyanobacterial blooms) has been recently highlighted, but its consequences for biodiversity and ecosystem functioning are not fully understood. We conducted a highly replicated indoor experiment with a species-rich subtropical freshwater phytoplankton community. The experiment tested the effects of three constant temperature scenarios (17, 20, and 23 °C) under high-nutrient supply conditions on community composition and proxies of ecosystem functioning, namely resource use efficiency (RUE) and CO2 fluxes. After 32 days, warming reduced species richness and promoted different community trajectories leading to a dominance by green algae in the intermediate temperature and by cyanobacteria in the highest temperature treatments. Warming promoted primary production, with a 10-fold increase in the mean biomass of green algae and cyanobacteria. The maximum RUE occurred under the warmest treatment. All treatments showed net CO2 influx, but the magnitude of influx decreased with warming. We experimentally demonstrated direct effects of warming on phytoplankton species sorting, with negative effects on diversity and direct positive effects on cyanobacteria, which could lead to potential changes in ecosystem functioning. Our results suggest potential positive feedback between the phytoplankton blooms and warming, via lower net CO2 sequestration in cyanobacteria-dominated, warmer systems, and add empirical evidence to the need for decreasing the likelihood of cyanobacterial dominance. With warming, natural phytoplankton communities became poorer but more productive, leading to a dominance by green algae at intermediate temperatures and by cyanobacteria (and lower overall phytoplankton diversity) and a greater Resource Use Efficiency (RUE) at higher temperatures. Warming also changed net fluxes of CO2, driving the systems towards a reduced net uptake of CO2 despite the higher primary production. [Display omitted] •Warming can promote changes in biodiversity and functioning of fresh waters.•We tested warming effects on phytoplankton diversity, resource use efficiency and CO2 fluxes.•Indoor warming experiment with natural subtropical phytoplankton communities.•Warming led to species sorting, dominance of cyanobacteria, higher RUE and lower CO2 uptake.•Warming can directly promote cyanobacteria and potentially result in contingent major ecosystem changes.