Climate and Nutrient-Driven Regime Shifts of Cyanobacterial Communities in Low-Latitude Plateau Lakes

Abstract

Cyanobacterial blooms that form in response to climate warming and nutrient enrichment in freshwater lakes have become a global environmental challenge. Historical legacy effects and the mechanisms underlying cyanobacterial community succession are not well understood, especially for plateau lakes that are important global freshwater resources. This study investigated the temporal dynamics of cyanobacterial communities over centuries in response to nutrient enrichment and climate warming in low-latitude plateau lakes using high-throughput DNA sequencing of sedimentary DNA combined with traditional paleolimnological analyses. Our results confirmed that nutrients and climate warming drive shifts in cyanobacterial communities over time. Cyanobacterial community turnover was pronounced with regime shifts toward new ecological states, occurring after exceeding a tipping point of aquatic total phosphorus (TP). The inferred species interactions, niche differentiation, and identity of keystone taxa significantly changed after crossing the aquatic TP ecological threshold, as demonstrated by network analysis of cyanobacterial taxa. Further, the contribution of aquatic TP to cyanobacterial community dynamics was greater than that of air temperature when lakes were in an oligotrophic state. In contrast, as the aquatic TP threshold was exceeded, the contribution to community dynamics by air temperature increased and potentially surpassed that of aquatic TP. Overall, these results provide new evidence for how past nutrient levels in lacustrine ecosystems influence contemporary cyanobacterial community responses to global warming in low-latitude plateau lakes.

Century-Long Homogenization of Algal Communities Is Accelerated by Nutrient Enrichment and Climate Warming in Lakes and Reservoirs of the North Temperate Zone

“…Lake Chaohu is a shallow eutrophic lake in eastern China located between the Huaihe River watershed and the Yangtze River Delta . Lakes Erhai, Lugu, and Fuxian are deep-water lakes located on the Yunnan–Guizhou Plateau, while Lake Erhai is a mesotrophic lake and the other two are oligotrophic lakes . Lake Constance is a typical large peri-alpine lake of glacial origin, has undergone oligotrophication–eutrophication–reoligotrophication in the past century, and provides a comparison with a different successional trajectory relative to the trophic states in the other lakes .…”

“…The Lake Constance sediment core data were derived from a previous study, while the sediment cores from the other six sites were collected in 2017 and 2018. The EA and CYA communities from Lake Chaohu and the CYA communities in Lakes Erhai, Lugu, and Fuxian were investigated in our previous studies. , Briefly, three duplicate sediment cores were retrieved from the deepest part of each lake site using a gravity corer and a PMMA tube on the corer. The core samples were subjected to molecular, dating, and chemical analyses.…”

“…137 Cs and 210 Pb fallout radionuclide analyses were used to date the sediment cores from the seven lakes and reservoirs using gamma ray spectrometry (ORTEC, USA) on a DSPEC jr 2.0 multichannel spectrometer coupled to a GWL-120-15 well detector. We have previously described detailed protocols for sediment dating and associated results. , Sediment accumulation rates and accurate chronologies were obtained for high-resolution sampling using the sediment age models (Table S1 and Supplementary Data 1).…”

“…In the present study, we used sed-DNA records to investigate the temporal patterns of eukaryotic algal (EA) and cyanobacterial (CYA) communities since the onset of the twentieth century by applying 18S and 16S rRNA gene-based high-throughput sequencing, respectively, in five lakes and two reservoirs in the North Temperate Zone. These lakes and reservoirs exhibit distinct geographic and limnological features including different trajectories of the trophic status, which enables the analysis of succession and assembly of phytoplankton communities among and within lakes over contrasting temporal and spatial scales. − In particular, the goal of this study was to thoroughly document changes in lacustrine EA and CYA diversity over the twentieth century, in addition to evaluating their mechanisms of community assembly. Molecular analysis via sed-DNA metabarcoding was used to address three primary questions: (i) what are the temporal trends of α and β diversity in EA and CYA communities over the last century within each lake or reservoir?…”

Changes in Ciliate Communities Reveal Modification of Lake Functioning Over the Last Century

“…The development of molecular biology techniques to target DNA molecules preserved in lake sediments (sed-DNA) largely expanded the eld of paleolimnology over the last decade 14 . For instance, applying molecular biology tools in paleolimnological investigations allowed to reconstruct historical freshwater biodiversity 15 , as well as uncovered past ecological changes of a wide range of organisms, including specimens for which visible remains are not preserved 16,17 . This includes the reconstruction of the long-term dynamic of micro-organisms 18 which represent the largest source of biodiversity and ecological functions, but have long been omitted from debates concerning the response of the global biodiversity, in part due to the lack of data 19 .…”