María Eugenia Llames

Shallow lakes are particularly sensitive to climate change and significantly affected by human activities. As hotspots of biodiversity, it is essential to understand how aquatic communities respond to hydroclimatic and terrestrial drivers, and how compositional changes translate into lake functioning. This study examines ecological transitions in Lake Kakel Huincul (Argentina, South America) over the past 400 years, from the late Little Ice Age (LIA) to the Current Warm Period (CWP). We analyzed zooplankton and zoobenthos composition and size structure, and reconstructed submerged macrophyte establishment and herbivory. We used Generalized Additive Models to detect ecological transitions and Dynamic Linear Models to identify regime shifts based on cladoceran remains. The first regime shift occurred around 1880-1900 CE, characterized by changes in zooplankton composition, including the collapse of Daphnia, a decrease in zooplankton size structure, and the recolonization of submerged macrophytes. These changes coincided with dry conditions during the end of the LIA to the onset of the wetter CWP, indicating hydroclimatic variability as the main driver. The second regime shift (1970-1980 CE) led to a eutrophic state, with a decline in pelagic cladocerans, an increase in benthic and rotifer species, and a rise in herbivory. Changes since the 1970s align with increased land use and hydrological imbalances, indicating that humid conditions and agricultural intensification drove the regime shift, reconfiguring ecosystem functions. Our results emphasize the importance of past ecosystem conditions and ecosystem characteristics in understanding shallow lake responses to climate and human impacts.

Soil microbial communities play a key role in carbon (C) cycling in agroecosystems; however, their long-term responses to contrasting management practices remain poorly understood in agricultural soils. In this study, we evaluated the effects of more than 20 years of no-till farming (NTF) and conventional tillage (CT) on soil physicochemical properties, bacterial and fungal community composition, and inferred functions related to C and nutrient cycling in the Argentine Pampas. We show that NTF increased total organic carbon (TOC) stocks in surface soils and promoted edaphic conditions associated with C stabilization, including higher cation exchange capacity and structural stability. Bacterial communities exhibited high functional redundancy and were primarily structured along sodium-related parameters, whereas fungal communities were more sensitive to management, with NTF favoring ligninolytic and symbiotic fungi that contribute to necromass formation and long-term carbon stabilization. In contrast, CT enriched opportunistic fungal guilds associated with disturbance and short-term nutrient turnover. Phylogenetic analyses revealed community assembly dominated by environmental filtering in both microbial domains. Overall, these results highlight the central role of fungi as mediators of soil C stabilization and suggest that conservation practices such as NTF enhance microbiome contributions to ecosystem services and climate change mitigation in intensively managed agroecosystems.

The biogeography of bacterial communities is a key topic in Microbial Ecology. Regarding continental water, most studies are carried out in the northern hemisphere, leaving a gap on microorganism’s diversity patterns on a global scale. South America harbours approximately one third of the world’s total freshwater resources, and is one of these understudied regions. To fill this gap, we compiled 16S rRNA amplicon sequencing data of microbial communities across South America continental water ecosystems, presenting the first database µSudAqua[db]. The database contains over 866 georeferenced samples from 9 different ecoregions with contextual environmental information. For its integration and validation we constructed a curated database (µSudAqua[db.sp]) using samples sequenced by Illumina MiSeq platform with commonly used prokaryote universal primers. This comprised ~60% of the total georeferenced samples of the µSudAqua[db]. This compilation was carried out in the scope of the µSudAqua collaborative network and represents one of the most complete databases of continental water microbial communities from South America.

Bacterial activities drive most of the Earth’s biogeochemical cycles and, thus, much effort has been devoted to understanding the mechanisms governing their community assemblies in nature. In freshwater ecosystems, selection has been found to be the main driver shaping bacterial communities. However, its relative importance compared with other processes (including dispersal, drift, and diversification) may depend on the spatial heterogeneity and the dispersal rates within a metacommunity. Here, we investigate the main ecological processes modulating bacterial assembly in the eutrophic shallow lakes of the pampa plain (Argentina) across spatial scales (regional, watershed, and local). To do this, 52 shallow lakes with contrasting limnological features and alternative states were studied. The bacterial composition was analysed using high-throughput sequencing (Illumina Miseq technology) of the 16S rDNA V4 region, and statistical inferences based on the phylogenetic and taxa turnover were applied. Based on this analysis, ASVs (amplicon sequence variants, unique DNA sequences obtained from massive sequencing) with a strong association with hypersaline environments and turbid water regimes were observed. In addition to this, processes such as dispersal and drift had a greater importance than that of selection, as expected in theory.

Factors that affect abundances of organisms in water bodies are influenced by extrinsic and intrinsic drivers that operate from outside and within a system. A high temporal coherence in the dynamics of abiotic parameters and biological communities among neighboring lakes evidences a strong extrinsic control operating similarly across lakes, and allows for prediction of ecosystems evolution in the context of global change and intensive land use. The Pampa region (Argentina) encompasses many shallow lakes submitted to different degrees of anthropic influence and showing contrasting alternative states. We studied an eutrophic clear and a hypertrophic turbid shallow lake during an annual cycle in order to evaluate whether they responded similarly to extrinsic factors or these were overridden by the effects of the steady state of each lake. Physical and chemical variables were highly coherent between both lakes, but accounted little for the large disparities among abundances and dynamics of microorganisms. While communities from the clear lake responded to a combination of extrinsic and intrinsic factors, the turbid lake showed a state less prone to be affected by climatic effects. We hypothesize that clear lakes would perform better as sentinels of climate change in the Pampa wetland.

The intensity and frequency of storms are projected to increase in many regions of the world because of climate change. Storms can alter environmental conditions in many ecosystems. In lakes and reservoirs, storms can reduce epilimnetic temperatures from wind‐induced mixing with colder hypolimnetic waters, direct precipitation to the lake's surface, and watershed runoff. We analyzed 18 long‐term and high‐frequency lake datasets from 11 countries to assess the magnitude of wind‐ vs. rainstorm‐induced changes in epilimnetic temperature. We found small day‐to‐day epilimnetic temperature decreases in response to strong wind and heavy rain during stratified conditions. Day‐to‐day epilimnetic temperature decreased, on average, by 0.28°C during the strongest windstorms (storm mean daily wind speed among lakes: 6.7 ± 2.7 m s⁻¹, 1 SD) and by 0.15°C after the heaviest rainstorms (storm mean daily rainfall: 21.3 ± 9.0 mm). The largest decreases in epilimnetic temperature were observed ≥2 d after sustained strong wind or heavy rain (top 5^th percentile of wind and rain events for each lake) in shallow and medium‐depth lakes. The smallest decreases occurred in deep lakes. Epilimnetic temperature change from windstorms, but not rainstorms, was negatively correlated with maximum lake depth. However, even the largest storm‐induced mean epilimnetic temperature decreases were typically <2°C. Day‐to‐day temperature change, in the absence of storms, often exceeded storm‐induced temperature changes. Because storm‐induced temperature changes to lake surface waters were minimal, changes in other limnological variables (e.g., nutrient concentrations or light) from storms may have larger impacts on biological communities than temperature changes.