Intraspecific variability of leaf form and function across habitat types.

Trait-based ecology has already revealed main independent axes of trait variation defining trait spaces that summarize plant adaptive strategies, but often ignoring intraspecific trait variability (ITV). By using empirical ITV-level data for two independent dimensions of leaf form and function and 167 species across five habitat types (coastal dunes, forests, grasslands, heathlands, wetlands) in the Italian peninsula, we found that ITV: (i) rotated the axes of trait variation that define the trait space; (ii) increased the variance explained by these axes and (iii) affected the functional structure of the target trait space. However, the magnitude of these effects was rather small and depended on the trait and habitat type. Our results reinforce the idea that ITV is context-dependent, calling for careful extrapolations of ITV patterns across traits and spatial scales. Importantly, our study provides a framework that can be used to start integrating ITV into trait space analyses.

Ecosystem services provided by marine and freshwater phytoplankton.

Phytoplankton, the ecological group of microalgae adapted to live in apparent suspension in water masses, is much more than an ecosystem's engineer. In this opinion paper, we use our experience as phytoplankton ecologists to list and highlight the services provided by phytoplankton, trying to demonstrate how their activity is fundamental to regulate and sustain Life on our Planet. Although the number of services produced by phytoplankton can be considered less numerous than that produced by other photosynthetic organisms, the ubiquity of this group of organisms, and their thriving across oceanic ecosystems make it one of the biological engines moving our biosphere. Supporting services provided by phytoplankton include almost half of the global primary and oxygen production. In addition, phytoplankton greatly pushes biogeochemical cycles and nutrient (re)cycling, not only in aquatic ecosystems but also in terrestrial ones. In addition, it significantly contributes to climate regulation (regulating services), supplies food, fuels, active ingredients and drugs, and genetic resources (provisioning services), has inspired artistic and craft works, mythology, and, of course, science (cultural services), and much more. Therefore, phytoplankton should be considered in all respects a true biosphere's engineer.

Iron enrichment from hypoxic hypolimnion supports the blooming of Raphidiopsis raciborskii in a tropical reservoir.

Occurring worldwide, blooms of Raphidiopsis raciborskii threaten the use of water resources especially in tropical and subtropical waterbodies. Its high flexibility in the uses of light and macronutrients (C, N, P) frustrates any bloom prediction and control based on macronutrients regulation. To identify the critical factors promoting periodic blooms of R. raciborskii, the trends of meteorological, hydrodynamic, physical, and chemical variables (including macro- and micronutrients: N, P, Fe) were analyzed in a Chinese tropical large reservoir (Dashahe reservoir) over five years. It was hypothesized that Fe availability, mediated by the mixing pattern of the reservoir, played a crucial role in the periodic blooms of the cyanobacterium. To have a more complete understanding, the effects of Fe on growth of a local R. raciborskii strain were tested in a monoculture experiment. The biomass and relative abundance of R. raciborskii in the reservoir showed a clear seasonal trend, with relative abundance > 50% in summer/autumn (July to October). Three habitat types along a dominance gradient were identified in the reservoir and 17 variables were used to compare them. Statistical analysis and habitat comparison showed that temperature and stratification, dissolved Fe and N concentrations in the epilimnion, and dissolved Fe and oxygen concentrations in the hypolimnion were the critical factors driving the dynamics of R. raciborskii in the study reservoir. The habitat dominated by R. raciborskii was characterized by a relatively low availability of macro resources (Zeu/Zm < 1, SRP < 0.01 mg/L, DIN < 0.3 mg/L) and by a high Fe availability supplemented from hypoxic hypolimnion. The dependence of growth on Fe concentration increase was confirmed in culture where the maximum was reached at 0.689 mg Fe /L. Our results suggest that a high Fe bioavailability, also originating from the hypoxic hypolimnion, influences the dynamics R. raciborskii and favors the blooms of the species. As a consequence, Fe concentrations in the water column as well as oxygen measurements along the water column should be routinely included in the monitoring programs aimed at predicting and controlling R. raciborskii blooms.

Combination of linear and nonlinear multivariate approaches effectively uncover responses of phytoplankton communities to environmental changes at regional scale.

The response of a community to environmental changes is either linear or non-linear, so that they can be investigated approximately by linear or nonlinear models. At community level, redundancy analysis (RDA) and canonical correspondence analysis (CCA), and Mantel test and Generalized Dissimilarity Modelling (GDM) are two pairs of fundamental multivariate approaches. Thus, it is necessary to determine how they are used for a given group of communities or a metacommunity. In the present study, we explored the applications of the two pairs of commonly used multivariate methods for the analysis of tropical phytoplankton communities. Phytoplankton were collected from 60 tropical reservoirs in southern China at two distinct regions and two hydrological seasons. Because of a short environmental gradient, response of phytoplankton communities to the environmental gradients was first explored with linear models: distance-based redundancy analysis (db-RDA) and Mantel test. Then, CCA and GDM were further applied to recognize the nonlinear relationship between phytoplankton community variation and environmental changes, and to detect the significant environmental and/or spatial variables. Our results strongly suggest that the combination of db-RDA and GDM provides a highly effective tool to uncover the linearity and nonlinearity in community responses and the important associated environmental and spatial variables, which were significantly different between flooding and dry seasons.

Evaluating anthropogenic impacts on naturally stressed ecosystems: Revisiting river classifications and biomonitoring metrics along salinity gradients.

Naturally stressed ecosystems hold a unique fraction of biodiversity. However, they have been largely ignored in biomonitoring and conservation programmes, such as the EU Water Framework Directive, while global change pressures are threatening their singular values. Here we present a framework to classify and evaluate the ecological quality of naturally stressed rivers along a water salinity gradient. We gathered datasets, including aquatic macroinvertebrate assemblages and environmental information, for 243 river locations across the western Mediterranean to: a) gauge the role of natural stressors (salinity) in driving aquatic community richness and composition; b) make river classifications by encompassing the wide range of environmental and biological variation exhibited by Mediterranean rivers; c) provide effective biomonitoring metrics of ecological quality for saline rivers. Our results showed that water salinity played a pivotal role in explaining the community richness and compositional changes in rivers, even when considering other key and commonly used descriptors, such as elevation, climate or lithology. Both environmental and biologically-based classifications included seven river types: three types of freshwater perennial rivers, one freshwater intermittent river type and three new saline river types. These new saline types were not included in previous classifications. Their validation by independent datasets showed that the saline and freshwater river types represented differentiable macroinvertebrate assemblages at family and species levels. Biomonitoring metrics based on the abundance of indicator taxa of each saline river type provided a much better assessment of the ecological quality of saline rivers than other widely used biological metrics and indices. Here we demonstrate that considering natural stressors, such as water salinity, is essential to design effective and accurate biomonitoring programmes for rivers and to preserve their unique biodiversity.

Toxic cyanobacterial blooms in reservoirs under a semiarid mediterranean climate: the magnification of a problem.

Sicilian reservoirs constitute the most important water resources available on the island. During summer 2001, the intense water utilization of Lake Arancio reservoir reduced the water level significantly, which coincided with the formation of intense blooms formed by the microcystin (MC)-producing cyanobacterium Microcystis aeruginosa. During summer 2003, Lake Arancio was continuously filled and the vertical stratification of the water column was maintained resulting in five to sixfold lower cell numbers of M. aeruginosa. For both years, a significant relationship between MC net production and Microcysytis cell growth was observed, implying that Microcystis cell numbers can be used to infer MC concentrations in water. Unexpectedly, dense blooms of the MC-producing cyanobacterium Planktothrix rubescens occurred during winter 2005/2006 in the reservoirs Lake Pozzillo, Prizzi, Nicoletti, and Garcia but have not been reported earlier. In this season, MC concentrations higher than those recorded in summer were measured, implying that monitoring of Mediterranean drinking water reservoirs needs to be intensified during winter, a season usually considered to be less prone to the formation of cyanobacterial blooms.