Global Patterns and Controls of Nutrient Immobilization On Decomposing Cellulose In Riverine Ecosystems

Microbes play a critical role in plant litter decomposition and influence the fate of carbon in rivers and riparian zones. When decomposing low-nutrient plant litter, microbes acquire nitrogen (N) and phosphorus (P) from the environment (i.e., nutrient immobilization), and this process is potentially sensitive to nutrient loading and changing climate. Nonetheless, environmental controls on immobilization are poorly understood because rates are also influenced by plant litter chemistry, which is coupled to the same environmental factors. Here we used a standardized, low-nutrient organic matter substrate (cotton strips) to quantify nutrient immobilization at 100 paired stream and riparian sites representing 11 biomes worldwide. Immobilization rates varied by three orders of magnitude, were greater in rivers than riparian zones, and were strongly correlated to decomposition rates. In rivers, P immobilization rates were controlled by surface water phosphate concentrations, but N immobilization rates were not related to inorganic N. The N:P of immobilized nutrients was tightly constrained to a molar ratio of 10:1 despite wide variation in surface water N:P. Immobilization rates were temperature-dependent in riparian zones but not related to temperature in rivers. However, in rivers nutrient supply ultimately controlled whether microbes could achieve the maximum expected decomposition rate at a given temperature

Importance of exposure route in determining nanosilver impacts on a stream detrital processing chain

Supplementary data to this article can be found online at https://doi.org/10.1016/j.envpol.2021.118088.The commercial use and spread of silver nanoparticles (AgNPs) in freshwaters have greatly increased over the last decade. Both AgNPs and ionic silver (Ag+) released from nanoparticles are toxic to organisms and compromise ecosystem processes such as leaf litter decomposition. Yet little is known about how AgNPs affect multitrophic systems of interacting species. Furthermore, past work has focused on waterborne exposure with scarce attention given to effects mediated by the consumption of contaminated food. We assessed the importance of direct (via water) and indirect (via diet) AgNP exposure to a processing chain comprising leaf litter, fungi, a shredder (Gammarus pulex) and a collector (Habroleptoides confusa) in microcosms. Direct exposure to contaminated water for 15 days impaired microbial leaf decomposition by similar to 50% and leaf-associated fungal biomass by 10%. Leaf consumption was reduced by similar to 20% but only when G. pulex was exposed to silver via contaminated leaves. There was no effect on FPOM production. Ag+ could impose oxidative stress on the shredders and collectors independent of exposure route, as indicated by increased catalase and glutathione S-transferase activities and decreased superoxide dismutase activity. The activity of a neuronal enzyme (cholinesterase) in collectors, but not shredders, also decreased by almost 50% when the animals were indirectly exposed to AgNP. Our results show that AgNPs and Ag+ may disrupt detrital processing chains through direct and indirect exposure routes, even at low concentrations. This highlights the importance of AgNP exposure pathways to interconnected stream biota and ecosystem processes for realistic assessments of risks to freshwater ecosystems.- We are grateful to Claudia Kuntz at the Chair of Soil Science of TU Berlin for Ag analyses and to Monika Degebrodt and Uta Mallok for assistance during the experiment and nutrient analyses, respectively. This work was supported by the Swiss National Science Foundation (SNF, 200020_134750/1) as part of the National Research Programme NRP 64 on Opportunities and Risks of Nanomaterials, the German Ac-ademic Exchange Service (DAAD, 57036658) , FEDER-POFC-COMPETE, the Portuguese Foundation for Science and Technology (PTDC/BIA-BMA/30922/2017, FCT-DAAD 2013-2014) , and a PhD fellowship to D. Batista (SFRH/BD/88181/2012)

Dissolved organic matter composition from a large scale enclosure experiment

During the summer of 2015, we reproduced three levels of browning and seven levels of nutrients using water from lake Stechlin (North-East Germany). We applied ultra-high-resolution mass-spectrometry and dissolved organic matter optical properties to retrieve the composition of the DOM at different levels of resolutions. Using a network analysis approach, we found that molecular formulas clustering together share a common origin

A niche for ecosystem multifunctionality in global change research

Concern about human modification of Earth's ecosystems has recently motivated ecologists to address how global change drivers will impact the simultaneous provisioning of multiple functions, termed ecosystem multifunctionality (EMF). However, metrics of EMF have often been applied in global change studies with little consideration of the information they provide beyond single functions, or how and why EMF may respond to global change drivers. Here, we critically review the current state of this rapidly expanding field and provide a conceptual framework to guide the effective incorporation of EMF in global change research. In particular, we emphasize the need for a priori identification and explicit testing of the biotic and abiotic mechanisms through which global change drivers impact EMF, as well as assessing correlations among multiple single functions because these patterns underlie shifts in EMF. While the role of biodiversity in mediating global change effects on EMF has justifiably received much attention, empirical support for effects via other biotic and physicochemical mechanisms are also needed. Studies also frequently stated the importance of measuring EMF responses to global change drivers to understand the potential consequences for multiple ecosystem services, but explicit links between measured functions and ecosystem services were missing from many such studies. While there is clear potential for EMF to provide novel insights to global change research, predictive understanding will be greatly improved by insuring future research is strongly hypothesis‐driven, is designed to explicitly test multiple abiotic and biotic mechanisms, and assesses how single functions and their covariation drive emergent EMF responses to global change drivers

Interactive effects of multiple drivers on ecosystem metabolism in a large-scale lake enclosure experiment

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TemBi 2014 mesocosm study - Impact of summer storms on long-term lake ecosystem dynamics

Extreme weather and disturbance events are expected to increase, influencing plankton community structure and biogeochemical element cycling in lakes. We simulated an experimental summer storm by mixing deeper water masses from the meta- and hypolimnion into the mixed layer (epilimnion). The mixing included the disturbance of a deep chlorophyll maximum (DCM) which was present at the same time of the experiment in the deep clear-water Lake Stechlin and situated in the metalimnion of each enclosure during filling. Plankton community structure, water physical variables and biogeochemical cycling was monitored for 42 days after the experimental summer storm disturbance event. The experiment was performed in large-volume (~1200 m3, ~16m depth) enclosures in Lake Stechlin (LakeLab; https://www.igb-berlin.de/en/lakelab)

Flagship umbrella species needed for the conservation of overlooked aquatic biodiversity

Despite a long-standing debate about the utility of species-centered conservation approaches (Roberge & Angelstam 2004), surrogate species remain popular by providing useful-or even necessary-"shortcuts" for successful conservation programs (Caro 2010). Flagship species, as one prime example of surrogates, are primarily intended to promote public awareness and to raise funds for conservation (Ver\uedssimo et\ua0al. 2011). In contrast, the protection of umbrella species is expected to benefit a wide range of co-occurring species (Roberge & Angelstam 2004; Caro 2010). Accordingly, the main criteria for selecting flagships should be based on socio-cultural considerations, whereas umbrellas are principally chosen based on ecological criteria (Caro 2010; Ver\uedssimo et\ua0al. 2011; see Table 1). Since these two concepts are often confused or mistakenly used interchangeably, Caro (2010, p. 248) coined the term "flagship umbrellas" for those species that explicitly integrate both functions. Indeed, Li and Pimm (2016) recently demonstrated that the classic flagship species, the giant panda (Ailuropoda melanoleuca), can simultaneously act as an umbrella species, as its protection benefits many co-occurring endemic mammals, birds and amphibians. This challenges the often held views that: (i) the umbrella concept has to be abandoned as it is not efficiently working at local scales (Caro 2015); (ii) most flagship species are weak predictors for efficient reserve planning (Caro 2010); and (iii) ecosystem- or landscape-based conservation approaches should consequentially be favored over species-based approaches whenever feasible (Roberge & Angelstam 2004; Caro 2010). Further commotion in the discussion is the increasingly demanded paradigm shift in conservation strategies to specifically target hidden or neglected biodiversity for its intrinsic value and its contribution to ecosystem processes (Dougherty et\ua0al. 2016)