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Este artículo contiene 18 páginas, 9 figuras. ; Planktonic communities are naturally subjected to episodic nutrient enrichments that may stress or redress the imbalances in limiting nutrients. Human-enhanced atmospheric nitrogen deposition has caused profound N:P imbalance in many remote oligotrophic lakes in which phosphorus has largely become limiting. These lakes offer an opportunity to investigate the relationship between the changes in plankton stoichiometry, productivity, and community structure occurring during nutrient fluctuations in P-limited conditions. We performed P (PO3 4 ) and N (NHþ 4 or NO 3 ) pulse additions to the summer epilimnetic community of an ultraoligotrophic lake using self-filling ~100-L enclosures and analyzed the response to varying P availability, N:P imbalance, and N source. Seston C:N:P proportions remained fairly unchanged to P additions that were within the range of values seasonally found in the lake. However, the seston N:P ratio abruptly shifted and approached Redfield's proportions at P additions typical of mesotrophic conditions that provided non-limiting conditions. N surplus did not affect seston C:N:P proportions. The patterns of seston N:P stability and shift were similar for both N sources. In contrast, productivity was highly sensitive to low and medium P additions and decelerated at high P additions. Phytoplankton biomass dominated particulate organic matter. The autotrophic community differentiated almost linearly across the P gradient. Chrysophytes' dominance decreased, and diatoms and cryptophytes relative abundance increased. Nonetheless, the stoichiometry stability and non-linear shift involved large biomass proportions of the same species, which indicates that the bulk stoichiometry was related to similar physiological behavior of phylogenetically diverse organisms according to the biogeochemical context. The C:N:P seston stability in P-limited conditions—with loose coupling with productivity, nutrient supply ratios, and species dominance—and the sudden shift to Redfield proportions in P-repleted conditions suggest a complex regulation of P scarcity in planktonic communities that goes beyond immediate acclimation growth responses and might include alternative physiological and biogeochemical states. ; The research was funded by research grants of the Spanish Government NitroPir (CGL2010–19737) and Transfer (CGL2016–80124-C2-1-P) and the Catalan Government GECA (2017 SGR 910). P.G-G (FPU AP2010-3596) and A.Z. (FPI BES-2014-070196) acknowledge their respective predoctoral scholarships ; Peer reviewed

Winter conditions are rapidly changing in temperate ecosystems, particularly for those that experience periods of snow and ice cover. Relatively little is known of winter ecology in these systems, due to a historical research focus on summer 'growing seasons'. We executed the first global quantitative synthesis on under-ice lake ecology, including 36 abiotic and biotic variables from 42 research groups and 101 lakes, examining seasonal differences and connections as well as how seasonal differences vary with geophysical factors. Plankton were more abundant under ice than expected; mean winter values were 43.2% of summer values for chlorophyll a, 15.8% of summer phytoplankton biovolume and 25.3% of summer zooplankton density. Dissolved nitrogen concentrations were typically higher during winter, and these differences were exaggerated in smaller lakes. Lake size also influenced winter-summer patterns for dissolved organic carbon (DOC), with higher winter DOC in smaller lakes. At coarse levels of taxonomic aggregation, phytoplankton and zooplankton community composition showed few systematic differences between seasons, although literature suggests that seasonal differences are frequently lake-specific, species-specific, or occur at the level of functional group. Within the subset of lakes that had longer time series, winter influenced the subsequent summer for some nutrient variables and zooplankton biomass. ; National Science Foundation (NSF DEB) [1431428, 1136637]; Washington State University; Russian Science Foundation [14-14-00400]; Ministry of education and science of Russia Gos-Zasanie project [1354-2014/51]; Natural Environment Research Council [NE/J00829X/1, 1230750, NE/G019622/1, NE/J010227/1] ; Funding was provided by the National Science Foundation (NSF DEB #1431428; NSF DEB #1136637) and Washington State University. M. Timofeyev and E. Silow were partially supported by Russian Science Foundation project No 14-14-00400 and Ministry of education and science of Russia Gos-Zasanie project No 1354-2014/51. We are grateful to Marianne Moore, Deniz Ozkundakci, Chris Polashenski and Paula Kankaala for discussions that greatly improved this work. We also gratefully acknowledge the following individuals for contributing to this project: John Anderson, Jill Baron, Rick Bourbonniere, Sandra Brovold, Lluis Camarero, Sudeep Chandra, Jim Cotner, Laura Forsstom, Guillaume Grosbois, Chris Harrod, Klaus D. Joehnk, T.Y. Kim, Daniel Langenhaun, Reet Laugaste, Suzanne McGowan, Virginia Panizzo, Giampaolo Rossetti, R.E.H. Smith, Sarah Spaulding, Helen Tammert, Steve Thackeray, Kyle Zimmer, Priit Zingel and two anonymous reviewers. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the US Government.