Increasing temperatures in northern high latitudes are causing permafrost to thaw 1 , making large amounts of previously frozen organic matter vulnerable to microbial decomposition 2 . Permafrost thaw also creates a fragmented landscape of drier and wetter soil conditions 3,4 that determine the amount and form (carbon dioxide (CO 2 ), or methane (CH 4 )) of carbon (C) released to the atmosphere. The rate and form of C release control the magnitude of the permafrost C feedback, so their relative contribution with a warming climate remains unclear 5,6 . We quantified the e ect of increasing temperature and changes from aerobic to anaerobic soil conditions using 25 soil incubation studies from the permafrost zone. Here we show, using two separate meta-analyses, that a 10 • C increase in incubation temperature increased C release by a factor of 2.0 (95% confidence interval (CI), 1.8 to 2.2). Under aerobic incubation conditions, soils released 3.4 (95% CI, 2.2 to 5.2) times more C than under anaerobic conditions. Even when accounting for the higher heat trapping capacity of CH 4 , soils released 2.3 (95% CI, 1.5 to 3.4) times more C under aerobic conditions. These results imply that permafrost ecosystems thawing under aerobic conditions and releasing CO 2 will strengthen the permafrost C feedback more than waterlogged systems releasing CO 2 and CH 4 for a given amount of C.High-latitude ecosystems store almost twice as much C in soils than what is contained in the atmosphere 7,8 . As the global climate warms, northern high latitudes are experiencing rapid increases in temperature 9 that have the potential to not only increase C emissions from previously frozen C in permafrost and the active layer 10 but also to indirectly affect the C cycle through changes in regional and local hydrology. Warmer temperatures increase thawing of icerich permafrost and the melting of ground ice, which causes the land surface to collapse into the space that was previously filled by ice resulting in thermokarst terrain 11 . Permafrost thawing can also gradually increase active layer thickness (seasonally thawed ground), causing poorly drained soil conditions in lowlands or drier conditions in uplands where natural drainage can increase 3 . On the other hand, permafrost thaw and collapse can cause soils to become waterlogged where anaerobic conditions prevail and C is released in the form of CO 2 and CH 4 . One major uncertainty in determining the climate forcing impact of permafrost ecosystems is understanding the relative magnitudes of the effects of shifting subsurface hydrology versus increasing temperatures on greenhouse gas release in permafrost ecosystems.In addition to soil temperature and moisture, the chemical composition (for example, carbon to nitrogen ratio) 12 , physical protection by soil minerals, microbial community dynamics, and other environmental controls, such as pH and nutrient availability, also impact the amount of C released to the atmosphere 13 . While temperature and soil moisture (that is, oxygen availability) a...

Abstract. Recognition of the extent and magnitude of night-time light pollution impacts on natural ecosystems is increasing, with pervasive effects observed in both nocturnal and diurnal species. Municipal and industrial lighting is on the cusp of a step change where energyefficient lighting technology is driving a shift from ''yellow'' high-pressure sodium vapor lamps (HPS) to new ''white'' light-emitting diodes (LEDs). We hypothesized that white LEDs would be more attractive and thus have greater ecological impacts than HPS due to the peak UVgreen-blue visual sensitivity of nocturnal invertebrates. Our results support this hypothesis; on average LED light traps captured 48% more insects than were captured with light traps fitted with HPS lamps, and this effect was dependent on air temperature (significant light 3 air temperature interaction). We found no evidence that manipulating the color temperature of white LEDs would minimize the ecological impacts of the adoption of white LED lights. As such, large-scale adoption of energy-efficient white LED lighting for municipal and industrial use may exacerbate ecological impacts and potentially amplify phytosanitary pest infestations. Our findings highlight the urgent need for collaborative research between ecologists and electrical engineers to ensure that future developments in LED technology minimize their potential ecological effects.

Summary1. Rapidly increasing atmospheric CO 2 is not only changing the climate system but may also affect the biosphere directly through stimulation of plant growth and ecosystem carbon and nutrient cycling. Although forest ecosystems play a critical role in the global carbon cycle, experimental information on forest responses to rising CO 2 is scarce, due to the sheer size of trees. 2. Here, we present a synthesis of the only study world-wide where a diverse set of mature broadleaved trees growing in a natural forest has been exposed to future atmospheric CO 2 levels (c. 550 ppm) by free-air CO 2 enrichment (FACE). We show that litter production, leaf traits and radial growth across the studied hardwood species remained unaffected by elevated CO 2 over 8 years. 3. CO 2 enrichment reduced tree water consumption resulting in detectable soil moisture savings. Soil air CO 2 and dissolved inorganic carbon both increased suggesting enhanced below-ground activity. Carbon release to the rhizosphere and/or higher soil moisture primed nitrification and nitrate leaching under elevated CO 2 ; however, the export of dissolved organic carbon remained unaltered. 4. Synthesis. Our findings provide no evidence for carbon-limitation in five central European hardwood trees at current ambient CO 2 concentrations. The results of this long-term study challenge the idea of a universal CO 2 fertilization effect on forests, as commonly assumed in climate-carbon cycle models.

Rising atmospheric [CO2 ], ca , is expected to affect stomatal regulation of leaf gas-exchange of woody plants, thus influencing energy fluxes as well as carbon (C), water, and nutrient cycling of forests. Researchers have proposed various strategies for stomatal regulation of leaf gas-exchange that include maintaining a constant leaf internal [CO2 ], ci , a constant drawdown in CO2 (ca  - ci ), and a constant ci /ca . These strategies can result in drastically different consequences for leaf gas-exchange. The accuracy of Earth systems models depends in part on assumptions about generalizable patterns in leaf gas-exchange responses to varying ca . The concept of optimal stomatal behavior, exemplified by woody plants shifting along a continuum of these strategies, provides a unifying framework for understanding leaf gas-exchange responses to ca . To assess leaf gas-exchange regulation strategies, we analyzed patterns in ci inferred from studies reporting C stable isotope ratios (δ(13) C) or photosynthetic discrimination (∆) in woody angiosperms and gymnosperms that grew across a range of ca spanning at least 100 ppm. Our results suggest that much of the ca -induced changes in ci /ca occurred across ca spanning 200 to 400 ppm. These patterns imply that ca  - ci will eventually approach a constant level at high ca because assimilation rates will reach a maximum and stomatal conductance of each species should be constrained to some minimum level. These analyses are not consistent with canalization toward any single strategy, particularly maintaining a constant ci . Rather, the results are consistent with the existence of a broadly conserved pattern of stomatal optimization in woody angiosperms and gymnosperms. This results in trees being profligate water users at low ca , when additional water loss is small for each unit of C gain, and increasingly water-conservative at high ca , when photosystems are saturated and water loss is large for each unit C gain.