We assembled data from a global network of automated lake observatories to test hypotheses regarding the drivers of ecosystem metabolism. We estimated daily rates of respiration and gross primary production (GPP) for up to a full year in each lake, via maximum likelihood fits of a free-water metabolism model to continuous highfrequency measurements of dissolved oxygen concentrations. Uncertainties were determined by a bootstrap analysis, allowing lake-days with poorly constrained rate estimates to be down-weighted in subsequent analyses. GPP and respiration varied considerably among lakes and at seasonal and daily timescales. Mean annual GPP and respiration ranged from 0.1 to 5.0 mg O 2 L 21 d 21 and were positively related to total phosphorus but not dissolved organic carbon concentration. Within lakes, significant day-to-day differences in respiration were common despite large uncertainties in estimated rates on some lake-days. Daily variation in GPP explained 5% to 85% of the daily variation in respiration after temperature correction. Respiration was tightly coupled to GPP at a daily scale in oligotrophic and dystrophic lakes, and more weakly coupled in mesotrophic and eutrophic lakes. Background respiration ranged from 0.017 to 2.1 mg O 2 L 21 d 21 and was positively related to indicators of recalcitrant allochthonous and autochthonous organic matter loads, but was not clearly related to an indicator of the quality of allochthonous organic matter inputs.Gross primary production (GPP) and respiration are perhaps the two most fundamental processes in ecosystems. At the cellular or organismal level, they describe biochemical pathways that make organic carbon molecules and energy available to cells. When these cellular processes are integrated across an entire ecosystem, the result-ecosystemlevel GPP, ecosystem respiration, or collectively ecosystem metabolism-describes biogeochemical and trophic processes occurring at the system level.There is substantial interest in understanding the controls on ecosystem metabolism in aquatic (Mulholland et al.

2. We present data from high frequency monitoring stations from lakes in Europe, North America and Asia that illustrate two classes of abiotic effects of weather events: (i) generally short-lived effects of storms on lake thermal structure and (ii) the more prolonged effects of high rainfall events on dissolved organic matter levels and water clarity. We further relate these abiotic effects to changes in dissolved oxygen or in chlorophyll a levels.3. Three differing causes for weather-related decreases in surface dissolved oxygen levels were observed: (i) entrainment of anoxic water from depth, (ii) reduction in primary productivity, and (iii) increased mineralisation of organic carbon delivered from the catchment.4. The duration of in-lake effects tended to be longer for events driven by weather conditions with a longer return period, that is, conditions which were relatively more severe and less frequent at a site. While the susceptibility of lakes to change was related in part to the severity of the meteorological drivers, the impacts also depended on site-specific factors in some cases.5. The availability of high frequency data at these sites provided insight into the capacity of the lakes to absorb current and future pressures. Several of the changes we observed, including increases in carbon availability, decreases in PAR and increased disturbance, have the capacity to shift lakes towards an increased degree of heterotrophy. The magnitude and direction of any such change will, however, also 3 depend on the magnitude and direction of climate change for a given location, and on lake and catchment characteristics.4

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Summary 1. We used high‐frequency in situ dissolved oxygen measurements to investigate the seasonal variability and factors regulating metabolism in a subtropical alpine lake in Taiwan between May 2004 and October 2005, specifically exploring how the typhoon season (from June or July to October) affects lake metabolism. 2. Gross primary production (GPP) and ecosystem respiration (R) both peaked in early summer and mid‐autumn but dropped during the typhoon season and winter. Yuan‐Yang Lake is a net heterotrophic ecosystem (annual mean net ecosystem production −39.6 μmole O2 m−3). 3. Compared to the summer peaks, seasonal averages of GPP and R decreased by approximately 50% and 25%, respectively, during the typhoon season. Ecosystem respiration was more resistant to external disturbances than GPP and showed strong daily variation during typhoon seasons. 4. Changes in the quality and quantity of dissolved organic carbon controlled the temporal dynamics and metabolic regulation. External disturbances (typhoons) caused increased allochthony, increasing DOC and water colour and influencing lake metabolism. 5. Seasonal winter mixing and typhoon‐induced water mixing in summer and autumn play a key role in determining the extent to which the lake is a seasonal carbon sink or source to the atmosphere.

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Lake mixing disrupts chemical and physical gradients that structure bacterial communities. A transplant experiment was designed to investigate the influence of post-mixing environmental conditions and biotic interactions on bacterial community composition. The experimental design was 3x2 factorial, where water was incubated from three different sources (epilimnion, hypolimnion, and mixed epilimnion and hypolimnion) at two different locations in the water column (epilimnion or hypolimnion). Three replicate mesocosms of each treatment were removed every day for 5 days for bacterial community profiling, assessed by automated ribosomal intergenic spacer analysis. There were significant treatment effects observed, and temperature was the strongest measured driver of community change (r=-0.66). Epilimnion-incubated communities changed more than hypolimnion-incubated. Across all treatments, we classified generalist, layer-preferential and layer-specialist populations based on occurrence patterns. Most classified populations were generalists that occurred in both strata, suggesting that communities were robust to mixing. In a network analysis of the mixed-inocula treatments, there was correlative evidence of inter-population biotic interactions, where many of these interactions involved generalists. These results reveal differential responses of bacterial populations to lake mixing and highlight the role of generalist taxa in structuring an emergent community-level response.

Moso bamboo is fast-growing and negatively allelopathic to neighboring plants. However, there is little information on the effects of its establishment and expansion to adjacent forest soil communities. To better understand the impacts of bamboo invasion on soil communities, the phylogenetic structure and diversity of the soil bacterial communities in moso bamboo forest, adjacent Japanese cedar plantation, and bamboo-invaded transition zone were examined using a combination of 16S rRNA gene clone libraries and bar-coded pyrosequencing techniques. Based on the number of operational taxonomic units (OTUs), Shannon diversity index, Chao1 estimator, and rarefaction analysis of both techniques, the bamboo soil bacterial community was the most diverse, followed by the transition zone, with the cedar plantation possessing the lowest diversity. The results from both techniques revealed that the Acidobacteria and Proteobacteria predominated in the three communities, though the relative abundance was different. The 250 most abundant OTUs represented about 70% of the total sequences found by pyrosequencing. Most of these OTUs were found in all three soil communities, demonstrating the overall similarity among the bacterial communities. Nonmetric multidimensional scaling analysis showed further that the bamboo and transition soil communities were more similar with each other than the cedar soils. These results suggest that bamboo invasion to the adjacent cedar plantation gradually increased the bacterial diversity and changed the soil community. In addition, while the 10 most abundant OTUs were distributed worldwide, related sequences were not abundant in soils from outside the forest studied here. This result may be an indication of the uniqueness of this region.