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Although most studies find temperature, soil moisture and water table to be important environmental factors that affect peatland carbon dynamics, the role of vegetation communities has been investigated less. Therefore, this study investigates whether peatland ecosystems produce heterogeneous CO2 fluxes due to differences in vegetation community. In addition, the study also examines which major environmental factors influence this vegetation. To achieve the aims of this study, four sites with different vegetation communities were established in a semi-natural peatland ecosystem in Poland. CO2 flux measurements were carried out using a closed dynamic chamber system. Measurement campaigns were carried out from April until December 2008, every 2–3 weeks. Measured ecosystem respiration (Reco) and net ecosystem exchange (NEE) rates showed daily and seasonal variation at all investigated sites. Reco presented a strong dependence on soil temperature at the 5 cm depth, while NEE showed a strong dependence on solar radiation. The mean temperature sensitivity (Q10) for the four sites ranged between 3.17 and 8.3. The highest NEE and Reco values were obtained at the site represented by Caricetum elatae and the lowest NEE and Reco at the site represented by Calamagrostietum neglectae.

Accurate predictions of net ecosystem productivity (NEPc) of forest ecosystems are essential for climate change decisions and requirements in the context of national forest growth and greenhouse gas inventories. However, drivers and underlying mechanisms determining NEPc (e.g., climate and nutrients) are not entirely understood yet, particularly when considering the influence of past periods. Here we explored the explanatory power of the compensation day (cDOY)-defined as the day of year when winter net carbon losses are compensated by spring assimilation-for NEPc in 26 forests in Europe, North America, and Australia, using different NEPc integration methods. We found cDOY to be a particularly powerful predictor for NEPc of temperate evergreen needleleaf forests (R2=0.58) and deciduous broadleaf forests (R2=0.68). In general, the latest cDOY correlated with the lowest NEPc. The explanatory power of cDOY depended on the integration method for NEPc, forest type, and whether the site had a distinct winter net respiratory carbon loss or not. The integration methods starting in autumn led to better predictions of NEPc from cDOY then the classical calendar method starting 1 January. Limited explanatory power of cDOY for NEPc was found for warmer sites with no distinct winter respiratory loss period. Our findings highlight the importance of the influence of winter processes and the delayed responses of previous seasons' climatic conditions on current year's NEPc. Such carry-over effects may contain information from climatic conditions, carbon storage levels, and hydraulic traits of several years back in time. (Less)

Although there have been many studies of the net ecosystem productivity (NEP) of different types of forests around the world, the CO 2 dynamics in afforested pine stands of Central Europe are poorly understood. To fill this gap, continuous eddy-covariance (EC) measurements of net ecosystem exchange (NEE) were made from January 2008 to December 2013 in a 62-year-old temperate afforested Scots pine stand near Tuczno. The site is located in north-western Poland, where forests account for almost 30% of the land area and are dominated by Scots pine. Weather conditions during this 5-year period were mostly warm and wet. In all 5 years, air temperature ( T a ) was higher than the 30-year (1983–2013) mean and by 3.3 °C during winter 2008, while precipitation ( P ) was noticeably higher only in summer months. The high productivity of the forest, which sequestered 118 Mg of CO 2 per ha over the 5-year period, is likely because it was planted on fertile meadowland. Annual net ecosystem productivity (NEP = −NEE) ranged from 494 g C m −2 in 2012 to 765 g C m −2 in 2009, with an average of 645 g C m −2 . The interannual variation in NEP was attributed more to the interannual variation in gross ecosystem photosynthesis (GEP) than to ecosystem respiration ( R ). Moreover, both annual NEP and GEP significantly decreased over the 5 years. This was the result of increasingly drier springs and wetter summers as time progressed during the 5-year period, as compared to the 30-year averages, which resulted in a gradual reduction in the growing season NEP and consequently the annual values. Seasonal values of NEP were highly correlated with T a , photosynthetic photon flux density and vapor pressure deficit. The sensitivity of NEP to T a was largely due to the much higher sensitivity of GEP to T a compared to that of R . Although the interannual variability in NEP for separate seasons could not be explained using seasonal values of individual meteorological variables, a hygrothermal index, defined as P /10 T a , explained a large proportion of the interannual variability in NEP in spring and summer.

Due to their unique flora, hydrology and environmental characteristics, peatlands are precious and specific habitats for microorganisms and microscopic animals. Their microbial network structure and their biomass are crucial for peatland carbon cycling, through primary production, as well as decomposition and mineralization of organic matter. Wetlands are one of the ecosystems most at risk from anthropogenic activities and climate change. Most recent scenarios of climate change for Central Europe predict an increase in air temperature and a decrease in annual precipitation. These changes may disturb the biodiversity of aquatic organisms, and the peat carbon sink. Considering the above climatic scenarios, we aimed to: i) assess the response of microbial community biomass to warming and reduced precipitation through the lens of a manipulative experiment in a peatland ecosystem ii) predict how global warming might affect microbial biodiversity on peatlands exposed to warmer temperatures and decreased precipitation conditions. Additionally, we wanted to identify ecological indicators of warming among microorganisms living in Sphagnum peatland. The result of a manipulative experiment carried out at Rzecin peatland (W Poland) suggested that the strongest reduction in microbial biomass was observed in heated plots and plots where heating was combined with a reduction of precipitation. The most pronounced changes were observed in the case of the very abundant mixotrophic testate amoeba Hyalosphenia papilio and cyanobacteria. Shifts in the Sphagnum microbial network can be used as an early warning indicator of peatland warming, especially a decrease in the biomass of important phototrophic microbes living on the Sphagnum capitula, e.g. Hyalosphenia papilio.

The Scots pine is one of the most important species in European and Asian forests. Due to a widespread occurrence of pine forests, their significance in the energy and mass exchange between the Earth surface and the atmosphere is also important, particularly in the context of climate change and greenhouse gases balance. The aim of this work is to present the relationship between the average annual net ecosystem productivity and growing season length, latitude and air temperature (tay) over Europe. Therefore, CO2 flux measurement data from eight European pine dominated forests were used. The observations suggest that there is a correlation between the intensity of CO2 uptake or emission by a forest stand and the above mentioned parameters. Based on the obtained results, all of the selected pine forest stands were CO2 sinks, except a site in northern Finland. The carbon dioxide uptake increased proportionally with the increase of growing season length (9.212 g C m-2 y-1 per day of growing season, R2 = 0.53, p = 0.0399). This dependency showed stronger correlation and higher statistical significance than both relationships between annual net ecosystem productivity and air temperature (R2 = 0.39, p = 0.096) and annual net ecosystem productivity and latitude (R2 = 0.47, p = 0.058). The CO2 emission surpassed assimilation in winter, early spring and late autumn. Moreover, the appearance of late, cold spring and early winter, reduced annual net ecosystem productivity. Therefore, the growing season length can be considered as one of the main factor affecting the annual carbon budget of pine forests.

International audience; Light use efficiency (LUE) models are widely used to simulate gross primary production (GPP). However, the treatment of the plant canopy as a big leaf by these models can introduce large uncertainties in simulated GPP. Recently, a two-leaf light use efficiency (TL-LUE) model was developed to simulate GPP separately for sunlit and shaded leaves and has been shown to outperform the big-leaf MOD17 model at six FLUX sites in China. In this study we investigated the performance of the TL-LUE model for a wider range of biomes. For this we optimized the parameters and tested the TL-LUE model using data from 98 FLUXNET sites which are distributed across the globe. The results showed that the TL-LUE model performed in general better than the MOD17 model in simulating 8 day GPP. Optimized maximum light use efficiency of shaded leaves (epsilon(msh)) was 2.63 to 4.59 times that of sunlit leaves (epsilon(msu)). Generally, the relationships of epsilon(msh) and epsilon(msu) with epsilon(max) were well described by linear equations, indicating the existence of general patterns across biomes. GPP simulated by the TL-LUE model was much less sensitive to biases in the photosynthetically active radiation (PAR) input than the MOD17 model. The results of this study suggest that the proposed TL-LUE model has the potential for simulating regional and global GPP of terrestrial ecosystems, and it is more robust with regard to usual biases in input data than existing approaches which neglect the bimodal within-canopy distribution of PAR.

The main goal of this paper is to estimate how the observed and predicted climate changes may affect the development rates and emergence of the codling moth in the southern part of the Wielkopolska region in Poland. In order to simulate the future climate conditions one of the most frequently used A1B SRES scenarios and two different IPCC climate models (HadCM3 and GISS modelE) are considered. A daily weather generator (WGENK) was used to generate temperature values for present and future climate conditions (time horizons 2020-2040 and 2040-2060). Based on the generated data set, the degree-days values were then calculated and the emergence dates of the codling moth at key stages were estimated basing on the defined thresholds. Our analyses showed that the average air surface temperature in the Wielkopolska region may increase from 2.8°C (according to GISS modelE) even up to 3.3°C (HadCM3) in the period of 2040-2060. With the warming climate conditions the cumulated degree-days values may increase at a rate of about 142 DD per decade when the low temperature threshold (T(low)) of 0°C is considered and 91 DD per decade when T(low) = 10°C. The key developmental stages of the codling moth may occur much earlier in the future climate conditions than currently, at a rate of about 3.8-6.8 days per decade, depending on the considered GCM model and the pest developmental stage. The fastest changes may be observed in the emergence dates of 95% of larvae of the second codling moth generation. This could increase the emergence probability of the pest third generation that has not currently occurred in Poland.

Aims Recent studies revealed convergent temperature sensitivity of ecosystem respiration (R e) within aquatic ecosystems and between terrestrial and aquatic ecosystems. We do not know yet whether various terrestrial ecosystems have consistent or divergent temperature sensitivity. Here, we synthesized 163 eddy covariance flux sites across the world and examined the global variation of the apparent activation energy (Ea), which characterizes the apparent temperature sensitivity of R e, and its interannual variability (IAV) as well as their controlling factors.Methods We used carbon fluxes and meteorological data across FLUXNET sites to calculate mean annual temperature, temperature range, precipitation, global radiation, potential radiation, gross primary productivity and R e by averaging the daily values over the years in each site. Furthermore, we analyzed the sites with >8 years data to examine the IAV of Ea and calculated the standard deviation of Ea across years at each site to characterize IAV.Important Findings The results showed a widely global variation of Ea, with significantly lower values in the tropical and subtropical areas than in temperate and boreal areas, and significantly higher values in grasslands and wetlands than that in deciduous broadleaf forests and evergreen forests. Globally, spatial variations of Ea were explained by changes in temperature and an index of water availability with differing contribution of each explaining variable among climate zones and biomes. IAV and the corresponding coefficient of variation of Ea decreased with increasing latitude, but increased with radiation and corresponding mean annual temperature. The revealed patterns in the spatial and temporal variations of Ea and its controlling factors indicate divergent temperature sensitivity of R e, which could help to improve our predictive understanding of R e in response to climate change.

Of a wide variety of international forest research and monitoring networks, several networks are dedicated to the effects of climate change on forests, while the effects of anthropogenic pollutants on forests have been a major area for both monitoring and research for decades. The large amounts of data already obtained within existing monitoring programmes and large-scale international projects can be used to increase understanding of the state and potential of forest mitigation and adaptation to climate change in a polluted environment, and a major challenge now is to evaluate and integrate the presently available databases. We present a meta-database with the main goal to highlight available data and integrate the information about research and monitoring of selected European Research and Monitoring Networks (ERMNs). Depending on the selected ERMNs, the list of variables and the measurement units differ widely in the databases. As a result, activities related to the identification, evaluation and integration of the presently available databases are important for the scientific community. Furthermore, and equally important, the recognition of current knowledge gaps and future needed research is made easier. This analysis suggests that: ground-level ozone is under-investigated, although it is one of the pollutants of greatest concern to forests; in addition to CO2, long-term other greenhouse gasses (GHG) flux measurements should be carried out; there is still a need of improving links between monitoring of atmospheric changes and impacts on forests; research-oriented manipulative experiments in the forests are missing.

This paper reports the results of the analysis of CO2 exchange from a one-month experiment conducted at a mixed deciduous forest, Camp Borden (80°65′W, 44°19′ N), Canada, in the summer of 1993. The mid-day CO2 flux from the forest under clear sky conditions was around −1.0 mg m−2 s−1, the average light and water use efficiencies 13 mmol CO2(mol photon)−1 and 7.95 mg CO2(gH2O)−1 , and the average nocturnal respiration rate 0.21 mg CO2m−2s−1. We observed different flow features at heights of 34.5 (14.5 m above the canopy) and 22.4 m at night. Wavelike structures were frequently encountered at z = 34.5 m. Depending on the phase angle between the vertical velocity and CO2 concentration time series, they could act to enhance the co-gradient (upward) flux or to create counter-gradient (downward) flux of CO2. We speculate that the wave events were limited to isolated regions in the upwind direction. Near the tree-tops (z = 22.4 m), the strong wind shear was able to maintain turbulence. Inverse temperature ramp structures were very common and flux of sensible heat was well behaved (directed downward).

Many wetland ecosystems such as peatlands and wet tundra hold large amounts of organic carbon (C) in their soils, and are thus important in the terrestrial C cycle. We have synthesized data on the carbon dioxide (CO2) exchange obtained from eddy covariance measurements from 12 wetland sites, covering 1-7 years at each site, across Europe and North America, ranging from ombrotrophic and minerotrophic peatlands to wet tundra ecosystems, spanning temperate to arctic climate zones. The average summertime net ecosystem exchange of CO2 (NEE) was highly variable between sites. However, all sites with complete annual datasets, seven in total, acted as annual net sinks for atmospheric CO2. To evaluate the influence of gross primary production (GPP) and ecosystem respiration (R-eco) on NEE, we first removed the artificial correlation emanating from the method of partitioning NEE into GPP and R-eco. After this correction neither R-eco (P = 0.162) nor GPP (P = 0.110) correlated significantly with NEE on an annual basis. Spatial variation in annual and summertime R-eco was associated with growing season period, air temperature, growing degree days, normalized difference vegetation index and vapour pressure deficit. GPP showed weaker correlations with environmental variables as compared with R-eco, the exception being leaf area index (LAI), which correlated with both GPP and NEE, but not with R-eco. Length of growing season period was found to be the most important variable describing the spatial variation in summertime GPP and R-eco; global warming will thus cause these components to increase. Annual GPP and NEE correlated significantly with LAI and pH, thus, in order to predict wetland C exchange, differences in ecosystem structure such as leaf area and biomass as well as nutritional status must be taken into account.

Ecosystem respiration (R eco ) is controlled by thermal and hydrologic regimes, but their relative importance in defining the CO2 emissions in peatlands seems to be site specific. The aim of the paper is to investigate the sensitivity of R eco to variations in temperature and water table depth (WTD) in a wet, geogenous temperate peatland with a wide variety of vegetation community groups. The CO2 fluxes were measured using chambers. Measurements were made at four microsites with different vegetation communities and peat moisture and temperature conditions every 3 to 4 weeks during the period 2008–2009, 2 years with contrasting WTD patterns. Models were used to examine the relative response of each microsite to variations in peat temperature and WTD and used to estimate annual total R eco . Temporal variations in R eco were strongly related to peat temperature at the 5 cm depth. However, two of the microsites did not show any significant change in this relationship while two others showed contrasting responses including an increase and decrease in temperature sensitivity with deeper WTD. Average R eco varied among the microsites and tended to be greatest for those with greatest leaf area which also positively correlated with deeper WTD, ash content and degree of peat decomposition at 20 cm. A combined temperature and WTD model explained up to 94 % of the temporal variation in daily average R eco and was used to show that on an annual basis, R eco was between 5 and 18 % greater in the warmer year with deeper WTD. Microsite-specific responses were related to differences in vegetation and peat characteristics among microsites. R eco may have remained insensitive to WTD variations at one microsite due to the dominance of autotrophic respiration from abundant sedge biomass. At a Sphagnum-dominated microsite, a lack of response may have been due to relatively small variations in WTD that did not greatly influence microbial respiration or due to offsets between decreasing and increasing respiration rates in near-surface and deeper peat. The microsite with the most recalcitrant peat had reduced R eco sensitivity to temperature under more aerobic conditions while another microsite showed the opposite response, perhaps due to less nutrient availability during the wet year. Ultimately, micro-site specific models with both soil temperature and WTD as explanatory variables described temporal variations in R eco and highlighted the significant spatial variations in respiration rates that may occur within a single wetland.