Temperature Sensitivity Of Ecosystem Respiration Research Articles

Exploring the ecological meanings of temperature sensitivity of ecosystem respiration from different methods

Temperature sensitivity (Q10) of ecosystem respiration (Re) is a critical parameter for predicting global terrestrial carbon dynamics and its response to climate warming. However, the determination of Q10 has been controversial. In this study, we scrutinized the underpinnings of three mainstream methods to reveal their relationships in estimating Q10 for Re in the Heihe River Basin, northwest China. Specifically, these methods are Q10 estimated from the long-term method (Q10_long), short-term method (Q10_short), and the low-frequency (Q10_lf) and high-frequency (Q10_hf) signals decomposed by the singular spectrum analysis (SSA) method. We found that: 1) Q10_lf and Q10_long are affected by the confounding effects caused by non-temperature factors, and are 1.8 ± 0.3 and 1.7 ± 0.3, respectively. 2) The high-frequency signals of the SSA method and short-term method have consistent roles in removing the confounding effects. Both Q10_short and Q10_hf reflect the actual response of respiration to temperature. 3) Overall, Q10_long has a larger variability (1.7 ± 0.3) across different biomes, whereas Q10_short and Q10_hf show convergence (1.4 ± 0.2 and 1.3 ± 0.1, respectively). These results highlight the fact that Q10 can be overestimated by the long-term method, whereas the short-term method and high-frequency signals decomposed by the SSA method can obtain closer and convergent values after removing the confounding effects driven by non-temperature factors. Therefore, it is recommended to use the Q10 value estimated by the short-term method or high-frequency signals decomposed by the SSA method to predict carbon dynamics and its response to global warming in Earth system models.

Ecosystem CO2 Exchange and Its Environmental Regulation of a Restored Wetland in the Liaohe River Estuary

Coastal wetlands are important carbon sinks， and they contribute to reducing the effects of global warming. This study used the eddy covariance method to detect the CO2 flux in the restoration wetland of the Liaohe River estuary in 2021 and investigate the characteristics of ecosystem CO2 exchange and its environmental control factors. The aim was to assess the carbon source/sink capacity of salt marshes in the restored area and to provide data support and theoretical basis for evaluating the effectiveness of ecological restoration projects. The study revealed "U" curves in spring and autumn， "V" curves in summer， and horizontal lines in winter for the average daily variation curve of net ecosystem CO2 exchange （NEE） in the restored area. Its carbon sink efficiencies were -40.06， -63.62， 2.33， and 34.43 g·m-2 in the spring， summer， autumn， and winter， respectively. In the restored area， the daily cumulative variation in NEE was "V" shaped， and the monthly cumulative changes in NEE， ecosystem respiration （Reco）， and gross primary productivity （GPP） were obviously different. Photosynthetically active radiation （PAR） was an important regulation factor of daytime NEE in the restored area in 2021， and they displayed a rectangular hyperbolic relationship. PAR could explain 53% of the variation in the daytime NEE. Air temperature （Ta） was the main control factor of Reco，night， and there was an exponential relationship between them. When Ta < 5.5 ℃， the temperature sensitivity of ecosystem respiration （Q10） was 2.19， and Ta could explain 42% of the variation in the Reco，night； when Ta ≥ 5.5 ℃， the Q10 was 1.81， and Ta could explain 51% of the variation in the Reco，night. Additionally， there were significant linear negative correlations between NEE and both soil water content （SWC） and vapor pressure deficit （VPD）， whereas NEE was not significantly correlated with soil temperature （Ts） or relative humidity （RH）. In 2021， the restored wetland in the Liaohe River estuary acted as a CO2 sink， and the total net carbon sequestration was -66.89 g·m-2. The restored salt plays a role as an important carbon sink and has long-term carbon sequestration potential.

Biome-scale temperature sensitivity of ecosystem respiration revealed by atmospheric CO2 observations.

The temperature sensitivity of ecosystem respiration regulates how the terrestrial carbon sink responds to a warming climate but has been difficult to constrain observationally beyond the plot scale. Here we use observations of atmospheric CO2 concentrations from a network of towers together with carbon flux estimates from state-of-the-art terrestrial biosphere models to characterize the temperature sensitivity of ecosystem respiration, as represented by the Arrhenius activation energy, over various North American biomes. We infer activation energies of 0.43 eV for North America and 0.38 eV to 0.53 eV for major biomes therein, which are substantially below those reported for plot-scale studies (approximately 0.65 eV). This discrepancy suggests that sparse plot-scale observations do not capture the spatial-scale dependence and biome specificity of the temperature sensitivity. We further show that adjusting the apparent temperature sensitivity in model estimates markedly improves their ability to represent observed atmospheric CO2 variability. This study provides observationally constrained estimates of the temperature sensitivity of ecosystem respiration directly at the biome scale and reveals that temperature sensitivities at this scale are lower than those based on earlier plot-scale studies. These findings call for additional work to assess the resilience of large-scale carbon sinks to warming.

Evaluation of the intrinsic temperature sensitivity of ecosystem respiration in typical ecosystems of an endorheic river basin

Evaluation of the intrinsic temperature sensitivity of ecosystem respiration in typical ecosystems of an endorheic river basin

Effects of different vegetation types on ecosystem respiration in semiarid Loess Hilly Region, Central Gansu Province, China

The principal channel of carbon export from ecosystems to the atmosphere, and an important connection in carbon exchange between land and atmosphere, is ecosystem respiration (ER). It has a significant impact on the global carbon cycle and the rate of CO2 increase in the atmosphere. The effects of different vegetation types [Medicago sativa grassland (MS); Xanthoceras sorbifolium forestland (XS); Caragana korshinskii bushland (CK); Hippophae rhamnoides shrubland (HR); and Stipa bungeana grassland (SB)] on ecosystem respiration fluxes in Loess Hilly Region (LHR) were studied via the static chamber technique. The results showed that different vegetation types had significant effects on ER fluxes, and the decreasing order of the cumulative fluxes was HR > MS > SB > CK > XS. Throughout the study period, the largest value of ER occurred in the summer and the lowest value occurred in the winter. Temperature (air temperature, soil temperature) and soil moisture were both significantly and positively linked with ER. For the temporal change of ER, the joint effect of soil temperature and moisture was a key regulating factor. The temperature sensitivity of ecosystem respiration varies greatly between vegetation types and seasons. In the process of LHR vegetation restoration, the ER, carbon sequestration capacity and ecological benefits of different plant types should be considered in order to select the vegetation type that is most conducive to reducing the greenhouse effect.

Higher Temperature Sensitivity of Ecosystem Respiration in Low Marsh Compared to High Elevation Marsh Ecosystems

AbstractSalt marsh habitats contain some of the highest quantities of soil organic carbon (C) per unit area, but increasing anthropogenic stressors threaten their ability to maintain themselves as large C reservoirs in some regions. We quantify rates of C gas exchange (methane [CH4] and carbon dioxide [CO2]) monthly across a 16‐month period from a low nitrogen “reference” salt marsh on Cape Cod in New England using static chambers. While the summer period is the most dynamic period of marsh C gas exchange, we observed substantial fluxes in the early summer through late fall, highlighting the importance of including shoulder seasons in studies of marsh C exchange. We estimate annual ecosystem respiration between 108 and 252 g C m−2 yr−1, which varied based on temperature and elevation. This flux is lower than in other nearby marshes, which we attribute to the frequently inundated, microtidal nature of the site, resulting in the majority of respired CO2 being exported via lateral, not vertical, fluxes from this marsh. We observed significantly higher temperature sensitivity from the low elevation of the marsh compared to the high marsh. Recent acceleration in the rate of sea level rise is leading to a well‐documented expansion of low marsh into high marsh vegetation zones in this marsh system and others in the region. While rates of C burial are higher in the low marsh compared to the high marsh, the higher temperature sensitivity of respiration in the low marsh may diminish the longevity of marsh C stocks with climate warming.

Net ecosystem exchange of Pinus sylvestris var. mongolica plantation in the western Liaoning Province, China

Pinus sylvestris var. mongolica is one of the important tree species for afforestation in Three-North Regions of China. Investigating net ecosystem exchange (NEE) and its influencing factors is of significance in understanding carbon balance of P. sylvestris var. mongolica plantation . We used the eddy covariance system and its supporting instruments to measure NEE and environmental factors of P. sylvestris var. mongolica plantation in the western Liaoning Province in 2020. The results showed that, at the half-hour scale, plantation emitted carbon during nighttime and sequestrated carbon over daytime. Carbon sequestration was inhibited by drought stress in the afternoon from May to August. At the daily scale, seasonal dynamics of nighttime NEE were mainly controlled by soil temperature and moisture, while that of daytime NEE were mainly controlled by soil moisture and vapor pressure deficit due to drought stress. When soil was dry, precipitation promoted nighttime and daytime NEE and improved photosynthetic and respiration parameters. At the month scale, there was significant negative linear relationship of daytime NEE with ecosystem apparent quantum yield and ecosystem maximum photosynthetic capacity. When air temperature was lower than 5 ℃, ecosystem respiration rate at 10 ℃ and temperature sensitivity of ecosystem respiration increased linearly with decreasing air temperature. The cumulative NEE of P. sylvestris var. mongolica plantation was -145.17 g C·m-2, indicating a weak carbon sink in 2020.

Warming homogenizes apparent temperature sensitivity of ecosystem respiration.

Warming-induced carbon loss through terrestrial ecosystem respiration (Re) is likely getting stronger in high latitudes and cold regions because of the more rapid warming and higher temperature sensitivity of Re (Q 10). However, it is not known whether the spatial relationship between Q 10 and temperature also holds temporally under a future warmer climate. Here, we analyzed apparent Q 10 values derived from multiyear observations at 74 FLUXNET sites spanning diverse climates and biomes. We found warming-induced decline in Q 10 is stronger at colder regions than other locations, which is consistent with a meta-analysis of 54 field warming experiments across the globe. We predict future warming will shrink the global variability of Q 10 values to an average of 1.44 across the globe under a high emission trajectory (RCP 8.5) by the end of the century. Therefore, warming-induced carbon loss may be less than previously assumed because of Q 10 homogenization in a warming world.

Diagnosing the Temperature Sensitivity of Ecosystem Respiration in Northern High‐Latitude Regions

AbstractThe accurate estimation of the temperature sensitivity of ecosystem respiration (Q10) is important to understanding the terrestrial ecosystem carbon cycle, especially in northern high‐latitude regions (NHLs). Q10 estimated by the conventional approach at the annual scale is influenced by seasonal confounding effects. Based on singular spectrum analysis, scale‐dependent parameter estimation (SCAPE) is considered an effective approach to eliminate confounding effects. Nevertheless, the performance of the decomposition and reconstruction schemes in the SCAPE approach in Q10 estimation remains limited, which hampers its further application in larger‐scale systems. In this study, we utilized an improved scale‐dependent parameter estimation (iSCAPE) approach to analyze trends of the unconfounded Q10 and its environmental controls in NHLs. The results showed that in NHLs, the confounding effects in forest ecosystems were smaller than those in cropland and grassland ecosystems. The apparent Q10 estimated by the conventional approach varied among 32 sites with a mean value of 2.82 (95% confidence interval (CI): 2.72–2.91), while the mean intrinsic Q10 estimated by the iSCAPE approach across the 32 sites was 1.53 (95% CI: 1.48–1.57). The apparent Q10 increased with the annual mean temperature. The intrinsic Q10 decreased with the increasing of spatial temperature gradient. The current study indicates that ecosystem respiration in NHLs is less sensitive to climate warming than previously reported. The seasonality of ecosystem respiration should be eliminated when estimating Q10 to avoid overestimating climate‐carbon cycle feedback.

Temperature thresholds of ecosystem respiration at a global scale.

Ecosystem respiration is a major component of the global terrestrial carbon cycle and is strongly influenced by temperature. The global extent of the temperature-ecosystem respiration relationship, however, has not been fully explored. Here, we test linear and threshold models of ecosystem respiration across 210 globally distributed eddy covariance sites over an extensive temperature range. We find thresholds to the global temperature-ecosystem respiration relationship at high and low air temperatures and mid soil temperatures, which represent transitions in the temperature dependence and sensitivity of ecosystem respiration. Annual ecosystem respiration rates show a markedly reduced temperature dependence and sensitivity compared to half-hourly rates, and a single mid-temperature threshold for both air and soil temperature. Our study indicates a distinction in the influence of environmental factors, including temperature, on ecosystem respiration between latitudinal and climate gradients at short (half-hourly) and long (annual) timescales. Such climatological differences in the temperature sensitivity of ecosystem respiration have important consequences for the terrestrial net carbon sink under ongoing climate change.

Divergence in ecosystem carbon fluxes and soil nitrogen characteristics across alpine steppe, alpine meadow and alpine swamp ecosystems in a biome transition zone

Alpine ecosystem carbon cycling is sensitive to climate change, particularly in the transition zones between biomes. Soil nitrogen conditions, including the ammonium to nitrate (NH4+/NO3−) ratio, regulate ecosystem carbon uptake by coupling carbon‑nitrogen cycle. The largest alpine pasture on Earth is distributed on the Tibetan Plateau, where alpine biome transition zones are also widely distributed. However, it is largely unknown how the soil NH4+/NO3− ratio and net ecosystem CO2 exchange vary among vegetation types in the alpine biome transition zones due to a lack of in situ field observations. Here, we investigated soil NH4+/NO3− ratio and ecosystem carbon fluxes across alpine steppe, alpine meadow and alpine swamp ecosystems in a biome transition zone on the central Tibetan Plateau. The results showed that soil NH4+/NO3− ratio was lowest in the alpine steppe (driest environment), which had the highest soil pH, and highest in the alpine swamp (wettest environment), which had the lowest soil pH. We proposed a theoretical framework describing how soil moisture regulates soil NH4+/NO3− ratio by altering both the denitrification process and soil pH. We further found that the growing season average net ecosystem CO2 exchange for the alpine steppe, alpine meadow and alpine swamp was −1.46, −1.90 and −5.43 μmol m−2 s−1, respectively. This divergence in net ecosystem CO2 exchange across the three grasslands is primarily explained by divergence in gross ecosystem photosynthesis, rather than ecosystem respiration. The air temperature sensitivity of ecosystem respiration (Q10) for the alpine steppe, alpine meadow and alpine swamp was 1.73 ± 0.05, 1.44 ± 0.03 and 2.43 ± 0.45, respectively. Our study highlights large differences in both soil nutrient and ecosystem carbon uptake across different vegetation types in an alpine biome transition zone. More in situ investigations in various biome transition zones are urgently needed to quantitatively understand the spatial pattern of alpine ecosystem carbon‑nitrogen cycling processes.

Watershed geomorphology modifies the sensitivity of aquatic ecosystem metabolism to temperature

The regulation of aquatic carbon cycles by temperature is a significant uncertainty in our understanding of how watersheds will respond to climate change. Aquatic ecosystems transport substantial quantities of carbon to the atmosphere and ocean, yet we have limited understanding of how temperature modifies aquatic ecosystem metabolic processes and contributions to carbon cycles at watershed to global scales. We propose that geomorphology controls the distribution and quality of organic material that forms the metabolic base of aquatic ecosystems, thereby controlling the response of aquatic ecosystem metabolism to temperature across landscapes. Across 23 streams and four years during summer baseflow, we estimated variation in the temperature sensitivity of ecosystem respiration (R) among streams draining watersheds with different geomorphic characteristics across a boreal river basin. We found that geomorphic features imposed strong controls on temperature sensitivity; R in streams draining flat watersheds was up to six times more temperature sensitive than streams draining steeper watersheds. Further, our results show that this association between watershed geomorphology and temperature sensitivity of R was linked to the carbon quality of substrates that changed systematically across the geomorphic gradient. This suggests that geomorphology will control how carbon is transported, stored, and incorporated into river food webs as the climate warms.

Temporal variations and temperature sensitivity of ecosystem respiration in three brackish marsh communities in the Min River Estuary, southeast China

Ecosystem respiration (Reco) is an important pathway for gaseous carbon loss in coastal wetland environments. However, little is known regarding the dynamics of Reco and its temperature sensitivity (Q10) under different tidal stages, and vegetation types. In this study, Reco was measured with dark chambers for nearly 2 years in three different brackish marsh stands dominated by Cyperus malaccensis, Phragmites australis, and Spartina alterniflora, respectively, in the Min River estuary of southeast China. The mean Reco across tidal stages and vegetation types exhibited strong temporal variations, and the Q10 value for Reco was higher in the warm months than in the cold months. The mean annual Reco was negatively correlated with electrical conductivity and soil water content, but positively correlated with both tidal water level and soil pH (P < 0.05). On the other hand, the seasonal variation in Reco and Q10 was largely driven by the thermal regimes and soil salinity. Also, we found that the mean Reco and Qs10 value were both relatively higher when the site was exposed before tidal inundation, as compared to that after tidal inundation for all the vegetation types studied (P > 0.05). Overall, the C. malacensis and S. alterniflora stands had the highest and lowest average rates of Reco, respectively, while the mean Qs10 values were lower in the Phragmites australis stand than the other two vegetation types. Our findings point to the need of strengthening the in situ measurements of gas fluxes at multiple time scales in order to develop a better understanding of the response of Reco to changing environmental conditions in the subtropical coastal wetlands. Our results also reiterate the importance of considering the influence of vegetation types in characterizing the magnitude and temperature sensitivity of Reco in estuarine tidal marshes for predicting ecosystem responses to future global change.

The transient shift of driving environmental factors of carbon dioxide and methane fluxes in Tibetan peatlands before and after hydrological restoration

Peatlands on the Tibetan Plateau play crucial roles in regional carbon cycling but faced serious degradation in recent decades, and hydrological restoration is being conducted to regain their ecosystem function. However, how restoration affects the environmental controls on carbon processes of these unique ecosystems remains unclear, and the role of vegetation community in regulating carbon processes in response to the restoration is unknown. A long dam was built at the outlet of a large shallow lake on the plateau in order to evaluate the effects of hydrological restoration on the carbon sequestration of the world’s largest alpine peatlands. The carbon dioxide (CO2) and methane (CH4) fluxes from three widely distributed peatland communities, i.e., Kobresia pusilla, Carex enervis, and Carex muliensis commuities, were investigated immediately before and after restoration. The water table rising as a consequence of restoration, at least temporarily, decreased the carbon consumption rate (plant respiration plus soil decomposition) for each unit of carbon fixation by plants, which is community dependent. However, a positive relationship between temperature sensitivity of ecosystem respiration (Reco) and optimal water table for respiration implies a positive feedback between water table rising and warming on Reco. Meanwhile, the dominant factor explaining the variance of Reco shifted from soil temperature (explained 56%) to water table (explained 68%) after restoration. Water table rising enhanced the CH4 emissions by 3–12 times, with significantly different changes in CH4 flux over a standard variation in water table level among the communities. Temperature was excluded while only water table and vegetation type were included in the model to predict CH4 fluxes after restoration in contrast to before. We argue that the shift of driving environmental factors and the role of vegetation community are essential in evaluating the effects of hydrological restoration on carbon cycling of Plateau peatlands, particularly during the transitional period.

Optimization of Terrestrial Ecosystem Model Parameters Using Atmospheric CO2 Concentration Data With the Global Carbon Assimilation System (GCAS)

AbstractThe Global Carbon Assimilation System that assimilates ground‐based atmospheric CO2 data is used to estimate several key parameters in a terrestrial ecosystem model for the purpose of improving carbon cycle simulation. The optimized parameters are the leaf maximum carboxylation rate at 25°C ( ), the temperature sensitivity of ecosystem respiration (Q10), and the soil carbon pool size. The optimization is performed at the global scale at 1° resolution for the period from 2002 to 2008. The results indicate that vegetation from tropical zones has lower values than vegetation in temperate regions. Relatively high values of Q10 are derived over high/midlatitude regions. Both and Q10 exhibit pronounced seasonal variations at middle‐high latitudes. The maxima in occur during growing seasons, while the minima appear during nongrowing seasons. Q10 values decrease with increasing temperature. The seasonal variabilities of and Q10 are larger at higher latitudes. Optimized and Q10 show little seasonal variabilities at tropical regions. The seasonal variabilities of are consistent with the variabilities of LAI for evergreen conifers and broadleaf evergreen forests. Variations in leaf nitrogen and leaf chlorophyll contents may partly explain the variations in . The spatial distribution of the total soil carbon pool size after optimization is compared favorably with the gridded Global Soil Data Set for Earth System. The results also suggest that atmospheric CO2 data are a source of information that can be tapped to gain spatially and temporally meaningful information for key ecosystem parameters that are representative at the regional and global scales.

Grassland types and season-dependent response of ecosystem respiration to experimental warming in a permafrost region in the Tibetan Plateau

Information regarding the response of ecosystem respiration (ER) to various warming levels, especially in different grassland types and seasons, is scarce at the field scale in the permafrost region of the Tibetan Plateau (TP). In this study, we examined how different warming levels during different seasons affected ER in Tibetan alpine meadow and swamp meadow after 6 years experimental warming. The interpolated annual ER of swamp meadow (387.0gCm−2) was higher than that of alpine meadow (284.5gCm−2) in natural conditions. A moderate warming of 2.4°C increased ER by 62.2% and 36.6%, and a high warming of 5.3°C increased ER by 101.3% and 52.0% in alpine meadow and swamp meadow, respectively. The warming effects on ER were greater in the non-growing season compared with the growing season; this significantly increased the contribution of non-growing season emissions to annual ER from 25% in natural conditions to 31% in high warming treatments. ER was significantly affected by soil temperature, aboveground biomass and the duration of thaw days. The temperature sensitivity of ER (Q10) was higher in the non-growing season (3.02–5.02) than in the growing season (2.11–2.75) and decreased with increasing temperature. Our results indicated that the magnitude of warming-induced increases in ER differed by grassland type and season, and there was strong potential for the non-growing season to serve as a positive feedback to annual carbon balance.

Carbon exchange of a rainfed spring maize cropland under plastic film mulching with straw returning on the Loess Plateau, China

Increasing attention has been paid to the potential of croplands to mitigate rising atmospheric CO2 concentrations by adopting appropriate cultivation practices. Plastic film mulching with straw returning to promote crop yields is widely used in rainfed agriculture; however, information about the effect of this practice on carbon exchange is limited. Eddy covariance measurements were used to investigate carbon fluxes in a rainfed spring maize cropland under plastic film mulching with straw returning on the Chinese Loess Plateau in 2013 and 2014. Carbon fluxes showed a clear seasonal variation, with the green leaf area index (GLAI) being the dominant control factor. The diurnal and seasonal ecosystem respiration (Re) values were driven by gross primary productivity (GPP), and the daily Re per unit daily GPP increased by 0.32gCm−2d−1. The ecosystem apparent quantum yield (α), ecosystem maximum photosynthetic capacity (Pmax), and ecosystem respiration rate at 10°C (R10) also showed clear seasonal variations, and the mean monthly α, Pmax, and R10 per unit mean monthly GLAI increased by 1.44×10−2μmolCO2μmol PAR−1, 1.12mgCO2m−2s−1, and 2.08×10−2mgCO2m−2s−1 respectively. The temperature sensitivity of ecosystem respiration was insensitive to GLAI, and ranged from 1.58 to 2.85, with the maximum value appearing in the non-growth seasons. Annual GPP values were 1547 and 1370gCm−2 in 2013 and 2014, respectively, approximately 60% of which was lost through Re, which resulted in annual net CO2 uptakes of 618 and 540gCm−2 in 2013 and 2014 respectively. Compared to the non-mulching spring maize field with straw returning, the spring maize field under plastic film mulching with straw returning was a stronger carbon sink (76 and 41gCm−2 in 2013 and 2014, respectively). Plastic film mulching with straw returning is recommended as an effective approach to sequester carbon in rainfed spring maize cropland on the Loess Plateau and to mitigate greenhouse effects.

Long-term enhanced winter soil frost alters growing season CO2 fluxes through its impact on vegetation development in a boreal peatland.

At high latitudes, winter climate change alters snow cover and, consequently, may cause a sustained change in soil frost dynamics. Altered winter soil conditions could influence the ecosystem exchange of carbon dioxide (CO2 ) and, in turn, provide feedbacks to ongoing climate change. To investigate the mechanisms that modify the peatland CO2 exchange in response to altered winter soil frost, we conducted a snow exclusion experiment to enhance winter soil frost and to evaluate its short-term (1-3years) and long-term (11years) effects on CO2 fluxes during subsequent growing seasons in a boreal peatland. In the first 3years after initiating the treatment, no significant effects were observed on either gross primary production (GPP) or ecosystem respiration (ER). However, after 11years, the temperature sensitivity of ER was reduced in the treatment plots relative to the control, resulting in an overall lower ER in the former. Furthermore, early growing season GPP was also lower in the treatment plots than in the controls during periods with photosynthetic photon flux density (PPFD) ≥800μmolm-2 s-1 , corresponding to lower sedge leaf biomass in the treatment plots during the same period. During the peak growing season, a higher GPP was observed in the treatment plots under the low light condition (i.e. PPFD 400μmolm-2 s-1 ) compared to the control. As Sphagnum moss maximizes photosynthesis at low light levels, this GPP difference between the plots may have been due to greater moss photosynthesis, as indicated by greater moss biomass production, in the treatment plots relative to the controls. Our study highlights the different responses to enhanced winter soil frost among plant functional types which regulate CO2 fluxes, suggesting that winter climate change could considerably alter the growing season CO2 exchange in boreal peatlands through its effect on vegetation development.

The temperature sensitivity of ecosystem respiration to climate change in an alpine meadow on the Tibet plateau: A reciprocal translocation experiment

Information about the potential effects of climate change, especially cooling, on ecosystem respiration (Re) in alpine meadows is scarce. We determined the effects of warming and cooling on Re on the Tibetan Plateau using a 2-year reciprocal translocation experiment with 4 different vegetation types (3 alpine meadows and 1 alpine shrub differentiated by plant community composition) along an elevation gradient from 3200 to 3800m (with vegetation types E2, E4, E6 and E8 at 3200, 3600, 3800 and 3800m, respectively) during the growing seasons in 2008 and 2009. Mean growing seasonal Re decreased by 13.6, 30.3 and 40.7% per 200m rise in elevation (cooling) for vegetation types E2, E4 and E6, but increased by 1.3, 35.9 and 58.8% per 200m decrease in elevation (warming) for vegetation types E4, E6 and E8, respectively. Soil temperature explained 49.3–64.0% of daily Re variation and aboveground biomass explained 21.5–61.6% of average Re variation of the growing season for all vegetation types, but the effect of soil moisture on Re was small over 2-year. The values of Re temperature sensitivity increased with an increase in elevation for both warming (3.3, 24.3 and 53.5%°C−1 for vegetation types E4, E6 and E8) and cooling (8.0, 19.1 and 24.4%°C−1 for vegetation types E2, E4 and E6), suggesting that alpine meadow at higher elevation was more sensitive to both warming and cooling. Based on the values of Re temperature sensitivity for all pooled vegetation types (25.4, 5.6 and 19.6%°C−1 for warming, cooling and pooled warming and cooling), it could be over-estimated by 23% for warming alone compared with pooled warming and cooling. Therefore, asymmetrical responses of Re to warming and cooling should be taken into account when we evaluate the effect of temperature change on Re using models in the future.

Comment on Demars et al. 2015, “Stream metabolism and the open diel oxygen method: Principles, practice, and perspectives”

AbstractDemars et al. present a review of stream ecosystem metabolism theory that provides the basis for a set of best practices. Here we clarify two technical and conceptual errors in reviewing the current state of research regarding inverse modeling of ecosystem metabolism. Specifically, the assertions by Demars et al. that inverse modeling of metabolism is limited to low reaereation, high productivity ecosystems and, when feasible, measurement of gas transfer by volatile tracer injection is the preferred method, are based on an incomplete conceptualization of current ecosystem metabolism models and does not recognize the unconstrained biases in tracer injection methods. In addition to these corrections, we highlight how inverse model fitting is a robust methodology to constrain key metabolic parameters by capturing the information contained in the dynamics of diel O2 data. When done in a Bayesian context, inverse model fitting also provides a means to incorporate multiple sources of available data, including those from tracer studies, and formally propagate uncertainties in parameter estimates. Last, we describe how model fitting of diel O2 data can also provide information on temperature sensitivity of ecosystem respiration.