Fernandez-Martinez M., Vicca S., Janssens I.A., Luyssaert S., Campioli M., Sardans J., Estiarte M., Penuelas J. (2014) Spatial variability and controls over biomass stocks, carbon fluxes, and resource-use efficiencies across forest ecosystems. Trees - Structure and Function. 28: 597-611.EnllaçDoi: 10.1007/s00468-013-0975-9
Key message: Stand age, water availability, and the length of the warm period are the most influencing controls of forest structure, functioning, and efficiency. We aimed to discern the distribution and controls of plant biomass, carbon fluxes, and resource-use efficiencies of forest ecosystems ranging from boreal to tropical forests. We analysed a global forest database containing estimates of stand biomass and carbon fluxes (400 and 111 sites, respectively) from which we calculated resource-use efficiencies (biomass production, carbon sequestration, light, and water-use efficiencies). We used the WorldClim climatic database and remote-sensing data derived from the Moderate Resolution Imaging Spectroradiometer to analyse climatic controls of ecosystem functioning. The influences of forest type, stand age, management, and nitrogen deposition were also explored. Tropical forests exhibited the largest gross carbon fluxes (photosynthesis and ecosystem respiration), but rather low net ecosystem production, which peaks in temperate forests. Stand age, water availability, and length of the warm period were the main factors controlling forest structure (biomass) and functionality (carbon fluxes and efficiencies). The interaction between temperature and precipitation was the main climatic driver of gross primary production and ecosystem respiration. The mean resource-use efficiency varied little among biomes. The spatial variability of biomass stocks and their distribution among ecosystem compartments were strongly correlated with the variability in carbon fluxes, and both were strongly controlled by climate (water availability, temperature) and stand characteristics (age, type of leaf). Gross primary production and ecosystem respiration were strongly correlated with mean annual temperature and precipitation only when precipitation and temperature were not limiting factors. Finally, our results suggest a global convergence in mean resource-use efficiencies. © 2013 Springer-Verlag Berlin Heidelberg.
Greenberg J.P., Penuelas J., Guenther A., Seco R., Turnipseed A., Jiang X., Filella I., Estiarte M., Sardans J., Ogaya R., Llusia J., Rapparini F. (2014) A tethered-balloon PTRMS sampling approach for surveying of landscape-scale biogenic VOC fluxes. Atmospheric Measurement Techniques. 7: 2263-2271.EnllaçDoi: 10.5194/amt-7-2263-2014
Landscape-scale fluxes of biogenic gases were surveyed by deploying a 100 m Teflon tube attached to a tethered balloon as a sampling inlet for a fast-response proton-transfer-reaction mass spectrometer (PTRMS). Along with meteorological instruments deployed on the tethered balloon and a 3 m tripod and outputs from a regional weather model, these observations were used to estimate landscape-scale biogenic volatile organic compound fluxes with two micrometeorological techniques: mixed layer variance and surface layer gradients. This highly mobile sampling system was deployed at four field sites near Barcelona to estimate landscape-scale biogenic volatile organic compound (BVOC) emission factors in a relatively short period (3 weeks). The two micrometeorological techniques were compared with emissions predicted with a biogenic emission model using site-specific emission factors and land-cover characteristics for all four sites. The methods agreed within the uncertainty of the techniques in most cases, even though the locations had considerable heterogeneity in species distribution and complex terrain. Considering the wide range in reported BVOC emission factors for individual vegetation species (more than an order of magnitude), this temporally short and inexpensive flux estimation technique may be useful for constraining BVOC emission factors used as model inputs. © 2014 Author(s).
Vicca S., Bahn M., Estiarte M., Van Loon E.E., Vargas R., Alberti G., Ambus P., Arain M.A., Beier C., Bentley L.P., Borken W., Buchmann N., Collins S.L., De Dato G., Dukes J.S., Escolar C., Fay P., Guidolotti G., Hanson P.J., Kahmen A., Kroel-Dulay G., Ladreiter-Knauss T., Larsen K.S., Lellei-Kovacs E., Lebrija-Trejos E., Maestre F.T., Marhan S., Marshall M., Meir P., Miao Y., Muhr J., Niklaus P.A., Ogaya R., Penuelas J., Poll C., Rustad L.E., Savage K., Schindlbacher A., Schmidt I.K., Smith A.R., Sotta E.D., Suseela V., Tietema A., Van Gestel N., Van Straaten O., Wan S., Weber U., Janssens I.A. (2014) Erratum: Can current moisture responses predict soil CO2 efflux under altered precipitation regimes? A synthesis of manipulation experiments (Biogeosciences (2014) 11 (2991-3013)). Biogeosciences. 11: 3307-3308.EnllaçDoi: 10.5194/bg-11-3307-2014
[No abstract available]
Vicca S., Bahn M., Estiarte M., Van Loon E.E., Vargas R., Alberti G., Ambus P., Arain M.A., Beier C., Bentley L.P., Borken W., Buchmann N., Collins S.L., De Dato G., Dukes J.S., Escolar C., Fay P., Guidolotti G., Hanson P.J., Kahmen A., Kröel-Dulay G., Ladreiter-Knauss T., Larsen K.S., Lellei-Kovacs E., Lebrija-Trejos E., Maestre F.T., Marhan S., Marshall M., Meir P., Miao Y., Muhr J., Niklaus P.A., Ogaya R., Peñuelas J., Poll C., Rustad L.E., Savage K., Schindlbacher A., Schmidt I.K., Smith A.R., Sotta E.D., Suseela V., Tietema A., Van Gestel N., Van Straaten O., Wan S., Weber U., Janssens I.A. (2014) Can current moisture responses predict soil CO2 efflux under altered precipitation regimes? A synthesis of manipulation experiments. Biogeosciences. 11: 2991-3013.EnllaçDoi: 10.5194/bg-11-2991-2014
As a key component of the carbon cycle, soil CO2 efflux (SCE) is being increasingly studied to improve our mechanistic understanding of this important carbon flux. Predicting ecosystem responses to climate change often depends on extrapolation of current relationships between ecosystem processes and their climatic drivers to conditions not yet experienced by the ecosystem. This raises the question of to what extent these relationships remain unaltered beyond the current climatic window for which observations are available to constrain the relationships. Here, we evaluate whether current responses of SCE to fluctuations in soil temperature and soil water content can be used to predict SCE under altered rainfall patterns. Of the 58 experiments for which we gathered SCE data, 20 were discarded because either too few data were available or inconsistencies precluded their incorporation in the analyses. The 38 remaining experiments were used to test the hypothesis that a model parameterized with data from the control plots (using soil temperature and water content as predictor variables) could adequately predict SCE measured in the manipulated treatment. Only for 7 of these 38 experiments was this hypothesis rejected. Importantly, these were the experiments with the most reliable data sets, i.e., those providing high-frequency measurements of SCE. Regression tree analysis demonstrated that our hypothesis could be rejected only for experiments with measurement intervals of less than 11 days, and was not rejected for any of the 24 experiments with larger measurement intervals. This highlights the importance of high-frequency measurements when studying effects of altered precipitation on SCE, probably because infrequent measurement schemes have insufficient capacity to detect shifts in the climate dependencies of SCE. Hence, the most justified answer to the question of whether current moisture responses of SCE can be extrapolated to predict SCE under altered precipitation regimes is "no" - as based on the most reliable data sets available. We strongly recommend that future experiments focus more strongly on establishing response functions across a broader range of precipitation regimes and soil moisture conditions. Such experiments should make accurate measurements of water availability, should conduct high-frequency SCE measurements, and should consider both instantaneous responses and the potential legacy effects of climate extremes. This is important, because with the novel approach presented here, we demonstrated that, at least for some ecosystems, current moisture responses could not be extrapolated to predict SCE under altered rainfall conditions. © Author(s) 2014.
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