Photosynthesis drives anomalies in net carbon-exchange of pine forests at different latitudes

The growth rate of atmospheric CO2 exhibits large temporal variation that is largely determined by year-to-year fluctuations in land‐atmosphere CO2 fluxes. This land‐atmosphere CO2-flux is driven by large-scale biomass burning and variation in net ecosystem exchange (NEE). Between- and within years, NEE varies due to fluctuations in climate. Studies on climatic influences on inter- and intra-annual variability in gross photosynthesis (GPP) and net carbon uptake in terrestrial ecosystems have shown conflicting results. These conflicts are in part related to differences in methodology and in part to the limited duration of some studies. Here, we introduce an observation-driven methodology that provides insight into the dependence of anomalies in CO2 fluxes on climatic conditions. The methodology was applied on fluxes from a boreal and two temperate pine forests. Annual anomalies in NEE were dominated by anomalies in GPP, which in turn were correlated with incident radiation and vapor pressure deficit (VPD). At all three sites positive anomalies in NEE (a reduced uptake or a stronger source than the daily sites specific long-term average) were observed on summer days characterized by low incident radiation, low VPD and high precipitation. Negative anomalies in NEE occurred mainly on summer days characterized by blue skies and mild temperatures. Our study clearly highlighted the need to use weather patterns rather than single climatic variables to understand anomalous CO2 fluxes. Temperature generally showed little direct effect on anomalies in NEE but became important when the mean daily air temperature exceeded 231C. On such days GPP decreased likely because VPD exceeded 2.0kPa, inhibiting photosynthetic uptake. However, while GPP decreased, the high temperature stimulated respiration, resulting in positive anomalies in NEE. Climatic extremes in summer were more frequent and severe in the South than in the North, and had larger effects in the South because the criteria to inhibit photosynthesis are more often met.

[1]  Tiina Markkanen,et al.  Effect of thinning on surface fluxes in a boreal forest , 2005 .

[2]  H. Tian,et al.  Effect of interannual climate variability on carbon storage in Amazonian ecosystems , 1998, Nature.

[3]  S. Wofsy,et al.  Factors Controlling Long- and Short-Term Sequestration of Atmospheric CO2 in a Mid-latitude Forest , 2001, Science.

[4]  T. A. Black,et al.  Effects of climatic variability on the annual carbon sequestration by a boreal aspen forest , 1999 .

[5]  Corinne Le Quéré,et al.  Regional changes in carbon dioxide fluxes of land and oceans since 1980. , 2000, Science.

[6]  Marc Aubinet,et al.  Estimation of the carbon sequestration by a heterogeneous forest: night flux corrections, heterogeneity of the site and inter‐annual variability , 2002 .

[7]  Arnaud Carrara,et al.  Net ecosystem CO2 exchange of mixed forest in Belgium over 5 years , 2003 .

[8]  Harden,et al.  Sensitivity of boreal forest carbon balance to soil thaw , 1998, Science.

[9]  Inez Y. Fung,et al.  Can climate variability contribute to the “missing” CO2 sink? , 1993 .

[10]  G. Meehl,et al.  More Intense, More Frequent, and Longer Lasting Heat Waves in the 21st Century , 2004, Science.

[11]  J. Randerson,et al.  Continental-Scale Partitioning of Fire Emissions During the 1997 to 2001 El Niño/La Niña Period , 2003, Science.

[12]  W. Oechel,et al.  Environmental controls over carbon dioxide and water vapor exchange of terrestrial vegetation , 2002 .

[13]  Jianwu Tang,et al.  Tree photosynthesis modulates soil respiration on a diurnal time scale , 2005 .

[14]  K. Davis,et al.  A multi-site analysis of random error in tower-based measurements of carbon and energy fluxes , 2006 .

[15]  Jehn-Yih Juang,et al.  Variability in net ecosystem exchange from hourly to inter-annual time scales at adjacent pine and hardwood forests: a wavelet analysis. , 2005, Tree physiology.

[16]  P. Ciais,et al.  Europe-wide reduction in primary productivity caused by the heat and drought in 2003 , 2005, Nature.

[17]  Ü. Rannik,et al.  Estimates of the annual net carbon and water exchange of forests: the EUROFLUX methodology , 2000 .

[18]  T. Vesala,et al.  On the separation of net ecosystem exchange into assimilation and ecosystem respiration: review and improved algorithm , 2005 .

[19]  M. Aubinet,et al.  Determinants of terrestrial ecosystem carbon balance inferred from European eddy covariance flux sites , 2007 .

[20]  Tiina Markkanen,et al.  Air temperature triggers the recovery of evergreen boreal forest photosynthesis in spring , 2003 .

[21]  Henry W. Loescher,et al.  Uncertainties in, and interpretation of, carbon flux estimates using the eddy covariance technique , 2006 .

[22]  Natascha Kljun,et al.  Climatic controls on the carbon and water balances of a boreal aspen forest, 1994–2003 , 2007 .

[23]  Michael G. Ryan,et al.  Interpreting, measuring, and modeling soil respiration , 2005 .

[24]  J. William Munger,et al.  Exchange of Carbon Dioxide by a Deciduous Forest: Response to Interannual Climate Variability , 1996, Science.

[25]  Wenjun Chen,et al.  Increased carbon sequestration by a boreal deciduous forest in years with a warm spring , 2000 .

[26]  Tiina Markkanen,et al.  Interannual variability and timing of growing‐season CO2 exchange in a boreal forest , 2003 .

[27]  T. Black,et al.  Inter-annual variability in the leaf area index of a boreal aspen-hazelnut forest in relation to net ecosystem production , 2004 .

[28]  D. Lüthi,et al.  The role of increasing temperature variability in European summer heatwaves , 2004, Nature.

[29]  Franz-W. Badeck,et al.  Interannual variation of carbon exchange fluxes in terrestrial ecosystems , 1996 .

[30]  M. Heimann,et al.  Comprehensive comparison of gap-filling techniques for eddy covariance net carbon fluxes , 2007 .

[31]  Ü. Rannik,et al.  Coniferous Forests (Scots and Maritime Pine): Carbon and Water Fluxes, Balances, Ecological and Ecophysiological Determinants , 2003 .

[32]  A. G. Barr,et al.  Response of Net Ecosystem Productivity of Three Boreal Forest Stands to Drought , 2006, Ecosystems.

[33]  T. Kohonen,et al.  Bibliography of Self-Organizing Map SOM) Papers: 1998-2001 Addendum , 2003 .

[34]  Kimmo Kiviluoto,et al.  Topology preservation in self-organizing maps , 1996, Proceedings of International Conference on Neural Networks (ICNN'96).

[35]  P. Hari,et al.  Eddy covariance measurements of CO2 and sensible and latent heat fluxes during a full year in a boreal pine forest trunk-space , 2005 .

[36]  R. Monson,et al.  Carbon sequestration in a high‐elevation, subalpine forest , 2001 .

[37]  Teuvo Kohonen,et al.  Self-Organizing Maps , 2010 .

[38]  P. Warnant,et al.  The interannual change of atmospheric CO2: Contribution of subtropical ecosystems? , 1999 .

[39]  Ü. Rannik,et al.  Productivity overshadows temperature in determining soil and ecosystem respiration across European forests , 2001 .

[40]  R. Valentini,et al.  A new assessment of European forests carbon exchanges by eddy fluxes and artificial neural network spatialization , 2003 .

[41]  M. Andersson,et al.  Brood parasitism: Female ducks can double their reproduction , 2001, Nature.

[42]  T. Vesala,et al.  Towards a standardized processing of Net Ecosystem Exchange measured with eddy covariance technique: algorithms and uncertainty estimation , 2006 .

[43]  Christopher B. Field,et al.  Increases in early season ecosystem uptake explain recent changes in the seasonal cycle of atmospheric CO2 at high northern latitudes , 1999 .

[44]  Berrien Moore,et al.  The response of global terrestrial ecosystems to interannual temperature variability , 1997 .

[45]  D. Baldocchi.  Assessing the eddy covariance technique for evaluating carbon dioxide exchange rates of ecosystems: past, present and future , 2003 .

[46]  A. J. Dolman,et al.  Radiation, temperature, and leaf area explain ecosystem carbon fluxes in boreal and temperate European forests , 2005 .

[47]  Eric A. Davidson,et al.  Spatial and temporal variability in forest–atmosphere CO2 exchange , 2004 .

[48]  Ü. Rannik,et al.  Respiration as the main determinant of carbon balance in European forests , 2000, Nature.

[49]  N. McDowell,et al.  13C content of ecosystem respiration is linked to precipitation and vapor pressure deficit , 2002, Oecologia.

[50]  Beverly E. Law,et al.  Climatic versus biotic constraints on carbon and water fluxes in seasonally drought‐affected ponderosa pine ecosystems , 2004 .