Impact of changing soil moisture distribution on net ecosystem productivity of a boreal aspen forest during and following drought

The interannual and seasonal variability of gross ecosystem photosynthesis (P), ecosystem respiration (R) and evapotranspiration (E), and their relationships to environmental factors were used to explain changes in net ecosystem productivity (F NEP) at the onset of, during, and following a 3-year-long (2001–2003) drought in a mature boreal aspen stand in central Saskatchewan, Canada. The forest was a moderate carbon (C) sink over its entire 11-year data record (F NEP = 153 � 99 g C m � 2 year � 1 ), including the peak drought years of 2002 and 2003. In 2001, the depletion of water near the soil surface likely reduced heterotrophic soil respiration while water remaining deep in the root zone maintained P above the pre-drought mean, resulting in above-average F NEP. In 2002 and 2003, the forest remained a C sink even though P was below average because R was also below average—a likely consequence of the influence of low soil water content in deep and shallow soil layers on both autotrophic and heterotrophic respiration. In 2004, the recharge of soil water in shallow soil layers allowed R to recover to its pre-drought values, whereas low spring temperatures, the slow recharge of soil water in deep soil layers in spring, late leaf emergence and diminished leaf area index combined to suppress P and produce the lowest annual F NEP of the 11-year record (4 g C m � 2 year � 1 ). The low F NEP and P were mirrored in the lowest stem growth and LAI values of the 11-year record. In 2005, a warm wet year, both the annual values and seasonal variations of F NEP, P and R returned to those of pre-drought years; the partial recovery of LAI to pre-drought values suggests that aspen P was able to adjust to this restriction on C assimilation. Growing season average dry surface conductance (gsv), the Priestley–Taylor coefficient (a) and light use efficiency (LUE) reached their lowest values in 2003 and became similar to predrought years in 2004–2005. Water use efficiency (WUE) was highest in 2003 and remained above average in 2004 and 2005. At the ecosystem scale, the above-average gains made in C sequestration in the first year of the drought were significantly offset by belowaverage stand F NEP in the final 2 years of the drought, and in the year following the drought. # 2006 Elsevier B.V. All rights reserved.

[1]  J. Morgan,et al.  Elevated CO2 increases soil moisture and enhances plant water relations in a long-term field study in semi-arid shortgrass steppe of Colorado , 2004, Plant and Soil.

[2]  N. Breda,et al.  A generic model of forest canopy conductance dependent on climate, soil water availability and leaf area index , 2000 .

[3]  E. Hogg,et al.  The aspen parkland in western Canada: a dry climate analogue for the future boreal forest? , 1995 .

[4]  T. A. Black,et al.  Spatial and temporal variability of CO2 concentration and flux in a boreal aspen forest , 1999 .

[5]  Richard H. Waring,et al.  Environmental Limits on Net Primary Production and Light‐Use Efficiency Across the Oregon Transect , 1994 .

[6]  J. Tenhunen,et al.  Severe drought effects on ecosystem CO2 and H2O fluxes at three Mediterranean evergreen sites: revision of current hypotheses? , 2002 .

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

[8]  T. A. Black,et al.  Comparing the carbon budgets of boreal and temperate deciduous forest stands , 2002 .

[9]  Corinna Rebmann,et al.  Productivity of forests in the Eurosiberian boreal region and their potential to act as a carbon sink –‐ a synthesis , 1999 .

[10]  V. Lieffers,et al.  Seasonal changes in carbohydrate reserves in mature northern Populus tremuloides clones , 2003, Trees.

[11]  E. Hogg.  Simulation of interannual responses of trembling aspen stands to climatic variation and insect defoliation in western Canada , 1999 .

[12]  Hans Peter Schmid,et al.  Photosynthetic and Water Use Efficiency Responses to Diffuse Radiation by an Aspen-Dominated Northern Hardwood Forest , 2004, Forest Science.

[13]  D. Dokken,et al.  Climate change 2001 , 2001 .

[14]  Natascha Kljun,et al.  Seasonal variation and partitioning of ecosystem respiration in a southern boreal aspen forest , 2004 .

[15]  R. J. Olson,et al.  NET PRIMARY PRODUCTION AND CARBON ALLOCATION PATTERNS OF BOREAL FOREST ECOSYSTEMS , 2001 .

[16]  Darrel L. Williams,et al.  BOREAS in 1997: Experiment overview, scientific results, and future directions , 1997 .

[17]  G. Katul,et al.  WATER BALANCE DELINEATES THE SOIL LAYER IN WHICH MOISTURE AFFECTS CANOPY CONDUCTANCE , 1998 .

[18]  F. Hall,et al.  Physically based classification and satellite mapping of biophysical characteristics in the southern boreal forest , 1997 .

[19]  C. D. Keeling,et al.  Increased activity of northern vegetation inferred from atmospheric CO2 measurements , 1996, Nature.

[20]  Ye Qi,et al.  Effects of climate variability on the carbon dioxide, water, and sensible heat fluxes above a ponderosa pine plantation in the Sierra Nevada (CA) , 2000 .

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

[22]  K. Morgenstern,et al.  Net ecosystem production of a Douglas‐fir stand for 3 years following clearcut harvesting , 2005 .

[23]  S. Long,et al.  What have we learned from 15 years of free-air CO2 enrichment (FACE)? A meta-analytic review of the responses of photosynthesis, canopy properties and plant production to rising CO2. , 2004, The New phytologist.

[24]  Christopher J. Still,et al.  Large‐scale plant light‐use efficiency inferred from the seasonal cycle of atmospheric CO2 , 2004 .

[25]  Hirofumi Hashimoto,et al.  El Niño–Southern Oscillation–induced variability in terrestrial carbon cycling , 2004 .

[26]  H. Policy,et al.  Increase in C3 plant water-use efficiency and biomass over Glacial to present C02 concentrations , 1993, Nature.

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

[28]  John Pastor,et al.  Response of northern forests to CO2-induced climate change , 1988, Nature.

[29]  E. Rastetter,et al.  Seasonal variation in net carbon exchange and evapotranspiration in a Brazilian rain forest: a modelling analysis , 1998 .

[30]  Peter D. Blanken,et al.  Energy balance and canopy conductance of a boreal aspen forest: Partitioning overstory and understory components , 1997 .

[31]  T. A. Black,et al.  The seasonal water and energy exchange above and within a boreal aspen forest , 2001 .

[32]  T. Barnett,et al.  Potential impacts of a warming climate on water availability in snow-dominated regions , 2005, Nature.

[33]  R. Oren,et al.  Stomatal sensitivity to vapor pressure deficit and its relationship to hydraulic conductance in Pinus palustris. , 2004, Tree physiology.

[34]  S. T. Gower,et al.  A cross‐biome comparison of daily light use efficiency for gross primary production , 2003 .

[35]  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 .

[36]  Dennis D. Baldocchi,et al.  Seasonal differences in carbon and water vapor exchange in young and old-growth ponderosa pine ecosystems , 2002 .

[37]  Peter D. Blanken,et al.  The canopy conductance of a boreal aspen forest, Prince Albert National Park, Canada , 2004 .

[38]  J. Canadell,et al.  Recent patterns and mechanisms of carbon exchange by terrestrial ecosystems , 2001, Nature.

[39]  C. Priestley,et al.  On the Assessment of Surface Heat Flux and Evaporation Using Large-Scale Parameters , 1972 .

[40]  John Moncrieff,et al.  Seasonal variation of carbon dioxide, water vapor, and energy exchanges of a boreal black spruce forest , 1997 .

[41]  Dennis D. Baldocchi,et al.  Measuring and modelling carbon dioxide and water vapour exchange over a temperate broad‐leaved forest during the 1995 summer drought , 1997 .

[42]  T. A. Black,et al.  Ecophysiological controls on the carbon balances of three southern boreal forests , 2003 .

[43]  T. Black,et al.  Postulated feedbacks of deciduous forest phenology on seasonal climate patterns in the Western Canadian interior. , 2000 .

[44]  A. Rohde,et al.  Quantitative trait loci and candidate gene mapping of bud set and bud flush in populus. , 2000, Genetics.

[45]  T. A. Black,et al.  Sensitivity and uncertainty of the carbon balance of a Pacific Northwest Douglas-fir forest during an El Niño/La Niña cycle , 2004 .

[46]  K. Wilson,et al.  A spectral analysis of biosphere-atmosphere trace gas flux densities and meteorological variables across hour to multi-year time scales , 2000 .

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

[48]  A. Goldstein,et al.  Carbon dioxide and water vapor exchange by young and old ponderosa pine ecosystems during a dry summer. , 2001, Tree physiology.

[49]  Markus Reichstein,et al.  Drought controls over conductance and assimilation of a Mediterranean evergreen ecosystem: scaling from leaf to canopy , 2003 .

[50]  E. Hogg,et al.  Factors affecting interannual variation in growth of western Canadian aspen forests during 1951-2000 , 2005 .

[51]  Philip Marsh,et al.  EFFECTS OF CLIMATE CHANGE ON THE FRESHWATERS OF ARCTIC AND SUBARCTIC NORTH AMERICA , 1997 .

[52]  A. Scott Denning,et al.  Effect of climate on interannual variability of terrestrial CO2 fluxes , 2002 .

[53]  R. Leuning,et al.  Evaporation and canopy characteristics of coniferous forests and grasslands , 1993, Oecologia.

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

[55]  V. Dantec,et al.  Interannual and spatial variation in maximum leaf area index of temperate deciduous stands , 2000 .

[56]  M. Steinbach,et al.  Global teleconnections of climate to terrestrial carbon flux , 2003 .

[57]  Dennis D. Baldocchi,et al.  Measuring and modelling seasonal variation of carbon dioxide and water vapour exchange of a Pinus ponderosa forest subject to soil water deficit , 2000 .

[58]  X. Lee,et al.  Nocturnal mixing in a forest subcanopy , 2000 .

[59]  A. Arneth,et al.  Forest–atmosphere carbon dioxide exchange in eastern Siberia , 1998 .

[60]  R. Betts,et al.  Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model , 2000, Nature.

[61]  C. Tucker,et al.  Increased plant growth in the northern high latitudes from 1981 to 1991 , 1997, Nature.

[62]  J. Dufresne,et al.  On the magnitude of positive feedback between future climate change and the carbon cycle , 2002 .

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

[64]  T. A. Black,et al.  Effects of short-term variation in weather on diurnal canopy CO2 flux and evapotranspiration of a juvenile douglas-fir stand , 1990 .

[65]  K. Rees.  ROOTING PATTERNS OF BOREAL TREE SPECIES , 1997 .

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

[67]  Nigel J. Livingston,et al.  Transfer conductance in second growth Douglas-fir (Pseudotsuga menziesii (Mirb.)Franco) canopies , 2003 .

[68]  Liukang Xu,et al.  Predicted versus measured photosynthetic water-use efficiency of crop stands under dynamically changing field environments. , 2004, Journal of experimental botany.

[69]  E. K. Webb,et al.  Correction of flux measurements for density effects due to heat and water vapour transfer , 1980 .

[70]  J. Monteith,et al.  Principles of Environmental Physics , 2014 .

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