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Water availability drives gas exchange and growth of trees in northeastern US, not elevated CO 2 and reduced acid deposition

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ABSTRACT

Dynamic global vegetation models (DGVM) exhibit high uncertainty about how climate change, elevated atmospheric CO2 (atm. CO2) concentration, and atmospheric pollutants will impact carbon sequestration in forested ecosystems. Although the individual roles of these environmental factors on tree growth are understood, analyses examining their simultaneous effects are lacking. We used tree-ring isotopic data and structural equation modeling to examine the concurrent and interacting effects of water availability, atm. CO2 concentration, and SO4 and nitrogen deposition on two broadleaf tree species in a temperate mesic forest in the northeastern US. Water availability was the strongest driver of gas exchange and tree growth. Wetter conditions since the 1980s have enhanced stomatal conductance, photosynthetic assimilation rates and, to a lesser extent, tree radial growth. Increased water availability seemingly overrides responses to reduced acid deposition, CO2 fertilization, and nitrogen deposition. Our results indicate that water availability as a driver of ecosystem productivity in mesic temperate forests is not adequately represented in DGVMs, while CO2 fertilization is likely overrepresented. This study emphasizes the importance to simultaneously consider interacting climatic and biogeochemical drivers when assessing forest responses to global environmental changes.

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Location of the study site and time series of the SO4 and total inorganic N deposition, climatic water balance, and atmospheric CO2 concentration.(a) Location of Black Rock Forest and distribution range of Liriodendron tulipifera L. and Quercus rubra L. in North America. Data source: https://gec.cr.usgs.gov/data/little/. (b) Total SO4 and inorganic N wet deposition per hectare for the water year (previous October to current September) at Black Rock Forest, NY. Deposition data were obtained from the National Acid Deposition Program (http://nadp.sws.uiuc.edu); 1981 to 1983 data are from Station NY51, located 6 km from Black Rock Forest, while 1984–2014 data are from Station NY99, located at Black Rock Forest. (c) Standardized climatic water balance during the summer (June–August) calculated as the difference between precipitation and potential evapotranspiration. Positive values in blue indicate wet conditions and negative values in red show dry conditions. Estimated atmospheric CO2 concentrations from ice core data for the period 1895–1958 (dashed black line) and measured data from 1958 to 2014 (black line), CO2 data source: http://www.columbia.edu/~mhs119/GHGs/CO2.1850-2015.txt. Figure created with R version 3.2.261.
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f1: Location of the study site and time series of the SO4 and total inorganic N deposition, climatic water balance, and atmospheric CO2 concentration.(a) Location of Black Rock Forest and distribution range of Liriodendron tulipifera L. and Quercus rubra L. in North America. Data source: https://gec.cr.usgs.gov/data/little/. (b) Total SO4 and inorganic N wet deposition per hectare for the water year (previous October to current September) at Black Rock Forest, NY. Deposition data were obtained from the National Acid Deposition Program (http://nadp.sws.uiuc.edu); 1981 to 1983 data are from Station NY51, located 6 km from Black Rock Forest, while 1984–2014 data are from Station NY99, located at Black Rock Forest. (c) Standardized climatic water balance during the summer (June–August) calculated as the difference between precipitation and potential evapotranspiration. Positive values in blue indicate wet conditions and negative values in red show dry conditions. Estimated atmospheric CO2 concentrations from ice core data for the period 1895–1958 (dashed black line) and measured data from 1958 to 2014 (black line), CO2 data source: http://www.columbia.edu/~mhs119/GHGs/CO2.1850-2015.txt. Figure created with R version 3.2.261.

Mentions: One region where the simultaneous influence of multiple environmental drivers on forest productivity can be tested is the northeastern United States (US). Over the last decades, this region has experienced simultaneous and significant shifts in moisture availability7, increases in atm. CO2 concentration, and reductions in acid and nitrogen deposition48 (Fig. 1). While there has been a substantial reduction in acid deposition in northeastern US, there is still not a consensus that reduced pollutant loads have enhanced tree growth in temperate mesic forests91011. The simultaneous increase in water availability and decrease in acid deposition complicate our understanding of the potential benefits of reduced acid deposition. At the same time, the divergent influences between moisture stress and potential CO2 fertilization have led to significant disagreement between remotely sensed (satellite) and modeled (DGVM) productivity of temperate mesic forests12. Investigating the concurrent effects of varying environmental drivers on growth and gas exchange of trees is critical to improve DGVM and better understand the rates, magnitude, and trajectory of terrestrial carbon budgets.


Water availability drives gas exchange and growth of trees in northeastern US, not elevated CO 2 and reduced acid deposition
Location of the study site and time series of the SO4 and total inorganic N deposition, climatic water balance, and atmospheric CO2 concentration.(a) Location of Black Rock Forest and distribution range of Liriodendron tulipifera L. and Quercus rubra L. in North America. Data source: https://gec.cr.usgs.gov/data/little/. (b) Total SO4 and inorganic N wet deposition per hectare for the water year (previous October to current September) at Black Rock Forest, NY. Deposition data were obtained from the National Acid Deposition Program (http://nadp.sws.uiuc.edu); 1981 to 1983 data are from Station NY51, located 6 km from Black Rock Forest, while 1984–2014 data are from Station NY99, located at Black Rock Forest. (c) Standardized climatic water balance during the summer (June–August) calculated as the difference between precipitation and potential evapotranspiration. Positive values in blue indicate wet conditions and negative values in red show dry conditions. Estimated atmospheric CO2 concentrations from ice core data for the period 1895–1958 (dashed black line) and measured data from 1958 to 2014 (black line), CO2 data source: http://www.columbia.edu/~mhs119/GHGs/CO2.1850-2015.txt. Figure created with R version 3.2.261.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5385545&req=5

f1: Location of the study site and time series of the SO4 and total inorganic N deposition, climatic water balance, and atmospheric CO2 concentration.(a) Location of Black Rock Forest and distribution range of Liriodendron tulipifera L. and Quercus rubra L. in North America. Data source: https://gec.cr.usgs.gov/data/little/. (b) Total SO4 and inorganic N wet deposition per hectare for the water year (previous October to current September) at Black Rock Forest, NY. Deposition data were obtained from the National Acid Deposition Program (http://nadp.sws.uiuc.edu); 1981 to 1983 data are from Station NY51, located 6 km from Black Rock Forest, while 1984–2014 data are from Station NY99, located at Black Rock Forest. (c) Standardized climatic water balance during the summer (June–August) calculated as the difference between precipitation and potential evapotranspiration. Positive values in blue indicate wet conditions and negative values in red show dry conditions. Estimated atmospheric CO2 concentrations from ice core data for the period 1895–1958 (dashed black line) and measured data from 1958 to 2014 (black line), CO2 data source: http://www.columbia.edu/~mhs119/GHGs/CO2.1850-2015.txt. Figure created with R version 3.2.261.
Mentions: One region where the simultaneous influence of multiple environmental drivers on forest productivity can be tested is the northeastern United States (US). Over the last decades, this region has experienced simultaneous and significant shifts in moisture availability7, increases in atm. CO2 concentration, and reductions in acid and nitrogen deposition48 (Fig. 1). While there has been a substantial reduction in acid deposition in northeastern US, there is still not a consensus that reduced pollutant loads have enhanced tree growth in temperate mesic forests91011. The simultaneous increase in water availability and decrease in acid deposition complicate our understanding of the potential benefits of reduced acid deposition. At the same time, the divergent influences between moisture stress and potential CO2 fertilization have led to significant disagreement between remotely sensed (satellite) and modeled (DGVM) productivity of temperate mesic forests12. Investigating the concurrent effects of varying environmental drivers on growth and gas exchange of trees is critical to improve DGVM and better understand the rates, magnitude, and trajectory of terrestrial carbon budgets.

View Article: PubMed Central - PubMed

ABSTRACT

Dynamic global vegetation models (DGVM) exhibit high uncertainty about how climate change, elevated atmospheric CO2 (atm. CO2) concentration, and atmospheric pollutants will impact carbon sequestration in forested ecosystems. Although the individual roles of these environmental factors on tree growth are understood, analyses examining their simultaneous effects are lacking. We used tree-ring isotopic data and structural equation modeling to examine the concurrent and interacting effects of water availability, atm. CO2 concentration, and SO4 and nitrogen deposition on two broadleaf tree species in a temperate mesic forest in the northeastern US. Water availability was the strongest driver of gas exchange and tree growth. Wetter conditions since the 1980s have enhanced stomatal conductance, photosynthetic assimilation rates and, to a lesser extent, tree radial growth. Increased water availability seemingly overrides responses to reduced acid deposition, CO2 fertilization, and nitrogen deposition. Our results indicate that water availability as a driver of ecosystem productivity in mesic temperate forests is not adequately represented in DGVMs, while CO2 fertilization is likely overrepresented. This study emphasizes the importance to simultaneously consider interacting climatic and biogeochemical drivers when assessing forest responses to global environmental changes.

No MeSH data available.


Related in: MedlinePlus