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Quantifying the impact of daily and seasonal variation in sap pH on xylem dissolved inorganic carbon estimates in plum trees

Fana G Erda, Jasper Bloemen (UGent) and Kathy Steppe (UGent)
(2014) PLANT BIOLOGY. 16(1). p.43-48
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BOF10/STA/042
Abstract
In studies on internal CO2 transport, average xylem sap pH (pH(x)) is one of the factors used for calculation of the concentration of dissolved inorganic carbon in the xylem sap ([CO2*]). Lack of detailed pH(x) measurements at high temporal resolution could be a potential source of error when evaluating [CO2*] dynamics. In this experiment, we performed continuous measurements of CO2 concentration ([CO2]) and stem temperature (T-stem), complemented with pH(x) measurements at 30-min intervals during the day at various stages of the growing season (Day of the Year (DOY): 86 (late winter), 128 (mid-spring) and 155 (early summer)) on a plum tree (Prunus domestica L. cv. Reine Claude d'Oullins). We used the recorded pH(x) to calculate [CO2*] based on T-stem and the corresponding measured [CO2]. No statistically significant difference was found between mean [CO2*] calculated with instantaneous pH(x) and daily average pH(x). However, using an average pH(x) value from a different part of the growing season than the measurements of [CO2] and T-stem to estimate [CO2*] led to a statistically significant error. The error varied between 3.25 +/- 0.01% under-estimation and 3.97 * 0.01% over-estimation, relative to the true [CO2*] data. Measured pH(x) did not show a significant daily variation, unlike [CO2], which increased during the day and declined at night. As the growing season progressed, daily average [CO2] (3.4%, 5.3%, 7.4%) increased and average pH(x) (5.43, 5.29, 5.20) decreased. Increase in [CO2] will increase its solubility in xylem sap according to Henry's law, and the dissociation of [CO2*] will negatively affect pH(x). Our results are the first quantifying the error in [CO2*] due to the interaction between [CO2] and pH(x) on a seasonal time scale. We found significant changes in pH(x) across the growing season, but overall the effect on the calculation of [CO2*] remained within an error range of 4%. However, it is possible that the error could be more substantial for other tree species, particularly if pH(x) is in the more sensitive range (pHx > 6.5).
Keywords
EXTERNAL FLUXES, RESPIRATION, STEM CO2 EFFLUX, BEECH FOREST STAND, VESSEL-ASSOCIATED CELLS, respiration, CO2, internal carbon transport, dissolved carbon dioxide, internal CO2 concentration, TEMPERATURE, RATES, TRANSPORT, PATTERNS, BRANCHES

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Citation

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Chicago
Erda, Fana G, Jasper Bloemen, and Kathy Steppe. 2014. “Quantifying the Impact of Daily and Seasonal Variation in Sap pH on Xylem Dissolved Inorganic Carbon Estimates in Plum Trees.” Plant Biology 16 (1): 43–48.
APA
Erda, F. G., Bloemen, J., & Steppe, K. (2014). Quantifying the impact of daily and seasonal variation in sap pH on xylem dissolved inorganic carbon estimates in plum trees. PLANT BIOLOGY, 16(1), 43–48.
Vancouver
1.
Erda FG, Bloemen J, Steppe K. Quantifying the impact of daily and seasonal variation in sap pH on xylem dissolved inorganic carbon estimates in plum trees. PLANT BIOLOGY. 2014;16(1):43–8.
MLA
Erda, Fana G, Jasper Bloemen, and Kathy Steppe. “Quantifying the Impact of Daily and Seasonal Variation in Sap pH on Xylem Dissolved Inorganic Carbon Estimates in Plum Trees.” PLANT BIOLOGY 16.1 (2014): 43–48. Print.
@article{3238799,
  abstract     = {In studies on internal CO2 transport, average xylem sap pH (pH(x)) is one of the factors used for calculation of the concentration of dissolved inorganic carbon in the xylem sap ([CO2*]). Lack of detailed pH(x) measurements at high temporal resolution could be a potential source of error when evaluating [CO2*] dynamics. In this experiment, we performed continuous measurements of CO2 concentration ([CO2]) and stem temperature (T-stem), complemented with pH(x) measurements at 30-min intervals during the day at various stages of the growing season (Day of the Year (DOY): 86 (late winter), 128 (mid-spring) and 155 (early summer)) on a plum tree (Prunus domestica L. cv. Reine Claude d'Oullins). We used the recorded pH(x) to calculate [CO2*] based on T-stem and the corresponding measured [CO2]. No statistically significant difference was found between mean [CO2*] calculated with instantaneous pH(x) and daily average pH(x). However, using an average pH(x) value from a different part of the growing season than the measurements of [CO2] and T-stem to estimate [CO2*] led to a statistically significant error. The error varied between 3.25 +/- 0.01\% under-estimation and 3.97 * 0.01\% over-estimation, relative to the true [CO2*] data. Measured pH(x) did not show a significant daily variation, unlike [CO2], which increased during the day and declined at night. As the growing season progressed, daily average [CO2] (3.4\%, 5.3\%, 7.4\%) increased and average pH(x) (5.43, 5.29, 5.20) decreased. Increase in [CO2] will increase its solubility in xylem sap according to Henry's law, and the dissociation of [CO2*] will negatively affect pH(x). Our results are the first quantifying the error in [CO2*] due to the interaction between [CO2] and pH(x) on a seasonal time scale. We found significant changes in pH(x) across the growing season, but overall the effect on the calculation of [CO2*] remained within an error range of 4\%. However, it is possible that the error could be more substantial for other tree species, particularly if pH(x) is in the more sensitive range (pHx {\textrangle} 6.5).},
  author       = {Erda, Fana G and Bloemen, Jasper and Steppe, Kathy},
  issn         = {1435-8603},
  journal      = {PLANT BIOLOGY},
  keyword      = {EXTERNAL FLUXES,RESPIRATION,STEM CO2 EFFLUX,BEECH FOREST STAND,VESSEL-ASSOCIATED CELLS,respiration,CO2,internal carbon transport,dissolved carbon dioxide,internal CO2 concentration,TEMPERATURE,RATES,TRANSPORT,PATTERNS,BRANCHES},
  language     = {eng},
  number       = {1},
  pages        = {43--48},
  title        = {Quantifying the impact of daily and seasonal variation in sap pH on xylem dissolved inorganic carbon estimates in plum trees},
  url          = {http://dx.doi.org/10.1111/plb.12009},
  volume       = {16},
  year         = {2014},
}

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