Examination of the parameters controlling the triple oxygen isotope composition of grass leaf water and phytoliths at a Mediterranean site: a model–data approach
<p>Triple oxygen isotopes (<span class="inline-formula"><sup>17</sup></span>O-excess) of water are useful to trace evaporation at the soil–plant–atmosphere interface. The <span class="inline-formula"><sup>17</sup></span>O-exce...
| Main Authors: | , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-06-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/20/2161/2023/bg-20-2161-2023.pdf |
| Summary: | <p>Triple oxygen isotopes (<span class="inline-formula"><sup>17</sup></span>O-excess) of water are useful to trace
evaporation at the soil–plant–atmosphere interface. The <span class="inline-formula"><sup>17</sup></span>O-excess
of plant silica, i.e., phytoliths, inherited from leaf water, was previously
calibrated in growth chambers as a proxy of atmospheric relative humidity
(RH). Here, using a model–data approach, we examine the parameters that
control the triple oxygen isotope composition of bulk grass leaf water and
phytoliths <i>in natura</i>, at the O<span class="inline-formula"><sub>3</sub></span>HP experimental platform located in the French
Mediterranean area. A grass plot was equipped to measure for 1 year, all
environmental and plant physiological parameters relevant for modeling the
isotope composition of the grass leaf water. In particular, the triple
oxygen and hydrogen isotope composition of atmospheric water vapor above the
grass was measured continuously using a cavity ring-down spectrometer, and
the grass leaf temperature was monitored at plot scale using an infrared
(IR) radiometer. Grass leaves were collected in different seasons of the
year and over a 24 h period in June. Grass leaf water was extracted by
cryogenic vacuum distillation and analyzed by isotope ratio mass
spectrometry (IRMS). Phytoliths were analyzed by IR–laser fluorination–IRMS
after chemical extraction. We showed that the traditional Craig–Gordon
steady-state model modified for grass leaves reliably predicts the triple
oxygen isotope composition of leaf water during daytime but is sensitive to
uncertainties on the leaf-to-air temperature difference. Deviations from
isotope steady state at night are well represented in the triple oxygen
isotope system and predictable by a non-steady-state model. The
<span class="inline-formula"><sup>17</sup></span>O-excess of phytoliths confirms the applicability of the
<span class="inline-formula"><sup>17</sup></span>O-excess<span class="inline-formula"><sub>phyto</sub></span> vs. RH equation established in previous growth
chamber experiments. Further, it recorded average daytime RH over the growth
period rather than daily RH, related to low transpiration and silicification
during the night. This model–data approach highlights the utility of the
triple oxygen isotope system to improve the understanding of water exchange
at the soil–plant–atmosphere interface. The <i>in natura</i> experiment underlines the
applicability of <span class="inline-formula"><sup>17</sup></span>O-excess of phytoliths as a RH proxy.</p> |
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| ISSN: | 1726-4170 1726-4189 |