Interaction of CO<sub>2</sub> concentrations and water stress in semiarid plants causes diverging response in instantaneous water use efficiency and carbon isotope composition
In the context of global warming attributable to the increasing levels of CO<sub>2</sub>, severe drought may be more frequent in areas that already experience chronic water shortages (semiarid areas). This necessitates research on the interactions between increased levels of CO<sub...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-07-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/14/3431/2017/bg-14-3431-2017.pdf |
| Summary: | In the context of global warming attributable to the increasing
levels of CO<sub>2</sub>, severe drought may be more frequent in areas that already experience chronic
water shortages (semiarid areas). This necessitates research on the
interactions between increased levels of CO<sub>2</sub> and drought and their effect on plant
photosynthesis. It is commonly reported that <sup>13</sup>C fractionation occurs as
CO<sub>2</sub> gas diffuses from the atmosphere to the substomatal cavity. Few
researchers have investigated <sup>13</sup>C fractionation at the site of
carboxylation to cytoplasm before sugars are exported outward from the leaf.
This process typically progresses in response to variations in environmental
conditions (i.e., CO<sub>2</sub> concentrations and water stress), including in
their interaction. Therefore, saplings of two typical plant species
(<i>Platycladus orientalis</i> and <i>Quercus variabilis</i>) from
semiarid areas of northern China were selected and cultivated in growth
chambers with orthogonal treatments (four CO<sub>2</sub> concentration ([CO<sub>2</sub>]) × five soil volumetric water content (SWC)). The <i>δ</i><sup>13</sup>C of
water-soluble compounds extracted from leaves of saplings was determined for
an assessment of instantaneous water use efficiency (WUE<sub>cp</sub>) after
cultivation. Instantaneous water use efficiency derived from gas-exchange
measurements (WUE<sub>ge</sub>) was integrated to estimate differences in
<i>δ</i><sup>13</sup>C signal variation before leaf-level translocation of primary
assimilates. The WUE<sub>ge</sub> values in <i>P. orientalis</i> and <i>Q.
variabilis</i> both decreased with increased soil moisture at 35–80 % of
field capacity (FC) and increased with elevated [CO<sub>2</sub>] by increasing
photosynthetic capacity and reducing transpiration. Instantaneous water use
efficiency (iWUE) according to environmental changes differed between the
two species. The WUE<sub>ge</sub> in <i>P. orientalis</i> was significantly
greater than that in <i>Q. variabilis</i>, while an opposite tendency was
observed when comparing WUE<sub>cp</sub> between the two species. Total <sup>13</sup>C
fractionation at the site of carboxylation to cytoplasm before sugar export
(total <sup>13</sup>C fractionation) was species-specific, as demonstrated in the
interaction of [CO<sub>2</sub>] and SWC. Rising [CO<sub>2</sub>] coupled with moistened
soil generated increasing disparities in <i>δ</i><sup>13</sup>C between
water-soluble compounds (<i>δ</i><sup>13</sup>C<sub>WSC</sub>) and estimates based on
gas-exchange observations (<i>δ</i><sup>13</sup>C<sub>obs</sub>) in <i>P. orientalis</i>,
ranging between 0.0328 and 0.0472 ‰. Differences between
<i>δ</i><sup>13</sup>C<sub>WSC</sub> and <i>δ</i><sup>13</sup>C<sub>obs</sub> in <i>Q. variabilis</i>
increased as [CO<sub>2</sub>] and SWC increased
(0.0384–0.0466 ‰). The <sup>13</sup>C fractionation from
mesophyll conductance (<i>g</i><sub>m</sub>) and post-carboxylation both contributed to
the total <sup>13</sup>C fractionation that was determined by <i>δ</i><sup>13</sup>C of
water-soluble compounds and gas-exchange measurements. Total <sup>13</sup>C
fractionation was linearly dependent on stomatal conductance, indicating that
post-carboxylation fractionation could be attributed to environmental
variation. The magnitude and environmental dependence of apparent
post-carboxylation fractionation is worth our attention when addressing
photosynthetic fractionation. |
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| ISSN: | 1726-4170 1726-4189 |