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Based on the text, applying the standard δ13C precipitation proxy to fossilized leaf waxes from coastal halophytes woul…

In paleoclimatology, the ratio of carbon isotopes (carbon-13 to carbon-12, or δ13C) in preserved plant leaf waxes is often used to reconstruct past rainfall. Terrestrial plants facing drought typically constrict their stomata to conserve water, which forces photosynthetic enzymes to incorporate proportionally more carbon-13. However, ecologist Laura Rossi and colleagues observed that this proxy behaves counterintuitively in coastal marsh halophytes (salt-tolerant shrubs). When subjected to prolonged droughts that increase soil salinity, these shrubs keep their stomata open to maintain high transpiration rates that prevent salt accumulation in root tissues. Conversely, during periods of prolonged freshwater flooding, the waterlogged, oxygen-depleted soil impairs the shrubs' root metabolism, triggering stomatal closure despite the abundance of surrounding water.

Based on the text, applying the standard δ13C precipitation proxy to fossilized leaf waxes from coastal halophytes would most likely lead researchers to

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Correct answer: A. mistakenly interpret historical periods of prolonged freshwater inundation as episodes of drought.

According to the text, the standard δ13C proxy assumes that stomatal closure reflects drought conditions because plants typically close stomata to conserve water, leading to higher carbon-13 uptake. In coastal halophytes, however, stomata close during periods of prolonged freshwater flooding due to root hypoxia caused by waterlogged soil. Consequently, leaf waxes formed during these wet periods would exhibit the elevated carbon-13 signature that standard proxy models associate with water stress, leading researchers to misidentify flood periods as droughts.

Choice B is incorrect because halophytes keep their stomata open during drought-induced salinity, which would prevent the elevation of carbon-13 rather than increase it.

Choice C is incorrect because the proxy data would fluctuate between open- and closed-stomata states rather than indicating static moisture levels.

Choice D is incorrect because the passage explicitly notes that hypoxia causes stomata to close, not remain open, and the proxy measures precipitation conditions rather than researchers directly observing stomatal apertures.

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Based on the text, applying the standard δ13C precipitation proxy to fossilized leaf waxes from coastal halophytes woul…

Based on the text, applying the standard δ13C precipitation proxy to fossilized leaf waxes from coastal halophytes would most likely lead researchers to

Answer & explanation

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