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<p>Desert winter ephemerals thrive in arid environments by exploiting brief seasonal windows of favorable conditions. Leaf nitrogen status, pigment composition, gas exchange, chlorophyll <i>a</i> fluorescence quenching, and polyphasic OJIP fluorescence transients were compared in three co-occurring annual forbs, <i>Medicago polymorpha</i>, <i>Malva parviflora</i>, and <i>Sisymbrium irio</i>, growing under natural high light desert conditions. All three species exhibited comparable net CO₂ assimilation rates, water-use efficiency, and photosystem II (PSII) maximum quantum efficiency (F<sub>v</sub>/F<sub>m</sub> ≈ 0.82), indicating similar functional photochemical capacity under field irradiance. However, <i>M. polymorpha</i> accumulated substantially greater above-ground biomass, exceeding that of the other two species by approximately 141–177%, coinciding with 30–47% higher foliar nitrogen content. Species-specific differences in chlorophyll <i>a</i>/<i>b</i> and carotenoid content indicated differences in light harvesting and photoprotection. OJIP-derived parameters associated with PSII photochemical efficiency (e.g., F<sub>v</sub>/F<sub>o</sub>, φP<sub>o</sub>) and electron transport efficiency (ψ<sub>o</sub>, φE<sub>o</sub>) were consistently highest in <i>M. polymorpha</i>. This species also exhibited the lowest steady-state non-photochemical quenching while showing the most responsive shift from photochemical energy utilization to thermal dissipation upon exposure to actinic light, without a concomitant rise in sustained photoinhibitory quenching. These responses were accompanied by enhanced energy conservation performance indices: efficiencies associated with excitation energy transfer to intersystem electron acceptors (PI<sub>ABS</sub>) were 25–32% higher in <i>M. polymorpha</i>, while those linked to terminal electron acceptor reduction (PI<sub>total</sub>) were ~ 50% higher in both <i>M. polymorpha</i> and <i>M. parviflora</i> relative to <i>S. irio</i>. Collectively, these findings demonstrate species-specific differences in PSII energy partitioning and photoprotective responsiveness under high light conditions.</p>

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Species-specific variation in photochemical efficiency and photoprotective responses among desert winter ephemerals under high light

  • 期刊论文

  • 发表日期：

    2026年4月17日

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  • Ahmad Zia

摘要

Desert winter ephemerals thrive in arid environments by exploiting brief seasonal windows of favorable conditions. Leaf nitrogen status, pigment composition, gas exchange, chlorophyll a fluorescence quenching, and polyphasic OJIP fluorescence transients were compared in three co-occurring annual forbs, Medicago polymorpha, Malva parviflora, and Sisymbrium irio, growing under natural high light desert conditions. All three species exhibited comparable net CO₂ assimilation rates, water-use efficiency, and photosystem II (PSII) maximum quantum efficiency (Fv/Fm ≈ 0.82), indicating similar functional photochemical capacity under field irradiance. However, M. polymorpha accumulated substantially greater above-ground biomass, exceeding that of the other two species by approximately 141–177%, coinciding with 30–47% higher foliar nitrogen content. Species-specific differences in chlorophyll a/b and carotenoid content indicated differences in light harvesting and photoprotection. OJIP-derived parameters associated with PSII photochemical efficiency (e.g., Fv/Fo, φPo) and electron transport efficiency (ψo, φEo) were consistently highest in M. polymorpha. This species also exhibited the lowest steady-state non-photochemical quenching while showing the most responsive shift from photochemical energy utilization to thermal dissipation upon exposure to actinic light, without a concomitant rise in sustained photoinhibitory quenching. These responses were accompanied by enhanced energy conservation performance indices: efficiencies associated with excitation energy transfer to intersystem electron acceptors (PIABS) were 25–32% higher in M. polymorpha, while those linked to terminal electron acceptor reduction (PItotal) were ~ 50% higher in both M. polymorpha and M. parviflora relative to S. irio. Collectively, these findings demonstrate species-specific differences in PSII energy partitioning and photoprotective responsiveness under high light conditions.