Kentucky bluegrass (Poa pratensis L.; drought resistant) and perennial ryegrass (Lolium perenne L.; drought sensitive) are economically important grass species contrasting in drought stress resistance. This study determined the optimal chlorophyll fluorescence parameters to indicate drought incidence and whether the parameters differentiate intra- and interspecies variations in drought stress. For each species, nine cultivars were exposed to well-watered or drought (water withheld) conditions in growth chambers containing high-throughput photosynthetic imagers to track real-time responses of maximum quantum efficiency of photosystem II (F_v/F_m), quantum yield of photosystem II (Φ_II), non-photochemical quenching (NPQ), energy-dependent quenching (qE), and photoinhibition-associated quenching (qI). Soil moisture content and relative water content of leaf tissues were evaluated. Due to drought, F_v/F_m and Φ_II decreased for cultivars of both species but earlier for perennial ryegrass compared to Kentucky bluegrass. The NPQ, qI, and qE values exhibited more dynamic and earlier changes due to drought compared to F_v/F_m and Φ_II and allowed for early, mid, and late drought responses to be illustrated. Drought induced an increase in NPQ, qI, and qE values, which corresponded to activation of photoprotection mechanisms, and was exhibited earlier for perennial ryegrass compared to Kentucky bluegrass. As the drought treatment progressed, a decrease or stabilization of low values of NPQ, qI, and qE was observed, and the lowest values were associated with the most drought-sensitive cultivars. These results indicate important stress tolerance protection mechanisms for grass species and will broadly impact basic and applied grass research as a nondestructive phenotyping tool.

中文翻译：

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通过测量叶绿素荧光参数早期检测肯塔基早熟禾和多年生黑麦草对干旱胁迫的反应

早熟禾（Poa pratensis L.；抗旱）和多年生黑麦草（Lolium perenne L.；干旱敏感）是经济上重要的草种，与干旱胁迫抗性形成对比。本研究确定了最佳叶绿素荧光参数来指示干旱发生率以及这些参数是否区分干旱胁迫的种内和种间变化。对于每个物种，将九个品种暴露在含有高通量光合成像仪的生长室中的充足浇水或干旱（禁水）条件下，以跟踪光系统 II 最大量子效率 (F v _/ F _m )、量子光系统 II (Φ _II )、非光化学猝灭 (NPQ)、能量依赖性猝灭 (qE) 和光抑制相关猝灭 (qI) 的产量。评估土壤含水量和叶组织的相对含水量。由于干旱，两个品种的F _v /F _m和 Φ _{II均下降，但与肯塔基早熟禾相比，多年生黑麦草下降得更早。}与 F _v /F _m和 Φ _II相比，NPQ、qI 和 qE 值因干旱而表现出更动态和更早的变化，并可以说明早期、中期和晚期的干旱反应。干旱导致 NPQ、qI 和 qE 值增加，这对应于光保护机制的激活，并且与肯塔基早熟禾相比，多年生黑麦草的表现更早。随着干旱处理的进行，观察到 NPQ、qI 和 qE 的低值降低或稳定，最低值与对干旱最敏感的品种相关。这些结果表明了草种重要的胁迫​​耐受保护机制，并将广泛影响草类作为无损表型工具的基础和应用研究。