Table_2_Nitrogen Supply Affects Photosynthesis and Photoprotective Attributes During Drought-Induced Senescence in Quinoa.DOCX

Drought during senescence has become more common in Mediterranean climates in recent years. Chenopodium quinoa Willd has been identified as tolerant to poor soil conditions and drought. Previous observations have found that sufficient nitrogen (N) supply mitigates yield losses under terminal drought conditions. However, there is no understanding of the mechanisms behind this effect. We hypothesized that N up-regulates both photosynthetic and photoprotective elements during drought-induced senescence, alleviating the negative impact of drought on yield. The role of N supply and terminal drought on photoprotection was tested using three Chilean quinoa genotypes from different climatic zones: Faro, UdeC9, and BO78. Plants were grown under high nitrogen (HN) or low nitrogen (LN) conditions and subjected to terminal drought at the onset of senescence. Photosynthetic and photochemical and non-photochemical processes were evaluated at both the onset of drought and after 15 days of drought conditions. N supplementation modified most of the physiological parameters related to photochemical dissipation of energy, photosynthesis, and yield in quinoa. In contrast, water restriction did not affect photosynthesis in quinoa, and its effect on yield was dependent on the genotype. A significant interaction N × G was observed in photosynthesis, relative water content, protein content, Fv/Fm, and chlorophylls. In general, Faro was able to maintain higher levels of these attributes under LN conditions than UdeC9 and BO78. In addition, the interacting effects of N × W regulated the level of most pigments in quinoa as well as the photoprotective induction of non-photochemical quenching (NPQ) during senescence. During terminal drought at LN conditions, Faro presented a larger NPQ induction under drought conditions than UdeC9 and BO78, which was supported by a larger zeaxanthin content and de-epoxidation state of the xanthophyll pool. Interestingly, BO78 did not induce NPQ in response to drought-induced senescence but instead enhanced the content of betacyanins. This response needs to be researched in future works. Finally, we observed that LN supply reduced the correlationship between the de-epoxidation state of the xanthophyll cycle and NPQ. This could be an indication that N supply not only compromised the capacity for photosynthetic performance in quinoa plants, but also affected the plasticity of thermal dissipation, restricting further changes during drought-induced senescence.

近年来，地中海气候区的衰老期干旱愈发频发。藜麦（Chenopodium quinoa Willd）已被证实可耐受贫瘠土壤与干旱胁迫。既往研究表明，充足的氮（N）供应可缓解终期干旱下的产量损失，但该效应的内在调控机制尚未明确。本研究假设，在干旱诱导的植物衰老过程中，氮可上调光合与光保护相关元件的表达，从而缓解干旱对作物产量的负面影响。本研究选取来自不同气候区的3个智利藜麦基因型（Faro、UdeC9与BO78），探究氮供应与终期干旱对光保护过程的调控作用。供试材料分别在高氮（HN）与低氮（LN）条件下栽培，并于衰老起始阶段施加终期干旱处理。分别于干旱起始时与干旱处理15天后，对光合、光化学及非光化学过程进行测定与分析。施氮可改变藜麦中多数与能量光化学耗散、光合作用及产量相关的生理参数。与之相反，水分胁迫并未对藜麦的光合作用产生显著影响，其对产量的调控效应则因基因型而异。研究发现，氮×基因型（N×G）互作在光合作用、相对含水量、蛋白质含量、最大光化学效率（Fv/Fm）及叶绿素含量中均存在显著效应。总体而言，在低氮条件下，Faro相较于UdeC9与BO78可维持更高水平的上述生理性状。此外，氮×水分（N×W）的互作效应可调控藜麦中多数色素的含量，以及衰老过程中非光化学淬灭（NPQ）的光保护诱导过程。在低氮条件下的终期干旱过程中，Faro的NPQ诱导程度显著高于UdeC9与BO78，这与其更高的玉米黄质（zeaxanthin）含量及叶黄素循环脱环氧化状态相一致。值得注意的是，BO78并未因干旱诱导的衰老而诱导NPQ，反而提升了甜菜红素（betacyanins）的含量，该响应的具体调控机制有待后续研究进一步阐明。最后，本研究发现低氮供应会削弱叶黄素循环脱环氧化状态与NPQ之间的相关性。这表明氮供应不仅会影响藜麦的光合性能，还会改变热耗散的可塑性，进而限制干旱诱导衰老过程中的进一步适应性变化。