Drought impairs herbivore-induced volatile terpene emissions by ponderosa pine but not through constraints on newly assimilated carbon
Drought impairs herbivore-induced volatile terpene emissions by ponderosa pine but not through constraints on newly assimilated carbon
复制标题
干旱会损害草食动物引起的黄松挥发性萜烯排放，但不是通过限制新同化的碳来实现的
DOI：
10.1093/treephys/tpad016
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发表时间：
2023
期刊：
影响因子：
4
通讯作者：
Schnitzler, ed., Jörg-Peter
中科院分区：
文献类型：
--
作者：
Malone, Shealyn C.;Simonpietri, Austin;Knighton, Walter B.;Trowbridge, Amy M.;Schnitzler, ed., Jörg-Peter
挥发性萜具有多种生物学作用，包括树木对食草动物的抗性。在全球森林中观察到的干旱压力的频率和严重程度的增加可能会阻碍树木产生与防御有关的挥发物以应对生物压力。为了评估干旱诱导的生理胁迫如何单独改变挥发物排放，并结合生物挑战，我们在三个干旱时期监测了黄松树苗黎明前的水势、气体交换、针叶萜烯浓度和萜烯挥发性排放，并通过施用茉莉酸甲酯模拟草食。尽管3周、6周和7周的干旱处理分别使净光合速率降低了20%、89%和105%，但挥发性通量的大小总体上保持对干旱的抗性。然而，食草动物引起的排放表现出类似阈值的行为；当黎明前水势低于近似零同化点时，树苗无法诱导高于本构水平的排放。通过比较排放组分与针状萜烯浓度的变化，我们发现干旱对组成和草食植物诱导的挥发通量和组成的影响主要是通过对新生组分的限制，这表明干旱期间光合作用的减少限制了可用于新生挥发性合成的碳基质。然而，随后的13co2脉冲追踪标记实验的结果证实，黄松的组成（标记<3%）和草食诱导（标记<8%）的新生排放主要来自较老的碳源，新光合产物的贡献很小。综上所述，我们提供的证据表明，在黄松中，干旱并没有通过光合作用减少的底物限制来限制草食动物诱导的从头排放，而是通过更复杂的分子和/或生物物理机制来表现，即树苗达到零同化点。这些结果强调了在评估对草食动物诱导的反应的影响时考虑干旱严重程度的重要性，并表明一旦超过生理阈值，干旱改变的挥发性代谢就会限制诱导排放。
Volatile terpenes serve multiple biological roles including tree resistance against herbivores. The increased frequency and severity of drought stress observed in forests across the globe may hinder trees from producing defense-related volatiles in response to biotic stress. To assess how drought-induced physiological stress alters volatile emissions alone and in combination with a biotic challenge, we monitored pre-dawn water potential, gas-exchange, needle terpene concentrations and terpene volatile emissions of ponderosa pine (Pinus ponderosa) saplings during three periods of drought and in response to simulated herbivory via methyl jasmonate application. Although 3-, 6- and 7-week drought treatments reduced net photosynthetic rates by 20, 89 and 105%, respectively, the magnitude of volatile fluxes remained generally resistant to drought. Herbivore-induced emissions, however, exhibited threshold-like behavior; saplings were unable to induce emissions above constitutive levels when pre-dawn water potentials were below the approximate zero-assimilation point. By comparing compositional shifts in emissions to needle terpene concentrations, we found evidence that drought effects on constitutive and herbivore-induced volatile flux and composition are primarily via constraints on the de novo fraction, suggesting that reduced photosynthesis during drought limits the carbon substrate available for de novo volatile synthesis. However, results from a subsequent13CO2pulse-chase labeling experiment then confirmed that both constitutive (<3% labeled) and herbivore-induced (<8% labeled) de novo emissions from ponderosa pine are synthesized predominantly from older carbon sources with little contribution from new photosynthates. Taken together, we provide evidence that in ponderosa pine, drought does not constrain herbivore-induced de novo emissions through substrate limitation via reduced photosynthesis, but rather through more sophisticated molecular and/or biophysical mechanisms that manifest as saplings reach the zero-assimilation point. These results highlight the importance of considering drought severity when assessing impacts on the herbivore-induced response and suggest that drought-altered volatile metabolism constrains induced emissions once a physiological threshold is surpassed.