Minguito-Frutos Mario, Adams Matthew P, Alcoverro Teresa, Vilas María P, Alonso David, Mayol Elvira, Bernardeu-Esteller Jaime, Marín-Guirao Lázaro, Ruiz Juan M, Boada Jordi
Centre d'Estudis Avançats de Blanes (CEAB-CSIC), Carrer d'Accés a la cala Sant Francesc, Girona, Spain.
School of Mathematical Sciences, Queensland University of Technology, Brisbane, QLD, Australia.
Front Plant Sci. 2023 Jul 21;14:1186538. doi: 10.3389/fpls.2023.1186538. eCollection 2023.
Light gradients are ubiquitous in marine systems as light reduces exponentially with depth. Seagrasses have a set of mechanisms that help them to cope with light stress gradients. Physiological photoacclimation and clonal integration help to maximize light capture and minimize carbon losses. These mechanisms can shape plants minimum light requirements (MLR), which establish critical thresholds for seagrass survival and help us predict ecosystem responses to the alarming reduction in light availability.
Using the seagrass as a case study, we compare the MLR under different carbon model scenarios, which include photoacclimation and/or self-facilitation (based on clonal integration) and that where parameterized with values from field experiments.
Physiological photoacclimation conferred plants with increased tolerance to reducing light, approximately halving their MLR from 5-6% surface irradiance (SI) to ≈ 3% SI. In oligotrophic waters, this change in MLR could translate to an increase of several meters in their depth colonization limit. In addition, we show that reduced mortality rates derived from self-facilitation mechanisms (promoted by high biomass) induce bistability of seagrass meadows along the light stress gradient, leading to abrupt shifts and hysteretic behaviors at their deep limit.
The results from our models point to (i) the critical role of physiological photoacclimation in conferring greater resistance and ability to recover (i.e., resilience), to seagrasses facing light deprivation and (ii) the importance of self-facilitating reinforcing mechanisms in driving the resilience and recovery of seagrass systems exposed to severe light reduction events.
在海洋系统中，光照梯度无处不在，因为光照会随着深度呈指数级减弱。海草具有一系列机制来帮助它们应对光照胁迫梯度。生理光适应和克隆整合有助于最大限度地捕获光照并最小化碳损失。这些机制可以塑造植物的最低光照需求（MLR），而最低光照需求为海草生存确立了关键阈值，并有助于我们预测生态系统对光照可用性急剧下降的响应。
以海草为例，我们比较了不同碳模型情景下的最低光照需求，这些情景包括光适应和/或自我促进（基于克隆整合），以及根据野外实验值进行参数化的情景。
生理光适应使植物对光照减弱的耐受性增强，其最低光照需求从表面辐照度（SI）的5 - 6%降至约3% SI，几乎减半。在贫营养水域，最低光照需求的这种变化可能使其深度定殖极限增加数米。此外，我们表明，自我促进机制（由高生物量促进）导致的死亡率降低会在光照胁迫梯度上引发海草草甸的双稳态，从而在其深度极限处导致突然转变和滞后行为。
我们模型的结果表明：（i）生理光适应在赋予面临光照剥夺的海草更大抗性和恢复能力（即恢复力）方面的关键作用；（ii）自我促进增强机制在推动遭受严重光照减少事件的海草系统恢复力和恢复方面的重要性。
