Zostera noltii development probing using chlorophyll a transient analysis (JIP-test) under field conditions: Integrating physiological insights into a photochemical stress index

Abstract

Beyond their undeniable role, nowadays we also must look to seagrass beds as endangered environmentswith urgent monitoring and conservation needs. In the present study Z. noltii photochemical performanceof under different stages of development/recovery was assessed and its results applied in the develop-ment of a photochemical stress index (PSI) to classify and efficiently assess the physiological conditionof seagrass beds. In order to investigate deeper into this metabolic network the JIP-test was applied,allowing to identify the reasons underlying the first signs of stress. Less developed beds low connectiv-ity between PS II antennae leading inevitably to an impairment of the energetic transport. Associatedto this also the quinone pool showed severe depletion both in number and function. Alongside the K-step presence in the Kautsky curve points to severe damage at donor side of the PS II, where the OxygenEvolving Complexes (OECs) are located. All these negative impacts increase the quantum yield of the non-photochemical reactions in stressed/less developed seagrass beds. In sum, more developed beds showproportionally higher light use efficiencies promoted by a higher number of oxidized reaction centrescoupled with an enhanced capacity in using the generated electron potential and relatively lower energydissipations. Coupling all the photochemical into an Integrated Biomarker Response (IBR) approach, aphotochemical stress index (PSI) was produced. The PSI showed that more developed sites present lowerphotochemical stress values with inverse significant correlation with biomass coverage, reinforcing theapplicability of this non-invasive index as a reflex of the seagrass bed development stage.