Improving Salicornia ramosissima photochemical and biochemical resilience to extreme heatwaves through rhizosphere engineering with Plant Growth-Promoting Bacteria.

The anticipated rise in the length, frequency, and intensity of heatwaves (HW) in the Mediterranean region poses a danger to the crops, as these brief but high-intensity thermal stress events halt plant productivity. This arises the need to develop new eco-friendly sustainable strategies to overcome food demand. Halophytes such as Salicornia ramosissima appear as cash crop candidates, alongside with new biofertilization approaches using Plant Growth Promoting Bacteria (PGPB). In the present work, S. ramosissima plants exposed to heatwave (HW) treatments with and without marine PGPB inoculation is studied to evaluate the physiological responses behind eventual thermal adaptation conditions. Plants exposed to HW inoculated with ACC deaminase and IAA-producing PGPB showed a 50% reduction in the photochemical energy dissipation, when compared to their non-inoculated counterparts, indicating higher light-use efficiency. The observed concomitant increase (76-234%) in several pigments indicates improved inoculated HW-exposed individuals' light harvesting and photoprotection under stressful conditions. This reduction of the physiological stress levels in inoculated plants was also evident by the significant reduction of several antioxidant enzymes as well as of membrane lipid peroxidation products. Additionally, improved membrane stability could also be observed, through the regulation of fatty acid unsaturation levels, decreasing the excessive fluidity imposed by HW treatment. All these improved physiological traits associated with specific PGP traits highlight a key potential of the use of these PGPB consortiums as biofertilizers for S. ramosissima cash crop production in the Mediterranean, where increasing frequency in HW-events is a major drawback to plant production, even to warm-climate plants.

Potential of Asparagopsis armata as a Biopesticide for Weed Control under an Invasive Seaweed Circular-Economy Framework.

Marine macroalgae have been increasingly targeted as a source of bioactive compounds to be used in several areas, such as biopesticides. When harvesting invasive species, such as Asparagopsis armata, for this purpose, there is a two-folded opportunity: acquiring these biomolecules from a low-cost resource and controlling its spreading and impacts. The secondary metabolites in this seaweed's exudate have been shown to significantly impact the physiology of species in the ecosystems where it invades, indicating a possible biocidal potential. Considering this in the present work, an A. armata exudate cocktail was applied in the model weed Thellungiella halophila to evaluate its physiological impact and mode of action, addressing its potential use as a natural biocide. A. armata greatly affected the test plants' physiology, namely, their photochemical energy transduction pathway (impairing light-harvesting and chemical energy production throughout the chloroplast electron transport chain), carotenoid metabolism and oxidative stress. These mechanisms of action are similar to the ones triggered when using the common chemical pesticides, highlighting the potential of the A. armata exudate cocktail as an eco-friendly biopesticide.

Physiological consequences of desiccation in the aquatic bryophyte Fontinalis antipyretica.

The moss Fontinalis antipyretica, an aquatic bryophyte previously described as desiccation-intolerant, is known to survive intermittent desiccation events in Mediterranean rivers. To better understand the mechanisms of desiccation tolerance in this species and to reconcile the apparently conflicting evidence between desiccation tolerance classifications and field observations, gross photosynthesis and chlorophyll a fluorescence were measured in field-desiccated bryophyte tips and in bryophyte tips subjected in the laboratory to slow, fast, and very fast drying followed by either a short (30 min) or prolonged (5 days) recovery. Our results show, for the first time, that the metabolic response of F. antipyretica to desiccation, both under field and laboratory conditions, is consistent with a desiccation-tolerance pattern; however, drying must proceed slowly for the bryophyte to regain its pre-desiccation state following rehydration. In addition, the extent of dehydration was found to influence metabolism whereas the drying rate determined the degree of recovery. Photosystem II (PSII) regulation and structural maintenance may be part of the induced desiccation tolerance mechanism allowing this moss to recover from slow drying. The decrease in the photochemical quenching coefficient (qP) immediately following rehydration may serve to alleviate the effects of excess energy on photosystem I (PSI), while low-level non-photochemical quenching (NPQ) would allow an energy shift enabling recovery subsequent to extended periods of desiccation. The findings were confirmed in field-desiccated samples, whose behavior was similar to that of samples slowly dried in the laboratory.