Salt Tolerance of Sea Flax (Linum maritimum L.), a Rare Species with Conservation Interest in Eastern Spain.

Seldom found in saltmarshes, Linum maritimum is a halophyte of great conservation interest in the eastern Iberian Peninsula. Although the species has been reported in different plant communities, there is no information on its range of salinity tolerance or mechanisms of response to environmental stress factors. In this study, L. maritimum plants were subjected to increasing salt concentrations in controlled conditions in a greenhouse. After six months of watering with salt solutions, only plants from the control, 50 mM and 100 mM NaCl treatment groups survived, but seeds were produced only in the first two. Significant differences were found between the plants from the various treatment groups in terms of their growth parameters, such as plant height, fresh weight, and the quantity of flowers and fruits. The main mechanism of salt tolerance is probably related to the species' ability to activate K+ uptake and transport to shoots to partly counteract the accumulation of toxic Na+ ions. A biochemical analysis showed significant increases in glycine betaine, flavonoids and total phenolic compounds, highlighting the importance of osmotic regulation and antioxidant compounds in the salt tolerance of Linum maritimum. These findings have implications for the conservation of the species, especially under changing climatic conditions that may lead to increased soil salinity in its Mediterranean distribution area.

Mitigation of salt stress in lettuce by a biostimulant that protects the root absorption zone and improves biochemical responses.

Horticultural crops constantly face abiotic stress factors such as salinity, which have intensified in recent years due to accelerated climate change, significantly affecting their yields and profitability. Under these conditions, it has become necessary to implement effective and sustainable solutions to guarantee agricultural productivity and food security. The influence of BALOX®, a biostimulant of plant origin, was tested on the responses to salinity of Lactuca sativa L. var. longifolia plants exposed to salt concentrations up to 150 mM NaCl, evaluating different biometric and biochemical properties after 25 days of treatment. Control plants were cultivated under the same conditions but without the biostimulant treatment. An in situ analysis of root characteristics using a non-destructive, real-time method was also performed. The salt stress treatments inhibited plant growth, reduced chlorophyll and carotenoid contents, and increased the concentrations of Na+ and Cl- in roots and leaves while reducing those of Ca2+. BALOX® application had a positive effect because it stimulated plant growth and the level of Ca2+ and photosynthetic pigments. In addition, it reduced the content of Na+ and Cl- in the presence and the absence of salt. The biostimulant also reduced the salt-induced accumulation of stress biomarkers, such as proline, malondialdehyde (MDA), and hydrogen peroxide (H2O2). Therefore, BALOX® appears to significantly reduce osmotic, ionic and oxidative stress levels in salt-treated plants. Furthermore, the analysis of the salt treatments' and the biostimulant's direct effects on roots indicated that BALOX®'s primary mechanism of action probably involves improving plant nutrition, even under severe salt stress conditions, by protecting and stimulating the root absorption zone.

Responses of different invasive and non-invasive ornamental plants to water stress during seed germination and vegetative growth.

Biological invasions represent a major threat to natural ecosystems. A primary source of invasive plants is ornamental horticulture, which selects traits related to invasiveness. This study evaluated the responses to water stress during germination and vegetative growth of six species used as ornamental or medicinal plants. Three of them are recognised as invasive weeds in many world areas. Seeds were exposed to increasing concentrations of polyethylene glycol (PEG) mimicking drought stress, and young plants in the vegetative growth stage were subjected to two levels of water stress. Results indicated that in the absence of stress in control conditions, the most competitive species were those reported as weeds, namely Bidens pilosa L., Oenothera biennis L., and Centaurea cyanus L., the last regarding germination velocity. Under stress, only two species, Limonium sinuatum (L.) Mill. and C. cyanus, maintained germination at -1 MPa osmotic potential, but in the recovery experiment, an osmopriming effect of PEG was observed. The most tolerant species during growth were two natives in the Mediterranean region, L. sinuatum and Lobularia maritima (L.) Desv., both accumulating the highest proline concentrations. The sixth species studied, Echinacea purpurea (L.) Moench., proved to be more susceptible to stress in the two developmental stages. This study reveals that the most significant traits associated with invasiveness were related to germination, especially in the absence of stress.

Evaluation of Drought Responses in Two Tropaeolum Species Used in Landscaping through Morphological and Biochemical Markers.

One of the most important challenges horticultural crops confront is drought, particularly in regions such as the Mediterranean basin, where water supplies are usually limited and will become even scarcer due to global warming. Therefore, the selection and diversification of stress-tolerant cultivars are becoming priorities of contemporary ornamental horticulture. This study explored the impact of water stress on two Tropaeolum species frequently used in landscaping. Young plants obtained by seed germination were exposed to moderate water stress (half the water used in the control treatments) and severe water stress (complete withholding of irrigation) for 30 days. Plant responses to these stress treatments were evaluated by determining several growth parameters and biochemical stress markers. The latter were analysed by spectrophotometric methods and, in some cases, by non-destructive measurements using an optical sensor. The statistical analysis of the results indicated that although the stress responses were similar in these two closely related species, T. minus performed better under control and intermediate water stress conditions but was more susceptible to severe water stress. On the other hand, T. majus had a stronger potential for adaptation to soil water scarcity, which may be associated with its reported expansion and naturalisation in different regions of the world. The variations in proline and malondialdehyde concentrations were the most reliable biochemical indicators of water stress effects. The present study also showed a close relationship between the patterns of variation of flavonoid and chlorophyll contents obtained by sensor-based and spectrophotometric methods.

Effect of Water Deficit on Germination, Growth and Biochemical Responses of Four Potentially Invasive Ornamental Grass Species.

Ornamental plant species introduced into new environments can exhibit an invasive potential and adaptability to abiotic stress factors. In this study, the drought stress responses of four potentially invasive ornamental grass species (Cymbopogon citratus, Cortaderia selloana, Pennisetum alopecuroides and P. setaceum) were analysed. Several seed germination parameters were determined under increasing polyethylene glycol (PEG 6000) concentrations. Additionally, plants in the vegetative stage were subjected to intermediate and severe water stress treatments for four weeks. All species registered high germination rates in control conditions (no stress treatment), even at high PEG concentrations, except C. citratus, which did not germinate at -1 MPa osmotic potential. Upon applying the water stress treatments, P. alopecuroides plants showed the highest tolerance, and C. citratus appeared the most susceptible to drought. Stress-induced changes in several biochemical markers (photosynthetic pigments, osmolytes, antioxidant compounds, root and shoot Na+ and K+ contents), highlighted different responses depending on the species and the stress treatments. Basically, drought tolerance seems to depend to a large extent on the active transport of Na+ and K+ cations to the aerial part of the plants, contributing to osmotic adjustment in all four species and, in the case of the most tolerant P. alopecuroides, on the increasing root K+ concentration under water deficit conditions. The study shows the invasive potential of all species, except C. citratus, in dry areas such as the Mediterranean region, especially in the current climate change scenario. Particular attention should be given to P. alopecuroides, which is widely commercialised in Europe as ornamental.