Wild Halophytes: Tools for Understanding Salt Tolerance Mechanisms of Plants and for Adapting Agriculture to Climate Change II

Dear Colleagues,

All our major crops and most plant wild species are glycophytes, sensitive to relatively low salt levels in the soil. On the contrary, a relatively small group of plants—the halophytes—are adapted to natural saline environments and can survive and complete their life cycle in habitats with soil salinity equivalent to 200 mM NaCl, although some can withstand salinities even higher than that of seawater. These saline habitats are fascinating from an ecological perspective, but also very much threatened by human activities and extremely sensitive to climate change effects. The general increase in average temperatures; the more extended, frequent and intense drought periods; floods; changes in normal weather patterns; and the increase in salinity levels in different saline environments brought about by climate change are altering the distribution of wild plants in Nature, significantly affecting halophytes. The study of their response mechanisms to these abiotic stress factors constitutes a relevant topic in current plant biology research.

Climate change also represents a major challenge for agriculture and food security, now and in the foreseeable future. Soil salinity is, together with drought, one of the leading causes of the reduction of crop yields worldwide, and climate change is contributing to the increasing loss of irrigated cropland due to secondary salinization, especially in arid and semiarid regions. The most promising strategy to address this problem should be based on the genetic improvement of crop salt tolerance. This approach, in turn, requires a deep understanding of salt tolerance mechanisms. All plants, tolerant or not, share a series of basic, conserved responses to salt stress (control of ion transport, osmolyte biosynthesis, activation of antioxidant systems, synthesis of ‘protective’ proteins), although the specific mechanisms of tolerance can vary widely in different species. Therefore, halophytes are ideal subjects for fundamental studies of salt-tolerance mechanisms in plants, in general, at the physiological, biochemical, and molecular levels. These studies complement and extend those most frequently carried out using non-tolerant model species, such as Arabidopsis thaliana. Besides a purely scientific interest in halophytes as a source of basic knowledge, halophytes can also provide biotechnological tools (i.e., salt-tolerance genes and salt-induced promoters) for the genetic improvement of the salt tolerance of conventional crops. Furthermore, some halophytes could represent the basis of a sustainable ‘saline agriculture’, being commercially grown for food, feed or the production of metabolites of medical, nutraceutical or industrial interest in salinized land and irrigated with brackish or saline water, not competing with our conventional crops for these limited resources, fertile land and good-quality water for irrigation.

The basic and applied aspects of halophytes research mentioned above have been addressed in a Plants Special Issue, “Wild Halophytes: Tools for Understanding Salt Tolerance Mechanisms of Plants and for Adapting Agriculture to Climate Change”, recently published as an eBook (https://doi.org/10.3390/books978-3-0365-6572-9). Most articles included in the Special Issue dealt with the elucidation of salt (and/or drought) stress tolerance mechanisms under controlled greenhouse conditions, in several cases performing comparative analyses of the stress responses of taxonomically related taxa, using physiological and biochemical approaches. Some other papers refer to field studies, phytochemical analyses, or biotechnological applications of halophytes in phytoremediation or as a source of metabolites of medical/nutritional interest.

We are proud to launch this Special Issue’s second edition, which will again cover all biological and biotechnological aspects of halophytes research mentioned above, reflected in original research papers, reviews, minireviews or opinion papers. Those topics or experimental strategies not addressed or underrepresented in the first edition will be especially welcome: halophyte ecophysiology, investigation of stress-tolerance mechanisms using molecular biology or ‘omics’ approaches, and agronomic assessments of halophytes as ‘new’ crops for saline agriculture.

Dr. Marius-Nicusor Grigore
Dr. Ricardo Mir
Prof. Dr. Oscar Vicente
Guest Editors

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• abiotic stress
• antioxidant systems
• climate change
• ecophysiology
• drought
• ion transport
• osmolyte accumulation
• plant breeding
• saline agriculture
• salinity
• salt stress responses
• salt tolerance

• Wild Halophytes: Tools for Understanding Salt Tolerance Mechanisms of Plants and for Adapting Agriculture to Climate Change in Plants (13 articles)