The irrigation salinity and harvesting affect the growth, chemical profile and biological activities of Polygonum maritimum L

Previously, our group identified the halophyte Polygonum maritimum L. (sea knotgrass) as a promising source of ingredients for the cosmetic, food, pharmaceutical and veterinarian industries. To further explore this species, and to guarantee the supply of biomass for commercial purposes, it is necessary to ensure its sustainable production while assuring the preservation of its chemical and biological properties. In this context, this work aimed to cultivate this species in greenhouse conditions and to determine the influence of specific agronomic conditions, namely irrigation salinity and harvest, on the plant’s growth performance and biological properties of obtained biomass. For that purpose, plants were grown in a greenhouse and irrigated with water with different salinities (0, 100, 200, 300 and 600 mM of sodium chloride - NaCl). After six weeks of irrigation, plants were cut 7 cm above soil level and submitted to an additional two harvests with a six-week interval. Plant growth performance was evaluated in terms of plant height, leaf number and surface area, moisture, and productivity. Acetone extracts were prepared from aboveground organs and evaluated for chemical composition (by spectrophotometric methods, and by ultra-high-resolution mass spectrometry - UHRMS), and for in vitro antioxidant properties [radical-scavenging activity (RSA) on DPPH and ABTS, ferric reducing antioxidant power (FRAP) and metal chelating activity on iron (ICA) and copper (CCA)]. Extracts were also appraised for in vitro anti-inflammatory activity on lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. Increased salinity and multiple harvests reduced plant growth and yields; the highest productivity was obtained in plants irrigated with freshwater at 2nd harvest (346 g/m2 of dried biomass). The extracts maintained the in vitro biological properties and interesting chemical profile, however, these depended on the irrigation salinity and harvest regime. The highest antioxidant activities were obtained in extracts from plants irrigated with freshwater at the 3rd harvest (DPPH: 96.2%; ABTS: 89.1%; CCA: 61.6%; FRAP: 136%). The extracts from biomass obtained in the 1st harvest of freshwater-irrigated plants, and from those treated with 100 and 200 mM of NaCl, had significant anti-inflammatory properties. The main compounds detected were mostly flavonols (myricetin and quercetin glycosides), which varied according to both irrigation salinity and harvest. Our results indicate that sea knotgrass can be cultivated in greenhouse conditions aiming industrial commercial applications, irrigated with freshwater or with irrigation solutions with moderate salinity. Moreover, produced biomass maintain the biological and chemical properties previously detected in plants collected from the wild.