Despite its economic relevance, little is known about salt tolerance mechanisms in pepper plants. To address this question, we compared differences in responses to NaCl in two Capsicum chinense varieties: Rex (tolerant) and Chichen-Itza (sensitive). Under salt stress (150 mM NaCl over 7 days) roots of Rex variety accumulated 50 times more compatible solutes such as proline compared to Chichen-Itza. Mineral analysis indicated that Na+ is restricted to roots by preventing its transport to leaves. Fluorescence analysis suggested an efficient Na+ compartmentalization in vacuole-like structures and in small intracellular compartments in roots of Rex variety. At the same time, Na+ in Chichen-Itza plants was compartmentalized in the apoplast, suggesting substantial Na+ extrusion. Rex variety was found to retain more K+ in its roots under salt stress according to a mineral analysis and microelectrode ion flux estimation (MIFE). Vanadate-sensitive H+ efflux was higher in Chichen-Itza variety plants, suggesting a higher activity of the plasma membrane H+-ATPase, which fuels the extrusion of Na+, and, possibly, also the re-uptake of K+. Our results suggest a combination of stress tolerance mechanisms, in order to alleviate the salt-induced injury. Furthermore, Na+ extrusion to apoplast does not appear to be an efficient strategy for salt tolerance in pepper plants.

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Groundwater represents almost half of the drinking water worldwide and more than one third of water used for irrigation. Agro-industrial activities affect water resources in several manners; one of the most important is leaching of agrochemical residues. This research identifies the major contributors of changes in groundwater quality comparing two contrasting land uses in a karstic area of the Yucatan peninsula as case study. Using a multiple approach, we assess the impact of land use with physicochemical data, multivariate analyses, hydrogeochemistry and nitrate isotopic composition. We confirmed that agricultural land use has a greater impact on groundwater quality, observed in higher concentration of nitrates, ammonium, potassium and electrical conductivity. Seasonality has an influence on phosphates and the chemical composition of the groundwater, increasing the concentration of dissolved substances in the rainy season. There was a clear effect of manure application in the agricultural zone and the nitrate isotopic composition of groundwater points toward recharge in certain areas. We consider that seasonality and land use effects are intertwined and sometimes difficult to separate, likely because of land use intensity and hydrogeochemical process at a local scale. Finally, we observed poor groundwater quality in the agricultural area during the wet season; thus, it is desirable to maintain nonagricultural areas that provide groundwater of appropriate quality.

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The chemical characteristics and hydrogeochemical processes that govern the groundwater in the sinkholes ring of the Yucatan Peninsula were assessed. The groundwater of the area studied is of the Ca–Mg–HCO3 type. Local geology (abundance of dolomite) determines Mg2+ enrichment relative to Ca2+. The absence of seawater intrusion was established. Sinkhole water chemistry is controlled by carbonate rock dissolution, with dominance of Ca2+, Mg2+ and HCO3–. The dynamic and controlling factors of trace elements were determined in sediments of the southern part of Mexico. The order of mean concentrations of trace elements in sediments is Sr>Pb>Cu>Zn>Cr>> Cd. With regard to the sequential extraction procedure, the potential importance of fractions in sediments is in the order residual>organic matter>carbonates>exchangeable>water soluble, confirming that sinkhole sediments works as a sink of trace elements, and that no anthropogenic pressure exists in the groundwater of the hydrogeological reserve area. Trace element stability in sediments decreased as follow: Cd>Pb>Zn>Cr>Cu>Sr. The study results describe the groundwater and sediment condition of the hydrogeological reserve area, and provide insights for stakeholders and authorities. Growing population and economic activities may be major threats to the groundwater in coming decades.