Chia (Salvia hispanica L.) is a species with seeds that have high essential fatty acid content, which has encouraged increased crop production worldwide. However, the expansion of chia is limited because it is a photoperiod-sensitive plant adapted to areas without cold. The objective of the present study was to determine the effect of different climatic conditions on the growth, grain yield and oil production of chia under irrigation in three geographic areas of Chile: Valle de Azapa (18 degrees 30' S lat) with a coastal desert climate, normal desert climate in Canchones (20 degrees 26' S lat), and Las Cruces (33 degrees 30' S lat) with dry Mediterranean climate with marine influence, and two chia phenotypes: white and dark. Results indicated that desert conditions in the Valle de Azapa (VA) and Canchones (CH) provided better conditions for plant growth; the highest yield (> 2900 kg ha(-1)) and oil production (> 550 L ha(-1)). In Las Cruces (LC), at higher latitude, low temperatures present beginning in April coincided with the reproductive stage, affecting yield which was no more than 129 kg ha(-1); thus this zone is not recommendable for chia cultivation. This study also determined an 11.8 h day length threshold for the beginning of flowering; when plants are exposed to shorter days flower initiation is more precocious, but when day length is not adequate plants only begin to flower when they have accumulated 600-700 degrees C d.FONDECYT 1120202 CONICYT, Government of Chil

Prosopis tamarugo Phil. is a legume tree native to the Atacama Desert, Chile. Tamarugo has physiological characteristics that are highly adapted to extreme life conditions in the Pampa del Tamarugal. Null precipitation makes tamarugo completely dependent on groundwater, developing in areas where the groundwater depth is closest to the surface. Groundwater extraction for domestic consumption, mining, and agriculture affects the desert ecosystem by lowering the water table. Measuring and describing the impacts on vegetation through the monitoring of physiological variables along with groundwater depletion in salt flats where extraction wells are located has contributed to a better understanding of tamarugo response to this stress factor. Integrated variables such as green canopy fraction, normalized difference vegetation index (NDVI), 18 O isotope enrichment in foliar tissue, and twig growth proved to be far more reactive toward groundwater depth increase and presented lower error values. These variables respond to mechanisms that tamarugo has to maintain a stable water condition when water offer (water table depth (WTD)) decreases regarding water demand (transpiration). Defoliation along with twig growth diminishment would combine toward a canopy reduction strategy in order to reduce water demand. Green biomass loss, beyond a certain WTD, would lead to complete drying of the tamarugo. Up to 10 m of groundwater table depth, Tamarugo grows, has photosynthetic activity, and has the ability to perform pulvinary movements. Beyond 20 m of water table depth, tamarugo survival is compromised and hydraulic failure is inferred to occur. The current scenario is of groundwater over-exploitation; if economic efforts will be made to conserve and/or restore tamarugo, habitat groundwater extraction is a key element in effective management. Reaching of the thresholds depends on the adequate authority management of groundwater. The objectives of this review are (a) to review information collected from scientific studies regarding tamarugo condition and its response, over time, to WTD increase, (b) to identify WTD thresholds that affect tamarugo’s functioning, and (c) to propose a sequence of physiological events triggered by groundwater (GW) depletion.

Prosopis tamarugo Phil. is a strict phreatophyte tree species endemic to the "Pampa del Tamarugal”, Atacama Desert. The extraction of water for various uses has increased the depth of the water table in the Pampa aquifers threatening its conservation. This study aimed to determine the effect of the groundwater table depth on the water relations of P. tamarugo and to present thresholds of groundwater depth (GWD) that can be used in the groundwater management of the P. tamarugo ecosystem. Three levels of GWD, 11.2 ± 0.3 m, 10.3 ± 0.3 m and 7.1 ± 0.1 m, (the last GWD being our reference) were selected and groups of 4 individuals per GWD were studied in the months of January and July of the years 2011 through 2014. When the water table depth exceeded 10 m, P. tamarugo had lower pre-dawn and midday water potential but no differences were observed in minimum leaf stomatal resistance when compared to the condition of 7.1 m GWD; the leaf tissue increased its δ13C and δ18O composition. Furthermore, a smaller green canopy fraction of the trees and increased foliage loss in winter with increasing water table depth was observed. The differences observed in the physiological behavior of P. tamarugo trees, attributable to the ground water depth; show that increasing the depth of the water table from 7 to 11 m significantly affects the water status of P. tamarugo. The results indicate that P. tamarugo has an anisohydric stomatal behaviour and that given a reduction in water supply it regulates the water demand via foliage loss. The growth and leaf physiological activities are highly sensitive to GWD. The foliage loss appears to prevent the trees from reaching water potentials leading to complete loss of hydraulic functionality by cavitation. The balance achieved between water supply and demand was reflected in the low variation of the water potential and of the variables related to gas exchange over time for a given GWD. This acclimation capacity of P. tamarugo after experiencing increases in GWD has great value for the implementation of conservation strategies. The thresholds presented in this paper should

Understanding the physiological mechanisms of response that allow plants to survive under suboptimal conditions such as drought stress is of particular interest, because of global climate change that threat the suitability of most terrestrial habitats for plant growth, as well as habitat disturbance of desert plants due to water extraction for human supply. Prosopis tamarugo Phil. of the Pampa del Tamarugal is frequently subjected to drought stress due to groundwater extraction for urban areas, mining industry and agriculture supply. The aim of this review is to analyze information concerning the plant growth response to drought stress and specifically P. tamarugo water relations and growth response to drought stress. P. tamarugo, being a desert plant, has physiological mechanisms that permit its adaptation to extreme environmental conditions like the Pampa del Tamarugal. It has mechanisms as osmotic adjustment, that allow some growth through osmoregulation; changes the angle of its leaflets to avoid high levels of radiation in the afternoon; partially closes its stomata to decrease water loss; maintains high stomata conductance to deal with increasing temperature and atmospheric demand.

(1) Background: Table grapes are often subjected to thermal stress during the growing season, affecting their production. Shading nets utilization has been proposed as an alternative to face this problem, but there is little available information about their effectiveness in hyperarid conditions. INIA-G2 vines were covered with kristall-colored mesh of 8% shade, and their ecophysiological responses were compared to uncovered vines during the daily cycle of two days with contrasting thermic conditions. (2) Methods: Net assimilation rate (A_N), stomatal conductance (g_s), transpiration (E), instantaneous water use efficiency (WUE: A_N E⁻¹), stem water potential (Ψ_s), air temperature (Ta) and vapor-pressure deficit (DPV) were determined in daily cycles (from 06:00 to 20:00 hrs) on two thermally contrasting days (330 DOY at 29.4 °C and 345 DOY at 22.6 °C) on grapevines without water restriction. (3) Results: The Ψ_s was not affected by treatment and day of measurement; nevertheless, A_N and g_s were statistically lower during 330 than 345 DOY (31% and 44% decrease, respectively). The covered vines presented less restrictive climatic conditions in terms of DPV in both DOY, reaching higher WUE values at 10, 12 and 14 h, which was associated with a decrease in E. (4) Conclusions: These results suggest that the use of shading nets can be an interesting alternative to cope with high temperatures in viticulture, improving the water use efficiency of vines. These are the first published results about the viticultural performance of the INIA-G2 variety.