Water Relations and Foliar Isotopic Composition of Prosopis tamarugo Phil., an Endemic Tree of the Atacama Desert Growing at Three Levels of Water Table Depth

Abstract

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 four 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 mid-day 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 behavior 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 prove useful for conservation purposes of this unique species.

Water relations and growth response to drought stress of Prosopis tamarugo Phil. A review

“…Aravena and Acevedo (1985) linked this isotopic enrichment to the source of different isotopic species in the liquid-vapor system. Low 13 C discrimination and more enriched 18 O was found by Garrido et al (2016) in leaf tissue of Prosopis tamarugo subjected to stress due to increased ground water table depth in the Pampa of Tamarugal.…”

“…Water potential decrease has been observed in conditions of drought stress, both at midday and at predawn in individuals of Prosopis tamarugo (Garrido et al, 2016, Time, 2017. Water potential (Ψw) is also a measure of how hydrated a plant is and thus provides a relative index of the drought stress the plant is experiencing.…”

“…Additionally, water deficit affects many variables and functions in tamarugo plants, such as stomata functioning (Garrido, et al, 2016, Time, 2017, hydric traits as pre-dawn, mid-day water potential and xylem hydraulic conductivity (Garrido et al, 2016;Time, 2017) and growth traits like twig elongation rate and specific leaf area (Time, 2017) have been reported. The performance of these and other traits and processes, may determine growth capacity and tamarugo plant survival as suggested by McDowell et al, (2008).…”

Algunos Usos De Técnicas De Isótopos Estables en Ciencia Forestal

“…Stable isotope studies of 13 C, 18 O and 2 H have proved useful in identifying the origin of water consumed, in knowing the photosynthetic pathway and studying possible changes in the transpiration rate in many species; an example of this is in Prosopis tamarugo Phil. (Garrido et al, 2016).…”

“…The δ 13 C measured in the dry matter has been a precise estimator of the intrinsic time-integrated water use efficiency for C 3 plants (Farquhar et al, 1989). Also, δ 13 C has been successfully used in the iWUE study of eucalyptus (Eucalyptus) forests (Zolfaghar et al, 2017) and Prosopis tamarugo (Garrido et al, 2016) submitted to depth gradients of water level, as well as roots depth estimation and use of groundwater in different forest communities (Rumman et al, 2018).…”