Garrido Marco, Silva Paola, Acevedo Edmundo
Programa de Doctorado en Ciencias Silvoagropecuarias y Veterinarias, Universidad de Chile Santiago, Chile.
Soil-Plant-Water Relations Laboratory, Agricultural Production Department, Faculty of Agronomical Sciences, University of Chile Santiago, Chile.
Front Plant Sci. 2016 Mar 30;7:375. doi: 10.3389/fpls.2016.00375. eCollection 2016.
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 δ(13)C and δ(18)O 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.
塔马鲁戈牧豆树（Prosopis tamarugo Phil.）是一种严格的潜水植物树种，为阿塔卡马沙漠“塔马鲁戈潘帕”地区所特有。因各种用途而进行的取水活动增加了潘帕含水层的地下水位深度，这对其保护构成了威胁。本研究旨在确定地下水位深度对塔马鲁戈牧豆树水分关系的影响，并给出可用于塔马鲁戈牧豆树生态系统地下水管理的地下水位深度（GWD）阈值。选取了三个GWD水平，分别为11.2±0.3米、10.3±0.3米和7.1±0.1米（最后一个GWD作为我们的参照），在2011年至2014年的1月和7月，对每个GWD水平下的四株树组成的组进行了研究。当地下水位深度超过10米时，塔马鲁戈牧豆树黎明前和中午的水势较低，但与GWD为7.1米的情况相比，叶片最小气孔阻力未观察到差异；叶片组织的δ(13)C和δ(18)O组成增加。此外，还观察到随着地下水位深度增加，树木的绿色冠层比例变小，冬季叶片损失增加。塔马鲁戈牧豆树的生理行为差异归因于地下水位深度；这表明地下水位从7米增加到11米会显著影响塔马鲁戈牧豆树的水分状况。结果表明，塔马鲁戈牧豆树具有非等渗气孔行为，在供水减少时，它通过叶片损失来调节水分需求。生长和叶片生理活动对GWD高度敏感。叶片损失似乎能防止树木达到因空化导致水力功能完全丧失的水势。在给定的GWD下，水分供应和需求之间实现的平衡反映在水势以及与气体交换相关变量随时间的低变化上。塔马鲁戈牧豆树在经历GWD增加后所具有的这种适应能力，对于实施保护策略具有重要价值。本文给出的阈值应证明对保护这一独特物种有用。
