Reliance on deep soil water in the tree species Argania spinosa

Abstract

In South-western Morocco, water scarcity and high temperature are the main factors determining species survival. Argania spinosa (L.) Skeels is a tree species, endemic to Morocco, which is suffering from ongoing habitat shrinkage. Argan trees play essential local ecological and economic roles: protecting soils from erosion, shading different types of crops, helping maintain soil fertility and, even more importantly, its seeds are used by the local population for oil production, with valuable nutritional, medicinal and cosmetic purposes. The main objective of this study was to identify the sources of water used by this species and to assess the effect of water availability on the photosynthetic rate and stem water potential in two populations: one growing on the coast and a second one 10 km inland. Stem water potential, photosynthetic rate and xylem water isotopic composition (δ18O) were seasonally monitored during 2 years. Trees from both populations showed a similar strategy in the use of the available water sources, which was strongly dependent on deep soil water throughout the year. Nevertheless, during the wet season or under low precipitation a more complex water uptake pattern was found with a mixture of water sources, including precipitation and soil at different depths. No evidence was found of the use of either groundwater or atmospheric water in this species. Despite the similar water-use strategy, the results indicate that Argania trees from the inland population explored deeper layers than coastal ones as suggested by more depleted δ18O values recorded in the inland trees and better photosynthetic performance, hence suggesting that the coastal population of A. spinosa could be subjected to higher stress.

Responses of two desert riparian species to fluctuating groundwater depths in hyperarid areas of Northwest China

“…Whether shift in water resources can actually compensate for drought, impacts on plant physiology has not been well studied. As was expected, more groundwater and deep soil water acquisition during the dry season contributed to the maintenance of relatively higher photosynthesis activity in many tree species (Drake, Froend, & Franks, 2011;Zunzunegui et al, 2017), however, other studies have reported that shifts in water sources did not alleviate the effects of drought stress on tree gas exchange (Grossiord et al, 2017;Sun, Meng, Zhang, & Wan, 2011). Understanding the differences in water uptake patterns, stomatal control and their link between species could provide insights into ecological adaptation strategies and could be used to predict the dynamics of desert riparian species in fluctuating environments.…”

“…Stomata closure can reduce transpirational water loss but at the expense of restricting CO 2 diffusion into leaves during photosynthesis (Hetherington & Woodward, 2003;McDowell et al, 2008). As was expected, more groundwater and deep soil water acquisition during the dry season contributed to the maintenance of relatively higher photosynthesis activity in many tree species (Drake, Froend, & Franks, 2011;Zunzunegui et al, 2017), however, other studies have reported that shifts in water sources did not alleviate the effects of drought stress on tree gas exchange (Grossiord et al, 2017;Sun, Meng, Zhang, & Wan, 2011). As was expected, more groundwater and deep soil water acquisition during the dry season contributed to the maintenance of relatively higher photosynthesis activity in many tree species (Drake, Froend, & Franks, 2011;Zunzunegui et al, 2017), however, other studies have reported that shifts in water sources did not alleviate the effects of drought stress on tree gas exchange (Grossiord et al, 2017;Sun, Meng, Zhang, & Wan, 2011).…”

Lithologically Controlled Subsurface Critical Zone Thickness and Water Storage Capacity Determine Regional Plant Community Composition

“…Plants in upland landscapes with thin soils may survive on water extracted from the weathered bedrock from below the soil, exploiting either groundwater (e.g., Miller et al, ) or rock moisture (sensu Salve et al, ; Rempe & Dietrich, ) from tens of meters below the ground surface (e.g., Anderson et al, ; Arkley, ; Bales et al, ; Eliades et al, ; Jones & Graham, ; Lewis & Burgy, ; Miller et al, ; Rempe & Dietrich, ; Rose et al, ; Sternberg et al, ; Zunzunegui et al, ; Zwieniecki & Newton, ). These and other previous studies in seasonally dry environments, however, have focused on local, site‐specific plant water use and have not explicitly addressed larger‐scale relationships between dominant vegetation patterns and the spatial availability of moisture beneath the soil.…”

Intensified Interspecific Competition for Water after Afforestation with Robinia pseudoacacia into a Native Shrubland in the Taihang Mountains, Northern China

“…Normally, plants preferentially absorb water from stable and continuous sources. For instance, deep-rooted species (e.g., trees and semi-arbors) can take up deeper water sources stably, enabling them to survive and tolerate seasonal water stress, i.e., go without rain for a long time [30][31][32][33][34]; in contrast, most shallow-rooted species (e.g., grasses and semi-shrubs) mainly depend on shallow soil water supplied by precipitation [19,[35][36][37][38][39][40]. The spatial complementarity of water sources causes niche segregation between species which make use of shallow and deep water, often referred to as the "two-layer hypothesis" [29,41].…”