Water use partitioning of native and non‐native tree species in riparian ecosystems under contrasting climatic conditions

Abstract

1. One of the suggested mechanisms behind the success of non-native plants in recipient ecosystems is competition avoidance with natives by means of different resource-use strategies, such as deeper water uptake under dry conditions.2. We aimed at evaluating water source partitioning between native and non-native tree species coexisting in central Spain floodplains; determining the dependency on drought stress of such water sources use; and assessing if the reliance on deeper water sources relates with physiological and growth performance.3. We assessed water uptake depth, leaf functional traits related to physiological performance and growth of native (Populus alba) and non-native trees (Ailanthus altissima, Robinia pseudoacacia) coexisting in riparian forests under different drought conditions (drier, intermediate and wetter). We analysed δ 2 H and δ 18 O isotopes in xylem water and in soil water from top, mid and deep soil depths and determined the contribution of each water source to overall plant xylem water. Leaf traits related with resource use and secondary growth were assessed for each species. 4. We found stronger differences between sites than between species, with all species taking more deep water in the driest site (~45% of the xylem water) than in the wettest (~15%). However, under drier conditions, species differences were significant for top-soil water use, with R. pseudocacia withdrawing more superficial water (~22%) than A. altissima (~8%). These results indicate stronger water partitioning under drier conditions. Non-native species showed a physiological strategy characterized by greater leaf N, water content, and enriched δ 13 C and δ 15 N values independently of the deep-water uptake. However, a positive relationship between deep soil water use and such strategy was found for P. alba.5. We highlight that those native and non-native species differences were more evident regarding physiological performance at leaf level than for deep-water uptake or growth. Furthermore, our results suggest that differences in water sources used by coexisting species may increase under drier conditions.

Water use strategies of Nitraria tangutorum in the lake-basin region of the Badain Jaran Desert

“…Temperature and drought stress further result in the dormancy of the surface root system or dehydration and death of fine roots, stimulating root growth in deep soils to absorb deep water sources ( Dai et al., 2015 ). Thus, N. tangutorum may have increased the availability of deep soil water and groundwater in August ( Figure 6 ) by developing its deep tap roots ( Granda et al., 2022 ). Continuous staged root growth is essential for improving soil WUE and overcoming water uptake restrictions caused by decreased soil water availability ( Fernandez and Caldwell, 1975 ).…”

“…Furthermore, in ecosystems where deep-rooted plants coexist with shallow-rooted plants that rely on the hydraulic lifting capacity of deep-rooted plants, shallow-rooted plants can indirectly use deep-water sources. In conclusion, N. tangutorum may respond to changes in groundwater depth by adjusting its root distribution to adapt to seasonal shifts in available water sources through rapid growth, activation, or dormancy of the root system at diverse depths ( Figure 9 ) to maximize water acquisition ( Brooks et al., 2015 ; Brunner et al., 2015 ; Granda et al., 2022 ). This phenomenon of exploiting different water sources in different seasons is prevalent in desert plants (( Dai et al., 2015 ; Hao and Li, 2021 ; Granda et al., 2022 ), which enhances water stress tolerance under natural conditions and serves as an invaluable strategy for allowing desert plants to survive in arid habitats.…”

“…In conclusion, N. tangutorum may respond to changes in groundwater depth by adjusting its root distribution to adapt to seasonal shifts in available water sources through rapid growth, activation, or dormancy of the root system at diverse depths (Figure 9) to maximize water acquisition (Brooks et al, 2015;Brunner et al, 2015;Granda et al, 2022). This phenomenon of exploiting different water sources in different seasons is prevalent in desert plants ( (Dai et al, 2015;Hao and Li, 2021;Granda et al, 2022), which enhances water stress tolerance under natural conditions and serves as an invaluable strategy for allowing desert plants to survive in arid habitats. N. tangutorum in the Ebinur Lake Basin mainly relied on surface soil water in spring, deep soil water in summer, and an increased percentage of middle soil water in autumn (Hao and Li, 2021), which is partially dissimilar to the results of this study.…”

The Invasive Ailanthus altissima: A Biology, Ecology, and Control Review

“…The differences between both studies probably lie in the fact that the first experiment lasted two years while the second lasted only one, suggesting that plants have mechanisms to adapt to a water-scarce environment. In adult plants, the ability of this species to cope with drought may also be related to its ability to take water mainly from deeper soil layers (more than 75 cm) than from the first 25 cm of soil layers [59]. Other authors pointed out that A. altissima was more efficient in terms of root-to-leaf water transport capacity than native species [60].…”

Dynamic hydrological niche segregation: how plants compete for water in a semiarid ecosystem

“…Water is the most limiting resource for plant survival and growth in arid and semiarid ecosystems. Coexisting plant species usually adopt diverse water use strategies (e.g., root biomass adjustment, shift in root water uptake depth, stomatal regulation) to compete for or apportion this limited resource (Granda et al, 2022;Kulmatiski et al, 2020b;Rodríguez-Robles et al, 2020). Silvertown et al (2015) introduced the concept of hydrological niche segregation (HNS) concerning the apportionment of soil water resources in a plant community.…”