Differential tolerance of native and invasive tree seedlings from arid African deserts to drought and shade

Authors: ABBAS, AHMED - University Of Sevilla; RUBIO-CASAL, ALFREDO - University Of Sevilla; DE CIRES, ALFONSO - University Of Sevilla; Grewell, Brenda; CASTILLO, JESUS - University Of Sevilla

Submitted to: South African Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2019
Publication Date: 3/28/2019
Citation: Abbas, A.M., Rubio-Casal, A., De Cires, A., Grewell, B.J., Castillo, J.M. 2019. Differential tolerance of native and invasive tree seedlings from arid African deserts to drought and shade. South African Journal of Botany. 123:228-240. https://doi.org/10.1016/j.sajb.2019.03.018.
DOI: https://doi.org/10.1016/j.sajb.2019.03.018

Interpretive Summary: An important research challenge in plant invasion ecology has been devoted to understanding why some species become successful invaders and why some habitats are easier to invade than others. With current global warming trends, improved understanding of how native species and alien invaders perform under extreme abiotic stress is especially important for conservation management. The range of invasive plant species may expand or contract as air temperatures, drought and evapotranspiration demand increase in some areas, and as global warming and atmospheric CO2 enrichment differentially affect particular plant species. In this global context, the effects of abiotic stresses on plant invasions are especially important in arid ecosystems. It is therefore important to predict and to control plant invasions into arid lands, and to improve our understanding of how water and light availability may differentially influence alien and native species. The aim of this study was to evaluate and compare the tolerance and responses of tree seedlings of Acacia tortilis subsp. raddiana, native to arid African deserts, and seedlings of the invasive neophyte tree Prosopis glandulosa, native to the southwestern United States and Mexico, to shade, water stress and their interactions. We conducted a greenhouse experiment with controlled conditions, and measured and recorded growth rates and morphological, biochemical and physiological plant traits for both species under two radiation and two water treatments. We hypothesized that invasive P. glandulosa would be less tolerant to abiotic stress, particularly to the combination of shade and water stress, than the native A. t. subsp. raddiana. Radiation intensity was a stronger driver of the performance of both species than water availability. Beyond the independent effects of shade and drought, the interactions of these factors yielded synergistic effects on seedlings of both tree species, affecting key plant traits. The seedlings of A. t. subsp. raddiana were able to implement important shifts in key functional traits in response to changing abiotic stress conditions, behaving as a stress-tolerant species that is well-adapted to the habitat it occupies in hot arid African deserts. In contrast, the fast-growing seedlings of P. glandulosa were stress-avoiding. The alien P. glandulosa seedlings were highly sensitive to water and shade stress, and particularly to their interaction. However, these invasive seedlings were able to avoid permanent damage to their photosynthetic apparatus and recover from stress. Our results are useful for conservation planning and restoration of invaded arid ecosystems. Disturbances and alterations leading to the formation of microenvironments with diminished abiotic stress, such as opening gaps in native vegetation and creating humid and nutrient-rich patches (i.e. due to camel endozoochory), should be avoided to prevent the invasion of P. glandulosa though limiting its seedling establishment. Moreover, the conservation of adult A. t. subsp. raddiana trees and augmentative restoration plantings of seeds or seedlings may provide a valuable biotool to promote invasion resistance through establishment of shade to limit the invasion of P. glandulosa.

Technical Abstract: Efforts to understand why some species become successful invaders and why some habitats are more at risk from invasive species is an important research focus in invasion ecology. With global warming, evaluation of the effects of shade and drought on coexisting native and invasive species from extreme ecosystems is especially important. The aim of this study was to evaluate and compare the tolerance and responses of tree seedlings of Acacia tortilis subsp. raddiana, native to arid African deserts, and seedlings of the invasive neophyte tree Prosopis glandulosa, native to the southwestern United States and Mexico, to shade, water stress and their interactions. We measured and recorded growth rates and morphological, biochemical and physiological plant traits under two radiation and two water treatments in greenhouse conditions. Radiation intensity was a stronger driver of the performance of both species than water availability. Beyond the independent effects of shade and drought, the interactions of these factors yielded synergistic effects on seedlings of both tree species, affecting key plant traits. The seedlings of A. t. subsp. raddiana were able to implement important shifts in key functional traits in response to changing abiotic stress conditions, behaving as a stress-tolerant species that is well-adapted to the habitat it occupies in hot arid African deserts. In contrast, the fast-growing seedlings of P. glandulosa were stress-avoiding. The alien P. glandulosa seedlings were highly sensitive to water and shade stress, and particularly to their interaction. However, these invasive seedlings were able to avoid permanent damage to their photosynthetic apparatus and recover from stress. Our results are useful for conservation planning and restoration of invaded arid ecosystems.