From facilitative to competitive interactions between woody plants and plants with crassulacean acid metabolism (CAM): The role of hydraulic descent

Abstract

Woody plants may facilitate the establishment of seedlings with crassulacean acid metabolism (CAM) by ameliorating the abiotic environment through an increase in soil water availability. Because of the low transpiration rate in shallow‐rooted CAM plants and the consequently high soil water contents in the shallow soil, deep‐rooted trees in tree–CAM associations could perform hydraulic descent transporting water from wetter shallow soil to drier deep soil in arid environments. It remains unclear, however, whether a high rate of hydraulic descent can turn the facilitation of CAM plants by woody plants into competition. In this study, we develop a mechanistic model to investigate the facilitation of shallow‐rooted CAM plants by deep‐rooted woody plants in the access to soil water resources along a rainfall gradient. The model results show that in the case of low‐to‐moderate root overlap woody plants could facilitate CAM plants in access to soil water; this effect is mainly induced by the reduction in evaporation from the soil surface due to shading. Both shading and hydraulic descent decrease (or hydraulic lift increases) along a rainfall gradient, thereby favoring facilitation. Investment in deep roots by woody plants is usually thought to increase niche differentiation with shallow‐rooted plants, thereby reducing the competition and promoting species coexistence. This study indicates that deep root development could also favor competition through the mechanism of hydraulic descent, thereby changing our understanding of the role of root depth in niche differentiation between shallow and deep‐rooted plants.

Hydraulic Water Redistribution by Silver Fir (Abies alba Mill.) Occurring under Severe Soil Drought

“…Typically, HR occurs during the night, when transpiration has ceased [3][4][5]. Water can be redistributed in the upward (i.e., hydraulic lift [2,6,7]), downward (i.e., hydraulic descent [8][9][10][11]), and lateral directions [12][13][14][15]. Field observations showed that HR plays an important role in terrestrial ecohydrological cycles.…”

Data-driven competitive facilitative tree interactions and their implications on nature-based solutions

“…Apart from the interest that facilitation exhibits from the perspective of basic biological knowledge, it has serious implications for soil surface water, degraded land restoration (Antonio et al, 2018;Víctor et al, 2017), as well as for agriculture and food security (Li et al, 2014;Moschitz et al, 2015). To that end, understanding the interplay between trees and the way they ameliorate their biotic and physical environment (Yu and D'Odorico, 2017) as well as climate and soil, is critical for ecosystem management, agricultural planning, and water management (Davis et al, 2017).…”

Influences of Root Hydraulic Redistribution on N2O Emissions at AmeriFlux Sites

“…Such hydraulic redistribution (HR) of soil water via plant roots can be upward (hydraulic lift), downward (hydraulic descent), or lateral (Horton & Hart, 1998;Neumann & Cardon, 2012;Prieto et al, 2012;Sardans & Peñuelas, 2014;Yu & D'Odorico, 2017). Such hydraulic redistribution (HR) of soil water via plant roots can be upward (hydraulic lift), downward (hydraulic descent), or lateral (Horton & Hart, 1998;Neumann & Cardon, 2012;Prieto et al, 2012;Sardans & Peñuelas, 2014;Yu & D'Odorico, 2017).…”

“…In seasonally dry ecosystems, plant roots transfer water from moist soil layers to dry soil layers along the soil water potential gradient. Such hydraulic redistribution (HR) of soil water via plant roots can be upward (hydraulic lift), downward (hydraulic descent), or lateral (Horton & Hart, 1998;Neumann & Cardon, 2012;Prieto et al, 2012;Sardans & Peñuelas, 2014;Yu & D'Odorico, 2017). The effects of HR on the hydrological, carbon, and nitrogen cycles have been demonstrated in numerous field studies (e.g., Cardon et al, 2013;Ryel et al, 2002;Scott et al, 2008).…”