Background:

Plants in arid ecosystems exhibit adaptive traits to periodic droughts. It is predicted that droughts will become more frequent and intense due to global change. Studying plant ecophysiological traits will help understand their adaptations to water limitations. In arid ecosystems of northwestern Mexico, evergreen and deciduous trees coexist, with little knowledge of their responsible hydrological functional traits.

Questions:

What are the differences in drought resistance and hydraulic traits for coexisting trees in a semi-arid community? Are we able to determine their coexistence mechanisms?

Studied species:

Olneya tesota, Ipomoea arborescens and Jatropha cordata.

Study site and dates:

Desert shrubland/subtropical shrubland community in central Sonora, Mexico, in 2021.

Methods:

Sap flux density (F d) was measured continuously with heat dissipation method probes, and predawn (Ψpd), midday (Ψmd) water potentials and stomatal conductance (gs) during the summer wet season.

Results:

Olneya (evergreen) was found to maintain F d throughout the year, but Ipomoea and Jatropha (deciduous) only during the wet summer season. The maximum F d of Ipomoea and Jatropha (~1,200 g cm-2 day-1) were two times higher than Olneya (600 g cm-2 day-1). During dry spells, deciduous trees decreased their F d. Water potentials and stomatal conductances allowed differentiation of the hydrologic niches of isohydric (Ipomoea and Jatropha) and anisohydric (O. tesota) functional types.

Conclusions:

We found a gradient of diminishing drought resistance from Ipomoea, Jatropha to Olneya. These species enhanced coexistence because of their hydrological niches, determined by their sap flow, iso-anisohydric strategies, and rooting depths.

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