Belowground inter‐ramet water transport capacity in Populus euphratica, a Central Asian desert phreatophyte

Abstract

Populus euphratica Oliv. is a widespread phreatophytic tree species that forms riparian forests in (hyper-)arid regions of Central Asia. Its recruitment strongly relies on vegetative propagation from 'root suckers' that emerge from underground root spacers. The water transport through the spacers, although decisive for emerging ramets, has only rarely been quantified, but is crucial for the vegetative regeneration of the forests.• In root spacers with different diameters collected from a mature poplar forest in northwest China, we calculated the hydraulic conductivity (k c ) from anatomical investigations on the basis of a modified Hagen-Poiseuille equation and measured it (k m ) with a perfusion solution in the laboratory. The k m values were compared with the water use by young and mature P. euphratica trees determined in previous studies.• We obtained a significant correlation between k m and k c (which, however, was higher by at least one order of magnitude). Due to the extensive occurrence of tyloses, particularly in older conduits and thicker spacers, and because the conduit area did not increase with spacer diameter, neither k c nor k m increased with an increase in spacer diameter. The water supply through the spacers would be sufficient to meet the water demand even of mature trees.• Our results provide a mechanistic explanation for the observed occurrence of P. euphratica clones across large areas and, provided that they are also valid for stands with larger distances to the water table, for the sustained growth and vegetative reproduction of P. euphratica stands growing at larger distances from the groundwater.

Growth and water relations of riparian poplar forests under pressure in Central Asia's Tarim River Basin

“…The same conclusion can be drawn from precipitation data and calculations of evapotranspiration for P. euphratica forests along the Tarim River (Thevs, Peng, et al, 2015) and the Amu Darya in north‐eastern Turkmenistan (Thevs, Ovezmuradov, Zanjani, & Zerbe, 2015). Anatomical and flux investigations on horizontally running underground root sections (“root spacers”) of P. euphratica that connect ramets originated from vegetative recruitment with their “parent” plants have demonstrated that water supply through those spacers would be sufficient to meet the water demand even of large mature trees (Figure 2; Hoppe et al, 2020).…”

“…Daily water demand per tree in the month with the highest transpiration rates in Populus euphratica growing in riparian forest stands at different locations at the fringes of the Taklamakan Desert (circles, 22‐year‐old coppice stand at the southern fringe of the Taklamakan Desert; triangles, mature stand at the middle reaches; squares, mature stand at the lower reaches of the Tarim River) and calculated water supply through root spacers with different diameters (10.5–12.5 mm, white symbols; 14.5–16.8 mm, grey symbols; 16.9–21.8 mm, black symbols) on the basis of laboratory flux measurements (data from Hoppe, Zhang, & Thomas, 2020)…”