Root system hydraulic conductivity in species with contrasting root anatomy

Abstract

Previous research suggested that the hydraulic properties of rootsystems of intact plants could be described by two parameters: thehydraulic conductivity (Lp(r)) or the slope of the flow-density/waterpotential gradient relationship, and the offset or minimum waterpotential gradient required to induce flow. In this study, Lp(r) andoffset were correlated with anatomical features of the root radial pathin plants with contrasting root anatomy. Two woody and three herbaceousspecies were examined which exhibit a range of root anatomical features:Asparagus densiflorus (Kunth) Jessop (asparagus), Dendrobium superbumRchb. f. (dendrobium), Glycine max (L.) Merr. (soybean), Prunus persica(L.) Batsch. (peach), Citrus aurantium L. (sour orange). Lp(r) variedabout 8-fold, and the offset varied about 6-fold among the five species.Lp(r) was inversely related to root diameter (r(2) = 0.39) and cortexwidth (r(2) = 0.55), suggesting that species with thinner roots or rootswith a thin cortex had the highest Lp(r). Further observations suggestedthat the cortex width was a stronger determinant of Lp(r) than rootdiameter. However, the offset was not correlated with root diameter,stele diameter or cortex width, but was >2-fold higher in species havingan exodermis in the root radial path (sour orange, asparagus, anddendrobium) compared to those lacking an exodermis (peach and soybean).The data of root Lp(r) obtained were similar to those given in theliterature for both intact plants and excised roots which have beenmeasured with different techniques. It is concluded that Lp(r) andoffset, which describe the flow-water potential relationship for intactroot systems, are related to differences in the root cortex;specifically, its thickness and the presence/absence of a suberizedexodermis. Hence, these anatomical differences may, in part, cause thevariability in root hydraulic properties that exists among plantspecies.