Partitioning of soil water among canopy trees during a soil desiccation period in a temperate mixed forest

[摘要] Complementary resource use is considered an important mechanism in the studyof biodiversity effects. Here we explore how species identity, speciesmixture and tree size influence the vertical partitioning of soil wateramong canopy trees during a soil desiccation period. In the Hainich Forest,Germany, the species Fagus sylvatica, Tilia sp. and Fraxinus excelsior were studied in single- and three-species mixedclusters, each consisting of three co-dominant trees situated within alarger mixed forest stand. Vertical soil water uptake depth was assessed byanalyzing the hydrogen stable isotope composition (deuterium, δD) ofwater from depth intervals throughout the soil profile and in tree xylemwater. For single species clusters, a mixing model suggested that Fagusdistinctively drew water from soil depths of 0.3–0.5 m, Tilia from 0.3–0.5 m and0.5–0.7 m and Fraxinus mainly used water from 0.5–0.7 m. In mixed clusters, theuptake patterns of Fagus and Tilia were similar to those of the single-speciesclusters (mainly uptake form 0.3–0.5 m), but Fraxinus showed a different uptakepattern. Fraxinus in mixture had a somewhat homogenously distributed uptake over thesoil depths 0.2–0.7 m. For single species clusters, there was no correlationbetween main soil water uptake depth and tree diameter, irrespective ofvariations in tree size. In contrast, for mixed clusters there was asignificant decrease in the main uptake depth with increasing tree size(P<0.001, R²_adj = 0.73), irrespective of species mix. Inconsequence, soil water partitioning was strongest where species were mixedand tree size varied. We further analyzed whether single and mixed-speciesclusters differed in the level of water uptake, e.g. due to complementarity,but our soil water budgeting did not indicate any such differences. Apossible explanation might be that the volume of water used is predominantlygoverned by properties at the stand level, such as aerodynamic roughness,rather than by processes acting at the meter scale between neighbouringtrees. With respect to application, we assume that the upcomingclose-to-nature forestry approach for the area, which fosters mixed standsof heterogonous diameters, may result in enhanced complementarity in soilwater uptake among canopy trees.

[学科分类] 地球化学与岩石