Can differences in root responses to soil drying and compaction explain differences in performance of trees growing on landfill sites?

摘要

Two tropical woody species, Acacia confusa and Litsea glutinosa, were grown under controlled conditions in PVC pipes filled with John Innes No. 2 soil. To investigate root distribution, physiological characteristics and hydraulic conductivity, foursoil treatments were imposed: well-watered and noncompacted (control); well-watered and compacted; unwatered and noncompacted; and unwatered and compacted. In L. glutinosa, rooting depth and root elongation were severely restricted when soil bulk densityincreased from around 1.12 to 1.62 g cm-3, whereas soil compaction had little effect on these parameters in A. confusa. As soil drying progressed, root water potential and osmotic potential declined more slowly in L. glutinosa than in A. confusa. Both the soil drying and compaction treatments significantly stimulated the accumulation of root abscisic acid in both species. Soil drying damaged the root cell membrane of A. confusa, but had little influence on the root cell membrane of L. glutinosa. Soil drying had a greater effect on root hydraulic conductivity (Lp) in L. glutinosa than in A. confusa, whereas the effect of soil compaction on Lp was less in L. glutinosa than in A. confusa. Soil drying enhanced the effects of soil compaction on root Lp. Itwas concluded that soil drying and compaction have large species-specific effects on the distribution, growth and physiology of roots. The relationships of these root properties to the species' ability to tolerate unfavourable soil conditions were examined.