Hydraulic resistance partitioning between shoot and root system and plant water status of Haloxyolon ammodendron growing at sites of contrasting soil texture

Hydraulic resistance components and water relations were studied on Haloxyolon ammodendron,a small xeric tree,growing at sites significantly differed in soil texture.Soil water content,leaf water potential (ψ1),xylem water potential (ψx),root water potential (ψroot),leaf transpiration rate (TR) and stomatal conductance (gs) were measured at the two sites during the growing season of 2005 and 2006.Leaf specific hydraulic resistance (Rplant) during the whole growing season,hydraulic resistance of plants (Rp),shoots (Rshoot) and roots (Rroot) in the August of both years were calculated and expressed on leaf area basis.The results showed the proportion of the hydraulic resistance of the aerial part (Rshoot) to the Rp was the same to the proportion of the hydraulic resistance of the soil part (Rroot) to the Rp,indicating that both parts were equivalent important to plant water hydraulic system from soil to leaf.Positive significant correlations were found between Rp and Rroot,suggesting that root hydraulics resistance was a major determinant of plant hydraulic resistance (Rp) and transpiration rate.The integrated effect of stomatal control,hydraulic regulation and morphology adjustment enabled plants at heavy soil site surviving the extreme water deficit period.