Vessel features of three Caragana species in their natural habitats in the inner Mongolia Plateau of China

Abstract

We studied the vessel features of ten populations of three Caragana species (C. microphylla Lam, C. davazamcii Sancz, C. korshinskii Kom.), which form a geographical cline in the inner Mongolia Plateau of China. All sampled shrubs had common vessel features of xeric plants, such as coexistence of wide and narrow vessels in one xylem, high vessel density, short element length, distinct helical thickenings, which were all associated with strong drought resistance. The quantitative vessel features changed gradually along the geographical gradient of the three Caragana species. Mean vessel diameter, D100, generally decreased from the east to the west. However, D95 (the mean diameter of vessels responsible for 95% of the total stem conductance) changed in an opposite direction to D100, which might be attributed to different proportions of wide and narrow vessels of the ten populations. The more xeric the habitat was, the smaller the proportion of wide vessels (which contributed mainly to water conductance). There was also a tradeoff between efficiency and safety in water transport. The intervessel pit size, density of vessel elements, intervessel pits and helical thickenings increased from the east to the west with the increase of environmental aridity. The trend of vessel element length and wall thickness was similar to that of D100, i.e. they decreased from the east to the west. All these gradually changing features confirmed the geographical transition among the three Caragana species, and indicated an order of drought resistance as C. korshinskii>C. davazamcii>C. microphylla. © 2007 The Authors.