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Response patt was investigated for seedlings of Salixpsammophila, a dominant shrub in Maowusu sandland, to the simulated precipitation change by artificially controlling water supply at four levels. The growth characters, in term of plant height, stemdiameter, total branch number, total leaf number and area, total bifurcation ratio, total branch length and branch number, length, leaf number, leaf area of each branch order, and leaf, branch, root mass significantly increased when water supply increased. Thatwater supply had significant effect on biomass allocation showed different investment patt of biomass resource of the seedlings grwn different water supply treatments. Stomatal density of abaxial leaf surface decreased, and stomatal apparatus length and width of adaxial and abaxial leaf surface increased with the increase in water supply, while Stomatal density of adaxial leaf surface was not affected by water supply. Water supply obviously affected the dial changes of photosynthetic rate, and the photo synthetic rate of the seedlings showed strongly midday depression growing under the 157.5 mm water supply, but not growing under higher water supply. Additionally the Assimilation-light response curves and fluorescence efficiency more showed that water supply improve photosynthesis capacity. Finally, S.psammophila seedlings stood out by their slow growth and relatively high investments in root growth in order to reduce tissue losing rate and consumption of water resource for keeping water balance under water stress. The seedlings that grown under high water supply did by their fast growth and relatively high investments in branch and leaf growth in order to improve the power of capturing light energy for higher photosynthesis.