Influence Of Soil Potential On The Water Status, Photosynthesis And Growth Of Mandshuran Ash Seedings

Under different osmotic irrigation conditions ,the soil water potential was controlled within the range of 0~20Kpa(W1), -20~-40Kpa(W2), -40~-60Kpa(W3), -60~-80Kpa(W4) and -80~-160Kpa (W5). Ash (Fraxinus mandshurica) seedlings were planted on water-controlled soils, and the water ecology, photosynthesis and growth properties of seedlings were studied. It resulted as the following:Transpiration of seedlings decreased in the sequence of soil water potential ,of which max transpiration rate was 5~6 mmol/ m2.s (W1),and min transpiration rate was 1~2 mmol/m2.s (W3~W5).It indicated that drought stress inhibited transpiration significantly .The water suction rate of fine roots of W1 reached 2.67 mmol/ m2 in daily average and 4.44 mmol/ m2at midday,but it was only 1.35 mmol/ m2 in the case of W5 treatment .Soil water stress brought about declination in water saction rate of fine roots . Low soil water potential led to lower fluctuation levels of the leaf water potential.The leaf water potential of W1 treatment fluctuated in the range of -0.76~-1.46Mpa ,root-water potential fluctuated in the range of -0.08~-0.19Mpa ;while the leaf water potential of W5 treatment only ranged from -1.25~-1.94Mpa. Soil water stress significantly increased the water resistance of SPAC system of which soil-fine-root resistance increased more rapidly than the other two resistances.W3~W5 treatment declined more rapidly than W1 and W2,forming deep valley of photosynthesis at midday. From a comprehensive consideration of stomatal conductance (Gs), intercellular Co2 concentration (Ci),leaf temperature and leaf water potential ,the mechanism of photosynthetic restrain of W3~W5 treatments should be that of non-stomatal.In the soil water sequence of W1~W5, the leaf area of seedlings decreased at the ratio of 100: 65: 37:33:30,fine root area decreased at the ratio of 100:54:30:25:20,hight of new shoot decreased at the ratio of 100:70:52:45:44 ,diameter of new shoot decreased at the ratio of 100:88:68:64:57,whole -plant biomass decreased at the ratio of 100:71:43:38:35.The root /canopy ratio of seedlings were 1.38,1.37,1.17,1.18 and 1.04 from W1 to W5 treatment, thus ,soil water stress did not impeled the plant to distribute relatively more biomass to root system .From a comprehensive consideration of plant water status photosynthesis and seedling growth ,the appropriate soil water conditions should be in the range of 0~-40Kpa ,that's from water saturation to filed capacity.