The effects of soil water availability on gas exchange characteristics and water consumption of
seedlings of Camellia oleifera were analyzed, including the influence of different soil moisture gradients
and weather conditions. Photosynthetic characteristics, water consumption and environmental factors
related to the growth of seedlings were measured in the field with a Li-6400 portable photosynthesis
system, an electronic balance and a Hobo Weather Station in Hunan Province of southern China. Four
soil water gradients were analyzed, i. e. W1 (soil moisture content was set at 95% - 100% of field
capacity (FC)), W2 (80% -85% of FC), W3 (65% -70% of FC) and W4 (45% -55% of FC);
for each of these four treatments, we measured the diurnal courses of stomatal conductance (Gs ), net
photosynthetic rate (Pn ), and transpiration (Tr ). Gs, Pn and Tr were graphed and showed unimodal
curves. Pn and Gs peaked in 10:00 to 12:00, and Tr and water consumption peaked in 12:00 to 14:00.
During the study period, Pn and Gs for each treatment were W2 W1 W3 W4. Under the W4
treatment, Pn, Gs, and water consumption reduced greatly, the peaks of above were lower than observed
in the other treatments with more soil moisture, and low soil moisture in W4 prevented the natural growth
of seedlings. Intrinsic water use efficiency decreased significantly during the W4 treatment. Our results
indicated that the W2 treatment was more suitable for seedling growth because seedling productivity was
greater under W2 than under W3 conditions. The maximum water consumption rate of seedling leaves was
153.7 g/(m2hour) and their average daily water consumption rate was 85.3 g/(m2hour) with adequate
water. Weather conditions and soil moisture had a combined effect on the water consumption of seedlings.
When soil moisture changed from high to low, water consumption of unit leaf area decreased unevenly,
and its diurnal course became flat, which may be a result of the reduction of soil water availability or
existence of a critical moisture point, which limits the seedling growth.