Study some of Garden Cress (Lepidium sativum L.) Physiological Traits at Levels of Irrigation and Ascorbic Acid

Drought seriously reduces the quality and quantity of agronomic and horticultural plants. In such condition, using factors to reduce these effects on plants is indispensible. To evaluate the effect of water stress and different levels of ascorbic acid on the leaf relative water content, pigments, canopy temprature and dry matter of cress (Lepidium sativum L.) a split plot experiment based on randomized complete block design with three replications at the Agricultural Research Station of Zahak was conducted in 2014 where three irrigation levels (at 100, 80 and 60 percent of field capacity) assigned to the main plots and three levels of ascorbic acid (0, 5 and 10 micromolar) to the sub-plots. The results showed that the effect of irrigation regimes, ascorbic acid and their interaction was significant on the traits under evaluation. Irrigation based on 60% of field capacity as compared with that of 100% F.C. reduced relative water content, chlorophyll a and b, carotenoids and dry matter weight by 20.89, 0.06, 0,034, 0.04 and 57.8 percent respectively and a 20% increase in canopy temperature, while applying of 10 micromolar ascorbic acid relative to control increased 12.22, 0.075, 0.15, 0.05 and 57.8 percent on traits mentioned above respectively and a 3% decrease in canopy temperature. Regression model revealed that application of ascorbic acid at irrigation in 100% field capacity was not effective on these traits, except on chlorophyll b and carotenoids contents, but in irrigation at 60 and 80% percent field capacities, increased amount of relative water content, chlorophyll a, chlorophyll b, carotenoids and dry matter. Although ascorbic acid could not reduce the negative impacts of 20% decrease in irrigation but application of 10 micromolar ascorbic acid in 60% and 80% irrigation at field capacities increased dry matter significantly, as compared to that of ascorbic acid under these conditions.