The Effect of Drought Stress on Root and Shoot Growth of Kochia (Kochia scoparia L.) under Greenhouse Conditions

Drought is undoubtedly one of the most important environmental stresses limiting the productivity of crop plants around the world. An optimal partitioning of dry matter between root and shoot, therefore is of crucial importance for crop yield under drought stress. Deficit irrigation strategy and planting crops with low water requirements and low expectations, for example, Kochia is very important under drought stress. Kochia is a salt- and drought-tolerant species that can be grown on drought soils, yielding fodder in quantities approaching that produced by alfalfa. The aim of this greenhouse study was investigating root and shoot growth of Kochia under drought stress conditions.

To study the effects of drought stress on root and shoot growth of kochia, a pot experiment was carried out as completely randomized design with three replications in University of Ferdowsi in 2013. There were 9 treatments included control (no stress) (NS-NS=100% field capacity (FC)), moderate drought stress (70% FC) during the vegetative phase (MS-NS), severe drought stress (30% FC) during the vegetative phase (SS-NS), moderate drought stress during the reproductive phase (NS-MS), severe drought stress during the reproductive phase (NS-SS), moderate drought stress during the vegetative phase and severe drought stress during the reproductive phase (MS-SS), severe drought stress during the vegetative phase and moderate drought stress during the reproductive phase (SS-MS), moderate drought stress during total growth period (MS-MS) and severe drought stress during total growth period (SS-SS). At the beginning of anthesis, plant height and branch number were recorded. Then plants were harvested and leaves, stems, and roots were separated. The fresh weight of the organs was recorded. Root volume was measured. Leaf area measured using a leaf area meter (LI-COR model) and root area was measured by Atkinson method. Then, leaves, stems, and roots dried in an oven at 75°C for 48 hours until mass reached and dry weight was recorded. For statistical analysis, analysis of variance (ANOVA) and LSD test were performed using SAS ver. 9.1 software.

Results showed that the highest and lowest plant height, leaf area, leaf, stem and total fresh and dry weight observed in control and severe drought stress during growth period, respectively. Significance of traits related to plant aerial parts due to morphological changes of root plants, which is actually a plant response to drought stress. Also, effect of drought stress was significant on root length, area and volume, fresh and dry weight, root length ratio to plant height. The highest and lowest of these traits were observed in control and severe drought stress during growth period, respectively. Drought stress thereby mostly reduced plant height and increased at least root length, leading to higher root/shoot ratio. Most importantly, the length of root was greater in the moderate drought-treated plants than the control plants at the end of the drought and recovery periods. Number of lateral branches and root dry weight/shoot dry weight ratio did not differ significantly with control. Generally, root and shoot growth under drought stress conditions is reduced that the amount of reduction depends on the growth stage of the plant, intensity and duration of the stress.

Finally, this study showed that the maximum amount of Kochia forage was obtained when the water is 100% FC to increase the number and size of the cells and, consequently, increase the yield. However, Kochia forage decreased 19% by decreasing 30% of irrigation water in treatments of moderate stress during total growth period in compared to the control plants. In addition to saving water, more land can be cultivated.