Abstract: Water stress is one of the most important abiotic stresses. A field experiment was conducted to evaluate the growth and physiological response of cotton plants to soil moisture stress under mulch drip irrigation. The total irrigation volumes of 5 400, 4 950, 4 500, 3 750, 2 850 and 2 550 m³/hm² were designed for each treatment according to the upper irrigation limits of 105%, 100%, 95%, 90%, 85% and 80% of field capacity, respectively. Differences in root vigor, chlorophyll, proline and malondialdehyde (MDA) contents were tested at cotton florescence and boll stage so as to reveal the physiological response of cotton plants to soil moisture stress. The relationships between soil moisture content and the praline and MDA contents as well as root vigor were analyzed. The results showed that the biomasses of dry shoots and leaves, leaf area, plant height, chlorophyll content and root vigor were significantly decreased due to water deficiency, while the rootshoot ratio, proline and MDA contents were sharply increased. The results also revealed that there was a negative correlation between soil moisture content and the proline and MDA contents, their correlation coefficients were -0.704 and -0.667 respectively, but the root vigor was decreased with the decrease of irrigation volume, their correlation was positive, and their correlation coefficient was 0.67. Moreover, this study revealed that the threshold level for water supply was 4 500 m³/hm² to keep crop away from water stress. These results also revealed that the proline content, root vigor and MDA content were sensitive to soil moisture content.

Key words: cotton, root vigor, drip irrigation, soil moisture stress, chlorophyll, proline, malondialdehyde