The response of mulberry trees after seedling hardening to summer drought in the hydro-fluctuation belt of Three Gorges Reservoir Areas

Abstract

Interest has developed in the potential of mulberry (Morus alba), a woody perennial, for revegetating the hydro-fluctuation belt of the Three Gorges Reservoir due to its resistance to water-logging stress. To be useful, the trees must also be able to withstand dry conditions in summer when temperatures can be very high and droughts become severe quickly. Here, we report a study in which mulberry seedlings were grown in a greenhouse under a variety of simulated soil water conditions reflecting potential summer scenarios in the hydro-fluctuation belt of the Three Gorges Reservoir Area. We compared the responses of two pretreatment groups of mulberry seedlings to different levels of drought stress. The pretreatment groups differed with respect to drought hardening: the daily-managed (DM) group had relative soil moisture held constant in the range 70-80 %, while the drought-hardened (DH) group had relative soil moisture held constant at 40-50 %. Following the month-long pretreatment of seedlings, the two groups of young trees (DM and DH) were then respectively subjected to three levels of drought stress for a month: normal watering, moderate drought stress, and severe drought stress. A series of measurements comparing the physiological status of the plants in the two groups were then made, and the following results were obtained: (1) As drought stress increased, the heights, base diameters, root surface areas, photosynthetic rates (Pn), stomatal conductances (Gs), and transpiration rates (Tr) of the mulberry trees in both groups (DM and DH) decreased significantly, while the specific root area and abscisic acid (ABA) contents had increasing trends. Root activity and instantaneous water use efficiency of mulberry trees in both groups (DM and DH) were all raised under drought stress conditions than under normal watering, but the root/shoot ratio and leaf water potential were lowered. (2) At the same level of soil water content, the heights, base diameters, root/shoot ratios, root surface areas, specific root areas, photosynthetic rates (Pn), stomatal conductances (Gs), and transpiration rates (Tr) of the young mulberry trees in the DH were all significantly higher than those of the control group (DM). Leaf water potential, instantaneous water use efficiency, and abscisic acid content of DH were all significantly lower than DM. Under different degrees of drought stress, the growth of mulberry trees will be inhibited, but the trees can respond to the stress by increasing the root absorptive area and enhancing capacity for water retention. Mulberry trees demonstrate strong resistance to drought stress, and furthermore drought resistance can be improved by drought hardening during the seedling stage.

Influence of drought hardening on the resistance physiology of potato seedlings under drought stress

“…In order to reduce the adverse impact of drought stress on crop production, several methods and technologies have been put to use to enhance the drought resistance of crops. Drought hardening is a convenient and feasible method and involves exposing plants to arid conditions such as reduced irrigation or partial drought during the seedling stage so as to improve the ability to adapt to subsequent serious drought (Thomas 2009;Huang et al 2013). The effectiveness of drought hardening lies in the fact that young plants are malleable and are usually more able to survive under arid conditions if they have undergone a previous period of low moisture stress.…”

“…It has been found that drought hardening applied in the nursery before planting improved the seedling survival rate under extreme xeric conditions (Driessche 1991). In addition, seedling hardening can improve the growth adaptability and drought resistance of mulberry (Huang et al 2013). This strategy has been widely adopted in wheat, rice and other plants.…”

Titanium Dioxide Nanoparticles and Sodium Nitroprusside Alleviate the Adverse Effects of Cadmium Stress on Germination and Seedling Growth of Wheat (Triticum aestivum L.)

“…The root length reduction may be attributed to lower cellular division and elongation during germination [47]. The root/shoot ratio is an important index for measuring the development of seedling roots, and plants with higher root/shoot ratios are more capable of absorbing water and minerals [48].…”

Cropping Mulberry (Morus alba) in the Drawdown Zone of the Three Gorges Reservoir

“…The ranges of tolerance related to these variables are not yet known. M. alba is a riparian species that is known to tolerate physiological stresses such as freezing, drought and water-logging [15], [19], [20], but it was not expected to survive the severe stress of long-term winter flooding to depths that cover the crown of the tree. Following observation of mulberry survival, new experimental plantations have been established recently in the TGR drawdown zone in Yunyang and Wanzhou (regions of Chongqing) and some young transplanted trees have survived for up to four annual cycles at submersion depths up to 7m (authors' personal observations of unreported experiments).…”