| It needs to improve methodology for afforestation in arid and saline areas in addition to screening salt- and drought-resistant plant material. In this research the intolerant tree species-P.popularis were chosen as an experiment material to investigate the different effects two kinds of hydrogel on drought and salt resistance. Polymers used are: Stocksorb 500 XL (granule type, crosslinked poly potassium-co-(acrylic resin polymer)-co-polyacrylamide hydrogel) that manufactured by Stockhausen GmbH Krefeld (Germany), and hydrogel-Luquasorb? series products,powder type, made from partially neutralised, lightly cross-linked poly(acrylic acid) by BASF company (Germany). The experimental results and the main conclusions are summarized:1. In gerneral, the two types of polymers enhanced the drought resistance of P.popularis, e.g. relative growth rates of height-RGRH was increased by 2.73-fold. Result is consistent to our further studies. Moreover, hydrogel amendment also increased the salt resistance of the P.popularis. The application of polymers decreased the intensity of salinity by diluting the salt ions in the soil solution, thus enhanced salt tolerance of this tree species.2. Water or salt stressed plants retained higher level of whole-plant water loss, indicating hydrogel amendment supplied water to plant roots. Whole-plant water loss was declined after 3 days of salt treatment, but hydrogel-treated plants exhibited deceased evaporation on day 9. Similarly, Whole-plant eveporation decreased after 6 days of drought treatment, but it occurred 9 day later in hydrogel-treated plants.3. Water and salt stress reduced the stomatal conductance (GS), leaf gas exchange and the maximum quantum yield of PS II (ΦPSII), however, hydrogel amendment decreased the drought- and NaCl-induced decline of these parameters. For Example, stomatal conductance rapidly decreased after the onset of salt stress, and reached the minimum, 80 mmol m-2 s-1 on day 30. In comparison, hydrogel-treated plants remaned GS at 90-100 mmol m-2 s-1. At the same time the ΦPSII of polymer-treated plants were 1.15 times higher than non–hydrogel-treated plants. Similarly, GS andΦPSII of polymer-treated plants were 1.71- and 1.14-fold higher than non–hydrogel-treated plants under water stress.4. The roots grewgrow through the granule polymers during the experimental period. The polymer retained large amount of water which could supply a lower salt condition for root growth, thus reducing the intensity of water shortage and salinity. Therefore, the concentration of toxic ions of Na+ and Cl- were greatly diluted. Moreover, and the hydrogels used in this study also are rich of K+, The polymer could supply this nutrient element for plant growth, which increased water and salt tolerance of P. popularis plants.5. Salt and drought stress weakened the defense system of plant, resulting in leaf damage. Hydrogel application reduced the drought- and salt-induced decline of ascorbic peroxidase (APX), and glutathione reductase (GR). As a result, stress-induced leaf damage was delayed by 51 days and biomass of polymer-treated plants was increased by 1.17-fold, as compared to stressed plants without hydrogel amendment.6. There were different effects of polymers on plant resistance although the two types of hydrogels enhanced salt and water tolerance of plants. The granule hydrogel absorbs less water then the powder one, but it supplied water more quickly. The powder hydrogel supplied less water per day, but it could prolong the supplying duration. As a result, the occurrence of drough-induced leaf damage in powder hydrogel-treated plants was 20 days later than the powder hydrogel-treated plants.
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