以黄土丘陵区常见灌木杠柳(Periploca sepium Bunge.)的两年生苗木为试验材料,模拟不同程度的土壤干旱环境,研究了土壤干旱对杠柳生长和生理生化特性的影响。结果表明,在3种土壤水分条件下杠柳的耗水和快速生长期均集中在6-8月,与黄土丘陵区雨热期重叠。在干旱胁迫下杠柳生长减慢,生物量累积减小,生物量优先向根系分配,根冠比显著增大。与适宜水分下相比,干旱胁迫下杠柳的水分利用效率随生物量与耗水量减小而显著升高,表明杠柳具有节约型水分利用对策。杠柳在干旱前期和中期丙二醛(MDA)含量下降、膜透性略有增加,干旱末期MDA含量和细胞膜透性与适宜水分相比显著升高。在中度干旱与严重干旱下,杠柳的超氧化物歧化酶与过氧化物保护酶活性持续上升直到试验末期才稍有下降。干旱胁迫对杠柳叶片渗透调节物质含量的影响显著,脯氨酸、可溶性糖和可溶性蛋白含量均随着干旱胁迫程度的加大而显著升高,且随着胁迫时间的延长,脯氨酸和可溶性糖含量一直保持上升趋势;可溶性蛋白含量在前期急剧上升,中、后期下降,但含量一直高于适宜水分处理。本研究表明,杠柳能够充分利用黄土丘陵区局部雨热资源优势、具备减少地上蒸发面积、增加地下生长、吸收深层土壤水源等御旱策略以及保持较高的抗氧化酶活性和渗透调节能力等生理学耐旱机制,本研究从生长、生理特征上揭示了杠柳在黄土高原植被自然恢复中普遍存在的原因。
Drought is a major limitation for plant growth, development and production worldwide. It becomes an increasingly serious problem due to global climate changes. Water deficit affects virtually every aspect of plant metabolisms. Periploca sepium Bunge (P. sepium) is a native and widespread shrub on the Loess Plateau, a typical drought-prone region in China. An experiment was conducted to investigate the effect of drought stress on growth, water relations, biomass partitioning, osmotic adjustment, lipid peroxidation, and oxidative enzyme activities of 2-year-old potted P. sepium plants. The plants grown under well-watered and water stressed conditions which were imposed by controlling the water supply. Results showed that the peak water consumption and fast-growing period of P. sepium plants under three different water treatments appeared the rainfall season (June to August) of the Loess hilly regions. P. sepium plants grown under the water deficit condition had much less growth rate and biomass accumulation than the plants grown under the well-watered condition. In contrast, P. sepium plants under drought condition had significantly greater root to shoot ratio and water use efficiency (WUE) than the well-watered plants. The increase in WUE with the decreases in biomass and water consumption under water stress condition seemed to be the water-saving strategy of P. sepium. The malondialdehyde (MDA) content and the membrane permeability are often used to estimate the degree of lipid peroxidation. The MDA content and the membrane permeability in leaves of P. sepium plants did not differ between the drought stress and well-watered treatments until the end of the experiment. The SOD and POD activities in the leaves increased throughout the experiment for both the well-watered and water stressed plants. Osmotic adjustment has long been proposed as an effective drought resistance mechanism of higher plants, which can help plants maintain turgor and turgor-dependent processes. Water deficit stimulated the accumulation of proline, soluble sugar and soluble proteins in P. sepium leaves under the moderate and severe drought stress conditions. The contents of these three solutes were highest under severe water stress condition and followed by those under moderate drought stress conditions. The proline and soluble sugar contents increased during the experiment, while the soluble proteins content showed an initial increase and then subsequent decrease. Our results indicate that some key physiological processes may facilitate P. sepium establishment and growth in the semi-arid and arid Loess hilly region, which include not only drought avoidant but also drought tolerant strategies. These strategies find expression in the abilities of taking the full advantage for the limit water resource, reducing transpiration, enlarging the roots for deeper soil moisture, keeping high activities of protective enzymes, and accumulating more organic solutes. As a native shrub on the Loess Plateau, therefore, P. sepium has been evolved many adaptations to counteract water deficit stress as a result of the long-term natural selection and co-evolution. This study provides useful information for vegetation restoration with P. sepium in the Loess plateau.