نوع مقاله : مقاله کامل علمی پژوهشی
نویسندگان
1 روستای کاسگرمحله_ دوراهی_ کوچه حاج حسین حامدیفر_پلاک9
2 دانشکده منابع طبیعی نور، دانشگاه تربیت مدرس
3 دانشکده منابع طبیعی، دانشگاه تربیت مدرس
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Background and objectives: Under natural conditions, plants frequently experience alternating cycles of drought stress and rewatering. Therefore, in addition to drought tolerance, their ability to recover physiological performance after stress relief is important. This study investigated the effects of different irrigation-withholding durations on the physiological responses of oriental arborvitae seedlings (Thuja orientalis L.) and evaluated their recovery capacity following rewatering.
Materials and methods: Sixty two-year-old oriental arborvitae seedlings were irrigated at field capacity for two weeks. Subsequently, the seedlings were subjected to four irrigation-withholding durations of 3, 6, 9, and 12 days in a completely randomized design with three replicates of five seedlings per treatment. The 3-day treatment was considered the baseline level. Net photosynthetic rate, stomatal conductance, transpiration rate, and intercellular CO₂ concentration were measured at the end of each irrigation-withholding period. Seedling survival, apparent carboxylation efficiency (An/Ci), and water-use efficiency were subsequently calculated. Thereafter, the drought-stressed seedlings were rewatered at field capacity for 12 days, and the same variables were measured again. After checking the assumptions of normality and homogeneity of variances, data were analyzed using one-way analysis of variance (ANOVA), Tukey’s HSD post hoc test, and paired-sample t-test.
Results: The results of the first experiment showed that the survival rate of Thuja orientalis seedlings was 100% after 3, 6, and 9 days of irrigation withholding. However, continued drought stress until day 12 significantly reduced seedling survival to 66.7% (P<0.01). All drought treatments caused significant reductions in net photosynthesis, stomatal conductance, transpiration, intercellular CO₂ concentration, and mesophyll conductance compared with the control treatment (P<0.01). In the second experiment, seedlings that had died during the drought-stress period did not recover after rewatering. Rewatering seedlings subjected to 6 days of irrigation withholding resulted in a significant recovery of net photosynthesis, stomatal conductance, transpiration, and intercellular CO₂ concentration to levels that were not significantly different from those of the control treatment. However, although these variables increased after rewatering in the 9- and 12-day treatments, their values remained significantly lower than those of the control treatment (P<0.05). Following rewatering, mesophyll conductance in the 6- and 9-day treatments did not differ significantly from that of the control treatment, whereas it remained significantly lower in the 12-day treatment (P<0.05). In contrast, water-use efficiency did not differ significantly among the drought-stress and rewatering treatments or between the drought and recovery stages (P>0.05).
Conclusion: The results of this study demonstrated that oriental arborvitae seedlings possess a satisfactory capacity for tolerance and recovery against drought stress induced by the cessation of irrigation for up to six days (a factor that may be linked to the high potassium levels in the potting soil); however, prolonged stress—extending to nine and twelve days—limits their physiological recovery capacity and survival. These findings can provide a sound scientific basis for irrigation management and the cultivation and maintenance of this species' seedlings in nurseries.
کلیدواژهها [English]
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