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Human activities, such as tree cutting and land-use change, have significantly altered the forests of Iran's Zagros Mountains. In plantation projects within these forests, maintaining soil structure and fertility is necessary for sustainable forest management. Ideally, the soil quality of tree plantations should be as good as that of natural forests. In this study, we investigated the long-term impact of land-use change, i.e. conversion of natural oak forest to tree plantations or cultivated fields, on soil quality (i.e., physicochemical, biological and biochemical soil properties) in the forests of the Zagros Mountains. We found that the conversion of natural oak forest to tree plantations (in this case Cupressus arizonica, Cedrus libani, Elaeagnus angustifolia, Quercus brantii (persica), Robinia pseudoacacia and Fraxinus rotundifolia) and agriculture caused declines in soil organic carbon content, especially in the cultivated fields where it fell by around 60%. Overall, the lowest contents of soil nutrients, except Cu, were measured in agricultural soils. Interestingly, the plantation of a non-native tree (Cedrus libani) sequestrated more atmospheric carbon and nitrogen than native Persian oak forests. The impact on soil biological activity remains unclear: the conversion of natural forests into cultivated fields reduced soil biological activity, while conversion from forest to tree plantations had little influence. Finally, the conversion of natural forest to tree plantations had less impact on soil properties than conversion to cultivated fields. In conclusion, to maintain soil fertility, forest managers should avoid forest conversion to agriculture. Moreover, we do not recommend plantation of Cupressus arizonica in the Zagros region for the purpose of carbon and nitrogen sequestration and the increase of soil productivity.

Fil: Ashkavand, Peyman. Tarbiat Modares University. Faculty of Natural Resources and Marine Sciences, Department of Forestry. Iran. Fil: Zarafshar, Mehrdad. Fars Agricultural and Natural Resources Research and Education Center. Department of Natural Resources. Fars, Iran. Fil: Tabari, Masoud. Tarbiat Modares University, Faculty of Natural Resources and Marine Sciences, Department of Forestry. Iran. Fil: Mirzaie, Javad. University of Ilam. Faculty of Agriculture. Department of Forest Sciences. Iran. Fil: Nikpour, Amirreza. University of Agricultural Sciences and Natural Resources. Department of Forest Sciences. Gorgan, Iran. Fil: Bordbar, Seyed Kazem. Fars Agricultural and Natural Resources Research and Education Center. Department of Natural Resources. Fars, Iran. Fil: Struve, Daniel. The Ohio State University. Department of Horticulture and Crop Science. USA. Fil: Striker, Gustavo Gabriel. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura (IFEVA). Buenos Aires, Argentina. We studied the physiological responses of Prunus mahaleb (Mahaleb) seedlings to drought stress when previously irrigated (or not) with different concentrations of SiO2 nanoparticles (SNPs). SNPs were applied at four concentrations (0, 10, 50 and 100 mg L-1) for 45 days, and then seedlings were subjected to three watering treatments including low (300 mL water every 3 d), moderate (150 mL water every 3 d) and severe drought stress (no irrigation) for 19 days. Results showed that gas exchange – photosynthesis, stomatal conductance, and transpiration rate – were significantly less impacted by severe drought stress when seedlings were pretreated with SNPs at high concentrations. Beneficial effects of SNPs pretreatment were evident in the nutritional status of the plants as the concentration of N, P and K, were maintained at similar levels than in well-watered seedlings. Pretreated seedlings were able to maintain the root length and to reduce the impact of severe drought on root dry mass accumulation. Therefore, application of SNPs as pretreatment should be considered as a promising agronomic practice in sites prone to suffer from water deficit. grafs., tbls.