Environmental influences of salinity resistance in forest plants

油砂开采涉及到阿尔伯塔东北部敏感的北方生态系统的地貌的完全移除和重建。由于土地扰动的严重性和油砂尾矿的特性，油砂开采后的土地复垦和植被重建工作具有挑战性。据预测，在许多开垦区的土壤将受到高pH值，有限的养分供应，缺氧，和盐水平升高。北方植物是已知的盐敏感，但是，目前还不清楚他们如何应对盐度在其他不利的土壤因素，往往伴随着盐碱地开垦地的存在。这一信息对于确保油砂矿区的成功重新植被至关重要。同样重要的是，要了解有助于植物从盐胁迫中恢复的过程，并学会如何认识到严重伤害不可逆转和植被生存受到威胁的关键阶段。在拟议的项目中，我们将研究根区pH值，土壤氧的有效性和矿物质营养对重要的油砂复垦树种的耐盐性和钠吸收的影响。我们还将研究从盐暴露中恢复的过程，并确定组织钠浓度是否可以用作比土壤盐度更可靠的参数，用于监测和预测盐度对植被的影响。由于避盐和盐螯合是植物中最有效的耐盐机制，增加钠吸收的预期后果包括死亡率显着增加和再生植物生长速度下降。已经有充分的文献证明，一旦芽中的钠水平达到一定的阈值水平，就会引发盐伤害。因此，如果发现组织钠水平升高与植物损伤和死亡率相关，则它们可以用作比单独的土壤盐分数据更有效的监测工具，用于缓解和管理受盐分影响的地点。由于植物对组织钠积累的反应可能受立地条件的影响，因此有必要研究环境因素如土壤pH值、缺氧和矿物质营养如何影响这种关系。本研究的主要目的是产生所需的基础知识，以制定协议，成功开垦油砂地区的盐度，伴随着其他不利的土壤因素。该项目产生的知识也将有助于提高对植物抵抗这些有害土壤因素的过程的基本理解。我们将检验以下假设：1）钠组织水平与植物损伤和死亡率相关，2）高和中性pH通过增加芽钠吸收来加剧盐的影响，并且这种影响的程度在植物物种之间变化，3）由于对根水通道蛋白的稳定作用，升高的钙水平减少钠吸收并减轻植物中的盐效应，4）矿物质缺乏加剧了盐的影响，5）树木从盐胁迫中有效的长期恢复机制包括液泡中的Na+封存和落叶树的叶子脱落，6）低氧促进了根中水分和离子的质外体运输，导致Na+的吸收和积累在芽和盐伤害的加速。

Oil sands mining involves a complete removal and reconstruction of landforms in sensitive boreal ecosystems in northeastern Alberta. Land reclamation and revegetation efforts following oil sands mining are challenging due to the severity of land disturbance and the properties of oil sands tailings. It is predicted that soils in many reclamation areas will be affected by high pH, limited nutrient supply, hypoxia, and elevated salt levels. Boreal plants are known to be sensitive to salt; however, it is unclear how they respond to salinity in the presence of other unfavorable soil factors which often accompany salinity in reclamation sites. This information is essential to ensure successful revegetation of oil sands mining areas. It is also important to develop understanding of the processes contributing to plant recovery from salt stress and learn how to recognize the critical stages beyond which severe injury is irreversible and vegetation survival is threatened. In the proposed project, we will examine the effects of root zone pH, soil oxygen availability and mineral nutrition on salt resistance and sodium uptake in important oil sands reclamation tree species. We will also study the processes of recovery from salt exposure and determine whether tissue sodium concentration could be used as a more reliable parameter than soil salinity level for monitoring and predicting salinity effects on vegetation. Since salt avoidance and salt sequestration are the most effective salt tolerance mechanisms in plants, the expected consequences of increased sodium uptake include significant increases in mortality and decreases in growth rates of reclamation plants. It has been well documented that salt injury is triggered once sodium levels in shoots reach a certain threshold level. Therefore, if elevated tissue sodium levels are found to correlate with plant injury and mortality, they could be used as a more effective monitoring tool for mitigation and management of salinity-affected sites than the soil salinity data alone. Since plant responses to tissue sodium accumulation may be influenced by site conditions, it will be necessary to examine how environmental factors such as soil pH, hypoxia, and mineral nutrition affect this relationship. The principal objective of the present study is to generate fundamental knowledge which is required to develop protocols for successful reclamation of oil sand areas affected by salinity that is accompanied by other unfavorable soil factors. The knowledge generated by this project will also help improve basic understanding of the processes which plants use to resist these detrimental soil factors. We will examine the following hypotheses: 1) Sodium tissue levels correlate with plant injury and mortality, 2) High and neutral pH aggravate the effects of salinity by increasing shoot sodium uptake and the magnitude of this effect varies between plant species, 3) Elevated calcium levels reduce sodium uptake and alleviate salt effects in plants due to the stabilizing effect on root aquaporins, 4) Mineral deficiencies aggravate the effects of salt, 5) Effective long-term recovery mechanisms in trees from salt stress include both Na+ sequestration in vacuoles and leaf abscission by deciduous trees, 6) Hypoxia increases the apoplastic transport of water and ions in roots resulting in a greater uptake and accumulation of Na+ in shoots and acceleration of salt injury.