Environmental influences of salinity resistance in forest plants

油砂开采涉及对阿尔伯塔省东北部敏感的北方生态系统中的地貌进行彻底的移除和重建。由于土地干扰的严重性和油砂尾矿的性质，开采油砂后的土地复垦和植被重建工作具有挑战性。据预测，许多垦区的土壤将受到高pH值、有限的养分供应、低氧和盐分水平升高的影响。众所周知，北方植物对盐分很敏感；然而，在存在其他不利的土壤因素的情况下，它们如何对盐分做出反应尚不清楚，这些因素往往伴随着开垦地的盐分。这些信息对于确保油砂矿区成功恢复植被至关重要。同样重要的是了解有助于植物从盐胁迫中恢复的过程，并学习如何认识到超过这些关键阶段的严重伤害是不可逆转的，植物的生存受到威胁。在拟议的项目中，我们将研究根区pH、土壤氧气有效性和矿物质营养对重要油砂围垦树种的抗盐性和钠吸收的影响。我们还将研究从盐分暴露中恢复的过程，并确定组织钠浓度是否可以作为比土壤盐分水平更可靠的参数来监测和预测盐分对植被的影响。由于盐避免和盐封存是植物最有效的耐盐机制，增加钠吸收的预期后果包括显著增加死亡率和降低复垦植物的生长速度。已经有充分的文献证明，一旦地上部的钠水平达到一定的阈值水平，就会触发盐害。因此，如果发现组织钠水平升高与植物伤害和死亡相关，它们可以作为一种更有效的监测工具，用于缓解和管理受盐分影响的地点，而不是仅仅使用土壤盐分数据。由于植物对组织钠积累的反应可能会受到立地条件的影响，因此有必要研究土壤pH、低氧和矿物质营养等环境因素如何影响这种关系。本研究的主要目的是获得所需的基本知识，以便为成功地复垦受盐碱化影响的油砂区以及伴随着其他不利土壤因素的油砂区制订议定书。该项目产生的知识还将有助于提高对植物抵御这些有害土壤因素的过程的基本了解。我们将检验以下假设：1)钠组织水平与植物伤害和死亡相关；2)高和中性pH通过增加地上部的钠吸收来加剧盐分的影响，这种影响的大小因植物种类而异；3)升高的钙水平减少了植物对钠的吸收并由于对根水孔蛋白的稳定作用而缓解了盐的影响；4)矿质缺乏加剧了盐的影响；5)树木从盐分胁迫中恢复的有效长期机制包括液泡中的Na+固存和落叶树木的叶片脱落。6)低氧增加了根质外体中水分和离子的运输，导致地上部对Na+的吸收和积累，加速了盐害的发生。

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.