Environmental influences of salinity resistance in forest plants

在艾伯塔省东北部，油砂开采涉及到对敏感的北方生态系统地貌的彻底清除和重建。由于油砂开采后土地扰动的严重程度和油砂尾矿的特性，油砂开采后的土地复垦和植被恢复具有挑战性。预计许多垦区的土壤将受到高pH值、养分供应有限、缺氧和高盐水平的影响。众所周知，北方植物对盐很敏感；然而，目前尚不清楚，在其他不利的土壤因素存在的情况下，它们是如何对盐度作出反应的，这些因素通常伴随着填海地点的盐度。这些信息对于确保油砂矿区成功的植被恢复至关重要。了解植物从盐胁迫中恢复的过程，并学习如何识别严重伤害不可逆转和植被生存受到威胁的关键阶段也很重要。在拟建项目中，我们将研究根区pH值、土壤氧有效性和矿质营养对重要油砂复垦树种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作为比土壤盐度水平更可靠的参数来监测和预测盐度对植被的影响。由于避盐和固盐是植物最有效的耐盐机制，钠吸收增加的预期后果包括复垦植物死亡率的显著增加和生长率的降低。有充分的证据表明，一旦枝条中的钠含量达到一定的阈值，就会引发盐伤。因此，如果发现组织钠水平升高与植物伤害和死亡有关，它们可以作为一种比单独的土壤盐度数据更有效的监测工具，用于减轻和管理受盐碱度影响的地点。由于植物对组织钠积累的反应可能受到场地条件的影响，因此有必要研究土壤pH、缺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产生基本的知识，以便制订方案，成功地复垦受盐和其他不利土壤因素影响的油砂地区。该项目产生的知识也将有助于提高对植物用来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：2)高pH和中性pH通过增加茎部钠吸收而加剧了盐的影响，且这种影响的程度因植物种类而异；3)钙水平升高通过对根部水通道蛋白的稳定作用减少了植物的钠吸收，减轻了盐的影响；5)树木从盐胁迫中有效的长期恢复机制包括液泡中Na+的吸收和落叶树木的叶片脱落；6)缺氧增加了根系中水分和离子的胞外运输，导致枝条中Na+的吸收和积累增加，加速了盐的伤害。

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.