Root identification, dynamics and plasticity of boreal species on reclaimed saline-sodic overburdens and naturally saline sites

在油砂区有大约6500公顷的填海土地，其中大部分由覆盖层中的高盐物质组成，覆盖层上覆盖着厚达1.5米的泥炭/矿物土壤。这些覆盖层的厚度具有生态学意义，因为较厚的覆盖层将最大限度地减少盐从覆盖层向覆盖层迁移对根系的负面影响，但也会减少下游湿地的产水量。此外，更厚的保护套设计成本更高，因此会对公司产生经济影响。这些盖子到底应该有多厚？为了回答这个问题，我们需要知道像白杨和云杉这样的北方树种的根系是如何受到覆盖厚度的影响的——这些种植树木的根系实际上占据了整个土壤剖面，还是由于向上迁移的盐剖面，它们仅仅局限于土壤表面？北方物种的根是否表现出足够的可塑性，在这些盐度条件下发育，以支持健康的森林？这些再生覆盖物上的根分布如何模拟天然盐碱地或非盐碱地上的根分布？最近的研究表明，从这些开垦景观中收集的根系样本发现于高盐覆盖层中。然而，由于形态学根系识别技术的不足，我们不知道这些根是否属于种植在那里的所需北方树种，还是来自林下植被或杂草。因此，本研究的目标是：1)利用DNA测序技术确定不同树种（白杨、云杉、特定林下植物）在自然林分、自然盐碱地和不同厚度盐碱地景观中的生根分布及其形态特征；2)利用minirhizotron（地下的透明管，利用相机捕捉根系图像）和示踪技术，结合DNA测序，量化复垦景观中与自然林分相比的根系动态和活动；3)利用三维根系结构模型确定杨树和云杉根系对盐碱化条件的可塑性。对于Obj. 1，将从不同厚度的天然林分、天然盐碱地和再生盐碱地中收集根系，并使用DNA测序技术进行鉴定，以确定根系在土壤剖面中的分布位置。还将测量根系特征，以确定与天然和天然盐碱地相比，覆盖层和覆盖层之间根系的可塑性。项目2中的根系动态将在填海和自然场地使用微型电子管进行测量，其中将透明塑料管插入地面，并用微型摄像机每月收集一次根系图像。根的活性将使用放置在不同深度的稳定示踪剂进行测量，并在植被的地上部分进行测量。为了研究这些根系的根系可塑性，本研究将使用三维根系构型模型，输入挖掘根系的参数，模拟不同覆盖厚度和迁移盐剖面对根系可塑性和根系发育的影响。这个项目的新颖之处在于，它使用DNA测序技术来实际识别单个根系，以了解覆盖厚度如何影响根系发育和树木生长，并为预测盐和覆盖厚度对根系发育的影响提供了一个工具。该项目将为油砂公司和监管机构提供重要的结果，以证明填海景观，并通过确保根系与天然林相比发育良好，最大限度地减少覆盖失败的风险。

There are about 6500 ha of reclaimed landscapes in the oil sands region, the majority of which consists of materials with high levels of salts in the overburden that is capped on top with a peat/mineral soil cover up to 1.5 m thick. The thickness of these covers has ecological implications in that thicker covers will minimize negative effects of salt migration from the overburden into the cover on root systems but also reduce water yield for downstream wetlands. In addition, thicker covers are more expensive to design and thus have economic ramifications for companies. How thick should these covers actually be? To answer that we need to know how root systems for boreal species such as aspen and spruce are impacted by cover thickness - do roots of these planted trees actually occupy the entire soil profile, or are they restricted to just the soil surface due to the upward migrating salt profiles? Do roots of boreal species demonstrate enough plasticity to develop under these salinity conditions in order to support a healthy forest and how do root distributions on these reclaimed covers mimic root distributions found on naturally saline or non-saline sites? Recent research has shown that root samples collected from these reclaimed landscapes are found in the high salt overburdens. However, we do not know if these roots belong to the desired boreal tree species planted there or from understory vegetation or weeds because of inadequacies of morphological root identification techniques. Therefore the objectives of this proposal are to 1) determine the rooting distribution by species (aspen, spruce, selected understory) using DNA sequencing techniques and their morphological traits in natural stands, naturally saline sites, and reclaimed saline-sodic landscapes of varying thickness; 2) quantify root dynamics and activity in reclaimed landscapes compared to natural stands using minirhizotron (clear tubes in the ground that use cameras to capture root images) and tracer techniques coupled with DNA sequencing; and 3) determine the plasticity of aspen and spruce roots to saline-sodic conditions using 3D root architecture models. For Obj. 1 roots will be collected from natural stands, naturally saline sites, and reclaimed saline-sodic landscapes of varying thickness and identified with DNA sequencing techniques to conclusively know where in the soil profiles the root systems are distributed. Root characteristics will also be measured to determine the plasticity of the roots between the overburden and cover layers compared with natural and naturally saline sites. Root dynamics in Obj. 2 will be measured in reclaimed and natural sites using minirhizotrons where clear plastic tubes are inserted into the ground and root images collected on a monthly basis with a miniature video camera. The activity of the roots will be measured using stable tracers placed at various depths and measured in the aboveground portion of the vegetation. To investigate root plasticity of these root systems in Obj. 3 a 3D root architecture model will be used with input parameters obtained from excavated root systems to model the effect of varying cover thicknesses and migrating salt profiles on root plasticity and root development. This project is novel in that it uses DNA sequencing techniques to actually identify individual roots to understand how cover thickness is affecting root development and thus tree growth as well as providing a tool for predicting the effects of salts and cover thickness on root development. This program will provide results that are significant to oil sand companies and regulators in certifying reclaimed landscapes and minimize risks of cover failure by ensuring that root systems are developing properly compared to natural forests.