The role of silicon in temperate and boreal forest ecosystems in a changing environment

气候变化及其预计的更高的干旱发生率和更长的生长季节可能会改变森林的养分供应和需求。硅是土壤中含量最丰富的元素之一，现在被认为是某些物种的营养物质。它最近因其在缓解二氧化碳浓度上升的影响方面的作用而引起了人们的极大兴趣。我最近的研究表明，糖枫和山毛榉这两种美国东北部的主要硬木可能是硅的活跃累积者。如果得到证实，这将表明它需要在最佳水平下生长，而且研究人员一直低估了它在这些物种中的作用。*因此，我的研究将集中在硅在糖枫和山毛榉的生理/营养中的作用，主要目的是更全面地了解它们的营养和生理，以及它们驱动森林土壤肥力的方式。第一步将是修改这两个物种的营养标准。为了全面衡量营养平衡，我们将把硅包括在营养指数/比率中。将对生长在不同土壤条件下的每个物种至少200棵树进行抽样。将根据边界线回归确定最佳的营养浓度和比例。第二步是评估硅的生理作用。我假设，生产一种“廉价的”硅酸盐结构所节省的能源将增加防御性化学物质的生产，例如酚类、单宁。在这项研究中，苗木将在加硅和不加硅的水培中生长。将监测和比较根和茎/叶的一系列形态变量和叶的化学成分。*作为活跃的硅积累者，人们预计糖枫和山毛榉已经开发出专门的机制来从矿物/岩石中获取硅和相关的养分。因此，我建议测试它们从三种用于生态农业的岩石中提取养分的能力：硅灰石(Ca)、磷灰石(P)和绿砂(K)。测试将在受控条件下(水培)和田间进行。有了更大的吸收土壤硅的能力，我也期待着更快的循环，以及在糖枫和山毛榉下植物来源的硅酸盐和硅酸盐闭塞C的更大积累。为了测试这些影响，我们将使用一个旨在最大化物种互动的种植园。有19种树生长在纯和混合的地块中，我们将能够测试加拿大东部常见树种的全光谱硅吸收潜力。*这些研究将为糖枫和山毛榉如何在加拿大东部的老森林中占据主导地位提供一些新的见解，同时可能在缓解大气二氧化碳增加的负面影响方面发挥重要作用。还将开发两种新的和简单的方法来评估土壤铝毒性和估计树木的蒸腾速率。

Climate change with its predicted higher incidence of droughts and longer growing seasons is likely to change the nutrient supply and requirements of forests. Silicon (Si), one of the most abundant element in soils, is now considered a nutrient for some species. It has attracted lots of interests lately for its role in mitigating the effects of increasing CO2 concentrations. My recent research indicates that sugar maple and beech, two dominant hardwoods in northeastern America, may be active accumulators of Si. If confirmed, this would suggest that it is required to grow at optimum levels and that researchers have been underestimating its role in these species.*** My research will therefore focus on the role of Si in the physiology/nutrition of sugar maple and beech with the primary objective of getting a more comprehensive understanding of their nutrition and physiology, and of the way they drive soil fertility in forests. The first step will consist in revising the nutritional norms for both species. To get a complete measure of the nutritional balance, we will include Si in the nutrient indices/ratios. A set of at least 200 trees per species growing on contrasting soil conditions will be sampled. Optimal nutrient concentrations and ratios will be determined based on boundary-line regressions. The second step will consist in assessing the physiological role of Si. I hypothesize that the energy saved by producing a "cheap" silicate structure will increase the production of defensive chemicals e.g. phenolics, tannins. For this study, seedlings will be grown in hydroponics with and without Si. A series of morphological variables of the roots and stems/leaves, and leaf chemistry will be monitored and compared.*** As active Si accumulators, one would expect sugar maple and beech to have developed specialized mechanisms to access Si and associated nutrients from minerals/rocks. I therefore propose to test their capacity to extract nutrients from three rocks used in ecological agriculture: wollastonite (Ca), apatite (P), and greensand (K). Testing would be done in controlled conditions (hydroponics) and in the field. With a greater capacity to absorb soil Si, I also expect a faster cycling and a greater accumulation of plant-derived silicates and silicate occluded C under sugar maple and beech. To test for these effects, we will make use of a plantation designed to maximize species interactions. With 19 species of trees grown in pure and mixed plots, we will be able to test the full spectrum of Si absorption potential of tree species commonly grown in eastern Canada. *** These studies will provide some new insights on how sugar maple and beech can become dominant in old forests of eastern Canada while likely playing a significant role in mitigating the negative effects of the increase in atmospheric CO2. Two novel and simple approaches will also be developed to assess soil Al toxicity and estimate the rate of transpiration in trees.