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

气候变化，加上预计干旱发生率增加和生长季节延长，很可能改变森林的养分供应和需求。硅（Si）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元素。它最近吸引了很多兴趣，因为它在减轻二氧化碳浓度增加的影响方面发挥了作用。我最近的研究表明，糖枫和山毛榉，两个主要的硬木在美国东北部，可能是积极的硅。如果得到证实，这将表明它需要以最佳水平生长，并且研究人员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。第一步将是修订这两个物种的营养标准。为了获得营养平衡的完整测量，我们将Si包括在营养指数/比率中。将对生长在不同土壤条件下的每种至少200棵树进行取样。将根据边界线回归确定最佳营养浓度和比例。第二步将包括评估Si的生理作用。我假设，通过生产“廉价”硅酸盐结构节省的能源将增加防御化学品的生产，例如酚类物质，单宁。对于本研究，将在含有和不含Si的水培中生长幼苗。将监测和比较根和茎/叶的一系列形态变量以及叶化学。* 作为活性硅源，人们会期望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营养物质。因此，我建议测试他们的能力，提取营养物质从三种岩石用于生态农业：硅灰石（钙），磷灰石（P），和绿砂（K）。测试将在受控条件（水培）和实地进行。随着吸收土壤硅的能力更强，我还希望在糖枫和山毛榉下有更快的循环和更大的植物来源的硅酸盐和硅酸盐封闭C的积累。为了测试这些影响，我们将利用一个旨在最大限度地提高物种相互作用的种植园。与19种树木生长在纯和混合地块，我们将能够测试全光谱的硅吸收潜力的树种通常生长在加拿大东部。*** 这些研究将为糖枫和山毛榉如何在加拿大东部的古老森林中占据主导地位提供一些新的见解，同时可能在减轻大气二氧化碳增加的负面影响方面发挥重要作用。两种新的和简单的方法也将被开发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.