Dynamic Silicon-Carbon Interactions in Terrestrial Vegetation

由于全球碳平衡对全球气候的主要影响，近年来一直是许多研究的焦点。在理解和确定全球碳循环(C循环)中的反馈方面已经做了大量的工作，但尚未充分研究与其他生物地球化学循环的相互作用。例如，硅(Si)的循环对C循环很重要，因为硅酸盐岩石的风化会从大气中去除二氧化碳。此外，海洋植物(特别是硅藻)的生产力受到硅的限制，因此任何影响“生物二氧化碳泵”(即海洋初级生产者对大气二氧化碳的去除)强度的东西都会影响大气中二氧化碳的浓度。除了影响硅的风化速率的植物外，许多植物都是风化硅的蓄积者；这些植物使用硅基化合物来增强茎的刚性或提高对疾病和食草动物的防御能力。大多数硅循环的生物地球化学模型忽略了陆地植物的作用，或者将所有陆地生态系统视为相同的。因此，将陆地植物-硅过程引入全球C-Si循环模型是这项研究拨款的总体目标。如果我们不考虑硅循环的反馈，我们将永远无法实现全球碳循环的平衡，如果我们忽略整个陆地生物圈，我们将永远无法实现正确的硅循环。确实有越来越多的文献关于植物-硅相互作用的生态生理学基础，可以进行定量分析并结合到现有的生物地球化学模型中。将对涉及植物吸收硅的机制以及涉及生物源硅的分解和硅浸出的过程的数据进行统计分析，目的是对这些生物过程中最重要的过程进行机械模拟。能够将硅的循环置于进化的背景下，也将有助于理解它在通过地质时间改变全球碳循环中的作用。白垩纪末期标志着陆地植被的一个转折点，因为开花植物(被子植物)的进化被认为导致了现有裸子植物(针叶树)主导的生态系统的取代。被子植物和地球上一些最大的硅植物蓄积器的进化在哪些方面影响了全球的碳循环？被子植物积累硅的能力(并将其用作碳的廉价替代品)是否改变了被子植物和裸子植物之间的竞争平衡？这些问题将构成为NSERC基金提出的研究基础。拟议研究的影响是巨大的，因为我们目前不认为陆地生物圈是硅循环的活跃组成部分，因此永远无法完全理解全球碳循环。

The global carbon balance has been the focus of much research recently because of its primary influence on global climate. Considerable work has gone into understanding and identifying feedbacks within the global carbon cycle (C-cycle), but what has not yet been investigated sufficiently is the interaction with other biogeochemical cycles. For example, the cycling of silicon (Si) is important for the C-cycle because the weathering of silicate rocks removes CO2 from the atmosphere. Furthermore, productivity of marine plants (particularly diatoms) is limited by Si and therefore anything that influences the strength of the "biological CO2 pump" (i.e. removal of atmospheric CO2 by ocean primary producers) influences concentration of CO2 in the atmosphere. In addition to plants influencing the rate of Si weathering, many plants are accumulators of weathered Si; these plants use Si-based compounds to enhance stem rigidity or to improve defences against disease and herbivores. Most biogeochemical models of Si cycling omit the role of terrestrial plants or treat all terrestrial ecosystems as if they are the same. It is the overall objective of this research grant, therefore, to introduce terrestrial plant-Si processes into global C-Si cycle models. We will never be able to get the global carbon cycle to balance if we don't consider feedbacks from the Si cycle, and we will never get the Si cycle right if we omit the entire terrestrial biosphere. There does exist growing literature on the ecophysiological basis of plant-Si interactions that could be quantitatively analyzed and incorporated into existing biogeochemical models. Data addressing the mechanisms involved in plant uptake of Si and the processes involved in the decomposition of biogenic Si and leaching of Si will be statistically analyzed with the intent to mechanistically model the most significant of these biological processes. Being able to place the cycling of Si in an evolutionary context will also be useful for understanding its role in altering the global C-cycle through geological time. The end-Cretaceous marks a turning point for terrestrial vegetation because the evolution of flowering plants (angiosperms) is thought to have led to the replacement of existing gymnosperm (conifer)-dominated ecosystems. In what ways did the evolution of angiosperms and some of the Earth's largest Si plant accumulators influence global C-cycling? Did the ability of angiosperms to accumulate Si (and use it as a cheap alternative to carbon) change the competitive balance between angiosperms and gymnosperms? Such questions will form the basis of research proposed for NSERC funding. The impact of the proposed research is substantial because we currently do not consider the terrestrial biosphere as an active component of Si-cycling therefore will never be able to fully understand the global carbon cycle.