Dynamic Silicon-Carbon Interactions in Terrestrial Vegetation

全球碳平衡因其对全球气候的主要影响而成为近年来研究的热点。在理解和识别全球碳循环（c循环）中的反馈方面已经做了大量的工作，但尚未充分研究的是与其他生物地球化学循环的相互作用。例如，硅（Si）的循环对碳循环很重要，因为硅酸盐岩石的风化作用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”强度的因素（即海洋初级生产者去除大气中的二氧化碳）都会影响大气中二氧化碳的浓度。除了植物影响硅的风化速率外，许多植物还是风化硅的蓄积者；这些植物使用硅基化合物来增强茎的硬度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都忽略了陆生植物的作用，或者将所有陆地生态系统视为相同的。因此，这项研究的总体目标是将陆地植物硅过程引入全球碳硅循环模型。如果我们不考虑硅循环的反馈，我们将永远无法使全球碳循环平衡，如果我们忽略整个陆地生物圈，我们将永远无法使硅循环正确。关于植物-硅相互作用的生态生理基础的文献越来越多，可以定量分析并纳入现有的生物地球化学模型。有关植物吸收硅的机制以及生物源硅分解和硅浸出过程的数据将进行统计分析，目的是对这些生物过程中最重要的过程进行机械建模。能够将硅的循环置于进化的背景下，也将有助于理解其在地质时期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。被子植物和一些地球上最大的硅积累植物的进化是如何影响全球碳循环的？被子植物积累Si（并将其作为碳的廉价替代品）的能力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NSERC资助研究的基础。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一个活跃组成部分，因此永远无法完全了解全球碳循环。

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.