Compensatory Adjustments in Plant Nutrient Uptake: Varying Responses to Rising Atmospheric CO2

巴西拉德9728785 氮（N）和磷（P）是自然和农业生态系统中最常限制植物生产的营养物质。这些养分的有限供应也是影响植物和生态系统对大气CO2水平上升的长期反应的主要因素，即，通常观察到的植物生物量的短期增加可能不会长期持续，除非营养物的可用性和/或获取能力与碳（C）增加一致地增加。因此，它是至关重要的，以获得一个机械的理解，是否升高的CO2可以引起补偿性调整，将规避植物生长的养分限制。补偿性调整，如（a）增加菌根的发展，（B）增加根N和P的吸收能力，（c）根的生长，可以使植物满足高CO2下增加的养分需求，但这些调整在多大程度上响应CO2富集是未知的。 在解决如何养分供应可以与植物和生态系统对高CO2的反应相互作用时，必须考虑几个问题：植物对N和P的需求增加，以响应CO2富集？ （需求作为一个概念，需要在时间和空间尺度上仔细定义，这将在这里讨论。如果在升高的CO2下营养需求确实增加，那么植物将做出什么补偿性调整来克服这种更大的需求？N和P吸收的规模与测量的相对生长速率（RGR）和光合N和P利用的变化？生长营养状况是否影响对CO2的补偿性调节？这些补偿机制是否与CO2诱导的发育阶段的变化成比例？不同功能群的植物， C3与C4，木本与草本与草，或丛枝菌根与外生菌根不同的营养吸收反应，以提高二氧化碳？ 并 更好的植物能力，以扩大养分吸收在CO2浓度升高赋予增强的竞争力？ 拟议的研究将解决这些问题， 强调根和菌根的N和P吸收动力学。PI将使用现场和实验室方法在最现实的条件下测试我们的假设。 实地工作将在目前资助的六个国家FACE站点进行，对不同的生态系统和功能组进行全面的交叉比较。在每个现场，N和P的吸收能力将测量完整的根的成熟植物进行因子组合的两个CO2处理的存在或不存在的菌根。 田间试验将提供一个独特的机会，比较 在竞争环境中，不同的生态系统、生命形式和植物功能群之间对CO2水平升高的补偿性调整。温室实验室实验，使用类似的物种，从外地将检查更详细的问题有关的调整吸收动力学，相对变化的根与菌根吸收动力学，植物生理需求。 将数据综合成综合功能平衡 模型将结合生理和 生物量分配参数。

BassiriRad 9728785 Nitrogen (N) and phosphorus (P) are nutrients that most often limit plant production in natural and agricultural ecosystems. Limited availability of these nutrients is also a major factor influencing long-term plant and ecosystem responses to rising atmospheric CO2 levels i.e., the commonly observed short-term increase in plant biomass may not be sustained over the long-term unless availability and/or acquisition capacity for nutrients increases in concert with carbon (C) gain. Therefore, it is critical to obtain a mechanistic understanding of whether elevated CO2 can elicit compensatory adjustments that would circumvent nutrient limitation of plant growth. Compensatory adjustment such as (a) increased mycorrhizal development, (b) increased root N and P absorption capacity, and (c) root growth can enable plants to meet increased nutrient demand under high CO2 yet the extent of these adjustments in response to CO2 enrichment is unknown. In addressing how nutrient availability could interact with plants and ecosystem responses to high CO2 several questions must be considered: Will plant demand for N and P increase in response to CO2 enrichment ? (Demand as a concept requires careful definition on temporal and spatial scales which will be addressed here.) If nutrient demand does increase under elevated C02, what compensatory adjustment(s) will plants make to overcome this greater demand? Will N and P uptake scale properly with measured changes in relative growth rate (RGR) and photosynthetic N and P utility? Does growth nutrient status affect the magnitude of the compensatory adjustments in response to CO2? Do these compensatory mechanisms scale with CO2-induced changes in stages of development? Do plants of various functional groups e.g., C3 vs. C4, woody vs. herbaceous vs. grasses, or arbuscular mycorrhizae vs. ectomycorrhizae differ in their nutrient uptake responses to elevated CO2? Does a better plant capacity to scale up nutrient uptake at elevated CO2 confer enhanced competitive ability? The proposed research will address these questions with an emphasis on root and mycorrhizal N and P uptake kinetics. The PI will use both field and laboratory approaches to test our hypotheses under the most realistic conditions possible. The field work will be conducted at six currently funded national FACE sites providing a comprehensive cross comparison of different ecosystems and functional groups. At each field site, N and P uptake capacity will be measured on intact roots of mature plants subjected to factorial combination of two CO2 treatments in the presence or absence of mycorrhizas. The field experiments will provide a unique opportunity to compare the response of these compensatory adjustments to elevated CO2 levels among different ecosystems, life forms, and functional groups of plants in a competitive setting. Greenhouse-laboratory experiments using species similar to those from the field will examine the more detailed questions related to adjustments in uptake kinetics, relative changes in root vs. mycorrhizal uptake kinetics, and plant physiological demand. The data will be integrated into a comprehensive functional balance model which will incorporate physiological and biomass allocation parameters.