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

BassiriRad 9728785氮(N)和磷(P)是自然和农业生态系统中最常限制植物产量的营养物质。这些养分的可获得性有限也是影响植物和生态系统对大气二氧化碳水平上升的长期反应的一个主要因素，即，除非养分的可用性和/或获取能力随着碳(C)的增加而增加，否则通常观察到的植物生物量的短期增长可能不会长期持续。因此，从机理上了解二氧化碳浓度升高是否会引发补偿性调整，从而绕过植物生长的营养限制，这一点至关重要。补偿性调节，如(A)菌根发育增加，(B)增加了根N和P的吸收能力，以及(C)根的生长可以使植物在高CO2下满足增加的营养需求，但这些调节对CO2增加的反应程度尚不清楚。在讨论养分有效性如何与植物和生态系统对高二氧化碳的反应相互作用时，必须考虑几个问题：植物对氮和磷的需求是否会随着二氧化碳浓度的增加而增加？(作为一个概念，需求需要在时间和空间尺度上仔细定义，这将在这里讨论。)如果在二氧化碳浓度升高的情况下，养分需求确实增加了，植物会做出什么补偿性调整来克服这种更大的需求？N和P的吸收是否会随着相对生长率(RGR)和光合作用N和P利用的变化而适当调整？生长营养状况是否影响对二氧化碳的补偿性调整的幅度？在发育阶段，这些补偿机制是否与二氧化碳引起的变化相适应？不同功能基团的植物，如C3与C4、木本植物与草本植物、丛枝菌根与外生菌根对二氧化碳浓度升高的养分吸收反应是否存在差异？在二氧化碳浓度升高的情况下，更好的植物能力扩大养分吸收是否会增强竞争能力？拟议的研究将解决这些问题，重点是根和菌根吸收N和P的动力学。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。实地工作将在目前得到资助的六个国家FACE地点进行，对不同的生态系统和功能群体进行全面的交叉比较。在每个田间地点，在有或没有菌根的情况下，经过两个CO2处理的因子组合，将测量成熟植物完整的根对N和P的吸收能力。田间实验将提供一个独特的机会，来比较这些补偿性调整在竞争环境中不同生态系统、生命形式和植物功能群体中对二氧化碳水平上升的反应。温室-实验室实验将使用与田间相似的物种来研究与吸收动力学的调节、根与菌根吸收动力学的相对变化以及植物生理需求相关的更详细的问题。这些数据将被整合到一个综合功能平衡模型中，该模型将纳入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.