Quantifying the temperature responses of symbiotic nitrogen fixation and its carbon cost

温度如何影响生理过程？这个基本问题帮助人们了解生物如何在极端环境中生存，如何适应日常/季节周期，以及如何应对气候变化。对于许多过程，如光合作用，其基本原理几十年前就已为人所知。然而，在一个过程中，知识受到技术的严重限制。这个过程被称为“固氮”，它吸收氮气（占空气的78%），并使其为生物所利用。它是由某些细菌完成的，通常与某些植物（豆类、豌豆和一些野生草本植物、灌木和树木）共生，是氮进入生态系统的主要自然方式。鉴于氮是蛋白质和DNA的重要组成部分，固氮对生命至关重要。它在气候变化中也起着重要作用。根据模型，如果固氮提供足够的氮来平衡植物的营养，植物将储存更多的碳。这就是温度的作用：目前的模型假设氮固定在25摄氏度时效果最好，这导致了预测，随着世界变暖，热带森林将固定更少的氮。研究者Menge和Griffin最近在实验室的工作中使用新技术表明，在少数物种中，氮固定在29-37摄氏度下效果最好，并能适应最近的温度。这项拟议的工作将使用这项新技术来测试这些发现是否适用于广泛的物种和生长条件。这项工作将培养学者，使生态学多样化，并改进用于制定气候政策的模型。共生固氮（SNF）的温度响应尚不清楚。曲线的基本形状是什么？它在不同的分类群中有什么不同？适应不断升高的温度有多普遍？这些基本问题的答案是生物学的基础。它们对于理解全球环境变化也至关重要，因为到本世纪末，不同的SNF建模方法将使C储存减少50 Pg C。包含SNF温度响应的模型使用的函数来自一小部分测量，几乎所有这些测量都来自非共生细菌。这个功能不包括驯化。该函数已在全球尺度上应用于SNF的速率和SNF的碳成本（尽管没有数据）。来自首席研究员实验室的初步数据表明，SNF的温度响应与目前使用的功能有很大不同。此外，初步数据揭示了适应生长温度的潜力。建议的工作将解决以下问题：SNF的温度响应和SNF的呼吸碳成本是什么？它们在不同的分类群和生长温度下是如何变化的？它们与光合作用的温度反应相比如何？为了做到这一点，它将使用连续的乙烯和二氧化碳分析仪来测量SNF活性，来自结节的呼吸二氧化碳通量，以及在不同温度下生长在生长室内的许多固氮共生生物的光合作用。这项工作将对一个可悲的研究不足的过程的基本理解取得重大进展。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

How does temperature affect physiological processes? This fundamental question helps people understand how organisms live in extreme environments, adjust to daily/seasonal cycles, and respond to climate change. For many processes, like photosynthesis, the basics have been known for decades. For one process, though, knowledge has been severely limited by technology. The process, “nitrogen fixation,” takes nitrogen gas (78% of air) and makes it available to organisms. It is done by certain bacteria, often in symbiosis with certain plants (beans, peas, and some wild herbs, shrubs, and trees), and is the main natural way that nitrogen gets into ecosystems. Given that nitrogen is an essential part of protein and DNA, nitrogen fixation is critical for life. It also plays a major role in climate change. According to models, plants will store more carbon if nitrogen fixation provides enough nitrogen to balance their nutrition. Here’s where temperature comes in: models currently assume that nitrogen fixation always works best at 25 degrees Celsius, leading to predictions that tropical forests will fix less nitrogen as the world warms. Recent work in the labs of investigators Menge and Griffin used new technology to show that, in a handful of species, nitrogen fixation works best at 29-37 degrees Celsius and adjusts to recent temperature. The proposed work will use this new technology to test whether these findings hold across a wide range of species and growing conditions. This work will train scholars, diversify ecology, and improve models that are used to set climate policy.The temperature response of symbiotic N fixation (SNF) is poorly understood. What’s the basic shape of the curve? How does it vary across taxa? How ubiquitous is acclimation to growing temperatures? Answers to these basic questions are fundamental to biology. They are also critical for understanding global environmental change, given that different ways of modeling SNF modify C storage by 50 Pg C by the end of the century. The models that include a temperature response of SNF use a function that comes from a small set of measurements, nearly all of which were from asymbiotic bacteria. The function does not include acclimation. This function has been applied at the global scale to both the rate of SNF and, despite zero data, to the carbon cost of SNF. Preliminary data from the principal investigator’s labs suggest that the temperature response of SNF is drastically different than the function currently in use. Furthermore, the preliminary data reveal the potential for acclimation to growing temperature. The proposed work will address the questions: What are the temperature responses of SNF and the respiratory carbon cost of SNF? How do they vary across taxa and growing temperatures? How do they compare to the temperature response of photosynthesis? To do so it will use continuous ethylene and carbon dioxide analyzers to measure SNF activity, respiratory carbon dioxide fluxes from nodules, and photosynthesis on many N-fixing symbioses grown at different temperatures in growth chambers. This work will make major progress toward fundamental understanding of a woefully under-studied process.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.