Collaborative Research: Does a transition in nitrogen fixation strategy explain the latitudinal distribution of nitrogen-fixing trees?

合作研究：固氮策略的转变能否解释固氮树木的纬度分布？

• 批准号: 1457650
• 负责人: Duncan Menge
• 金额: $ 95.63万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-05-15 至 2020-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1457650&HistoricalAwards=false
• 关键词: Collaborative; Research; Does; transition; nitrogen

Nitrogen (N) is a necessary nutrient for plant growth. Although the atmosphere mainly consists of nitrogen gas (N2), this form of N is extremely stable. Most plants can't directly access N2 and their rate of growth is limited by the presence of available N in the soil. Therefore, some species of trees have evolved a symbiosis with a special class of bacteria that fix atmospheric N2 and convert it into a plant available form. These N-fixing trees have abundant access to N, but there is a cost to this symbiotic association: these trees provide carbon to bacteria and therefore sacrifice some of their own growth to maintain the symbiosis. As a result, N-fixing trees comprise only a small proportion of tree species on earth. In theory, N fixation is only advantageous in ecosystems that have very limited amounts of N in the soil. N-limited forests tend to be more common at high latitudes than at lower latitudes (the tropics and subtropics), but curiously, N-fixing trees are actually most common at lower latitudes. In fact, N-fixing trees are ten times less abundant at higher latitudes than at lower latitudes. Why is this the case? This proposal will test a potential explanation. The "differential regulation hypothesis" states that variation in the degree to which N-fixing trees regulate N fixation can explain the pattern. N-fixing trees that rapidly adjust N-fixation to meet N demand should be more abundant, as is the case in lower-latitude forests. In contrast, species that cannot regulate N-fixation should be less abundant, as observed in higher-latitude forests. This project will measure the extent to which the regulation of N-fixation actually varies across latitudes, as well as the metabolic costs of regulating N-fixation and the relationship of these costs to temperature. The results will provide a long sought after explanation for the distribution of N-fixing trees on earth, which is an essential component of the growth of forests worldwide.The project will involve a field experiment in forests at different latitudes as well as two greenhouse experiments. The field experiment will fertilize forests with labeled N to vary the degree of N limitation and measure the regulation of N fixation in the field. The experimental locations are Oregon (with Alnus rubra), New York (with Robinia pseudoacacia), and Hawaii (with Morella faya, Casuarina equisetifolia, Acacia koa, and Sophora chrysophylla) and span the latitudinal threshold for N-fixing tree abundance (35° N). There are two major types of N fixing symbioses (actinorhizal and rhizobial) and the field sites were chosen to capture both. The greenhouse experiments will test a larger number of species and involve more highly controlled conditions. The greenhouse experiments will also evaluate how quickly plants can regulate N fixation. The experiments and laboratory analyses will involve participation of Title 1 high school students as well as undergraduate and graduate students in New York, California and Oregon.

氮（N）是植物生长所必需的营养元素。 虽然大气主要由氮气（N2）组成，但这种形式的N非常稳定。大多数植物不能直接获得N2，它们的生长速度受到土壤中有效氮的限制。 因此，一些树种已经进化出与一类特殊细菌的共生关系，这些细菌固定大气中的N2并将其转化为植物可用的形式。这些固氮树有充足的氮源，但这种共生关系是有代价的：这些树为细菌提供碳，因此牺牲了一些自己的生长来维持共生关系。 因此，固氮树只占地球上树种的一小部分。 从理论上讲，固氮只有在土壤中氮含量非常有限的生态系统中才是有利的。 氮限制森林在高纬度地区比低纬度地区（热带和亚热带）更常见，但奇怪的是，固氮树实际上在低纬度地区最常见。 事实上，高纬度地区的固氮树比低纬度地区少十倍。 为什么会这样呢？ 这一提议将检验一种可能的解释。 “差异调节假说”认为，固氮树调节固氮的程度的变化可以解释这种模式。 能够迅速调整固氮作用以满足氮需求的固氮树应该更丰富，就像低纬度森林的情况一样。 相反，不能调节固氮的物种应该不那么丰富，在高纬度森林中观察到。 该项目将测量固氮调节在不同纬度之间的实际变化程度，以及调节固氮的代谢成本以及这些成本与温度的关系。研究结果将为固氮树在地球上的分布提供一个长期寻求的解释，固氮树是全球森林生长的一个重要组成部分。该项目将包括在不同纬度的森林中进行一个实地实验以及两个温室实验。 田间试验将用标记的氮素对森林施肥，以改变氮素限制的程度，并测量田间的氮素固定规律。 实验地点是俄勒冈州（有赤杨）、纽约（有刺槐）和夏威夷（有莫雷拉法亚、木麻黄、相思树和金槐），跨越了固氮树丰度的纬度阈值（35° N）。 有两种主要类型的固氮共生体（放线菌和根瘤菌）和现场的网站被选择捕获。 温室实验将测试更多的物种，并涉及更严格的控制条件。 温室实验还将评估植物调节固氮的速度有多快。实验和实验室分析将涉及纽约、加州和俄勒冈州的一级高中学生以及本科生和研究生的参与。

项目成果

Tree symbioses sustain nitrogen fixation despite excess nitrogen supply

尽管氮供应过剩，树木共生仍维持固氮作用

• DOI: 10.1002/ecm.1562
• 发表时间: 2023
• 期刊: Ecological Monographs
• 影响因子: 6.1
• 作者: Menge, Duncan N. L.;Wolf, Amelia A.;Funk, Jennifer L.;Perakis, Steven S.;Akana, Palani R.;Arkebauer, Rachel;Bytnerowicz, Thomas A.;Carreras Pereira, K. A.;Huddell, Alexandra M.;Kou‐Giesbrecht, Sian
• 通讯作者: Kou‐Giesbrecht, Sian