Widespread herbivory cost in tropical nitrogen-fixing tree species
Widespread herbivory cost in tropical nitrogen-fixing tree species
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DOI：
10.1038/s41586-022-05502-6
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发表时间：
2022-12-07
期刊：
影响因子：
64.8
通讯作者：
Batterman, Sarah A. A.
中科院分区：
文献类型：
--
作者：
Barker, Will;Comita, Liza S. S.;Batterman, Sarah A. A.
最近的观察表明，成熟和恢复森林中的大量碳汇可能受到氮的强烈限制(1-3)。与细菌共生的固氮树（固定剂）为热带森林提供新氮的主要天然来源(3,4)。然而，固定剂的丰度受到严格限制(5-7)，这凸显了一个尚未解答的基本问题：是什么限制了新的氮进入热带生态系统。在这里，我们研究动物的食草行为是否限制了热带森林中的共生固氮。我们评估固氮树是否比其他树木经历更多的食草，食草是否会带来大量的碳成本，以及高食草性是否是食草动物瞄准固氮植物富含氮的叶子的结果(8,9)。我们分析了巴拿马 43 个热带树种的 350 棵幼苗的 1,626 片叶子，发现：（1）虽然食草会降低所有幼苗的生长和存活率，但固氮树比非固氮树多经历 26% 的食草； (2) 固定者因草食性而产生的碳机会成本比非固定者高34%，超过了固氮的代谢成本； (3)固定植物的高食草性并不是由高叶氮驱动的。我们的研究结果表明，食草可能足以限制热带共生固氮，并可能限制其在缓解热带碳汇氮限制方面的作用。
Recent observations suggest that the large carbon sink in mature and recovering forests may be strongly limited by nitrogen(1-3). Nitrogen-fixing trees (fixers) in symbiosis with bacteria provide the main natural source of new nitrogen to tropical forests(3,4). However, abundances of fixers are tightly constrained(5-7), highlighting the fundamental unanswered question of what limits new nitrogen entering tropical ecosystems. Here we examine whether herbivory by animals is responsible for limiting symbiotic nitrogen fixation in tropical forests. We evaluate whether nitrogen-fixing trees experience more herbivory than other trees, whether herbivory carries a substantial carbon cost, and whether high herbivory is a result of herbivores targeting the nitrogen-rich leaves of fixers(8,9). We analysed 1,626 leaves from 350 seedlings of 43 tropical tree species in Panama and found that: (1) although herbivory reduces the growth and survival of all seedlings, nitrogen-fixing trees undergo 26% more herbivory than non-fixers; (2) fixers have 34% higher carbon opportunity costs owing to herbivory than non-fixers, exceeding the metabolic cost of fixing nitrogen; and (3) the high herbivory of fixers is not driven by high leaf nitrogen. Our findings reveal that herbivory may be sufficient to limit tropical symbiotic nitrogen fixation and could constrain its role in alleviating nitrogen limitation on the tropical carbon sink.