Does long-term drought or repeated defoliation affect seasonal leaf N cycling in young beech trees?

IF 3.5 2区 农林科学 Q1 FORESTRY Tree physiology Pub Date : 2024-06-03 DOI:10.1093/treephys/tpae054
Catherine Massonnet, Pierre-Antoine Chuste, Bernhard Zeller, Pascal Tillard, Bastien Gerard, Loucif Cheraft, Nathalie Breda, Pascale Maillard
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Abstract

Forest trees adopt effective strategies to optimize nitrogen (N) use through internal N recycling. In the context of more recurrent environmental stresses due to climate change, the question remains of whether increased frequency of drought or defoliation threatens this internal N recycling strategy. We submitted 8-year-old beech trees to 2 years of either severe drought (Dro) or manual defoliation (Def) to create a state of N starvation. At the end of the second year before leaf senescence, we labeled the foliage of the Dro and Def trees, as well as that of control (Co) trees, with 15N-urea. Leaf N resorption, winter tree N storage (total N, 15N, amino acids, soluble proteins) and N remobilization in spring were evaluated for the three treatments. Defoliation and drought did not significantly impact foliar N resorption or N concentrations in organs in winter. Total N amounts in Def tree remained close to those in Co tree, but winter N was stored more in the branches than in the trunk and roots. Total N amount in Dro trees was drastically reduced (-55%), especially at the trunk level, but soluble protein concentrations increased in the trunk and fine roots compared with Co trees. During spring, 15N was mobilized from the trunk, branches and twigs of both Co and Def trees to support leaf growth. It was only provided through twig 15N remobilization in the Dro trees, thus resulting in extremely reduced Dro leaf N amounts. Our results suggest that stress-induced changes occur in N metabolism but with varying severity depending on the constraints: within-tree 15N transport and storage strategy changed in response to defoliation, whereas a soil water deficit induced a drastic reduction of the N amounts in all the tree organs. Consequently, N dysfunction could be involved in drought-induced beech tree mortality under the future climate.

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长期干旱或反复落叶是否会影响山毛榉幼树的季节性叶片氮循环?
林木采取有效策略,通过内部氮循环来优化氮(N)的利用。在气候变化导致环境压力日益频繁的背景下,干旱或落叶频率的增加是否会威胁到这种内部氮循环策略仍然是个问题。我们让 8 年树龄的榉树经历了两年的严重干旱(Dro)或人工落叶(Def),以制造氮饥饿状态。在叶片衰老前的第二年年底,我们用 15N-urea 标记了 Dro 和 Def 树以及对照(Co)树的叶片。对三种处理的叶片氮吸收、冬季树木氮储存(总氮、15N、氨基酸、可溶性蛋白质)和春季氮再动员进行了评估。落叶和干旱对叶片的氮吸收和冬季器官中的氮浓度没有显著影响。Def树的氮总量与Co树接近,但冬季氮更多地储存在树枝而不是树干和根部。Dro 树的氮总量急剧减少(-55%),尤其是树干,但与 Co 树相比,树干和细根中的可溶性蛋白质浓度有所增加。在春季,Co 树和 Def 树的树干、树枝和小枝都动员了 15N 以支持叶片生长。而 Dro 树只通过树枝 15N 再动员来提供,因此 Dro 树叶中的氮含量极度减少。我们的研究结果表明,应激诱导的氮代谢发生了变化,但其严重程度因限制因素而异:落叶改变了树体内部的 15N 运输和储存策略,而土壤缺水则导致所有树体器官中的氮含量急剧下降。因此,在未来气候条件下,氮功能失调可能与干旱导致的榉树死亡有关。
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来源期刊
Tree physiology
Tree physiology 农林科学-林学
CiteScore
7.10
自引率
7.50%
发文量
133
审稿时长
1 months
期刊介绍: Tree Physiology promotes research in a framework of hierarchically organized systems, measuring insight by the ability to link adjacent layers: thus, investigated tree physiology phenomenon should seek mechanistic explanation in finer-scale phenomena as well as seek significance in larger scale phenomena (Passioura 1979). A phenomenon not linked downscale is merely descriptive; an observation not linked upscale, might be trivial. Physiologists often refer qualitatively to processes at finer or coarser scale than the scale of their observation, and studies formally directed at three, or even two adjacent scales are rare. To emphasize the importance of relating mechanisms to coarser scale function, Tree Physiology will highlight papers doing so particularly well as feature papers.
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