Blasi Charlotte, Houle Daniel, Vacherand Gaëlle, Bellenger Jean-Philippe
Centre Sève, Département de Chimie, Université de Sherbrooke, Sherbrooke, QC, J1K 2R1, Canada.
Directorat des Sciences et Technologie de l'eau, Environnement et Changement climatique Canada, 105 rue McGill, Montréal, H27 2E7, Canada.
Oecologia. 2025 Jul 2;207(7):119. doi: 10.1007/s00442-025-05751-y.
Biological nitrogen fixation in feathermosses provides an important source of exogenous nitrogen to boreal forest ecosystems. Yet there is a limited understanding of how canopy condition and throughfall influence N fixation rates. To decipher the effect of climatic variables (i.e., temperature, humidity, and light) and nitrogen deposition chemistry (i.e., inorganic and organic N) on moss BNF, we monitored climatic variables, biological N-fixation, cyanobacteria biomass, and some moss traits of two co-occurring moss species in black spruce forests in Eastern Canada (Pleurozium schreberi and Ptilium crista-castrensis) over two growing seasons in undisturbed mature forests and forest gaps (windfalls). We further investigated the ability of both species to retrieve nitrogen from deposition using N tracers in the field and the lab. Both species achieved comparable BNF in forest gaps. In the mature forest, BNF decreased in both species compared to the forest gap but was significantly higher in P. crista-castrensis (about 10 fold) than in P. schreberi. In both species, the decrease in BNF activity between forest gaps and mature forests was likely driven by the slightly less favorable climatic conditions for BNF (e.g., temperature and light). However, BNF was further reduced in P. schreberi due to better nitrogen sorption from the throughfall leading to reduced cyanobacteria colonization and cyanobacteria-specific BNF activity. These results show that co-occurring moss species are affected in a contrasted manner by changes in the composition of nitrogen deposition.
羽藓中的生物固氮作用为北方森林生态系统提供了重要的外源氮源。然而，对于冠层条件和穿透水如何影响固氮率，人们的了解还很有限。为了阐明气候变量（即温度、湿度和光照）以及氮沉降化学性质（即无机氮和有机氮）对苔藓生物固氮的影响，我们在加拿大东部黑云杉林（尖叶拟垂枝藓和粗枝藓）中，于两个生长季节内，在未受干扰的成熟森林和林窗（风倒木区域）监测了气候变量、生物固氮、蓝细菌生物量以及两种共生苔藓的一些苔藓特征。我们还在野外和实验室中使用氮示踪剂进一步研究了这两个物种从沉降物中获取氮的能力。两个物种在林窗中的生物固氮量相当。在成熟森林中，与林窗相比，两个物种的生物固氮量均有所下降，但粗枝藓的生物固氮量显著高于尖叶拟垂枝藓（约10倍）。在这两个物种中，林窗和成熟森林之间生物固氮活性的下降可能是由于生物固氮的气候条件略逊（如温度和光照）。然而，由于从穿透水中更好地吸附氮，导致蓝细菌定殖减少和蓝细菌特异性生物固氮活性降低，尖叶拟垂枝藓的生物固氮量进一步减少。这些结果表明，共生苔藓物种受氮沉降组成变化的影响方式截然不同。
