Zackrisson O, DeLuca T H, Gentili F, Sellstedt A, Jäderlund A
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå 901 83, Sweden.
Oecologia. 2009 May;160(2):309-19. doi: 10.1007/s00442-009-1299-8. Epub 2009 Feb 28.
The pleurocarpus feather moss, Hylocomium splendens, is one of two co-dominant moss species in boreal forest ecosystems and one of the most common mosses on earth, yet little is known regarding its capacity to host cyanobacterial associates and thus contribute total ecosystem N. In these studies, we evaluated the N-fixation potential of the H. splendens-cyanobacteria association and contrasted the N-fixation activity with that of the putative N-fixing moss-cyanobacteria association of Pleurozium schreberi. Studies were conducted to: quantify N-fixation in H. splendens and P. schreberi in sites ranging from southern to northern Fennoscandia; assess N and P availability as drivers of N-fixation rates; contrast season-long N-fixation rates for both mosses; and characterize the cyanobacteria that colonize shoots of H. splendens. Nitrogen-fixation rates were generally low at southern latitudes and higher at northern latitudes (64-69 degrees N) potentially related to anthropogenic N deposition across this gradient. Nitrogen fixation in H. splendens appeared to be less sensitive to N deposition than P. schreberi. The season-long assessment of N-fixation rates at a mixed feather moss site in northern Sweden showed that H. splendens fixed a substantial quantity of N, but about 50% less total N compared to the contribution from P. schreberi. In total, both species provided 1.6 kg fixed N ha(-1) year(-1). Interestingly, H. splendens demonstrated somewhat higher N-fixation rates at high fertility sites compared to P. schreberi. Nostoc spp. and Stigonema spp. were the primary cyanobacteria found to colonize H. splendens and P. schreberi. These results suggest that H. splendens with associated Nostoc or Stigonema communities contributes a significant quantity of N to boreal forest ecosystems, but the contribution is subordinate to that of P. schreberi at northern latitudes. Epiphytic cyanobacteria are likely a key factor determining the co-dominant presence of these two feather mosses across the boreal biome.
侧蒴羽藓（Hylocomium splendens）是北方森林生态系统中两种共优势藓类物种之一，也是地球上最常见的藓类之一，但对于其容纳蓝藻共生体并因此对生态系统总氮含量做出贡献的能力，人们所知甚少。在这些研究中，我们评估了侧蒴羽藓与蓝藻共生体的固氮潜力，并将其固氮活性与假定的具固氮能力的白齿藓（Pleurozium schreberi）与蓝藻的共生体进行了对比。开展的研究包括：量化从斯堪的纳维亚半岛南部到北部各地点的侧蒴羽藓和白齿藓的固氮量；评估作为固氮率驱动因素的氮和磷的有效性；对比两种藓类整个生长季的固氮率；以及鉴定定殖于侧蒴羽藓茎枝上的蓝藻。固氮率通常在低纬度地区较低，而在北纬64 - 69度的高纬度地区较高，这可能与该梯度上的人为氮沉降有关。侧蒴羽藓的固氮似乎比白齿藓对氮沉降的敏感性更低。在瑞典北部一个混合羽藓地点对固氮率进行的整个生长季评估表明，侧蒴羽藓固定了大量的氮，但与白齿藓的贡献相比，总氮量约少50%。这两个物种总共提供了1.6千克固定氮每公顷每年。有趣的是，与白齿藓相比，侧蒴羽藓在高肥力地点表现出略高的固氮率。念珠藻属（Nostoc spp.）和伪枝藻属（Stigonema spp.）是定殖于侧蒴羽藓和白齿藓上发现的主要蓝藻。这些结果表明，与念珠藻或伪枝藻群落共生的侧蒴羽藓对北方森林生态系统贡献了大量的氮，但在高纬度地区，其贡献低于白齿藓。附生蓝藻可能是决定这两种羽藓在整个北方生物群落中共优势存在的关键因素。
