Cloud forests have been found to lose more nitrogen in stream discharge than they gain from atmospheric deposition. They also support a large diversity and biomass of tree epiphytes, predominately composed of cryptogams. Since cryptogam epiphytes harbor nitrogen fixing cyanobacteria, they may help make up for the nitrogen loss from ecosystems. We assessed cryptogam biomass on the ground, boles and branches in Quercus costaricensis dominated stands near the tree line in the Cordillera de Talamanca, Costa Rica. Nitrogen fixation was assayed using ¹⁵N₂ uptake. Total cryptogam biomass was 2 977 kg ha⁻¹, with 67% being found on the lower branches. Bryophytes and chlorolichens made up 53% and 44%, respectively, of the biomass. Half of the bryophyte mass was composed of the liverwort Plagiochila heterophylla, and 66% of the chlorolichen of Lobariella pallida. There were no significant differences in nitrogen fixation rates between the cryptogam species, with a mean rate of 5.04 µg N g⁻¹ day⁻¹ during the predominantly wet condition in the forest. The overall nitrogen input from fixation was 6.1 kg N ha⁻¹ year⁻¹, of which 78% came from bryophytes, 18% from chlorolichens, and 4% from cyanolichens. Only 2.0% of the fixation occurred in cryptogams on the ground, whereas 67%, 24%, and 7% occurred on the lower branches, boles, and upper branches, respectively. These results show that tree epiphytes constitute a significant source of nitrogen for these forests, due to the trees’ large surface area, and can make up for the nitrogen lost from these ecosystems.

人们发现云林在河流排放中损失的氮量超过了其从大气沉积中获得的氮量。它们还支持主要由隐藻组成的树木附生植物的大量多样性和生物量。由于隐藻附生植物具有固氮蓝细菌，因此它们可能有助于弥补生态系统中的氮损失。我们评估了哥斯达黎加科尔迪勒拉·塔拉曼卡山脉附近林木中栎，栎和树枝支配的地面，树干和树枝上的隐球菌生物量。使用¹⁵ N ₂吸收来测定固氮。隐藻生物质总量为2977 kg ha ^-1，其中67％位于较低的分支机构。苔藓植物和绿藻类分别占生物量的53％和44％。苔藓植物质量的一半由苔的Plagiochila太子参，和的chlorolichen 66％Lobariella淡紫。隐孢子虫之间固氮率没有显着差异，在森林中主要是潮湿的条件下，平均固氮率为5.04 µg N g ^-1天^-1。固氮的总氮输入量为6.1 kg N ha ^-1  year ^-1，其中78％来自苔藓植物，18％来自氯地衣，4％来自氰油菜。仅2.0％的固定发生在地面上的隐球菌中，而67％，24％和7％分别发生在下部分支，树干和上部分支上。这些结果表明，树的附生植物由于树木的大表面积而构成了这些森林的重要氮源，并可以弥补这些生态系统中损失的氮。