Weltzin Jake F, Harth Calvin, Bridgham Scott D, Pastor John, Vonderharr Mark
Department of Ecology and Evolutionary Biology, University of Tennessee, 569 Dabney Hall, 37996, Knoxville, TN, USA.
Natural Resources Research Institute, University of Minnesota, 55811, Duluth, MN, USA.
Oecologia. 2001 Aug;128(4):557-565. doi: 10.1007/s004420100691. Epub 2001 Aug 1.
Boreal peatlands, which contain a large fraction of the world's soil organic carbon pool, may be significantly affected by changes in climate and land use, with attendant feedback to climate through changes in albedo, fluxes of energy or trace gases, and soil carbon storage. The response of peatlands to changing environmental conditions will probably be dictated in part by scale-dependent topographic heterogeneity, which is known to interact with hydrology, vegetation, nutrients, and emissions of trace gases. Because the bryophyte community can contribute the majority of aboveground production in bogs, we investigated how microscale topography affects the response of bryophyte species production and cover to warming (using overhead infrared lamps) and manipulations of water-table height within experimental mesocosms. We removed 27 intact peat monoliths (2.1-m surface area, 0.5-0.7 m depth) from a bog in northern Minnesota, USA, and subjected them to three warming and three water-table treatments in a fully crossed factorial design. Between 1994 and 1998, we determined annual production of the four dominant bryophyte taxa within three microtopographic zones (low, medium, and high relative to the water table). We also estimated species cover and calculated changes in topography and roughness of the bryophyte surface through time. Total production of all bryophytes, and production of the individual taxa Polytrichum strictum, Sphagnum magellanicum, and Sphagnum Section Acutifolia, were about 100% greater in low microtopographic zones than in high zones, and about 50% greater in low than in medium zones. Production of bryophytes increased along the gradient of increasing water-table heights, but in most years, total production of bryophytes was negatively correlated with height above the set water table only for the wettest water-table treatment. Although bryophyte production was unaffected by the warming treatments, the bryophyte surface flattened in proportion to the degree of warming. These results indicate that production of bryophytes is driven most strongly by the absolute and relative height of the bryophyte surface above the water table. Predicted changes in water-table height commensurate with changes in surface temperature may thus affect both production and superficial topography of bryophyte communities.
北方泥炭地储存了全球土壤有机碳库的很大一部分，可能会受到气候和土地利用变化的显著影响，并通过反照率、能量或微量气体通量以及土壤碳储存的变化对气候产生相应反馈。泥炭地对不断变化的环境条件的响应可能部分取决于与地形相关的尺度异质性，已知这种异质性会与水文、植被、养分和微量气体排放相互作用。由于苔藓植物群落可贡献沼泽地上大部分的生产量，我们研究了微尺度地形如何影响苔藓植物物种生产量以及覆盖度对变暖（使用顶置红外灯）和实验中型生态系统内地下水位高度操纵的响应。我们从美国明尼苏达州北部的一个沼泽地中取出27块完整的泥炭岩芯（表面积2.1平方米，深度0.5 - 0.7米），并按照完全交叉析因设计对它们进行三种变暖处理和三种地下水位处理。在1994年至1998年期间，我们确定了三个微地形区域（相对于地下水位低、中、高）内四种主要苔藓植物类群的年产量。我们还估计了物种覆盖度，并计算了苔藓植物表面随时间的地形和粗糙度变化。所有苔藓植物的总产量，以及单个类群硬叶金发藓、麦氏泥炭藓和尖叶泥炭藓组的产量，在低微地形区域比在高微地形区域大约高100%，在低微地形区域比在中微地形区域大约高50%。苔藓植物的产量随着地下水位高度增加的梯度而增加，但在大多数年份，仅在最湿润的地下水位处理中，苔藓植物的总产量才与设定地下水位以上的高度呈负相关。尽管苔藓植物的产量不受变暖处理的影响，但苔藓植物表面会随着变暖程度成比例地变平。这些结果表明，苔藓植物的产量受苔藓植物表面相对于地下水位的绝对和相对高度影响最大。因此，与地表温度变化相称的地下水位高度预测变化可能会影响苔藓植物群落的产量和表面地形。
