Jenkins Michael A, Jose Shibu, White Peter S
National Park Service, Great Smoky Mountains National Park, Twin Creeks Natural Resources Center, 1314 Cherokee Orchard Road, Gatlinburg, Tennessee 37738, USA.
Ecol Appl. 2007 Apr;17(3):869-81. doi: 10.1890/06-1027.
Because of the high calcium content of its foliage, Cornus florida (flowering dogwood) has been described as a calcium "pump" that draws calcium from deeper mineral soil and enriches surface soil horizons. However, over the last two decades an exotic fungal disease (dogwood anthracnose, Discula destructiva) has decimated populations of this once-common understory species. Its loss, combined with forest stand development, could alter intra-stand calcium cycling. We used data from long-term vegetation monitoring plots to examine the ecological role of C. florida in calcium cycling and to identify changes in annual foliar calcium cycling over a 20-year period between two sampling intervals, 1977-1979 (preanthracnose) and 1995-2000 (post-anthracnose). Published equations were used to estimate foliar biomass per species for five forest types: alluvial, typic cove, acid cove, oak-hickory, and oak-pine. Calcium concentrations derived from foliage samples were used to estimate annual foliar calcium production per species for understory woody stems (<20 cm dbh) and total foliar calcium production for overstory stems (> or =20 cm dbh). At a given level of soil calcium availability, C. florida foliage contained greater concentrations of calcium than three other dominant understory species (Tsuga canadensis, Acer rubrum, and Rhododendron maximum). Between 1977-1979 and 1995-2000, the annual calcium contributions of understory woody vegetation declined across all forest types, ranging from 26% in oak-pine stands to 49% in acid coves. Loss of C. florida was responsible for only 13% of this decline in oak-pine stands, but accounted for 96% of the decline in typic coves. In oak-hickory and oak-pine stands, we observed large increases in the foliar biomass of T. canadensis, a species whose calcium-poor foliage increases soil acidity. Increases in overstory foliar biomass and calcium offset understory losses in three forest types (alluvial, typic coves, and oak-pine) but not in oak-hickory and acid cove stands. Overall, calcium cycling in oak-hickory stands was more negatively affected by the loss of C. florida than the other forest types. Oak-hickory forests comprise over a third of the total forest cover in the eastern United States, and decreases in annual calcium cycling could have cascading effects on forest biota.
由于其叶片中钙含量高，多花梾木（花楸树）被描述为一个钙“泵”，它从更深层的矿质土壤中吸收钙并富集表层土壤层。然而，在过去二十年里，一种外来真菌病害（山茱萸炭疽病，毁灭盘多毛孢）使这种曾经常见的林下物种数量锐减。它的消失，再加上林分发育，可能会改变林分内的钙循环。我们利用长期植被监测样地的数据，研究多花梾木在钙循环中的生态作用，并确定在1977 - 1979年（炭疽病之前）和1995 - 2000年（炭疽病之后）这两个采样间隔之间的20年里，每年叶片钙循环的变化。使用已发表的方程来估算五种森林类型中每个物种的叶片生物量：冲积林、典型小海湾林、酸性小海湾林、橡木 - 山核桃林和橡木 - 松林。从叶片样本中得出的钙浓度用于估算林下木质茎（胸径<20厘米）每个物种的年叶片钙产量以及林冠层茎（胸径≥20厘米）的总叶片钙产量。在给定的土壤钙有效性水平下，多花梾木叶片中的钙浓度高于其他三种主要林下物种（加拿大铁杉、红槭和大花杜鹃）。在1977 - 1979年至1995 - 2000年期间，所有森林类型林下木质植被的年钙贡献都有所下降，从橡木 - 松林的26%到酸性小海湾林的49%不等。在橡木 - 松林，多花梾木的消失仅导致了这种下降的13%，但在典型小海湾林下降中占96%。在橡木 - 山核桃林和橡木 - 松林，我们观察到加拿大铁杉的叶片生物量大幅增加，该物种叶片含钙量低会增加土壤酸度。在三种森林类型（冲积林、典型小海湾林和橡木 - 松林）中，林冠层叶片生物量和钙的增加抵消了林下的损失，但在橡木 - 山核桃林和酸性小海湾林样地中没有抵消。总体而言，与其他森林类型相比，多花梾木的消失对橡木 - 山核桃林的钙循环负面影响更大。橡木 - 山核桃林占美国东部森林总面积的三分之一以上，年钙循环的减少可能会对森林生物群产生连锁反应。
