Hurd T M, Raynal D J, Schwintzer C R
Faculty of Environmental and Forest Biology, State University of New York College of Environmental Science and Forestry, 13210, Syracuse, NY, USA.
Department of Biological Sciences, University of Maine, Orono, 04469-5722, Orono, ME, USA.
Oecologia. 2001 Jan;126(1):94-103. doi: 10.1007/s004420000500. Epub 2001 Jan 1.
Surface waters in forested watersheds in the Adirondack Mountains and northern New York State are susceptible to nitrogen (N) saturation. Atmospheric deposition of N to watersheds in this region has been measured but the extent of internal N inputs from symbiotic N fixation in alder-dominated wetlands is not known. We estimated N fixation by speckled alder in these wetlands by the N natural abundance method and by acetylene reduction using a flow-through system. Foliar N derived from fixation (%N) was estimated for five wetlands. The δN of speckled alder foliage from four of the five sites did not differ significantly (P≤0.05) from that of nodulated speckled alders grown in N-free water culture (-1.2±0.1‰). Estimates from the N natural abundance method indicated that alders at these sites derive 85-100% of their foliar N from N fixation. At one of the sites, we also measured biomass and N content and estimated that the alder foliage contained 43 kg N ha of fixed N in 1997. This estimate was based on a foliar N content of 55.4±7 kg N ha (mean±SE), 86±4%N, and an assumption that 10% of foliar N was derived from reserves in woody tissues. At this site, we further estimated via acetylene reduction that 37±10 kg N ha was fixed by speckled alders in 1998. This estimate used the theoretical 4:1 CH reduction to N fixation ratio and assumed no night-time fixation late in the season. Nitrogen inputs in wet and dry deposition at this site are approximately 8 kg N ha year. We conclude that speckled alder in wetlands of northern New York State relies heavily on N fixation to meet N demands, and symbiotic N fixation in speckled alders adds substantial amounts of N to alder-dominated wetlands in the Adirondack Mountains. These additions may be important for watershed N budgets, where alder-dominated wetlands occupy a large proportion of watershed area.
阿迪朗达克山脉和纽约州北部森林流域的地表水易受氮（N）饱和影响。该地区流域的大气氮沉降已被测量，但桤木主导的湿地中来自共生固氮的内部氮输入程度尚不清楚。我们通过氮自然丰度法和使用流通系统的乙炔还原法估算了这些湿地中斑点桤木的固氮量。对五个湿地的固氮衍生叶氮（%N）进行了估算。五个地点中有四个地点的斑点桤木叶的δN与在无氮水培中生长的结瘤斑点桤木的δN没有显著差异（P≤0.05）（-1.2±0.1‰）。氮自然丰度法的估算表明，这些地点的桤木叶氮的85 - 100%来自固氮。在其中一个地点，我们还测量了生物量和氮含量，并估计1997年桤木叶含有43千克氮/公顷的固定氮。该估计基于叶氮含量为55.4±7千克氮/公顷（平均值±标准误差），86±4%N，并假设10%的叶氮来自木质组织中的储备。在该地点，我们通过乙炔还原进一步估算，1998年斑点桤木固定了37±10千克氮/公顷。该估计使用了理论上4:1的乙炔还原与固氮比率，并假设季节后期没有夜间固氮。该地点的湿沉降和干沉降中的氮输入约为8千克氮/公顷·年。我们得出结论，纽约州北部湿地中的斑点桤木严重依赖固氮来满足氮需求，斑点桤木中的共生固氮为阿迪朗达克山脉中桤木主导型湿地增加了大量的氮。这些增加对于流域氮预算可能很重要，因为桤木主导的湿地在流域面积中占很大比例。
