Nitrogen deposition potentially contributes to oak regeneration failure in the Midwestern temperate forests of the USA
Nitrogen deposition potentially contributes to oak regeneration failure in the Midwestern temperate forests of the USA
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DOI：
10.1007/s00442-014-3119-z
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发表时间：
2015-01-01
期刊：
影响因子：
2.7
通讯作者：
Borden, Kara K.
中科院分区：
文献类型：
--
作者：
BassiriRad, Hormoz;Lussenhop, John F.;Borden, Kara K.
为了验证美国中西部北部森林中红橡树再生失败的部分原因是氮负荷增加的假设，我们在两个以橡树为主、大气氮沉降不同的林点进行了为期7年的野外研究。这些地点分别位于伊利诺伊州库克县的Swallow Cliffs （SC）和印第安纳州波特县的Indiana Dunes National lakesshore （IDNL）。试验前22年的NO3（-）年湿沉降在IDNL显著高于SC站点。普通园林试验结果表明，与SC相比，IDNL对橡树幼苗生物量降低了60%，而对枫幼苗生长几乎没有场地效应。试验施氮也使杉木幼苗总生物量减少45%，但对无氮生长条件下的生物量影响不显著。枫树幼苗对试验施肥反应不大。在IDNL处理下，成熟栎树的生长速率也较低，但比幼苗的生长速率低得多。枫树在不同地点间差异不显著。结果表明：(1)慢性氮负荷对红橡树苗木生长不利，对糖枫苗木生长不利；(2)幼苗建立期而非成树期可能是氮素负荷不利影响的目标期。氮素对这些共生物种差异效应的确切机制尚不清楚，但可能与生物量分配和氮素分配的可塑性不同有关。
We conducted a 7-year field study at two oak-dominated forest sites which differ in their atmospheric N deposition to test the hypothesis that red oak regeneration failure in the upper Midwestern US forests, at least in part, results from increased N load. The sites are located in Swallow Cliffs (SC) in Cook County, Illinois, and Indiana Dunes National Lakeshore (IDNL) in Porter County, Indiana. Annual wet NO3 (-) deposition for the 22 years immediately prior to the experiments was significantly higher in IDNL than in the SC site. Results from common garden experiments showed that oak seedling biomass was 60 % lower at IDNL compared with SC, but there was little site effect on growth of maple seedlings. Experimental N addition also resulted in a 45 % decrease in the total biomass of the oak seedlings at SC, but had no significant effect on the biomass at IDNL. Maple seedlings responded little to experimental fertilization. The growth rate of mature oak trees was also lower at IDNL but to a much smaller extent than that of seedlings. Maple trees did not significantly differ between sites. We conclude that: (1) chronic N load adversely affects seedling performance of red oak, but not sugar maple, in these temperate forests; and (2) the seedling establishment phase rather than the adult tree is the likely target stage for this adverse effect of N loading. The exact mechanisms for the differential effects of N on these co-occurring species are not clear, but different plasticity in fractional biomass and N allocation to the leaves might be involved.