Downs Martha R, Nadelhoffer Knute J, Melillo Jerry M, Aber John D
Marine Biological Laboratory, The Ecosystems Center, 02543, Woods Hole, MA, USA.
Complex Systems Research Center, University of New Hampshire, 03824, Durham, NH, USA.
Oecologia. 1996 Jan;105(2):141-150. doi: 10.1007/BF00328539.
Effects of chronic HNO and HSO additions on decomposition of senesced birch leaf, beech leaf, spruce needle, and wood chip litters were examined. Litters were incubated for up to 4 years in fiberglass mesh (1 mm) bags on experimental plots in a mixed-species forest near the Bear Brooks Watershed Manipulation (BBWM) site in eastern Maine, United States. Plot treatments included HNO additions at 28 and 56 kg N·ha·year, HSO additions at 128 kg S·ha·year, and a combined HNO and HSO treatment at 28 kg N and 64 kg S ·ha·year. The N content of all NO added was artificially increased to 344% δN. Litter bags were collected each fall and analyzed for organic matter loss, nitrogen concentration, and N abundance throughout the 4-year experiment. Extractive (non-polar-soluble+water-soluble), cellulose (acid-soluble), and lignin (acid-insoluble) fractions were analyzed for the first 2 years. In wood chips, nitrogen additions increased mass loss and N concentration, but not the mass of N after 4 years. Neither N nor S additions had large effects on mass loss, N concentration, or N content of leaf litters. All litters immobilized and mineralized N simultaneously, but we were able to place a lower bound on gross N immobilization by mass balancing N additions. Birch and spruce litters showed net mineralization, while beech leaf and wood chip litters showed net immobilization. Net immobilizing litters were those with the highest initial cellulose concentration (wood chips=80% beech leaves=54%), and we attribute the higher capacity for immobilization to more readily available carbon. Lignin mass increased initially in all litter types except spruce needles. Also, extractives in net immobilizing litters either increased initially (wood chips) or decreased at a slower rate than bulk litter (beech leaves). We calculate the potential of decomposing litter to immobilize exogenous nitrate in this system to be 1-1.5 kg N·ha·year, which is about half of the usual NO deposition at this site, but only a small fraction of the experimental addition.
研究了长期添加硝酸（HNO）和硫酸（HSO）对衰老桦树叶、山毛榉叶、云杉针叶和木屑凋落物分解的影响。在美国缅因州东部熊溪流域操纵（BBWM）站点附近的混交林中，将凋落物置于玻璃纤维网袋（1毫米）中，在实验地块上培养长达4年。地块处理包括每年每公顷添加28千克和56千克氮的硝酸添加处理、每年每公顷添加128千克硫的硫酸添加处理，以及每年每公顷添加28千克氮和64千克硫的硝酸与硫酸联合添加处理。所有添加的硝酸中的氮含量人为提高到344%δN。在整个4年的实验中，每年秋季收集凋落物袋，分析其有机质损失、氮浓度和氮含量。对前两年的提取物（非极性可溶性+水溶性）、纤维素（酸溶性）和木质素（酸不溶性）部分进行了分析。在木屑中，添加氮增加了质量损失和氮浓度，但4年后氮的质量没有增加。添加氮和硫对树叶凋落物的质量损失、氮浓度或氮含量都没有很大影响。所有凋落物同时固定和矿化氮，但我们能够通过对添加氮进行质量平衡来确定总氮固定的下限。桦树和云杉凋落物表现出净矿化，而山毛榉叶和木屑凋落物表现出净固定。净固定凋落物是那些初始纤维素浓度最高的凋落物（木屑=80%，山毛榉叶=54%），我们将较高的固定能力归因于更易获得的碳。除云杉针叶外，所有凋落物类型的木质素质量最初都有所增加。此外，净固定凋落物中的提取物要么最初增加（木屑），要么比整体凋落物（山毛榉叶）下降得更慢。我们计算出该系统中分解凋落物固定外源硝酸盐的潜力为每年每公顷1 - 1.5千克氮，这约为此处通常的硝酸沉降量的一半，但只是实验添加量的一小部分。
