Buchmann N, Schulze E-D, Gebauer G
Lehrstuhl Pflanzenökologie, Universität Bayreuth, Postfach 10 12 51, D-95440, Bayreuth, Germany.
Oecologia. 1995 Jun;102(3):361-370. doi: 10.1007/BF00329803.
Throughfall nitrogen of a 15-year-old Picea abies (L.) Karst. (Norway spruce) stand in the Fichtelgebirge, Germany, was labeled with either N-ammonium or N-nitrate and uptake of these two tracers was followed during two successive growing seasons (1991 and 1992). N-labeling (62 mg N m under conditions of 1.5 g N m atmospheric nitrogen deposition) did not increase N concentrations in plant tissues. The N recovery within the entire stand (including soils) was 94%±6% of the applied N-ammonium tracer and 100%±6% of the applied N-nitrate tracer during the 1st year of investigation. This decreased to 80%±24% and 83%±20%, respectively, during the 2nd year. After 11 days, the N tracer was detectable in 1-year-old spruce needles and leaves of understory species. After 1 month, tracer was detectable in needle litter fall. At the end of the first growing season, more than 50% of the N taken up by spruce was assimilated in needles, and more than 20% in twigs. The relative distribution of recovered tracer of both N-ammonium and N-nitrate was similar within the different foliage age classes (recent to 11-year-old) and other compartments of the trees. N enrichment generally decreased with increasing tissue age. Roots accounted for up to 20% of the recovered N in spruce; no enrichment could be detected in stem wood. Although N-ammonium and N-nitrate were applied in the same molar quantities (NH : NO =1:1), the tracers were diluted differently in the inorganic soil N pools (NH /NH : NO /NO =1:9). Therefore the measured N amounts retained by the vegetation do not represent the actual fluxes of ammonium and nitrate in the soil solution. Use of the molar ammonium-to-nitrate ratio of 9:1 in the soil water extract to estimate N uptake from inorganic N pools resulted in a 2-4 times higher ammonium than nitrate uptake by P. abies.
在德国菲希特尔山，对一片15年生的欧洲云杉（Picea abies (L.) Karst.）林分的穿透雨氮分别用铵态氮或硝态氮进行标记，并在连续两个生长季节（1991年和1992年）跟踪这两种示踪剂的吸收情况。在大气氮沉降量为1.5 g N m 的条件下进行氮标记（62 mg N m ），并未增加植物组织中的氮浓度。在调查的第一年，整个林分（包括土壤）中铵态氮示踪剂的氮回收率为施用氮的94%±6%，硝态氮示踪剂的氮回收率为施用氮的100%±6%。在第二年，这一比例分别降至80%±24%和83%±20%。11天后，在1年生云杉针叶和林下物种的叶片中可检测到氮示踪剂。1个月后，在针叶凋落物中可检测到示踪剂。在第一个生长季节结束时，云杉吸收的氮中超过50%在针叶中被同化，超过20%在小枝中被同化。铵态氮和硝态氮示踪剂回收物在不同叶龄类（新叶至11年生叶）和树木的其他部分中的相对分布相似。氮富集一般随组织年龄增加而降低。云杉根系中回收的氮占比高达20%；在茎干木材中未检测到富集。尽管铵态氮和硝态氮的施用量摩尔比相同（NH : NO =1:1），但示踪剂在无机土壤氮库中的稀释情况不同（NH /NH : NO /NO =1:9）。因此，植被保留的实测氮量并不代表土壤溶液中铵和硝酸盐的实际通量。使用土壤水提取物中铵与硝酸盐的摩尔比为9:1来估算从无机氮库中吸收的氮，导致欧洲云杉吸收的铵比硝酸盐高2至4倍。
