Sah Shambu P, Ilvesniemi Hannu
Department of Forest Ecology, University of Helsinki, Latokartanonkaari 7, PL 27, FIN 00014 Helsinki, Finland.
Isotopes Environ Health Stud. 2006 Dec;42(4):367-77. doi: 10.1080/10256010600991094.
This study presents the impacts of clear-cutting and site preparation on soil and needle 15N-fractionation of Scots pine (Pinus sylvestris, L.) and Norway spruce (Picea abies (L.), Karst). Three microsites on different methods of site preparation were used: (i) mound (broken O/E/B horizons piled upside down over undisturbed humus), (ii) deep (exposed C-horizon) and (iii) shallow (exposed E/B horizon). We found significant differences between species, between closed forest and clear-cuts as well as between different site preparations. For instance, in the context of interspecific variations, the mean needle nitrogen concentrations of both seedlings (1.15,+/-0.10 %) and mature (1.09,+/-0.07 %) pine trees were significantly higher compared to corresponding needle concentrations of seedlings (0.88,+/-0.06 %) and mature trees (0.79,+/-0.02 %) of spruce. Similarly, we observed significantly more 15N-enriched needles of mature spruces (-4.0,+/-0.20 per thousand) as well as of seedlings (-5.0,+/-0.11 per thousand) relative to that of mature pine needles (-5.6,+/-0.10 per thousand) and seedlings (-6.0,+/-0.31 per thousand). These variations were assumed to be caused by the variation in mycorrhizal associations between the species. We assume that the proportion of mycorrhizal N-uptake of pines might have been larger than that of spruce. Regarding the clear-cut effects on N and 15N of both tree species, we observed that, in the mature natural stand, needle N concentrations of both pine (1.09,+/-0.07 %) and spruce (0.79,+/-0.02 %) tree species did not change significantly after clear-cutting (pine: 1.01,+/-0.06 %; spruce: 0.74,+/-0.04 % ). However, clear-cutting resulted in the significant increase in needle 15N natural abundance of both pine (-2.70,+/-0.06 per thousand) and spruce (-2.09,+/-0.05 per thousand) in comparison to that of natural stand (pine:-5.60,+/-0.10 per thousand; spruce:-4.00,+/-0.20 per thousand), which is assumed to be due to the increased level of nitrification and leaching of nitrate after clear-cutting. In the context of site preparation methods, soil and needle N were observed to be more 15N-enriched in deep and shallow treatment sites compared to that of closed forest site and untreated clear-cut site, which indicated that the main source of N uptake seems to be mainly directly from the soil of the corresponding horizons of mineral soil with higher delta15N.
本研究展示了皆伐和整地对苏格兰松（Pinus sylvestris, L.）和挪威云杉（Picea abies (L.), Karst）土壤及针叶氮同位素分馏的影响。研究采用了三种不同整地方法的微生境：（i）土堆（将破碎的O/E/B层颠倒堆放在未扰动的腐殖质上），（ii）深翻（暴露C层）和（iii）浅翻（暴露E/B层）。我们发现不同物种之间、郁闭森林和皆伐地之间以及不同整地方法之间存在显著差异。例如，在种间差异方面，与云杉幼苗（0.88±0.06%）和成熟树木（0.79±0.02%）相应的针叶浓度相比，松树幼苗（1.15±0.10%）和成熟树木（1.09±0.07%）的平均针叶氮浓度显著更高。同样，相对于成熟松树针叶（-5.6±0.10‰）和幼苗（-6.0±0.31‰），我们观察到成熟云杉（-4.0±0.20‰）以及幼苗（-5.0±0.11‰）中有显著更多的15N富集针叶。这些差异被认为是由物种间菌根共生关系的差异所导致。我们推测松树菌根氮吸收的比例可能大于云杉。关于皆伐对两种树种氮和15N 的影响，我们观察到，在成熟天然林中，皆伐后松树（1.09±0.07%）和云杉（0.79±0.02%）的针叶氮浓度均未显著变化（松树：1.01±0.06%；云杉：0.74±0.04%）。然而，与天然林相比（松树：-5.60±0.10‰；云杉：-4.00±0.20‰），皆伐导致松树（-2.7±0.06‰）和云杉（-2.09±0.05‰）针叶15N自然丰度显著增加，这被认为是由于皆伐后硝化作用水平提高和硝酸盐淋溶增加所致。在整地方法方面，与郁闭森林地和未处理的皆伐地相比，深翻和浅翻处理地的土壤和针叶氮的15N富集程度更高，这表明氮吸收的主要来源似乎主要直接来自具有较高δ15N的矿质土壤相应层位的土壤。
