Carbon (C) and nitrogen (N) cycling are key ecosystem functions potentially altered by heavy metal pollution. We used an ecosystem approach to study the long-term effect of lead (Pb) on C and N cycles in a natural grassland in a former shooting range. Microbial activity was evaluated by substrate-induced respiration (SIR) in situ, adding isotopically labelled C4-sugar to the soil. C and N contents and natural abundance of isotopes were measured in grass leaves, soil and microbial biomass together with root biomass. A reduced microbial activity and microbial biomass per area, together with a higher soil C stock and C:N ratio suggested a lower microbial decomposition in high Pb compared to low Pb areas. A more closed N cycle in the high Pb area was indicated by 2–3‰ lower δ15N in leaves and soil compared to low Pb areas. Higher δ13C in leaves and higher root biomass but similar leaf nutrient contents indicated plant responses and adaptions to the high Pb. The applied ecosystem approach revealed that Pb slowed down the C and N cycles, possibly by indirect effects rather than by direct toxicity. The ecosystem seems to have adapted to altered conditions.

中文翻译：

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使用稳定同位素（δ13C 和 δ15N）和微生物、植物和土壤参数评估铅污染草地的碳和氮循环

碳（C）和氮（N）循环是可能被重金属污染改变的关键生态系统功能。我们使用生态系统方法研究了铅 (Pb) 对原射击场天然草地 C 和 N 循环的长期影响。通过原位底物诱导呼吸 (SIR) 评估微生物活性，将同位素标记的 C4-糖添加到土壤中。在草叶、土壤和微生物生物量以及根生物量中测量了 C 和 N 含量以及同位素的自然丰度。微生物活性和单位面积微生物生物量的降低，以及较高的土壤碳储量和 C:N 比表明，与低铅地区相比，高铅地区的微生物分解较低。与低 Pb 区域相比，叶子和土壤中的 δ15N 低 2–3‰，表明高 Pb 区域的 N 循环更加封闭。叶子中较高的 δ13C 和较高的根生物量但相似的叶子营养成分表明植物对高铅的反应和适应。应用的生态系统方法表明，铅减缓了 C 和 N 循环，可能是通过间接影响而不是直接毒性。生态系统似乎已经适应了变化的条件。