Purpose

Although plant functional type can modulate soils and their processes in natural, nitrogen (N)-limited ecosystems, little is known about their ability to influence soil N dynamics in urban ecosystems that have high excess N input. We investigated whether i) plant functional type effects on soil N dynamics in urban parks follow the same pattern as those in undisturbed natural/semi-natural forests, and ii) park age influences plant functional type effects on soil N dynamics under boreal climate.

Methods

We selected 13 urban parks of varying ages (young: 10 to 15, old: > 70 years), and 5 undisturbed natural/semi-natural forests (> 80 years) in southern Finland. In these parks and forests, we measured soil total N concentration, availability of inorganic N, nitrous oxide (N₂O) flux and earthworm biomass under three plant functional types (evergreen tree, deciduous tree, lawn).

Results

Our results showed that plant functional type influenced N dynamics also in urban greenspace soils, which may relate to the clear effect of plant functional type on earthworm biomass. Evergreen trees tended to have the highest ability to foster N accumulation and reduce N₂O emissions in urban parks. Moreover, with increasing park age, N accumulation increased under trees but decreased under lawns, further emphasising the role of vegetation in affecting soil N dynamics in urban greenspaces.

Conclusions

Our results show that, similar to natural/semi-natural forests, plant functional type, irrespective of park age, can influence soil N dynamics in urban parks.

中文翻译：

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植物功能类型对城市公园土壤中氮动态的影响与北方森林土壤相似

目的

尽管植物功能类型可以调节土壤及其在自然、氮 (N) 限制的生态系统中的过程，但人们对它们在具有大量过量 N 输入的城市生态系统中影响土壤 N 动态的能力知之甚少。我们调查了 i) 植物功能类型对城市公园土壤 N 动态的影响是否遵循与未受干扰的天然/半天然森林相同的模式，以及 ii) 公园年龄是否影响植物功能类型对北方气候下土壤 N 动态的影响。

方法

我们在芬兰南部选择了 13 个不同年龄的城市公园（年轻：10 到 15，老：> 70 岁）和 5 个未受干扰的天然/半天然森林（> 80 岁）。在这些公园和森林中，我们测量了三种植物功能类型（常绿乔木、落叶乔木、草坪）下的土壤总氮浓度、无机氮的有效性、一氧化二氮 (N ₂ O) 通量和蚯蚓生物量。

结果

我们的研究结果表明，植物功能类型也影响城市绿地土壤中的氮动态，这可能与植物功能类型对蚯蚓生物量的明显影响有关。常绿树木往往具有最高的促进氮积累和减少城市公园N _{2 O 排放的能力。}此外，随着公园年龄的增加，树下的氮积累增加而草坪下的积累减少，进一步强调了植被在影响城市绿地土壤氮动态中的作用。

结论

我们的研究结果表明，与天然/半天然林相似，植物功能类型，无论公园年龄如何，都会影响城市公园的土壤氮动态。