Purpose

The short growing season and cold climate of the boreal forest can restrict soil nitrogen availability, limiting plant growth and ecosystem productivity. Vascular nitrogen-fixing plants should have an advantage in low nitrogen environments. Yet, their abundance in the boreal forest is low. How nitrogen fixation is affected when temperature differences occur between the soil and air, especially in the spring when soil temperatures remain cool, has not been documented in actinorhizal shrubs.

Methods

A lab study was performed on Alnus alnobetula subsp. crispa (Aiton) Raus. For 13 weeks, soil was kept at either 10˚C, 14˚C or 16˚C, independently of shoot temperature, at 20˚C.

Results

Soils at 14˚C and 10˚C inhibited whole-plant nitrogen fixation (by 53% and 68%) and photosynthesis (by 43% and 39%), respectively, compared to soils at 16˚C. Reductions in photosynthetic rate were mainly attributed to a reduction in the fixed nitrogen supply and subsequent reduction in chlorophyll formation. Photosynthesis was not reduced immediately, suggesting some utilization of a nitrogen source not supplied from current fixation. Reduced amounts of fixed nitrogen and photosynthates resulted in diminished biomass production and relative growth rate.

Conclusion

The assumed advantages of being a nitrogen-fixing plant in a low nitrogen environment may be constrained by soil temperature to a larger extent than previously considered. This may restrict the abundance of nitrogen-fixing species in the boreal forest.

中文翻译：

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土壤温度限制了北方放线根灌木的固氮、光合作用和生长

目的

北方森林短暂的生长季节和寒冷的气候会限制土壤氮的可用性，限制植物生长和生态系统生产力。维管固氮植物在低氮环境中应具有优势。然而，它们在北方森林中的数量很少。当土壤和空气之间出现温差时，尤其是在土壤温度保持凉爽的春季，固氮作用如何受到影响，尚未在放线根灌木中得到记载。

方法

对Alnus alnobetula subsp.进行了一项实验室研究。脆皮（艾顿）劳斯。在 13 周内，土壤保持在 10°C、14°C 或 16°C，与地上部温度无关，保持在 20°C。

结果

与 16°C 的土壤相比，14°C 和 10°C 的土壤分别抑制了整株植物的固氮（53% 和 68%）和光合作用（43% 和 39%）。光合速率的降低主要归因于固定氮供应的减少和随后叶绿素形成的减少。光合作用并没有立即减少，这表明对当前固定不提供的氮源进行了一些利用。固定氮和光合产物的减少导致生物质产量和相对增长率的降低。

结论

在低氮环境中作为固氮植物的假定优势可能在更大程度上受到土壤温度的限制。这可能会限制北方森林中固氮物种的丰度。