PDF(Pubmed)
Abstract：
OBJECTIVE: Reduced snow cover and increased air temperature variability are predicted to expose overwintering herbaceous plants to more severe freezing in some northern temperate regions. Legumes are a key functional group that may exhibit lower freezing tolerance than other species in these regions, but this trend has been observed only for non-native legumes. Our aim was to confirm if this trend is restricted to non-native legumes or whether native legumes in these regions also exhibit low freezing tolerance.
METHODS: First, we transplanted legumes (five non-native species and four native species) into either an old field (non-native) or a prairie (native) and used snow removal to expose the plots to increased soil freezing. Second, we grew plants in mesocosms (old field) and pots (prairie species) and exposed them in controlled environment chambers to a range of freezing treatments (control, 0, -5 or -10 °C) in winter or spring. We assessed freezing responses by comparing differences in biomass, cover and nodulation between freezing (or snow removal) treatments and controls.
RESULTS: Among legume species, lower freezing tolerance was positively correlated with a lower proportion of nodulated plants and active nodules, and under controlled conditions, freezing-induced reductions in above-ground biomass were lower on average in native legumes than in non-native legumes. Nevertheless, both non-native and native legumes (except Desmodium canadense) exhibited greater reductions in biomass in response to increased freezing than their non-leguminous neighbours, both in controlled environments and in the field.
CONCLUSIONS: These results demonstrate that both native and non-native legumes exhibit low freezing tolerance relative to other herbaceous species in northern temperate plant communities. By reducing legume biomass and nodulation, increased soil freezing could reduce nitrogen inputs into these systems.
METHODS: First, we transplanted legumes (five non-native species and four native species) into either an old field (non-native) or a prairie (native) and used snow removal to expose the plots to increased soil freezing. Second, we grew plants in mesocosms (old field) and pots (prairie species) and exposed them in controlled environment chambers to a range of freezing treatments (control, 0, -5 or -10 °C) in winter or spring. We assessed freezing responses by comparing differences in biomass, cover and nodulation between freezing (or snow removal) treatments and controls.
RESULTS: Among legume species, lower freezing tolerance was positively correlated with a lower proportion of nodulated plants and active nodules, and under controlled conditions, freezing-induced reductions in above-ground biomass were lower on average in native legumes than in non-native legumes. Nevertheless, both non-native and native legumes (except Desmodium canadense) exhibited greater reductions in biomass in response to increased freezing than their non-leguminous neighbours, both in controlled environments and in the field.
CONCLUSIONS: These results demonstrate that both native and non-native legumes exhibit low freezing tolerance relative to other herbaceous species in northern temperate plant communities. By reducing legume biomass and nodulation, increased soil freezing could reduce nitrogen inputs into these systems.
摘要：
目的：预计降雪和气温变化的增加将使越冬草本植物在一些北温带地区遭受更严重的冰冻。豆科植物是一个关键的官能团，可能比这些地区的其他物种表现出更低的耐冻性，但这种趋势仅在非本地豆类中观察到。我们的目的是确认这种趋势是否仅限于非本地豆类，或者这些地区的本地豆类是否也表现出低的耐冻性。
方法：首先，我们将豆科植物（五个非本地物种和四个本地物种）移植到旧田地（非本地）或草原（本地）中，并使用除雪将地块暴露于增加的土壤冻结中。第二,我们在mesocosms（老田）和盆栽（草原物种）中种植植物，并将它们暴露在受控环境室中进行一系列冷冻处理（对照，0，-5或-10°C）在冬季或春季。我们通过比较生物量的差异来评估冻结反应，冷冻(或除雪)处理和控制之间的覆盖和结瘤。
结果：在豆科植物种类中，较低的耐冻性与较低的结瘤植物和活跃结节比例呈正相关，在受控条件下，天然豆科植物中冻结引起的地上生物量减少平均低于非天然豆科植物。然而，非本地豆科植物和本地豆科植物（除加拿大山楂属植物外）比非豆科植物的近邻因冻结增加而表现出更大的生物量减少，在受控环境和现场。
结论：这些结果表明，相对于北部温带植物群落中的其他草本物种，本地和非本地豆科植物均表现出较低的耐冻性。通过减少豆类生物量和结瘤，增加土壤冻结可以减少这些系统的氮输入。
方法：首先，我们将豆科植物（五个非本地物种和四个本地物种）移植到旧田地（非本地）或草原（本地）中，并使用除雪将地块暴露于增加的土壤冻结中。第二,我们在mesocosms（老田）和盆栽（草原物种）中种植植物，并将它们暴露在受控环境室中进行一系列冷冻处理（对照，0，-5或-10°C）在冬季或春季。我们通过比较生物量的差异来评估冻结反应，冷冻(或除雪)处理和控制之间的覆盖和结瘤。
结果：在豆科植物种类中，较低的耐冻性与较低的结瘤植物和活跃结节比例呈正相关，在受控条件下，天然豆科植物中冻结引起的地上生物量减少平均低于非天然豆科植物。然而，非本地豆科植物和本地豆科植物（除加拿大山楂属植物外）比非豆科植物的近邻因冻结增加而表现出更大的生物量减少，在受控环境和现场。
结论：这些结果表明，相对于北部温带植物群落中的其他草本物种，本地和非本地豆科植物均表现出较低的耐冻性。通过减少豆类生物量和结瘤，增加土壤冻结可以减少这些系统的氮输入。
