Winter as a driver of nitrogen cycle responses to environmental change: responses of leguminous plants to variability in freezing

氮是植物生长的关键土壤养分。因此，深入了解影响氮素有效性的因素对于预测植物对环境变化的反应至关重要。冬季条件变化引起的土壤冻结变化会对土壤微生物和植物根系的活动产生重大影响，从而改变植物在接下来的生长季节中的氮素有效性和吸收。然而，一个重要的问题是，土壤氮素对严重冰冻事件的反应是否可以持续较长时间。虽然被冻结破坏的土壤微生物和植物根系的数量可以在第二年恢复，但冻结驱动的不同多年生植物物种的类型和丰度的变化可能对土壤氮产生持久的影响，因为分解植物材料的氮含量在物种之间存在差异。豆科植物可以通过与专门的细菌合作直接从空气中获得氮，可能比其他植物物种对冷冻更敏感。鉴于豆类的分解可以大大增加土壤氮，豆类数量的变化对冬季变化的反应可能对土壤肥力产生强烈影响。关于这一主题的研究特别及时和重要，因为暖冬导致积雪减少，这可能增加土壤中越冬植物的冻结。 我的研究计划的总体目标是解决如何限制豆科植物的耐冻性可以影响冬季过程控制土壤氮的可用性在自然植物群落（如草地）和管理的生态系统（农田）的程度。在受控生长条件下和在现场使用的实验相结合，我将测试新的假设，增加冷冻强度降低了豆科植物的生存和生长不成比例地相对于非豆科植物。然后，我将使用更大规模的多年田间试验结合氮示踪技术，以研究如何致命或亚致命的冻害豆类影响的数量和时间的氮供应在随后的植物生长季节。除了提供有关自然环境土壤肥力变化的重要知识，以应对天气和气候变化的变化，这项研究将大大有助于在应用场景中有效利用豆科植物，如农业覆盖作物混合物和选择物种恢复本地植物群落。虽然冬季生物学在高山和北极系统中得到了最广泛的探索，但我的研究将集中在北方温带地区的植物上，其中包括加拿大人口最多的农业地区。

Nitrogen is a key soil nutrient for plant growth. Therefore, a thorough understanding of the factors that affect nitrogen availability is crucial for predicting plant responses to environmental variation. Changes in soil freezing resulting from variation in winter conditions can have a substantial influence on the activities of soil microbes and plant roots, and thus can alter nitrogen availability and uptake by plants over the following growing season. However, an important question is whether soil nitrogen responses to severe freezing events can persist over the longer term. Although populations of soil microbes and plant root systems disrupted by freezing can recover by the next year, freezing-driven changes in the types and abundances of different perennial plant species could have lasting effects on soil nitrogen, because the nitrogen content of decomposing plant material differs among species. Legumes, which are plants that can obtain nitrogen directly from the air by partnering with specialized bacteria, may be more sensitive to freezing than other plant species. Given that the decomposition of legumes can increase soil nitrogen substantially, changes in legume numbers in response to changing winters could have strong effects on soil fertility. Research on this topic is particularly timely and important given that warmer winters are resulting in decreased snow cover, which can increase the freezing of plants that overwinter in soil. The overarching objective of my research program is to address how limits to the freezing tolerances of legumes can influence the extent to which winter processes control soil nitrogen availability both in natural plant communities (e.g. grassland) and managed ecosystems (cropland). Using a combination of experiments under controlled growth conditions and in the field, I will test the novel hypothesis that increased freezing intensity reduces the survival and growth of legumes disproportionately relative to non-leguminous plants. I will then use larger scale, multi-year field experiments in combination with nitrogen tracer techniques to examine how lethal or sublethal freezing damage to legumes affect the amount and timing of nitrogen availability over subsequent plant growing seasons. In addition to providing important knowledge regarding changes in the soil fertility of natural environments in response to variation in weather and climate change, this research will contribute significantly to the effective use of legumes in applied scenarios, such as in agricultural cover crop mixtures and in the selection of species for the restoration of native plant communities. Although winter biology has been explored most extensively in alpine and arctic systems, my research will focus on plants in northern temperate regions, which include the most highly populated and agricultural regions of Canada.