华北落叶松种子萌发与幼苗生长对暖干化气候的响应机制研究

The climate is increasingly warming and drying in northern China, which is obviously unfavorable for development of the cold temperate coniferous forests in this region. Effects of climate change on the radial growth of large trees have been well studied. While seedling is essential to tree population dynamics, which is mostly sensitive to the changes of temperature and water, seedling responses of early growth to climate change has become concerned now. Larix principis-rupprechitii is one of the dominant trees of cold temperate coniferous forests in mountainous regions of northern China. In the proposed project, we will study response mechanisms of seed germination and seedling growth of Larix principis-rupprechitii to warming and drying climate. We will collect seeds along an elevation gradient (high, middle and low) and establish reciprocal sowing and transplanting experiments at the seed collection sites. At the same time，we will conduct controlled greenhouse experiments to carry out the research. We will determine seed germination phenology, seedling morphological and anatomical (microscopic and ultramicroscopic structure) responses of absorption, transportation and photosynthetic tissues, as well as physiological regulations of water transportation, water use and physiological photosynthesis. On these bases, we will analyze the relationship between the seedling growth characteristics and the changes of environment factors such as water and temperature, reveal response mechanisms of seed germination and seedling growth to warming and drying. The results from this project will improve our understanding of the impacts of warming and drying to cold temperate coniferous forests in northern China. It will significantly benefit to accurately assess the dynamics of forest communities in the future of northern China, and it also has theoretical and practical significances in making corresponding strategies to mitigate the impacts of climate change.

中国华北山地暖干化气候趋势显著，不利于寒温性针叶林的生存与发展，目前多侧重于气候变化对大树径向生长的影响研究，而树木早期生长对水热条件的变化更加敏感，影响种群发展动态，逐渐受到关注。本项目以华北山地寒温性针叶林主要建群种华北落叶松(Larix principis-rupprechtii) 为研究对象，通过林区不同海拔种源的交互播种和栽植试验，结合温室气候控制试验，追踪种子出苗物候变化特征，分析幼苗水分吸收、输导与光合组织的形态结构响应，测定幼苗水分运输、利用与光合生产的生理反应，探讨幼苗生长特性与环境水热因子变化之间的关系，揭示华北落叶松种子萌发与幼苗生长对暖干化气候的响应机制。该项目的成功研究将增进气候变化对华北寒温性针叶林影响作用的理解，对准确评估华北森林群落发展动态并制定应对气候变化策略具重要的理论意义和实践价值。

森林对气候变化敏感，林木早期生长对气候变化的响应研究日益受到关注。华北山地气候暖干化趋势明显，不利于寒温性针叶林的生存与发展。本项目以华北山地寒温性针叶林主要建群种华北落叶松（Larix principis-rupprechtii）为研究对象，通过温室气候控制结合林区栽植试验，研究气候变化对林木种子萌发与幼苗生长的影响，集中于水分的吸收、运输与利用等关键生命问题，从形态响应、结构变化和生理调节等层面，揭示林木早期生长对气候变化的响应能力、生长策略与生态适应性。结果表明：（1）华北落叶松对暖干化气候敏感，种子出苗期延迟，出苗率降低，针叶碳摄取与根部碳储藏受到限制，幼苗死亡率增加。（2）干旱时，幼苗株高降低，叶面积减少，根系活力、茎部导水率与组织相对含水量下降，光合速率与蒸发率降低。幼苗通过器官之间协调统一的生长与结构调整、生理调节等，减弱气候变化造成的伤害。（3）幼苗采取增加根部生物量分配、优先满足根系的生长策略；启动抗氧化系统、积累渗透调节物质、增加针叶保水力、提高水分利用效率等生理调节。（4）根冠、表皮、周皮等保护组织更发达，根、茎、针叶皮层细胞内容物增多，茎部木质部增加，气孔器数量减少，气孔开度降低，叶肉细胞的细胞壁更多下陷皱褶。（5）幼苗虽可通过生长调整、结构变化与生理调节等，一定程度上适应气候变化，但未来暖干化气候趋势下，幼苗将遭受更严重胁迫，影响种群发展。本研究可为干旱地区的人工林营造和苗木管护提供理论依据，并有助于认识气候变化对华北山地寒温性针叶林更新动态过程的影响机制。