温带树木体内氮素向新梢的再循环分配对倒春寒的响应机制研究

The spring phenology for temperate ecological systems has been advanced under global warming, which leads to an increased risk of the late frost following a false spring. Some temperate regions have suffered a great ecological damage by late spring frost (LSF); hence it is of the necessary urgency to develop an available strategy to cope with the impact of LSF on temperate tree growth. During the spring growth of temperate trees, the major nitrogen (N) demand is met by the retranslocation of stored N towards newly growing shoots, but quite little has been documented about inherent N retranslocation (INR) and its driven mechanism during LSF. In the current Project plan, Changchun city will be chosen as the research area due to its overt false springs in continuously recent years. Four typical ornamental tree species are suggested to be employed as research materials, which will be studied as mature trees and juvenile seedlings under in field- and simulated-experiments, respectively, for the determinations of growth dynamic, photosynthetic and respiratory rates, carbohydrate metabolism, and membrane damage in newly growing shoots in response to LSF. Based on the technique of Labeling N by N-15 isotope, the response of INR will be precisely quantified, which will be subsequently used for the analysis on their relationship with growth, carbohydrate metabolism, and the activities of key enzymes in newly growing shoots so as to reveal the driven mechanism of INR. Results from these determinations and analyses can supply theoretical references for the strategies of tree growth management to cope with LSF.

在全球暖化作用下物候的提前增加了温带树木遭遇倒春寒冻害的风险，目前倒春寒已经给一些温带地区造成了大规模的生态损失，因此人们正在积极的探索应对倒春寒干扰的温带树木生长管理策略。树体内贮存氮（N）素向新梢的再循环分配是温带树木春季生长期间的主要N源，而有关倒春寒发生期间树体内源N素的再循环分配的响应机制的研究中尚存在诸多的盲点和不确定性。本项目拟以我国东北地区连续多年表现出倒春寒天气特征的长春市为研究区，以当地4个典型的绿化树种为研究对象，通过野外样地调查和室内模拟试验相结合的手段调查倒春寒的发生对树木的新梢生长、光合和呼吸速率、碳水化合物代谢和细胞膜损伤程度的影响，同时利用N-15同位素示踪技术精确计量内源N素春季再循环分配的响应，通过分析其与新梢生长和碳水化合物代谢及关键作用酶活性之间的关系来揭示内源N素再循环分配对倒春寒天气的关键响应机制，为制定应对倒春寒的树木生长管理策略提供理论参考。

在气候暖化的背景下，由春季提前回暖引发的倒春寒冻害事件的发生概率将可能继续增加。树体内贮存氮（N）素向新梢的再循环分配是温带树木春季生长期间的主要N源，是支持树木春季发芽生长的主要动力来源。本项目以长春市为研究区，以当地5个典型的绿化树种为研究对象，通过野外样地调查和室内模拟试验相结合的手段调查倒春寒的发生对树木的新梢生长、光合和呼吸速率、碳水化合物代谢和细胞膜损伤程度的影响，揭示受倒春寒影响生理生态学机理。结果显示：（1）长春地区倒春寒特征与其他国家相近纬度地区的历史结果接近，均呈现近年异常提前回暖后骤降的特征；（2）通过对最近10年以来的历史气象资料数据分析发现，长春地区的倒春寒天气迹象多次出现在两个阶段。一个是3月中下旬、另一个是4月早期。每次倒春寒发生规律不同，3月回暖期较为连续之后迅速骤降，而4月回暖期多呈波动跳跃式而后骤降频次高且影响期长；（3）当地5种园林绿化树木的新梢在4月上旬相继表现出受倒春寒冻害的迹象，山杏和柳树发芽较早因此受冻害较为明显，京桃和花楸次之，黑皮油松受冻害程度较轻；（4）控制实验结果表明，倒春寒发生期间正值树木转运大量体内N素至新梢器官以用于光合生产和干物质积累，同时根系开始萌生并消耗大量淀粉，并未发现倒春寒对可溶性糖的水解具有显著影响；（5）倒春寒发生期间，新梢器官中抗氧化酶浓度升高以应对冻害导致的电解质解离胁迫，同时淀粉颗粒内聚酶活性下降并伴随淀粉大量水解以为新梢和根系的呼吸提供能量。通过本项目的实施初步查明了长春地区倒春寒天气发生的规律、对树木新梢生长的影响和C-N循环干扰规律，为温带地区城市树木的春季生长经营提供了理论根据。