北京山区典型植被幼苗非结构性碳水化合物存储机制研究

Higher future precipitation variability will trigger more frequent occurrences of drought. Although plant responses of drought being well understood, drought effects on non-structural carbohydrates (NSC) internal to plant organs, stressed generation of NSC, and plant recovery mechanism for NSC migration after re-watering were needed to be further discussed. The potted seedlings of typical tree species, including Pinus tabulaeformis Carr., Platycladus orientalis (Linn.) Franco, Robinia pseudoacacia Linn. and Populus davidiana Dode in mountainous areas of Beijing were selected combining the observations of environmental and soil factors. Water controlling tests were conducted on these potted seedlings. The characteristic concentrations of NSC in different plant tissues were observed during drying and re-watering processes. Based on stable isotope technology, carbon-13 isotope compositions (δ13C) of NSC in different plant tissues were compared to explain the top-down 13C discrimination within plants in the processes of drought and re-water recovery. The relationships between soil water content, NSC concentration and δ13C in plant tissues were determined, which was aimed to reveal the selected metabolic pathways and carbon reserve strategy of NSC. It is of importance to underlie the evaluation of reconstruction and resilience of vegetation function and carbon balance on forest ecosystem of Beijing.

未来多变的降水格局变化可引发极端干旱事件的频繁发生。尽管目前植物对干旱胁迫的响应机制能够被很好地理解，但干旱如何影响植物组织非结构性碳水化合物活性及其应激产生途径，以及旱后复水有关非结构性碳迁移的植物恢复机制函待进一步探讨。本研究拟以北京山区典型植被油松、侧柏、刺槐和山杨盆栽幼苗为研究对象，设置干旱胁迫、复水恢复处理，以掌握干旱胁迫、复水恢复过程中，植物组织（主干、当年生枝基部和根部韧皮部组织、成熟叶片组织）非结构性碳水化合物（NSC）浓度变化特征；基于碳稳定同位素技术，比较干旱胁迫、复水恢复过程中植物组织NSC碳稳定同位素组成（δ13C）异同，以解析植物组织自上而下的13C分馏机制；掌握土壤水分与植物组织NSC浓度及其δ13C值间关系，以揭示干旱胁迫、复水恢复过程中植物组织NSC优先选取地代谢途径与碳存储机制，为多变降水、干旱气候背景下，评估北京山区植被功能恢复及森林碳平衡提供科学依据。

持续气候变化导致陆地生态系统中极端天气事件发生的频率和强度不断增加。作为植物生长和代谢的重要底物，近期合成碳水化合物（如可溶性糖）在干旱碳平衡失调时的转运机理尚未得到定论。因此，本研究连续监测、探究干旱—旱后复水处理期内四种典型树种幼苗光合生理及其可移动碳源的器官迁移规律。结果表明：1）轻、中度干旱使山杨、刺槐、侧柏幼苗受气孔与非气孔限制，叶绿体类囊体膜和PSII光化学反应中心受到可逆损伤，光合能力下降；而油松更适应中度土壤干旱环境，其光合能力与对照组无差异。四种盆栽幼苗旱后恢复光合能力的差异性与其各自受干旱胁迫的程度相关，其中油松恢复最快。2）不同树种水分利用效率对土壤水分变化的响应策略存在差异。山杨与刺槐幼苗达到瞬时水分利用效率（WUEi）峰值的土壤水分小于油松、侧柏。四种盆栽幼苗WUEi在土壤水分胁迫解除后恢复、超过各自对照水平。常绿树种干旱阶段平均水分利用效率（WUEL）明显大于落叶树种。且随着干旱胁迫时长与程度的加剧，刺槐、侧柏WUEL略低于对照，而山杨、油松WUEL均高于对照。3）由四种盆栽幼苗器官可溶性糖浓度及其δ13C分配模式发现，山杨对干旱胁迫较其他三种树种更为敏感，表现为干旱阶段山杨转运其叶可溶性糖（TSS）至茎干、粗根和细根（可溶性糖富集13C），维持根部水分捕获和运输功能。而刺槐、油松和侧柏将枝条TSS转运至近端叶片，使同化光合产物继续维持叶片碳同化与渗透功能。刺槐和油松优先分配TSS至茎干、粗根和细根，支撑水力输导与吸收功能。四种盆栽幼苗叶、枝条、茎干葡萄糖含量比例增减程度影响其对应部位TSS含量增减趋势，而粗根以蔗糖组分为主，细根以葡萄糖和果糖组分为主。四种盆栽幼苗可溶性总糖复水恢复速度存在差异，且可溶性总糖含量与各糖组分比例的恢复时长间存在一定的时滞性。本研究为区域植被恢复自身机能潜力以及森林碳平衡的评估提供科学依据与理论基础。