桉树人工林生产力对旱季水分输入变化的响应机理研究

Eucalyptus plantation production in China has been promoted steadily through a long-term scientific research and practical exploration, but it is far below the world's average level. Production promotion of Eucalyptus plantation even in south China with good hydrothermal conditions is also currently stuck in bottleneck, a hypothesis is raised that it is associated with climatic stress from seasonal drought which is caused by uneven rainfall distribution and asynchronous changes between temperature and precipitation, but it lacks empirical study. In present study, based on field control experiment platform, Eucalyptus urophylla × E. grandis clone DH32-29 plantation was selected to conduct a field control test during the dry season in south China (October to the next March), including three treatments: water reduction (artificial interception rainfall), water increase.(irrigation), and natural control. The continuous real-time response of growth, biomass yield, radial growth, and carbohydrate and water metabolism at individual-level and stand-level production of Eucalyptus urophylla × E. grandis was observed, the key uncertainty of whether reduction or increase of water would lead to reduction or increase of production was verified, and the relationship between soil water supply during the dry season, carbohydrate and water metabolism, radial growth, and production. Main results can reveal the influence of reduction or increase of soil water on stand-level production and individual-level carbohydrate and water metabolism of Eucalyptus urophylla × E. grandis and its mechanism, answer the key scientific issue of whether production limitation result from seasonal drought, and it has important theoretical value and practical significance to promote production and enrich cultivation theory for fast growing and high yield of Eucalyptus plantation.

经过长期的科学研究和实践探索，我国桉树产量稳步提升，但仍远低于世界平均水平。即使在水热条件较好的华南地区，桉树产量提升同样遭遇瓶颈，该现象可能与降雨分配不均和水热不同步引起的季节性干旱的气候限制有关，但缺乏实证研究。本项目以尾巨桉无性系DH32-29人工林为研究对象，通过野外控制实验平台，在华南地区旱季（当年10月~翌年3月）实施人工截雨减水和补水灌溉处理，并设置自然对照。连续实时监测不同处理下桉树个体生长、生物量、径向生长和碳水代谢过程以及人工林生产力的响应规律，验证旱季减水或增水是否导致减产或增产，并重点解析旱季土壤水分供给、碳水代谢过程、径向生长和生产力的关系。研究成果可以揭示华南旱季土壤水分减少或增加对桉树生产力内在作用机理，回答季节性干旱是否限制了桉树产量这一科学问题，对挖掘桉树生产潜力和丰富桉树人工林速生丰产栽培理论具有重要的科学价值和实践意义。

经过长期的科学研究和实践探索，我国桉树产量稳步提升，但仍远低于世界平均水平。即使在水热条件较好的华南地区，桉树产量提升同样遭遇瓶颈，该现象可能与季节性干旱的气候限制有关，但缺乏实证研究。为了回答季节性干旱是否限制了桉树产量这一科学问题，本项目以尾巨桉无性系DH32-29人工林为研究对象，构建旱季补水和截雨处理两个野外控制实验平台，基于长期田间实测的土壤理化性质、酶活性和微生物群落结构、树木生长（胸径、树高、生物量等）、形态（叶面积、叶片解剖结构、气孔特征等）与生理指标（气体交换参数、水力结构参数、非结构性碳水化合物浓度等）以及凋落物量与分解速率等数据，探究了水分输入变化对桉树人工林生产力的影响与作用机制。研究结果表明，旱季补水缓解了季节性干旱胁迫和土壤酸化，增加了水分和养分供给，提高了光合叶面积，进而促进了光合生产；与此同时，由于旱季补水解除了干旱胁迫，促使桉树减少了碳水化合物对在抵御干旱方面的投入，使其优先供应生长，最终显著提升了桉树人工林生产力。另一方面，截雨处理试验结果显示，穿透雨减少加剧了土壤干旱胁迫，显著影响了旱季的水力结构、叶片形态与结构和净光合速率，致使水分传导和光合作用功能下降，最终抑制了生产力。此外，研究发现，截雨处理导致土壤水分和有效磷含量显著下降，进而显著影响了表层土壤细菌的群落结构。总体而言，研究成果证实了季节性干旱是限制桉树产量的重要原因，预测了全球气候变化背景下桉树存在产量下降的潜在风险，揭示了水分输入变化对桉树生产力的生理生态学作用机理，对挖掘桉树生产潜力和丰富桉树人工林速生丰产栽培理论具有重要的科学价值和实践意义。