亚热带退化红壤丘陵区典型先锋树种碳吸存与水分利用耦合机制

Coupling mechanism of ecosystem carbon sequestration and water use is among the main research contents of global change and sustainable development. And it is also the important link of vegetation physiological and ecological characteristics and functions research on different scales.Subtropical red soil hilly area is a special ecological type region,once became the red desert of Southern China due to long-term man-made unreasonable use,faced with key challenges of vegetation recovery and sustainable forest management.Study on carbon and water coupling mechanism of typical pioneer species (illustrated by Pinus elliottii and Pinus manssoniana ) could not only provide the theoretical basis for ecological restoration measure optimization and scientific managenemnt, but also clarify the contribution of subtropical plantation to global forest ecosystem carbon and water cycle. The main research contents include: (1) Estimation of plantation sub-chamber carbon pool based on forest biomass, litter standing crop and soil carbon pool measurements; (2) Analysis of carbon sequestration dynamic based on plantation net primary productivity, litterfall and soil heterotrophic respiration measurements; (3) Calculation of stand water use based on sap flow density and soil evaporation measurements, combined with spatial scale conversion; (4) Investigation of water use efficiency based on leaf gas exchange measurements; (5) Perfectification of trunk respiration theory through analysis of correlation between tree sap flow and trunk respiration; (6) Revelation of plantation ecosystem carbon cycle water cycle coupling mechanism on different scales (including leaf, single tree,stand scale) based on carbon sequestration and water use dynamic measurements.

生态系统碳-水耦合机制是全球变化与可持续发展研究的主要内容之一。我国亚热带红壤丘陵区是一个特殊的生态类型区，面临着植被恢复重建与森林可持续经营的重大挑战。研究该区典型先锋树种（湿地松、马尾松）碳-水耦合机制，不仅可以为优化该区生态恢复措施、科学经营管理南方人工林提供理论依据，还可以阐明我国亚热带人工林对全球森林生态系统碳循环与水循环的贡献。研究内容包括：（1）基于森林生物量、凋落物现存量及土壤碳库的测定，估算人工林各分室碳库；（2）基于净初级生产力、凋落物量及土壤异养呼吸的测定，分析人工林碳吸存动态；（3）基于液流密度与土壤蒸发量的测定，结合空间尺度转换，推算林分耗水量（4）基于叶片气体交换的测定，探讨叶片水分利用效率；（5）分析树干液流与树干呼吸的相关性，完善树干呼吸理论；（6）基于碳吸存与水分利用动态的测定，揭示不同尺度（叶片、单木、林分）人工林生态系统碳-水耦合机制。

项目以亚热带退化红壤区湿地松、马尾松为主要研究对象，系统监测了人工林碳蓄积、树干液流、树干呼吸、土壤呼吸及土壤蒸发特征，揭示了叶片、单木及林分尺度森林碳蓄积与水分利用耦合机制。结果如下：（1）湿地松、马尾松人工林生态系统碳贮量为88.74～97.47 t•hm-2和70.04～73.57 t•hm-2，乔木层占总碳贮量的60.88%～67.12%，且比重随林龄的增大而增加；土壤层占总碳贮量的26.31%～32.81%，且随林龄的增大而减小。湿地松、马尾松林年固碳量分别为4.54和2.45 t•hm-2•a-1。（2）湿地松林土壤总呼吸和异养呼吸速率平均值为2.01和1.62 μmol•m-2•s-1，马尾松林土壤总呼吸和异养呼吸速率平均值为1.73和1.43 μmol•m-2•s-1。土壤总呼吸速率、异养呼吸速率与5 cm土壤温度间存在显著的指数相关关系，与土壤湿度间均不存在显著的相关关系。土壤温度能解释2种林分土壤总呼吸速率、异养呼吸速率的季节变化的50%以上。考虑土壤温湿度的线性双因素模型可以解释2种林分土壤呼吸速率变化的88%以上。（3）各个径阶湿地松、马尾松树干CO2释放速率(FCO2)呈现出明显的单峰季节变化格局，生长季FCO2大于生长停滞期。FCO2与树干温度间均存在显著的指数函数关系，同时表现出大径阶FCO2与树干温度的指数相关性比小径阶好。FCO2与DBH间呈显著的线性相关关系，表明DBH可作为针叶树种树干呼吸预测和上推的一个简便实用指标。（4）液流速率与空气温度、光合有效辐射呈显著正相关，与相对湿度呈显著负相关。湿地松、马尾松液流速率与气象因子相关程度大小顺序分别为：相对湿度（-0.708）＞光合有效辐射（0.688）＞空气温度（0.538）和光合有效辐射（0.823）＞相对湿度（-0.744）＞空气温度（0.683）。（5）构建了拓扑结构为4-10-1的湿地松树干液流BP神经网络模型，模型对树干液流速率具有较高的模拟精度和泛化能力，能够很好地反映气象因子与液流速率之间的非线性函数关系。（6）树干CO2释放速率与液流速率间存在显著的负相关关系，在研究期内白天液流水平最高的情况下，树干CO2释放速率实测值相比指数方程预测值小25%。