毛竹冠层叶片氮素梯度分布的光驱动及水力调节机制

Moso bamboo (Phyllostachys pubescens) is an important forest resources in South China, and its carbon sequestration capacity is more than that of the ordinary trees. Forest carbon sinks enhancement and biomass accumulation are mainly formed through the canopy photosynthesis. The bamboo yield depends mainly on the stand structure regulation and soil management, and the potential space to further enhance bamboo shoot yield through intensive management is more and more small. The relationship between canopy leaf nitrogen gradient distribution and light is an important ecological and physiological relation for the trees, which is a very good reference index to understand the best density for the different age structure of bamboo stand, and nowdays the relationship between light and nitrogen and hydraulic conductance within bamboo canopy is lack of systematic research. This project is to, basing on canopy meteorological gradient observation tower (30M ) in bamboo forest, confirm the " light -nitrogen " hypothesis applicability in bamboo forest and reveal the light drive mechanism for leaf nitrogen gradient distribution within the bamboo canopy, according to the correlation between the light gradient distribution and the leaf biochemical properties, such as leaf area, leaf nitrogen content per unit leaf area and leaf nitrogen fractions content changes, within the canopy in different growth stages of bamboo. Based the proportional and mutual relations among leaf hydraulic conductivity, nitrogen content and light within the canopy, this study is to reveal the co-regulation mechanism of light and water for canopy leaf nitrogen gradient distribution. Through the correlation analysis among the canopy leaf gas exchange, chlorophyll fluorescence parameters, leaf nitrogen biochemical components content and the hydraulic conductance, this project will clear the influence of canopy " light –nitrogen- hydraulic conduntance " driving mechanism on canopy photosynthesis. The study will fill the research blank of Moso bamboo canopy photosynthesis, and provide scientific basis for sustainable and efficient nutrient and water management philosophy, technology improvement and carbon sequestration enhancement techniques for Moso bamboo ecological system in China.

毛竹（phyllostachys pubescens）是重要森林资源。目前提高毛竹单产主要依赖林分结构调控和土壤管理，通过集约经营进一步提高竹材、笋产量的潜力空间越来越小。冠层叶片氮素梯度分布和光照、叶片水力导度关系是树木重要的生理生态关系，是竹林造林质量提升、不同年龄结构组成需要最佳密度控制的很好参考指标，迄今对毛竹冠层“光-氮”关系及其水力调节机制缺乏系统研究。项目通过对不同生长发育阶段毛竹冠层内光辐射梯度分布特征、气孔行为及其与冠层叶片氮组分含量变化的相关性分析，应用实际系统观测数据，揭示冠层叶片氮素梯度分布光驱动机制，建立毛竹“光-氮”假说；基于毛竹冠层内叶片水力导度、氮素含量和光照三者优化协同分配关系，进一步阐明和揭示冠层叶片氮素梯度分布的光、水协同调节机制。冠层“光-氮-水力导度”理论将为揭示毛竹林生态系统光、水、氮素群落发展与生长理论基础、建立科学栽培技术提供重要理论依据。

毛竹是重要森林资源。目前提高毛竹单产主要依赖林分结构调控和土壤管理，通过集约经营进一步提高竹材、笋产量的潜力空间越来越小。冠层叶片氮素梯度分布和光照、叶片水力导度关系是树木重要的生理生态关系，是竹林造林质量提升、不同年龄结构组成需要最佳密度控制的很好参考指标，迄今对毛竹冠层“光-氮”关系及其水力调节机制缺乏系统研究。项目通过不同生长发育阶段毛竹冠层内光辐射梯度分布特征、气孔行为及与冠层叶片氮含量变化的相关性分析，应用实际系统观测数据，发现毛竹叶片氮素含量随冠层呈垂直梯度分布，与叶片最大净光合速率梯度分布显著相关，氮素垂直分布梯度的尖削度受生长季节影响。自然生长下，叶片氮素含量在春季和冬季有随着冠层高度增加而下降的趋势，而夏季和秋季其含量基本随着冠层高度增加而增加。与自然生长毛竹相比，截雨干旱改变了不同年龄毛竹叶片氮素含量竹龄差异随季节的变化。阐明了毛竹叶片和冠层水平光合特性、叶绿素、氮素时空分布格局及其与太阳辐射、温度、湿度等关键气象因子梯度分布的耦合关系，发现叶片光合速率、水分利用效率与太阳辐射、温度和湿度相关性较高，且受季节影响。研究印证了“光-氮”假说在毛竹的适用性，揭示了叶片氮素梯度分布的光驱动机制，建立毛竹“光-氮”假说。研究发现各生长季节，不同林龄个体叶片氮素含量、比叶重随冠层高度垂直变化趋势与叶片Pn日均值的垂直变化趋势一致。研究认为，毛竹不同冠层部位叶片通过改变形态、氮素含量来适应不同生长季节生长环境的变化，以便充分利用光能提高光合能力。毛竹叶片水势冠层梯度分布受生长季节和竹龄大小显著影响，通过截雨模拟干旱试验可改变其冠层梯度分布模式；毛竹叶片氮素时空分布与叶片含水量、叶片水势及土壤含水量显著正相关。基于毛竹冠层内叶片水力导度、氮素含量和光照三者优化协同分配关系，进一步阐明和揭示冠层叶片氮素梯度分布的光、水协同调节机制。冠层“光-氮-水力”理论将为揭示毛竹林生态系统光、水、氮素群落发展与生长理论基础、建立科学栽培技术提供重要理论依据。