不同树形龙安柚冠层特性

Analysis of the canopy structural characteristics of different training systems for Citrus grandis var. longanyou

以开心形、Y字形、双层分层形和自然圆头形的龙安柚为试验材料,比较不同树形的冠层特性、叶片结构和生理特征,以期为龙安柚果园小环境的调控提供理论基础。结果表明:(1)开心形间隙分数阈值最高,是自然圆头形的4.33倍。开心形与Y字形的冠层光合辐射与透射系数均显著高于其他树形,但二者无显著差异,表明开心形和Y字形的冠层通风透光特性较好。(2)开心形与Y字形叶片厚度增加,叶面积和气孔密度较大,栅栏/海绵组织厚度和组织紧密度较高,叶片组织疏密度较低,且二者无显著差异,表明开心形与Y字形利于提高叶片的光合作用,降低蒸腾作用。(3)Y字形和开心形净光合速率、水分利用率、最大表观电子传递速率、初始斜率和半饱和光强较高,而蒸腾速率较低,二者对强光的耐受能力较强;其中开心形蒸腾速率最低为2.43 mmol m^(-2)s^(-1),且其结果枝光抑制参数最小,为0.629。说明开心形为最佳的高光效树形。(4)冠层微环境因子、叶片结构及光合生理指标之间多呈极显著相关关系,但开心形叶片结构和生理的大部分指标与冠层环境因子之间相关性较低,说明开心形树形不同部位的营养枝和结果枝的叶片性状差异较小,其光渗透性好,整个冠层的光截获能力和有效光辐射的分布差异较小,笔者认为开心形是龙安柚栽培中的适宜高光效树形。

In this study, four types of training systems for Citrus grandis var. longanyou, natural round shape, double-layered shape, open center shape, and Y-shape, were used, and structural characteristics of the different canopies and structural and physiological characteristics of the leaves were compared for a better understanding of the canopy microclimate and correlation with canopy growth to provide guidance and support for orchard production practices such as pruning, watering, and fertilizing. The results showed that：（1） The gap fraction threshold of open center shape was the highest, which was 4.33 times of the natural round shape. Photosynthetically active radiation （PAR） and transmission coefficient of the open center shape and Y-shape systems were significantly higher than those of the other two training systems, which indicates that the capabilities of the open center shape and Y-shape systems to intercept and distribute light in the canopy were better than those of the other two systems. （2） Parameters such as Leaf thickness （LT）, Stomata density （SD）, Leaf area （LA）, Thickness rate of palisade and sponge tissue （PTT/STT）, and Organizational structure closely degrees （CTR） measured for the open center shape and Y-shape systems were higher than those of the other two systems, which indicates that the leaves of the former two systems show improved photosynthesis and reduced transpiration. （3） Parameters such as Net photosynthetic rate （Pn）, Water use efficiency （WUE）, Max apparent electron transport rate （ETR max）, Initial slope （α）, and Half-saturation light intensity （Ik） measured for the open center shape and Y-shape were higher, which indicates that these two training systems have better tolerance to strong light. However, Transpiration rate （Tr=2.43 mmol m-2 s-1） and the photoinhibition parameters （β=0.629） of the bearing branches were minimum for the open center shape system, which is the best system to photosynthetic efficiency. （4） The measured parameters＇ correlativity between canopy microclimate and structural and physiological characteristics of the leaves was highly significant, but the correlation for the open center shape system was lower than that of the other systems. This indicates that the leaves of the vegetative and bearing branches show the lowest differences in the whole canopy of the open center shape system and that the open center shape is the best training system for light interception and distribution in the canopy.