苹果密植园与间伐园树冠层内叶片光合潜力比较

通过对成龄苹果密植园和间伐园树冠不同层次和部位叶片光合潜力及辐射通量密度、叶片N含量和比叶重等指标的比较分析，研究了苹果园改造前后辐射能和氮素利用效率差异及其与产量品质的关系.结果表明：间伐显著改善了冠层内的辐射环境，间伐园冠层内的辐射分布明显比密植园均匀，相对辐射通量密度小于30%的无效光区接近0，而密植园冠层内的最低相对辐射通量密度为17%，在相对高度03以下均为无效光区；间伐园内冠层叶片的光合效率显著提高，间伐园树冠中、下部叶片的光合速率比密植园分别提高了78%和102%；叶片的最大羧化速率和最大电子传递速率也有较大幅度的提升.苹果园冠层叶片的光合效率与叶片N含量存在显著的相关关系，而叶片N含量又与辐射通量密度存在显著的相关关系，因此，可根据冠层叶片相对N含量的垂直分布间接和定量地判断叶片的光合效率或相对辐射通量密度的空间分布.

Leaf photosynthetic potential in canopy layers of un-thinned and thinned apple orchards

Through the comparison of leaf photosynthetic potential and of photosynthetically active radiation (PAR), leaf nitrogen concentration (N_l), and mass per unit leaf area (M_l) in different canopy layers of un-thinned orchard (UOD) and thinned orchard (TOD), this paper studied the effects of UOD rebuilding on the use efficiencies of PAR and nitrogen, and their relationships to the fruit yield and quality. Thinning obviously improved the radiation environment in canopy. The radiation distribution in TOD canopy was more uniformly than that in UOD canopy, and the invalid space with relative PAR (PAR_r) less than 30% in TOD approached to zero, while the minimum mean PAR_r in UOD was 17%, and the space under 0.3 of relative canopy height was invalid. The leaf photosynthetic efficiency in TOD was notably improved. Comparing with that in UOD, the photsynthetic rate (P_n) at the middle and bottom of the canopy in TOD was increased by 7.8% and 10.2%, respectively. Meanwhile, the photosynthetic potential parameters such as maximum carboxylation rate (V_max) and maximum electron transfer rate (J_max) also increased remarkably in TOD. The leaf photosynthetic potential had significant correlation with N_l, and the N_l was strongly correlated with PAR_r. As a result, leaf photosynthetic potential and PAR_r could be estimated according to the spatial distribution of relative leaf nitrogen concentration (N_lr).