遮光对香果树幼苗光合特性及叶片解剖结构的影响

设置了全光照(L0)、透光率60%(L1)、透光率25%(L2)、透光率10%(L3)4种光环境,研究了不同遮光处理对香果树幼苗光合作用及叶片解剖结构的影响。结果表明:(1)遮光对香果树幼苗净光合速率(P_n)、蒸腾速率(T_r)、气孔导度(G_s)、气孔限制值(L_s)、胞间CO_2浓度(C_i)、蒸汽压亏缺(V_(pdl))均产生了显著影响。全光和L1处理下Pn和Tr日变化呈明显的双峰曲线,中午出现了明显的"午休",其余处理的变化相对缓和,双峰和"午休"现象不明显;G_s的日变化规律与Pn基本一致;C_i的日变化整体呈先期缓慢降低后期抬升的趋势,与对照相比遮光显著提高了叶片胞间CO_2浓度;Ls和V_(pdl)呈现出先升后降的弧形变化,并且遮光下L_s和V_(pdl)日均值显著低于全光照。一天中P_n和T_r的日均值大小排序为L1L0L2L3。(2)不同光环境下香果树幼苗的光合响应特征明显不同。全光下,香果树幼苗能够维持较高的净光合作用速率而未呈现明显的光抑制,表现出一定的光忍耐和喜光性。L1处理下的最大净光合速率(P_(max))、暗呼吸速率(R_d)和表观量子效率(AQY)显著增加,说明香果树对光强具有一定的可塑性,轻度遮光有利于光合效率提高;强度遮光(L2、L3)导致光补偿点(LCP)和光饱和点(LSP)显著降低,有利于充分利用弱光,但P_(max)、R_d明显下降,光合效率受到抑制。(3)遮光显著影响了香果树叶片的气孔分布。遮光条件下香果树叶片的气孔密度显著减小,气孔器长度、宽度与单个气孔器面积也呈现类似的变化。(4)遮光条件下香果树叶片厚度减小,上表皮增厚,下表/ST增加;维管束内单列导管数目和导管直径均有明显增大,促进了叶片水分传导运输。(5)在育苗生产中,为了适应香果树幼苗生长发育的需求,建议有效辐射强度保持在自然光强的60%以上。

Effects of shading on photosynthetic characteristics and leaf anatomical structure of Emmenopterys henryi seedlings

Effects of shading on photosynthesis characteristics and leaf anatomical structure of Emmenopterys henryi seedlings were studied using four shading treatments including full sunlight (L0), 60% sunlight (L1), 25% sunlight (L2), and 15% sunlight (L3), respectively. The results showed that:(1) Shading had an significant effect on the net photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance (G_s), stomatal limitation value (L_s), intercellular CO₂ concentration (C_i), and vapor pressure deficit (V_pdl) of E. henryi seedlings. The diurnal changes of P_n and T_r under L0 and L1 treatments showed obviously bimodal curves, and the "noon break" appeared at 12:00. Their changes under L2 and L3 treatments were relatively mild, and the "noon break" were not obvious. The variation of G_s was basically consistent with that of P_n. The variation of C_i showed a tendency of declining slowly at early stage and rising rapidly later. Compared with the control, the shading promoted significantly increase of the C_i. Both L_s and V_pdl showed the arc changes of slow rising in advance and decreasing in the latter stage, and the daily averages under shading were lower significantly than the control. The order of daily averages of P_n and T_r was L1 > L0 > L2 > L3. (2) The photosynthesis-light response characteristics of E. henryi seedlings under four light regimes were obviously different. The seedlings grown under the full sunlight condition could maintain a higher P_n without obvious photoinhibition, showing a certain degree of shading-tolerance and light-demanding. The maximum net photosynthetic rate (P_max), dark respiration rate (R_d), and apparent quantum efficiency (AQY) under L1 treatment increased more significantly than the control. Therefore, the E. henryi seedlings had some plasticity to light intensity. The mild shading was beneficial to the improvement of photosynthetic efficiency. Serious shading (L2 and L3) resulted in a significant decrease of light compensation point (LCP) and light saturation point (LSP), which was beneficial to make full use of weak light. But they resulted in P_max and R_d decrease obvious, which inhibited photosynthetic efficiency. (3) The shading significantly affected the stomatal distribution on leaves surface of E. henryi seedlings. Under shading condition, the stomata density decreased significantly, and the stomata length, the stomata width, and single stomatal area was similar. (4) Under shading, the leaf thickness decreased, the upper epidermis thickened, and the lower epidermis thinned. The thickness of palisade tissue (PT) decreased and sponge tissue (ST) was not fully developed, and the value of PT/ST increased. Moreover, the number of vessel in vascular bundle and the vessel diameter increased significantly, which promoted the transport of water in leaves. (5) In order to meet the needs of growth and development of E. henryi seedlings in cultivation, we suggested that the effective radiation intensity should be above 60% of natural light intensity.