分株数量或生物量比例差异会明显影响克隆系统对资源异质性环境的生态适应性, 地下茎木质化、连接稳固的竹类植物在生长过程中相连克隆分株通常会生活在异质光环境中, 但其叶片光合生理特性对异质光环境的响应及其分株比例效应则未见报道。该研究以地下茎相连的美丽箬竹(Indocalamus decorus)克隆系统为实验材料, 设置2个遮光率(分别为50% ± 5%和75% ± 5%)和3个分株比例(遮光与未遮光分株比例分别为1:3、2:2、3:1)处理, 分株数量为4株。分别测定了遮光处理后30、90、150天遮光和未遮光分株叶片光响应特征、气体交换参数、光合色素含量, 分析了异质光环境下美丽箬竹光合生理的变化规律。结果显示: 分株比例对美丽箬竹光合生理有显著影响, 且其与遮光、处理时间交互作用显著。美丽箬竹克隆系统遮光分株比例越大, 即遮光相对分株数量越多, 其表观量子效率(AQE)、光饱和点、最大净光合速率(P_{n max})、净光合速率(P_n)、气孔导度(G_s)、蒸腾速率(T_r)、水分利用效率越大, 光补偿点、暗呼吸速率越小, 其光合效率越高, 光能利用能力越强, 而与之相连的未遮光分株则相反; 随遮光分株比例的增大, 遮光分株叶片叶绿素a、叶绿素b含量呈先升高而后下降的变化趋势, 类胡萝卜素(Car)含量则持续下降, 而与之相连的未遮光分株叶片光合色素含量则呈下降趋势; 遮光率提高, 相同分株比例美丽箬竹克隆系统遮光分株叶片AQE、P_{n max}、P_n、G_s、胞间CO₂浓度(C_i)和光合色素含量总体升高, 而与之相连的未遮光分株叶片P_{n max}、C_i以及Car含量则总体下降。研究结果表明异质光环境下, 遮光分株光合效率和弱光利用能力明显增强, 而未遮光分株则相反, 克隆系统内分株间发生了明显的克隆分工, 且2:2、3:1分株比例克隆系统较1:3分株比例对异质光环境具有更好的适应能力。美丽箬竹克隆系统可通过差异性调节分株光合生理特性和光合色素含量, 提高遮光分株光能利用和光合效率来适应异质光环境, 以提高克隆系统的适合度。

Aims Differences in number of ramets or biomass ratio might have remarkable effects on the adaptability of plant clonal systems to resource heterogeneity. Connected-ramets of bamboo, with lignified rhizomes, usually grow in heterogeneous light environment, but little is known about the response of photosynthetic physiological characteristics in the ramet leaves to heterogeneous light environment and the effects of ramet ratio. Methods The clonal system with four-connected ramets of Indocalamus decorus was grown in the two different shading rates (50% ± 5% and 75% ± 5%) and in the three levels of ramet ratios (the ratios of shaded to unshaded ramets are 1:3, 2:2 and 3:1, respectively). The light response characteristics, gas exchange parameters and photosynthetic pigment content of shaded and unshaded ramets under heterogeneous light conditions were measured at 30, 90 and 150 days after shading treatment, respectively. Important findings The ramet ratio, and its interaction with shading and treatment time had significant effects on photosynthetic physiology of I. decorus. With the increase in the proportion of shaded ramets, leaves apparent quantum efficiency (AQE), light saturation point, maximum net photosynthetic rate (P_{n max}), net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), and water use efficiency increased, but light compensation point and dark respiration rate decreased, indicating higher photosynthetic efficiency and light utilization of shaded ramets, whereas the reverse was true for connected unshaded ramets. Furthermore, leaves chlorophyll a and chlorophyll b contents of the shaded ramets firstly increased and then decreased, while both the carotenoid content of shaded ramet and photosynthetic pigment (chlorophyll a, chlorophyll b and carotenoid) contents of the unshaded ramets all decreased continuously. Besides, under the same ramet ratio, AQE, P_{n max}, P_n, G_s, C_i and photosynthetic pigments content of leaves in shaded ramets increased with the increment of shading rate, while leaves P_{n max}, C_i and carotenoid contents of the unshaded ramets decreased. Our results indicated that photosynthetic efficiency and light utilization of shaded ramets significantly increased in the heterogeneous light environment, whereas the reverse was true for unshaded ramets. These exhibited obvious division of labor in the clonal system, and ramet ratio of 2:2 and 3:1 showed the better adaptability to heterogeneous light environment than that of 1:3. Therefore, those findings highlighted I. decorus could largely enhance the fitness of the clonal system to adapt to the heterogeneous light environment by modifying the leaf photosynthetic physiology and photosynthetic pigments content, which improved the light utilization and photosynthetic efficiency of the shaded ramets.