不同光强下4种鸭跖草科植物的生物量分配、水分生理及光响应特征

以紫鸭跖草、‘花叶’水竹草、吊竹梅和‘绿叶’水竹草为试验材料，利用遮光网人工模拟5个光强梯度，研究不同光强对4种鸭跖草科植物生物量分配、水分生理以及光响应曲线特征的影响。结果表明：随光强的降低，4种植物的地上生物量均呈先升后降的趋势，并在遮光度25%至75%期间显著升高（P<0.05），除紫鸭跖草的总生物量无显著变化外，其他3种植物的总生物量也呈先升后降趋势；不同光强对4种植物的物质分配规律及冠根比的影响不同，但4种植物的茎贡献率均呈上升趋势；正午水势随光强的降低而增加，且与失水速率的变化趋势具有较高的一致性，其中紫鸭跖草和吊竹梅的失水速率较低；在不同光强处理下，4种植物的光响应曲线均呈现出随着光合有效辐射（PAR）的增加而先增加后趋于平缓的趋势；随着光强的降低，4种植物的最大净光合速率、表观量子效率和光饱和点均呈现出先升后降的趋势；紫鸭跖草和吊竹梅具有较高的最大净光合速率、表观量子效率、光饱和点以及较低的暗呼吸速率，且水分利用效率在不同处理间无显著差异，均表现出较高的水平。综上所述，4种植物在适当的弱光环境中（遮光度25%~75%），可以通过调整形态、物质分配规律及光响应特征的方式去更有效的利用弱光资源，但不同种植物的应对能力呈现出一定的差异性，其中紫鸭跖草和吊竹梅的光适应性较强。

Biomass allocation,water use characteristics,and photosynthetic light response of four Commelinaceae plants under different light intensities

The aim of this study was to explore the effects of different light intensities on the biomass allocation， water use characteristics， and photosynthetic light response of Commelinaceae plants. The experimental materials were ramets of Commelina purpurea， Tradescantia fluminensis ‘Variegata’， Tradescantia zebrina， and Tradescantia fluminensis ‘Vairidia’. These materials were subjected to light at five different intensities， which were obtained using a shading net. It was found that， as the light intensity decreased （shading intensity 25%-75%）， the aboveground biomass of the four plants initially increased and then decreased （P<0.05）. The total biomass also increased and then decreased as the light intensity decreased， except that of C. purpurea， which showed no significant change. The effects of different light intensities on biomass allocation and the crown∶root ratio of the four plants were diverse， however， the proportion of the stem to total biomass tended to increase in all four plants as the light intensity decreased. The midday water potential increased with decreasing light intensity， and was strongly related to the trend in the water loss rate. Both C. purpurea and T. zebrina showed low rates of water loss. As the amount of photosynthetically active radiation increased， the net photosynthetic rates of the four plants first increased and then gradually stabilized. As the light intensity decreased， the maximum net photosynthetic rate， apparent quantum efficiency， and light saturation point of the four plants tended to first increase and then decrease. Compared with T. fluminensis ‘Variegata’ and ‘Vairidia’， C. purpurea and T. zebrina showed higher values for maximum net photosynthetic rate， apparent quantum efficiency， and light saturation point， and a lower dark respiration rate. The water use efficiencies of C. purpurea and T. zebrina did not differ significantly among the light intensity treatments， but were higher than those of T. fluminensis ‘Variegata’ and ‘Vairidia’. Together， the results suggest that these four plants are able to make more effective use of weak light resources by adjusting their morphology， biomass allocation， and photosynthetic light responses in weak light （shade density of 25%-75%）. Our results show that C. purpurea and T. zebrina are better able to cope with low light intensity than are T. fluminensis ‘Variegata’ and ‘Vairidia’.