轻木幼苗光合特性和生长对干旱胁迫的响应

Responses of Photosynthetic Traits and Growth of Ochroma lagopus Seedlings to Drought Stress

摘要:

为揭示轻木(Ochroma lagopus)幼苗对干旱胁迫的响应机制，设置梯度水分胁迫处理，通过测定净光合速率(P_n)、气孔导度(g_s)、胞间CO₂浓度(C_i)、蒸腾速率(T_r)、水分利用效率(WUE)等关键的光合参数，并监测株高和基径等生长指标，以及根茎叶的干重及其占比等生物量分配特征，系统研究干旱胁迫对轻木幼苗光合生理和生长特性的影响。结果表明，干旱胁迫显著抑制轻木幼苗株高、基径和生物量的积累；在轻度干旱胁迫条件下，P_n、g_s和C_i同步下降，表明气孔限制是导致光合抑制的主要原因；轻-中度干旱处理下生物量的显著降低，主要源于光合作用受限引起的碳同化物的供应不足；同时，WUE的提高则有助于维持干旱条件下保水与碳同化的平衡。因此，在轻木的大田栽培过程中，干季通过滴管等节水灌溉技术给予适宜的水分供给，使土壤水分维持在田间持水量的80%~85%，能够显著提升轻木的光合效率和生物量积累能力，从而达到优化轻木栽培管理和提高木材蓄积量的目的。

Abstract:

Ochroma lagopus, an important fast-growing tropical timber tree species, has been successfully introduced and cultivated in the tropical regions of southwest China. However, the region’s distinct tropical monsoon climate, characterized by a pronounced seasonal drought lasting half a year, poses significant challenges to growth and large-scale industrial production of O. lagopus. To reveal the response mechanism of O. lagopus seedlings to drought, gradient water stress treatments were set up. The key photosynthetic parameters, such as net photosynthetic rate (P_n), stomatal conductance (g_s), intercellular CO₂ concentration (C_i), transpiration rate (T_r), and water use efficiency (WUE) were measured. Growth indicators, such as plant height and basal diameter, as well as biomass allocation characteristics, such as dry weight and proportion of roots, stems, and leaves were monitored. The effects of drought stress on the photosynthetic physiology and growth characteristics of O. lagopus seedlings were systematically studied. The results showed that drought stress significantly inhibited the plant height, ground diameter and biomass accumulation of O. lagopus seedlings. Under mild drought stress, P_n, g_s and C_i decreased simultaneously, indicating that stomatal limitation was the main cause of photosynthetic inhibition. The significant reduction in biomass under mild to moderate drought was mainly due to the insufficient supply of carbon assimilates caused by restricted photosynthesis. At the same time, the increase in WUE helped maintain the balance between water conservation and carbon assimilation under drought conditions. Therefore, in the field cultivation of O. lagopus, providing appropriate water supply through water-saving irrigation techniques such as drip irrigation during the dry season to maintain soil moisture at 80% to 85% of field capacity can significantly improve the photosynthetic efficiency and biomass accumulation capacity of O. lagopus, thereby achieving the purpose of optimizing the cultivation management of O. lagopus and increasing wood volume.