白刺花光合生理对土壤水分的响应及光合生产力水分分级

Photosynthetic physiological responses of Sophora davidii to soil moisture and the classification of soil moisture levels based on photosynthetic productivity

摘要

【目的】针对澜沧江干暖河谷水分受限的生境特征，本研究通过定量分析白刺花对土壤水分梯度的光合生理响应与限制阈值，并基于光合生产力构建水分分级体系，旨在为区域植被修复的精准水分管理提供理论依据。【方法】采用自然干燥法设置 5 个土壤相对含水量（RSWC）梯度（95%、80%、65%、50% 和 35%），通过称重法维持水分平衡并诱导植株达到生理稳态。利用 Li-6400XT 测定叶片光响应曲线与气体交换参数，运用非线性模型拟合光合参数对土壤水分的响应特征，并结合生理拐点构建水分与光合生产力分级体系。【结果】（1）随土壤水分亏缺加剧（RSWC ≤ 80%），白刺花最大净光合速率与表观量子效率总体呈下降趋势，其中在较低 RSWC 条件下下降明显。当 RSWC 由 80% 降至 35% 时，光补偿点由 27.95 升高至 38.88 µmol/（m²·s），光饱和点由 1 423.72 降至 1 159.56 µmol/（m²·s），光合有效利用区间显著缩减。在 RSWC 为 50% 和 35% 时，当光合有效辐射超过 1 200 µmol/（m²·s）后白刺花表现出明显的光抑制现象。（2）净光合速率（P_n）与气孔导度随土壤水分降低呈先增加后降低的单峰趋势，均在 RSWC 为 80% 时达到最大值。白刺花气孔限制向非气孔限制的转变可能发生在 RSWC 为 35% ~ 50% 区间内，在 RSWC 由 80% 降至 50% 的过程中，P_n 下降主要受气孔因素限制；随着干旱加剧，在 RSWC 降至 35% 的过程中，胞间 CO₂ 浓度由降转升、气孔限制值由升转降，表明随干旱程度加剧，非气孔限制作用增强。（3）P_n 与水分利用效率的理论峰值分别位于 RSWC75.6% 和 61.8% 处。在 RSWC 由 80% 降至 65% 的过程中，蒸腾速率（T_r）下降 26.1%，而 P_n 仅下降 1.1%，表明水分受限初期 P_n 与 T_r 对土壤水分降低的响应幅度存在差异。模型外推得到白刺花 P_n 的水分补偿点 RSWC 为 26.3%，并基于理论峰值、P_n 水分补偿点及光合限制方式转变区间等关键指标，将水分−光合生产力划分为无产无效水、低产低效水、中产高效水、高产稳效水及盈余低效水 5 个等级。【结论】白刺花在适度水分亏缺条件下能够维持较高的光合能力和水分利用效率，表现出对干暖河谷水分环境的适应能力。建议将 RSWC 50% 作为生态补水的参考预警值；模型外推得到的 RSWC 26.3% 可作为严重水分亏缺条件下的参考性生理阈值，其生态适用性需进一步试验验证。该量化体系为干暖河谷人工植被的稳定性评估提供了科学方案，对于解决该生境下植被修复水分精准管理具有重要的实践意义。

Abstract

[Objective] In view of the water-limited habitat characteristics in the dry-warm valley of the Lancang River, this study quantitatively analyzed the photosynthetic physiological responses ofSophora davidii across soil moisture gradients and determined its limitation thresholds. Based on these findings, a soil moisture classification system based on photosynthetic productivity was established to provide a theoretical basis for precise water management in regional vegetation restoration. [Method] Using a natural drying protocol, five relative soil water content (RSWC) levels (95%, 80%, 65%, 50%, and 35%) were established. Physiological homeostasis was induced via gravimetric moisture control. Leaf gas exchange and light-response curves were quantified using a Li-6400XT system. Nonlinear models were employed to characterize the response of photosynthetic parameters to soil moisture. A soil moisture classification system based on photosynthetic productivity was constructed using key physiological inflection points. [Result] (1) With the intensification of soil water deficit (RSWC ≤ 80%), the maximum net photosynthetic rate and apparent quantum yield ofS. davidii generally declined, with pronounced reductions under lower RSWC conditions. As RSWC decreased from 80% to 35%, the light compensation point shifted from 27.95 to 38.88 µmol/(m²·s), while the light saturation point decreased from 1 423.72 to 1 159.56 µmol/(m²·s), substantially narrowing the effective light-utilization range. At 50% and 35% RSWC, pronounced photoinhibition was observed when photosynthetically active radiation exceeded 1 200 µmol/(m²·s). (2) Both net photosynthetic rate (P_n) and stomatal conductance exhibited a unimodal response to declining soil moisture, peaking at 80% RSWC. The transition from stomatal to non-stomatal limitation in S. davidii may occur within the RSWC range of 35%–50%. As RSWC decreased from 80% to 50%, the decline in P_n was primarily driven by stomatal factors. As drought intensified and RSWC fell toward 35%, the intercellular CO₂ concentration shifted from decreasing to increasing, while the stomatal limitation value shifted from increasing to decreasing, suggesting an increasing contribution of non-stomatal limitation with increasing drought severity. (3) Theoretical optima forP_n and water use efficiency were identified at 75.6% and 61.8% RSWC, respectively. When RSWC decreased from 80% to 65%, the transpiration rate (T_r) decreased by 26.1%, whereas P_n decreased by only 1.1%, indicating that in the early stage of water limitation, the response magnitudes of P_n and T_r to decreasing soil moisture differed. The model-extrapolated water compensation point for net photosynthesis was 26.3% RSWC. Based on key indicators such as theoretical optima, the water compensation point for net photosynthesis, and the transition range of photosynthetic limitation, soil moisture availability and photosynthetic productivity were jointly categorized into five hierarchical grades: non-productive and ineffective water, low-productivity and low-efficiency water, moderate-productivity and high-efficiency water, high-productivity and stable-efficiency water, and surplus and low-efficiency water. [Conclusion]S. davidii maintained relatively high photosynthetic capacity and water-use efficiency under moderate soil water deficit, indicating its physiological adaptability to the water conditions of dry-warm valley habitats. We propose 50% RSWC as a reference early-warning value for supplemental irrigation, whereas the model-extrapolated value of 26.3% RSWC may serve as a reference physiological threshold under severe soil water deficit, and its ecological applicability requires further experimental validation. This quantitative framework provides a scientific approach for assessing the stability of planted vegetation in the dry-warm valley and has important practical significance for precise water management in vegetation restoration in this habitat.

关键词

白刺花 / 澜沧江干暖河谷 / 气孔限制 / 水分利用效率 / 水分−光合生产力分级

Key words

Sophora davidii / dry-warm valley of the Lancang River / stomatal limitation / water use efficiency / soil moisture–photosynthetic productivity classification

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基金资助

国家重点研发计划(2024YFF1307805)

澜沧江流域高寒区高陡边坡植被恢复及灌溉技术研究及示范项目(HY2024/S36)

西藏自治区科技计划(XZ202501JX0012)