夜间不同环境稳定性条件下杨树水分生理过程的生物物理控制

Biophysical Control of Water Physiological Processes in Poplar under Various Nighttime Environmental Stability Conditions

【目的】以杨树人工林生态系统为研究对象,研究环境因子与内源性昼夜节律对树木叶片水分生理和树干液流的生物物理调控机制,旨在揭示树木水分生理过程(叶片气孔导度、叶片蒸腾、叶片水势和树干液流)在夜间对不同环境稳定性条件的响应模式和影响因素。【方法】对位于北京市顺义区潮白河沿岸的欧美杨人工林,在生长季期间选定7个晴朗的昼夜,连续监测3棵样树的叶片气体交换和叶片水势。同时,使用热扩散探针技术监测样树的树干液流密度变化,同步记录环境因子变化,并使用日落后历时量化昼夜节律的影响。【结果】1)夜间出现树木气孔开放的现象,叶片蒸腾和液流同步发生。夜间环境稳定(v=0且ΔVPD≤0.1 kPa)条件下,树木水分生理指标主要受大气和土壤温度影响(P<0.05),且较弱。夜间液流与叶片气孔导度显著负相关(P<0.01),表明液流主要用于茎干补水。2)夜间环境波动(v>0或ΔVPD≥0.1 kPa)条件下,叶片气孔导度和树干液流密度受大气温度(T_(a))和VPD的正向调控,与空气湿度(RH)显著负相关(P<0.05),且T_(a)为主导影响因素。叶水势主要受T_(a)、土壤含水量(SWC)和温度(ST)的共同影响。夜间液流与叶片气孔导度、蒸腾速率和水势显著正相关(R^(2)=0.67)。3)日间环境波动较强,叶片水分生理指标与树干液流密度的相关性显著高于夜间,但叶片气孔导度与VPD呈负相关,且气孔导度与液流密度之间表现出解耦现象(P=0.078)。4)以日落后历时为表征的昼夜节律对树木水分生理指标的作用方式随夜间环境稳定性变化而不同。在夜间环境稳定条件下,日落后历时显著影响叶片气孔导度、叶片水势和叶片蒸腾(P<0.01);而在夜间环境波动条件下,该因子对叶片水分生理指标的影响程度均有所降低且对气孔导度和叶片水势的影响不显著(P_(1)=0.066,P_(2)=0.08),说明夜间环境波动影响了昼夜节律对树木水分生理过程的作用方式和程度。【结论】在夜间不同环境稳定性条件下,树木水分生理的生物物理过程和调控机制有显著差异,当环境因子波动较小时,树木水分生理过程受昼夜节律调控形成了显著的夜间模式,此时应考虑其对植物水分的影响。本研究强调了昼夜节律在调控林木水利用中的关键作用,并建议制定基于时间和环境稳定性的灌溉策略,以优化水分管理和应对气候变化。

【Objective】In the context to the global trend of decreasing surface wind speeds,known as"atmospheric stilling",differences in diurnal environmental stability primarily driven by vapor pressure deficit(VPD)and wind speed(v)are becoming increasingly pronounced.However,the biophysical control mechanisms of tree water physiological processes under different environmental stability conditions remain unclear.In this study,an ecological system of poplar plantations was targeted and the biophysical regulation mechanisms of environmental factors and endogenous circadian rhythms on leaf water physiology and trunk sap flow in trees were investigated.This study aims to explore the response patterns and influencing factors of tree water-related physiological processes,such as leaf stomatal conductance,leaf-level transpiration rate,leaf water potential,and trunk sap flow,under different nighttime environmental conditions.【Method】The research was conducted in a Populus×euramericana plantation along the Chaobai River in Shunyi District,Beijing.During the growing season,gas exchange at the leaf-level and leaf water potential were measured continuously over seven clear day-night cycles on three sample trees.Simultaneously,sap flux density in the sample trees was monitored using heat diffusion probe technology,with concurrent recording changes in environmental factor,and the impact of diurnal rhythms was quantified using hours after dusk.【Result】1)Nighttime stomatal opening was observed,with synchronized occurrences of leaf transpiration and sap flux.Under stable nocturnal conditions(v=0 andΔVPD≤0.1 kPa),tree water physiological indicators were primarily influenced by air and soil temperatures(P<0.05),albeit relatively weak.There was a significant negative correlation between nocturnal sap flux and leaf stomatal conductance(P<0.01),indicating that sap flux was mainly used for stem water replenishment.2)Under fluctuating nighttime environmental conditions(v>0 orΔVPD≥0.1 kPa),leaf stomatal conductance and sap flux density were positively regulated by air temperature(T_(a))and VPD,and negatively correlated with relative humidity(RH),with T_(a)being the dominant factor.Leaf water potential was mainly influenced by T_(a),soil water content(SWC),and soil temperature(ST).Nighttime sap flux density showed significant positive correlations with leaf stomatal conductance,transpiration rate,and water potential(R^(2)=0.67).3)Daytime environmental conditions fluctuated strongly,showing a significantly higher correlation between leaf water physiological indicators and sap flux density compared to nighttime.However,there was a negative correlation between leaf stomatal conductance and VPD,and there was a decoupling phenomenon between stomatal conductance and sap flux density(P=0.078).4)The impact of the circadian rhythm,as characterized by hours after dusk,varied with changes in nighttime environmental stability.Under stable nocturnal conditions,duration after dusk significantly affected leaf stomatal conductance,leaf water potential,and transpiration(P<0.01).Under fluctuating nocturnal conditions,the influence of this factor on leaf water physiological indicators were reduced,with no significant impact on stomatal conductance and leaf water potential(P_(1)=0.066,P_(2)=0.08),indicating that nocturnal environmental fluctuations affected the manner and extent to which the circadian rhythm influenced tree water-related physiological processes.【Conclusion】Under varying nighttime environmental stability conditions,there are significant differences in the biophysical processes and regulatory mechanisms of tree water physiology.When environmental fluctuations are minimal,tree water physiology processes are regulated by circadian rhythms,forming a pronounced nocturnal pattern.At this time,its impact on plant hydration should be considered.This research emphasizes the pivotal role of circadian rhythms in controlling forest water usage and recommends formulating irrigation strategies based on temporal factors and environmental stability to optimize water management and adapt to climate change.Furthermore,this study provides theoretical support for understanding forest hydrological cycles and assessing the adaptability of riparian plantations to climate change.