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• Different temperatures, air humidity, soil moisture content, and light intensity had significant effects on the photosynthesis and chlorophyll fluorescence characteristics of Distylium chinense from heterogeneous habitats. • D. chinense adopted different photosynthetic acclimation patterns and species-specific water use strategies under heterogeneous habitats. • D. chinense adjusted leaf area, specific leaf area, stomatal conductance, photochemical quenching coefficient and non-photochemical quenching to photochemically fix and store more carbon to meet their needs for growth under heterogeneous habitats. Distylium chinense is an evergreen dominant shrub with strong adaptability under heterogeneous habitats, including natural riparian zone (NRZ), anti-seasonal water level fluctuation zone (ASWLFZ), and no water level fluctuation zone (NWLFZ) in the Three Gorges Reservoir Region (TGRR) in China. In order to understand the photosynthetic ecological adaptability and habitat adaptation strategies of D. chinense under heterogeneous habitats, its photosynthesis and chlorophyll fluorescence parameters were investigated. The results showed that photosynthetic characteristics were significantly different among heterogeneous habitats (p <0.05). The PSII potential activity and PSII maximum photochemical efficiency (F v /F m) of D. chinense in the ASWLFZ were the highest among heterogeneous habitats. Non-photochemical quenching coefficient (qN) in the NWLFZ was higher than that in the NRZ and ASWLFZ (p <0.05). Stepwise regression analysis showed that water use efficiency and stomatal conductance were correlated with specific leaf area (SLA), leaf area and leaf dry weight. Regression curve fitting and canonical correspondence analysis revealed that light intensity, soil water content, air humidity and temperature were the main factors affecting photosynthetic characteristics and leaf functional traits. Our results evidenced that D. chinense adapted to the high water content and low light intensity environments, especially in the valley waterfall habitats, by increasing stomatal conductance and net photosynthetic rate, reducing SLA and maintaining moderate qN and F v /F m with adopting a profligate water use pattern to improve photosynthetic productivity. Therefore, D. chinense has a wide photosynthetic acclimation to different environments, which provided baseline information for the conservation and ecological restoration in the newly formed hydro-fluctuation zone and other similar degenerative riparian ecosystem. [ABSTRACT FROM AUTHOR]

Black locust (Robinia pseudoacacia) is widely planted throughout semiarid and subhumid regions of the Loess Plateau of China. Determining the changes in transpiration of this species in different climatic areas is important for revealing the acclimation mechanism of black locust and developing suitable forest management practices, particularly in the context of global climate change. Here, sap flow and canopy conductance of black locust plantation trees in semiarid (Yan'an) and subhumid (Yongshou) sites were quantified using Granier-type thermal dissipation probes and concurrent environmental observations from 2012 to 2017. Several physiological parameters were measured throughout the growing season. The results showed that sap flow was correlated with phenological factors across seasons within a year. However, interannual changes in sap flow were affected mainly by the reference evapotranspiration (ET 0) at the Yongshou site, and jointly by precipitation (P), soil water content, and P / ET 0 at the Yan'an site. Sap flow response to meteorological factors showed less discrepancy between pre- and post-rainfall periods at the Yan'an site. Moreover, canopy conductance fluctuated less with a wider range of vapor pressure deficit (VPD) and the slope of canopy resistance as a function of VPD was lower, indicating relatively lower sensitivity of stomatal conductance to environmental factors in Yan'an site. Physiological parameters, except for predawn leaf water potential, were significantly different between the two sites. The results suggested that black locust tended to reduce transpiration, modify leaf morphology, and improve water use efficiency to enhance its adaptability to the dryer site. The species changes stomatal regulation characteristics and general growth rate to acclimatize to distinct water habitats. • Sap flow characteristics of black locust differ between semiarid and subhumid sites. • Dominant environmental factors controlling transpiration varied with habitats. • Adaptability and responses to long-term and short-term drought are different. • Longterm soil water shortage weakened stomatal regulation and growth. • Future intensified drought potentially threatens the plantation stability. [ABSTRACT FROM AUTHOR]

Climate models predict rising temperatures and more frequent and prolonged urban heat islands (UHI) in southern China. The urban vegetations have become a focal point to mitigate the detrimental effects of UHI and to provide cooling through transpiration. However, transpiration in trees such as Ficus concinna in relation to extreme long-term conditions of UHI is scarcely documented. Here, we investigated the transpiration dynamics and its cooling effects in F. concinna induced by changes in site environmental variables in a subtropical megacity, Shenzhen over five consecutive years (2015–2019) based on continuous sap flow measurements. Seasonally, the transpiration (T r) and its cooling effect (i.e., heat energy absorbed (Q) and temperature reduction (ΔT) by T r) were highest in summer, peaking in the month of July with the mean values of 1.98 mm d−1, 4.91 MJ m−2 d−1 and 3.93 °C m−2 d−1, respectively. The highest cooling effect was shown during warmer and wet years. Daily T r had a positive linear relationship with shortwave radiation (R s) in May-June, air temperature (T a) and volumetric soil water content (SWC 30) in July-August and vapor pressure deficit (VPD) in September, respectively. Furthermore, the main regulatory variables of T r within each season were found to be the spring R s , summer T a and SWC 30 , and autumn R s and VPD, which explain 49, 82 and 74% of the variation, respectively. The influence of these variables (i.e., T a , R s and VPD) on T r was modified by the effect of SWC 30. Interannually, T a , SWC 30 and precipitation (PPT) were responsible for most of the observed variation in T r , individually explaining 72, 81, and 66% of the variation. Furthermore, multiple regression model indicated that together T a , SWC 30 and PPT explained 89% of the variation in T r. The diminished sensitivity of T r to environmental variables and enhanced sensitivity to SWC 30 during dry years point to species acclimatization to soil dryness. Our findings clearly indicate the temporal dynamics in T r and its cooling effectiveness for F. concinna over longer timescales. It is suggested that F. concinna could be better suited in response to increasing temperature in subtropical urban areas, as the species may be capable to provide efficient cooling based on its high T r rate and has the potential to mitigate the UHI effect. [ABSTRACT FROM AUTHOR]

The acclimation of plants to water deficit is the result of many different physiological and biochemical mechanisms. To gain a better understanding of drought stress acclimation and tolerance mechanisms in Populus cathayana Rehder, we carried out an integrated physiological and comparative proteomic analysis on the drought stress responses of two contrasting populations originating from wet and dry regions in western China. The plantlets were subjected to continuous drought stress by withholding soil water content at 25% of field capacity (FC) for 45 days, while the control treatments were kept at 100% FC. Drought stress significantly inhibited plant growth, decreased net photosynthetic rate and stomatal conductance of leaves, increased the relative electrolyte leakage and malondialdehyde (MDA) content, and, at the same time, accumulated soluble sugars and free proline in both populations tested. The population from the dry climate region exhibited stronger tolerance to drought stress compared with the wet climate population. The proteomic analyses resulted in the identification of 40 drought-responsive proteins. The functional categories of these proteins include the regulation of transcription and translation, photosynthesis, cytoskeleton, secondary metabolism, HSPs/chaperones, redox homeostasis and defense response. The results suggest that poplars’ tolerance to drought stress relates to the control of reactive oxygen species (ROS) and to osmoprotective capacity. The differential regulation of some drought-responsive proteins, such as HSPs and the enzymes related to redox homeostasis and regulation of secondary metabolism, plays an important role in poplars’ tolerance and acclimation to drought stress. In conclusion, acclimation to water deficit involves changes in cellular metabolism and the regulation of gene networks. The present study not only provides new insights into the mechanisms of acclimation and tolerance to drought stress in different poplar populations but also provides clues for improving poplars’ drought tolerance through breeding or genetic engineering. [ABSTRACT FROM AUTHOR]

• Nighttime sapflow per leaf area J s n exhibited thresholded-response to T a , VPD and G s. • Seasonal variation in T a and VPD controlled J s n in wet and G s and SWC in dry years. • Interannual variation in T a and G s directly controlled J s n , while indirectly by SWC. • J s n responses to biophysical factors underscores the acclimation to dry conditions. • J s n significantly contributed to the daily total sap flow with interannual mean of 11%. The impact of extreme desert conditions on long-term nighttime sap flow dynamics in desert-dwelling shrubs is poorly understood. Based on heat-balance measurements in a semiarid area of northwest China, we investigated the nighttime sap flow (transpiration) dynamics in Salix psammophila as affected by changes in site biophysical variables over a six-year period (2012-2017). Nocturnally, sap flow rate per leaf area (J s n) formed a positive linear relationship with air temperature (T a), water vapor pressure deficit (VPD) and stomatal conductance (G s), when T a < 17 °C, VPD < 1 kPa, and G s < 0.004 mol m−2 s−1, remaining unchanging or forming a negative linear relationship, when T a , VPD and G s were greater than these limits. This relationship was modified by soil water content (SWC) through its effects on G s. The multiple regression model showed that together T a , VPD and G s explained 63% of the variation in J s n. Seasonally, pairwise relationships between T a and VPD and G s and SWC explained 76 and 70% of the variation in J s n during wet and dry years, respectively. Interannually, T a and G s were able to explain a significant portion of observed variation in J s n , individually explaining about 74 and 83% of that variation. Interannual control on J s n also varied with SWC, T a and G s explaining 84% of the variation. The diminished sensitivity of J s n to both T a and VPD and increased sensitivity to SWC during dry years, suggested that the shrubs had a physiological capacity to adapt to dry soil conditions. Daytime sap flow rates (J s d) were significantly greater than those at night (i.e., J s n), with an interannual mean difference of 0.15 ± 0.04 g cm−2 d−1 and coefficient of variation of 27%. In addition, J s n formed a positive linear association with J s d during the growing season. Mean J s n contributed to the daily total sap flow (i.e., J s n /J s 24-h × 100) by 8-14% over the six years, with an interannual mean of 11%. Our findings underscore the importance of nighttime sap flow in S. psammophila and the importance of temperature and SWC in controlling nighttime water losses through transpiration. It is suggested that the proportion of nighttime sap flow could increase during plant acclimatization in response to increasing temperature and water shortages with future climate change. [ABSTRACT FROM AUTHOR]