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ABSTRACT Transpirational cooling is crucial for plant thermal regulation to avoid overheating; however, during prolonged and/or acute heat stress it often necessitates stomatal closure to reduce the risk of hydraulic failure due to dehydration. The intricate interplay between thermal regulation, water transport and use may govern plant performance in water‐limited and simultaneously heat‐stressed environments, yet this remains inadequately understood. Here, in a common garden, we evaluated the functional associations among physiological characteristics related to leaf thermoregulation, heat tolerance, xylem water transport, and stomatal regulation in eight shrub species commonly used for fixing active sand dunes in northern China. Our study showed that traits associated with heat adaptation and xylem hydraulics were closely related to stomatal regulation. More isohydric shrub species with higher water transport efficiency possessed stronger transpirational cooling capacity; whereas the more anisohydric species demonstrated greater tolerance to overheating. Moreover, leaf heat tolerance was strongly coordinated with drought tolerance reflected by leaf turgor loss point. These results underscore the importance of stomatal regulation in shaping plant thermal adaptive strategies and provide valuable insights into the coupling of water and heat‐related physiological processes in plants adapted to sandy land environments prone to combined drought and heat stresses. [ABSTRACT FROM AUTHOR]

Crown removal revitalises sand‐fixing shrubs that show declining vigour with age in drought‐prone environments; however, the underlying mechanisms are poorly understood. Here, we addressed this knowledge gap by comparing the growth performance, xylem hydraulics and plant carbon economy across different plant ages (10, 21 and 33 years) and treatments (control and crown removal) using a representative sand‐fixing shrub (Caragana microphylla Lam.) in northern China. We found that growth decline with plant age was accompanied by simultaneous decreases in soil moisture, plant hydraulic efficiency and photosynthetic capacity, suggesting that these interconnected changes in plant water relations and carbon economy were responsible for this decline. Following crown removal, quick resprouting, involving remobilisation of root nonstructural carbohydrate reserves, contributed to the reconstruction of an efficient hydraulic system and improved plant carbon status, but this became less effective in older shrubs. These age‐dependent effects of carbon economy and hydraulics on plant growth vigour provide a mechanistic explanation for the age‐related decline and revitalisation of sand‐fixing shrubs. This understanding is crucial for the development of suitable management strategies for shrub plantations constructed with species having the resprouting ability and contributes to the sustainability of ecological restoration projects in water‐limited sandy lands. Summary statement: Embolism accumulation restricted carbon assimilation in aging shrubs and resulted in growth decline, while the crown‐removal treatment revitalised plants by promoting the construction of new hydraulic systems in resprouts and enhancing carbon balance through the removal of dysfunctional old stems. [ABSTRACT FROM AUTHOR]

Drought-associated tree mortality and forest decline have been increasingly observed across the globe due to warmer and drier climates, particularly in drought-prone environments. Understanding how forests respond to the increasing inter-annual climate variability and frequent severe drought events in the context of global change is of great significance for predicting the dynamics of forest ecosystems under future warming-drying climate scenarios. This study combined tree-ring series, xylem anatomy, wood isotope signatures, and remote sensing methods to examine the physiological mechanisms underlying the response of natural H. davidii forests in Horqin Sandy Land, a water-limited area in northern China, to the identified severe drought events and long-term climatic variability. Our results indicated that the climatic variables related to environmental moisture conditions exert the most profound influence on the performance of the studied species, with severe drought events significantly reducing growth vigor. The concurrent reduction in water-transporting conductivity and increase in water-use efficiency signified the prevalence of a more conservative water-use strategy in response to severe droughts at the holistic level of the whole tree, which physiologically accounts for the increased hydraulic safety and diminished radial growth during the period. Remotely sensed vegetation indices appeared to respond less conspicuously to severe drought events compared to radial growth, xylem anatomical traits, and water use efficiency. Nonetheless, a coordinated response to climatic variability between tree canopy and individual-level performance was found over the long-term time series, implying that a multiscale approach enhances our comprehension of the long-term forest responses to climatic variability. In short, this study highlights the role of water-related physiology in modulating the performance of H. davidii trees during severe droughts by adjusting xylem hydraulic functioning and tree water use efficiency. The findings lay a theoretical foundation for the use of native tree species for sustainable afforestation in vulnerable sandy land environments. • Multiple approaches were used to examine Hemiptelea davidii forest responses. • Inter-annual responses to climate at individual and stand levels were coordinated. • Water exerts the strongest influence on forest performance of different levels. • Xylem hydraulics and water use efficiency adjusted significantly during droughts. [ABSTRACT FROM AUTHOR]

Ginkgo biloba is an important urban ornamental tree species, but poor growth and damages often occur in urban environments. As a street tree species, the decline and death of G. biloba is particularly frequent, with the relevant physiological mechanism being unclear. In this study, we compared hydraulic characteristics, non-structural carbohydrate (NSC) contents and health status between G. biloba trees growing along the streets and those in parks in Shenyang City. The results showed that G. biloba growing along the streets showed higher degrees of branch and leaf mortality than those growing in the parks. Branches of G. biloba growing in both conditions showed lower degrees of xylem embolism. Branch hydraulic vulnerable curves of G. biloba under the two growing conditions also showed no significant difference, with the average P 50 being lower than -2.8 MPa. G. biloba growing along the streets had lower leaf area specific conductivity, smaller tracheid diameter, smaller hydraulic diameter, lower soluble sugar content and total NSC than those growing in parks. Hydraulic failure was not the direct reason for the decline and mortality of G. biloba growing along streets. Under the more stressed growth conditions along the streets, G. biloba had smaller tracheid diameters in stems and lower Huber values, which limited the ability of water transport and photosynthetic carbon assimilation at the whole branch level. In addition, in order to deal with more serious stress such as greater heat and drought stresses, G. biloba might need to invest more NSC to repair damage, which further decreaded NSC contents in branches and increased the risk of carbon imbalance. At the same habitat (street or park), xylem hydraulics and NSC contents of G. biloba also showed relatively large difference among sampling sites, which reflected large heterogeneity of urban environment for tree growth.

Three dew amount gradients,i.e., few amount of dew (W 0 ), natural amount of dew (W 1 ) and the doubled amount of natural dew (W 2 ) were set to study the response strategies of the morphology, physiology and the dry matter allocation of Lappula semiglabra seedlings on dew amount in Ebinur Lake Wetland National Nature Reserve in Xinjiang, China. The results showed that plant traits in connection with absorbing water by plant leaves, involving in relative content of chlorophyll, leaf water potential, plant height, crown breadth, stem mass and leaf mass ratio increased significantly with the amount of dew. On the contrary, the main stem diameter, root length and root diameter which associated with water absorption and transportation by root had no significant change with the amount of dew. Plant height and the relative content of chlorophyll were the most obvious traits in response to dew amount among all leaf absorption water traits. The proportion of stem biomass had no significant difference along the dew amount gradient. However, the root mass ratio declined gradually along the growth of seedlings, and seedlings in W 0 had the smallest decline rather than W 1 and W 2 . In conclusion, L. semiglabra seedlings changed aboveground traits in response to the change of dew amount. Specifically, it increased its photosynthetic capacity and ratio of leaf dry matter to adapt to the variation on dew amount.