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Populus tree species are commonly used for creating shelter forests in vast areas of northern China, at least partially due to their fast growth. However, they are facing severe problems of decline and mortality caused by drought. In contrast, tree species native to water-limited environments usually have slow growth and are currently not commonly used in afforestation, while these species are gaining more attention in forestry for their greater resilience to drought. In Horqin Sandy Land, we conducted a comparative analysis of xylem hydraulics and associated physiological traits between six Populus tree species and six tree species native to drought-prone areas. Compared to the native species, the Populus species exhibited significantly higher stem hydraulic conductivity but lower resistance to drought-induced xylem embolism than the native tree species. The observed interspecific variations and contrasts in xylem hydraulics between the two species groups were predominantly attributed to xylem anatomical characteristics at the pit level rather than at the tissue level. In line with the divergences in hydraulics, we found significantly lower intrinsic water use efficiency (WUE i ) in Populus than in the native species, suggesting that the two groups adopted relatively acquisitive and conservative water use strategies, respectively. The trade-off between hydraulic efficiency and safety, as well as that between hydraulic efficiency and WUE i , underlies the contrasts in performance between Populus species and the native tree species, that is, fast growth of Populus species but high risk of hydraulic dysfunction when facing drought, and vice versa., (© 2025 Scandinavian Plant Physiology Society.)

Drought combined with extreme heatwaves has been increasingly identified as the important trigger of worldwide tree mortality in the context of climate change; nonetheless, our understanding of the potential hydraulic and thermal impairments of hot droughts to trees and the subsequent post-recovery process remains limited. To investigate the response of tree water and carbon relations to drought, heatwave, and combined drought-heatwave stresses, three-year-old potted seedlings of Fraxinus mandshurica Rupr., a dominant tree species in temperate forests of northeast China, were grown under well-watered and drought-stressed conditions and exposed to a rapid, acute heatwave treatment. During the heatwave treatment with a maximum temperature exceeding 40 °C for two days, the leaf temperature of drought-stressed seedlings was, on average, 5 °C higher than that of well-watered counterparts due to less effective evaporative cooling, indicating that soil water availability influenced leaf thermoregulatory capacity during hot extremes. Consistently, more pronounced crown damage, as shown by 13 % irreversible leaf scorch, was found in seedlings under the drought-heatwave treatment relative to sole heatwave treatment, alongside the more severe stem xylem embolism and leaf electrolyte leakage. While the heatwave treatment accelerated the depletion of non-structural carbohydrates in drought-stressed seedlings, the increase of branch soluble sugar concentration in response to heatwave might be related to the requirement for maintaining hydraulic functioning via osmoregulation under high dehydration risk. The coordination between leaf stomatal conductance and total non-structural carbohydrate content during the post-heatwave recovery phase implied that plant-water relations and carbon physiology were closely coupled in coping with hot droughts. This study highlights that, under scenarios of aggravating drought co-occurring with heatwaves, tree seedlings could face a high risk of crown decline in relation to the synergistically increased hydraulic and thermal impairments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

This document discusses the challenges faced by plants in arid and semi-arid regions due to harsh environmental conditions such as limited rainfall, high temperatures, and poor soil nutrition. The document highlights the importance of understanding plant adaptation strategies to extreme environments in order to protect and manage local vegetation and ecosystems. The document presents research papers that cover various aspects of plant adaptation in arid regions, including water uptake mechanisms, physiological and biochemical adaptations, plant-soil microbial interactions, and ecosystem services. The research findings provide insights into how plants in arid regions adapt to environmental changes and maintain ecological balance. However, further research is needed to fully understand the processes and mechanisms of plant adaptation in extreme environments. [Extracted from the article]

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]

Differences in key physiological characteristics between plant species can result in their contrasting performances in vegetation restoration projects, but ecophysiological comparative studies in close relation to ecological restoration projects are scarce. Hedysarum fruticosum Pall. and Caragana microphylla Lam. are two leguminous shrub species widely used in combination for fixation of active sand dunes in semiarid regions of northern China, but they clearly differ in fitness at different stages of dune vegetation development; that is, H. fruticosum quickly gains a community dominance at the initial stage but yields to C. microphylla in a few years after the fixation of dunes. To reveal the underlying mechanism of such a pattern, key physiological characteristics related to xylem water transport, leaf water use, and drought tolerance were compared between these two species at a typical site of sand dune fixation project in Inner Mongolia. Compared with C. microphylla, H. fruticosum shows an acquisitive and risky water management strategy with substantially higher hydraulic efficiency and photosynthetic capability but reduced resistance to drought‐induced xylem embolism, which endows it an advantage under conditions of relatively high soil water availability at the early stage of dune fixation. In contrast, C. microphylla exhibits more conservative water use and characteristics of greater drought tolerance, which results in greater dominance under the more drought‐stressed conditions of the later stage of dune fixation. Our study for the first time provides a potential mechanistic explanation for the clear switching of dominant positions between the two important sand‐fixing shrub species during the sand dune revegetation process. [ABSTRACT FROM AUTHOR]

Mongolian pine (Pinus sylvestris var. Mongolica) is among the most commonly used coniferous afforestation tree species for building shelter forests in vast areas of northern China, yet it is at a high risk of mortality in the context of increased frequency of extreme drought events associated with anticipative climate change. Understanding the long-term ecophysiological response to climate extremes is of great relevance for taking appropriate practices for the sustainability-oriented management of Mongolian pine plantations in drought-prone environments. Here, the hydraulic strategy behind the response of the radial growth of Mongolian pine trees planted in a water-limited area of northern China to the extreme drought event from 2001 to 2004 was retrospectively investigated by combining standard dendrochronological methods and quantitative wood anatomy. We found that water-related climatic variables acted as the main factors regulating the radial growth and xylem tracheid size of the Mongolian pine trees at the study site, and the extreme drought significantly reduced xylem theoretical hydraulic conductivity and almost stagnated the trunk radial increment. Immediately after this climatic extreme, the stem growth sharply increased to a level substantially higher than that preceding the extreme drought, which was probably attributable to the reduction of inter-tree competitions for resources due to the mortality of a large number of trees caused by the extreme drought event. Around the extreme drought event, tree ring width was significantly proportional to the number of earlywood tracheid cell layers but was uncorrelated with tracheid size metrics, alongside a clear hydraulic safety-efficiency trade-off among the stem xylem traits obtained from tree ring series. This study stresses the role that xylem hydraulics play in modulating the radial growth of plantation-grown Mongolian pine trees during extreme droughts by adjusting xylem structural characteristics and hence hydraulic transport functions. • Precipitation was the main climatic variable affecting ring width and tracheid size. • The extreme drought around 2003 minimized the radial growth of Mongolian pine trees. • Retained trees showed a strong growth release effect after the extreme drought event. • Drought-induced growth decline was mainly due to tracheid number not size reduction. • Adjustments during extreme drought showed a hydraulic safety-efficiency trade-off. [ABSTRACT FROM AUTHOR]

Intensifying drought around the globe poses strong challenges to the growth and survival of trees, emphasizing the urgency of understanding the physiological mechanisms of drought-induced tree decline and mortality and the necessity of using silvicultural approaches to mitigate drought effects on tree growth. We experimentally explored whether thinning enhances tree growth vigor and drought resilience in early aging Mongolian pine (Pinus sylvestris var. mongolica Litv.) plantations in a water-limited area of Northeast China using dendrochronological methods. Meanwhile, we compared plant hydraulic traits, water relations, and non-structural carbohydrate concentrations between trees growing in the thinned and un-thinned stands with the aim of unraveling the physiological mechanisms underlying the density effects on tree growth performance. The results showed that basal area increments of Mongolian pine trees in the high-density plantations started to decline continuously at tree cambium age of around 15 years over about a decade, while thinning effectively reversed their growth decline. Trees in thinned stands exhibited significantly higher predawn leaf water potentials, higher stem hydraulic conductivities, and larger carbon reserves than trees in un-thinned stands. Although trees growing in high-density stands maintained as low risks of xylem hydraulic dysfunction as trees growing in low-density stands, that was at the cost of substantially reducing tree crown size through branch mortality that unavoidably undermined their carbon balance at the whole-plant level. Consistently, trees growing in the thinned low-density stands showed significantly higher levels of non-structural carbohydrate reserve in stems and enhanced growth resilience to extreme drought than trees growing in the high-density reference stands. Our results suggest that thinning can effectively enhance xylem hydraulic transport efficiency and reduce the risk of carbon imbalance by increasing soil water availability and hence mitigates the early aging of Mongolian pine plantations in water-limited environments. • Thinning improved growth vigor and drought resilience of aging plantations. • Trees exhibited higher hydraulic efficiency and better water status after thinning. • Higher nonstructural carbohydrate content contributed to greater drought resilience. [ABSTRACT FROM AUTHOR]