Global warming has been linked to declines in tree growth. However, it is unclear how the asymmetry in daytime and nighttime warming influences this response. Here, we use 2947 residual tree‐ring width chronologies covering 32 species at 2493 sites, between 1901 and 2018, across the Northern Hemisphere, to analyze the effects of daytime and nighttime temperatures, precipitation, and drought stress on the radial growth of trees. We show that drought stress was primarily triggered by daytime rather than nighttime warming. The radial growth of trees was more sensitive to drought stress in warm regions than in cold regions, especially for angiosperms. Our study provides robust evidence that daytime warming is the primary driver of the observed declines in forest productivity related to drought stress and that daytime and nighttime warming should be considered separately when modelling forest–climate interactions and feedbacks in a future, warmer world.

We selected four Populus euphratica Oliv. forest plots (100 m × 100 m) in the upper reaches of the Tarim River in the Xinjiang Uygur Autonomous Region of China. Each of the four forest plots was chosen to represent a different growth and death stage of P. euphratica forest: juvenile forest, mature forest, dying forest, and dead forest. In each plot, we measured the coordinates, DBH, height, and status of all P. euphratica individuals. We used (1) spatial pattern analysis to explore spatial distribution patterns and associations of live trees and dead trees, (2) a random mortality model to test whether the tree death was random or non-random, and (3) a generalized linear mixed-effect model (GLMM) to analyse factors related to tree survival (or death). In the juvenile plot, live trees were significantly aggregated at all scales (p < 0.05); while in the mature and dying plots, live trees were more aggregated at small scales and randomly distributed at larger scales. Live trees and dead trees showed a significantly positive association at all scales in the juvenile plot (p < 0.05). While in the mature and dying plots, live trees and dead trees only showed a significantly positive association at scales of 0-3 m (p < 0.05). There was significant density-dependent mortality in the juvenile plot; while mortality was spatially random at all scales in the mature and dying plots. The distance from the river showed significantly negative correlations with tree survival (p < 0.01). DBH and height had significantly positive associations with tree survival in the juvenile, mature, and dying plots (p < 0.05). In extreme drought, dying trees appeared to be shape-shifting into more shrub-like forms with clumps of root sprouts replacing the high canopies. The shift under extreme drought stress to more shrub-like forms of P. euphratica may extend their time to wait for a favourable change.Populus euphratica Oliv., the desert poplar, is a prominent component of Tugai floodplain ecosystems along river valleys in arid and semi-arid regions with a very wide range, occurring naturally from North Africa, across the Middle East and Central Asia to western China 1,2 . The P. euphratica forests, which are also known as Tugai forests, are the main component of the desert riparian vegetation in Central Asian inland rivers. These P. euphratica forests provide an important habitat for plants and animal life and harbour the highest plant biodiversity in desert regions [3][4][5] , which is likely also to enhance local biodiversity of animals, such as birds and insects. Additionally, these Tugai forests provide major natural resources (timber, fuelwood, livestock fodder, etc.) and provide critical environmental benefits such as increasing watershed protection, including stabilization of riverbanks and providing windbreaks to reduce erosion of sand and soil 1,4,6 .The expansion and decline processes of P. euphratica forests are closely related to hydrological events (e.g., river diversion, variation of river discharge, and groundwater depth) coupled...

Gloiopeltis furcata (Postels & Ruprecht) J. Agardh, a macroalga, which grows in an upper, intertidal zone, can withstand drastic environmental changes caused by the periodic tides. In this study, the photosynthetic and morphological characteristics of G. furcata were investigated. The photosynthetic performance and electron flows of the thalli showed significant variations in response to desiccation and salinity compared with the control group. Both PSII and PSI activities declined gradually when the thalli were under stress. However, the electron transport rate of PSI showed still a low value during severe conditions, while the rate of PSII approached zero. Furthermore, PSI activity of the treated thalli recovered faster than PSII after being submerged in seawater. Even though the linear electron flow was inhibited by DCMU [3-(3, 4-dichlorophenyl)-1,1-dimethylurea], the cyclic electron flow could still be restored. The rate of cyclic electron flow recovery declined with the increasing time of dark treatment, which suggested that stromal reductants from starch degradation played an important role in the donation of electrons to PSI. This study demonstrated that PSII was more sensitive than PSI to desiccation and salinity in G. furcata and that the cyclic electron flow around PSI played a significant physiological role. In addition, G. furcata had branches, which were hollow inside and contained considerable quantities of funoran. These might be the most important factors in allowing G. furcata to adapt to adverse intertidal environments.

Background: Leaf functional traits can influence the ability of plants to grow when facing stresses. Climate changes can impose fundamental impacts on plant growth, especially at high mountains. Yet little is known about the relationships between leaf functional traits and elevations in tree species above 4000 m a.s.l. Aims:Our objective was to investigate and compare the trend in water use efficiency (WUE) in the Tibetan juniper (Juniperus tibetica) along elevation gradients under different climate conditions, and by presenting evidence from leaf functional traits, to simultaneously clarify the underlying mechanisms. Methods:We investigated five leaf functional traits in J. tibetica, a dominant tree species of the treeline, along elevation gradients at three study sites between 4150 and 4950 m a.s.l. in the Qinghai-Tibet Plateau. Results:As elevation increased, leaf δ 13 C, used as a proxy for WUE, increased, whereas leaf δ 18 O decreased in J. tibetica. Leaf nitrogen concentrations per unit area (Narea) also increased with elevation. Conclusions:We deduced that increasing WUE with elevation was due to enhanced photosynthetic capacity at all three study sites, and increased Narea may enhance photosynthesis and hence WUE.