Tree Physiology

Nitrogen (N) plays an important role in mitigating salt stress in tree species. We investigate the genotypic differences in the uptake of ammonium (NH4+) and nitrate (NO3-) and the importance for salt tolerance in two contrasting poplars, salt-tolerant Populus euphratica and salt-sensitive P. popularis. Total N content, growth, and photosynthesis were significantly reduced in P. popularis after 7 days exposure to NaCl (100 mM) supplied with 1 mM NH4+ and 1 mM NO3-, while the salt effects were not pronounced in P...

Land surface temperature is predicted to increase by 0.2 °C per decade due to climate change although with considerable regional variability, and heatwaves are predicted to increase markedly in the future. These changes will affect where crops can be grown in the future. Understanding the thermal limits of plant physiological functioning and how flexible such limits are is thus important. Here we report on measurements of a core foliar thermotolerance trait, T50, defined as the temperature at which the maximum quantum yield (Fv/Fm) of photosystem II declines by 50%, across nine different Malaysian Hevea brasiliensis clones...

Fire-induced heating of stems can impair plant water transport by deforming xylem and increasing vulnerability to cavitation, but it is not clear whether these effects can result in tree death, nor how quickly this may occur. In field experiments, we heated stems of Symplocos tinctoria saplings to 90 °C using a thin-film resistive heater, and we monitored stomatal conductance, leaf water potential, sap flow, and hydraulic conductivity until stem death. Sap flow and stomatal conductance declined quickly after heating, while whole-plant hydraulic conductance and leaf water potential remained high for the first week...

No abstract text is available yet for this article.

Peumus boldus, a tree native to Chile, is extensively used for medicinal purposes due to its richness in alkaloids and antioxidant polyphenols. A species of galling insect, Dasineura sp. induces structural and chemical changes on P. boldus stems while its galls are established and developed. Taking into account the antioxidant properties of P. boldus polyphenols, it would be expected that Dasineura sp. induce changes in the accumulation sites, chemical profile, and antioxidant activity of the P. boldus stem polyphenols, related to different ROS production levels during gall development...

In temperate evergreen conifers, growth occurs mostly in summer but photosynthesis precedes year-round; thus, nonstructural carbohydrates (NSC) increase in winter but decrease in summer. Given that mild drought reduces growth but not photosynthesis, a drought in summer should increase NSCs more than one in winter. However, the active regulation hypothesis suggests that to increase future drought resilience, plants might downregulate growth to increase NSCs after a winter drought even if NSCs do not increase during the drought...

As climate change exacerbates drought stress in many parts of the world, understanding plant physiological mechanisms for drought survival is critical to predicting ecosystem responses. Stem net photosynthesis, which is common in arid environments, may be a drought survival trait, but whether the additional carbon fixed by stems contributes to plant hydraulic function and drought survival in arid land plants is untested. We conducted a stem light exclusion experiment on saplings of a widespread North American desert tree species, Parkinsonia florida, and after shading acclimation, we then subjected half of the plants to a drought treatment to test the interaction between light exclusion and water limitation on growth, leaf and stem photosynthetic gas exchange, xylem embolism assessed with micro-CT and gravimetric techniques, and survival...

C4 photosynthesis outperforms C3 photosynthesis in natural ecosystems by maintaining a high photosynthetic rate and affording higher water-use and nitrogen-use efficiencies. C4 plants can survive in environments with poor living conditions, such as high temperatures and arid regions, and will be crucial to ecological and agricultural security in the face of global climate change in the future. However, the genetic architecture of C4 photosynthesis remains largely unclear, especially the genetic regulation of C4 Kranz anatomy...

Woody plants rely on the remobilization of carbon (C) and nitrogen (N) reserves to support growth and survival when resource demand exceeds supply at seasonally predictable times like spring leaf flush and following unpredictable disturbances like defoliation. However, we have a poor understanding of how reserves are regulated and whether distance between source and sink tissues affects remobilization. This leads to uncertainty about which reserves-and how much-are available to support plant functions like leaf growth...

Tropical karst habitats are characterized by limited and patchy soil, large rocky outcrops, and porous substrates, resulting in high habitat heterogeneity and soil moisture fluctuations. Xylem hydraulic efficiency and safety can determine the drought adaptation and spatial distribution of woody plants growing in karst environments. In this study, we measured sapwood-specific hydraulic conductivity (Ks), vulnerability to embolism, wood density, saturated water content, and vessel and pit anatomical characteristics in the branch stems of 12 evergreen tree species in a tropical karst seasonal rainforest in southwestern China...

Stomata are pivotal in modulating water and carbon processes within plants. However, our understanding of the temporal dynamics of water- and carbon-related traits, as influenced by stomatal behavior, remains limited. Here, we explore how stomatal regulation behavior and water- and carbon-related traits vary with changing environments by examining the seasonal variations in these traits of the native tree species Schima superba in low subtropical China. In February, April, and July of 2022, a series of water- and carbon-related traits were measured in the leaves and stems...

Mongolian willow (Salix linearistipularis) is a naturally occurring woody dioecious plant in the saline soils of northeastern China that has a high tolerance to alkaline salts. Although transcriptomics studies have identified a large number of salinity-responsive genes, the mechanism of salt tolerance in Mongolian willow is not clear. Here, we found that in response to Na2CO3 stress, Mongolian willow regulates osmotic homeostasis by accumulating proline and soluble sugars, and scavenges ROS by antioxidant enzymes and non-enzymatic antioxidants...

No abstract text is available yet for this article.

Limited information is available on the variation of plant leaf hydraulic traits in relation to soil rock fragment content (RFC), particularly for xerophytes native to rocky mountain areas. In this study, we conducted a field experiment with four gradients of RFC (0%, 25%, 50% and 75% ν ν-1) on three different xerophytic species (Sophora davidii, Cotinus szechuanensis, and Bauhinia brachycarpa). We measured pre-dawn and midday leaf water potential (Ψleaf), leaf hydraulic conductance (Kleaf), Ψleaf induced 50% loss of Kleaf (P50), pressure-volume curve traits, and leaf structure...

Plants can improve their resistance against feeding damage by insects if they have perceived insect egg deposition prior to larval feeding. Molecular analyses of these egg-mediated defence mechanisms have until now focused on angiosperm species. It is unknown how the transcriptome of a gymnosperm species responds to insect eggs and subsequent larval feeding. Scots pine (Pinus sylvestris) is known to improve its defences against larvae of the herbivorous sawfly Diprion pini if it has previously received sawfly eggs...

The level of Cadmium (Cd) accumulation in orchard soils is increasing, excess Cd will cause serious damage to plants. Melatonin is potent natural antioxidant and has a potential role in alleviating cadmium stress. This study aimed to investigate the effects of exogenous melatonin on a root endophyte bacteria community and metabolite composition under Cd stress. The results showed that melatonin significantly scavenged reactive oxygen species (ROS), and restored the photosynthetic system (manifested by the improved photosynthetic parameters, total chlorophyll content (TCC), and the chlorophyll fluorescence parameters (Fv/Fm)), increased the activity of antioxidant enzymes (the activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), ascorbate oxidase (APX)), and reduced the concentration of Cd in the roots and leaves of apple plants...

Stem respiration (RS) substantially contributes to the return of photo-assimilated carbon to the atmosphere and, thus, to the tree and ecosystem carbon balance. Stem CO2 efflux (ECO2) is often used as a proxy for RS. However, this metric has often been challenged because of the uncertain origin of CO2 emitted from the stem due to post-respiratory processes. In this Insight, we (i) describe processes affecting the quantification of RS, (ii) review common methodological approaches to quantify and model RS, and (iii) develop a research agenda to fill the most relevant knowledge gaps that we identified...

Sap exudation is the process whereby trees such as sugar (Acer saccharum) and red maple (Acer rubrum) generate unusually high positive stem pressure in response to repeated cycles of freeze and thaw. This elevated xylem pressure permits the sap to be harvested over a period of several weeks and hence is a major factor in the viability of the maple syrup industry. The extensive literature on sap exudation documents competing hypotheses regarding the physical and biological mechanisms that drive positive pressure generation in maple, but to date relatively little effort has been expended on devising mathematical models for the exudation process...

As wildfires increase in size and severity, large areas of forest are undergoing substantial increases in shrub cover. In forests where water is the limiting resource, the partitioning of soil water between shrubs and young trees may determine how shrubs affect tree growth and water-stress. Here we evaluated juvenile trees (average age = 32 years) of two dominant conifer species in the southern Sierra Nevada of California (Abies concolor (white fir) and Pinus jeffreyi (Jeffrey pine)) growing in the presence or absence of shrubs...

Understanding the within-tree variability of non-structural carbohydrates (NSC) is crucial for interpreting point measurements and calculating whole-tree carbon balances. Yet, little is known about how the vertical light gradient within tree crowns influences branch NSC concentrations and dynamics. We measured NSC concentrations, irradiance and key leaf traits in uppermost, sun-exposed and lowest, shaded branches in the crowns of mature, temperate trees from nine species with high temporal resolution throughout one growing season...