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Key message

This article studied the effect of exogenous SA on the metabolites of blueberry leaves under high temperature conditions. Heat and exogenous SA induce changes in the accumulation of secondary metabolites in blueberry.

Abstract

Exogenous salicylic acid (SA) can enhance plant resistance to abiotic stress, particularly heat tolerance and play a protective role in alleviating oxidative damage. Flavonoids have antioxidant activity and are considered as secondary ROS scavenging systems in plants, playing an important role under high temperature stress. Therefore, this study investigated the accumulation and alterations of secondary metabolites, particularly flavonoids, in blueberries following exogenous SA application under high-temperature stress. Using non-targeted LC-MS analysis, 646 and 350 metabolites were identified in positive and negative modes, respectively, of which 464 and 304 were known metabolites. Metabolites were annotated through KEGG, HMDB, LIPID MAPS databases, and 11, 39 and 47 flavonoids were annotated, respectively. KEGG pathway annotation showed that metabolites in blueberry leaves were most enriched in the biosynthesis of secondary metabolites pathway under positive mode, followed by the glutathione metabolism pathway. In the negative mode, metabolites are most enriched in the metabolic pathways, followed by the biosynthesis of secondary metabolites pathway. Notably, 11 differential metabolites were annotated within the flavonoid biosynthesis pathway. Based on the accumulation of flavonoids in various groups (CK0, CK12, CK96, SA12, SA96), it is concluded that caffeoyl shikimic acid and kaempferol may be key metabolites to alleviate blueberry heat damage, and that exogenous SA can induce the biosynthesis of the two flavonoids.

Key message

Climate significantly influenced plant functional traits of different forest types of the Western Himalayan region, revealing adaptive response and evolving resource allocation strategies under changing climatic conditions.

Abstract

The present study assesses the plant functional traits of dominant and co-dominant species in long-term ecological monitoring (LTEM) sites in the Western Himalaya. The aim is to quantify ecosystem processes and adaptations to environmental fluctuations from 2018 to 2023, providing insights into the resilience of these forests under climatic variability. The current study assessed the plant’s functional, morphological, physiological, and biochemical traits, as well as soil analysis, for each selected species. Results revealed stable species richness across all life forms, coupled with an increasing trend in tree and seedling densities, particularly pronounced in the Sal forest, which exhibited the highest average tree density of 59.5 ± 20.4 individuals/ha, reflecting a notable increase in all the LTEM sites. Further the relationship between climate parameter and plant functional traits was evident, with temperature positively influencing transpiration rate (E), stomatal conductance (GsW), and photosynthetic rate (A), while rainfall showed a strong positive relation with transpiration rate and leaf water potential (LWP). In addition, analysis of variance revealed significant (p < 0.001 and p < 0.05) effect of species, season, and year on most of the physiological, morphological and biochemical traits of dominant and co dominant tree, shrub and herb species. Furthermore, principal component analysis and correlation highlight shifts in trait relationship, suggesting evolving resource allocation strategies of the species. This study elucidates the intricate relationship between environmental factors and plant functional traits in the Western Himalaya, emphasizing the importance of ongoing long-term monitoring to evaluate the impacts of climate change on key species. This approach will refine the understanding of vegetation dynamics and strengthen predictive modelling of ecosystem responses.

The responses of tree growth to climate change are highly divergent even within the same species because of the ecological context of their microhabitats. Coarse woody debris, which acts as nurse logs, is an essential microhabitat for trees in subboreal forests. However, little is understood about how nurse logs may alter the response of tree growth to climate change. In this study, we used the interannual branch length over 10–14 years as a proxy for long-term interannual tree growth and compared the correlations with various interannual macroclimate variables for Abies sachalinensis saplings that regenerated either on coarse woody debris (CWD saplings) or those that regenerated from soil (SOIL saplings) in a subboreal forest. While there was a negative relationship between the variation in interannual growth and the maximum temperature of the previous year in both microhabitats, the slope of the relationship was steeper for the CWD saplings. Furthermore, while the positive relationships between the variation in interannual growth and the maximum snow depth of the previous year were significant in both microhabitats, the slope of the relationship was steeper for the CWD saplings. These results indicate that the predicted increase in maximum air temperature and decrease in snow can have more severe negative effects on the growth of conifers regenerated from nurse logs than those from soil. Considering that more than 90% of the saplings of evergreen conifers regenerate from logs in northern Hokkaido, our results provide a warning of the decline in evergreen conifers under the expected future climate in subboreal forests.

Key message

Divergent shrub growth-temperature relationships were observed in adjacent shrubline sites under similar climates, demonstrating that site-specific factors such as topographic conditions modulate shrub growth sensitivity to climate warming.

Abstract

Alpine shrubs are expected to show enhanced growth and upslope shifts as climate keeps warming. However, climate-growth relationships are often contingent on site conditions. Herein, the climate–growth relationships of alpine R. aganniphum shrubs were investigated at a dry (LZ45) and a wet (GB45) site located at an elevation of above 4500 m on the southeastern Tibetan Plateau. Ring-width data were collected from 50 Rhododendron shrubs, and two standardized ring-width chronologies spanning 143 and 178 years were developed for LZ45 and GB45 sites, respectively. Minimum winter temperature was identified as the most significant climatic constraint of shrub radial growth at the dry site, whereas warmer summer conditions enhanced growth at the wet site. Results of linear mixed-effects models demonstrated that combining climatic and topographic factors improved the explained variance of shrub growth at both sites. A lower value of soil moisture and topographic wetness index in the dry site resulted in a lower growth confirming the importance of water shortage in that site. By synthesizing findings on alpine Rhododendron shrubs across several regions, this study highlights the topographical modulation of growth responses of alpine shrubs to climate change. Alpine Rhododendron shrubs in dry sites may be at an increasing risk of growth decline under warmer and drier future climate conditions, with negative implications for alpine ecosystems. Our study illustrates how regional climate and site conditions should be carefully accounted when studying alpine woody communities.

In this study, we analyse the suitability of the machine learning algorithm Random Forest in exploring dendroclimatic relationships. Linear methods are commonly used to explain climate related changes in radial growth, but inherently fail to capture thresholds and nonlinear effects contained in the data. Machine learning applications like Random Forest can potentially fill this gap. We use tree ring chronologies from three temperate coniferous tree species Picea abies, Pseudotsuga menziesii and Pinus sylvestris from northern Germany as well as a chronology from Cedrela odorata grown in a tropical forest in Suriname to compare response function correlation and Random Forest variable importance for monthly temperature and precipitation values on tree ring width. We further explore the possibilities of using Accumulated Local Effects to display nonlinear effects on tree ring increment. Our results show that Random Forest importance aligns well with response function analysis for the temperate species and mostly aligns with the results on Cedrela odorata. Accumulated Local Effect plots offer valuable insights into nonlinear climate effects and help in explaining unexpected correlations. While the Random Forest algorithm is not a complete substitute for established methods like response function analysis to analyse climate-growth relations, it is a valuable addition to the available toolset in exploring the hidden information in dendrochronological data.

Key message

Under drought, carbohydrates initially increase in almond tree organs and, ultimately, their root exudates diversify, suggesting shifts in carbon dynamics may impact osmoregulation and exudation under stress.

Abstract

While root exudation allows trees to shape the rhizosphere, mobilize nutrients, and recruit beneficial microbes, it may be costly during abiotic stress like drought and be expected to decrease to conserve carbon (C) for survival. However, the cost of root exudation under typical and stressed conditions remains unknown, especially for tree crops. To determine whether tree crops allocate C to root exudation and if the metabolite profile shifts under drought, we exposed almond saplings to experimental drought, and once stomatal closure was reached, conditions were maintained for 1, 7, or 10 days prior to collecting root exudates for untargeted metabolomics. We also quantified nonstructural carbohydrate (NSC) concentrations in aboveground and belowground organs. Drought plants had higher sugar concentrations in all organs than well-watered controls, suggesting that osmotic adjustment was occurring at the whole-plant level in response to drought. In the roots, total NSC concentrations were higher in the drought plants and declined over time, likely to support respiration and other root-level functions such as root exudation. However, the decrease was small enough that the amount of C allocated to root exudation may have been negligible, and instead root exudates diversified over time. From day 1 to day 10, the number of metabolites that significantly changed between drought and well-watered control plants went from 25 to 332, a nearly 1250% increase. Further, non-metric multidimensional scaling (NMDS) ordination revealed that the metabolite profiles of drought and well-watered plants differed. Overall, our results indicate that diversifying the C compounds exuded into the rhizosphere may be a strategy to maximize the chances of alleviating drought stress, and provides foundational knowledge for future studies to quantify root exudation profiles in other perennial tree crops.

Fine roots play a critical role in water and nutrient uptake, contributing significantly to the ecosystem carbon cycle. This study investigates the effects of soil water availability on the vertical distribution of fine root annual production and turnover rates in hybrid poplar (Populus nigra × P. maximowiczii, clone J-105) short-rotation coppice plantation. We hypothesized that reduced throughfall would lead to a deeper vertical distribution of fine roots and affect their annual production and turnover rates. The study was conducted in a drought experiment established in a coppiced poplar plantation in the Czech Republic. Root biomass and in-growth cores were used to quantify root vertical distribution, production, and turnover rates under control and drought (throughfall reduction) treatments. Root distributions were modeled using the asymptotic equation and the logistic dose-response curve. Although total fine root biomass (255 g DM m^− 2; 0–60 cm) and production (298 g DM m^− 2 y^− 1; 0–60 cm) were not significantly affected by drought, the vertical distribution of fine roots was influenced by soil water availability. Model results show that at lower soil water content in May (20%) corresponded to a greater proportion of roots (50% roots) at deeper soil layers as compared with higher soil water content (35%), where only 20% of roots were allocated to deeper layers. Our findings highlight the importance of accounting for the plasticity in root distributions when modeling drought impacts on ecosystem processes. Shifts in the vertical distribution of fine roots can profoundly impact soil carbon inputs and nutrient uptake efficiencies, which are not fully captured by changes in total root biomass alone. Ecosystem models should incorporate root distribution dynamics to improve predictions of terrestrial carbon cycling under drought conditions.