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• Early-stage fitness variation has been seldom evaluated at broad scales in forest tree species, despite the long tradition of studying climate-driven intraspecific genetic variation. In this study, we evaluated the role of climate in driving patterns of population differentiation at early-life stages in Pinus sylvestris and explored the fitness and growth consequences of seed transfer within the species range. • We monitored seedling emergence, survival and growth over a 2-yr period in a multi-site common garden experiment which included 18 European populations and spanned 25° in latitude and 1700m in elevation. • Climate–fitness functions showed that populations exhibited higher seedling survival and growth at temperatures similar to their home environment, which is consistent with local adaptation. Northern populations experienced lower survival and growth at warmer sites, contrary to previous studies on later life stages. Seed mass was higher in populations from warmer areas and was positively associated with survival and growth at more southern sites. Finally, we did not detect a survival–growth trade-off; on the contrary, bigger seedlings exhibited higher survival probabilities under most climatic conditions. • In conclusion, our results reveal that contrasting temperature regimes have played an important role in driving the divergent evolution of P. sylvestris populations at early-life stages.

A trade-off between growth and defence functions is commonly observed in plants. We propose that the association of plants with Epichloë fungal endophytes may eliminate this trade-off. This would be a consequence of the double role of these endophytes in host plants: the stimulation of plant growth hormones (e.g. gibberellins) and the fungal production of antiherbivore alkaloids. We put forward a model that integrates this dual effect of endophytes on plant growth and defence and test its predictions by means of meta-analysis of published literature. Our results support the notion that the enhanced plant resistance promoted by endophytes does not compromise plant growth. The limits and ecological benefits of this endophyte-mediated lack of plant growth–defence trade-off are discussed.

Questions: Do composition and richness of woody plants differ between gaps and closed canopy in subtropical forests, and does this difference vary across life stages of tree species? Is tree species richness in gaps a function of regeneration density? Location: Subtropical Shorea robusta Gaertn (Sal) forest, central Nepal. Methods: We collected vegetation data from two old-growth S. robusta forest stands. We sampled 128 plots of 100 m2 equally spread between the two habitats: gap and closed canopy. In each plot, we recorded the total number of woody species, number of individuals of seedlings and saplings of tree species and measured the DBH of all saplings. We compared species richness and composition of total woody species, seedlings and saplings between the two habitats. We used ordination to analyse species composition, and an individual-based species accumulation curves to illustrate the effect of density on species richness. Results: The species composition of total woody species and seedlings was similar in both habitats, but species composition of saplings differed between habitats. Total woody and seedling richness were similar between habitats at one site, but were richer under closed canopy at the other site. Sapling richness was higher in gaps at both sites and was a function of stem density at one site, but not at the other site. Conclusions: Gaps are not always areas of higher woody species richness and therefore may be less important than expected for the overall species richness of woody plants. Instead, they are potentially important for enhancing local tree richness by increasing sapling richness. Gap disturbance is the primary driver of structural heterogeneity in forests where topographic and edaphic gradients are negligible.

Summary Beneficial microorganisms (BMs) promote plant growth and enhance stress resistance. This review summarizes how BMs induce growth promotion by improving nutrient uptake, producing growth‐promoting hormones and stimulating root development. How BMs enhance disease resistance and help protect plants from abiotic stresses has also been explored. Growth‐defense trade‐offs are known to affect the ability of plants to survive under unfavourable conditions. This review discusses studies demonstrating that BMs regulate growth‐defense trade‐offs through microbe‐associated molecular patterns and multiple pathways, including the leucine‐rich repeat receptor‐like kinase pathway, abscisic acid signalling pathway and specific transcriptional factor regulation. This multifaceted relationship underscores the significance of BMs in sustainable agriculture. Finally, the need for integration of artificial intelligence to revolutionize biofertilizer research has been highlighted. This review also elucidates the cutting‐edge advancements and potential of plant‐microbe synergistic microbial agents.

Connecting the selective forces that drive the evolution of phenotypes to their underlying genotypes is key to understanding adaptation, but such connections are rarely tested experimentally. Threespine stickleback (Gasterosteus aculeatus) are a powerful model for such tests because genotypes that underlie putatively adaptive traits have been identified. For example, a regulatory mutation in the Ectodysplasin (Eda) gene causes a reduction in the number of bony armor plates, which occurs rapidly and repeatedly when marine sticklebacks invade freshwater. However, the source of selection on plate loss in freshwater is unknown. Here, we tested whether dietary reduction of phosphorus can account for selection on plate loss due to a growth advantage of low-plated fish in freshwater. We crossed marine fish heterozygous for the 16 kilobase freshwater Eda haplotype and compared the growth of offspring with different genotypes under contrasting levels of dietary phosphorus in both saltwater and freshwater. Eda genotype was not associated with growth differences in any treatment, or with mechanisms that could mitigate the impacts of phosphorus limitation, such as differential phosphorus deposition, phosphorus excretion, or intestine length. This study highlights the importance of experimentally testing the putative selective forces acting on phenotypes and their underlying genotypes in the wild.

Summary The reduction in crop yield caused by pathogens and pests presents a significant challenge to global food security. Genetic engineering, which aims to bolster plant defence mechanisms, emerges as a cost‐effective solution for disease control. However, this approach often incurs a growth penalty, known as the growth‐defence trade‐off. The precise molecular mechanisms governing this phenomenon are still not completely understood, but they generally fall under two main hypotheses: a “passive” redistribution of metabolic resources, or an “active” regulatory choice to optimize plant fitness. Despite the knowledge gaps, considerable practical endeavours are in the process of disentangling growth from defence. The plant microbiome, encompassing both above‐ and below‐ground components, plays a pivotal role in fostering plant growth and resilience to stresses. There is increasing evidence which indicates that plants maintain intimate associations with diverse, specifically selected microbial communities. Meta‐analyses have unveiled well‐coordinated, two‐way communications between plant shoots and roots, showcasing the capacity of plants to actively manage their microbiota for balancing growth with immunity, especially in response to pathogen incursions. This review centers on successes in making use of specific root‐associated microbes to mitigate the growth‐defence trade‐off, emphasizing pivotal advancements in unravelling the mechanisms behind plant growth and defence. These findings illuminate promising avenues for future research and practical applications.

Trees in urban ecosystems are valued for shade and cooling effects, reduction of CO 2 emissions and pollution, and aesthetics, among other benefits. However, in arid and semiarid regions, urban trees must be maintained through supplemental irrigation. In these regions it is desirable to identify tree species that are especially efficient in the balance between water loss and carbon uptake. We used a common-garden approach to compare water-use efficiency (WUE) at leaf and tree scales for commonly planted, nonnative tree species in the Los Angeles Basin (California, USA), in order to evaluate WUE as a metric of the trade-off between water use and growth in urban trees. Leaf-level gas exchange, sap flux density, leaf δ 13 C, and stem growth measurements were conducted on eight species within the Los Angeles County Arboretum: Brachychiton discolor , B. populneus , Eucalyptus grandis , Ficus microcarpa , Jacaranda chelonia , Gleditsia triacanthos , Lagerstroemia indica , and Koelreuteria paniculata . We found species with high instantaneous WUE also had the highest tree-level seasonal WUE (stem basal-area increment (BAI)/total transpiration). High tree-level WUE resulted from low water use in B. discolor , B. populneus , and E. grandis . In contrast, high basal-area growth explained moderately high WUE in F. microcarpa . Notably, high WUE was not associated with low BAI. At a monthly time scale, nearly all species showed the highest WUE during late spring/early summer, when the majority of basal-area growth occurred. Although leaf- and tree-level WUE were reasonably well correlated, leaf δ 13 C was not significantly related to leaf- or tree-level WUE. Overall, the most water-efficient species were evergreen, or from regions that experience high vapor-pressure deficit (VPD). These results suggest that whole-tree WUE is a useful measure of the balance between some critical costs and benefits of irrigated urban trees and may be helpful in determining which trees should be planted to maximize growth while conserving water. Although measuring whole-tree WUE directly provides the most complete understanding of urban tree costs and benefits, this study suggests that leaf-level instantaneous measurements of WUE and knowledge of species native climates may be reasonable proxies.

Plant immune responses mediated by the hormone jasmonoyl-L-isoleucine (JA-Ile) are metabolically costly and often linked to reduced growth. Although it is known that JA-Ile activates defense responses by triggering the degradation of JASMONATE ZIM DOMAIN (JAZ) transcriptional repressor proteins, expansion of the JAZ gene family in vascular plants has hampered efforts to understand how this hormone impacts growth and other physiological tasks over the course of ontogeny. Here, we combined mutations within the 13-member Arabidopsis JAZ gene family to investigate the effects of chronic JAZ deficiency on growth, defense, and reproductive output. A higher-order mutant (jaz decuple, jazD) defective in 10 JAZ genes (JAZ1–7, -9, -10, and -13) exhibited robust resistance to insect herbivores and fungal pathogens, which was accompanied by slow vegetative growth and poor reproductive performance. Metabolic phenotypes of jazD discerned from global transcript and protein profiling were indicative of elevated carbon partitioning to amino acid-, protein-, and endoplasmic reticulum body-based defenses controlled by the JA-Ile and ethylene branches of immunity. Resource allocation to a strong defense sink in jazD leaves was associated with increased respiration and hallmarks of carbon starvation but no overt changes in photosynthetic rate. Depletion of the remaining JAZ repressors in jazD further exaggerated growth stunting, nearly abolished seed production and, under extreme conditions, caused spreading necrotic lesions and tissue death. Our results demonstrate that JAZ proteins promote growth and reproductive success at least in part by preventing catastrophic metabolic effects of an unrestrained immune response.

Carbon (C) allocation plays a central role in tree responses to environmental changes. Yet, fundamental questions remain about how trees allocate C to different sinks, for example, growth vs storage and defense. In order to elucidate allocation priorities, we manipulated the whole‐tree C balance by modifying atmospheric CO2 concentrations [CO2] to create two distinct gradients of declining C availability, and compared how C was allocated among fluxes (respiration and volatile monoterpenes) and biomass C pools (total biomass, nonstructural carbohydrates (NSC) and secondary metabolites (SM)) in well‐watered Norway spruce (Picea abies) saplings. Continuous isotope labelling was used to trace the fate of newly‐assimilated C. Reducing [CO2] to 120 ppm caused an aboveground C compensation point (i.e. net C balance was zero) and resulted in decreases in growth and respiration. By contrast, soluble sugars and SM remained relatively constant in aboveground young organs and were partially maintained with a constant allocation of newly‐assimilated C, even at expense of root death from C exhaustion. We conclude that spruce trees have a conservative allocation strategy under source limitation: growth and respiration can be downregulated to maintain ‘operational’ concentrations of NSC while investing newly‐assimilated C into future survival by producing SM.

Plant defense to microbial pathogens is often accompanied by significant growth inhibition. How plants merge immune system function with normal growth and development is still poorly understood. Here, we investigated the role of target of rapamycin (TOR), an evolutionary conserved serine/threonine kinase, in the plant defense response. We used rice as a model system and applied a combination of chemical, genetic, genomic and cell-based analyses. We demonstrate that ectopic expression of TOR and Raptor (regulatory-associated protein of mTOR), a protein previously demonstrated to interact with TOR in Arabidopsis, positively regulates growth and development in rice. Transcriptome analysis of rice cells treated with the TOR-specific inhibitor rapamycin revealed that TOR not only dictates transcriptional reprogramming of extensive gene sets involved in central and secon dary metabolism, cell cycle and transcription, but also suppresses many defense-related genes. TOR overexpression lines displayed increased susceptibility to both bacterial and fungal pathogens, whereas plants with reduced TOR signaling displayed enhanced resistance. Finally, we found that TOR antagonizes the action of the classic defense hormones salicylic acid and jasmonic acid. Together, these results indicate that TOR acts as a molecular switch for the activation of cell proliferation and plant growth at the expense of cellular immunity.