Trees最新文献

Key message

Eucalyptus grandis and hybrids with red gums and E. urophylla exhibit different strategies to deal with long-term drought, involving differences in stomatal regulation, plant hydraulics, and growth.

Abstract

Eucalyptus species are important in commercial forestry for their rapid growth and adaptability. In the context of climate change, evaluating the drought responses of different genotypes is critical for enhancing resilience and productivity. Genetic improvement often involves crossing fast-growing, high-quality species with drought-tolerant ones. Understanding trade-offs in pure species and hybrids is essential for optimizing forest management. This study examined physiologic and growth responses to water restriction (WR) of E. grandis (GG), E. grandis × E. camaldulensis (GC), E. grandis × E. tereticornis (GT), and E. grandis × E. urophylla (GU1 and GU2) clones at the sapling stage across two drought cycles. Measurements included leaf-water potential (Ψ), relative water content (RWC), stomatal conductance (g_S), pressure–volume traits, hydraulic conductivities (k_S, k_L), percentage loss of hydraulic conductivity (PLC), specific leaf area (SLA), and chlorophyll content. Results revealed different drought response strategies among clones. GC and GT hybrids were more “water spenders”, exhibiting high PLC (> 80%) due to limited stomatal closure, along with higher chlorophyll levels that maximized carbon gain and growth under drought. GC exhibited both elastic and osmotic adjustment, while GT showed only elastic adjustment. GG was the most drought-sensitive clone, relying on strong stomatal control, osmotic adjustment, and low cavitation, which limited carbon assimilation and resulted in the greatest growth reduction. GU hybrids shared physiologic similarities with GG but showed varying growth responses to WR. These findings suggest some hybrid clones may outperform pure E. grandis under WR, with significant genotype variation even among hybrids sharing similar parental species.

Key message

Photosynthetic induction was rapid in three shade-tolerant understory saplings, and surprisingly, native and non-native Acer species gained induction more quickly when exposed to sequential lightflecks, relative to constant saturating light.

Abstract

Growing regeneration mismatch between forest canopy and understory environments is evident in broadleaf forests of the eastern U.S., leading to novel understory forest composition. Three co-occurring shade-tolerant tree species in forest understories of southeastern Pennsylvania are the natives Acer rubrum and Fagus grandifolia and the non-native Acer platanoides. Physiological attributes contributing to these species’ relative success in the understory’s dynamic light environment are poorly characterized. Three saplings per species from three sites were sampled to examine photosynthetic induction and lightfleck responses. Predictors of photosynthesis (A) and stomatal conductance (g_s) during lightflecks were also examined. The rate and magnitude of photosynthetic induction were similar among species, with all gaining induction rapidly, as expected for shade-tolerant species. However, physiological strategies supporting induction responses varied by species, as A. rubrum had more responsive stomata and significantly lower stomatal limitation during induction, as well as significantly higher A/g_s when fully induced. Surprisingly, lightfleck responses differed from induction responses for the two Acer species, both of which exhibited significantly greater cumulative carbon assimilation than when exposed to constant saturating light, particularly during short-duration lightflecks. Leaf nitrogen and g_s were significant predictors of lightfleck responses, while species identity was not. Although induction gain under saturating light was rapid for all species, variable lightfleck responses favoring the Acer species provide an advantage given the intermittent nature of understory light availability. As eastern broadleaf forest composition continues to change in response to diverse pressures, the Acer species are well-positioned to persist.

Key message

Transient overexpression of PeSUS3 using a BaMV vector in D. brandisii ‘Manxie Tianzhu’ enhanced tillering bud germination and growth, suggesting a crucial role for sucrose metabolism in bamboo development.

Abstract

Bamboo shoots are highly sought after in China for their nutritional value. Dendrocalamus brandisii ‘Manxie Tianzhu’ (Manxie Sweet Dragon Bamboo) faces supply challenges due to limited distribution, necessitating faster growing, higher yielding varieties. The sucrose synthase gene, particularly PeSUS3, is vital for sucrose metabolism, nutrient transport, and regulating dormancy release and bud germination, yet its role in bamboo shoot production is not well understood. This study used a bamboo mosaic virus vector (BaMV) to overexpress PeSUS3 in D. brandisii ‘Manxie Tianzhu’ seedlings. PeSUS3 was cloned into the BaMV-P19-EGFP-2 vector, introduced into Agrobacterium tumefaciens, and used to infect tobacco leaves. The resulting virus was mechanically inoculated into the bamboo seedlings. Analysis revealed that PeSUS3 overexpression increased the number of tiller buds and accelerated germination by 1–2 days compared to controls. Despite the transient overexpression of PeSUS3, the increased sucrose content in the overexpressing plants suggests a role for sucrose metabolism in these processes. These findings emphasize the importance of the transient overexpression of PeSUS3 in promoting tillering bud germination and growth in D. brandisii ‘Manxie Tianzhu’, providing a foundation for future research on its function and mechanisms.

Key message

Seed germination responses to variation in temperature and light differed among six dry forest species, results that will inform ecological restoration and climate change adaptation projects.

Abstract

In dry forests, where opportunities for plant establishment occur in a narrow window of opportunity, seeds must respond to cues to germinate when conditions for growth are suitable. Knowledge of the strategies and adaptations of seeds to the seasonal dry-forest ecosystems, being under constant threat, is needed to guide restoration and management actions in the face of climate change. We investigated the effects of scarification, temperature and light in germination percentage, germination time and synchrony of six woody Fabaceae species. The species have ecological potential for restoration and are of cultural or economic importance for the local people in the Tehuacán-Cuicatlán Valley, Mexico. We carried out a multifactorial germination experiment with five temperatures, two light regimes and two scarification conditions for Mimosa luisana, M. polyantha, M. adenantheroides, M. lactiflua, Acaciella angustissima and Vachellia constricta. All germinated in a wide range of temperatures (10–40 °C), and mechanical scarification highly increased the germination percentage. Higher temperature increased and speeded up germination in dark conditions for most of the species, but they exist heterogeneous responses in their germination synchrony. Studied species had high germination percentages in warm temperatures, but their recruitment in nature might be negatively affected by warmer and drier conditions, and by the loss of shade and seed dispersers due to deforestation and changes in land use. It is crucial to study not just germination percentage and time but also other aspects of the germination process such as the germination synchrony, since it might reveal useful information for management actions.

Key message

Distance from the tree tip strongly influences axial variations in the elasticity (MOE) and strength (MOR) of fresh Scots pine wood, with both properties increasing towards the base of the stem.

Abstract

Scots pine (Pinus sylvestris L.), one of Europe's most used timber species, is valued in the construction, furniture, and paper industries. The anatomical structure of Scots pine wood follows the universal conduit widening model, where tracheid lumen size increases in each tree ring from the tip to the base of the stem, enhancing hydraulic efficiency. However, whether the physical and mechanical properties of the wood mirror its axial anatomical pattern remains unclear. For this study, we sampled an 8.6 m tall Scots pine and analysed its fresh wood mechanical, physical and anatomical properties of the outermost growth ring along the stem. In addition to the expected axial increase in tracheid size towards the base, we observed axial variations in latewood percentage and the density of rays and resin ducts. These anatomical differences correspond to axial trends in physical and mechanical properties, which show predictable patterns described by power law scaling. All three measured physical and mechanical traits, namely basic wood density, modulus of elasticity (MOE), and modulus of rupture (MOR), decrease from the stem base towards the tip. Mechanical properties correlate more strongly with distance from the tree tip than basic density or latewood proportion. These findings have practical implications for optimising timber selection in load-bearing applications and inspire new avenues for research and innovation in wood material science.

Key message

Urban trees can acclimate to their growth environment through changes in vessel anatomy. Vessel lumen area and vessel frequency following a gradient from park trees to inner-city street trees.

Abstract

Urban trees stand in potentially stressful growth environments occurring along gradients of urban heat and impermeable surface cover and, to survive, can adjust their function and structure. The consequent tree-to-tree variations in hydraulic xylem traits can shed light on tree hydraulics and capacity to acclimate to diverse conditions, as well as identify limitations to tree growth and survival. Using microscopic analysis of increment cores, we compared early wood vessel traits of the ring-porous angiosperm Celtis occidentalis in three urban site types: central streets, residential streets and parks, within the city of Montreal. We explored differences in vessel traits (mean vessel lumen area, vessel frequency, vessel grouping index and derived variables) between site types, vessel trait intercorrelations and correlations with monthly temperature, precipitation and heat-moisture index over 10 years. The vessel traits significantly differed between site types. Park trees had the largest and central street trees had the smallest vessel lumen area and theoretical hydraulic conductivity; traits supporting efficient water transport. Central street trees had the largest vessel frequency and smallest theoretical vulnerability to cavitation; traits connected to hydraulic safety. Residential street tree traits were in between. Among central and residential street trees, water transport efficiency traits correlated positively with cool springs or arid summers, whereas among park trees, mainly vessel frequency and grouping index responded to climate variations. These results highlight the capacity of C. occidentalis to acclimate to urban environments and the potential of anatomical traits for quantifying the effects of urban environments on tree functioning.

Graphical Abstract

Key message

Clones originating from the young seed progeny of mutational witches’ broom have a compact crown and no flowering phenotype caused by the combined effect of the mutation and biological age of the source plant material.

Abstract

Mutational witches’ broom (WB), which is formed on trees, is a bud sport that has a modified crown structure. Phenotypically, it differs from the normal crown part in its high density, abundant branching and usually shorter needles. Grafted WBs have a high ornamental value and are propagated for landscaping purposes. WB seed progeny and their clones have also been successfully used in breeding for a long time. However, it is still unknown how the two types of clones differ from each other. To reveal the differences, a comparative analysis of clones from the original mature 170–200-year-old trees of Pinus sibirica with cone-bearing WBs and clones from the 9-year-old mutant seed progeny was carried out in the uniform environment of a common garden. Unlike the initial WB clones, the derivative clones did not flower, which was the most pronounced influence of the age of the source plant material. The growth of derivative WB clones was also affected by the age of the source plant material, which reduced linear growth in addition to the mutation. They were 1.5 times less than in the initial clones, and their crowns were even more compact due to the decreased branching threshold and apical dominance. Significant variation was observed amongst groups of derivative clones derived from different saplings in the progeny of an original WB. The obvious source of the variation was the effect of recombination in the WB seed progeny, which gave rise to the clones. Thus, the influence of the age of the source plant material is fully manifested in the WB of Pinus sibirica, just as it occurs in normal trees. Together with great variation in morphological traits, this made the WB seed progeny an almost inexhaustible source of material for ornamental breeding.

Key message

Seed morphological traits and antioxidant defense mechanisms determine desiccation sensitivity differences between Quercus species, enabling development of species-specific seed storage protocols.

Abstract

Despite extensive research on the desiccation sensitivity of Quercus seeds, the factors and physiological mechanisms driving interspecific variations remain poorly understood. This study investigated the differences in desiccation sensitivity between Q. chenii and Q. acutissima seeds by examining the effects of desiccation on seed moisture content, detecting reactive oxygen species production, antioxidant enzyme activities, soluble sugars and proteins, and exploring the relationships among initial seed traits, water loss rates, and seed viability. Results showed that despite similar initial moisture content (41.9% for Q. chenii and 42.9% for Q. acutissima), Q. acutissima seeds exhibited more rapid water loss under identical desiccation conditions (same seed: silica gel ratio and temperature), primarily due to their larger scar area and seed mass, leading to a decline in germination percentage below 80% within just 7 days, while Q. chenii seeds maintained high germination percentage for up to 27 days. Regarding physiological mechanisms, Q. chenii seeds demonstrated a more efficient antioxidant defense system, characterized by higher superoxide dismutase activity and early increased catalase activity, which effectively reduced hydrogen peroxide accumulation and membrane lipid peroxidation. Additionally, Q. chenii showed significantly increased soluble protein content during early desiccation stages. These findings contribute to a deeper understanding of desiccation sensitivity mechanisms and their interspecific variations in recalcitrant seeds, providing physiological bases for optimizing recalcitrant seed conservation strategies.