Congde Huang

Soil organic carbon (SOC) is a critical component of the soil carbon pool, significantly influencing soil fertility and forest ecosystem productivity. Eucalyptus grandis (Rose Gum), one of the most widely introduced and economically valuable fast-growing tree species worldwide, plays an indispensable role in pulpwood production, construction, and bioenergy, and is commonly established and managed in successive rotations in operational practice. Despite its importance, the effects of successive planting on SOC and its labile fractions in plantation soils remain poorly understood. In May 2017, a space-for-time substitution approach was employed to study the effects of successive planting of E. grandis plantations on SOC and its labile fractions, including dissolved organic carbon, light-fraction organic carbon, particulate organic carbon, microbial biomass carbon, and readily oxidizable carbon. The results indicated that the content of SOC and labile organic carbon (LOC) fractions declined concomitant with an increase in successive planting generations. Specifically, total SOC content significantly decreased from 12.63 g·kg⁻¹ in the first-generation forest to 9.37 g·kg⁻¹ in the third-generation forest. The contents of LOC fractions also showed a significant decrease from the first to the second generation, but the rate of this decline slowed in the third generation. The soil carbon pool management index (CPMI) decreased significantly from 100 in the control forest to 46.64 in the third-generation plantation. Redundancy analysis identified water-soluble nitrogen and total nitrogen as the principal common factors exerting influence over SOC and its labile fractions in E. grandis plantations. These findings indicate that successive planting of E. grandis in artificial forests primarily reduces SOC and LOC fractions by lowering soil nutrient content, leading to a decline in soil carbon pool quality. The findings of this study may help provide a scientific basis for the sustainable development of E. grandis plantations in this region.

Populus kangdingensis and P. ciliata are important tree species distributed across the Qinghai–Tibet Plateau, yet the structure and evolutionary characteristics of their mitochondrial genomes remain unclear. To elucidate these features and their phylogenetic relationships, we assembled the mitochondrial genomes of these two species using PacBio HiFi sequencing data with PMAT2, and annotated them with PMGA. The results showed that the mitochondrial genome of P. kangdingensis consists of three independent circular molecules with a total length of 785,824 bp, while that of P. ciliata exhibits a branched structure comprising two circular molecules and one linear molecule, totaling 798,807 bp. Both genomes contain 57 functional genes, including 34 highly conserved protein-coding genes. Comparative genomic analyses revealed differences in repeat sequences, RNA editing patterns, and chloroplast-derived sequences, suggesting species-specific evolution at the organellar genome level. Ka/Ks analysis identified genes such as atp4, ccmB, and mttB as potentially under positive selection, reflecting adaptation to high-altitude environments. Phylogenetic trees constructed using 30 mitochondrial and 58 chloroplast protein-coding genes confirmed the monophyly of Populus and Salix, and identified them as sister groups. However, topological inconsistencies observed within Populus suggest the influence of lineage sorting, hybridization, and differences in mutation rates. This study provides the first high-quality mitochondrial genomes of P. kangdingensis and P. ciliata, revealing the structural diversity of multi-circular and branched conformations in Populus mitochondrial genomes, and offering new insights into organellar genome evolution and high-altitude adaptation in this genus.

Leaf functional traits are important indicators that reveal plant adaptation and response to environmental changes. Characteristics and adaptive strategies of leaf functional traits of staple bamboo species (SBSs) for the giant panda (Ailuropoda melanoleuca) remain unclear, which limits conservation management of the giant panda and its habitat. Here, this study investigated 10 SBSs in 15 nature reserves across 36 counties, measured eight leaf functional traits, analyzed trait characteristics, variation, and drivers of variation, and examined trait-based strategies and strategy–environmental constraint relationships. Our results indicate that: coefficients of variation in leaf functional traits spanned from 9.58% to 79.16%, and significant differences were found among SBSs for leaf functional traits except chlorophyll concentration. The linear mixed-effects models revealed that the taxonomic factors explained 20.16 to 77.94% of variation, and environmental factors explained 17.03 to 29.12%. Leaf functional traits exhibited distinct environmental associations, primarily driven by geographic location, topography, and soil phosphorus availability. Hierarchical clustering and principal component analysis revealed 10 SBS clustered into two groups, corresponding to conservative and acquisitive resource-use strategies. Canonical correspondence analysis revealed that SBSs with conservative strategies were distributed in warm and moist habitats, and SBSs with acquisition strategies were distributed in habitats with high solar radiation. Our results reveal the key trait characteristics of SBSs and the strategy-environmental constraint model based on traits, which can provide scientific basis for the ecological management practice of SBSs.

Carbon use efficiency (CUE) of microbial communities in soil quantifies the proportion of organic carbon (C) taken up by microorganisms that is allocated to growing microbial biomass as well as used for reparation of cell components. This C amount in microbial biomass is subsequently involved in microbial turnover, partly leading to microbial necromass formation, which can be further stabilized in soil. To unravel the underlying regulatory factors and spatial patterns of CUE on a large scale and across biomes (forests, grasslands, croplands), we evaluated 670 individual CUE data obtained by three commonly used approaches: (i) tracing of a substrate C by ¹³C (or ¹⁴C) incorporation into microbial biomass and respired CO₂ (hereafter ¹³C‐substrate), (ii) incorporation of ¹⁸O from water into DNA (¹⁸O‐water), and (iii) stoichiometric modelling based on the activities of enzymes responsible for C and nitrogen (N) cycles. The global mean of microbial CUE in soil depends on the approach: 0.59 for the ¹³C‐substrate approach, and 0.34 for the stoichiometric modelling and for the ¹⁸O‐water approaches. Across biomes, microbial CUE was highest in grassland soils, followed by cropland and forest soils. A power‐law relationship was identified between microbial CUE and growth rates, indicating that faster C utilization for growth corresponds to reduced C losses for maintenance and associated with mortality. Microbial growth rate increased with the content of soil organic C, total N, total phosphorus, and fungi/bacteria ratio. Our results contribute to understanding the linkage between microbial growth rates and CUE, thereby offering insights into the impacts of climate change and ecosystem disturbances on microbial physiology with consequences for C cycling.

Leaf dry matter content (LDMC) is an important determinant of plant flammability. Investigating global patterns of LDMC could provide insights into worldwide plant flammability patterns, informing wildfire management. We characterised global patterns of LDMC across 4074 species from 216 families, revealing that phylogenetic and environmental constraints influence LDMC. LDMC varied across growth forms and taxonomic groups, displaying phylogenetic niche conservatism. Temperature, precipitation, aridity index, soil total nitrogen content and wildfire activity affected LDMC, and the effect of wildfire activity was stronger than other environmental factors across species with postfire regeneration abilities. Such species had higher LDMC, and their LDMC was less phylogenetically conserved and more strongly associated with fire activity. Our results suggest that, although LDMC shows phylogenetic niche conservatism, LDMC is determined by environmental factors, especially wildfire activity. Wildfire has likely acted as a selective pressure towards high LDMC across species that persist through fire using postfire regeneration.

Pleioblastus amarus (bitter bamboo) shoots are a traditional forest vegetable in China, renowned for its nutritional composition and associated health benefits. This study aimed to investigate the dynamic changes in nutritional quality and bitterness-related metabolites, as well as corresponding gene expression in P. amarus shoots at three distinct growth stages, specifically at heights of 10 cm (BT1), 20 cm (BT2), and 40 cm (BT3). The results showed that the content of soluble sugars decreased while the content of total phenols and flavonoids, which contribute to bitterness, increased during the growth of P. amarus shoots. In addition, comparative analysis of BT2 vs. BT1, BT3 vs. BT1, and BT3 vs. BT2 revealed 14, 43, and 36, respectively, differentially accumulated metabolites (DAMs). Notably, BT2 exhibited upregulation of flavonoids, such as apigenin, while bitter amino acids, including phenylalanine and arginine, showed a marked increase in BT3. Moreover, differential gene expression analysis revealed 3161, 13268, and 3742 differentially expressed genes (DEGs) in the BT2 vs. BT1, BT3 vs. BT1, and BT3 vs. BT2 comparisons, respectively. An integrated analysis of metabolomic and transcriptomic data indicated that the metabolites and genes associated with the biosynthesis pathways of phenylalanine, tyrosine, tryptophan, arginine, and the branched-chain amino acids valine, leucine, and isoleucine were significantly enriched during the growth of P. amarus shoots. The study indicates that early-stage (≤20 cm) P. amarus shoots are mainly bitter due to flavonoids like apigenin, while the bitterness in later-stage (around 40 cm) shoots is largely due to bitter amino acids such as phenylalanine, arginine, valine, and isoleucine. This research highlights key compounds and genes related to bitterness, providing a basis for future research on enhancing the nutritional value and flavor of P. amarus shoots.

Background: Woody bamboos are the only diverse large perennial grasses in mesic-wet forests and are widely distributed in the understory and canopy. The functional trait variations and trade-offs in this taxon remain unclear due to woody bamboo syndromes (represented by lignified culm of composed internodes and nodes). Here, we examined the effects of heritable legacy and occurrence site climates on functional trait variations in leaf and culm across 77 woody bamboo species in a common garden. We explored the trade-offs among leaf functional traits, the connection between leaf nitrogen (N), phosphorus (P) concentrations and functional niche traits, and the correlation of functional traits between leaves and culms. Results: The Bayesian mixed models reveal that the combined effects of heritable legacy (phylogenetic distances and other evolutionary processes) and occurrence site climates accounted for 55.10–90.89% of the total variation among species for each studied trait. The standardized major axis analysis identified trade-offs among leaf functional traits in woody bamboo consistent with the global leaf economics spectrum; however, compared to non-bamboo species, the woody bamboo exhibited lower leaf mass per area but higher N, P concentrations and assimilation, dark respiration rates. The canonical correlation analysis demonstrated a positive correlation (ρ = 0.57, P-value < 0.001) between leaf N, P concentrations and morphophysiology traits. The phylogenetic principal components and trait network analyses indicated that leaf and culm traits were clustered separately, with leaf assimilation and respiration rates associated with culm ground diameter. Conclusion: Our study confirms the applicability of the leaf economics spectrum and the biogeochemical niche in woody bamboo taxa, improves the understanding of woody bamboo leaf and culm functional trait variations and trade-offs, and broadens the taxonomic units considered in plant functional trait studies, which contributes to our comprehensive understanding of terrestrial forest ecosystems.