Syringa oblata is an important garden plant whose leaf colour turns from green to red in autumn when air temperature and daylength decrease. This study explored the reasons for leaf reddening by detecting phenotypic characteristics and pigment types and contents. With leaf reddening, luminance L^* increased and chrominance a^* decreased significantly. Chlorophyll and carotenoid contents significantly decreased in accordance with the distribution change of green pigment in leaf cells. Conversely, the red pigment distribution increased and the total polyphenol, total flavonoid and total anthocyanin contents evidently increased. Anthocyanin accumulation was the important reason for leaf reddening. Of the anthocyanins detected in leaves, cyanidin and delphinidin-3-O-rutinoside contents gradually increased with leaf reddening and were negatively correlated with L^*. They were considered key anthocyanins influencing leaf colour. Apigenin and syringic acid were correlated with delphinidin-3-O-rutinoside and cyanidin, and they could be the anthocyanin co-pigments. Cyanidin-3-O-arabinoside and taxifolin were more abundant polyphenols in leaves. In summary, anthocyanin accumulation and chlorophyll degradation occurred along with leaf reddening. Temperature, light, and other co-pigments influenced the anthocyanin and chlorophyll contents. This study provides evidence for applications of S. oblata as a coloured-leaf plant in gardens and as a source of active ingredients in the commercial market.

The mechanism of biochar and compost as soil amendments in urban green spaces remains unclear. Using Euonymus kiautschovicus as a model system, this study established eight treatment gradients, 0 (CK), single biochar applications: 4% (BC4), 8% (BC8), 12% (BC12), 7.5% compost (COM), and their combinations BCC4 (BC4 + 7.5% COM), BCC8 (BC8 + 7.5% COM), BCC12 (BC12 + 7.5% COM). Through metagenomic sequencing and metagenome-assembled genomes (MAGs) analysis, we investigated soil microbiome structure, carbon sequestration functional genes, and their interactions in response to amendments. The combined application of medium-low dose biochar (4–8%) with compost significantly optimized the physicochemical properties and microbial functions in soils. Compared to single amendments, hybrid treatments synergistically enhanced soil moisture content. Specifically, BCC8 increased by 27% compared to the CK, organic carbon levels reached 12.8 g/kg with BCC12, and available nutrients showed 45% higher available phosphorus with BCC4. Metagenomic analysis revealed that hybrid treatments reshaped microbial community structure, with BCC8 significantly enriching Acidobacteria (8.72%) and Nitrospira (1.42%), driving an increased abundance of carbon fixation genes. Among key carbon fixation pathways, the reductive tricarboxylic acid cycle (rTCA) exhibited the highest gene abundance (mean 15.03), dominated by MAG176. The Calvin-Benson-Bassham (CBB) cycle displayed broad adaptability, with MAG59 identified as a core carbon-fixing strain. This study has significant implications for the application of biochar-compost combinations in carbon management of urban green spaces.

Trees can build fine-root systems with high variation in root size (e.g., fine-root diameter) and root number (e.g., branching pattern) to optimize belowground resource acquisition in forest ecosystems. Compared with leaves, which are visible above ground, information about the distribution and inequality of fine-root size and about key associations between fine-root size and number is still limited. We collected 27,573 first-order fine-roots growing out of 3,848 second-order fine-roots, covering 51 tree species in three temperate forests (Changbai Mountain, CBS; Xianrendong, XRD; and Maoershan, MES) in Northeastern China. We investigated the distribution and inequality of fine-root length, diameter and area (fine-root size), and their trade-off with fine-root branching intensity and ratio (fine-root number). Our results showed a strong right-skewed distribution in first-order fine-root size across various tree species. Unimodal frequency distributions were observed in all three of the sampled forests for first-order fine-root length and area and in CBS and XRD for first-order fine-root diameter, whereas a marked bimodal frequency distribution of first-order fine-root diameter appeared in MES. Moreover, XRD had the highest and MES had the lowest inequality values (Gini coefficients) in first-order fine-root diameter. First-order fine-root size showed a consistently linear decline with increasing root number. Our findings suggest a common right-skewed distribution with unimodality or bimodality of fine-root size and a generalized trade-off between fine-root size and number across the temperate tree species. Our results will greatly improve our thorough understanding of the belowground resource acquisition strategies of temperate trees and forests.