Research Institute of Tropical Forestry

Eucalyptus is a highly diverse genus of the Myrtaceae family that is planted worldwide. Many changes occur during callus development, an important process during in vitro plant regeneration. In this study, we conducted methylome and transcriptome analyses to reveal such changes. The results showed that differentially expressed genes between E. camaldulensis (voucher ID: c0009; high embryogenic potential) and E. grandis × urophylla (voucher ID: j0017; low embryogenic potential) during callus development were enriched in plant hormone signal transduction and MAPK (Mitogen-activated protein kinase) signaling pathways. qRT-PCR analysis showed AHP, BAK1, BSK, CRE1, GID1, MKS1, PR-1, PYL, RbohD, and TCH4 could be involved in the callus development and plantlet regeneration capacity. The differences observed in regenerative potential during callus maturation between the two species under study provide a reliable molecular basis for the study of Eucalyptus regeneration mechanisms.

Vegetation carbon turnover time (τveg) dominates the uncertainty in terrestrial carbon cycle dynamics. Reports have shown that the τveg of mature or old-growth forests in North America and Europe has decreased because of faster carbon loss under global climate change. However, the temporal trend of τveg in widespread younger forests, which exhibit different growth patterns, remains inconclusive. Here, we consistently revealed a significant overall increase in τveg (0.025±0.002years per year) across China's forests that are characterized by a relatively young forest age structure, using multisource data-model assimilation and long-term network observations. In young forests that receive high nitrogen deposition, increasing levels of CO2 accelerate vegetation growth, causing it to grow faster than it dies or decomposes, leading to increases in the τveg. The effects of forest age on τveg dynamics and the high sensitivity of enhanced carbon sinks to τveg should be incorporated into future land surface models to ensure that the τveg dynamics and their impacts on terrestrial carbon cycling and climate mitigation are accurately assessed. Our results also provide valuable insights for forest management aimed at enhancing carbon retention and sequestration through optimizing age-related stand dynamics.

Pruning is a regular and essential urban tree maintenance practice aimed at sustaining overall health, ecosystem services, and public safety. However, knowledge of post-pruning recovery dynamics remains limited, which in turn hinders accurate assessments of growth and ecological functions. To address this, we examined recovery dynamics of Acacia auriculiformis, a common urban species. Tree height and crown radius were recorded monthly for 12 months after pruning. Trees were classified into two size groups based on diameter at breast height (DBH, trunk diameter measured at 1.3 m above ground): medium (DBH < 45 cm) and large (DBH ≥ 45 cm). A generalized linear mixed model (GLMM), appropriate for repeated measures and non-normal data, was fitted using a Tweedie distribution and a log-link function to model the recovery pattern. Results showed continuous growth over time, with medium-sized trees presenting significantly higher crown radius growth than large trees (p = 0.006), while height growth did not differ (p = 0.788). The best model for height included time (AIC = −846.4), whereas crown recovery was best modelled by time and size class (AIC = −1586.6). These findings demonstrate that, in this study, medium-sized A. auriculiformis generally recover faster, especially in crown expansion. This exploratory study suggests that tree size may influence post-pruning recovery and can provide a reference for subsequent differentiated management studies. The morphological modeling further provides preliminary quantitative evidence for annual recovery dynamics in urban A. auriculiformis.

Mixed planting of fir and broadleaf trees is an effective management method for improving the productivity. We investigated soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) contents, along with their stoichiometric ratios across 10 different combinations of Chinese fir and broadleaf species (Mytilaria laosensis, Michelia macclurei, Michelia maudiae, Cinnamomum porrectum, Castanopsis hystrix, Cinnamomum burmanni, Liquidambar formosana, Michelia chapensis, Schima superba, and Michelia odora, respectively) with the stand age of 20 yr. Additionally, we examined the activities and stoichiometric characteristics of various enzymes: β-1,4-glucosidase, β-xylosidase, cellobiohydrolase, β-1,4-N-acetylaminoglucosidase, leucine aminopeptidase, and acid phosphatase to analyze nutrient limitation status in different mixed stands. The results showed that: 1) In the 0-10 cm and 10-30 cm soil layers, the highest SOC and TN contents were found in M. macclurei, whereas in the 30-50 cm soil layer, the highest contents were observed in S. superba. The highest TP content across all three soil layers was recorded in C. burmanni. Soil SOC and TN contents of the 10 forest stands decreased with the soil depth, while TP was not affected by the soil depth. 2) The measured ranges across the 10 stand types were 4.82-32.69 g·kg-1 for SOC, 0.50-2.16 g·kg-1 for TN, and 0.24-0.55 g·kg-1 for TP, indicating nutrient deficiency. Only the stands of M. macclurei and S. superba reached national average levels for SOC and TN, while the TP content of all forest stands was below the national average. 3) The results of the enzyme quantification vector model indicated that soil microbial metabolism was jointly limited by nitrogen and phosphorus. 4) Redundancy analysis revealed that TN, available phosphorus (AP), ammonium (NH4+-N), soil water content (SWC), pH, and TP were the primary factors influencing enzyme activities. Additionally, pH, AP, TP, SWC, and the carbon-to-phosphorus (C:P) ratio emerged as key determinants of enzymatic stoichiometry. In summary, M. macclurei and S. superba were effective in promoting soil nutrient levels in mixed forests of fir and broadleaf trees, being the optimal tree species for the mixed forest renovation in the South subtropical region. Given the prevalent limitations of nitrogen and phosphorus, external nitrogen and phosphorus inputs should be considered in future management practices.

Rhizosphere microorganisms mediate the material exchange and chemical cycling between plant roots and soil. However, the response mechanisms of the rhizosphere microbial community, especially its co-occurrence patterns, to thinning remain poorly understood. We investigated the rhizosphere microbial communities of Pinus massoniana under different thinning intensities, including control (CK, 0%), light-intensity thinning (LIT, 10%), moderate-intensity thinning (MIT, 30%), and high-intensity thinning (HIT, 50%). Basic taxonomic information was obtained through high-throughput sequencing, while R software was utilized to identify thinning-sensitive operational taxonomic units (tsOTUs), construct co-occurrence networks, and perform other statistical analyses. Although no discernible patterns were observed in α-diversity changes, the Kruskal–Wallis test indicated that season was the primary factor driving α-diversity variation. Meanwhile, thinning intensity significantly shaped the rhizosphere microbial community structures, with each intensity harboring a specific tsOTUs subset. Although the top three modules of the meta-co-occurrence networks in summer and winter exhibited consistent tsOTU composition, winter triggered changes in network connectivity. Regardless of summer or winter, the number of network nodes under MIT was the highest. Additionally, after thinning, the relative abundances of most keystone taxa declined; however, MIT facilitated the enrichment of certain keystone taxa. Collectively, thinning profoundly shapes microbial community composition and network characteristics. Moderate thinning intensity may represent the optimal thinning intensity for the studied P. massoniana plantations.