Juan Liu

To understand how geography shapes the genetic variation of Melia azedarach, we sequenced the whole genomes of 91 accessions from 91 maternal half-sib families across 15 provenances maintained in the National Germplasm Bank of China, an ex situ collection representing conserved germplasm. Genetic diversity increased from south to north (He: 0.098 to 0.333), whereas the Hainan population showed relatively low within-population diversity and, as confirmed by pairwise Fst, was highly differentiated from the mainland, forming an independent group. A Mantel test confirmed a significant isolation-by-distance (IBD) pattern (r = 0.307, p = 0.001). Redundancy analysis (RDA) explained 17.23% of the individual-level genetic variance, but a partial redundancy analysis (partial RDA) showed that most of this association was attributable to population structure, with the environmental variables explaining negligible independent variance after conditioning on population structure. Genome-wide association analysis (GWAS) further identified candidate loci potentially associated with climate-related traits, including a temperature-associated gene encoding a leucine-rich receptor-like protein kinase and a precipitation-associated gene encoding the stress-related protein RAR1. Together, these results map the genome-wide genetic diversity and spatial–climatic associations of M. azedarach. This study provides a genetic basis for evaluating banked resources, molecular breeding, and protecting this important tree species.

Background: Camellia oleifera Abel, the dominant woody oil crop of southern China, often suffers from limited productivity due to the prevalence of phosphorus (P) stress in acidic soils. While grafting is an effective strategy to mitigate nutrient scarcity, the mechanistic basis of rootstock-mediated P tolerance in this species remains poorly understood. This study investigated the morphological, physiological, and molecular responses of two contrasting C. oleifera rootstocks, the P-tolerant Ganwu 1 (GW1) and the P-sensitive Ganwu 2 (GW2) under P-deficient conditions. Results: Our findings identified rootstock types as the primary determinant of P tolerance. GW1 exhibited superior resilience by re-engineering its root architecture, achieving a 4.12-fold higher root biomass and significantly greater 66.5% increase in fine root volume than GW2 under low P stress. In contrast, GW2 showed a compensatory but inefficient root expansion that failed to enhance soil exploration. Specifically, GW1 demonstrated a 3.7-fold higher root P accumulation and a 52.4% increase in root P-utilization efficiency under stress, reflecting a significantly higher capacity for P acquisition and internal allocation. This was coupled with enhanced nutrient rebalancing, particularly through robust potassium (K) accumulation in shoots, whereas GW2 suffered from a significant decline in soluble protein content and higher lipid peroxidation (MDA). Additionally, GW1 sustained high root acid phosphatase (ACP) activity during late-stage stress to further mobilize P. At the molecular level, GW1 was characterized by the accelerated induction of the CoARF22 , CoPHR1 , and CoPHT1;1 and earlier activation (70 days) of CoALMT -mediated organic acid genes. These proactive responses enabled GW1 to effectively mobilize soil P and maintain structural integrity, establishing it as a highly efficient rootstock for P-limited acid soils. Conclusions: This integrated "morphology-physiology-signaling" framework grants GW1 a superior low-P adaptive advantage. These results identify GW1 as a promising, P-efficient rootstock for sustainable C. oleifera production in P-deficient environments.

Rootstock choice offers a powerful lever for tailoring economically important trees to adverse environments. Camellia oleifera Abel., a premier oil-producing species cultivated widely on red-soil hills, suffers large yield losses under chronic phosphorus deficiency. We grafted a single elite scion (CL4) onto three contrasting rootstocks (CL4, CL3, CL53) and monitored growth and root transcriptomes for 1.5 years under adequate (1 mM) or limiting (0 mM) P supply. Under low-P stress, the rootstock identity reshaped the root architecture: CL4/CL3 produced the longest, most extensive network, increasing the total root length by 49.7%, the surface area by 52.9%, and the volume by 42.6% relative to the control, whereas leaf morphology responded solely to P supply, not to the graft combination. CL4/CL3 also accumulated up to more than 17.5% of root biomass and 28.25% of whole-plant biomass than any other combination. Physiologically, CL4/CL3 acted as an aggressive P miner, accumulating 67.8% more P in its roots than the self-grafted control under P limitation, while CL4/CL4 maximized the internal P use efficiency, showing a 44.74% higher root P use efficiency than CL4/CL53—two contrasting yet effective strategies for coping with low-P stress. Transcriptome profiling uncovered 1733 DEGs in the CL4/CL3 and 2585 in the CL4/CL4 roots, with 150 and 255 uniquely co-expressed genes, respectively. CL4/CL3 up-regulated organic-acid and phenylpropanoid pathways; CL4/CL4 activated defense and phosphate transport networks. qRT-PCR of six genes confirmed that CL4/CL3 mounted a stronger low-P response via MAPK, hormonal, and lipid–metabolic signaling. These results provide a mechanistic framework for rootstock-mediated P efficiency and establish a foundation for the molecular breeding of C. oleifera under nutrient-limited conditions.

Soil microbes play a crucial role in driving biogeochemical cycles and are closely linked with aboveground plants during forest succession. Moso bamboo (Phyllostachys edulis) encroachment into adjacent forests of varying composition is known to alter plant diversity in subtropical and tropical regions. However, how soil microbial communities respond to this vegetation type transformation has not fully explored. To address this knowledge gap, a time-alternative spatial method was employed in the present study, and we investigated the effect of Moso bamboo expansion into subtropical broad-leaved forest and coniferous forest on soil microbial phospholipid fatty acids (PLFAs). We also measured the dynamics of key soil properties during the Moso bamboo expansion processes. Our results showed that Moso bamboo encroachment into subtropical broad-leaved forest induced an elevation in soil bacterial PLFAs (24.78%) and total microbial PLFAs (22.70%), while decreasing the fungal-to-bacterial (F:B) ratio. This trend was attributed to declines in soil NO₃⁻-N (18.63%) and soil organic carbon (SOC) concentrations (28.83%). Conversely, expansion into coniferous forests promoted soil fungal PLFAs (40.41%) and F:B ratio, primarily driven by increases in soil pH (4.83%) and decreases in SOC (36.18%). These results provide mechanistic insights into how contrasting expansion trajectories of Moso bamboo restructure soil microbial communities and highlight the need to consider vegetation context-dependency when evaluating the ecological consequences of Moso bamboo expansion.

Litsea cubeba (Lour.) Pers. is an important woody spice tree in southern China, and its fruit is a rich source of valuable essential oil. We surveyed and sampled L. cubeba germplasm resources from 36 provenances in nine Chinese provinces, and detected rich phenotypic diversity. The survey results showed that plants of SC-KJ, SC-HJ, and SC-LS provenance presented higher leaf area (LA); YN-SM and YN-XC plants had larger thousand-grain fresh weight (TFW); and HN-DX plants had the highest essential oil content (EOC). To explain the large differences in the phenotypes of L. cubeba among different habitats, we used Pearson’s correlation analysis, multiple stepwise regression path analysis, and redundancy analysis to evaluate the phenotypic diversity of L. cubeba. It was found that compared to other traits, leaf and fruit traits had more significant geographical distributions, and that leaf phenotypes were correlated to fruit phenotypes. The results showed that elevation, latitude, longitude, total soil porosity (SP), soil bulk density (SBD), and average annual rainfall (AAR, mm) contributed significantly to the phenotypic diversity of L. cubeba. Geographical factors explained a higher percentage of variation in phenotypic diversity than did soil factors and climate factors. Plants of SC-KJ and HN-DX provenances could be important resources for domestication and breeding to develop new high-yielding varieties of this woody aromatic plant. This study describes significant phenotypic differences in L. cubeba related to adaptation to different environments, and provides a theoretical basis for the development of a breeding strategy and for optimizing L. cubeba cultivation.

Camellia oleifera Abel. is an economically important woody edible-oil species that is mainly cultivated in hilly areas of South China. The phosphorus (P) deficiency in the acidic soils poses severe challenges for the growth and productivity of C. oleifera. WRKY transcription factors (TFs) have been proven to play important roles in biological processes and plant responses to various biotic/abiotic stresses, including P deficiency tolerance. In this study, 89 WRKY proteins with conserved domain were identified from the C. oleifera diploid genome and divided into three groups, with group II further classified into five subgroups based on the phylogenetic relationships. WRKY variants and mutations were detected in the gene structure and conserved motifs of CoWRKYs. Segmental duplication events were considered as the primary driver in the expanding process of WRKY gene family in C. oleifera. Based on transcriptomic analysis of two C. oleifera varieties characterized with different P deficiency tolerances, 32 CoWRKY genes exhibited divergent expression patterns in response to P deficiency stress. qRT-PCR analysis demonstrated that CoWRKY11, -14, -20, -29 and -56 had higher positive impact on P-efficient CL40 variety compared with P-inefficient CL3 variety. Similar expression trends of these CoWRKY genes were further observed under P deficiency with longer treatment period of 120d. The result indicated the expression sensitivity of CoWRKYs on the P-efficient variety and the C. oleifera cultivar specificity on the P deficiency tolerance. Tissue expression difference showed CoWRKYs may play a crucial role in the transportation and recycling P in leaves by affecting diverse metabolic pathways. The available evidences in the study conclusively shed light on the evolution of the CoWRKY genes in C. oleifera genome and provided a valuable resource for further investigation of functional characterization of WRKY genes involved to enhance the P deficiency tolerance in C. oleifera.

Improving the economic benefits of Camellia oleifera is a major problem for C. oleifera growers, and girdling and foliar fertilizer have significant effects on improving the economic benefits of plants. This study explains the effects of girdling, girdling + foliar fertilizer on nutrient distribution, and the economic benefits of C. oleifera at different times. It also explains the N, P, and K contents of roots, leaves, fruits, and flower buds (sampled in March, May, August, and October 2021) and their economic benefits. The results showed girdling promoted the accumulation of N and K in leaves in March 2021 (before spring shoot emergence) but inhibited the accumulation of P, which led to the accumulation of P in roots and that of N in fruits in August 2021 (fruit expansion period). Foliar fertilizer application after girdling replenished the P content of leaves in March 2021, and P continued to accumulate in large quantities at the subsequent sampling time points. The N and P contents of the root system decreased in March. In October (fruit ripening stage), girdled shrubs showed higher contents of N and K in fruits and flower buds, and consequently lower relative contents of N and K in roots and leaves but higher content of P in leaves. Foliar fertilizer application slowed down the effects of girdling on nutrient accumulation in fruits and flower buds. Spraying foliar fertilizer decreased the N:P ratio in the flower buds and fruits of girdled plants. Thus, foliar fertilizer spray weakened the effects of girdling on the nutrient content and economic benefits of C. oleifera. In conclusion, girdling changed the nutrient accumulation pattern in various organs of C. oleifera at different stages, increased leaf N:K ratio before shoot emergence, reduced root K content at the fruit expansion stage and the N:K ratio of mature fruit, and promoted economic benefits.

Grafting provides a way to improve tolerance to low phosphorus (P) stress for plants, and has been extensively applied in commercial cultivars grafted onto appropriate rootstocks. However, little literature is available concerning the scion-mediated effect on P efficiency in grafted plants. In this study, three different Camellia oleifera Abel. scion cultivars (G8, G83-1, and W2) were grafted onto the same rootstock (W2) under controls (0.5 mM) and low-P (0 mM) availability for eight months. The results showed that the scions significantly affected root-to-shoot weight ratios, the root morphology with a diameter larger than 1 mm, P accumulation, and the P utilization efficiency (PUE) of the root. A higher increase in the root-to-shoot weight ratio under the low-P supply was observed in the G83-1/W2 (26.15%) than in the G8/W2 (0%) and the W2/W2 (5.32%). Root PUE of the scion G8, G83-1, and W2 was improved by up to 113.73%, 45.46%, and 20.97% under the low-P supply. Moreover, G8/W2 exhibited higher shoot P accumulation and the highest root PUE under the low-P supply, indicating a high capability to tolerate P deficiency by maximizing the cost-effectiveness of P remobilization to photosynthetic organs. This suggested the vigorous variety of G8 could be a promising scion to improve grafted C. oleifera tolerance to low-P stress. Our results would have important implications for exploration and identification of a superior scion variety to enhance the ability of resistance concerning P deficiency stress in C. oleifera.