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The knowledge concerning the relationship between vegetation restoration and soil microorganisms is limited, especially at high altitudes. In order to evaluate the restoration efficacy of the reforestation on the soil microbial community, we have examined vegetation composition, edaphic properties and structure and function of different soil microbial groups in two different aged (25- and 40-year-old) Picea likiangensis var. rubescens Rehder & E. H. Wilson (P. rubescens) plantations and the primeval coniferous forest (PCF) dominated by Abies squamata Masters by plot-level inventories and sampling in western Sichuan Province, China. Our results suggested that only the fungal samples in 25-year-old P. rubescens plantation could be distinguished from those in the PCF in both structure and function. The structure and function of the fungal community recovered relatively slowly compared with bacterial and archaeal communities. In addition to the soil chemical properties and tree species composition, the shrub composition was also a key factor influencing the soil microbial community. The P. rubescens plantations were conducive to restoring the soil microbial community in both structure and function. However, there were uncertainties in the variations of the bacterial and archaeal communities with increasing the P. rubescens plantation age.

Repeated homoploid hybrid speciation (HHS) events with the same parental species have rarely been reported. In this study, we used population transcriptome data to test paraphyly and HHS events in the conifer Picea brachytyla. Our analyses revealed non-sister relationships for two lineages of P. brachytyla, with the southern lineage being placed within the re-circumscribed P. likiangensis species complex (PLSC) and P. brachytyla sensu stricto (s.s.) consisted solely of the northern lineage, forming a distinct clade that is paratactic to both the PLSC and P. wilsonii. Our phylogenetic and coalescent analyses suggested that P. brachytyla s.s. arose from HHS between the ancestor of the PLSC before its diversification and P. wilsonii through an intermediate hybrid lineage at an early stage and backcrossing to the ancestral PLSC. Additionally, P. purpurea shares the same parents and an extinct lineage with P. brachytyla s.s. but backcrossing to the other parent, P. wilsonii at a later stage. We reveal the first case that backcrossing to different parents of the same extinct hybrid lineage produced two different hybrid species. Our results highlight the existence of more reticulate evolution during species diversification in the spruce genus and more complex homoploid hybrid events than previously identified.

Background Picea species are distributed and planted world-wide due to their great ecological and economic values. It has been reported that Picea species vary widely in growth traits in a given environment, which reflects genetic and phenotypic differences among species. However, key physiological processes underlying tree growth and the influencing factors on them are still unknown. Results Here, we examined needle structures, needle chemical components, physiological characteristics and growth traits across five Picea species in a common garden in Tianshui, Gansu province in China: Picea glauca , P. mariana , P. likiangensis , P. koraiensis , and P. crassifolia , among which P. glauca and P. mariana were introduced from North America, P. likiangensis was from Lijiang, Yunan province in China, P. koraiensis was from Yichun, Heilongjiang province in China, and P. crassifolia was native to the experimental site. It was found that nearly all traits varied significantly among species. Tissue-level anatomical characteristics and leaf mass per area (LMA) were affected by needle size, but the variations of them were not associated with the variations in photosynthetic and biochemical capacity among species. Variations in area-based maximum photosynthesis (P nmax ) were affected by stomatal conductance (g s ), mesophyll conductance (g m ) and biochemical parameters including maximum carboxylation rate (V cmax ), and maximum electron transport rate (J max ). The fraction of N allocated to different photosynthetic apparatus displayed contrasting values among species, which contributed to the species variations in photosynthetic nitrogen use efficiency (PNUE) and P nmax . Additionally, all growth traits were positively correlated with P nmax and PNUE. Conclusion Needle structures are less important than needle biochemical parameters in determining the variations in photosynthetic capacity across the five Picea species. P nmax and PNUE are closedly associated with the fraction of N allocated to photosynthetic apparatus (P photo ) compared with leaf N content per area (N area ). The tremendous growth differences among the five Picea species were substantially related to the interspecies variation in P nmax and PNUE.

Predicting hydroclimatic changes on the Tibetan Plateau (TP) is crucial for managing water and ecosystems for the well-being of millions of people. Our understanding of the synoptic conditions on the TP is, however, still limited due to the paucity of meteorological measurements and proxy-based, high-resolution climate reconstructions. Here, we use state-of-the-art dendroclimatological techniques to investigate the paleoclimatic potential of drought-sensitive Picea likiangensis var. balfouriana forests between 4000 and 4500 m asl on the southeastern TP (SETP). The newly developed tree-ring width chronology correlates significantly with yearly changes in regional relative air humidity (RH) (r = 0.85, P < 0.001, 1978–2011). A new 407-year-long reconstruction of RH over the hydrological year from previous year August to July of the year of ring formation shows that, despite the generally humid conditions, four of the ten driest years are observed in the twentieth century with 1983 having been the driest. On the other hand, seven out of the ten most humid years were found in the eighteenth century. Our reconstruction reveals that the Pacific Decadal Oscillation (PDO) is the dominant climate driver at multi-decadal scales, but the relationships are not stable over time, with unknown underlying mechanisms. Although our study demonstrates the importance of the PDO for hydroclimate projections on the TP, caution is advised when considering only its most recent fluctuations.

Heat treatment is admittedly a significant value-adding step in wood processing. However, the decrease in mechanical properties of wood caused by heat treatment has always been an urgent problem to be solved. This study aimed to overcome this barrier by impregnating Balfour spruce ( Picea likiangensis var. balfouriana ) wood with low-molecular-weight lignin before heat treatment. The low-molecular-weight lignin impregnated more effectively and distributed uniformly in wood cell wall. The equilibrium moisture content of the heat-treated wood with lignin impregnation decreased significantly compared to those without lignin impregnation. The low-molecular-weight lignin impregnation combined with heat treatment improved the dimensional stability and humidity resistance effectively. The impregnated cell walls with lignin were integrated and seldom spoiled during heat treatment. The heat-treated wood impregnated with low-molecular-weight lignin showed an increased MOE, MOR, and compressive strength (CS) of 52, 177, and 25%, respectively, compared with the heat-treated wood without lignin impregnation. The indentation modulus of the secondary walls of heat-treated wood with impregnated low-molecular-weight lignin increased by 300%. These findings provide some insights into the relationship between lignin content and the strength of wood and show a way to enhance the mechanical properties of heat-treated wood without damage to its dimensional stability.

The members of the genus Picea form a dominant component in many alpine and boreal forests which are the major sink for atmospheric CO2. However, little is known about the growth response and acclimation of CO2 exchange characteristics to high temperature stress in Picea taxa from different altitudes. Gas exchange parameters and growth characteristics were recorded from four year old seedlings of two alpine (Picea likiangensis vars. rubescens and linzhiensis) and two lowland (P. koraiensis and P. meyeri) taxa. Seedlings were grown at moderate (25°C/15°C) and high (35°C/25°C) day/night temperatures, for four months. The approximated biomass increment (ΔD2H) for all taxa decreased under high temperature stress, associated with decreased photosynthesis and increased respiration. However, the two alpine taxa exhibited lower photosynthetic acclimation and higher respiratory acclimation than either lowland taxon. Moreover, higher leaf dry mass per unit area (LMA) and leaf nitrogen content per unit area (Narea), and a smaller change in the nitrogen use efficiency of photosynthesis (PNUE) for lowland taxa indicated that these maintained higher homeostasis of photosynthesis than alpine taxa. The higher respiration rates produced more energy for repair and maintenance biomass, especially for higher photosynthetic activity for lowland taxa, which causes lower respiratory acclimation. Thus, the changes of ΔD2H for alpine spruces were larger than that for lowland spruces. These results indicate that long term heat stress negatively impact on the growth of Picea seedlings, and alpine taxa are more affected than low altitude ones by high temperature stress. Hence the altitude ranges of Picea taxa should be taken into account when predicting changes to carbon fluxes in warmer conditions.

Key messageWe found that embryogenic tissues of Picea balfouriana adopt different physiological pathways for long-term proliferation with 6-benzylaminopurine treatment and identified the miRNAs closely associated with proliferation.The long-term maintenance of somatic embryo production capacity in conifer embryogenic tissue (ET) is essential for the production of vigorous somatic seedlings. However, this ability is often lost after several months of proliferation in many conifer species including Picea balfouriana. Cytokinins are known to influence several important physiological processes during plant growth and development, including somatic embryogenesis (SE). In this study, we found that the 6-benzylaminopurine (BA) concentration influenced the yields of P. balfouriana somatic embryos and their germination response. Only ET of P. balfouriana proliferated on medium supplemented with 3.6 µM BA produced somatic embryos that germinated into normal plants. Most hormone levels increased in ET after prolonged proliferation. Moreover, antioxidant enzyme activities and polyamine contents were also significantly changed after 8 months of culture, which might be modulated by accumulated zeatin riboside (ZR). Finally, some selected microRNAs and their target genes were confirmed to be involved in the proliferation of ET of P. balfouriana and they also might be regulated by accumulated ZR. These findings may facilitate efforts to clarify basic physiological processes after the long-term proliferation stage of SE in conifers and delay the decreased production capacity of somatic embryos.

Key messageWarming-induced drought stress leads to convergent and negative growth responses to temperature between sympatric tree species, implying an increasing interspecific competition for soil moisture.In mixed forests, sympatric tree species avoid competition by partitioning their niches according to available environment resources. We raise the hypothesis that climate warming leads to a convergence in growth responses to climate, thus increasing the competition among sympatric species in drought-prone forests. In this study, we selected a mixed forest located at ca. 3600 m a.s.l in the Baima Snow Mountains, an inner dry valley of the southeastern Tibetan Plateau. We measured width of the tree rings produced during 1910–2016 in 60 trees belonging to three sympatric species: Abies georgei, Picea likiangensis, and Betula delavayi. We analyzed the changes in radial growth and their responses to climate. We detected shifts in the responses to climate after the 1990s. The radial growth of all species was positively correlated with precipitation from 1964 to 1990, but negatively correlated with March–June temperature from 1991 to 2016. Compared to the period 1964–1990, convergent and negative growth responses to warmer temperatures in the period 1991–2016 probably reflect less available soil moisture for growing in this mixed forest. We conclude that climate warming will affect the niches of sympatric species in mixed forests subjected to seasonal drought, thus increasing competition and altering structure and composition of the stands in dry regions.

As a feature of global warming, climate change has been a severe issue in the 21st century. A more comprehensive reconstruction is necessary in the climate assessment process, considering the heterogeneity of climate change scenarios across various meteorological elements and seasons. To better comprehend the change in minimum temperature in winter in the Jinsha River Basin (China), we built a standard tree-ring chronology from Picea likiangensis var. balfouri and reconstructed the regional mean minimum temperature of the winter half-years from 1606 to 2016. This reconstruction provides a comprehensive overview of the changes in winter temperature over multiple centuries. During the last 411 years, the regional climate has undergone seven warm periods and six cold periods. The reconstructed temperature sensitively captures the climate warming that emerged at the end of the 20th century. Surprisingly, during 1650–1750, the lowest winter temperature within the research area was about 0.44 °C higher than that in the 20th century, which differs significantly from the concept of the “cooler” Little Ice Age during this period. This result is validated by the temperature results reconstructed from other tree-ring data from nearby areas, confirming the credibility of the reconstruction. The Ensemble Empirical Mode Decomposition method (EEMD) was adopted to decompose the reconstructed sequence into oscillations of different frequency domains. The decomposition results indicate that the temperature variations in this region exhibit significant periodic changes with quasi-3a, quasi-7a, 15.5-16.8a, 29.4-32.9a, and quasi-82a cycles. Factors like El Niño–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and solar activity, along with Atlantic Multidecadal Oscillation (AMO), may be important driving forces. To reconstruct this climate, this study integrates the results of three machine learning algorithms and traditional linear regression methods. This novel reconstruction method can provide valuable insights for related research endeavors. Furthermore, other global climate change scenarios can be explored through additional proxy reconstructions.

Thaumatin-like proteins (TLPs) are involved in the plant defense response against pathogens, and most of them exhibit antifungal activity. However, the role of TLPs in pathogen-induced defense responses in spruce is not fully understood. In this study, four TLP genes encoding thaumatin-like protein, designated as PlTLP1–4, were isolated and identified from Picea likiangensis needles. Sequence analysis showed that PlTLP1, PlTLP3, and PlTLP4 contained 16 conserved cysteine residues, while PlTLP2 had only 10 conserved cysteine residues. qPCR analysis showed that PlTLPs were expressed in all tissues tested, PlTLP1, PlTLP3, and PlTLP4 had the highest expression levels in young fruits, while PlTLP2 had the highest expression levels in roots. In addition, the expression levels of four PlTLPs were significantly upregulated during infection by Lophodermium piceae. Four recombinant PlTLPs expressed in Escherichia coli exhibited obvious β-1,3-glucanase activity. The antifungal activity assay showed that four recombinant PlTLPs had significant inhibitory effects on the mycelial growth of L. piceae, Fusarium proliferatum, Botrytis cinerea, and Roussoella doimaesalongensis. Microscopic observation revealed that the recombinant PlTLP1–4 induced the morphological changes of the mycelia of L. piceae, and the recombinant PlTLP2 and PlTLP3 induced the morphological changes of the mycelia of F. proliferatum and R. doimaesalongensis, while all the recombinant PlTLPs had no obvious negative effect on the morphology of B. cinerea mycelium. These results suggest that PlTLP genes may play an important role in the defense response of P. likiangensis against L. piceae invasion.