Evergreen Conifer Research Articles

Photoinhibition Sensitivity of Abies sachalinensis Saplings Under Different Leaf Mass per Area Conditions: Insights into Acclimation to Current and Future Light Environments

Photoinhibition, a common physiological obstacle in forest regeneration, results from rapid light elevations after removing upper-layer trees, thereby impeding sapling growth and survival. The leaf mass per area (LMA), which reflects the current light environment, may predict saplings’ responses to future elevations in light intensity. However, the relationship between the LMA and photoinhibition sensitivity in boreal forest evergreen conifers remains unclear. In this study, we explored whether the LMA was related to photoinhibition sensitivity in A. sachalinensis saplings. Saplings with a high LMA exhibited higher excitation pressure (1−qP) under the current light environment, leading to increased stress even at low relative light intensities of 3%–17%. A model illustrating the dependence of photosynthetic physiological parameters on the photosynthetic photon flux density (PPFD) revealed that 1−qP significantly decreased with an increasing LMA, while the electron transfer rate (ETR) and non-photochemical quenching (NPQ) significantly increased. Additionally, regardless of the LMA, 1−qP reached near saturation (≈1.0) at a PPFD of 1000 μmol m−2 s−1, likely owing to the inefficient consumption of excess energy by electron transfer, as indicated by the low maximum ETR (approximately 25 μmol m−2 s−1). These findings suggest that although A. sachalinensis exhibits high sensitivity to photoinhibition, a high LMA may reflect physiological acclimation to forthcoming elevations in light exposure, thereby reducing the susceptibility to photoinhibition at present and in the future.

Relationship Between Evolutionary Diversity and Aboveground Biomass During 150 Years of Natural Vegetation Regeneration in Temperate China.

While the link between plant species diversity and biomass has been well-studied, the impact of evolutionary diversity on community biomass across long timescales or ongoing change remains a subject of debate. We elucidated the association between evolutionary diversity and community aboveground biomass (AGB) using an ideal experimental system with over 150-year history of natural vegetation regeneration. Higher phylogenetic diversity facilitated the sampling effect under the influence of environmental filtering, and caused an increase in AGB. Phylogenetic structure varied from aggregation to dispersion during the later period of vegetation recovery (70-150 years), which was correlated with increases in niche complementarity and increasing AGB. Woody plant evolutionary diversity was used as a key to predict the relationship between vegetation recovery and AGB, with a total explanatory power of ~84.7%. Mixed forests composed of evergreen conifers and deciduous broadleaf forests had higher carbon sequestration potential than that of pure forests, which is advantageous for increasing top-stage AGB. This research expands our knowledge of the causes and effects of biodiversity and ecosystem function dynamics over time and space, which is important for accurately predicting future climate change effects.

Assessing the phenological state of evergreen conifers using hyperspectral imaging time series

Phenology is a reliable indicator of vegetation condition and ecological changes in the environment. Plant Spectral Phenology (PSP) offers the potential for the development of automated, rapid, and wide-area vegetation monitoring systems. The spectral characteristics of plants (vegetation) are employed as metrics of PSP, which can be sensed both proximally and remotely. A key objective is to undertake a comparative analysis of the results of PSP versus those of phenology based on visual observations. The resolution of this issue is of paramount importance for the coordination of phenological studies at diverse levels (ground, surface, and remote), thus ensuring the continuity of phenological studies conducted prior to the advent of PSP. This issue is particularly pronounced in the case of evergreen conifers. The present study focuses on four evergreen conifers: Thuja occidentalis, Platycladus orientalis, Pinus sylvestris and P. nigra subsp. pallasiana. Hyperspectral imaging was performed under laboratory conditions using a Cubert UHD-185 hyperspectral camera. Concomitantly, phenological observations were conducted. The spectral time series yielded 79 chlorophyll-sensitive and carotenoid-sensitive Vegetation Indices (VIs), which were then used to construct double logistic functions. A significant proportion of the VIs exhibited a high degree of correctness with regard to the aforementioned functions, as indicated by the value of R2 exceeding 0.7. The values of the principal stages of seasonal development of evergreen conifers, namely the Start of Season (SOS), End of Season (EOS), Position of Peak value (POP) and Length of Season (LOS), were calculated using double logistic functions. These stages were matched to the phenological phases of development of the experimental plants. The values of SOS, EOS, POP and LOS varied significantly depending on the VIs used as a metric as well as the evergreen conifers. The lowest variability by metrics is observed in SOS, while the maximum is observed in EOS and POP. The results obtained may be of importance for the choice of criterion for the comparison of PSP with phenology based on visual observations and the most suitable VIs for these purposes.

Identification and analysis of gibberellin 2-oxidase (GA2ox) members in Cunninghamia lanceolate and the negative regulatory character of ClGA2ox12 in tree stature and xylem lignin deposits

Cunninghamia lanceolata (Lamb.) Hook (C. lanceolate) is a fast-growing evergreen coniferous tree species with high wood yield and fantabulous timber quality. To date, numerous studies have revealed that gibberellins (GAs) regulate the formation of plant wood (secondary xylem). Moreover, GA 2-oxidases (GA2oxs) are known as the major enzymes that deactivate GAs. However, a small or no number of the GA2oxs involved in xylem development and lignin biosynthesis mediated by the GA pathway in woody plants have been identified previously. In this study, 5 GA2oxs members were identified in C. lanceolate, including 4 ClGA2ox12s and one ClGA2ox8-like. Exogenous gibberellin not only promoted lignin deposition in the stem of C. lanceolate but also up-regulated the expression of the lignin biosynthesis gene ClCAD1 by 2–3 folds and one of ClGA2ox12s (designated ClGA2ox12) by 4 folds, suggesting that ClGA2ox12 may be involved in the modulation of lignin deposition by the gibberellin signaling pathway in C. lanceolate. Furthermore, transgenic Populus tomentosa overexpressing ClGA2ox12 exhibited growth retardation and a typical dwarfing phenotype, with a reduction of approximately 40 % in the number of xylem cell layers and a decrease of approximately 16.7 %-26.9 % in lignin content relative to wild-type plants. At the same time, the expression level of lignin biosynthetic genes and lignin content were down-regulated in transgenic plants. Together, these results suggested that ClGA2ox12 functioned as a GA 2oxs catabolic enzyme that plays pivotal roles in plant growth processes, xylem development, and lignin biosynthesis, which gives insights into producing dwarf and low-lignin varieties of C. lanceolate.

Tree-Climbing Behavior of a Forest-Dwelling Ungulate: The Formosan Serow.

Ungulates are terrestrial herbivores, basically adapted to running fast on the ground; tree-climbing behavior has been reported only in seven species, and five of them live in open habitats (Capra hircus, C. aegagrus, C. falconeri, C. cylindricornis, Oreotragus oreotragus). Tree-climbing behavior may also be evolved in ungulates inhabiting dense forests with abundant trees; however, this has rarely been reported in such species (Moschus leucogaster, M. moschiferus), probably due to the difficulty of observing in the wild. The numerous publicly available records in social networks hold potentially valuable information on the atypical behaviors of wild ungulates. Here, we explored the tree-climbing behavior of a forest-dwelling ungulate, the Formosan serow in Taiwan, a subtropical island, by extracting information from online social media platforms. We researched images and videos of Formosan serows through Facebook and YouTube and collected a total of 15 tree-climbing events. In these materials, Formosan serows climbed 10 tree species, including evergreen coniferous and broad-leaved trees, and a variety of parts, ranging in height from 0.6 to 4 m, and from branches of shrubs to trunks of tall trees. Tree-climbing behavior was recorded throughout Taiwan and from lowlands to subalpine zones, suggesting that tree climbing may be a common behavior in this species. Foraging while climbing trees was frequently observed (53.3%), suggesting that the purpose or benefit for climbing is to obtain additional food other than plants growing near the ground surface. In contrast to other tree-climbing ungulates, Formosan serows climbed trees not only in winter, but also in other seasons, when food is relatively abundant. This is the first scientific report of tree-climbing behavior in the Formosan serow that is typically a forest dweller.

What makes decomposition faster under conspecific trees? The factors controlling the magnitude of home‐field advantage

The ‘home‐field advantage (HFA)' for decomposition means that leaf litter decomposes faster on soils under the conspecific species (i.e. the home field) than on soils under different species (i.e. ‘away'). Many previous studies have demonstrated the HFA, but the underlying mechanisms remain unclear. We conducted a reciprocal litter‐decomposition experiment using two species with different leaf traits: Abies mariesii, an evergreen conifer, and Fagus crenata, a deciduous broad‐leaved tree. Dominance of these species shifts along an elevation gradient with a transition zone where both species coexist. In mixed forests of the transition zone along the elevation gradient, we explored how the magnitude of HFA between these two species was influenced by temperature, soil properties, or leaf litter traits which could directly affect the decomposition rate. The magnitude of HFA observed between the two species varied widely from −3.89 to 28.3%. Our modeling showed that the magnitude of HFA increased with decreasing soil pH and leaf litter N, i.e. in more acidic soil and for less decomposable litter. Soil pH affected leaf litter decomposition in the home plots of each species, whereas leaf litter N did not. The magnitude of the HFA increased as the difference in soil pH between the F. crenata and A. mariesii plots at the same elevation became greater, but decreased as the difference in soil C became greater. Thus, the response of leaf litter decomposition to environmental changes might vary not only through direct effects of vegetation traits but also through indirect effects of the HFA. This highlights the importance of considering HFA for accurately predicting the response of local carbon and nutrient cycles to climate change, particularly in communities where a replacement of dominant species by others is expected due to climate change.

Effects of soil compaction and vegetation weeding on the above-, and belowground growth of boreal evergreen conifer seedlings

Effects of soil compaction and vegetation weeding on the above-, and belowground growth of boreal evergreen conifer seedlings

Investigating into the Death Years of Evergreen Conifers in Landslide Areas of Jirisan National Park and the Abrupt Growth Reduction During Their Living

Investigating into the Death Years of Evergreen Conifers in Landslide Areas of Jirisan National Park and the Abrupt Growth Reduction During Their Living

Isotope-Based Techniques to Investigate Factors Influencing Water Use Efficiency in Pinus koraiensis Leaves during Plant Growth.

Plant water use efficiency (WUE) is a comprehensive physiological indicator of plant growth and ability to adapt to drought. However, research on the mechanisms controlling WUE during plant growth and development remains weak. Here, we studied Pinus koraiensis as a typical evergreen conifer species in Northeast China. After collecting 80 tree samples with varying diameters at breast height (DBH), we measured δ13C and δ18O as an indicator of WUE, leaf morphology (volume, dry weight, and total epidermal area), ecological stoichiometry (carbon, nitrogen, and phosphorus content), and abiotic factors (light environment, soil pH, soil water content, and soil nutrient content). Correlational analysis of these variables revealed distinct differences between smaller/younger and larger/older plants: (1) In plants with DBH less than 52 cm, δ13C was positively related to DBH, and δ18O was negatively related to DBH. Plants with DBH greater than 52 cm showed no relationship between δ13C and DBH, and δ18O was positively related to DBH. (2) In plants with DBH less than 52 cm, there was a negative correlation between δ13C and δ18O and between δ13C and leaf phosphorus content (LP), but a positive correlation between δ13C and DBH, leaf mass per area (LMA), and leaf density (LD). The slopes of DBH-δ13C, δ18O-δ13C, leaf nitrogen content (LN)-δ13C, and LMA-δ13C correlations were greater in smaller plants than large plants. (3) Structural equation modelling showed that in smaller plants, DBH had a direct positive effect on δ13C content and a direct negative effect on δ18O, and there was a direct positive effect of light environment on δ18O. In larger plants, there was a direct negative effect of light environment on δ13C and a direct positive effect of DBH on light environment, as well as a negative effect of soil nitrogen content on leaf nitrogen. In smaller plants, DBH was the most important factor influencing δ13C, followed by δ18O and soil moisture, with light and soil pH showing minimal influence. In larger plants, light environment influenced δ13C the most, followed by soil nitrogen content and soil moisture content, with leaf nitrogen and DBH contributing little. The results suggest that water use efficiency strategies of P. koraiensis vary according to growth stage, and the effects of abiotic factors and functional traits vary at different growth stages.

Transcriptome and widely metabolomic analysis reveal hormones and sugar signaling pathways contribute to the normal growth of seeds in young Picea neoveitchii Mast. trees

Abnormal seed growth is a problem in Picea neoveitchii Mast. in China that threatens the existence of this evergreen coniferous tree. However, the degree of abnormal seed growth varies in different age groups; regrettably, the causes behind abnormal seed growth at different ages are totally unclear. Thus, we compared the seeds of two ages: Gansu (GS) province, a 50-year-old tree (GS50), and a 300-year-old tree (GS300). Results indicated that 22187 unigenes were commonly found in both groups, whereas 5328 and 6079 unigenes were uniquely found in GS50 and GS300, respectively. Furthermore, a total of 5129 differentially expressed unigenes were identified between GS50 and GS300, with 2431 upregulated and 2698 downregulated. On the basis of Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, plant hormone signal transduction and starch and sucrose metabolism pathways were further selected for their potential involvement in seed growth at both ages. A wide-targeted metabolomics-based approach using liquid chromatography mass spectrometry (LC-MS) was applied to study the difference between GS50 and GS300. The results showed that there were 35 different metabolites in total being detected, mainly amino acids and sugars. Subsequently, GS50 revealed the highest number of normal seeds and the lowest number of abnormal seeds in comparison with GS300 by improving endogenous indole-3-acetic acid (IAA), zeatin riboside (ZR), and gibberellic acid 3 (GA3) contents and reducing methyl jasmonate (JA-me), abscisic acid (ABA), and brassinosteroid (BR) contents. Our research provides important evidence on the growth of seeds in different age groups of trees that might help improve seed growth in old trees.

Significant phenological response of forest tree species to climate change in the Western Carpathians

Abstract This study aims to analyse the phenological dynamics of tree species in response to changes in climatic conditions over the last two climate-normal periods (CLINO 1961−1990 and 1991−2020). We focused on the main climax tree species (Quercus species, Fagus sylvatica L., Abies alba Mill., Picea abies [L.] Karst., and Pinus mugo Turra) dominating eight altitudinal forest vegetation zones (FVZ) and alluvial forests of Western Carpathians and adjacent lowlands in Central Europe. The phenological phases analysed in this study were first leaf (BBCH11) and general leaf colouring (BBCH94) for deciduous species, and the onset of new shoots (BBCH10) for evergreen conifers. The results of partial correlations confirmed that temperature is the main driving factor explaining the shifted onset of phenological phases for the species considered. Furthermore, deciduous species growing in the lower (and warmer) FVZ showed a certain level of drought sensitivity related to the earlier BBCH94. The identified trends in phenology were species-specific and differed between the individual FVZs. The most pronounced shifts toward the earlier BBCH10 and BBCH11 were found in the upper FVZ of the vertical distribution range of species. The presented results will support our understanding of the mechanisms underlying environmental control of tree phenology. This is crucial for predicting how the growing season of trees will be constrained by climate change-induced conditions in individual FVZ.

Disparities in tree mortality among plant functional types (PFTs) in a temperate forest: Insights into size-dependent and PFT-specific patterns

Tree mortality significantly influences forest structure and function, yet our understanding of its dynamic patterns among a range of tree sizes and among different plant functional types (PFTs) remains incomplete. This study analysed size-dependent tree mortality in a temperate forest, encompassing 46 tree species and 32,565 individuals across different PFTs (i.e., evergreen conifer vs. deciduous broadleaf species, shade-tolerant vs. shade-intolerant species). By employing all-subset regression procedures and logistic generalized linear mixed-effects models, we identified distinct mortality patterns influenced by biotic and abiotic factors. Our results showed a stable mortality pattern in evergreen conifer species, contrasted by a declining pattern in deciduous broadleaf and shade-tolerant, as well as shade-intolerant species, across size classes. The contribution to tree mortality of evergreen conifer species shifted from abiotic to biotic factors with increasing size, while the mortality of deciduous broadleaf species was mainly influenced by biotic factors, such as initial diameter at breast height (DBH) and conspecific negative density. For shade-tolerant species, the mortality of small individuals was mainly determined by initial DBH and conspecific negative density dependence, whereas the mortality of large individuals was subjected to the combined effect of biotic (competition from neighbours) and abiotic factors (i.e., convexity and pH). As for shade-intolerant species, competition from neighbours was found to be the main driver of tree mortality throughout their growth stages. Thus, these insights enhance our understanding of forest dynamics by revealing the size-dependent and PFT-specific tree mortality patterns, which may inform strategies for maintaining forest diversity and resilience in temperate forest ecosystems.

Mass Spectrometry-Imaging Analysis of Active Ingredients in the Leaves of Taxus cuspidata.

Taxus cuspidata is an endangered evergreen conifer mainly found in Northeast Asia. In addition to the well-known taxanes, several active ingredients were detected in the leaves of T. cuspidata. However, the precise spatial distribution of active ingredients in the leaves of T. cuspidata is largely unknown. in the present study, timsTOF flex MALDI-2 analysis was used to uncover the accumulation pattern of active ingredients in T. cuspidata leaves. In total, 3084 ion features were obtained, of which 944 were annotated according to the mass spectrometry database. The principal component analysis separated all of the detected metabolites into four typical leaf tissues: mesophyll cells, upper epidermis, lower epidermis, and vascular bundle cells. Imaging analysis identified several leaf tissues that specifically accumulated active ingredients, providing theoretical support for studying the regulation mechanism of compound biosynthesis. Furthermore, the relative accumulation levels of each identified compound were analyzed. Two flavonoid compounds, ligustroflavone and Morin, were identified with high content through quantitative analysis of the ion intensity. our data provides fundamental information for the protective utilization of T. cuspidata.

Accounting for photosystem I photoinhibition sheds new light on seasonal acclimation strategies of boreal conifers.

The photosynthetic acclimation of boreal evergreen conifers is controlled by regulatory and photoprotective mechanisms that allow conifers to cope with extreme environmental changes. However, the underlying dynamics of photosystem II (PSII) and photosystem I (PSI) remain unresolved. Here, we investigated the dynamics of PSII and PSI during the spring recovery of photosynthesis in Pinus sylvestris and Picea abies using a combination of chlorophyll a fluorescence, P700 difference absorbance measurements, and quantification of key thylakoid protein abundances. In particular, we derived a new set of PSI quantum yield equations, correcting for the effects of PSI photoinhibition. Using the corrected equations, we found that the seasonal dynamics of PSII and PSI photochemical yields remained largely in balance, despite substantial seasonal changes in the stoichiometry of PSII and PSI core complexes driven by PSI photoinhibition. Similarly, the previously reported seasonal up-regulation of cyclic electron flow was no longer evident, after accounting for PSI photoinhibition. Overall, our results emphasize the importance of considering the dynamics of PSII and PSI to elucidate the seasonal acclimation of photosynthesis in overwintering evergreens. Beyond the scope of conifers, our corrected PSI quantum yields expand the toolkit for future studies aimed at elucidating the dynamic regulation of PSI.

Temporal Transcriptome Profiling of Pinus densiflora Infected with Pine Wood Nematode Reveals Genetically Programmed Changes upon Pine Wilt Disease.

Pine, an evergreen conifer, is widely distributed worldwide. It is economically, scientifically, and ecologically important. However, pine wilt disease (PWD) induced by the pine wood nematode (PWN) adversely affects pine trees. Many studies have been conducted on the PWN and its beetle vectors to prevent the spread of PWD. However, studies providing a comprehensive understanding of the pine tree transcriptome in response to PWN infection are lacking. Here, we performed temporal profiling of the pine tree transcriptome using PWD-infected red pine trees, Pinus densiflora, inoculated with the PWN by RNA sequencing. Our analysis revealed that defense-responsive genes involved in cell wall modification, jasmonic acid signaling, and phenylpropanoid-related processes were significantly enriched 2 weeks after PWD infection. Furthermore, some WRKY-type and MYB-type transcription factors were upregulated 2 weeks after PWD infection, suggesting that these transcription factors might be responsible for the genome-wide reprogramming of defense-responsive genes in the early PWD stage. Our comprehensive transcriptome analysis will assist in developing PWD-resistant pine trees and identifying genes to diagnose PWD at the early stage of infection, during which large-scale phenotypic changes are absent in PWD-infected pine trees.

Season of drought affects growth, but not nonstructural carbohydrates dynamics, in Pinus taeda saplings.

In temperate evergreen conifers, growth occurs mostly in summer but photosynthesis precedes year-round; thus, nonstructural carbohydrates (NSC) increase in winter but decrease in summer. Given that mild drought reduces growth but not photosynthesis, a drought in summer should increase NSCs more than one in winter. However, the active regulation hypothesis suggests that to increase future drought resilience, plants might downregulate growth to increase NSCs after a winter drought even if NSCs do not increase during the drought. To test if so, potted Pinus taeda saplings (age $< 1$ yr) were subjected to six-month droughts in a greenhouse with one treatment receiving drought during winter (Sep-Mar), and another during summer (Mar-Sep). Both treatments were compared to a control. To measure dry biomass and NSCs, we harvested plants monthly following each drought, while to assess changes in growth rates, we measured height and diameter monthly. While we observed seasonal variation and an overall increase during the study, we found no drought-related changes in NSC dynamics; however, drought did reduce growth. Furthermore, drought in winter did reduce growth during the following summer, but the reduction was less than for a drought in summer. We conclude that the effect of drought on NSCs was too small to detect in our plants. While better control of soil water would have reduced a major source of uncertainty, plants with larger NSC reserves or more intense stress would also yield easier-to-detect effects. Although not definitive, our results suggest that water stress does not lead to dramatic changes in seasonal NSC dynamics in its aftermath, despite what one might expect under the active regulation hypothesis.

Metabolome integrated with transcriptome reveals the mechanism of three different color formations in Taxus mairei arils.

Maire yew (Taxus mairei), an evergreen conifer, has high ornamental and medicinal value. The arils of this species has three different colors. However, the variation mechanisms of arils color formation remains unclear. Here, the gene expression and metabolite concentration were profiled for red (RTM), yellow (YTM), and purple (PTM) arils in different developmental stages. A total of 266 flavonoids and 35 carotenoids were identified. The predominant pigments identified in YTM were epiafzelechin, lutein, and β-Cryptoxanthin, while malvidin-3,5-di-O-glucoside and apigenin played crucial roles in PTM. And significant differential expression was observed among the HCT, DFR, LAR, ANS, crtB, NCED, and CCoAOMT genes across different color arils. During the maturation of yellow arils, the upregulation of HCT was strongly correlated with the accumulation of epiafzelechin. The diminished expression of DFR, LAR, and ANS seemed to inhibit the production of delphinidin-3-O-rutinoside. The decrease in crtB expression and concurrent increase in NCED expression potentially regulate the heightened accumulation of lutein. Meanwhile, the accumulation of β-cryptoxanthin appeared seemed to be positively influenced by NCED. As aril turning purple, the decreased expression of CCoAOMT seemed to facilitate the synthesis of apigenin. The substantial upregulation of DFR promoted the production of malvidin-3,5-di-O-glucoside. Additionally, the overexpression of MYBs may plays the important role in regulating the formation of different colored arils. In total, 14 genes were selected for qRT-PCR validation, the results indicated the reliability of the transcriptome sequences data. Our findings could provide valuable insight into the molecular breeding, development, and application of Maire yew resources.

Effects of Pieris japonica (Ericaceae) dominance on cool temperate forest altered-understory environments and soil microbiomes in Southern Japan.

The number of plants unpalatable to deer increases with increasing deer numbers. In the Kyushu Mountain area of Southern Japan, Pieris japonica (Ericaceae), an unpalatable shrub, has become the monodominant vegetation under evergreen conifer and deciduous broad-leaved tree stands. The monodominance of unpalatable plants in the understory has potential advantages and drawbacks; however, the effects of Pieris dominance are not well understood. To assess the effects of P. japonica dominances on forest environments and ecosystems, we investigated understory environments and soil microbiomes in Pieris-dominant sites. Under the deciduous broad-leaved trees, Pieris dominance leads to considerable Pieris leaf litter and humus weights and low soil bulk density and canopy openness. In the soil fungal community and fungal functional groups, the relative abundance of symbiotrophic fungi, particularly ectomycorrhizal fungi in Pieris-dominant sites were lower than in other-vegetation understory sites and saprotrophic fungi vice versa. Because few seedlings and saplings were found under Pieris shrubs, Pieris dominance in the understory might exclude other plant species. The results of this study will contribute to the Pieris population and forest management following deer overgrazing.

Fine-Root Distribution and Soil Physicochemical Property Variations in Four Contrasting Urban Land-Use Types in South Korea.

Urbanization and associated forest conversions have given rise to a continuum of native (forest fragments) and modified (artificial grasslands and perennial ecosystems) land-use types. However, little is known about how these shifts affect soil and fine-root compartments that are critical to a functioning carbon and nutrient circulation system. In this study, soil physicochemical properties, fine-root mass, and vertical distribution patterns were investigated in four representative urban land-use types: grassland (ZJ), perennial agroecosystem (MP), broadleaf deciduous forest patch (QA), and coniferous evergreen forest patch (PD). We quantified the fine-root mass in the upper 30 cm vertical profile (0-30 cm) and at every 5 cm depth across three diameter classes (<2 mm, 2-5 mm, and <5 mm). Soil physicochemical properties, except for phosphorus, nitrogen, ammonium nitrogen, and sodium cations, varied significantly across land-use types. The total root biomass (<5 mm) decreased in the order of QA (700.3 g m-2) > PD (487.2 g m-2) > ZJ (440.1 g m-2) > MP (98.3 g m-2). The fine-root mass of ZJ and MP was correlated with soil nutrients, which was attributed to intensive management operations, while the fine-root mass of QA and PD had a significant relationship with soil organic matter due to the high inputs from forest litter. Very fine roots (<2 mm) presented a distinct decremental pattern with depth for all land-use types, except for MP. Very fine roots populated the topmost 5 cm layer in ZJ, QA, and PD at 52.1%, 49.4%, and 39.4%, respectively. Maintaining a woody fine-root system benefits urban landscapes by promoting soil stabilization, improving ground infiltration rates, and increasing carbon sequestration capacity. Our findings underscore the importance of profiling fine-root mass when assessing urban expansion effects on terrestrial ecosystems.

Simulating long-term wildfire impacts on boreal forest structure in Central Yakutia, Siberia, since the Last Glacial Maximum

BackgroundWildfires are recognized as an important ecological component of larch-dominated boreal forests in eastern Siberia. However, long-term fire-vegetation dynamics in this unique environment are poorly understood. Recent paleoecological research suggests that intensifying fire regimes may induce millennial-scale shifts in forest structure and composition. This may, in turn, result in positive feedback on intensifying wildfires and permafrost degradation, apart from threatening human livelihoods. Most common fire-vegetation models do not explicitly include detailed individual-based tree population dynamics, but a focus on patterns of forest structure emerging from interactions among individual trees may provide a beneficial perspective on the impacts of changing fire regimes in eastern Siberia. To simulate these impacts on forest structure at millennial timescales, we apply the individual-based, spatially explicit vegetation model LAVESI-FIRE, expanded with a new fire module. Satellite-based fire observations along with fieldwork data were used to inform the implementation of wildfire occurrence and adjust model parameters.ResultsSimulations of annual forest development and wildfire activity at a study site in the Republic of Sakha (Yakutia) since the Last Glacial Maximum (c. 20,000 years BP) highlight the variable impacts of fire regimes on forest structure throughout time. Modeled annual fire probability and subsequent burned area in the Holocene compare well with a local reconstruction of charcoal influx in lake sediments. Wildfires can be followed by different forest regeneration pathways, depending on fire frequency and intensity and the pre-fire forest conditions. We find that medium-intensity wildfires at fire return intervals of 50 years or more benefit the dominance of fire-resisting Dahurian larch (Larix gmelinii (Rupr.) Rupr.), while stand-replacing fires tend to enable the establishment of evergreen conifers. Apart from post-fire mortality, wildfires modulate forest development mainly through competition effects and a reduction of the model’s litter layer.ConclusionWith its fine-scale population dynamics, LAVESI-FIRE can serve as a highly localized, spatially explicit tool to understand the long-term impacts of boreal wildfires on forest structure and to better constrain interpretations of paleoecological reconstructions of fire activity.