Haibo Du

Understanding how treeline and nontreeline trees allocate carbon at their upper elevation limits is key to forecasting species shifts under climate warming. We compared a treeline deciduous broadleaf, Betula ermanii , with a nontreeline evergreen conifer, Picea jezoensis , at their species‐specific upper limits and lower sites on Changbai Mountain. We measured leaf gas exchange and traced recent photoassimilates using in situ ¹³ CO ₂ pulse labeling. Within species, photosynthetic traits and carbon stocks did not differ between elevations, indicating no carbon‐acquisition limitation. In contrast, allocation patterns diverged at the upper limits: B. ermanii retained a larger share of recent ¹³ C aboveground and showed slower carbon flow with longer mean residence time in leaves, whereas P. jezoensis allocated more ¹³ C belowground and exhibited faster turnover. These patterns indicate that aboveground carbon allocation is primarily determined by species‐specific leaf habits (deciduous broadleaf vs. evergreen conifer), whereas belowground allocation is more strongly shaped by stress conditions associated with upper elevational limits. Patterns were consistent with the functional type driving aboveground allocation and elevation‐related site context shaping belowground allocation. We infer that treeline B. ermanii prioritizes aboveground investment to maximize short‐season carbon gain and support cold tolerance, while nontreeline P. jezoensis invests belowground to enhance resource uptake and cope with competition. Overall, contrasting sink‐mediated allocation strategies, rather than source limitations, govern species responses at upper limits and inform predictions of composition, distribution, and upward migration under future climate change.

Large soil organic carbon (SOC) stocks in alpine tundra play a critical role in the global carbon budget but are increasingly vulnerable to loss under climate warming. These losses are partly driven by vegetation shifts, such as the upward migration of herbaceous plants, which alter soil food web structure and influence SOC sequestration. Although interactive effects between these processes are expected, they remain largely unclear or hidden. Here, we conducted a ¹³ C‐labeled glucose tracing experiment in the alpine tundra of Changbai Mountain to investigate how upward migration of Deyeuxia angustifolia affects soil food web structure, energy flows, and ultimately SOC sequestration. Compared with soils without migration (NM), heavily herb‐migrated (HM) soils showed intensified carbon fluxes within trophic cascade, increasing carbon transfer to higher trophic levels, including fungivores, omnivores‐predators, plant‐parasites, meso‐ and macrofauna. Predators in HM soils progressively increased ¹³ C assimilation over the 30‐day period, while microbivores showed a 5‐day lag behind microbial ¹³ C uptake. This predator‐driven energy dissipation was 2–14 times greater in HM than in NM soils and constituted an inefficient carbon sequestration pathway that limited the formation of stable carbon pools. As a result, SOC turnover in HM soils was more than 50% lower than in NM soils, indicating a shift toward less stable organic matter forms and reduced net carbon accumulation. Overall, our findings demonstrate that soil food webs play a pivotal role in both “belowground shaping” and “aboveground feedback” processes during herbaceous plant migration and that strengthened trophic cascade effects redirect carbon flow toward inefficient pathways, thereby constraining SOC sequestration in alpine tundra ecosystems.

Seasonal climate warming affects temperate plant phenology differently. Early winter warming can delay dormancy release and budburst due to insufficient chilling, while late winter or spring warming advances budburst. Additionally, the influence of pre-spring non-structural carbohydrate (NSC) availability on leaf phenology remains poorly understood. We explored the effects of previous late-summer defoliation and winter–spring warming on NSC dynamics and spring leaf phenology in two species: deciduous sessile oak with low chilling sensitivity and evergreen Scots pine with intermediate chilling sensitivity. We observed species-specific responses of leaf phenology to warming and defoliation. Winter warming delayed leaf unfolding in pine but not in oak, likely reflecting the greater chilling requirement of the pine. Defoliation significantly reduced pre-spring NSC levels in twigs and roots of both species, and led to earlier needle emergence in pine, with no impact on oak's leaf out date. Our findings indicate a dual dependency of pine leaf unfolding on temperature and internal carbon reserves, suggesting that defoliation, e.g. through herbivory or diseases, affects the following year’s spring phenology and leaf growth in evergreen species but not in deciduous trees. These findings are important for understanding the adaptive strategies of different plant functional types under uneven warming conditions.

As global warming drives plant upward migration, the alpine tundra of Changbai Mountain is experiencing encroachment by Deyeuxia angustifolia (Komarov) Y. L. Chang, a low-elevation herb. However, its impact on native shrubs such as Rhododendron aureum Georgi remains unclear. Here, we analyzed the radial growth trends and climate sensitivity of R. aureum across elevations and encroachment gradients using linear and mixed-effects model methods, and explored the mediating roles of soil properties and plant traits. Our study revealed that R. aureum exhibited stronger positive long-term growth trend at higher elevations compared to lower elevations. Mild and moderate encroachment of D. angustifolia enhanced the positive growth trend of R. aureum, especially at the low elevations. Moreover, R. aureum showed weak climate sensitivity at mid-elevation but stronger responses to winter temperatures at low elevation and to spring–summer temperatures and precipitation at high elevation. D. angustifolia encroachment further intensified this sensitivity, characterized by stronger negative responses to spring, autumn and winter temperatures but positive responses to summer temperatures and autumn precipitation. Overall, elevation primarily influenced R. aureum growth and its sensitivity to precipitation through soil conditions and plant size traits, while soil conditions and leaf economic traits influence temperature sensitivity. These findings advance understanding of alpine vegetation dynamics and contribute to ecosystem conservation under climate change.

Quantifying and removing urbanization-induced biases in existing precipitation datasets is critical for climate change detection, model assessment, and attribution studies in Northwest China (NWC). The precipitation observational stations of NWC were divided into rural (reference) stations and urban stations using the percentage of urban areas calculated from the land use/land cover (LULC) satellite data of the European Space Agency (ESA) Climate Change Initiative (CCI) Land Cover project. The annual extreme precipitation index series for urban stations (all stations) and rural stations from 1961 to 2022 were calculated based on the categorization of meteorological stations, and the urbanization effects and their contributions to precipitation index series were quantitatively evaluated through estimating trends in the difference series between all stations and the rural stations. The results showed that the urbanization effect varies among different regions and indices. The R10mm, R95pTOT, R99pTOT, and PRCPTOT indices in the sampled urban areas of NWC exhibited statistically significant negative urbanization effects, reaching −0.075 days decade⁻¹, −0.038 % decade⁻¹, −0.024 % decade⁻¹, and −0.035 % decade⁻¹, respectively. However, the R95pTOT, SDII, CDD, and CWD indices at the urban station of the largest city, Urumqi, have been significantly positively affected by urbanization, which is inconsistent with the sampled urban areas of NWC, where the urbanization effect reached 0.069 % decade⁻¹, 0.054 mm·d⁻¹ decade⁻¹, 2.319 days decade⁻¹, and 0.112 days decade⁻¹, respectively. Our analysis shows that the previously reported regional increase in total precipitation and extremes has been underestimated due to the negative urbanization effects in the precipitation data series of urban stations.

The effects of rising atmospheric CO₂ concentrations (C_a) with climate warming on intrinsic water-use efficiency (iWUE) and radial growth in boreal forests are still poorly understood. We measured tree-ring cellulose δ¹³C, δ¹⁸O, and tree-ring width in Larix dahurica (larch) and Betula platyphylla (white birch), and analyzed their relationships with climate variables in a boreal permafrost region of northeast China over past 68 years covering a pre-warming period (1951–1984; base period) and a warm period (1985–2018; warm period). We found that white birch but not larch significantly increased their radial growth over the warm period. The increased iWUE in both species was mainly driven by elevated C_a but not climate warming. White birch but not larch showed significantly positive correlations between tree-ring δ¹³C, δ¹⁸O and summer maximum temperature as well as vapor pressure deficit in the warm period, suggesting a strong stomatal response in the broad-leaved birch to temperature changes. The climate warming-induced radial growth enhancement in white birch is primarily associated with a conservative water use strategy. In contrast, larch exhibits a profligate water use strategy. It implies an advantage for white birch over larch in the warming permafrost regions.

Large explosive volcanic eruptions can cover wide areas of land with tephra, profoundly disturbing ecological and societal systems. However, while consequences of tephra fallout and flow deposits have been well studied on annual to decadal timescale, little is known about centennial and longer-term changes in vegetation composition. Here, we reconstruct the pre-eruption vegetation and local climatic conditions on Changbaishan (aka Mt. Paektu) volcano from relict trees recovered from the deposits of its colossal 946 CE ‘Millennium Eruption’. A comparison of forest composition and structure deduced from the subfossil material with today’s forests on the mountain reveals still ongoing impacts more than thousand years after the eruption occurred. Today’s higher abundance of broad-leaved species reflects the long-term vegetation recovery following the eruption rather than the effects of anthropogenic warming that have been suggested previously. Further ecological succession, accelerated by global warming, is likely to reduce or eliminate the alpine tundra now prevalent on the upper slopes of Changbaishan. Our study emphasizes the value of assessing post-volcanic vegetation responses in a long temporal context.