Objective We aimed to understand the basic characteristics of the underground seed bank of Pinus densata forest and its relationship with aboveground vegetation, to provide a theoretical basis for vegetation restoration. Methods The study sites were Dongjiu Bridge (DJ), Linji Bridge (LZ), and Birishen Mountain Scenic Spot (RB) in Gongbu Nature Reserve, Southeast Tibet, China. Species composition and distribution pattern of the underground seed bank in P. densata forest were analyzed. Germination data and field investigations were used to examine the similarities between aboveground vegetation and underground seed banks, and their responses to the environment. Results There were 47 species belonging to 27 families in the underground seed bank of the P. densata forest. Asteraceae, Rosaceae, Labiatae, and Poaceae were dominant, accounting for 40.4% of the total number of families. Underground seed density was 2,114, 1,952, and 1,141 seeds/m² in DJ, LZ, and BR, respectively. The percentage of different life‐forms in each sampling location was shown to be perennial herbs > shrubs > annual herbs > trees > subshrubs. The Shannon–Wiener diversity index, Margalef richness index, and Simpson's dominance index of each sample showed that species decreased with higher elevation, while the Pielou evenness index showed the opposite trend. Elevation, slope position, slope aspect, and slope were positively correlated with the Pielou evenness index and negatively correlated with the Shannon–Wiener diversity index, Margalef richness index, and Simpson's dominance index. The Sørensen index, comparing the similarity between the underground seed bank and aboveground vegetation of DJ, LZ, and BR was 0.46, 0.35, and 0.31, respectively. Conclusion The underground seed bank of P. densata forest has high seed density and high species richness, but there was little similarity between aboveground vegetation and underground seed bank. Elevation and slope position had a great influence on the uniformity of species distribution.

To explore the adaptation strategies of the aboveground and underground functional traits of alpine plants along an altitudinal gradient, a typical stand of primitive dark coniferous forests (Abies georgei var. smithii.) in southeastern Tibet was taken as the research object in the present study. PCA and correlation analyses were carried out for different organ functional traits (19 key indicators in total), then RDA analysis was done in conjunction with 12 environmental factors. The variation characteristics of the functional traits of leaves, current-year twigs, trunks and fine roots in 6 continuous altitude gradients and the relationships between functional traits and environmental factors were explored. The results showed that soil organic carbon (SOC) may exert a positive effect on the construction of plant defense tissue via changes in functional traits, altitude (Alt) represents the primary influencing factor of wood density (WD) variation, particulate organic carbon (POC) content mainly affected fine root dry matter (RDWC) content and specific root length (SRL), and total potassium (TK) content was the main factor that affected fine root tissue density (RTD). Leaves, current-year twigs, and fine roots exhibited high production or nutrient acquisition capacity at an altitude of 4,000m and showed strong defense and relatively stable water and nutrient transport capacity. In conclusion, the ecological strategy of Abies georgei var. smithii. in Sejila Mountain was more conservative, and the optimal survival area of Abies georgei var. smithii. was located at 4, 000m on the shady slope of Sejila Mountain. It is of paramount significance for exploring the essence of terrestrial ecosystems and their functional processes in extremely high-altitude environments.

Net ecosystem productivity (NEP) is a crucial measurement for understanding ecosystem function and carbon cycling. On the basis of Moderate Resolution Imaging Spectroradiometer (MODIS) data, meteorological data, and topographic data, combined with the enhanced Carnegie Ames Stanford Approach (CASA) model, we analyzed the spatiotemporal trends and changes in the vegetation NEP in southeastern Xizang from 2000 to 2020. Additionally, we employed the GeoDetector model to identify the driving factors influencing the vegetation NEP. The results indicated that: (1) from 2000 to 2020, the annual vegetation NEP in southeastern Xizang exhibited a fluctuating increasing trend. The multiyear average vegetation NEP was 519.06 gC m ⁻² a ⁻¹ , ranging from 11.23 to 1,333.40 gC m ⁻² a ⁻¹ . The minimum and maximum values occurred in 2010 and 2015, respectively. (2) The spatial distribution pattern of the vegetation NEP revealed an overall trend of higher values in southern areas and lower values in northern areas, with higher values in eastern areas compared to western areas. The average area of the carbon source regions (NEP < 0) was approximately 70,119 km ² , whereas the average area of the carbon sink regions (NEP > 0) was approximately 82,017 km ² . Overall, the region exhibited a carbon sink characteristic. (3) Altitude, precipitation, and temperature were the primary drivers influencing the vegetation NEP. In regions at lower elevations and in the southern and eastern parts of the study area—where thermal and moisture conditions are relatively favorable—NEP values were generally higher. In contrast, NEP was markedly lower in the northern and high-elevation areas characterized by low temperatures and limited water availability. The interactions between any two of these factors had a greater impact on the vegetation NEP than the independent effect of any single factor did, highlighting a synergistic dual-factor enhancement effect.