Knowledge concerning the processes involved in defining the boundaries between rainforests (fire-sensitive) and open formations (fire-tolerant) is essential to safeguarding biodiversity and ecosystem services, especially under climate change and increased anthropogenic pressure. Here, we investigated the main environmental factors involved in the co-occurrence of forest islands and humid grasslands located in a protected area in the Espinhaço Biosphere Reserve, southeastern Brazil. We used permanent plots to collect the soil variables (moisture and chemical properties) in the forest islands. For sampling in wet grasslands, we installed four lines of 30 m from the edge of the islands in different directions. Subsequently, we delimited three points on each line10 m apart, totaling 12 points per area. We also surveyed the vegetation cover before and after prescribed burns. The environmental variables were subjected to tests of means and principal component analysis. We observed higher values of potassium, sum of bases, cation exchange capacity and organic matter in soils from forest islands than in wet grasslands. Therefore, the boundaries’ definition between the two vegetation types appeared to be primarily related to soil fertility and moisture gradients. After prescribed burning of the areas, no regeneration of arboreal individuals was detected near the edges of the islands. Therefore, our results suggest that forest islands are unable to expand due to well-defined edapho-climatic conditions. Thus, these environments should be a target focus for designing public conservation policies because they increase the complexity of the landscape of Campos Rupestres vegetation (mountain rocky grasslands).

Changes in soil nitrogen mineralization can impact nutrient availability, and further affect plant growth. It is unclear, however, how temperature elevation in alpine grassland will affect soil net N mineralization rate (N_min) across altitudes. At six altitudes (3200-4200 m with an interval of 200 m) along a slope in Lenglong mountain in the northern Qinghai-Tibetan Plateau, we performed an in situ soil incubation experiment by using the resin-core method to assess altitudinal variations of N_min. Meanwhile, we evaluated the effects of temperature elevation on N_min and its temperature sensitivity (Q₁₀) through a soil downward transplantation experiment based on three reference baseline altitudes (3800, 4000 and 4200 m). The results showed that high altitudes generally led to low values of N_min. Structural equation modeling analysis revealed that N_min along the altitude was mainly controlled by soil temperature. Increased temperature caused by the altitude transplantation significantly elevated N_min for all of the three reference altitudes. The value of Q₁₀ was 3.4 for soil samples transplanted from the reference altitude of 4200 m, which was about twice that of the lower reference altitudes of 4000 and 3800 m.

Understanding how community phylogenetic and functional structures change over succession has gained increasing attention during the last decades, but the lack of long-term time-series data has limited our understanding of the patterns and mechanisms of these changes. This is especially the case for forest communities. Here, we used an exceptionally long-term data over 68 years to analyze the secondary succession dynamics of a subtropical forest in Southeast China. We found that community phylogenetic and functional structures showed opposite temporal trends. The mean pairwise phylogenetic distance between species increased, but the mean nearest taxon distance decreased over succession, indicating both phylogenetically distantly related and sister species co-occurred in late-successional communities. In contrast, both the mean pairwise functional distance and mean nearest functional distance between species decreased over time, and community functional structure switched from overdispersion to clustering. We further distinguished the contributions of species colonization and extinction to community structural changes. We found that the new colonists were generally more distantly related to each other and to the residents than the local extinct species, resulting in increased phylogenetic overdispersion over succession. In contrast, from a functional perspective, we found that species with more similar traits to the resident species had a greater chance to colonize but a lower chance to go locally extinct, which shifted community functional structure toward clustering. Together, our study highlights the critical role of species colonization and extinction in disentangling assembly mechanisms underlying community phylogenetic and functional structures over long-term succession.

Expansion of global trade and acceleration of climate change dramatically promote plant invasions. As a result, a large number of habitats harbor multiple invasive plant species. However, patterns of invasive interactions and the drivers mediating their interactions remain unclear. In this greenhouse, potted plant study, we tested the impacts of 18 invasive plant species on the growth of target invader Erigeron canadensis which is dominant in central China. Neighboring invasive species belong to three functional groups (grass, forb and legume) and have different levels of relatedness to E. canadensis. Growth of E. canadensis’ strongly depended on the identity of neighboring invaders. Some neighboring invasive species suppressed growth of E. canadensis, others had no effect, while some promoted growth of E. canadensis. Through analyses of functional and phylogenetic similarities between the target species and neighboring invaders, we showed that two factors probably play roles in determining the relative responses of E. canadensis. Generally, E. canadensis responded negatively to invasive grasses and forbs, while it responded positively to invasive legumes. Furthermore, the negative responses to neighboring invasive grasses and forbs increased with increasing phylogenetic distance between the neighbors and E. canadensis. In contrast, the positive responses to invasive legumes did not depend on phylogenetic distance from E. canadensis. Our results suggest that successful invasion of E. canadensis probably depends on the identity of co-occurring invasive plant species. Interactions between E. canadensis and other invasive species should help managers select management priorities.

A better understanding the mechanisms driving plant biomass allocation in different ecosystems is an important theoretical basis for illustrating the adaptive strategies of plants. To date, the effects of habitat conditions on plant biomass allocation have been widely studied. However, it is less known how plant community traits and functions (PCTF) affect biomass allocation, particularly in alpine grassland ecosystems. In this study, community-weighted means (CWM) were calculated at the community level using five leaf functional traits, and the relationships between PCTF and biomass trade-offs were explored using correlation analysis, variation partitioning analysis and structural equation modeling. We found that the trade-off values were greater than zero in both alpine meadow (AM) and alpine steppe (AS) across the Tibetan Plateau, with different values of 0.203 and 0.088 for AM and AS, respectively. Moreover, the critical factors determining biomass allocation in AS were species richness (SR; scored at 0.69) and leaf dry matter content of CWM (CWM_LDMC’, scored at 0.42), while in AM, the key factors were leaf dry matter content (CWM_LDMC’, scored at 0.48) and leaf carbon content of CWM (CWM_LC’, scored at -0.45). In particular, both CWMLDMC and SR in AS, as well as CWM_LDMC and CWM_LC in AM were primarily regulated by precipitation. In summary, precipitation tends to drive biomass allocation in alpine grasslands through its effects on PCTF, hence highlighting the importance of PCTF in regulating plant biomass allocation strategies along precipitation gradients.

Kobresia meadows are the main pastures for animal husbandry on the Qinghai-Tibet Plateau, and may represent alternative steady states associated with different grazing intensities. The ability of other plant communities to succeed these meadows remains unclear. In this study, the historical data of plant communities were analyzed in terms of the soil profile, and the present characteristics were identified by investigating their plant communities. Four types of steady states were identified, corresponding to grazing intensities of >11, 8-11, 5.5-8 and <5.5 sheep/ha. Drought alpine swamp meadows and shrub meadows could succeed to K. pygmaea meadows and K. humilis meadows under overgrazing, and their total biomass and edible biomass (estimated by Gramineae and Cyperaceae) decreased with increasing grazing intensity. The regime shift of the states occurred at a grazing intensity of 8-11 sheep/ha. This value thus represented the threshold of significant change in the production and ecological service function in the Kobresia meadow succession process. In general, increasing grazing intensities can adversely affect the service ability of meadows for livestock production and ecosystem stabilization. Our results revealed the potential degraded succession process of the alpine Kobresia meadow and the succession direction in the restoration process of degraded meadows. Additionally, this study provided a theoretical basis for evaluating the fitness between the livestock bearing capacity and carrying capacity in steady states and academic reference for policy setting pertaining to the utilization of Kobresia meadows in a sustainable development framework.

Through its role in regulating pollinator behavior, floral display size and nectar gradient within inflorescences may alter the extent of geitonogamy and thus female reproductive success in protandrous species. However, this has seldom been examined. By quantifying selfing rate, seed number and male donor number, we estimated the effects of floral display size, nectar gradient and their interactions on plant reproduction in protandrous Aconitum gymnandrum. At plant level, selfing rate and seed number increased with a larger floral display of both main and lateral inflorescences but reduced with a declining nectar gradient. The effects of floral display of the main inflorescence on selfing rate and seed number were altered by the nectar gradient and floral display of lateral inflorescences as shown by their interactions. Larger floral display of the main inflorescence reduced male donor diversity. At flower level, the selfing rate and the seed number varied among flower positions, in which bottom flowers had lower selfing rate and higher seed number than top flowers. The effects of floral traits on geitonogamous selfing rate and seed number were inconsistent among flower positions. Although low cost of geitonogamous selfing for reproduction was tested by hand-pollination, the selfing rate was negatively correlated with seed number and male donor number in open-pollinated population. Our results suggest the potential role of trade-off between geitonogamy cost and reproductive benefit in evolution of floral traits. The variation of selfing rate and reproductive success among flowers may alter the trade-off and thus complicate evolution of traits.

Rhizosheaths can form on the surface of rice (Oryza sativa L.) roots and improve the water-use efficiency of rice under drought stress. The microbes in rhizosheaths can also offer the potential to increase the resilience of rice to future drought. However, little is known about the microbial community in rhizosheath of rice under drought stress. In this study, we compared the root traits, rhizosheath formation and microbial community in the rhizosheath under three irrigation regimes, including well-watered and drought treatments I and II. The irrigation plays important roles in influencing the microbial composition and co-occurrence networks. Drought can promote the accumulation of beneficial microorganisms in rhizosheaths, such as bacteria that are members of the phylum Patescibacteria and the Massilia, Nocardioides, Frateuria and Angustibacter genera and fungi in the genus Talaromyces. However, drought can also induce risk factors for harmful fungi in rice rhizosheaths. Our results suggest that both the rhizosheath and microbes in rhizosheath can offer the potential to improve the resistance of rice to drought. In the future, the isolation and application of beneficial microorganisms in rhizosheaths and scientific planting methods should be studied for the green cultivation of rice.

Nitrogen deposition has increased rapidly in eastern China, which can affect the stoichiometric characteristics of plants. However, the effects of N addition on the nitrogen (N) and phosphorous (P) allocation strategies for various plant life forms (e.g. trees, shrubs and herbs) have rarely been studied. In this study, we evaluated the effects of N addition on N and P stoichiometry and their scaling exponents in the leaves and fine roots of the different life form groups. N and P concentrations in the leaves of shrubs and herbs increased under N addition treatments, whereas tree leaves exhibited a more stable response. In contrast, N addition had no significant effect on N and P concentrations in the fine roots of the three plant life forms. N addition enhanced the allocation of more N and P to the leaves than to the fine roots in all three life forms. Furthermore, the N-P allocation scaling exponents of the leaves and fine roots of the trees were equal to 1.0, indicating an isometric pattern. In contrast, the N-P allocation scaling exponents of shrubs and herbs were less than 1.0, indicating an allometric pattern. Although high N availability promoted shrubs and herbs to distribute P to leaves at a higher proportion than N, only slight effects were detected in tree leaves. These changes in N-P allocation patterns indicate that life forms and N addition levels work together to modulate plants allocation strategies. These results suggest the importance of life form categories when evaluating N-P allocation strategies in forest plants.