Effects of deterministic assembly of communities caused by global warming on coexistence patterns and ecosystem functions.

Seasonal rhythms in biological and ecological dynamics are fundamental in regulating the structuring of microbial communities. Evaluating the seasonal rhythms of microorganisms in response to climate change could provide information on their variability and stability over longer timescales (>20-year). However, information on temporal variability in microorganism responses to medium- and long-term global warming is limited. In this study, we aimed to elucidate the temporal dynamics of microbial communities in response to global warming; to this end, we integrated data on the maintenance of species diversity, community composition, temporal turnover rates (v), and community assembly process in two typical ecosystems (meadows and shrub habitat) on the Qinghai-Tibet Plateau. Our results showed that 21 years of global warming would increase the importance of the deterministic process for microorganisms in both ecosystems across all seasons (R2 of grassland (GL) control: 0.524, R2 of GL warming: 0.467; R2 of shrubland (SL) control: 0.556, R2 of SL warming: 0.543), reducing species diversity and altering community composition. Due to environmental filtration pressure from 21 years of warming, the low turnover rate (v of warming: -3.13/-2.00, v of control: -2.44/-1.48) of soil microorganisms reduces the resistance and resilience of ecological communities, which could lead to higher community similarity and more clustered taxonomic assemblages occurring across years. Changes to temperature might increase selection pressure on specialist taxa, which directly causes dominant species (v of warming: -1.63, v of control: -2.49) primarily comprising these taxa to be more strongly impacted by changing temperature than conditionally (v of warming: -1.47, v of control: -1.75) or always rare taxa (v of warming: -0.57, v of control: -1.33). Evaluation of the seasonal rhythms of microorganisms in response to global warming revealed that the variability and stability of different microbial communities in different habitats had dissimilar biological and ecological performances when challenged with an external disturbance. The balance of competition and cooperation, because of environmental selection, also influenced ecosystem function in complex terrestrial ecosystems. Overall, our study enriches the limited information on the temporal variability in microorganism responses to 21 years of global warming, and provides a scientific basis for evaluating the impact of climate warming on the temporal stability of soil ecosystems.

Long-term warming impacts grassland ecosystem function: Role of diversity loss in conditionally rare bacterial taxa.

The impact of microbial communities on ecosystem function varies due to the diverse biological attributes and sensitivities exhibited by different taxonomic groups. These groups can be classified as always rare (ART), conditionally rare (CRT), dominant, and total taxa, each affecting ecosystem function in distinct ways. Thus, understanding the functional traits of organisms within these taxa is crucial for comprehending their contributions to overall ecosystem function. In our study, we investigated the influence of climate warming on the biogeochemical cycles of the ecosystem in the Qinghai-Tibet Plateau, utilizing an open top chamber experiment. Simulated warming significantly lowered ecosystem function in the grassland but not in the shrubland. This discrepancy was due to the diverse responses of the various taxa present in each ecosystem to warming conditions and their differing roles in determining and regulating ecosystem function. The microbial maintenance of ecosystem function was primarily reliant on the diversity of bacterial dominant taxa and CRT and was less dependent on ART and fungal taxa. Furthermore, bacterial CRT and dominant taxa of the grassland ecosystem were more sensitive to changing climatic conditions than grassland ART, resulting in a more pronounced negative diversity response. In conclusion, the biological maintenance of ecosystem function during climate warming is dependent on microbiome composition and the functional and response characteristics of the taxa present. Thus, understanding the functional traits and response characteristics of various taxa is crucial for predicting the effects of climate change on ecosystem function and informing ecological reconstruction efforts in alpine regions of the plateau.

Effects of long-term nitrogen & phosphorus fertilization on soil microbial, bacterial and fungi respiration and their temperature sensitivity on the Qinghai-Tibet Plateau.

BACKGROUND: The microbial decomposition of soil organic carbon (SOC) is a major source of carbon loss, especially in ecologically fragile regions (e.g., the Tibetan Plateau), which are also affected by global warming and anthropogenic activities (e.g., fertilization). The inherent differences between bacteria and fungi indicate that they are likely to play distinct roles in the above processes. However, there still have been no reports on that, which is restricting our knowledge about the mechanisms underlying SOC decomposition. METHODS: A long-term nitrogen (N) and phosphorus (P) addition field experiment was conducted to assess their effects on soil microbial, fungal, and bacterial respiration (RM, RF, and RB, respectively) and temperature sensitivity (Q10; at 15 °C, 25 °C, and 35 °C) using cycloheximide and streptomycin to inhibit the growth of fungi and bacteria. RESULTS: We found that N suppressed RM and RF at all temperatures, but RB was only suppressed at 15 °C, regardless of the addition of P. The addition of N significantly decreased the ratio of RF/RM at 35 °C, and the combined NP treatment increased the Q10 of RB but not that of RF. Results of the redundancy analysis showed that variations in soil respiration were linked with NO3 --N formation, while the variations in Q10 were linked with SOC complexity. Long-term N addition suppressed RM by the formation of NO3 --N, and this was mediated by fungi rather than bacteria. The contribution of fungi toward SOC decomposition was weakened by N addition and increasing temperatures. Combined NP addition increased the Q10 of RB due to increased SOC complexity. The present study emphasizes the importance of fungi and the soil environment in SOC decomposition. It also highlights that the role of bacteria and SOC quality will be important in the future due to global warming and increasing N deposition.

ZmDREB2A regulates ZmGH3.2 and ZmRAFS, shifting metabolism towards seed aging tolerance over seedling growth.

Seed aging tolerance and rapid seedling growth are important agronomic traits for crop production; however, how these traits are controlled at the molecular level remains largely unknown. The unaged seeds of two independent maize DEHYDRATION-RESPONSIVE ELEMENT-BINDING2A mutant (zmdreb2a) lines, with decreased expression of GRETCHEN HAGEN3.2 (ZmGH3.2, encoding indole-3-acetic acid [IAA] deactivating enzyme), and increased IAA in their embryo, produced longer seedling shoots and roots, than the null segregant (NS) controls. However, the zmdreb2a seeds, with decreased expression of RAFFINOSE SYNTHASE (ZmRAFS) and less raffinose in their embryo, exhibit decreased seed aging tolerance, than the NS controls. Overexpression of ZmDREB2A in maize protoplasts increased the expression of ZmGH3.2, ZmRAFS genes and that of a Rennila LUCIFERASE reporter (Rluc) gene, which was controlled by either the ZmGH3.2- or ZmRAFS-promoter. Electrophoretic mobility shift assays and chromatin immunoprecipitation assay quantitative polymerase chain reaction showed that ZmDREB2A directly binds to the DRE motif of the promoters of both ZmGH3.2 and ZmRAFS. Exogenous supplementation of IAA to the unaged, germinating NS seeds increased subsequent seedling growth making them similar to the zmdreb2a seedlings from unaged seeds. These findings provide evidence that ZmDREB2A regulates the longevity of maize seed by stimulating the production of raffinose while simultaneously acting to limit auxin-mediated cell expansion.