Arbuscular mycorrhizal fungal community composition is altered by long-term litter removal but not litter addition in a lowland tropical forest

Tropical forest productivity is sustained by the cycling of nutrients through decomposing organic matter. Arbuscular mycorrhizal (AM) fungi play a key role in the nutrition of tropical trees, yet there has been little experimental investigation into the role of AM fungi in nutrient cycling via decomposing organic material in tropical forests. We evaluated the responses of AM fungi in a long-term leaf litter addition and removal experiment in a tropical forest in Panama. We described AM fungal communities using 454-pyrosequencing, quantified the proportion of root length colonised by AM fungi using microscopy, and estimated AM fungal biomass using a lipid biomarker. AM fungal community composition was altered by litter removal but not litter addition. Root colonisation was substantially greater in the superficial organic layer compared with the mineral soil. Overall colonisation was lower in the litter removal treatment, which lacked an organic layer. There was no effect of litter manipulation on the concentration of the AM fungal lipid biomarker in the mineral soil. We hypothesise that reductions in organic matter brought about by litter removal may lead to AM fungi obtaining nutrients from recalcitrant organic or mineral sources in the soil, besides increasing fungal competition for progressively limited resources

Regenerated woody plants influence soil microbial communities in a subtropical forest

10 páginas.- 4 figuras.- 3 tablas.- referencias.- upplementary data to this article can be found online at https://doi. org/10.1016/j.apsoil.2023.104890Forests are critical for supporting multiple ecosystem services such as climate change mitigation. Microbial diversity in soil provides important functions to maintain and regenerate forest ecosystems, and yet a critical knowledge gap remains in identifying the linkage between attributes of regenerated woody plant (RWP) communities and the diversity patterns of soil microbial communities in subtropical plantations. Here, we investigated the changes in soil microbial communities and plant traits in a nine hectare Chinese fir (Cunninghamia lanceolata; CF) plantation to assess how non-planted RWP communities regulate soil bacterial and fungal diversity, and further explore the potential mechanisms that structure their interaction. Our study revealed that soil bacterial richness was positively associated with RWP richness, whereas soil fungal richness was negatively associated with RWP basal area. Meanwhile, RWP richness was positively correlated with ectomycorrhizal (ECM) fungal richness but negatively correlated with the richness of both pathogenic and saprotrophic fungi, suggesting that the RWP-fungal richness relationship was trophic guild-specific. Soil microbial community beta diversity (i.e., dissimilarity in community composition) was strongly coupled with both RWP beta diversity and the heterogeneity of RWP basal area. Our study highlights the importance of community-level RWP plant attributes for the regulation of microbial biodiversity in plantation systems, which should be considered in forest management programs in the future.This work was funded by the National Key Research and Development Program of China (2021YFD2201301 and 2022YFF1303003), the National Natural Science Foundation of China (U22A20612), and the Key Project of Jiangxi Province Natural Science Foundation of China (20224ACB205003).Peer reviewe

Synergistic effect of elevated CO2 and straw amendment on N2O emissions from a rice–wheat cropping system

13 págnas.- 4 figuras.- 1 tabla.- referencias.- The online version contains supplementary material available at https://doi.org/10.1007/s00374-024-01866-1Nitrous oxide (N2O) is one of the most important climate-forcing gases, and a large portion of global anthropogenic N2O emissions come from agricultural soils. Yet, how contrasting global change factors and agricultural management can interact to drive N2O emissions remains poorly understood. Here, conducted within a rice–wheat cropping system, we combined a two-year field experiment with two pot experiments to investigate the influences of elevated atmospheric carbon dioxide (eCO2) and crop straw addition to soil in altering N2O emissions under wheat cropping. Our analyses identified consistent and significant interactions between eCO2 and straw addition, whereby eCO2 increased N2O emissions (+ 19.9%) only when straw was added, and independent of different N fertilizer gradients and wheat varieties. Compared with the control (i.e., ambient CO2 without straw addition), eCO2 + straw addition increased N2O emission by 44.7% and dissolved organic carbon to total dissolved nitrogen (DOC/TDN) ratio by 115.3%. Similarly, eCO2 and straw addition significantly impacted soil N2O-related microbial activity. For instance, the ratio of the abundance of N2O production genes (i.e., nirK and nirS) to the abundance of the N2O reduction gene (i.e., nosZ) with straw addition was 26.0% higher than that without straw under eCO2. This indicates an increased denitrification potential and suggests a change in the stoichiometry of denitrification products, affecting the balance between N2O production and reduction, leading to an increase in N2O emissions. Taken together, our results emphasize the critical role of the interaction between the specific agronomic practice of straw addition and eCO2 in shaping greenhouse gas emissions in the wheat production system studied, and underline the need to test the efficacy of greenhouse gas mitigation measures under various management practices and global change scenarios.This work was supported by the earmarked fund for CARS-Green manure [CARS-22], the National Natural Science Foundation of China [32271635, 32022061, 32272218], the United Nations Development Program Project [00121838-SR-2021-05], and the China Scholarship Council [202303250050]. Manuel Delgado-Baquerizo acknowledges support from TED2021-130908B-C41/AEI/ European Next Generation EU/PRTR and from the Spanish Ministry of Science and Innovation for the I + D + i project PID2020-115813RA-I00 funded by MCIN/AEI/Peer reviewe

Responses of arbuscular mycorrhizal fungi to long-term inorganic and organic nutrient addition in a lowland tropical forest

Improved understanding of the nutritional ecology of arbuscular mycorrhizal (AM) fungi is important in understanding how tropical forests maintain high productivity on low-fertility soils. Relatively little is known about how AM fungi will respond to changes in nutrient inputs in tropical forests, which hampers our ability to assess how forest productivity will be influenced by anthropogenic change. Here we assessed the influence of long-term inorganic and organic nutrient additions and nutrient depletion on AM fungi, using two adjacent experiments in a lowland tropical forest in Panama. We characterised AM fungal communities in soil and roots using 454-pyrosequencing, and quantified AM fungal abundance using microscopy and a lipid biomarker. Phosphorus and nitrogen addition reduced the abundance of AM fungi to a similar extent, but affected community composition in different ways. Nutrient depletion (removal of leaf litter) had a pronounced effect on AM fungal community composition, affecting nearly as many OTUs as phosphorus addition. The addition of nutrients in organic form (leaf litter) had little effect on any AM fungal parameter. Soil AM fungal communities responded more strongly to changes in nutrient availability than communities in roots. This suggests that the 'dual niches' of AM fungi in soil versus roots are structured to different degrees by abiotic environmental filters, and biotic filters imposed by the plant host. Our findings indicate that AM fungal communities are fine-tuned to nutrient regimes, and support future studies aiming to link AM fungal community dynamics with ecosystem function

BioCON rhizobacteria metadata

Tab-delimited file. All headers are explanatory; ring = Free-Air Carbon Enrichment ring for elevated atmospheric CO2 addition in the field. </p

50-year fire legacy regulates soil microbial carbon and nutrient cycling responses to new fire

Fire disturbances are becoming more common, more intense, and further-reaching across the globe, with consequences for ecosystem functioning. Importantly, fire can have strong effects on the soil microbiome, including community and functional changes after fire, but surprisingly little is known regarding the role of soil fire legacy in shaping responses to recent fire. To address this gap, we conducted a manipulative field experiment administering fire across 36 soils with varying fire legacies, including combinations of 1-7 historic fires and 1-33 years since most recent fire. We analyzed soil metatranscriptomes, determining for the first time how fire and fire legacy interactively affect metabolically-active soil microorganisms, the microbial regulation of important carbon (C), nitrogen (N) and phosphorus (P) cycling, expression of carbohydrate-cycling enzyme pathways, and functional gene co-expression networks. Experimental fire strongly downregulated fungal activity while upregulating many bacterial and archaeal phyla. Further, fire decreased soil capacity for microbial C and N cycling and P transport, and drastically rewired functional gene co-expression. Perhaps most importantly, we highlight a novel role of soil fire legacy in regulation of microbial C, N, and P responses to recent fire. We observed a greater number of functional genes responsive to the interactive effects of fire and fire legacy than those affected solely by recent fire, indicating that many functional genes respond to fire only under certain fire legacy contexts. Therefore, without incorporating fire legacy of soils, studies will miss important ways that fire shapes microbial roles in ecosystem functioning. Finally, we showed that fire caused significant downregulation of carbon metabolism and nutrient cycling genes in microbiomes under abnormal soil fire histories, producing a novel warning for the future: human manipulation of fire legacies, either indirectly through global change-induced fire intensification or directly through fire suppression, can negatively impact soil microbiome functional responses to new fires

Biocrusts enhance soil organic carbon stability and regulate the fate of new-input carbon in semiarid desert ecosystems

13 páginas.- 6 figuras.- 3 tablas.- referencias.- Supplementary data to this article can be found online at https://doi.org/10.1016/j.scitotenv.2024.170794Given their global prevalence, dryland (including hyperarid, arid, semiarid, and dry subhumid regions) ecosystems are critical for supporting soil organic carbon (SOC) stocks, with even small changes in such SOC pools affecting the global carbon (C) cycling. Biocrusts play an essential role in supporting C cycling in semiarid ecosystems. However, the influence of biocrusts and their successional stages on SOC and its fraction contents, as well as their role in regulating new input C into SOC fractions remain largely unknown. In this study, we collected continuous samples of bare soil (BS) and three successional stages of biocrust soils (cyanobacterial (CC), low-cover moss (LM), and high-cover moss (HM)) at 0–5 cm depth every month for one year in a semiarid desert ecosystem. We analyzed SOC changes among the samples and their fraction contents including: labile organic C (LOC) (composed of microbial biomass C (MBC), dissolved organic C (DOC), and easily oxidized organic C (EOC)) and recalcitrant organic C (ROC) fractions, soil nutrient content including: ammonium (NH4+-N), nitrate (NO3−-N), and available phosphorus (AP), and soil temperature and moisture. We also conducted a 13C pulse-labelling experiment in the field to accurately quantify the effects of biocrust successional stage on exogenous C allocation to SOC fractions. Our results showed that the three successional stages of biocrust (CC-LM-HM) increased SOC and ROC contents by an average of 5.3 ± 3.6 g kg−1 and 4.0 ± 3.0 g kg−1, respectively; and the MBC, DOC, and EOC contents increased by an average of 41.7 ± 24.8 mg kg−1, 28.7 ± 12.6 mg kg−1, and 1.2 ± 0.6 g kg−1, respectively, compared to that of BS. These increases were attributed to an increase in photosynthetic pigment content, higher nutrient levels, and more suitable microclimates (e.g., higher moisture and more moderate temperature) during biocrust succession. More importantly, SOC stability was greatly improved with biocrust succession from cyanobacteria to moss, as evidenced by the reduction in soil EOC:SOC and EOC:ROC ratios by an average of 50 ± 34 % and 99 ± 67 %, respectively, while the ROC:SOC ratio increased by 33 ± 16 % with biocrust succession compared to those of BS. The biocrust SOC, DOC, and MBC 13C contents at different stages were on average 0.096 ± 0.034 mg kg−1, 0.010 ± 0.005 mg kg−1, and 0.014 ± 0.005 mg kg−1 higher than those of BS. Similarly, the allocation of new-input C among the DOC and MBC at different biocrust stages (19 ± 10 %) was significantly higher than that of BS (9 ± 6 %). New-input C into the biocrusts was fixed by microbes (43 ± 18 %) within ∼10 days and converted into other forms of C (85 ± 5 %) after 80 days. Our study provides a new perspective on how biocrusts support C cycling in semiarid desert ecosystems by mediating new C inputs into diverse fractional contents, and highlights the significance of biocrust successional stages in maintaining soil C stocks and stability in the dryland soil system.This work was supported by the National Natural Science Foundation of China (No. 42077010), the “Light of West China” Program of the Chinese Academy of Sciences (No. 2019), the Open Fund for Key Laboratory of Land Degradation and Ecological Restoration in Northwestern China of Ningxia University (No. LDER2022Z02), and the Chinese Universities Scientific Fund (No. 2023TC174). M.D-B. acknowledges the support from TED2021-130908B-C41/AEI/10.13039/501100011033/Unión Europea Next Generation EU/PRTR and from the Spanish Ministry of Science and Innovation for the I + D + i project PID2020-115813RA-I00 funded by MCIN/AEI/10.13039/501100011033Peer reviewe

Biocrust adaptations to microhabitat alter bacterial communities in a semiarid ecosystem

15 páginas.- 6 figuras.- 4 tablas.- 52 referencias.- Supplementary Information The online version contains supplementary material available at https:// doi.org/ 10. 1007/ s11104- 023- 06184-3Aims Biocrusts, the living skin of dryland ecosystems, contain diverse soil microorganisms that are essential to biocrust formation and the maintenance of multiple ecological functions including nitrogen fixation, carbon sequestration, soil stability, and rainfall redistribution. We know that biocrusts are important modulators of the soil microbiomes, however, much less is known about how local conditions influence biocrust adaptation and subsequently alter the soil microbiomes. Methods To understand the effects of microhabitat on bacterial communities via changes in biocrust traits, we collected biocrusts and analyzed soil microbiomes from eight representative microhabitats present in a semiarid ecosystem from the Chinese Northern Loess Plateau. These microhabitats were located a) outside plant canopy on level land, on shady gentle slope, and sunny gentle slope; b) under plant canopy on level land, on shady gentle, and sunny gentle slope; and c) outside plant canopy on shady and sunny steep slope, respectively. We then used structural equation modeling to investigate the relative contribution of microhabitat factors on important bacterial community metrics through quantifying the changes in biocrust traits. Results Observed microhabitat conditions significantly (P ≤ 0.033) altered the traits of biocrusts (e.g., thickness, biomass, and chlorophyll content), which were associated with significant changes in the soil bacterial community. For example, the bacterial richness in biocrusts developing under plant canopy, on shady slopes, and on gentle slopes was 20.1%, 19.9%, and 15.4% higher than that of the biocrusts developing outside plant canopy, on sunny slopes, and on steep slopes, respectively. We further showed that microhabitat conditions significantly impacted the network structure of bacterial communities under biocrusts, and structural equation modeling revealed that microhabitat metrics had strong indirect effects on network connectivity through changing biocrust traits. Conclusions Our findings suggest that microhabitat factors can strongly influence soil bacterial communities via the changes in locally-adapted biocrust traits and soil properties. This knowledge is critical to understand the impacts of changing environments on biocrusts and associated soil bacterial communities, particularly as climate change progresses.This study was funded by the National Natural Science Foundation of China (No. 42077010), the "Light of West China" Program of the Chinese Academy of Sciences (No. 2019), and the Open Fund for Key Laboratory of Land Degradation and Ecological Restoration in Northwestern China of Ningxia University (No. LDER2022Z02)Peer reviewe