China has experienced a widespread increase in N deposition due to intensive anthropogenic activities, particularly in the subtropical regions. However, the effects of long-term N deposition on soil ...bacterial and fungal abundance, diversity, and community composition remain largely unclear. We assessed the effects of N deposition on soil microbial communities in summer and winter, using quantitative polymerase chain reaction and Illumina Miseq sequencing of bacterial 16S rRNA and fungal ITS genes from subtropical natural forest soils. The abundance of both soil bacteria and fungi exhibited a decreasing pattern with increasing N deposition rates. Nitrogen deposition increased bacterial diversity in both summer and winter, whereas fungal diversity was significantly decreased in summer, but greatly increased under the highest level of N deposition (150 kg N ha−1 yr−1) in winter. Nitrogen deposition significantly increased the relative abundance of bacterial phyla Actinobacteria, Chloroflexi, and WPS-2, but decreased that of Acidobacteria and Verrucomicrobia. In addition, N deposition significantly decreased the relative abundance of Ascomycetes, but did not exert any significant effect on Basidiomycetes. The bacterial and fungal community compositions were greatly influenced by N deposition, with soil N availability and soil pH identified as the two most influential soil properties. This study demonstrates that the fungal community was more sensitive than the bacterial community to N deposition, and further emphasizes the importance of simultaneously evaluating soil bacterial and fungal communities in response to global environmental changes.
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•The abundances of bacteria and fungi showed decreasing patterns with N deposition.•Nitrogen deposition increased bacterial diversity in summer and winter.•Fungal diversity decreased in summer, but increased under N deposition in winter.•Fungal community was more sensitive than the bacterial community to N deposition.
Soil microorganisms are key to biological diversity and many ecosystem processes in terrestrial ecosystems. Despite the current alarming loss of plant diversity, it is unclear how plant species ...diversity affects soil microorganisms. By conducting a global meta-analysis with paired observations of plant mixtures and monocultures from 106 studies, we show that microbial biomass, bacterial biomass, fungal biomass, fungi:bacteria ratio, and microbial respiration increase, while Gram-positive to Gram-negative bacteria ratio decrease in response to plant mixtures. The increases in microbial biomass and respiration are more pronounced in older and more diverse mixtures. The effects of plant mixtures on all microbial attributes are consistent across ecosystem types including natural forests, planted forests, planted grasslands, croplands, and planted containers. Our study underlines strong relationships between plant diversity and soil microorganisms across global terrestrial ecosystems and suggests the importance of plant diversity in maintaining belowground ecosystem functioning.
•Soil pH decreased over the last 60 years across the whole soil profile.•Exchangeable Ca2+ and Mg2+ decreased similarly or greater in deep soil as compared to topsoil.•The magnitudes of acidification ...varied among ecosystems and elevations.•Multiple global change drivers contributed to the soil acidification.
Soil acidity plays a central role in the diversity and function of terrestrial ecosystems. Recent studies have revealed that acid deposition has acidified topsoil over time. However, uncertainties relating to how the acidity of the entire soil profile, including deep soil, responds to multiple global change drivers make it challenging to predict the effects of the ongoing global change on soil functions. Using data from 2952 observations of 200 montane sites in subtropical China, we show that the soil pH decreased over the last 60 years across the whole soil profile (0–150 cm), though there was less reduction in deep soils. The contents of exchangeable Ca2+ and Mg2+ decreased at the same rate, or more quickly, in the deep soil than topsoil. Soil pH and base cations decreased more in forests and shrublands at low elevations, but less in mountain meadows at high elevations. Our sensitivity analysis indicated that regional N deposition, S deposition, warming, and decreasing water availability have contributed to the temporal decreases in pH and base cations in natural ecosystems across tropical and subtropical China. The results extend the previous findings of changes in acidity in surface soil layers and demonstrate that deep soils of natural systems across a large area can be acidified over a few decades. Our results suggest that ongoing global changes are reducing the base nutrients across the entire soil profile, and thus, the diversity and functionality of subtropical forests.
The recent discovery of comammox Nitrospira capable of converting ammonia to nitrate in a single organism radically challenged our century-long perception of the classic two-step nitrification ...performed by ammonia oxidizers and nitrite oxidizers. However, our understanding of the niche separation of comammox Nitrospira and canonical nitrifiers in forest ecosystems remains limited, especially under a global scenario of elevated nitrogen (N) deposition. Here we evaluated the impacts of six-year N deposition on the dynamics of comammox Nitrospira, ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in a subtropical forest soil. Soil inorganic N concentrations significantly increased under the six-year simulation of N deposition, while soil pH, available phosphorus, total carbon (C), C/N ratio and microbial biomass significantly decreased. Quantitative PCR showed that the amoA gene abundances of comammox Nitrospira clade B and AOA substantially increased under the increasing rates of N deposition. By contrast, the AOB amoA gene abundance significantly decreased with the higher levels of N deposition (100 and 150 kg N ha−1 yr−1). Increased 13CO2 incorporation into the AOA communities, rather than comammox Nitrospira or AOB, was demonstrated in a DNA-stable isotope probing microcosm, indicative of the capacity of AOA to assimilate 13CO2 through autotrophic nitrification in the investigated subtropical forest soil under long-term N deposition. Phylogenetic analysis revealed that the autotrophic AOA assemblages belonged to the Nitrosotalea cluster, and their capacity for assimilating CO2 through autotrophic nitrification was not affected by the long-term N deposition. Taken together, we provided new evidence for the niche separation of comammox Nitrospira and canonical ammonia oxidizers in soil nitrification under the long-term N deposition in the acidic subtropical forest soil.
•The abundances of comammox Nitrospira clade B and AOA increased with N input.•The abundance of AOB decreased with N input rates higher than 100 kg N ha−1 yr−1.•Increased 13CO2 was only incorporated into soil AOA through autotrophic pathway.•N input showed no effect on autotrophic AOA within the Nitrosotalea cluster.
The impact of long‐term nitrogen (N) deposition is under‐studied in phosphorus (P)‐limited subtropical forests. We exploited historically collected herbarium specimens to investigate potential ...physiological responses of trees in three subtropical forests representing an urban‐to‐rural gradient, across which N deposition has probably varied over the past six decades. We measured foliar N and P and stable carbon (δ¹³C), oxygen (δ¹⁸O) and nitrogen (δ¹⁵N) isotopic compositions in tissue from herbarium specimens of plant species collected from 1947 to 2014. Foliar N and N : P increased, and δ¹⁵N and P decreased in the two forests close to urban centers. Consistent with recent studies demonstrating that N deposition in the region is ¹⁵N‐depleted, these data suggest that the increased foliar N and N : P, and decreased P, may be attributable to atmospheric deposition and associated enhancement of P limitation. Estimates of intrinsic water use efficiency calculated from foliar δ¹³C decreased by c. 30% from the 1950s to 2014, contrasting with multiple studies investigating similar parameters in N‐limited forests. This effect may reflect decreased photosynthesis, as suggested by a conceptual model of foliar δ¹³C and δ¹⁸O. Long‐term N deposition may exacerbate P limitation and mitigate projected increases in carbon stocks driven by elevated CO₂ in forests on P‐limited soils.
AIMS: This study aimed to determine the influence of tree species on soil microbial community structure. METHODS: We conducted a litter and root manipulation and a short-term nitrogen (N) addition ...experiment in 19-year-old broadleaf Mytilaria laosensis (Hamamelidaceae) and coniferous Chinese fir (Cunninghamia lanceolata) plantations in subtropical China. Phospholipid fatty acid (PLFA) analysis was used to examine treatment effects on soil microbial community structure. Redundancy analysis (RDA) was performed to determine the relationships between individual PLFAs and soil properties (soil pH, carbon (C) and N concentration and C:N ratio). RESULTS: Soil C:N ratio was significantly greater in M. laosensis (17.9) than in C. lanceolata (16.2). Soil C:N ratio was the key factor affecting the soil microbial community regardless of tree species and the litter, root and N treatments at our study site. The fungal biomarkers, 18:1ω9 and 18:2ω6,9 were significantly and positively related to soil C:N ratio and the abundance of bacterial lipid biomarkers was negatively related to soil C:N ratio. N addition for 8 months did not change the biomass and structure of the microbial community in M. laosensis and C. lanceolata soils. Soil nutrient availability before N addition was an important factor in determining the effect of N fertilization on soil microbial biomass and activity. PLFA analysis showed that root exclusion significantly decreased the abundance of the fungal biomarkers and increased the abundance of the Gram-positive bacteria. Rootless plots had a relatively lower Gram-positive to Gram-negative bacteria ratio and a higher fungi to bacteria ratio compared to the plots with roots under both M. laosensis and C. lanceolata. The response of arbuscular mycorrhizal fungi (16:1ω5) to root exclusion was species-specific. CONCLUSIONS: These observations suggest that soil C:N ratio was an important factor in influencing soil microbial community structure. Further studies are required to confirm the long-term effect of tree species on soil microbial community structure.
ABSTRACT
Soil organic carbon (SOC) is a valuable resource for mediating global climate change and securing food production. Despite an alarming rate of global plant diversity loss, uncertainties ...concerning the effects of plant diversity on SOC remain, because plant diversity not only stimulates litter inputs via increased productivity, thus enhancing SOC, but also stimulates microbial respiration, thus reducing SOC. By analysing 1001 paired observations of plant mixtures and corresponding monocultures from 121 publications, we show that both SOC content and stock are on average 5 and 8% higher in species mixtures than in monocultures. These positive mixture effects increase over time and are more pronounced in deeper soils. Microbial biomass carbon, an indicator of SOC release and formation, also increases, but the proportion of microbial biomass carbon in SOC is lower in mixtures. Moreover, these species‐mixture effects are consistent across forest, grassland, and cropland systems and are independent of background climates. Our results indicate that converting 50% of global forests from mixtures to monocultures would release an average of 2.70 Pg C from soil annually over a period of 20 years: about 30% of global annual fossil‐fuel emissions. Our study highlights the importance of plant diversity preservation for the maintenance of soil carbon sequestration in discussions of global climate change policy.
Although decaying wood plays an important role in global carbon (C) cycling, how changes in microbial community are related to wood C quality and then affect wood organic C loss during wood ...decomposition remains unclear. In this study, a chronosequence method was used to examine the relationships between wood C loss rates and microbial community compositions during Chinese fir (Cunninghamia lanceolata) stump decomposition. Our results showed that microbial community shifted from fungi-dominated at early stages (0–15 years) to relatively more bacteria-dominated at later stages (15–35 years) of wood decomposition. Fungal phospholipid fatty acid (PLFA) content primarily explained wood C loss rates at early stages of wood decomposition. Fungal biomass was positively correlated with proportions of relatively high-quality C (e.g., O-alkyl C), but bacterial biomass was positively correlated with low-quality C. In addition, fungi appeared to be the dominated community under low wood moisture (<20%) at early stages, but fungal biomass tended to decrease and bacterial biomass increased with increasing wood moisture at later stages. Our findings suggest that the fungal community is the dominant decomposer of wood at early stages and may be positively influenced by relatively high-quality wood C and low wood moisture. Bacterial community may benefited from low-quality wood C and high wood moisture at later stages. Enhanced understanding of microbial responses to wood quality and environment is important to improve predictions in wood decomposition models.
•Microbial community shifted during wood decomposition.•Fungi dominated at the early stages due to high-quality wood C and low moisture.•Low-quality wood C and high moisture benefited bacteria during the late stages.•Fungal PLFA content primarily explained wood C loss rates at early stages of decomposition.
•Detection of soil aggregate stability related to soil organic carbon stability under N addition.•Fine roots play a major role in decreasing soil aggregate stability in response to N addition.•N ...addition enhances SOC stability with evidence of the decrease in C mineralization.•Stable mixed model revealed the promotion of mineral-associated C formation under N addition.•SOC stability in large macroaggregates was more vulnerable than that in small macroaggregates.
Soil aggregates and the stability of their associated soil organic carbon (SOC) are important factors mediating soil carbon (C) sequestration and soil functions. However, the response of SOC stability to nitrogen (N) deposition is highly divergent, and the combined influences of N deposition and soil aggregates on SOC stability are poorly understood. The mechanisms underlying these influences were explored in a six-year field N-addition experiment covering a wide range of soil aggregates, root morphologies, soil properties and several SOC stability indices (represented by heterotrophic respiration and δ13C or δ15N) in a deciduous broad-leaved forest in Northeast China. The results showed that N addition significantly decreased the proportion of large macroaggregates (2–8 mm), reducing the soil aggregate mean weight diameter (MWD) by 10.0–17.2 %, which was negatively correlated with root length density (RLD) and root weight density (RWD). Organic C stability in soil aggregates was enhanced by N addition, as indicated by the decrease in the decomposition rate of organic C and the increase in the δ13C values but not the C content in microaggregates within macroaggregates (mM) or δ15N values. Furthermore, the promotion of mineral-associated organic C formation after N addition was detected by stable isotopic mixed model analysis (SIMM), indicating increased C protection by minerals. With the use of a structural equation model (SEM), the variation in the C stability of large macroaggregates (2–8 mm) was explained by the changes in fine roots, MWD and N availability but not those in small macroaggregates (0.25–2 mm) due to the instability of large macroaggregates. These results demonstrate that N addition may enhance soil C stability in all the soil aggregate sizes by promoting mineral sorption of C, with the C stability in large macroaggregates being more vulnerable to multiple environmental changes than that in small macroaggregates. Therefore, the soil C stability response to N deposition in the temperate forests of Northeast China could be modulated by soil aggregate sizes and may cause negative feedbacks to global warming.
We investigated microbial biomass and composition (lipid profile), mineral N pools and soil physicochemical parameters in the top 5-cm soils 19 years after reforestation of Chinese fir (Cunninghamia ...lanceolata (Lamb.) Hook) woodland with itself or a native broadleaf species, Mytilaria laosensis. The results suggested that tree species transition had a large impact on microbial biomass and a small impact on the composition of the microbial community as indicated by the relative abundance of individual lipid biomarkers. Between November 2011 and October 2012, there was on average 50% greater microbial biomass carbon (C) measured by the fumigation extraction procedure under M. laosensis than under C. lanceolata. A one-time measurement of phospholipid fatty acids in soil samples collected in May 2012 suggested M. laosensis plots had greater content of individual lipid biomarkers than C. lanceolata plots. Using a litter manipulation experiment, we found that the increases in content of lipid biomarkers under M. laosensis can be attributed to changed litter chemistry. Analysis of soil mineral N pools indicated that there were significantly lower NH4+ and NO3− pools as well as potential net N mineralization rates in M. laosensis soil than in C. lanceolata soil. The relationships among N dynamics, soil chemistry and microbial properties were analysed. The results suggested tree species induced differences in soil N mineralization rates and mineral N pools were related to labile C availability, soil C:N ratio and the composition of the microbial community. Our data of mineral N pools and soil δ15N implied that the transition of land use from C. lanceolata to M. laosensis leads to an enhanced N retention in the plantation.
•Tree species transition from conifer to broadleaf increased soil microbial biomass.•Species and litter quality had small impacts on soil microbial community composition.•Changed N cycling under different species may be due to varied labile soil C pool.•Tree species transition resulted in an enhanced N retention.
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