•There were positive rhizosphere effects on soil organic C-cycling in terrestrial ecosystems.•Positive rhizosphere effects on microbial biomass and enzyme activities were universal.•Rhizosphere ...effects on soil respiration were positively related to that on soil organic C and total N.•Rhizosphere effects on soil respiration were negatively related to that on bacterial and fungal biomass.
Rhizosphere processes are one of the most important ways in which plants affect carbon (C) cycling in terrestrial ecosystems. However, how rhizosphere processes related to C cycling are regulated by microorganisms is still poorly understood. Here, using a meta-analysis based on data compiled from 110 published articles and our measured data, we quantified the magnitudes of the rhizosphere effects on soil organic C (SOC), microbial biomass C (MBC), respiration (Rs), microbial biomass and enzymes involved in C acquisition, and discovered the linkages between the rhizosphere effect on Rs and microbial characteristics. This study provided a global-scale assessment in which positive rhizosphere effects on SOC, MBC, and Rs were observed across terrestrial ecosystems worldwide. We also found that the positive rhizosphere effects on microbial biomass and enzyme activities were likely widespread phenomena in terrestrial ecosystems. The results of the structural equation model also indicated that the rhizosphere effects on SOC and total nitrogen had positive effects on the rhizosphere effect on Rs, but the rhizosphere effects on fungal and bacterial biomass showed negative effects. Our findings highlight the importance of microbial-mediated rhizosphere Rs in global SOC cycling and suggest that the consideration of the rhizosphere effects on C cycling processes in Earth system models may improve the accuracy of predicting global SOC dynamics.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The multifunctional trans-activator Tat is an essential regulatory protein for HIV-1 replication and is characterized by high sequence diversity. Numerous experimental studies have examined Tat in ...HIV-1 subtype B, but research on subtype C Tat is lacking, despite the high prevalence of infections caused by subtype C worldwide. We hypothesized that amino acid differences contribute to functional differences among Tat proteins. In the present study, we found that subtype B NL4-3 Tat and subtype C isolate HIV1084i Tat exhibited differences in stability by overexpressing the fusion protein Tat-Flag. In addition, 1084i Tat can activate LTR and NF- Kappa B more efficiently than NL4-3 Tat. In analyses of the activities of the truncated forms of Tat, we found that the carboxyl-terminal region of Tat regulates its stability and transactivity. According to our results, we speculated that the differences in stability between B-Tat and C-Tat result in differences in transactivation ability.
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FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UL, UM, UPUK, VKSCE, ZAGLJ
The response of soil organic carbon (SOC) decomposition to global warming is a potentially major source of uncertainty in climate prediction. However, the magnitude and direction of SOC cycle ...feedbacks under climate warming remain uncertain because of the knowledge gap about the global‐scale spatial pattern and temperature sensitivity (Q10) mechanism of SOC decomposition.
Here, we collected data of Q10 and corresponding soil variables from 81 peer‐reviewed papers using laboratory incubation to explore how Q10 varied among different ecosystems at the global scale and whether labile and recalcitrant SOC pools had equal Q10 values.
Q10 with a global average of 2.41 substantially varied among different ecosystems, ranging from the highest in cropland soils (2.76) and the lowest in wetland soils (1.84). Hump‐shaped correlations of Q10 values with the maximum at SOC = 190 g/kg and the minimum at clay = 37% were observed. However, the main influencing factors of Q10 differed among various ecosystems. Q10 values showed a clear decrease with increasing incubation temperature but no significant decrease above 25°C. In general, labile SOC was less sensitive than recalcitrant SOC to warming. Structural equation model analyses showed that total N and SOC accounted for 53% and 46%, respectively, of the variation in Q10 of labile SOC and recalcitrant SOC. This finding suggested that Q10 values of labile and recalcitrant SOC pools had different controlling factors.
Our findings highlighted the importance of Q10’s variations in ecosystem types and the response of recalcitrant SOC to warming in predicting the soil C cycling and its feedback to climate change. Therefore, ecosystem type and difference in Q10 of labile and recalcitrant SOC should be considered to precisely predict the soil C dynamics under global warming.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Plant- and microbial-derived organic carbon, two components of the soil organic carbon (SOC) pool in terrestrial ecosystems, are regulated by increased atmospheric nitrogen (N) deposition. However, ...the spatial patterns and driving factors of the responses of plant- and microbial-derived SOC to N deposition in forests are not clear, which hinders our understanding of SOC sequestration. In this study, we explored the spatial patterns of plant- and microbial-derived SOC, and their responses to N addition and elucidated their underlying mechanisms in forest soils receiving N addition at four sites with various soil and climate conditions. Plant- and microbial-derived SOC were quantified using lignin phenols and amino sugars, respectively. N addition increased the total microbial residues by 20.5% on average ranging from 9.4% to 34.0% in temperate forests but not in tropical forests, and the increase was mainly derived from fungal residues. Lignin phenols increased more in temperate forests (average of 63.8%) than in tropical forests (average of 15.7%) following N addition. The ratio of total amino sugars to lignin phenols was higher in temperate forests than in tropical forests and decreased with N addition in temperate forests. N addition mainly regulated soil microbial residues by affecting pH, SOC, exchangeable Ca2+, gram-negative bacteria biomass, and the C:N ratio, while it mainly had indirect effects on lignin phenols by altering SOC, soil C:N ratio, and gram-negative bacteria biomass. Overall, our findings suggested that N deposition caused a greater increase in plant-derived SOC than in microbial-derived SOC and that plant-derived SOC would have a more important role in sequestering SOC under increasing N deposition in forest ecosystems, particularly in temperate forests.
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•N deposition increased the SOC-normalized concentrations of plant-derived SOC.•Increased microbial-derived SOC due to N deposition in temperate forests originated mainly from fungal-derived SOC.•N deposition led to a greater increase in lignin phenols in temperate forests than in tropical forests.•N deposition had a higher increase in total lignin phenols than microbial residues.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Aim
Soil organic carbon (SOC) stabilization has become an important topic in recent years in the context of global climate change. Microbial residues represent a significant component of stabilized ...SOC pools. However, spatial variations in the contributions of bacterial and fungal residues to SOC and their determinants at a continental scale remain poorly understood. We aimed to evaluate the spatial variations and controls of the contributions of microbial residues to SOC in forest topsoil.
Location
North–south transect in eastern China.
Time period
2014.
Major taxa studied
Forest ecosystems.
Methods
A total of 195 surface (0–10 cm) soils were sampled from 28 forest sites across tropical and boreal forests in eastern China from July to August to assess how biotic and abiotic factors govern the geographic patterns of the contributions of soil microbial residues (indicated by amino sugars) to SOC.
Results
Fungal residues (30.0%) had a greater average contribution to SOC than bacterial residues (15.5%). The contributions of bacterial (CBR) and total microbial residues (CMR) to SOC showed negative latitudinal patterns and were positively correlated with mean annual temperature (MAT). In contrast, the contribution of fungal residues to SOC (CFR) showed no clear geographic or climatic patterns. On average, the CBR (9.7%), CFR (21.1%) and CMR (30.8%) were lower in boreal forests than in other biome forests. SOC concentration negatively mediated CBR, CFR and CMR. The piecewise structural equation model results showed that MAT was the primary driver of the geographic pattern of CBR, whereas SOC and soil carbon : nitrogen ratio were more directly associated with the CFR. Additionally, plant factors and microbial properties (i.e., microbial biomass and composition) played relatively little roles in regulating CBR, CFR and CMR.
Main conclusions
These findings advance the current knowledge of the different geographic patterns of CBR and CFR regulated by different potential mechanisms in forest ecosystems. This highlights that the dynamics of microbial residues could potentially have unexpected consequences for topsoil SOC stocks under climate change.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
•Microbial respiration (MR) showed a hump-shaped latitudinal distribution.•Soil physicochemical variables primarily controlled MR.•Soil organic carbon was the best indicator of MR across the ...north-south transect.•The significance of soil organic carbon in regulating MR decreased in low-latitude region.
Soil microbial respiration (MR) is a key process controlling the soil-atmosphere CO2 flux, and is widely studied at individual sites. Yet its spatial variation and underlying mechanism at larger spatial scales are still poorly understood, limiting our estimates of the carbon cycle in terrestrial ecosystems and its feedbacks to climate change. Here, a novel incubation experiment based on the mean annual temperature of soil origin sites along a 4,200 km north–south forest transect of eastern China was conducted to investigate the spatial variations in MR. MR showed a hump-shaped relationship with latitude and peaked around 32° N, which coincided exactly with the ecotone of subtropical and temperate forests. Climate, soil physicochemical and microbial traits explained 56.1% of the total variations in MR across the transect, whereas explained 77.4% and 34.6% in tropical and subtropical versus temperate region, respectively. Soil physicochemical properties were consistently more important in controlling the MR's variation than other variables. Specifically, soil organic carbon was the most important factor in regulating the MR's variation across the transect, whereas its significance decreased when scaling down to tropical and subtropical regions. The mean annual temperature turned into the best indicator of MR in tropical and subtropical forests, whereas the combination of soil organic carbon with total nitrogen concentrations primarily regulated the variations in MR in temperate region. Collectively, our study showed a non-linear latitudinal pattern of soil MR and revealed the diverged controlling factors and mechanisms of MR in different climatic regions. These findings can potentially improve our capacity to predict the soil CO2 flux in Earth system models and the feedbacks to climate change.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•The SOC decomposition rates were more sensitive to warming in rhizosphere soils than in bulk soils.•P. glanduligera had higher rhizosphere effects (REs) on temperature sensitivity (Q10) than C. ...lanceolata.•As the most important driver, the REs on nitrogen component positively mediated the REs on Q10.•The rhizospheric microbial biomass had a positive relationship with the REs on Q10.
Rhizosphere processes play a critical role in soil organic carbon (SOC) cycling that is primarily regulated by temperature. Understanding the response of rhizospheric SOC decomposition to global warming, which is called temperature sensitivity (Q10), is pivotal for predicting the feedback of SOC cycling to global warming. However, the rhizosphere effects (REs) on Q10 and their underlying mechanisms in forest ecosystems remain unclear. Here, the REs on Q10 for Cunninghamia lanceolata and three understory ferns (e.g., Woodwardia japonica, Parathelypteris glanduligera and Microlepia marginata) in a subtropical forest were explored using a novel incubation procedure with periodically changing temperatures based on the mean annual temperature. Our results showed that the positive REs on Q10 were observed for all plant species, which ranged from 33% to 88%, and P. glanduligera exhibited higher REs on Q10 than C. lanceolata. The positive REs on Q10 were associated with the rhizospheric nitrogen (N) availability and microbial properties. The REs on N component (i.e., the REs on total N, NH4+ and NO3− along the first PCA axis), which is the most important driver, had a positive direct effect on the REs on Q10. Furthermore, the rhizospheric microbial biomass and the REs on microbial residues were also positively related to the REs on Q10. Overall, these findings highlight that plant-covered soils have high risks of C emissions under planetary warming, underscore the importance of root-soil interactions for accurately predicting SOC dynamics and reveal that rhizospheric nutrients and microbial properties drive the feedback of the root-associated SOC cycle to global warming.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The temperature sensitivity (Q10) of soil organic carbon (SOC) decomposition is an important parameter for those seeking accurate projections of SOC dynamics and its feedback on climate change in ...terrestrial ecosystems. However, how Q10 responds to N deposition across environmental gradients and the underlying mechanism remain largely unresolved. We conducted a novel incubation experiment with periodically varying temperature based on the of soil origin sites to elucidate the responses of Q10 to N addition across China. Our results demonstrated that N addition effects (NAEs) on Q10 were negatively related to latitude and were strongly site dependent. Bioclimatic, edaphic, and microbial variables together explained 50.1% of the total variation in NAEs on Q10, but bioclimate (16.0%) had the greater explanation than edaphic (11.8%) and microbial properties (6.3%). The response of soil exchangeable Ca2+ to N addition was a predictive power for NAEs on Q10, contributing 7.2% relative importance in regulating this variation. Furthermore, arbuscular mycorrhizal fungi indicated by Glomeromycota were the best microbial predictor and contributed 10.9% relative importance in the variation regulating NAEs on Q10. Overall, our results suggest that increasing N addition will increase the sensitivity of SOC decomposition to global warming and highlight the importance of bioclimate, exchangeable Ca2+, and arbuscular mycorrhizal fungi in predicting the response of Q10 to N deposition in natural terrestrial ecosystems. The biogeographic variation in response of Q10 to N deposition should be considered in carbon‐climate models to decrease the prediction uncertainties of SOC dynamics and its feedback to global warming.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Influenced by nitrogen (N) deposition, changes in soil organic carbon (SOC) sequestration in terrestrial ecosystems could provide strong feedback to climate change. Mounting evidence showed that ...microbial necromass contributes substantially to SOC sequestration; however, how N deposition influences microbial necromass accumulation in soils remains elusive. We investigated the impacts of N deposition on soil microbial necromass, assessed by amino sugars, at seven forest sites along a north-south transect in eastern China. We found that the responses of fungal and bacterial necromass accumulation to N deposition depended on the deposition rate, with high N deposition (>50 kg N ha−1 yr−1) stimulating fungal necromass accumulation from 29.1 % to 35.2 %, while low N deposition damaging the accumulation of bacterial necromass in soil by 12.1 %. On the whole, N deposition benefitted the dominance of fungal over bacterial necromass, with their ratio being significantly greater at high-N level. The accumulation of microbial necromass was primarily governed by soil properties, including nutrients stoichiometry, clay content and pH, while the composition of microbial necromass was conjointly affected by soil properties and microbial community structure. The latitudinal distribution of microbial necromass contributions to SOC pool was not altered by N deposition, and was firmly controlled by the climatic and edaphic factors. Collectively, our results reveal the impacts of N deposition on microbial necromass accumulation in soil and the geographical pattern across forest ecosystems in eastern China, providing implications for our accurate predictions of global change impacts on SOC sequestration.
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•Low N deposition damaged the accumulation of bacterial necromass.•High N deposition benefitted fungal necromass accumulation.•The accumulation of microbial necromass was primarily governed by soil properties.•N deposition didn't change the latitudinal distribution of microbial necromass accumulation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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