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"soil warming"
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Effects of whole‐soil warming on ecosystem carbon fluxes in an alpine grassland
Background Global warming impacts ecosystem carbon exchange, thus altering the carbon sink capacity of terrestrial ecosystems. However, the response of ecosystem carbon fluxes to whole‐soil‐profile warming remains unclear. Methods We first investigated the effect of whole‐soil warming on ecosystem carbon fluxes in an alpine grassland ecosystem on the Qinghai‐Tibet Plateau. We also compiled a database of 48 articles to examine the general patterns of experimental warming effects on these fluxes using a global meta‐analysis. Results Our results showed that whole‐soil warming elevated gross ecosystem productivity (GEP) by 14% and ecosystem respiration (ER) by 11%, but had a minor impact on net ecosystem carbon exchange (NEE) in the alpine grassland. In the meta‐analysis, warming also enhanced GEP (10%–11%) and ER (13%), but did not alter NEE. Warming‐induced shifts in plant community and extension of growing season may be the main reasons for the higher GEP and ER under warming, and the offset of both fluxes likely caused the minor response of NEE to warming. Conclusions More attention should be paid to the long‐term response of ecosystem carbon fluxes to whole‐soil or whole‐ecosystem warming throughout the year. These novel findings may help us better predict and mitigate future climate‐carbon feedback under realistic warming scenarios. The three‐year (2018‐2020, growing season) averages of (a) net ecosystem carbon exchange (NEE), (b) gross ecosystem productivity (GEP), and (c) ecosystem respiration (ER) in the alpine grassland. Red corresponds to the warming (W) treatment, and blue represents the control (CK) treatment. Statistical significance between control and warming treatment is marked with asterisks (†p < 0.10, *p < 0.05, n = 4) or labeled as non‐significant (ns, p > 0.10).
Journal Article
Rhizosphere influence on microbial functions: consequence for temperature sensitivity of soil organic matter decomposition at early stage of plant growth
Aims
Accurate predictions of soil carbon (C) feedbacks to climate change depend on an improved understanding of temperature sensitivity (Q
10
) of soil organic matter (SOM) decomposition. Although rhizosphere processes play a critical role in SOM decomposition, the rhizosphere effects on Q
10
and their underlying microbial mechanisms remain unclear.
Methods
Natural abundance approach was used to measure the rhizosphere priming effect (RPE) of maize under two temperature regimes in a 50-day pot experiment. We further determined the impact of rhizosphere process on the Q
10
of SOM decomposition. Enzymatic kinetics, microbial growth rate, as well as
13
C-phospholipid fatty acid (
13
C-PLFA) biomarkers were identified to evaluate the responses of microbial activity.
Results
Warming relative to ambient increased the plant-derived C input, stimulated microbial growth rate, and enzyme activities by 87%, 23%, and 7–18%, respectively. Consequently, warming increased the RPE of maize up to 1-folds, and further caused a larger net C loss as compared to ambient after 50 days of transplanting. Gram negative bacteria and actinobacteria were important groups controlling the RPE, which was supported by the positive correlations between RPE and the abundance of gram negative and actinobacteria. Furthermore, we concluded a literature review and the results were consistent with our case study, where the presence of roots increased the temperature sensitivity of SOM decomposition by 0.17–0.56. This was because rhizodeposition activated microorganisms which produce more enzymes and increase SOM-derived substrate availability. This indicates that planted soils face higher risks of C emissions under future climate warming.
Conclusions
Overall, root-soil interactions via RPE play a pivotal role in determining the temperature sensitivity of SOM decomposition.
Journal Article
Short-term effects of soil warming and nitrogen addition on the N:P stoichiometry of Cunninghamia lanceolata in subtropical regions
Aims Increasing temperature and nitrogen (N) deposition are major drivers of global change that will influence plant-soil systems. We aimed to understand how plant stoichiometry and nutrient limiting types could change with continued warming and N inputs in subtropical regions. Methods In 2014, the experiments were established in 30 mini-plots (2 × 2 m) with the following treatments: control, high N addition, low N addition, warming, warming + high N addition, and warming + low N addition. We sampled the leaf and root of Cunninghamia lanceolata and soils to assess their elemental and stoichiometric variables and δ¹⁵N under all six conditions. Results Both experimental warming and N fertilization consistently induced an increase in fine-root N, P, and N:P. The N:P ratio of the mature green-leaf and soil was 7.24-11.63 and 4.79-6.56, respectively. On average, C. lanceolata showed higher proportional P resorption, but lower N resorption. The δ¹⁵N enrichment factor significantly increased in the warming and N addition treatments. Conclusions N addition decrease leaf N content, and increased the plant growth, which was due to the effect of the N dilution of C. lanceolata. In subtropical regions, N-limitation affects the growth of C. lanceolata, and the concurrent increase in warming and N fertilization should help relieve N-limiting conditions.
Journal Article
Experimental soil warming shifts the fungal community composition at the alpine treeline
Increased CO2 emissions and global warming may alter the composition of fungal communities through the removal of temperature limitation in the plant–soil system, faster nitrogen (N) cycling and changes in the carbon (C) allocation of host plants to the rhizosphere.
At a Swiss treeline featuring Larix decidua and Pinus uncinata, the effects of multiple years of CO2 enrichment and experimental soil warming on the fungal community composition in the organic horizons were analysed using 454-pyrosequencing of ITS2 amplicons. Sporocarp production and colonization of ectomycorrhizal root tips were investigated in parallel.
Fungal community composition was significantly altered by soil warming, whereas CO2 enrichment had little effect. Tree species influenced fungal community composition and the magnitude of the warming responses. The abundance of ectomycorrhizal fungal taxa was positively correlated with N availability, and ectomycorrhizal taxa specialized for conditions of high N availability proliferated with warming, corresponding to considerable increases in inorganic N in warmed soils.
Traits related to N utilization are important in determining the responses of ectomycorrhizal fungi to warming in N-poor cold ecosystems. Shifts in the overall fungal community composition in response to higher temperatures may alter fungal-driven processes with potential feedbacks on ecosystem N cycling and C storage at the alpine treeline.
Journal Article
Biogeochemical evolution of soil organic matter composition after a decade of warming and nitrogen addition
Forest soils are an important carbon (C) sink and critical component of the global C cycle. Warmer temperatures and increased atmospheric nitrogen (N) deposition are altering the biogeochemistry in forest soils and disrupting the intricate balance between C storage and C respired across the globe. The molecular biogeochemistry of soil organic matter (SOM) with warming, N-addition, and simultaneous warming and N-addition was analyzed in soil samples from the Soil Warming × Nitrogen Addition Study at the Harvard Forest Long-term Ecological Research Site using advanced techniques. The results unequivocally demonstrate that warming and N-addition alter the molecular composition of SOM as individual stressors uniquely and in combination. Warming alone and in combination with N-addition accelerated SOM decomposition while N-addition alone slowed SOM degradation. The two-factor N-addition and warming plots contain SOM more like the warming only plots but exhibited unique changes over time (from 4 to 10 years) that could not be predicted by studying N-addition or warming alone. The specific SOM components and the overall SOM decomposition suggests that N-addition and warming impacts are not additive. N-addition may hinder warming impacts antagonistically over time but not to the extent where advanced SOM decomposition from warming is supplanted. As such, the results from warming alone and N-addition alone are not necessarily additive compared to the observed SOM molecular compositional changes when these treatments are applied simultaneously. Marked evolution in the molecular biogeochemistry of SOM demonstrates the sensitivity of SOM trajectories to multiple interactive global environmental changes and the continued need to study long-term impacts more holistically.
Journal Article
Microorganisms in subarctic soils are depleted of ribosomes under short-, medium-, and long-term warming
Physiological responses of soil microorganisms to global warming are important for soil ecosystem function and the terrestrial carbon cycle. Here, we investigate the effects of weeks, years, and decades of soil warming across seasons and time on the microbial protein biosynthesis machineries (i.e. ribosomes), the most abundant cellular macromolecular complexes, using RNA:DNA and RNA:MBC (microbial biomass carbon) ratios as proxies for cellular ribosome contents. We compared warmed soils and non-warmed controls of 15 replicated subarctic grassland and forest soil temperature gradients subject to natural geothermal warming. RNA:DNA ratios tended to be lower in the warmed soils during summer and autumn, independent of warming duration (6 weeks, 8–14 years, and > 50 years), warming intensity (+3°C, +6°C, and +9°C), and ecosystem type. With increasing temperatures, RNA:MBC ratios were also decreasing. Additionally, seasonal RNA:DNA ratios of the consecutively sampled forest showed the same temperature-driven pattern. This suggests that subarctic soil microorganisms are depleted of ribosomes under warm conditions and the lack of consistent relationships with other physicochemical parameters besides temperature further suggests temperature as key driver. Furthermore, in incubation experiments, we measured significantly higher CO2 emission rates per unit of RNA from short- and long-term warmed soils compared to non-warmed controls. In conclusion, ribosome reduction may represent a widespread microbial physiological response to warming that offers a selective advantage at higher temperatures, as energy and matter can be reallocated from ribosome synthesis to other processes including substrate uptake and turnover. This way, ribosome reduction could have a substantial effect on soil carbon dynamics.
Journal Article
Long-term warming in a temperate forest accelerates soil organic matter decomposition despite increased plant-derived inputs
Climate change may alter soil microbial communities and soil organic matter (SOM) composition. Soil carbon (C) cycling takes place over multiple time scales; therefore, long-term studies are essential to better understand the factors influencing C storage and help predict responses to climate change. To investigate this further, soils that were heated by 5 °C above ambient soil temperatures for 18 years were collected from the Barre Woods Soil Warming Study at the Harvard Forest Long-term Ecological Research site. This site consists of large 30 × 30 m plots (control or heated) where entire root systems are exposed to sustained warming conditions. Measurements included soil C and nitrogen concentrations, microbial biomass, and SOM chemistry using gas chromatography–mass spectrometry and solid-state 13C nuclear magnetic resonance spectroscopy. These complementary techniques provide a holistic overview of all SOM components and a comprehensive understanding of SOM composition at the molecular-level. Our results showed that soil C concentrations were not significantly altered with warming; however, various molecular-level alterations to SOM chemistry were observed. We found evidence for both enhanced SOM decomposition and increased above-ground plant inputs with long-term warming. We also noted shifts in microbial community composition while microbial biomass remained largely unchanged. These findings suggest that prolonged warming induced increased availability of preferred substrates, leading to shifts in the microbial community and SOM biogeochemistry. The observed increase in gram-positive bacteria indicated changes in substrate availability as gram-positive bacteria are often associated with the decomposition of complex organic matter, while gram-negative bacteria preferentially break down simpler organic compounds altering SOM composition over time. Our results also highlight that additional plant inputs do not effectively offset chronic warming-induced SOM decomposition in temperate forests.
Journal Article
Warming effects on biomass and composition of microbial communities and enzyme activities within soil aggregates in subtropical forest
This study investigated the effects of warming (about 1 °C) on the biomass and composition of microbial communities and enzyme activities in soil macroaggregates and microaggregates. We fractionated the bulk soils from the control and warming treatments into large macroaggregates (>2000 μm), small macroaggregates (250–2000 μm) and microaggregates (<250 μm) using the optimal moist sieving approach. Warming did not significantly affect soil microbial biomass in all aggregate fractions, but significantly altered the soil microbial community composition in the large macroaggregates. The G
+
:G
−
ratio was significantly higher in the small macroaggregates and microaggregates than that in the large macroaggregates in warmed soils, while the stress ratio was significantly higher in the large and small macroaggregates than that in the microaggregates. Soil warming did not significantly affect β-glucosidase, cellobiohydrolase and
N
-acetylglucosaminidase activities, but significantly decreased acid phosphomonoesterase activity and increased oxidase activities. Our results suggest that soil microbial community composition in the large macroaggregates might be more sensitive to warming. The differential responses of soil microbial communities and enzyme activities in different aggregate fractions in the warmed soils may have important implications for C cycling in subtropical forest ecosystems.
Journal Article