Microorganisms are vital in soil organic carbon (SOC) mineralization. The deposition of atmospheric nitrogen (N) and phosphorus (P), as well as leaf-litter addition, may affect SOC mineralization and ...microbial community structure by changing the availability of soil nutrients and carbon (C). In this study, we added leaf-litters labeled by 13C (Pinus massoniana and Michelia macclurei) and nutrients (ammonium chloride and monopotassium phosphate) alone and in combination to soils collected from a coniferous forest in subtropical China. We aimed to investigate the effect of leaf-litter and nutrient addition on SOC mineralization and soil microbial community. CO2 production was continuously measured during 120-day laboratory incubation, and CO2 sources were partitioned using 13C isotopic techniques. The addition of P. massoniana and M. macclurei leaf-litters increased SOC mineralization by 7.4% and 22.4%, respectively. N and P addition alone decreased soil respiration by 6.6% and 7.1%, respectively. Compared with P addition, N addition exerted a higher inhibitory effect on SOC mineralization induced by leaf-litter addition. Leaf-litter addition stimulated soil microbial activity and decreased the ratio of bacteria to fungi as a result of greater promotion on fungal growth. Moreover, 16:0 and 18:1ω9c phospholipid fatty acids (PLFAs) had greater amount of 13C incorporation than other PLFAs, especially in nutrient-addition treatments. These results suggested that increased C input through leaf litter can stimulate SOC mineralization, whereas atmospheric N and P deposition can reduce this stimulatory effect and promote soil C storage in subtropical forests. Our results also illustrated that the use of 13C-labeled leaf litter coupled with 13C-PLFA profiling is a powerful tool for determining the microbial utilization of C.
•Lower-quality litter induced a greater priming effect on SOC mineralization.•N addition had higher inhibitory effect on priming effect than P addition.•Adding leaf litter and nutrients decreased in the bacteria:fungi ratio.•The 16:0 and 18:1ω9c PLFAs preferentially utilize fresh substrate-C added to soils.
•Contributions of aboveground litter and roots to total soil CO2 efflux were similar.•Litter addition and root trenching reduced effect of soil moisture on respiration.•C input manipulation altered ...the composition of soil microbial community.•Root inputs exerted more impact on the soil microbial community than litter inputs.
We determined the effects of aboveground and belowground C inputs on soil CO2 efflux and microbial community composition by phospholipid fatty acids using aboveground litter addition or removal and root trenching in a subtropical forest in Southern China. From January 2011 to December 2011, soil respiration varied with the seasonal changes in soil temperature and water content, but its pattern was not altered by C input manipulation. The effects of C input manipulation on the temperature sensitivity of soil respiration was season-dependent, which were greater in the dormant season than in the growing season. Litter addition increased the soil respiration by 33% compared with the control, whereas litter removal decreased it by 22.6%. Root trenching decreased soil respiration by 20.4%. Aboveground litter decomposition, root and rhizosphere respiration, and mineral soil respiration contributed to 22.3%, 20.1%, and 57.6% of total soil CO2 efflux, respectively. We also found that increase in soil CO2 efflux induced by litter addition was 10.4% greater than decrease by litter removal. Litter removal increased 21.6% of the concentration of Gram-positive bacteria and decreased 32.8% of the bacteria to fungi ratio, compared with the control. Root trenching increased the concentrations of bacteria, fungi, and actinomycetes by 28.8%, 161.2% and 32.5%, respectively, but decreased the Gram-negative to Gram-positive bacteria and the bacteria to fungi ratios by 57.4% and 107.9%. C input treatment did not increase the Gram-positive bacteria but nor decreased the Gram-negative to Gram-positive bacteria ratio. The concentration of the 16:0 PLFA and the Gram-negative to Gram-positive bacteria ratio were significantly correlated with soil respiration. These results suggest that root C input has greater influence on soil microbial community composition than the aboveground litter C input.
In terrestrial ecosystems, deep soils are a major reservoir of organic carbon (C). Improving knowledge of how deep soil organic carbon (SOC) mineralization responds to fresh C supply and nitrogen (N) ...availability is essential to better understand whether this C pool will react to climate change. However, little is known about the effects of C and N inputs on SOC mineralization and microbial communities in forest deep soils. To quantify the effects of C and N inputs on SOC mineralization, we apply two species of 13C–labeled leaf litters and ammonium chloride solution while incubating soils collected from 60 cm to 70 cm depth in a coniferous forest in subtropical China. The soil phospholipid fatty acid (PLFA) profiles are also determined to establish the effects of C and N supply on microbial community structure, and the δ13C in PLFAs is used to establish pathways of leaf litter-derived C flux among microbial communities. The addition of leaf litters stimulates deep SOC mineralization, indicating that the stability of deep SOC is attributed to a lack of fresh C input, but the addition of Michelia macclurei litter with higher C:P ratio has a greater positive priming effect than adding Pinus massoniana litter. N addition reduces the magnitude of positive priming and alters the direction of priming in soils with P. massoniana litter addition, suggesting that N deposition may suppress deep SOC mineralization and favor the maintenance of SOC storage. Leaf litter addition enhances the biomass of individual PLFA and increases the fungi:bacteria ratio, suggesting that microbes are limited by energy and that soil microbial community composition is modified by C inputs. N addition decreases the fungi:bacteria ratio, but increases the Gram–positive:Gram–negative bacteria ratio. The highest 13C–enrichment and distribution of litter–derived C are found in 16:0 and 18:1ω9c PLFAs, but litter species and N addition do not affect total PLFA–C and litter-derived PLFA–C. These results support the views that a lack of fresh C supply and N deposition may prevent the mineralization of SOC pool in deep layers and that the utilization of labile substrate by 16:0 and 18:1ω9c populations promotes positive SOC priming.
•The first study to quantify effect of C supply on deep SOC decomposition in forests.•Fresh C input increased the mineralization of deep SOC and decreased its stability.•N addition decreased the priming effect induced by C addition in deep forest soils.•C and N addition altered microbial community in deep forest soils.•Utilization of labile C by 16:0 and 18:1ω9c populations promotes positive SOC–priming.
► This is the first study on effect of forest fire on labile SOM by meta-analysis. ► The study’s aim was to identify general patterns of effects of fire on labile SOM. ► Labile SOM were significantly ...affected by fire type, soil sampling depth and time. ► Fire decreased potential rates of C sequestration and storage in forest soils.
The effects of fire on labile soil C and N in forest ecosystems are important for understanding C sequestration and N cycling not only because labile soil C and N are often variables that determine soil fertility but also because the role of soils as a source or sink for C is important on an ecosystem and on the regional level. In the current study, the literature on the effects of fire on soil organic C, total N, microbial biomass C and N, dissolved organic C, and total N, respiration, and N mineralization in mineral soil was reviewed, and the results of a meta-analysis on literature data were reported. Overall, fire significantly increased the soil total N, microbial biomass N, dissolved organic C, and total N, but decreased soil organic C, microbial biomass C, respiration and N mineralization. Among the significant effects of different fire types, wildfire had the higher effects on the soil organic C, total N, microbial biomass C and N, dissolved total N and respiration of soil than prescribed fire. In addition, responses of soil organic C, total N and N mineralization to wildfire depended on forest type and natural zone. Positive responses of soil organic C, total N were found in broadleaved forests and Mediterranean zones, and negative responses in coniferous forests and temperate zones. Wildfire significantly decreased N mineralization in coniferous forests. The effects of fire on soil microbial biomass C and N, dissolved organic C and N mineralization generally decreased with time after the fire. In general, the effects of fire on soil organic C, microbial biomass C, and dissolved total N and N mineralization decreased with increasing soil depth. These results suggest that fire increases C and N availability and increases microbial activity, which consequently decreases the potential rates of C sequestration.
Extensive studies have been conducted to evaluate the effect of external organic Carbon on native soil organic carbon (SOC) decomposition. However, the direction and extent of this effect reported by ...different authors is inconsistent.
The objective was to provide a synthesis of existing data that comprehensively and quantitatively evaluates how the soil chemical properties and incubation conditions interact with additional external organic C to affect the native SOC decomposition.
A meta-analysis was conducted on previously published empirical studies that examined the effect of the addition of external organic carbon on the native SOC decomposition through isotopic techniques.
The addition of external organic C, when averaged across all studies, enhanced the native SOC decomposition by 26.5%. The soil with higher SOC content and fine texture showed significantly higher priming effects, whereas the soil with higher total nitrogen content showed an opposite trend. The soils with higher C:N ratios had significantly stronger priming effects than those with low C:N ratios. The decomposition of native SOC was significantly enhanced more at early stage of incubation (<15d) than at the later stages (>15d). In addition, the incubation temperature and the addition rate of organic matter significantly influenced the native SOC decomposition in response to the addition of external organic C.
Soil organic carbon (SOC) dynamics and nutrient availability determine the soil quality and fertility in a Chinese fir plantation forest in subtropical China. Uniformly 13C-labeled Chinese fir ...(Cunninghamia lanceolata) and alder (Alnus cremastogyne) leaf litter with or without 100mg NH4+ or NO3− were added to the soil. The purpose was to investigate the influence of N availability on the decomposition of the litter and native SOC. The production of CO2, the natural abundance of 13C–CO2, and the inorganic N dynamics were monitored. The results showed that Chinese fir (with a high C:N ratio) and alder (with a low C:N ratio) leaf litter caused significant positive priming effects (PEs) of 24% and 42%, respectively, at the end of the experiment (235d). The PE dynamics showed that positive PE can last for at least 87d. However, the possible occurrence of a significant negative PE with a sufficient incubation period is difficult to confirm. The application of both NH4+ and NO3− was found to have a stimulating effect on the decomposition of Chinese fir and alder leaf litter in the early stage (0–15d) of incubation, but an adverse effect in the late stage. Compared with NO3−, NH4+ caused a greater decrease in the PE induced by both Chinese fir and alder leaf litter. The effects of NH4+ and NO3− on the PE dynamics had different patterns for different incubation stages. This result may indicate that the stability or recalcitrance of SOC, especially in such plantation forest soils, strongly depends on available leaf litter and application of N to the soil.
Dynamics of the priming effect in different treatments. Vertical bars are standard errors (n=3). The priming effect in each time interval was calculated only when the amount of CO2–C in each treatment significantly differed from that of the control treatment. Significant differences are denoted by asterisks (p<0.001). Display omitted
► Positive PE induced by added litters can last for at least 87d. ► NH4+ caused a greater decrease in the PE than NO3−. ► The effects of NH4+ and NO3− on added litters and native SOC decomposition depend on incubation stages.
We report the preparation of epoxy-based composites by intercalating low loading of core–shell silicon carbide nanowire-silica-amino (named as SiCnw–SiO
2
–NH
2
) hybrids, exhibiting simultaneously ...high permittivity and thermal conductivity (TC) and maintaining rather low dielectric loss. More interestingly, the epoxy composites with the cobweb-structured SiCnw–SiO
2
–NH
2
hybrids exhibited high thermal conductivity at low filler loading due to space micro-structures and hydrogen bond interaction. Specifically, permittivity of the sample with 3.0 vol% SiCnw–SiO
2
–NH
2
hybrids reaches 61.9 under 0.1 Hz, while its dielectric loss is only 0.012, and possessing a high TC of 1.59 W/m K, respectively.
AIMS : Globally, extensive areas of native forest have been almost replaced by plantations to meet the demands for timber, fuel material and other forest products. This study aimed to evaluate the ...effects of forest conversion on labile soil organic C (SOC), soil respiration, and enzyme activity, and to quantify their relationship in subtropical forest ecosystems. METHODS : Surface mineral soil (0–20 cm) was collected from a Cunninghamia lanceolata Hook. plantation, Pinus massoniana Lamb. plantation, Michelia macclurei Dandy plantation, and an undisturbed native broadleaf forest. Soil microbial biomass C, dissolved organic C, permanganate-oxidizable C, basal respiration, and six enzyme activities were investigated. RESULTS : Soil microbial biomass C was higher by 45.9 % in native broadleaf forest than that in M. macclurei Dandy plantation. The ratio of soil microbial biomass C to total SOC was 27.6 % higher in the M. macclurei Dandy plantation than in the native broadleaf forest. The soil respiration increased by 25.2 % and 21.7 % after conversion from native broadleaf forest to P. massoniana Lamb. and M. macclurei Dandy plantations respectively. The effects of forest conversion on the soil enzyme activities differed among the tree species. Soil microbial biomass C had higher correlation with soil respiration than with the other SOC fractions. Moreover, soil microbial biomass C was positively correlated with urease and negatively correlated with cellulase activity. Soil respiration had higher correlation with soil microbial biomass C, dissolved organic C and permanganate-oxidizable C. CONCLUSION : Forest conversion affected the soil microbial biomass C, soil respiration, invertase, cellulase, urease, catalase, acid phosphatase, and polyphenol oxidase activities, but their response depended on tree species. Soil respiration was mainly controlled by labile SOC, not by total SOC.
Polymer-based composites with high thermal conductivity and dielectric breakdown strength have gained increasing attention due to their significant application potential in both power electronic ...devices and power equipment. In this study, we successfully prepared novel sandwich AlN/epoxy composites with various layer thicknesses, showing simultaneously and remarkably enhanced dielectric breakdown strength and thermal conductivity. The most optimized sandwich composite, with an outer layer thickness of 120 μm and an inner layer thickness of 60 μm (abbreviated as 120-60) exhibits a high through-plane thermal conductivity of 0.754 W/(m·K) (4.1 times of epoxy) and has a dielectric breakdown strength of 69.7 kV/mm, 8.1% higher compared to that of epoxy. The sandwich composites also have higher in-plane thermal conductivity (1.88 W/(m·K) for 120-60) based on the novel parallel models. The sandwich composites with desirable thermal and electrical properties are very promising for application in power electronic devices and power equipment.
Aims
Mixed-species plantations are generally thought to increase soil carbon stocks, but it is unclear whether they can enhance soil water-holding capacity. By quantifying the contribution of ...rainwater to soil water (CRSW) following three different scales of rainfall events in
Pinus massoniana
and
Schima superba
monoculture plantations and a mixed
P. massoniana
and
S. superba
plantation, we aimed to examine the variations in CRSW and influencing factors for different plantations.
Methods
Stable hydrogen isotope compositions of rainwater, soil water and groundwater were analyzed to assess the CRSW of three plantations following three rainfall events in a subtropical monsoon region in China. We further used regression analysis to quantify the relative importance of canopy openness, litter characteristics, soil physical properties and root biomass to the CRSW.
Results
The CRSW in the
P. massoniana
monoculture plantation and mixed plantation was higher than that in the
S. superba
monoculture plantation following the three rainfall events. No significant difference in the CRSW was found between the
P. massoniana
plantation and the mixed plantation within nine days following the 8.7 mm rainfall event. Furthermore, the CRSW was significantly higher in the mixed plantation than in the two monoculture plantations within 11 days following the 15.3 mm and 36.9 mm rainfall events. The most important factors affecting the CRSW were canopy openness and root biomass after the 8.7 mm rainfall event, whereas root biomass and litter characteristics acted as the primary regulatory factors after the 15.3 mm rainfall event. Under the 36.9 mm rainfall event, dry weight and saturation moisture capacity within the semi-decomposed litter layer had the greatest influence on the CRSW.
Conclusion
Mixed-species plantations in humid subtropical regions have a higher capacity to intercept and maintain heavy rainfall than their respective monoculture plantations, and thus can enhance their adaptation to extreme rainfall events, as well as after frequent droughts.
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