The continuous increase of nitrogen (N) deposition may exacerbate phosphorus (P) deficiency, which affects soil organic carbon (SOC) decomposition by changing microbial community characteristics in ...subtropical forests with highly weathered soils. However, there is currently little information about the role of P and the N × P interaction in SOC dynamics. Here, a field nutrient manipulation experiment was established in a subtropical plantation forest in China. Soils collected from simulated N deposition and P addition treatments for 5 years were incubated at 25 °C for 130 days. Soil microbial composition was measured using the phospholipid fatty acid method and the enzyme activities related to SOC hydrolysis were measured. The SOC concentration and δ13C in bulk soil and three particle-size fracfractions were also determined. The cumulative CO2 respired over 9 days, representing the utilization of carbon sources under field conditions, increased with N deposition levels under the without-P treatment, while no significant differences were found among the three N deposition levels in the with-P treatment. Meanwhile, P addition generally suppressed the SOC decomposition during 130 days incubation. Similarly, P addition decreased the potential organic carbon decomposition (C0) and C0/SOC ratio. In contrast, C0 increased with N deposition in the without-P treatment, while was unaffected by N deposition under the with-P treatment, suggesting the response of SOC decomposition to N deposition was affected following P addition by alteration of SOC quality. Moreover, N deposition tended to deplete the δ13C of the SOC and P addition enriched the δ13C of the macro-particulate organic carbon. Addition of P increased total microbial, fungal and bacterial biomass values by 41.6%, 90.0% and 46.9%, respectively, whereas N deposition had no significant effect. Soil fungi/bacteria ratio significantly increased by N deposition and P addition, which partly explained the reduction of SOC decomposition after P addition. The cellobioside activity significantly decreased by 48.3% after P addition, while cellobioside and β-xylosidase activities increased with N deposition, suggesting that N deposition and P addition had opposite roles in the SOC stability. These results indicate that the positive effect of N deposition on SOC decomposition was suppressed when P was added by changing microbial community and enzyme activity and enhanced P availability may result in increased SOC accumulation under N deposition scenarios in subtropical forests.
•P addition counteracted the stimulatory effect of N deposition on SOC decomposition.•P addition generally inhibited soil organic carbon (SOC) decomposition.•N deposition depleted the δ13CSOC while P addition enriched the δ13Cmacro-POC.•P addition increased total microbial biomass and fungi/bacteria ratio.•The cellobioside activity decreased with P addition but increased with N deposition.
It is unclear how or even if phosphorus (P) input alters the influence of nitrogen (N) deposition in a forest. In theory, nutrients in leaves and twigs differing in age may show different responses ...to elevated nutrient input. To test this possibility, we selected Chinese fir (Cunninghamia lanceolata) for a series of N and P addition experiments using treatments of +N1 - P (50 kg N ha(-1) year(-1)), +N2 - P (100 kg N ha(-1) year(-1)), -N + P (50 kg P ha(-1) year(-1)), +N1 + P, +N2 + P and -N - P (without N and P addition). Soil samples were analyzed for mineral N and available P concentrations. Leaves and twigs in summer and their litters in winter were classified as and sorted into young and old components to measure N and P concentrations. Soil mineral N and available P increased with N and P additions, respectively. Nitrogen addition increased leaf and twig N concentrations in the second year, but not in the first year; P addition increased leaf and twig P concentrations in both years and enhanced young but not old leaf and twig N accumulations. Nitrogen and P resorption proficiencies in litters increased in response to N and P additions, but N and P resorption efficiencies were not significantly altered. Nitrogen resorption efficiency was generally higher in leaves than in twigs and in young vs old leaves and twigs. Phosphorus resorption efficiency showed a minimal variation from 26.6 to 47.0%. Therefore, P input intensified leaf and twig N enrichment with N addition, leaf and twig nutrients were both gradually resorbed with aging, and organ and age effects depended on the extent of nutrient limitation.
Phosphate-solubilizing fungi (PSF) generally enhance available phosphorus (P) released from soil, which contributes to plants' P requirement, especially in P-limiting regions. In this study, two PSF, ...TalA-JX04 and AspN-JX16, were isolated from the rhizosphere soil of moso bamboo (Phyllostachys edulis) widely distributed in P-deficient areas in China and identified as Talaromyces aurantiacus and Aspergillus neoniger, respectively. The two PSF were cultured in potato dextrose liquid medium with six types of initial pH values ranging from 6.5 to 1.5 to assess acid resistance. Both PSF were incubated in Pikovskaya's liquid media with different pH values containing five recalcitrant P sources, including Ca3(PO4)2, FePO4, CaHPO4, AlPO4, and C6H6Ca6O24P6, to estimate their P-solubilizing capacity. No significant differences were found in the biomass of both fungi grown in media with different initial pH, indicating that these fungi could grow well under acid stress. The P-solubilizing capacity of TalA-JX04 was highest in medium containing CaHPO4, followed by Ca3(PO4)2, FePO4, C6H6Ca6O24P6, and AlPO4 in six types of initial pH treatments, while the recalcitrant P-solubilizing capacity of AspN-JX16 varied with initial pH. Meanwhile, the P-solubilizing capacity of AspN-JX16 was much higher than TalA-JX04. The pH of fermentation broth was negatively correlated with P-solubilizing capacity (p<0.01), suggesting that the fungi promote the dissolution of P sources by secreting organic acids. Our results showed that TalA-JX04 and AspN-JX16 could survive in acidic environments and both fungi had a considerable ability to release soluble P by decomposing recalcitrant P-bearing compounds. The two fungi had potential for application as environment-friendly biofertilizers in subtropical bamboo ecosystem.
Background and aims
Atmospheric nitrogen (N) deposition affects litter decomposition. However, how endogenous litter quality and exogenous resource supply alter the N deposition effect on litter ...decomposition and deposited N immobilized by microbes remains unclear.
Methods
We conducted a laboratory experiment to examine how the N deposition effect on litter decomposition varies with endogenous litter quality (needle litter with higher C/nutrients, low quality litter versus leaf litter with low C/nutrients, high quality litter) and exogenous resource supply (five treatments: N addition alone; N plus non-N nutrient and/or carbon addition; control) using a
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N tracing method.
Results
Nitrogen deposition increased the % mass and % N remaining across the decomposition process. Adding non-N nutrients increased the N deposition effect on % mass and % N remaining in the decomposing high quality litter but not in the low quality litter. Moreover, the % P remaining was increased in the low quality litter but was decreased in the high quality litter under N deposition. However, adding N and non-N nutrients together increased the % P remaining in both decomposing litters. The immobilized exogenous
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N abundance (IEN) was much higher in the decomposing low quality litter than high quality litter. For low quality litter, resource addition treatments affected IEN, but their effects depended on decomposition stages. For high quality litter, carbon addition alone generally increased IEN across the 720 days.
Conclusions
Nitrogen deposition effect on litter decomposition could be altered by exogenous resource supply, but the pattern ultimately depended on endogenous litter quality. Nitrogen deposition generally suppressed the litter decomposition and non-N nutrients addition enhanced the inhibition effects of N deposition on litter decomposition, especially of high quality litter, while lower quality litter tended to immobilize more exogenous deposited N. Thus, the magnitude of both non-N nutrient availability and litter quality needs to be taken into consideration when assessing the effects of N deposition on litter decomposition.
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•Leaf nutrient fractions indicate the responses of wetland plants to nutrient enrichment.•Responses of leaf N and P allocation patterns to nutrient enrichments were ...species-specific.•Plasticity in leaf nutrient fractions drives nutrient enrichment-induced shifts in plant biomass.•Leaf nutrient allocation patterns may be a potential indicator of vegetation community composition.
Temperate wetlands have been experienced increased nitrogen (N) and phosphorus (P) loadings, but how plant N and P fractions respond to nutrient enrichments and its role in driving vegetation dynamics remain elusive in these ecosystems. Here, we used a 3-year N (6.0 g N m−2 year−1) and P (1.2 g P m−2 year−1) addition experiment to investigate the effects of nutrient enrichment on aboveground plant biomass, leaf N, P, structural N (NS), non-structural N (NNS), inorganic P (PI), and organic P (PO) concentrations of five common species belonging to two growth forms (grass and sedge) in a freshwater marsh, Northeast China. Our results showed that, although leaf N and P concentrations increased with respective nutrient additions, the responses of aboveground plant biomass and leaf nutrient allocation patterns to nutrient enrichments were idiosyncratic. Specifically, N addition simultaneously increased leaf NNS:NN ratio and aboveground biomass of grass species (Deyeuxia angustifolia and Glyceria spiculosa), while P addition increased leaf PI:PO ratio and aboveground biomass of sedge species (Carex meyeriana, C. lasiocarpa, and C. humida). This indicated that the species-specific responses of leaf nutrient fractions to N and P addition may explain the altered vegetation structure in this wetland. Our findings suggest that leaf nutrient fractions are more reliable than total nutrient concentrations to indicate the adaptative strategies of wetland plants to nutrient enrichments, and highlight that the shifts in leaf N and P allocation patterns would be a potential tool to predict the effect of nutrient enrichments on vegetation dynamics in temperate wetlands.
Stand density regulation is an important measure of plantation forest management, and phosphorus (P) is often the limiting factor of tree productivity, especially in the subtropics and tropics. ...However, the stand density influence on ecosystem P cycling is unclear in Chinese fir (Cunninghamia lanceolata) plantations of subtropical China. We collected rhizosphere and bulk soils, leaves and twigs with different ages and roots with different orders to measure P and nitrogen (N) variables in Chinese fir plantations with low density (LDCF) and high density (HDCF) at Fujian and Hunan provinces of subtropical China. Rhizosphere soil labile P, slow P, occluded P and extractable P were higher in LDCF than HDCF at two sites. Meanwhile, P and N concentrations of 1-year-old leaves and twigs were higher in LDCF than HDCF and leaf N/P ratio generally increased with increasing leaf age at two sites. Rhizosphere vs. bulk soil labile P and occluded P were greater in LDCF than HDCF at Fujian. Nitrogen resorption efficiencies (NRE) of leaves and twigs were higher in LDCF than HDCF at Fujian, while their P resorption efficiencies (PRE) were not different between two densities at two sites. The average NRE of leaves (41.7%) and twigs (65.6%) were lower than the corresponding PRE (67.8% and 78.0%, respectively). Our results suggest that reducing stem density in Chinese fir plantations might be helpful to increase soil active P supplies and meet tree nutrient requirements.
•Litter mass remaining was slightly higher in the air than on the ground.•Litter mass remaining correlated negatively with microbial respiration only on the ground.•Home-field advantage during ...decomposition occurred on the ground, but disappeared in the air.•Litter decomposition pathway differed between on the ground and in the air.•Litter decomposition in the air should not be neglected in subtropical forests.
Litter decomposition is an indispensable component of carbon and nutrient cycles in forests. Plant litter is often intercepted by tree branches or understory vegetation in the air, yet aerial litter decomposition dynamics are overlooked in these ecosystems. Here, we collected leaf litter of four common tree species (Liquidambar formosana, Schima superba, Pinus elliottii, and Pinus massoniana) from subtropical plantations of southern China, and used the litterbag method to measure litter mass remaining and microbial respiration on the ground and in the air by reciprocally transplanting leaf litter in the four plantations. The main objectives were to compare the differences in litter decomposition rates and the home-field advantage between on the ground and in the air over 360 days of decomposition. Irrespective of decomposition habitats and incubation periods, litter mass remaining was slightly higher in the air (37.0%) than on the ground (32.0%), and microbial respiration was much lower in the air (2.2 μg CO2-C h−1 g−1) than on the ground (18.2 μg CO2-C h−1 g−1). Litter mass remaining correlated negatively with microbial respiration on the ground, despite no significant relationship in the air. In addition, the home-field advantage during decomposition only occurred on the ground (4.86–12.33%), but disappeared in the air. These contrasting patterns indicated that litter decomposition was driven by microbial processes on the ground and abiotic processes in the air. Our findings highlight that decomposition position predominantly regulates leaf litter decomposition patterns, and suggest that litter decomposition in the air should not be neglected in subtropical forests.
The impact of reforestation on soil organic carbon (OC), especially in deep layer, is poorly understood and deep soil OC stabilization in relation with aggregation and vegetation type in afforested ...area is unknown. Here, we collected topsoil (0-15 cm) and deep soil (30-45 cm) from six paired coniferous forests (CF) and broad-leaved forests (BF) reforested in the early 1990s in subtropical China. Soil aggregates were separated by size by dry sieving and OC stability was measured by closed-jar alkali-absorption in 71 incubation days. Soil OC concentration and mean weight diameter were higher in BF than CF. The cumulative carbon mineralization (Cmin, mg CO2-C kg-1 soil) varied with aggregate size in BF and CF topsoils, and in deep soil, it was higher in larger aggregates than in smaller aggregates in BF, but not CF. The percentage of soil OC mineralized (SOCmin, % SOC) was in general higher in larger aggregates than in smaller aggregates. Meanwhile, SOCmin was greater in CF than in BF at topsoil and deep soil aggregates. In comparison to topsoil, deep soil aggregates generally exhibited a lower Cmin, and higher SOCmin. Total nitrogen (N) and the ratio of carbon to phosphorus (C/P) were generally higher in BF than in CF in topsoil and deep soil aggregates, while the same trend of N/P was only found in deep soil aggregates. Moreover, the SOCmin negatively correlated with OC, total N, C/P and N/P. This work suggests that reforested vegetation type might play an important role in soil OC storage through internal nutrient cycling. Soil depth and aggregate size influenced OC stability, and deep soil OC stability could be altered by vegetation reforested about 20 years.
To retrospectively evaluate risk factors related to incomplete computed tomography (CT)-guided radiofrequency (RF) ablation of metastatic and primary lung tumors.
This study included 93 patients with ...147 tumors: 70 men, 23 women; median age 54 y (range, 19-81 y); 24 cases of primary lung tumors, 69 cases of metastases; average largest diameter of tumors, 1.8 cm ± 1.2 (range, 0.3-6.0 cm). Local efficacy was evaluated based on CT follow-up scans. Complete ablation rates (CARs) for tumors were calculated according to several variables; independent risk factors for local tumor progression (LTP) were examined by binary logistic regression analysis.
CAR of tumors was 60.54% within first 6 months after lung RF ablation; median interval of LTP was 1.5 months (mean, 1.3 months ± 1.0; range, 0 days to 3 months). Compared with tumors > 3 cm, CAR of tumors ≤ 3 cm was significantly higher (68.55% vs 17.39%, P < .001). CAR of tumors with complete ablation margin (AM) was dramatically higher compared with tumors with incomplete AM (74.77% vs 16.67%, P < .001). Among tumors with complete AM, CAR of tumors with shortest distance between outer edge of tumor and AM (ablative margin D) ≥ 5 mm was compared with tumors with ablative margin D 1-4 mm (85.96% vs 62.96%, P = .005). Multivariate regression analysis showed that lobulation and/or spicules, contact with blood vessels, and ablative margin D < 5 mm were independent risk factors for incomplete lung RF ablation. LTP was likely to develop at the edge of ablated lesions and especially the site of incomplete AM or shortest AM.
RF ablation for lung cancers should be individualized based on tumor size, morphology, and tumor type to obtain an adequate AM.
Urbanization causes increases in temperature and alters soil carbon (C), nitrogen (N), and phosphorus (P) cycles, but the degree to which these processes vary in temperature sensitivity along the ...urban-rural gradient are unclear. We selected three typical vegetation types (forests, shrub, and lawn) along an urban-subruban-rural gradient in Nanchang, China, and collected topsoil (at 0–15 cm depth) from 27 plots in each to measure the C, N, and P mineralization rates using thermostatic incubation. This was performed at ambient temperatures of 5 °C, 15 °C, 25 °C, 35 °C and 45 °C, respectively. Our results showed that soil microbial C and N content, as well as the rates of soil C mineralization, nitrification, and P mineralization generally decreased along the urban-rural gradient (P < 0.05). Moreover, the temperature sensitivity (Q10) of soil C mineralization was highest at urban sites, followed by suburban, then at rural sites. In contrast, the Q10 value of ammonification was lower in urban than suburban and rural sites, and a difference in nitrification response to temperature alteration was only found at urban sites. The phosphorus mineralization rate showed minimal variation across incubation temperatures. Taken together, we found that soil C and nutrient fluxes in response to elevated temperature might be more asynchronous in urban than in rural sites, and thus urbanization may aggravate imbalances in the active C, N and P pools of terrestrial ecosystems. Global warming may thus help accelerate soil organic C decomposition, N leaching, and P enrichment in urban vegetations in subtropical China.
•Soils from 27 plots were thermostatic incubated along an urban-rural gradient.•Urbanization increases soil C and P mineralization, as well as nitrification rates.•Urbanization increases Q10 values of soil C mineralization and nitrification rate.•Urbanization aggravates the differentiations of soil C, N and P fluxes to warming.•Elevated temperature and urbanization may lead urban area water eutrophication.
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