The availabilities of carbon (C) and nitrogen (N) in soil play an important role in soil carbon dioxide (CO2) emission. However, the variation in the soil respiration (Rs) and response of microbial ...community to the combined changes in belowground C and N inputs in forest ecosystems are not yet fully understood. Stem girdling and N addition were performed in this study to evaluate the effects of C supply and N availability on Rs and soil microbial community in a subtropical forest. The trees were girdled on 1 July 2012. Rs was monitored from July 2012 to November 2013, and soil microbial community composition was also examined by phospholipid fatty acids (PLFAs) 1 year after girdling. Results showed that Rs decreased by 40.5% with girdling alone, but N addition only did not change Rs. Interestingly, Rs decreased by 62.7% under the girdling with N addition treatment. The reducing effect of girdling and N addition on Rs differed between dormant and growing seasons. Girdling alone reduced Rs by 33.9% in the dormant season and 54.8% in the growing season compared with the control. By contrast, girdling with N addition decreased Rs by 59.5% in the dormant season and 65.4% in the growing season. Girdling and N addition significantly decreased the total and bacterial PLFAs. Moreover, the effect of N addition was greater than girdling. Both girdling and N addition treatments separated the microbial groups on the basis of the first principal component through principal component analysis compared with control. This indicated that girdling and N addition changed the soil microbial community composition. However, the effect of girdling with N addition treatment separated the microbial groups on the basis of the second principal component compared to N addition treatment, which suggested N addition altered the effect of girdling on soil microbial community composition. These results suggest that the increase in soil N availability by N deposition alters the effect of belowground C allocation on the decomposition of soil organic matter by altering the composition of the soil microbial community.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Soil microbes are both drivers and contributors of soil organic C (SOC) dynamics. However, information on how the multiple co-occurring environmental changes affecting microbial community and ...residues is unclear. Here, we measured phospholipid fatty acids and amino sugars (ASs) to explore how soil microbial community and residues changed under soil warming, throughfall reduction, root exclusion and their interactions in a natural deciduous broad-leaved oak forest. Soil warming significantly increased the Gram-positive to Gram-negative bacteria (G+/G−) ratio, and its interaction with root exclusion significantly reduced fungi-to-bacteria (F/B) ratio but stimulated the contributions of ASs to SOC (AS/SOC). Throughfall reduction also marginally increased G+/G− and AS/SOC, and suppressed F/B ratio. However, no interactive effects of soil warming and throughfall reduction on soil microbial community and residues were observed. Light fraction organic C and inorganic nitrogen were the key drivers in regulating the variation in the microbial community structure, and SOC was the controlling factor of microbial residue accumulations. Hence, soil C quality instead of water dominates the responses of microbial community structure and residues contribution to SOC to soil warming. Our results highlight the importance of soil substrate quality when predicting the terrestrial climate-C feedback.
•Soil warming reshaped bacterial community towards Gram-positive bacteria.•Soil warming had greater effects on microbes in the root absence subplots.•Throughfall reduction marginally impacted microbial community and residues.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
The response of soil carbon release to global warming is largely determined by the temperature sensitivity of soil respiration, yet how this relationship will be affected by increasing ...atmospheric nitrogen deposition is unclear. Here, we present a global synthesis of 686 observations from 168 field studies to investigate the relationship between nitrogen enrichment and the temperature sensitivity of soil respiration. We find that the temperature sensitivity of total and heterotrophic soil respiration increased with latitude. In addition, for total and autotrophic respiration, the temperature sensitivity responded more strongly to nitrogen enrichment with increasing latitude. Temperature and precipitation during the Last Glacial Maximum were better predictors of how the temperature sensitivity of soil respiration responds to nitrogen enrichment than contemporary climate variables. The tentative legacy effects of paleoclimate variables regulate the response through shaping soil organic carbon and nitrogen content. We suggest that careful consideration of past climate conditions is necessary when projecting soil carbon dynamics under future global change.
To study the effects of L-Arginine (Arg) on immune responses and intestinal structure in a hybrid grouper (Epinephelus fuscoguttatus ♀× Epinephelus lanceolatus ♂), intraperitoneal injection of ...different Arg doses (0, 50, 100, 200 mg per kg body weight of grouper) was administered once every seven days, repeating the process three times in the present study. A total of 216 groupers (initial weight of 349.42 ± 0.67 g) were randomly divided into four groups with three replicates, and each of the replicates comprised 18 fish. Serum was sampled at the seven, 14, and 21 days post-injection. The results showed that injection of Arg had a significant effect on serum albumin, immunoglobulin M (IgM), total protein (TP) and nitric oxide (NO) content, as well as nitric oxide synthase (NOS) and lysozyme activity (P < 0.05). With an increase of Arg dose, serum NO, TP, and albumin levels initially increased and subsequently decreased, and were significantly higher in fish injected with Arg at doses of 50 and 100 mg/kg in comparison to the control group. On days seven and 14, the highest serum albumin, TP, and IgM levels were observed in the 100 mg/kg group. With an increase in injection time and frequency, the 50 mg/kg group showed the optimal immune status after the third injection. Based on the results of the intestinal digestive enzyme activity and morphology, the injection of Arg at 50 mg/kg was the most beneficial, followed by the 100 mg/kg dose. Injection of 200 mg/kg Arg, especially after three injections, had adverse effects on immune responses and intestinal structure. These findings indicated that the intraperitoneal injection of L-Arg at a certain concentration can enhance the immunity and intestinal morphology of groupers. Notably, the most significant benefits were observed after three consecutive injections of Arg at 50 mg/kg in this experiment.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Potential changes in the quality and quantity of C inputs in soil during environmental changes may affect soil CO2 efflux in forest ecosystems. Therefore, a field debris exclusion experiment and a ...laboratory debris addition experiment were conducted to assess the response of soil CO2 efflux to C input manipulation. Our experiments were the first to be conducted in a subtropical Chinese fir (Cunninghamia lanceolata) plantation. The field debris exclusion experiment included the following treatments: leaf litter exclusion (NL), leaf litter and root exclusion (NLR), and control (CT). In the laboratory experiment, leaf litter and fine and coarse roots were added to soils collected from the same site and incubated for 100days at 15.0°C using the isotopic partitioning approach to determine the priming effect on soil C. The field-experimental results showed that soil CO2 efflux decreased significantly by 22.9% and 49.1% in the NL and NLR plots, respectively, compared with the CT plots. However, debris exclusion did not affect the diurnal and seasonal patterns of soil CO2 efflux. The contributions of leaf litter and roots to total soil CO2 efflux were 22.9% and 26.2%, respectively, which were positively related to soil temperature and moisture. In the laboratory experiment, the cumulative amount of soil CO2 efflux increased 1.25, 0.51, and 0.43 times in the soils with leaf litter, fine root, and coarse root additions, respectively, compared with the control soil (without debris addition) at the end of the incubation period. The amount of CO2 derived from leaf litter, fine root, and coarse root additions accounted for 44.0%, 31.1%, and 27.9% of the total amount of soil CO2 efflux, respectively. During the experimental period, the priming effect induced by fast-decomposing leaf litter (25.9%) was significantly higher than the priming effect induced by slow-decomposing fine roots (3.8%) and coarse roots (2.9%). The priming effect was negatively correlated with the initial lignin content and the lignin:N ratios of the added debris. The similar contributions of leaf litter and roots to soil CO2 efflux from the field experiment and the greater contributions of the priming of leaf litters to the fluxes from the laboratory experiment suggest that root inputs are more important than litter inputs in regulating soil C storage in Chinese fir forests.
► This was the first study conducted in a subtropical Chinese fir plantation. ► Examine in situ the effects of leaf litter and root removal on soil CO2 efflux. ► Leaf litter and/or root exclusion significantly decreased soil respiration. ► Contributions of leaf litter and roots to soil respiration were similar. ► Root rather than litter inputs are more important in regulating soil C storage.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Soil microbial residues contribute to the majority of stable soil organic carbon (SOC) pools, and their distribution among aggregate fractions determines long-term soil carbon (C) stability and, ...consequently, soil productivity. However, how microbial residue accumulation and distribution respond to stand age remains unexplored. To fill this knowledge gap, we investigated microbial residues in bulk soil and soil aggregate fractions under a chronosequence of Chinese fir (Cunninghamia lanceolata Lamb. Hook) plantations with stands aged 3, 17, 27, and 36 years. The results showed that microbial residues in topsoil did not change across the different stand ages, but the residues in the subsoil increased from 3 to 17 years of age and then remained constant. Moreover, microbial residue distribution in microaggregates decreased with stand age, and the residue distribution in small macroaggregates was lower at age 17 years than at other stand ages. The effect of stand age on microbial residue distribution was due to the fact of their effect on aggregate distribution but not microbial residue concentrations in aggregate fractions. Collectively, our results indicate that microbial residue stability decreased with stand age, which has significant implications for the management of SOC in subtropical plantations.
Soil heterotrophic respiration (Rh) is an important pathway of carbon (C) dioxide release from terrestrial soils to the atmosphere. It is often measured using sieved soil in a laboratory, but the ...uncertainty of how it is influenced by soil sieving persists, which limits the accuracy of predicting soil organic C dynamics in C models. To address how soil sieving during laboratory incubation affects Rh and its response to increased carbon availability, we investigated Rh in sieved and intact soil cores and its response to 13C-glucose addition. This was conducted through a 27-day laboratory incubation in four forests, including two ectomycorrhizal-dominated (ECM) forests and two arbuscular mycorrhizal-dominated forests. The significant influence of soil sieving on Rh in all forests was not observed during incubation when glucose was not added. After adding glucose, the Rh in the sieved soils on the 5th day of incubation was averaged 27.2% lower than that in intact soils in ECM forests. On the 27th day it was 22.1% lower in the Pinus massoniana forest, but 78.0% higher in the Castanea mollissima forest. Strong relationships were detected between Rh in sieved and intact soils (r2 = 0.888), and in soils both with and without the addition of glucose (r2 = 0.827). The measured soil variables explained 74.7% and 49.7% of the variation in Rh on the 5th and 27th day of incubation, and the role of soil nutrients and microbial PLFA groups in regulating Rh varied temporally. Our findings suggest that plant mycorrhizal types influenced the role of increased C availability to microbes in regulating the response of Rh to sieving in forest ecosystems.
Forest soil carbon (C) is an important component of the global C cycle. However, the mechanism by which tree species influence soil organic C (SOC) pool composition and mineralization is poorly ...understood. To understand the effect of tree species on soil C cycling, we assessed total, labile, and recalcitrant SOC pools, SOC chemical composition by
13
C nuclear magnetic resonance spectroscopy, and SOC mineralization in four monoculture plantations. Labile and recalcitrant SOC pools in surface (0–10 cm) and deep (40–60 cm) soils in the four forests contained similar content. In contrast, these SOC pools exhibited differences in the subsurface soil (from 10 to 20 cm and from 20 to 40 cm). The alkyl C and
O
-alkyl C intensities of SOC were higher in
Schima superba
and
Michelia macclurei
forests than in
Cunninghamia lanceolata
and
Pinus massoniana
forests. In surface soil,
S. superba
and
M. macclurei
forests exhibited higher SOC mineralization rates than did
P. massoniana
and
C. lanceolata
forests. The slope of the straight line between
C
60
and labile SOC was steeper than that between
C
60
and total SOC. Our results suggest that roots affected the composition of SOC pools. Labile SOC pools also affected SOC mineralization to a greater extent than total SOC pools.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Background
Microbial residues are significant contributors to stable soil organic carbon (SOC). Soil aggregates effectively protect microbial residues against decomposition; thus, microbial residue ...accumulation and distribution among soil aggregates determine long-term SOC stability. However, how tree species influence accumulation and distribution of soil microbial residues remains largely unknown, hindering the chances to develop policies for SOC management. Here, we investigated microbial residue accumulation and distribution in soil aggregates under four subtropical tree species (
Cunninghamia lanceolata
,
Pinus massoniana
,
Michelia macclurei
, and
Schima superba
) after 29 years of afforestation.
Results
Accumulation of microbial residues in the 0–10 cm soil layer was 13.8–26.7% higher under
S. superba
than that under the other tree species. A structural equation model revealed that tree species affected the accumulation of microbial residues directly by altering fungal biomass. Additionally, tree species significantly affected microbial residue distribution and contribution to SOC in the top 20 cm soil. In particular, microbial residue distribution was 17.2–33.4% lower in large macro-aggregates (LMA) but 60.1–140.7% higher in micro-aggregates (MA) under
S. superba
than that under the other species in the 0–10 cm soil layer, and 14.3–19.0% lower in LMA but 43–52.1% higher in MA under
S. superba
than that under
C. lanceolata
and
M. macclurei
in the 10–20 cm soil layer. Moreover, the contribution of microbial residues to SOC was 44.4–47.5% higher under
S. superba
than under the other tree species. These findings suggest a higher stability of microbial residues under
S. superba
than that under the other studied tree species.
Conclusions
Our results demonstrate that tree species influence long-term microbial persistence in forest soils by affecting accumulation and stabilization of microbial residues.
This study compared litter production, litter decomposition and nutrient return in pure and mixed species plantations. Dry weight and N, P, K, Ca, Mg quantities in the litterfall were measured in one ...pure Cunninghamia lanceolata plantation (PC) and two mixed-species plantations of C. lanceolata with Alnus cremastogyne (MCA) and Kalopanax septemlobus (MCK) in subtropical China. Covering 6 years of observations, mean annual litter production of MCA (4.97 Mg·ha-¹) and MCK (3.97 Mg·ha-¹) was significantly higher than that of PC (3.46 Mg·ha-¹). Broadleaved trees contributed 42% of the total litter production in MCA and 31% in MCK. Introduction of broadleaved tree species had no significant effect on litterfall pattern. Total litterfall was greatest in the dry season from November to March. Nutrient returns to the forest floor through leaf litter were significantly higher in both MCA and MCK than in PC (P < 0.05). The amounts of N, K, and Mg returned to the forest floor through leaf litter were highest in the MCA, and P and Ca returns were highest in the MCK. Percent contribution of broadleaf litter to total nutrient returns ranged from 41.7% to 86.9% in MCA and from 49.3% to 74.8% in MCK. The decomposition rate of individual leaf litter increased in the order: C. lanceolata < K. septemlobus < A. cremastogyne. Litter mixing had a positive effect on decomposition rate of the more recalcitrant litter and promoted nutrient return. Relative to mass loss of A. cremastogyne decomposing alone, higher mass loss of the mixture of C. lanceolata and A. cremastogyne was observed after 330 days of decomposition. These results indicate that mixed plantations of different tree species have advantages over monospecific plantations with regards to nutrient fluxes and these advantages have relevance to restoration of degraded sites.
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BFBNIB, DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NMLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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