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Open Access

Peer-reviewed

Research Article

Seasonality, Rather than Nutrient Addition or Vegetation Types, Influenced Short-Term Temperature Sensitivity of Soil Organic Carbon Decomposition

  • Yu-Qi Qian,

    Affiliation Department of Ecology, College of Urban and Environmental Sciences, and Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing, 100871, China

    ⨯
  • Feng-Peng He,

    Affiliation Shenzhen Graduate School, Peking University, Shenzhen 518055, China

    ⨯
  • Wei Wang

    wangw@urban.pku.edu.cn

    Affiliation Department of Ecology, College of Urban and Environmental Sciences, and Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing, 100871, China

    ⨯

Abstract

The response of microbial respiration from soil organic carbon (SOC) decomposition to environmental changes plays a key role in predicting future trends of atmospheric CO2 concentration. However, it remains uncertain whether there is a universal trend in the response of microbial respiration to increased temperature and nutrient addition among different vegetation types. In this study, soils were sampled in spring, summer, autumn and winter from five dominant vegetation types, including pine, larch and birch forest, shrubland, and grassland, in the Saihanba area of northern China. Soil samples from each season were incubated at 1, 10, and 20°C for 5 to 7 days. Nitrogen (N; 0.035 mM as NH4NO3) and phosphorus (P; 0.03 mM as P2O5) were added to soil samples, and the responses of soil microbial respiration to increased temperature and nutrient addition were determined. We found a universal trend that soil microbial respiration increased with increased temperature regardless of sampling season or vegetation type. The temperature sensitivity (indicated by Q10, the increase in respiration rate with a 10°C increase in temperature) of microbial respiration was higher in spring and autumn than in summer and winter, irrespective of vegetation type. The Q10 was significantly positively correlated with microbial biomass and the fungal: bacterial ratio. Microbial respiration (or Q10) did not significantly respond to N or P addition. Our results suggest that short-term nutrient input might not change the SOC decomposition rate or its temperature sensitivity, whereas increased temperature might significantly enhance SOC decomposition in spring and autumn, compared with winter and summer.

Citation: Qian Y-Q, He F-P, Wang W (2016) Seasonality, Rather than Nutrient Addition or Vegetation Types, Influenced Short-Term Temperature Sensitivity of Soil Organic Carbon Decomposition. PLoS ONE 11(4): e0153415. https://doi.org/10.1371/journal.pone.0153415

Editor: Raffaella Balestrini, Institute for Sustainable Plant Protection, C.N.R., ITALY

Received: November 25, 2015; Accepted: March 29, 2016; Published: April 12, 2016

Copyright: © 2016 Qian et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the paper and its Supporting Information files.

Funding: This work was supported by Projects of the National Natural Science Foundation of China (No. 31222011, 31270363, and 31321061) http://www.nsfc.gov.cn/; National Basic Research Program of China (No. 2013CB956303) http://www.most.gov.cn/eng/programmes1/200610/t20061009_36223.htm; University Construction Projects from Central Authorities in Beijing and Research Fund of State Key Laboratory of Soil and Sustainable Agriculture, Nanjing Institute of Soil Science, Chinese Academy of Science (Y412201439) http://english.issas.cas.cn/au/bi/. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Introduction

The Earth’s mineral soils represent a large terrestrial reservoir of soil organic carbon (SOC) derived from the accumulation of detritus residues and by-products of microbial decomposition processes [1]. Soil carbon storage is larger than the sum of carbon storage in the atmosphere and plants, reaching 3300 Pg [2]. Taking into account rising global temperatures [3] and the large size of the SOC pool, if SOC decomposition by microbial activity is strongly temperature sensitive, even small increases in temperature may prompt a large release of C from soils, resulting in an increase in atmospheric CO2 and a positive feedback on future warming [3–6]. Although climate-carbon models suggest that warming will accelerate the release of CO2 from soils, the magnitude of this feedback is uncertain, mostly because of uncertainty in the temperature sensitivity of SOC decomposition [7–11].

Most simulation models of regional and global carbon cycles use a single, fixed, Q10 coefficient (defined as the increase in respiration rate per 10°C increase in temperature) to express the temperature sensitivity of SOC decomposition [12]. As decomposer microbes might differ in their ability or strategy to efficiently use SOC within different phases of the year [13–16], the temperature sensitivity of SOC decomposition might differ across different seasons [11]. Previous studies have demonstrated a distinct transition in the microbial community structure and function from winter to summer [17–19]. For instance, in the temperate area of north China, a shift in soil microbial community composition occurred with higher fungal: bacterial biomass ratio and gram negative (G-): gram positive (G+) bacterial biomass ratio in winter than in summer [19]. Fungi could release a large number of extracellular enzymes that can digest a wide variety of substrates, even complex organic compounds such as lignin [20, 21]. Different gram-staining groups of bacteria, categorized by their cell wall composition, were also found to have various substrate preferences and survival strategies [22]. Different microbial groups in different seasons have distinct optimal temperature ranges for growth and activity, and therefore increased temperature might differentially affect the response of the microbial community [23–26]. The feedback responses caused by altered temperature might also differ among different ecosystems types [6]. Nevertheless, it is still unclear whether a universal pattern in the seasonal change in temperature sensitivity of SOC decomposition exists among different ecosystems.

Apart from global warming, anthropogenic activities have greatly altered soil nitrogen (N) and phosphorus (P) availability in terrestrial ecosystems, making the prediction of soil microbial respiration and its temperature sensitivity more complicate. Nutrient addition, as a test of nutrient limitation and simulation of nutrient enrichment, has been extensively conducted in previous field fertilization experiments. N addition has been reported to commonly suppress soil microbial respiration in a series of in situ studies [27–29] and meta-analysis [30], probably due to a decrease in soil acidification, microbial biomass, extracellular enzyme activity and microbial N mining. N addition reduced Gram-positive bacterial biomass, which changed the microbial community composition and, furthermore, reduced the amount of enzymes produced by Gram-positive bacteria [31–33], indicating a possible potential decrease in temperature sensitivity of decomposition rates. P addition might result in a reduction in SOC decomposition via dropping the availability of C substrate for microbial growth or by forming a non-labile compound with P and metal oxides in soil [34, 35]. A research conducted on Alaskan arctic and boreal soils implies that the response of microbial respiration to N addition largely depends on soil type, temperature, and incubation time [36]. However, further experiment should be conducted to clarify the effect of nutrient addition on soil organic decomposition and its temperature sensitivity in different vegetation types.

We sampled soils in spring, summer, autumn, and winter from five vegetation types, including evergreen coniferous forest (Pinus sylvestris var. mongolica), deciduous coniferous forest (Larix principis-rupprechtii), deciduous broadleaved forest (Betula platyphylla), shrubland (Malus baccata), and grassland (Leymus chinensis) in Saihanba, Hebei Province, northern China, from May 2013 to July 2014. Soil samples were incubated at three temperatures (1, 10 and 20°C). N and P were added to soil samples, and soil microbial respiration was measured. Our objective was to investigate whether soil microbial respiration showed a universal response to increasing temperature and whether this trend was affected by sampling season, vegetation, or nutrient addition. Specifically, we expected that: (1) the temperature sensitivity of soil microbial respiration would be highest in winter and lowest in summer, due to the commonly reported negative correlation between soil temperature and Q10 [37]; and (2) N and P addition would suppress soil microbial respiration and its temperature sensitivity due to a decrease in soil acidification, microbial biomass, extracellular enzyme activity and microbial N mining with N addition [27–29] and a decrease in the availability of C substrate for microbial growth or a formation of a non-labile compound with P and metal oxides in soil with P addition [34, 35].

Methods

The administration of the Saihanba Forestry Center gave permission for this research at each study site. We confirm that the field studies did not involve endangered or protected species. The study site was situated at Saihanba Forestry Center in Hebei Province, northern China (117°12′-117°30′E, 42°10′-42°50′N, 1400 m a.s.l.). The study site is characterized by semi-arid and semi-humid temperate climate, with long winters (November to March) and short summers. Climate records from 1964 to 2004 indicate an annual mean air temperature of −1.4°C and annual mean precipitation of 450.1 mm [6]. Soil in this area consists of Aeolian soil, meadow soil, and boggy soil [38].

The study site was within a typical forest-steppe ecotone in a temperate area of northern China. Primary forests were harvested via large-scale industrial logging in the late 1900s and have been replaced by secondary forests and plantations. This site contains the largest area of plantation forests in China, with dominant species of P. sylvestris var. mongolica (Mongolia pine, evergreen coniferous forest) and L. principis-rupprechtii (Prince Rupprecht’s larch, deciduous coniferous forest). The secondary forest mainly consists of B. platyphylla (birch, deciduous broadleaved forest). In addition, shrublands dominated by M. baccata (Siberian crabapple, shrubland) and meadow grassland (L. chinensis) are also very common. Wang et al. [6] provideed further details of the study site.

We sampled five local dominant vegetation types, including P. sylvestris var. mongolica (pine), L. principis-rupprechtii (larch), B. platyphylla (birch), M. baccata shrublands and L. chinensis grassland. The annual means of soil pH, moisture, bulk density, SOC and total nitrogen of the sampled sites are described (Table 1). Six 20 m × 20 m sampling plots were established in September 2012, in each of the five vegetation types, with 10 m buffer zones between each sampling plot. Topsoil (0–10 cm mineral soil) samples were collected from each of the sampling plots. Sampling was conducted in spring, summer, autumn, and winter (April 2013, July 2013, September 2013, and January 2014, respectively). Growing season soil was collected using a soil auger with a diameter of 5.8 cm, while frozen winter soil was collected with a shovel after clearing the snow cover (4–16 cm). Each soil used in the experiment was passed through a 2-mm sieve, thoroughly homogenized and then brought to the laboratory. Visible roots and stones were carefully removed prior to the incubation experiment. Data for winter grassland soils were not obtained.

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Table 1. Soil physical and chemical characteristics at 0–10 cm depth (n = 6) of five sampled vegetation types.

https://doi.org/10.1371/journal.pone.0153415.t001

Soils were kept in -70°C immediately after sampling for no more than 1 week, then were incubated in the laboratory under a factorial combination of temperature (3 levels: 1, 10 and 20°C) and nutrient addition (4 levels: no addition (water), nitrogen addition, phosphorus addition, and a combination of nitrogen and phosphorus addition). Each soil sample was divided into four subsamples for the nutrient addition experiment. Nitrogen (N) and phosphorus (P) were added as 0.035 mM NH4NO3 (equivalent to 5 g N per m2 or 0.35 mg N per g dry soil) and 0.03 mM P2O5 (equivalent to 5 g P per m2 or 0.36 mg P per g dry soil) [39]. Deionized water or nutrient solutions were added to control and treated soils, respectively, at a rate of 1 mL nutrient solution or water per 5 g fresh soil. Before starting the incubation, soil moisture was adjusted to 60% of water-holding capacity through the addition of deionized H2O. During the incubation period, soil moisture was kept stable by weighing and adjusted by adding deionized water. Soil microbial respiration rate was determined using the alkali absorption method [40]. Approximately 25 g of fresh soils were placed into 250 mL glass gas tight jars and incubated at 1, 10, and 20°C for 5–7 days. Respired CO2 was captured by a connecting vial with 5 mL 1 M NaOH and determined by titration with 0.25 M HCl. Because labile carbon is exhausted gradually with the increase in incubation time [23, 41, 42], we used the short-term response of microbial respiration to temperature and nutrient addition [43, 44].

The total microbial biomass and microbial community composition were determined using phospholipid fatty acids (PLFAs) analysis. The fatty acid 18:2ω6, 9 was recognized as the fungal biomarker [45]. Bacterial biomass was quantified as the sum of i14:0, i15:0, a15:0, 16:1ω9, 16:1ω7, i17:0, a17:0, cy17:0, 17:0, and cy19:0 [46]. We calculated the total lipids as an indicator of microbial biomass [47]. The details of the method can be seen in [19].

Multifactor analysis of variance (ANOVA) was used to examine the effects of sampling season, incubation temperature and nutrient addition on soil microbial respiration, followed by Tukey’s multiple comparison if significance was tested. Q10 was estimated by an exponential model of soil CO2 efflux and temperature (with least squares technique) as follows: (1) where F is soil CO2 efflux rate, T is soil temperature, and β0 and βt are constants. The Q10 values were calculated as shown below: (2)

Linear regression analysis was used to examine the relationship between the Q10 and the microbial biomass and fungal: bacterial ratios. Statistical analysis was performed using SPSS 18.0 for Windows (SPSS Inc., Chicago, IL, USA) and R software (version 0.98.490). Significant effects were determined at P < 0.05 unless otherwise stated.

Results

Effect of increased temperature on microbial respiration rate

Microbial respiration rates were significantly different among 1, 10 and 20°C incubations (Fig 1), regardless of sampling time or vegetation type. Microbial respiration increased as temperature increased, and the soil microbial respiration rates at 1, 10 and 20°C were 6.34 ± 0.36 (mean ± s.e.), 26.32 ± 1.07, and 48.68 ± 1.85 mg CO2 kg−1 soil day−1 in spring soil; 10.69 ± 0.5, 11.13 ± 0.61, and 16.22 ± 0.68 mg CO2 kg−1 soil day−1 in summer soil; 3.96 ± 0.21, 12.14 ± 0.77 mg CO2 kg−1 soil day−1, and 26.83 ± 1.35 in autumn soil; 10.23 ± 0.5, 16.2 ± 0.66, and 23.31 ± 0.72 mg CO2 kg−1 soil day−1 in winter soil, respectively.

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Fig 1. Comparison of soil microbial respiration at three incubation temperatures.

SPR, SUM, AUT, and WIN represent spring, summer, autumn, and winter, respectively. Control, N, P, and NP represent different nutrient additions, including no nutrient addition but water; nitrogen addition, phosphorus addition, and a combination of nitrogen and phosphorus addition. Boxplot includes the data from five vegetation types. Significant differences among nutrient addition treatments are indicated by different letters. Values are means (n = 30) ± standard errors.

https://doi.org/10.1371/journal.pone.0153415.g001

Effect of sampling seasons on microbial respiration rates and Q10

When incubated at the same temperature, soil sampled from different seasons presented significantly different respiration rates (Fig 2). At 1°C, even though summer and winter soil had higher respiration rates than spring and autumn soil (P <0.05), the absolute respiration rates of all four seasons were very low. At 10 and 20°C, spring soil had a higher respiration rate than any other soil (P < 0.05). Temperature sensitivities of soil microbial respiration, expressed as Q10, were 3.13 (spring, R2 = 0.584, P < 0.001), 1.35 (summer, R2 = 0.076, P < 0.001), 2.78 (autumn, R2 = 0.521, P < 0.001), and 1.45 (winter, R2 = 0.179, P < 0.001). Soils from all of the five vegetation types showed higher Q10 in spring and autumn than in summer and winter. The seasonal pattern in Q10 was significantly correlated with microbial biomass (Y = 0.06 X + 1.01; R2 = 0.60, P = 0.02, Fig 3) and fungal: bacterial biomass ratio (Y = 18.93 X + 0.32; R2 = 0.82; P < 0.01, Fig 4).

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Fig 2. Comparison of soil microbial respiration among four seasons.

Data are from all the nutrient treatment combinations. SPR, SUM, AUT, and WIN represent spring, summer, autumn, and winter, respectively. Significant differences among different sampling season are indicated by different letters. Values for winter and summer soil data incubated at 10°C in the grassland were absent because of accidents in sampling and experiments.

https://doi.org/10.1371/journal.pone.0153415.g002

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Fig 3. Relationship between Q10 of soil microbial respiration and microbial biomass.

Data are from all the nutrient treatment combinations, vegetation types, and seasons.

https://doi.org/10.1371/journal.pone.0153415.g003

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Fig 4. Relationship between Q10 of soil microbial respiration and fungal: bacterial biomass ratio.

Data are from all the nutrient treatment combinations, vegetation types, and seasons.

https://doi.org/10.1371/journal.pone.0153415.g004

Effect of vegetation types on microbial respiration rates and Q10

Grassland soil had lower respiration rates than the other soils, while soil from the birch forest had the highest respiration rate except in autumn (Fig 5). The coefficients of variation of respiration rates were 0.85 in pine forest, 0.94 in larch forest, and 0.97 in birch forest, 1.03 in shrubland, and 0.71 in grassland. Q10 values of soil microbial respiration estimated in the five vegetation types were 2.33 (pine forest, R2 = 0.377), 2.02 (larch forest, R2 = 0.351), 2.55 (birch forest, R2 = 0.530), 2.25 (grassland, R2 = 0.372), and 1.57 (shrubland, R2 = 0.099). There was no significant difference in Q10 across vegetation types (P > 0.05).

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Fig 5. Comparison of soil microbial respiration among vegetation types.

Data are from all the nutrient treatment combinations. Significant differences among different vegetation types are indicated by different letters. Samples from all seasons were included. Data are from all the nutrient treatment combinations.

https://doi.org/10.1371/journal.pone.0153415.g005

Effect of nutrient addition on microbial respiration rates and Q10

Mean soil microbial respiration rates among all the vegetation types were 18.61 ± 0.73, 18.93 ± 0.74, 18.11 ± 0.72 and 17.58 ± 0.74 mg CO2 kg−1 soil day−1 for control (water only), N addition, P addition, and combination of N and P addition treatments, respectively. For all soil samples, we did not find any significant response of soil microbial respiration to N, P or NP addition (Fig 6, multi-comparison, P>0.05). Using three-way ANOVA to determine the effects of nutrient addition, sampling season, and vegetation type, we did not find any significant response to nutrient addition, but significant responses occurred for sampling season and vegetation types (Table 2). No significant effect was observed for N or P addition on the temperature sensitivity of soil microbial respiration. Q10 values for control, N addition, P addition, and NP addition treatments were 2.08, 2.10, 1.97, and 2.01, respectively.

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Fig 6. Effect of nutrient addition on soil microbial respiration rates.

Data are from all temperature treatments. SPR, SUM, AUT, and WIN represent spring, summer, autumn, and winter. Significant differences among different nutrient addition treatments are indicated by different letters. Values from winter soil of grassland was absent because of accidents in sampling and experiments.

https://doi.org/10.1371/journal.pone.0153415.g006

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Table 2. Results of the two-way ANOVA used for detecting the effects of incubation temperature and nutrient addition on soil microbial respiration.

Data are derived from all vegetation types.

https://doi.org/10.1371/journal.pone.0153415.t002

Discussion

Seasonal dynamics of temperature sensitivity of SOC decomposition

In our study, Q10 values in spring and autumn were close to those recorded by Mo et al. [48] in a cool-temperate deciduous broad-leaved forest in Japan, but our winter Q10 was lower than in previous studies [48, 49]. An in situ field experiment conducted in a beech forest observed short-term Q10 values ranging between 0.9 and 38, with the lowest Q10 values in summer and the highest in winter. In summer Q10 averaged 4.3, whereas in winter mean Q10 was 16 [50]. Mikan et al. [49] observed a stronger response of microbial respiration to increased temperature in winter than in summer. The discrepancy between our results and the previous studies might be because of different incubation temperatures. Our incubation temperatures for winter soil ranged from 1 to 20°C, whereas previous studies used lower temperatures, such as −10 to −0.5°C [49]. At incubation temperatures below 0°C, thawing can lead to diffusion of organic molecules through water films and cell metabolism, and can also activate dormant microbes, resulting in rapid changes in the microbial population and thus C mineralization [50]. To avoid the changes in soil moisture caused by freezing and thawing at temperatures under 0°C, we set the lowest temperature as 1°C. Considering the differences between previous studies and our research, our short-term Q10 should not be directly compared with previous studies using different incubation temperatures.

Unexpectedly, soil sampled in spring and autumn had higher temperature sensitivities (Q10 values were 3.13 and 2.78 in spring and autumn, respectively) than in summer and winter (Q10 values were 1.35 and 1.45 in summer and winter, respectively). These results were consistent with the seasonal plasticity hypothesis, which states that the temperature sensitivity of microbial respiration varies distinctly across seasons, without a directional pattern in response to soil temperature [51]. Unlike our results, some experiments observed constant temperature sensitivity [52–55], while others found that temperature sensitivity of microbial respiration declined with increasing temperature [56, 57].

The higher Q10 in spring and autumn in our study could mainly be attributable to two reasons. First, higher microbial biomass in spring (unpublished data) indicates that increased efficiency of carbon usage promotes the biomass of microbial decomposers and increases the loss of soil carbon. Similarly, Allison et al 2010 [58] found that decline in microbial biomass and degradative enzymes can explain the observed attenuation of soil-carbon emissions in response to warming. Secondly, various decomposer microbes differ in their ability/strategy to efficiently use soil organic matter [59, 60, 61], so shifting within the community composition may affect decomposition rates. Higher fungi to bacteria ratio in autumn (unpublished data) could contribute to its higher Q10 of microbial respiration due to the fact that fungi could release a great number of extracellular enzymes which can digest a wide variety of substrates, even complex organic compound as lignin [62,63]. Fungi and extracellular enzymes catalyze the conversion of polymeric SOC to dissolved organic carbon (DOC), which is presumed to be the rate-limiting step in SOC decomposition [64, 65]. We also observed that Q10 increased with increased microbial biomass (Fig 3) and fungal: bacterial ratio (Fig 4). Our results therefore indicated that microbial physiology, including biomass and community composition, exerted a significant influence on the response of microbial respiration to increased temperature. Our results were similar to studies conducted in coniferous forests of the Rocky Mountains, where significant seasonal succession of microbial communities largely explained the seasonal patterns of soil respiration [66]. However, previous studies did not quantify the association between soil microbial respiration and microbial community composition. In this study we found for the first time that higher fungal: bacterial ratios led to larger responses of microbial respiration to increasing temperature, apart from spring soil samples (Fig 4). These results suggest that any changes in microbial community composition resulting from changing environmental conditions (including temperature, precipitation and nitrogen deposition) will significantly influence microbial carbon emission in response to temperature changes. This has important applications for predicting microbial activity responses to global changes.

In addition to microbial biomass and composition, substrate availability may affect SOC decomposition and temperature sensitivities in different seasons via influencing microbial composition, biomass, and metabolism [67]. For instance, bacteria are the first group to trap and metabolize most of the easily-available organics [68, 69]. Fungi commonly target recalcitrant substrates compared with bacteria [70]. A shift in microbial community composition along with different substrate quality across different seasons may subsequently change the enzyme production since that microbes with different preference will ultimately influence the SOC decomposition and its temperature sensitivity. However, we did not conduct measurements of substrate usage across different seasons. Future studies should be conducted on the seasonal dynamics of substrate usage for soil microbe in order to explore the mechanisms of seasonal differences in temperature sensitivity of soil microbial respiration.

Response of microbial respiration and its temperature sensitivity to nutrient addition

There was no response of soil microbial respiration or Q10 values to N or P addition. There are limited studies addressing the effects of nutrient additions on soil microbial respiration [34–36, 70], or temperature sensitivity of soil microbial respiration [35]. Field studies found that N addition could lead to lower soil microbial respiration by changing microbial composition and reducing microbial N mining [28, 30, 71, 72, 73]. Temperature sensitivity of total soil respiration was not influenced by N fertilization in larch and ash plantations [74] but was enhanced in subtropical forest, crop field, temperate grassland and shrubland [30, 75, 76]. Field experiments are limited because they cannot isolate the response of soil microbes from the plant response to N addition. There are limited studies involving P addition [77, 78], and no universal conclusion was reached on the effect of P addition on soil respiration and temperature sensitivity. Iyamuremye and Dick [79] and Nziguheba et al. [80] found that microbes accumulated P as polyphosphates in cells rather than utilizing P in microbial growth or activity, while Malik et al. [35] reported that inorganic P addition enhanced microbial respiration in a laboratory incubation experiment. In our study, the fact that microbial respiration was not significantly influenced by nutrient addition indicated that soil microbes might not be limited by nutrients in the short term. A field experiment conducted in pine forest in our sampling area also found no response of microbial respiration to N or P addition (unpublished data). The lack of response might have also resulted from the low level of nutrient addition as well as the short incubation time; therefore, further research involving these two factors is needed to determine the possible nonlinear and long-term effects of nutrient addition on soil microbial respiration.

Conclusions

Temperature sensitivity of soil microbial respiration is of increasing importance for its application in modeling and predicting terrestrial C flow in the context of global warming. Specifying the seasonal changes in temperature sensitivity of soil microbial respiration has improved our ability to build models with higher accuracy. By measuring the temperature sensitivity of soil microbial respiration rate among different vegetation types and seasons, our study found summer and winter soil had lower temperature sensitivity than spring and autumn soil, irrespective of vegetation types, indicating that microbial respiration had a distinct seasonal pattern in its response to increased temperature. Microbial biomass and fungal: bacterial biomass ratio significantly correlated with the seasonal pattern in the temperature sensitivity of microbial respiration. Our results suggest that any changes in microbial community composition resulting from changing environmental conditions (including temperature, precipitation and nitrogen deposition) will influence microbial carbon emission in response to temperature changes, which has important applications for predicting microbial activity responses to global change. In addition, soil microbial respiration and its temperature sensitivity were not influenced by nitrogen and phosphorus addition. Even though previous evidence suggested potential effects of nutrient addition on soil microbial respiration, contradictory results, including those obtained in this study, revealed that N and P availability might be a minor factor influencing carbon mineralization compared to increased temperature in the short-term.

Supporting Information

S1 Appendix. Respiration Season Vegetation Nutrient.

Sample season SPR, SUM, AUT, and WIN represent spring, summer, autumn, and winter, respectively. Control, N, P, and NP represent different nutrient additions, including no nutrient addition but water; nitrogen addition, phosphorus addition, and a combination of nitrogen and phosphorus addition. Incubation Temperature 1, 10, 20 represent 1°C, 10°C, and 20°C. Unit of Respiration is mg CO2 kg−1 soil day−1.

https://doi.org/10.1371/journal.pone.0153415.s001

(XLSX)

S2 Appendix. Biomass FB ratio Q10.

https://doi.org/10.1371/journal.pone.0153415.s002

(XLSX)

Acknowledgments

The help of Xinyue Zhang, Na Tao, Yuan Fang, and Chengcheng Dong in soil sample collection and data analysis is gratefully acknowledged.

Author Contributions

Conceived and designed the experiments: WW. Performed the experiments: YQ FH. Analyzed the data: YQ FH. Contributed reagents/materials/analysis tools: YQ FH WW. Wrote the paper: YQ FH WW.

References

  1. 1. Bond-Lamberty B, Thomson A. Temperature-associated increases in the global soil respiration record. Nature. 2010 Mar 25;464(7288): 579–82. pmid:20336143
  2. 2. Tarnocai C, Canadell J, Schuur E, Kuhry P, Mazhitova G, Zimov S. Soil organic carbon pools in the northern circumpolar permafrost region. Glob Biogeochem Cycle. 2009 Jun 1;23(2).
  3. 3. Lemke P, Ren R, Alley I. The physical science basis. Contribution of working group I to the fourth assessment report of the intergovernmental panel on climate change.: Clim Chang 2007. (2007): 337–83.
  4. 4. Conant RT, Steinweg JM, Haddix ML, Paul EA, Plante AF, Six J. Experimental warming shows that decomposition temperature sensitivity increases with soil organic matter recalcitrance. Ecology. 2008 Sep;89(9):2384–91. pmid:18831158
  5. 5. Singh JS, Raghubanshi AS, Singh RS, Srivastava SC. Microbial biomass acts as a source of plant nutrients in dry tropical forest and savanna. Nature. 1989 Apr 6;338(6215):499–500.
  6. 6. Wang W, Peng S, Fang J. Root respiration and its relation to nutrient contents in soil and root and EVI among 8 ecosystems, northern China. Plant Soil. 2010 Aug 1; 333(1–2): 391–401.
  7. 7. Cox PM, Betts RA, Jones CD, Spall SA, Totterdell IJ. Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model. Nature. 2000 Nov 9; 408(6809): 184–7. pmid:11089968
  8. 8. Luo Y, Wan S, Hui D, Wallace LL. Acclimatization of soil respiration to warming in a tall grass prairie. Nature. 2001 Oct 11; 413(6856): 622–5. pmid:11675783
  9. 9. Bååth E, Wallander H. Soil and rhizosphere microorganisms have the same Q10 for respiration in a model system. Glob Chang Biol. 2003 Dec 1; 9(12): 1788–91.
  10. 10. Reichstein M, Rey A, Freibauer A, Tenhunen J, Valentini R, Banza J, et al. Modeling temporal and large‐scale spatial variability of soil respiration from soil water availability, temperature and vegetation productivity indices. Global Biogeochem Cycles. 2003 Dec 1;17(4).
  11. 11. Suseela V, Conant RT, Wallenstein MD, Dukes JS. Effects of soil moisture on the temperature sensitivity of heterotrophic respiration vary seasonally in an old‐field climate change experiment. Glob Chang Biol. 2012 Jan 1;18(1):336–48.
  12. 12. Kirschbaum MUF. The temperature dependence of organic-matter decomposition—still a topic of debate. Soil Biol Biochem. 2006 Sep 30;38(9):2510–8.
  13. 13. Balser TC, Wixon DL. Investigating biological control over soil carbon temperature sensitivity. Global Change Biol. 2009 Dec 1;15(12):2935–49.
  14. 14. Keiblinger KM, Hall EK, Wanek W, Szukics U, Hämmerle I, Ellersdorfer G, et al. The effect of resource quantity and resource stoichiometry on microbial carbon-use-efficiency. FEMS Microbiol Ecol. 2010 Sep 1;73(3):430–40. pmid:20550579
  15. 15. Lipson DA, Monson RK, Schmidt SK, Weintraub MN. The trade-off between growth rate and yield in microbial communities and the consequences for under-snow soil respiration in a high elevation coniferous forest. Biogeochemistry. 2009 Aug 1;95(1):23–35.
  16. 16. Liptzin D, Silver WL. Effects of carbon additions on iron reduction and phosphorus availability in a humid tropical forest soil. Soil Biol Biochem. 2009 Aug 31;41(8):1696–702.
  17. 17. Lipson D, Schadt C, Schmidt S. Changes in soil microbial community structure and function in an alpine dry meadow following spring snow melt. Microbial Ecol. 2002 May 24;43(3):307–14.
  18. 18. Schadt CW, Martin AP, Lipson DA, Schmidt SK. Seasonal dynamics of previously unknown fungal lineages in tundra soils. Science. 2003 Sep 5;301(5638):1359–61. pmid:12958355
  19. 19. Zhang X, Wang W, Chen W, Zhang N, Zeng H. Comparison of seasonal soil microbial process in snow-covered temperate ecosystems of northern China. PloS ONE. 2014 Mar 25;9(3):e92985. pmid:24667929
  20. 20. Waldrop M, Balser T, Firestone M. Linking microbial community composition to function in a tropical soil. Soil Biol Biochem. 2000 Nov 30;32(13):1837–46.
  21. 21. Sinsabaugh R, Carreiro M, Repert D. Allocation of extracellular enzymatic activity in relation to litter composition, N deposition, and mass loss. Biogeochemistry. 2002 Aug 1;60(1):1–24.
  22. 22. McMahon SK, Wallenstein MD, Schimel JP. Microbial growth in Arctic tundra soil at -2°C. Environ Microbiol Rep. 2009 Apr 1;1(2):162–6. pmid:23765747
  23. 23. Dalias P, Anderson JM, Bottner P, Coûteaux M-M. Temperature responses of carbon mineralization in conifer forest soils from different regional climates incubated under standard laboratory conditions. Glob Chang Biol. 2001 Feb 1;7(2):181–92.
  24. 24. Six J, Frey SD, Thiet RK, Batten KM. Bacterial and fungal contributions to carbon sequestration in agroecosystems. Soil Sci Soc Am J. 2006 Mar 1;70(2):555–69.
  25. 25. Singh BK, Bardgett RD, Smith P, Reay DS. Microorganisms and climate change: terrestrial feedbacks and mitigation options. Nat Rev Microbiol. 2010 Nov 1;8(11):779–90. pmid:20948551
  26. 26. Vanhala P, Karhu K, Tuomi M, Björklöf K, Fritze H, Hyvärinen H, et al. Transplantation of organic surface horizons of boreal soils into warmer regions alters microbiology but not the temperature sensitivity of decomposition. Global Change Biol. 2011;17(1):538–50.
  27. 27. Vose JM, Elliott KJ, Johnson DW, Walker RF, Johnson MG, Tingey DT. Effects of elevated CO2 and N fertilization on soil respiration from ponderosa pine (Pinus ponderosa) in open-top chambers. Can J For Res. 1995 Aug 1;25(8):1243–51.
  28. 28. Bowden RD, Davidson E, Savage K, Arabia C, Steudler P. Chronic nitrogen additions reduce total soil respiration and microbial respiration in temperate forest soils at the Harvard Forest. For Ecol Manage. 2004 Jul 12;196(1):43–56.
  29. 29. Olsson P, Linder S, Giesler R, Högberg P. Fertilization of boreal forest reduces both autotrophic and heterotrophic soil respiration. Glob Chang Biol. 2005 Oct 1;11(10):1745–53.
  30. 30. Zhou L, Zhou X, Zhang B, Lu M, Luo Y, Liu L, et al. Different responses of soil respiration and its components to nitrogen addition among biomes: a meta-analysis. Glob Chang Biol. 2014 Jul 1; 20(7):2332–43. pmid:24323545
  31. 31. Gallo M, Amonette R, Lauber C, Sinsabaugh RL, Zak DR. Microbial community structure and oxidative enzyme activity in nitrogen-amended north temperate forest soils. Microbial Ecology. 2004 Oct 1;48(2):218–29. pmid:15546042
  32. 32. Billings S, Gaydess E. Soil nitrogen and carbon dynamics in a fragmented landscape experiencing forest succession. Landscape Ecology. 2008 May 1;23(5):581–93.
  33. 33. Zak DR, Pregitzer KS, Burton AJ, Edwards IP, Kellner H. Microbial responses to a ccreases decomposition. Ecology. 2007 Aug;88(8):2105–13.
  34. 34. Craine JM, Morrow C, Fierer N. Microbial nitrogen limitation increases decomposition. Ecology. 2007 Aug;88(8):2105–13. pmid:17824441
  35. 35. Malik MA, Marschner P, Khan KS. Addition of organic and inorganic P sources to soil–Effects on P pools and microorganisms. Soil Biol Biochem. 2012 Jun 30;49:106–13.
  36. 36. Lavoie M, Mack MC, Schuur EAG. Effects of elevated nitrogen and temperature on carbon and nitrogen dynamics in Alaskan arctic and boreal soils. J Geophys Res Biogeosci. 2011 Sep 1;116(G3).
  37. 37. Wang W, Peng SS, Wang Tao, Fang JY. Winter soil CO2 efflux and its contribution to annual soil respiration in different ecosystems of a forest-steppe ecotone, north China. Soil Biol Biochem. 2010 Mar 31;42(3): 451–8
  38. 38. Lili S. Soil Types Distribution and Evolution of Saihanba National Nature Reserve. J Anhui Agric Sci. 2008;36(10):4185.
  39. 39. Buckeridge KM, Grogan P. Deepened snow alters soil microbial nutrient limitations in arctic birch hummock tundra. Appl Soil Ecol. 2008 Jun 30;39(2):210–22.
  40. 40. Kirita H. Re-examination of the absorption method of measuring soil respiration under field conditions. IV. An improved absorption method using a disc of plastic sponge as absorbent holder. Japanese J Ecol. 1971.
  41. 41. Trumbore S. Age of soil organic matter and soil respiration: radiocarbon constraints on belowground C dynamics. Ecol Appl. 2000 Apr;10(2):399–411.
  42. 42. Leifeld J, Fuhrer J. The temperature response of CO2 production from bulk soils and soil fractions is related to soil organic matter quality. Biogeochemistry. 2005 Sep 1;75(3):433–53.
  43. 43. Pendall E, King JY. Soil organic matter dynamics in grassland soils under elevated CO2: insights from long-term incubations and stable isotopes. Soil Biol Biochem. 2007 Oct 31;39(10):2628–39.
  44. 44. Schädel C, Luo Y, Evans RD, Fei S, Schaeffer SM. Separating soil CO2 efflux into C-pool-specific decay rates via inverse analysis of soil incubation data. Oecologia. 2013; Mar 1171(3):721–32.
  45. 45. Zelles L. Phospholipid fatty acid profiles in selected members of soil microbial communities. Chemosphere. 1997 Jul 31;35(1):275–94.
  46. 46. Fierer N, Schimel JP, Holden PA. Variations in microbial community composition through two soil depth profiles. Soil Biol Biochem. 2003 Jan 31;35(1):167–76.
  47. 47. Gutknecht JL, Field CB, Balser TC. Microbial communities and their responses to simulated global change fluctuate greatly over multiple years. Glob Chang Biol. 2012 Jul 1;18(7):2256–69.
  48. 48. Mo W, Lee M-S, Uchida M, Inatomi M, Saigusa N, Mariko S, et al. Seasonal and annual variations in soil respiration in a cool-temperate deciduous broad-leaved forest in Japan. Agric For Meteorol. 2005 Nov 30;134(1):81–94.
  49. 49. Mikan CJ, Schimel JP, Doyle AP. Temperature controls of microbial respiration in arctic tundra soils above and below freezing. Soil Biol Biochem. 2002 Nov 30;34(11):1785–95.
  50. 50. Janssens IA, Pilegaard KIM. Large seasonal changes in Q10 of soil respiration in a beech forest. Glob Chang Biol. 2003 Jun 1;9(6):911–8.
  51. 51. Drake J, Giasson M-A, Spiller K, Finzi A. Seasonal plasticity in the temperature sensitivity of microbial activity in three temperate forest soils. Ecosphere. 2013 Jun 1;4(6):1–77.
  52. 52. Jones C, McConnell C, Coleman K, Cox P, Falloon P, Jenkinson D, et al. Global climate change and soil carbon stocks; predictions from two contrasting models for the turnover of organic carbon in soil. Glob Chang Biol. 2005 Jan 1;11(1):154–66.
  53. 53. Hartley IP, Ineson P. Substrate quality and the temperature sensitivity of soil organic matter decomposition. Soil Biol Biochem. 2008 Jul 31;40(7):1567–74.
  54. 54. Malcolm GM, Lopez-Gutierrez JC, Koide RT. Little evidence for respiratory acclimation by microbial communities to short‐term shifts in temperature in red pine (Pinus resinosa) litter. Glob Chang Biol. 2009 Oct 1;15(10):2485–92.
  55. 55. Mahecha MD, Reichstein M, Carvalhais N, Lasslop G, Lange H, Seneviratne SI, et al. Global convergence in the temperature sensitivity of respiration at ecosystem level. Science. 2010 Aug 13;329(5993):838–40. pmid:20603495
  56. 56. Bradford MA, Davies CA, Frey SD, Maddox TR, Melillo JM, Mohan JE, et al. Thermal adaptation of soil microbial respiration to elevated temperature. Ecol Lett. 2008 Dec 1;11(12):1316–27. pmid:19046360
  57. 57. Brzostek ER, Finzi AC. Substrate supply, fine roots, and temperature control proteolytic enzyme activity in temperate forest soils. Ecol. 2011 Apr;92(4):892–902.
  58. 58. Allison SD, Wallenstein MD, Bradford MA. Soil-carbon response to warming dependent on microbial physiology. Nat. Geosci. 2010 May 1;3(5):336–40.
  59. 59. Balser TC, Wixon DL. Investigating biological control over soil carbon temperature sensitivity. Glob Chang Biology. 2009 Dec 1;15(12): 2935–49.
  60. 60. Keiblinger KM, Hall EK, Wanek W, Szukics U, Ha¨mmerle I, Ellersdorfer G, et al. The effect of resource quantity and resource stoichiometry on microbial carbon-useefficiency. FEMS Microbiol Ecol. 2010 Sep 1;73(3):430–40. pmid:20550579
  61. 61. Lipson DA, Monson RK, Schmidt SK, Weintraub MN. The trade-off between growth rate and yield in microbial communities and the consequences for under-snow soil respiration in a high elevation coniferous forest. Biogeochemistry. 2009 Aug 1;95(1): 23–5.
  62. 62. Waldrop M, Balser T, Firestone M. Linking microbial community composition to function in a tropical soil. Soil Biol Biochem. 2000 Nov 30;32(13):1837–46.
  63. 63. Sinsabaugh RL, Carreiro MM, Repert DA. Allocation of extracellular enzymatic activity in relation to litter composition, N deposition, and mass loss. Biogeochemistry. 2002 Aug 1;60(1): 1–24.
  64. 64. Schimel JP, Weintraub MN. The implications of exoenzyme activity on microbial carbon and nitrogen limitation in soil: A theoretical model. Soil Biol Biochem. 2003 Apr 30;35(4): 549–63.
  65. 65. Fontaine S, Barot S. Size and functional diversity of microbe populations control plant persistence and long-term soil carbon accumulation. Ecol. Lett. 2005 Oct 1;8,(10):1075–1087.
  66. 66. Monson RK, Lipson DL, Burns SP, Turnipseed AA, Delany AC, Williams MW, et al. Winter forest soil respiration controlled by climate and microbial community composition. Nature. 2006 Feb 9;439(7077):711–4. pmid:16467835
  67. 67. Kuzyakov Y. Priming effects: Interactions between living and dead organic matter. Soil Biol Biochem. 2010 Sep 30;42(9):1363–71.
  68. 68. Paterson E. Comments on the regulatory gate hypothesis and implications for C-cycling in soil. Soil Biol Biochem. 2009 Jun 30;41(6):1352–4.
  69. 69. Moore-Kucera J, Dick RP. Application of 13C-labeled litter and root materials for in situ decomposition studies using phospholipid fatty acids. Soil Biol Biochem, 2008 Oct 31;40(10):2485–93.
  70. 70. Cleveland CC, Liptzin D. C: N: P stoichiometry in soil: is there a “Redfield ratio” for the microbial biomass? Biogeochemistry. 2007 Sep 1;85(3):235–252
  71. 71. Wallenstein MD, McMahon S, Schimel J. Bacterial and fungal community structure in Arctic tundra tussock and shrub soils. FEMS Microbiol Ecol. 2007 Feb 1;59(2):428–35. pmid:17313585
  72. 72. Wang WJ, Baldock JA, Dalal RC, Moody PW. Decomposition dynamics of plant materials in relation to nitrogen availability and biochemistry determined by NMR and wet-chemical analysis. Soil Biol Biochem. 2004 Dec 31;36(12):2045–58.
  73. 73. Phillips RP, Fahey TJ. Fertilization effects on fineroot biomass, rhizosphere microbes and respiratory fluxes in hardwood forest soils. New Phyto. 2007 Nov 1;176(3):655–64.
  74. 74. Jia S, Wang Z, Li X, Sun Y, Zhang X, Liang A. N fertilization affects on soil respiration, microbial biomass and root respiration in Larix gmelinii and Fraxinus mandshurica plantations in China. Plant Soil. 2010 Aug 1;333(1–2):325–36.
  75. 75. Ding W, Yu H, Cai Z, Han F, Xu Z. Responses of soil respiration to N fertilization in a loamy soil under maize cultivation. Geoderma. 2010 Mar 15;155(3):381–9.
  76. 76. Ding F, Huang Y, Sun W, Jiang G, Chen Y. Decomposition of organic carbon in fine soil particles is likely more sensitive to warming than in coarse particles: an incubation study with temperate grassland and forest soils in northern China. PloS ONE. 2014 Apr 15;9(4):e95348. pmid:24736659
  77. 77. Cleveland CC, Townsend AR, Schmidt SK. Phosphorus limitation of microbial processes in moist tropical forests: Evidence from short-term laboratory incubations and field studies. Ecosystems. 2002 Nov 1;5(7):680–91.
  78. 78. Gnankambary Z, Ilstedt U, Nyberg G, Hien V, Malmer A. Nitrogen and phosphorus limitation of soil microbial respiration in two tropical agroforestry parklands in the south-Sudanese zone of Burkina Faso: the effects of tree canopy and fertilization. Soil Biol Biochem. 2008 Feb 29;40(2):350–9.
  79. 79. Iyamuremye F, Dick R. Organic amendments and phosphorus sorption by soils. Adv in Agron (USA). 1996.
  80. 80. Nziguheba G, Palm CA, Buresh RJ, Smithson PC. Soil phosphorus fractions and adsorption as affected by organic and inorganic sources. Plant Soil. 1998 Jan 1;198(2):159–68.