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Change in water extractable organic carbon and microbial PLFAs of biochar during incubation with an acidic paddy soil.


Biochar is a carbon-rich, solid and porous material produced by pyrolysis of biomass feedstock under anaerobic conditions (Lehmann and Joseph 2009). Biochars can be manufactured from a wide range of agro-forest residues and industrial wastes (Singh et al. 2010b; Yuan and Xu 2012). Biochar has been proposed as a soil amendment to sequester carbon (Ouyang et al. 2014), reduce greenhouse gas emissions (Singh et al. 2010a), enhance soil nutrient retention and fertility (Glaser et al. 2002; Steiner et al. 2008), and improve crop yield (Jones et al. 2012). Singh et al. (2014) also concluded that biochar affects pesticide efficacy, adsorbs inorganic and organic contaminants, and can induce many other changes within the soil ecosystem.

Significant studies have been undertaken to determine the mechanisms by which biochars are stabilised in soil and how the biochar itself changes the properties of soils (Fang et al. 2014; Kuzyakov et al. 2014). Studies suggested that the change of biochar morphological and chemical properties (Brodowski et al. 2005; Joseph et al. 2010), and the biodegradation of biochar can happen within a very short period after application to soil (Kuzyakov et al. 2014; Santos et al. 2012). However, little attention has been paid to the transformation of biochars' labile components, especially sensitive indicators such as the WEOC components (Jones et al. 2012; Lin et al. 2012). WEOC, although only a minor components of biochar can have a significant affect in terms of inducing resistance to plant disease, germination, changes in microbial population and redox reactions (Joseph et al. 2013). Biochar WEOC are composed of organic acids, phenols, and carbohydrates (Chia et al. 2014), and high molecular compounds that have characteristics of biopolymers, humics and oxidised humics (Lin et al. 2012). The components of biochar WEOC are available to soil microorganisms as an energy source and can stimulate the microbial activity (Wamock et al. 2007; Lehmann et al. 2011). WEOC content can directly add to the pool of dissolved organic carbon in soil ecosystem (Lin et al. 2012). Biochar can adsorb soil organic compounds such as catechol and humic acids (Kasozi et al. 2010), and affect the transformation of soil organic matter due to its catalytic properties (Cross and Sohi 2011).

Application of biochar to soil affects the relative abundance and activity of soil microbes, through complicated mechanisms that involve changes in habitat, availability of macro and micronutrients, and water pore content (Kolb et al. 2009; Luo et al. 2013), pH and Eh (Farrell et al. 2013). Kolb et al. (2009) observed that biochar application increases the soil microbial biomass and activity. Farrell et al. (2013) found that the composition of microbial community shifted with biochar addition to an aridic soil. Moreover, Jones et al. (2012) concluded at the end of a three year field study, that changes in microbial population persisted even though biochar was not changing soil properties. Although there have been a significant number of studies that examine the changes in soil microbial population after biochar amendment (Kolb et al. 2009; Jindo et al. 2012), the mechanisms by which these changes occur are not well understood. In particular, there have been no studies that relate the changes in microbial population to changes in the WEOC of the aging biochar and the soil surrounding the biochar particle (the charsphere, Luo et al. 2013). PLFAs analysis is a useful tool for characterising the profile of microbial community structure in response to environmental change (Zelles 1999), and provides information about the abundance of different microbial groups that are involved in the decomposition of biochar in soil (Santos et al. 2012).

Thus, through an incubation experiment, we mixed the coarse fraction (2-5 mm) of six biochar samples with an acidic paddy soil to: (i) determine the changes of biochar WEOC content and its absorbance characteristics at 280 nm; (it) examine the profile of biochar microbial PLFAs concentration and community composition after incubation; and (iii) evaluate the relationship between biochar chemical properties and its biological profile within short-term incorporation into soil.

Materials and methods

Biochar production

Biochars were produced from three crop residues (rice, peanut and com straw) and two types of wood (bamboo and pine chips). Feedstocks were oven-dried for 12 h at 80[degrees]C and then pyrolysed in an oxygen starved environment using a patented slow pyrolysis process (China Patent No. ZL200920232191.9). Crop straw was pyrolysed at 300[degrees]C, 400[degrees]C and 500[degrees]C, while wood chips were pyrolysed at 400[degrees]C. Temperatures were increased by 5[degrees]C [min.sup.-1] to the target temperature and maintained for 4h (Chun et al. 2004). Biochars were cooled to room temperature inside the furnace reactor and carefully stored in a vacuum desiccator.

Soil sampling and characteristics

After the harvest of late rice in Dec 2012, soil samples were collected from paddy fields at the Ecological Station of Red Soil Chinese Academy of Sciences in Yingtan, Jiangxi Province, China (28[degrees]15'3"N, 116[degrees]55'30"E). The studied soil was identified as Anthrosols base on China Soil Taxonomy (Chen et al. 2015). This region is characterised by a typical subtropical monsoon climate with an annual precipitation of 1795 mm, annual evaporation of 1318 mm and mean annual temperature of 17.6[degrees]C. Soil samples were taken from a depth of 0-20 cm, removed visible plant debris, then air-dried and passed through a 2-mm sieve. Soil basic properties as follows: pH, 5.57; organic carbon, 20.9 g [kg.sup.-1]; total N, 2.17 g [kg.sup.-1]; available P, 54.6 mg [kg.sup.-1]; available K, 130.0 mg [kg.sup.-1]; cation exchange capacity (CEC), 8.37 cmol [kg.sup.-1].

Soil pH was determined using a pH meter in a 1 : 5 (v/v) suspension of soil and deionised water (Lu 1999). Organic carbon, total N, available P and K were respectively determined by Tyurin, Kjeldahl, Olsen and burnt-luminosity methods. Soil CEC was determined using the ammonium acetate method at pH 7.0 (Lu 1999).

Measurement of biochars' elemental composition and chemical properties

Biochar samples were passed through a 0.15 mm sieve before analysis. Elemental contents were analysed using an Elementary Analyzer (Vario EL III, Germany), while ash content (%) was determined base on the weight before and after dry combustion in a muffle furnace at 800[degrees]C for 4h. Oxygen content (%) was estimated as follows: 0%= 100% - (C% + H% + N% +Ash%). Three replicates were used for each analysis. The pH value of biochar was measured in deionised water (1:25 w/v) with a pH meter (pHS-2F, China). The CEC, total P and cation concentration ([K.sup.+], [Na.sup.+], [Ca.sup.+] and [Mg.sup.2+]) for the biochars were measured using the method described by Yuan and Xu (2012).

Design of laboratory incubation experiment

Six biochar samples were tested: com straw produced at 300[degrees]C, 400[degrees]C and 500[degrees]C (CB300, CB400, CB500 respectively); rice straw pyrolysed at 500[degrees]C (RB500) and peanut straw and bamboo chips produced at 400[degrees]C (PB400 and BB400, respectively). These biochars were passed through a 5-rnm sieve, followed by a 2-mm sieve to obtain the coarse fraction (2-5 mm) and such fraction accounted for 50-70% of the total biochar material. 250 g of air-dried soil samples were thoroughly mixed with 2.5 g of each biochar (equal to 1% w/w) and placed in 500 mL plastic bottles. Deionised water was added to bring soil water content to 60% of field water-holding capacity. Bottles were covered with sterile membranes that permit gaseous exchange and minimise moisture loss. All bottles were placed in a temperature-constant incubator at 25[degrees]C for 75 days and deionised water was added every seven days to maintain constant moisture content. Each treatment had three replicates.

Extraction of biochar WEOC and microbial PLFAs contents

Biochar fragments were carefully collected from biocharamended soils using tweezers after 15, 45 and 75 days of incubation. Whenever possible, only particles and pieces of biochar were picked up, while those with visible adhering soil particles were avoided (Luo et al. 2013). A portion of the fresh sample was stored for one week at 4[degrees]C when analysis of WEOC was carried out. A portion of the fresh sample was stored at -20[degrees]C and freeze-dried before microbial PLFAs analyses.

Biochar (0.20 g) was weighed, dispersed in 50 mL ultrapure water, shaken for 30 min and then centrifuged at 1660 g for 20 min. The samples were subsequently passed through 0.45 [micro]m polytetrafluoroethylene filters. The WEOC concentration of the filtrate was determined with a Multi N/C 3100 analyzer (Jena, Germany), while the UV absorbance characteristic at 280 nm was measured by UV/VIS-2450 to evaluate the aromaticity of biochar WEOC content (Weishaar et al. 2003).

Phospholipid fatty acid analysis was adapted to investigate the microbial biomass and community composition of biochar. A weight of 0.80 g biochar sample was analysed by the modified Bligh-Dyer technique to determine the PLFAs concentration (Bligh and Dyer 1959). Briefly, biochar samples were incubated in a solution of methanol, chloroform, and phosphate buffer in ratio of 2 : 1 : 0.8, shaken for 2 h and centrifuged, after which the chloroform phases were collected and stored. Phospholipids were then separated from glycolipids and neutral lipids, saponified and methylated to fatty-acid methyl esters (FAME), and then were identified by gas chromatography (Agilent 7890GC, USA). Peaks were identified based on the comparison of retention times with known standards, and the concentration of each PLFA was calculated by comparing the peak area of internal standard. Patterns of PLFA were determined according to Frostegard et al. (1993) and Zelles (1999). Twenty two individual PLFAs were detected and grouped as follows: general bacteria (12:0, 13:0, 14:0, 16:0, 16:0N, 17:0, 18:0, 20:0), Gram-positive bacteria (i15:0, al5:0, i16:0, al6:0, i17:0, al7:0, i18:0), Gram-negative bacteria (16:1[omega]6c, 18:0 2OH, 17:0 3OH, 18:1[omega]7c), fungi (18:1[omega]9c, 18:2[omega]6,9c) and 10Me 18:1[omega]7c as actinobacteria (Frostegard et al. 1993). Microbial biomass was indicated by the sum of PLFAs concentration.

Statistical analysis

Data analysis was conducted using SPSS for windows Version 18.0. Differences in properties of biochar were determined by ANOVA with the Least Significant Difference (l.s.d.) method at P < 0.01. Nonlinear regressions were conducted to determine the correlation coefficients between microbial PLFA concentrations and initial properties of biochar. Redundancy analysis (RDA) is an ordination technique based on principal component analysis, in which ordination axes are constrained to be linear combinations of environmental factors, thus allowing direct assessment of the relationship between environmental factors (biochar chemical properties) and variations in the multivariate data (microbial PLFAs community structure). Monte Carlo permutation test and 'envfit' function were carried out to examine the significances of axes and environmental variables. Multivariate analysis was carried out using the Vegan package in R software (2.15.0) and artwork was obtained by using Origin 8.0 and Sigmaplot 12.0


Elemental composition and chemical properties of biochars

Biochar samples became richer in carbon contents as pyrolysis temperature increased from 300[degrees]C to 500[degrees]C, while nitrogen, hydrogen and oxygen content decreased. Woodchip-based biochar had higher C/N ratios than the straw-based ones (Table 1). Both the O/C and H/C molar ratios decreased with the increasing pyrolysis temperature and all biochar products had lower O/C value than their precursor. Both feedstock type and pyrolysis temperature had significant effects on biochar pH, total P, base cations and CEC (Table 2; P<0.01). The pH values of biochar samples were alkaline and ranged from 7.67 to 10.25. Both total P and base cations increased with the increasing temperature and straw biochars were higher than woodchip biochars. The CEC content decreased from 35.8 to 3.98 cmol [kg.sup.-1] with the increasing temperature.

Change of biochar WEOC content and the UV absorbance

At beginning, the WEOC content of biochar samples varied from 359.5 to 2844.0 mg [kg.sup.-1]. Sample BB400 contained the lowest WEOC content, whereas RB500 and PB400 were significantly higher in WEOC than other biochars (Fig. 1a). The content of WEOC decreased with the increasing pyrolysis temperature for com straw biochars. Most of these values significantly reduced to 27.5-81.1% of their initial values (Fig. 1a), when measured on day 75. However, BB400 significantly increased from 359.5 to 900.0 mg [kg.sup.-1], and there was no significant change for CB500 (Fig. 1a). After 15 days, the WEOC significantly decreased by up to 61.2% (P<0.05), except for BB400 which showed no significant change during this period (P > 0.05, Fig. 1a). There was no significant change in WEOC contents of all the six biochar samples between day 15 and 45 (P>0.05). During the last 30 days, the WEOC increased on average from 491.3 to 742.8 mg [kg.sup.-1] (P< 0.05, Fig. 1a).

Before incubation, the UV absorbance values of WEOC varied from 0.013 to 0.064, with the highest in CB300 and the lowest in BB400 (Fig. 1b). After 75 days of incubation, the absorbance values of biochar WEOC significantly decreased to then range of 0.002- 0.008 (P< 0.05). Except for PB400, the absorbance values of WEOC for the other biochars significantly decreased by an average of 52.5% at day 15 (P< 0.05, Fig. 16). For example, the UV absorbance value of WEOC content in sample CB300 decreased from 0.064 to 0.037. No significant change in the absorbance value of biochar WEOC was measured between day 15 and 45 (P>0.05), mirroring the WEOC results. In the last 30 days of incubation, the absorbance values of WEOC for three com biochars significantly decreased by 58.8% (Fig. 1b, P< 0.05), whereas no significant change for samples RB500, PB400 and BB400 (P> 0.05) was measured.

Profiles of biochar microbial phospholipid fatty acids

The concentrations of microbial total PLFAs differed among biochars, with the three com straw biochars being higher than RB500, PB400 and BB400 (Table 3, P< 0.05). General bacteria dominated the microbial community and the percentage ranged from 58.9 to 81.7% for all biochars. CB300 and CB400 were significantly richer in bacteria than other four biochars (P< 0.05). Sample CB500 had the highest gram-positive bacterial concentration of 16.17 [+ or -] 2.85 nmol [g.sup.-1], while no gram-positive species was detected in BB400. Fungi were less abundant than bacterial group for all biochar samples, with PB400 fungal concentration being 1.93 [+ or -] 0.24 nmol [g.sup.-1]. The gram-negative group was observed in CB300 and CB400, while actinobacteria was only detected in CB300 (Table 3).

Regression analysis showed that there was a correlation between some of the biochars' chemical properties and microbial total PLFAs concentration. A quadratic model fitted the TN and TP data, which suggests a U shaped response to concentration of biochar (Fig. 2). Similar findings have been reported by Kammen and Graber (2015). The lowest concentration of total PLFAs was measured when biochar TN and TP were 11.0 and 2.5 g [kg.sup.-1], respectively. Although sample BB400 had a lower concentration of TN and TP than RB500 and PB400, it had a higher total PLFAs concentration (Fig. 2a, b). As shown in Fig. 2, the total PLFAs concentration was negatively correlated with biochar pH ([r.sup.2] = 0.79, P < 0.01), base cations ([r.sup.2] = 0.86, P < 0.05) and WEOC content ([r.sup.2] = 0.64, P < 0.05), respectively. The highest concentration of total PLFAs was found when the biochar pH was 8.33 (Fig. 2c) and the content of WEOC was 1.15 g [kg.sup.-1] (Fig. 2e), respectively. Besides, there was no significant correlation between total PLFA concentration and the UV absorbance properties (P > 0.05, Fig. 2f).

RDA analysis suggested that a total of 60.51 % variation in the PLFA data can be explained by the first two axes (Fig. 3), and the selected biochar chemical properties significantly affect the microbial community composition (Monte Carlo Permutation tests, P < 0.01). Biochar pH and WEOC were positively correlated with axis of RDA 1, while TN, TP were negatively related to RDA1. Analysis results also indicated that the effects of each selected biochar chemical properties on microbial PLFA community structure were significant (data not shown, P<0.05). The biplot of RDA also showed that the composition of PLFA community varied among biochar samples, and the sum of 22 fatty acids were recognised (Fig. 3). Furthermore, three com straw biochars had a higher abundance of microbial species compared with sample RB500, PB400 and BB400 (Fig. 3). For example, the subpoints of general and gram-positive bacteria were closer to CB300 and CB400 when compared with other biochar samples. Consistent with the results shown in Fig. 2, the concentrations of categorical PLFAs were also positively correlated with biochar TN and TP, but are negatively related to biochar pH, BFG and WEOC (Fig. 3).


Properties of biochar water extractable organic carbon content

Though the WEOC fraction accounts for a small proportion, as shown only 0.04-0.52% of the biochars' total carbon content in our study, it is responsible for many important processes in soil biochemical cycles including of stimulating microbial growth, increasing rates of germination and enhancing nutrient uptake (Lin et al. 2012; Farrell et al. 2013; Joseph et al. 2013). In our study, it was found that the greatest reduction of biochar WEOC content is detected in the first 15 days of incubation (Fig. 1a). There are several possible reasons for this reduction in biochar WEOC quantity: (i) the porous structure of biochar was likely to provide a suitable habitat for microbial growth, and then the microorganisms could decompose the WEOC that adsorbed on the surface and within pores of biochar (Santos et al. 2012; Farrell et al. 2013); and (ii) the labile organic components of biochar could immediately contribute to the C[O.sub.2] evolution from soil, even within short-term incorporation (Cross and Sohi 2011). Moreover, the complex reactions between biochar and soil components, consisting of dissolution-precipitation, redox, surface cation charge, sorption and interaction of biocharorganic matter-mineral, could also be responsible for the decrease in biochar WEOC content (Joseph et al. 2010). However, a significant increase in WEOC content for biochar samples was also recognised during the last 30 days of incubation (Fig. 1a). The adsorption of a range of high and low molecular weight organic compounds to biochar from the soil could change the total WEOC measured on the biochar (Nguyen et al. 2007; Joseph et al. 2010). Luo et al. (2013) mentioned that the accumulation of soil microorganisms and their metabolites that colonised the biochar could increase WEOC.

The absorbance values of biochar WEOC significantly decreased with the increasing pyrolysis temperature for com straw biochars (Fig. 1b), due to the reduction of low molecular weight neutrals and humic acids components in biochar (Lin et al. 2012). Moreover, the WEOC of BB400 was much lower in UV absorbance than straw derived biochars, which might result from the relative proportions of lignin, cellulose, hemicellulose, extractives and minerals of the raw material (Lin et al. 2012). It had been suggested that different molecular weight organic compounds may be utilised by different microorganisms at different rates of consumption (Kalbitz et al. 2000; Lin et al. 2012; Chia et al. 2014). Microbial decomposition of the low molecular labile carbon will probably occur rapidly which could explain the initial decrease in WEOC content (Fig. 1a) and its absorbance value (Fig. 1b). Once these were depleted, the soil microbes metabolise the more recalcitrant high molecular weight compounds such as biopolymers, humics and oxidised humics (Lin et al. 2012). A significant positive correlation was observed between biochar WEOC content and its UV absorbance value in our study (Pearson coefficient t = 0.30, P = 0.011, n = 72), which would indicate the utilisation of those high molecular weight compounds after the first 15 days. However, the changes of biochar WEOC content and its UV absorbance were inconsistent during the last 30 days of incubation in this study (Fig. 1). Since the interaction between biochar particles and soil components will accelerate after the first 2 weeks of incorporation, it is conceivable that the adsorption of dissolved organic carbon, nitrate and cations to the biochar may influence the UV absorbance properties of biochar WEOC (Weishaar et al. 2003).

Properties of biochar microbial biomass and community composition

Previous studies suggested that the biochar material could be colonised by soil microorganisms during a short-term laboratory incubation (Luo et al. 2013) or during longer term field trials (Jones et al. 2012), due to the high pore volume with a diameter >1 micron providing habitat (Jindo et al. 2012), and the availability of labile organic contents (Lehmann et al. 2011). In this study, we also observed that various kinds of microorganisms colonised the porous biochar structure (Table 3). Further, we quantified the microbial biomass and community structure of such colonisation by PLFAs analysis, and found that the general bacteria are the dominant microbial group (Table 3). Although previous studies suggested that gram-positive bacteria can decompose the aromatic structure of biochar (Farrell et al. 2013; Santos et al. 2012), we found that gram-positive bacteria had a much lower abundance than general bacteria for most biochar samples, except for CB500 (Table 3). Fungi content had a much lower abundance for all biochar samples compared with the general bacteria group (Table 3). This could be due to the greater ability of bacteria to utilise the biochar nutrients (Farrell et al. 2013) or also because of the poor mobility of fungi hyphal network (Wamock et al. 2007). The results of these experiments indicated that the general bacteria group played an important role in biochar decomposition within such a short-term incubation period (Table 3). However, it is important to note that the effect of biochar addition on microbial community structure is always soil type dependent (Rousk et al. 2013), and the biological profile of the soil will have a significant effect on the microbial community composition on the biochar's surfaces (Chen et al. 2015).

It has been shown that addition of biochar can influence the activity and structure of soil microbial community through altering soil organic matter availability (Lehmann and Joseph 2009), ameliorating the acidic pH condition (Farrell et al. 2013), and other aspects of soil physical and chemical properties (Lehmann et al. 2011). There was a positive correlation between total PLFAs concentration and biochar nutrient content (Fig. 2a, b), and in particular there was a significant influence of biochar TN and TP on the composition of microbial community (Fig. 2, Fig. 3). Different biochars with varying chemical and physical properties could induce different changes to total microbial biomass and community composition (Atkinson et al. 2010). The highest measured microbial biomass and greatest abundance of microbial species was measured in the three com straw biochars (Table 3). This could be due to their high nutrient content or open porous structure (Table 1, Table 2) or their ability to increase availability of nutrients in acid soil (Slavich et al. 2013). Although BB400 had a lower TN and TP content than RB500 and PB400 (Fig. 2), it had a higher concentration of PLFAs concentration, which might due to its specific structural properties and the composition and concentration of its labile organic molecules (Atkinson et al. 2010). Though previous studies indicated that biochar pyrolysed at lower temperature resulted in increased colonisation of microorganisms (Luo et al. 2013) and altered intercellular communication (Masiello et al. 2013), we found no significant difference in total PLFAs contents between the three com straw biochars (Table 3).

Our study indicated that biochar pH and content of base cations are correlated with total PLFAs content (Fig. 2c, d), and significantly affect the microbial PLFAs community composition of biochar (Fig. 3). Such results are in agreement with those of biochar amended soils, where pH is the main driver of microbial community change (Farrell et al. 2013; Nielsen et al. 2014) and a lower pH can lead to a more favourable habitat for the growth of microbes (Luo et al. 2013). We found that com straw biochars with lower pH value had a higher concentration of PLFAs than other biochars (Table 3). The highest abundance of microorganism occurred at a pH of ~8.3 (Fig. 2c). Previous studies demonstrated that the WEOC content of biochar could be an important regulator for the microbial activity in the charsphere as well as in soil (Thies and Rilling 2009; Schmidt et al. 2011). Though higher concentrations of biochar WEOC have been shown to be responsible for the higher microbial biomass (Luo et al. 2013), regression results in this study indicated that initial biochar WEOC concentration has a negative correlation with total PLFAs concentration (Fig. 2e). Moreover, biochar initial concentration of WEOC had less influence on the composition of microbial community compared than other measured chemical properties of biochar (Fig. 3). This in part could be due to the make up of the organic compounds some of which may not be initially available as a source of food for microbes (Lin et al. 2012). Joseph et al. (2010, 2013) have observed that the surfaces of biochar can act as catalysts promoting both the decomposition and formation of minerals and labile organic compounds as soil and environmental conditions change. As these chemical and physical changes occur on the surface of the biochars, the microbial diversity and abundance will change. In addition, Jones et al. (2012) noted that the components of soil will influence microbial population dynamics on the reacting biochar surfaces.


The elemental composition and chemical properties of biochar varied with feedstock type and pyrolysis temperature. The WEOC content of biochars decreased during the incubation period, except for BB400. The majority in reduction of biochar WEOC occurred within the first 15 days, no significant change was observed for biochars between day 15 and 45, while an apparent increase was measured for all biochars in the last 30 days. There was a positive relationship between biochar WEOC content and its UV absorbance properties, and the reactions between biochar and soil components during this short period of incorporation. Com straw biochars were more abundant in microbial PLFAs concentrations and species than other types of biochars. General bacterial was the dominant group in colonising biochar samples compared with other kinds of microbes. The chemical properties were correlated with microbial total PLFAs concentration, and significantly related to the microbial community composition of biochar.


This study was jointly supported by funding from the National Natural Science Foundation of China (No. 41171233) and the National Basic Research Program of China (2014CB441000). We acknowledge Helen Gould for her help in improving the readability of the paper and thank Associate Prof. F. X. Han for his constructive comments on this manuscript, which greatly improved the quality of our article.


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Ming Li (A,B), Ming Liu (A), Stephen Joseph, (C,D,E), Chun-Yu Jiang (A), Meng Wu (A), and Zhong-Pei Li, (A,B,F)

(A) State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.

(B) University of Chinese Academy of Sciences, Beijing 100049, China.

(C) Discipline of Chemistry, University of Newcastle, Callaghan, NSW 2308, Australia.

(D) University of New South Wales, School of Material Science and Engineering, NSW 2052, Australia,

(E) Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China.

(F) Corresponding author. Email:

Table 1. Elemental composition and atomic ratios of biochars
produced under different feedstock and pyrolysis temperature

Feedstock         Pyrolysis                Elemental compositAsh (%)
                ([degrees]C)      C      H      N       O

Rice straw             0        41.57  6.45   0.74   39.31   11.93
                     300        55.90  5.97   1.38   13.08   23.67
                     400        55.73  4.70   1.11   10.35   28.11
                     500        56.93  3.55   1.26    7.06   31.19
Peanut straw           0        44.73  6.69   1.36   38.98    8.24
                     300        54.24  5.58   2.09   15.92   22.18
                     400        54.72  4.25   1.75    8.97   30.31
                     500        57.01  3.34   1.35    5.32   32.98
Com straw              0        43.58  6.45   1.15   40.29    8.53
                     300        63.32  5.88   3.11   14.97   12.72
                     400        63.39  5.04   2.74   12.92   15.92
                     500        65.09  4.18   2.75    3.75   24.22
Bamboo chips           0        46.45  6.57   0.74   45.69    0.55
                     400        88.99  3.50   0.18    4.62    2.70
Pine chips       0[degrees]C    70.15  1.85   0.32   26.69    0.98
                400[degrees]C   76.45  4.47   0.29   16.25    2.53

Feedstock            Atomic ratio

                  C/N    O/C    H/C

Rice straw       56.55   0.95   0.16
                 40.50   0.23   0.11
                 50.19   0.19   0.08
                 45.36   0.12   0.06
Peanut straw     32.97   0.87   0.15
                 25.96   0.29   0.10
                 31.31   0.16   0.08
                 42.14   0.09   0.06
Com straw        37.81   0.92   0.15
                 20.37   0.24   0.09
                 23.15   0.20   0.08
                 23.63   0.06   0.06
Bamboo chips     62.67   0.98   0.14
                498.88   0.05   0.04
Pine chips      217.53   0.38   0.03
                261.39   0.21   0.06

Table 2. Chemical properties of biochars produced under
different feedstock and pyrolysis temperature

Within columns, means followed by different letters are
significantly different at P<0.01 (n = 3). BC, base cations,
the sum of the total [Ca.sup.2+], [Mg.sup.2+], [K.sup.+] and
[Na.sup.+]; CEC, cation exchange capacity groups

Feedstock        Pyrolysis      pH      Total P (g
                temperature            [kg.sup.-1])

Rice straw          300        9.3d       2.80d
                    400        9.9g       3.05e
                    500        I0.2h      3.64f

Peanut straw        300        9.3d       2.41c
                    400        I0.3h      2.78d
                    500        9.6ef      2.97e

Com straw           300        7.7a       5.17g
                    400        8.7c       5.64h
                    500        9.7f       6.22i

Bamboo chips        400        9.5e       0.81b
Pine chips          400        8.1b       0.39a

Feedstock          BC (g           CEC
                [kg.sup.-1])      (cmol

Rice straw         60.4f          35.8e
                   66.2g          19.6cd
                   79.2h          12.8b

Peanut straw       53.8e          19.8cd
                   67.0g          7.00a
                   79.6h          7.21a

Com straw          37.7c          21.9d
                   43.9d          17.0c
                   46.6d          3.98a

Bamboo chips       14.5b          7.14a
Pine chips         8.60a          16.8c

Table 3. Concentration of phospholipid fatty acids (PLFAs)
assigned to different microbial groups, i.e. general
bacteria, [G.sup.+] (Gram-positive bacteria), [G.sup.-]
(Gram-negative bacteria), fungi and actinobacteria of
biochars after 75 days of incubation

Values in table are the mean [+ or -] s.d. of three
replicates. ND, Not detected. Within the same column, means
followed by different letters indicate significant
differences at P< 0.05. CB300, CB400, CB500 are com straw
biochars pyrolysed at 300[degrees]C, 400[degrees]C, and
500[degrees]C, respectively; RB500 is rice straw biochar
pyrolysed at 500[degrees]C; PB400 is peanut straw biochar
pyrolysed at 400[degrees]C; BB400 is bamboo chips biochar
pyrolysed at 400[degrees]C

Biochars                 Concentrations of PLFA
                        groups (nmol [g.sup.-1])

                   Total                General

CB300       54.3 [+ or -] 1.5b    40.3 [+ or -] 1.6b
CB400       60.4 [+ or -] 12.7b   50.1 [+ or -] 10.7b
CB500       49.8 [+ or -] 3.7b    29.0 [+ or -] 3.2ab
RB500       16.8 [+ or -] 2.0a    13.8 [+ or -] 1.2a
PB400       15.6 [+ or -] 7.4a    13.0 [+ or -] 7.6a
BB400       31.7 [+ or -] 8.7ab   28.1 [+ or -] 8.0ab

Biochars                 Concentrations of PLFA
                        groups (nmol [g.sup.-1])

                  [G.sup.+]             [G.sup.-]

CB300        1.94 [+ or -] 0.62a    6.55 [+ or -] 1.12
CB400        2.73 [+ or -] 0.10a    0.51 [+ or -] 0.72
CB500       16.17 [+ or -] 2.85b            ND
RB500        0.46 [+ or -] 0.03a            ND
PB400        0.62 [+ or -] 0.37a            ND
BB400                ND                     ND

Biochars                 Concentrations of PLFA
                        groups (nmol [g.sup.-1])

                    Fungi             Actinobacteria

CB300       4.70 [+ or -] 0.52ab    0.78 [+ or -] 0.11
CB400        7.06 [+ or -] 1.10b            ND
CB500       4.64 [+ or -] 2.32ab            ND
RB500       2.54 [+ or -] 0.76ab            ND
PB400        1.93 [+ or -] 0.24a            ND
BB400       3.60 [+ or -] 0.7 lab           ND
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Author:Li, Ming; Liu, Ming; Joseph, Stephen; Jiang, Chun-Yu; Wu, Meng; Li, Zhong-Pei
Publication:Soil Research
Article Type:Report
Geographic Code:9CHIN
Date:Oct 1, 2015
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