Effects of Different Biochars on Pinus elliottii Growth, N Use Efficiency, Soil N2O and CH4 Emissions and C Storage in a Subtropical Area of China

Pedosphere 27(2): 248–261, 2017 doi:10.1016/S1002-0160(17)60314-X ISSN 1002-0160/CN 32-1315/P c 2017 Soil Science Society of China ⃝ Published by Elsevier B.V. and Science Press

Effects of Different Biochars on Pinus elliottii Growth, N Use Efficiency, Soil N2 O and CH4 Emissions and C Storage in a Subtropical Area of China LIN Zhibin1,2 , LIU Qi1,2 , LIU Gang1 , Annette L. COWIE3 , BEI Qicheng1 , LIU Benjuan1,2 , WANG Xiaojie1,2 , MA Jing1,2 , ZHU Jianguo1 and XIE Zubin1,4,∗ 1 State

Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China) 2 University of Chinese Academy of Sciences, Beijing 100049 (China) 3 University of New England, Rural Climate Solutions, Armidale NSW 2351 (Australia) 4 Jiangsu Biochar Engineering Center, Nanjing 210008 (China) (Received April 16, 2016; revised January 16, 2017)

ABSTRACT Intensive management of planted forests may result in soil degradation and decline in timber yield with successive rotations. Biochars may be beneficial for plant production, nutrient uptake and greenhouse gas mitigation. Biochar properties vary widely and are known to be highly dependent on feedstocks, but their effects on planted forest ecosystem are elusive. This study investigated the effects of chicken manure biochar, sawdust biochar and their feedstocks on 2-year-old Pinus elliottii growth, fertilizer N use efficiency (NUE), soil N2 O and CH4 emissions, and C storage in an acidic forest soil in a subtropical area of China for one year. The soil was mixed with materials in a total of 8 treatments: non-amended control (CK); sawdust at 2.16 kg m−2 (SD); chicken manure at 1.26 kg m−2 (CM); sawdust biochar at 2.4 kg m−2 (SDB); chicken manure biochar at 2.4 kg m−2 (CMB); 15 N-fertilizer alone (10.23 atom% 15 N) (NF); sawdust biochar at 2.4 kg m−2 plus 15 N-fertilizer (SDBN) and chicken manure biochar at 2.4 kg m−2 plus 15 N-fertilizer (CMBN). Results showed that the CMB treatment increased P. elliottii net primary production (aboveground biomass plus litterfall) and annual net C fixation (ANCF) by about 180% and 157%, respectively, while the the SDB treatment had little effect on P. elliottii growth. The 15 N stable isotope labelling technique revealed that fertilizer NUE was 22.7% in CK, 25.5% in the NF treatment, and 37.0% in the CMB treatment. Chicken manure biochar significantly increased soil pH, total N, total P, total K, available P and available K. Only 2% of the N in chicken manure biochar was available to the tree. The soil N2 O emission and CH4 uptake showed no significant differences among the treatments. The apparent C losses from the SD and CM treatments were 35% and 61%, respectively; while those from the CMB and SDB treatments were negligible. These demonstrated that it is crucial to consider biochar properties while evaluating their effects on plant growth and C sequestration. Key Words:

biochar properties, C sequestration,

15 N-fertilizer

application, emissions of greenhouse gases, planted forest, soil fertility

Citation: Lin Z B, Liu Q, Liu G, Cowie A L, Bei Q C, Liu B J, Wang X J, Ma J, Zhu J G, Xie Z B. 2017. Effects of different biochars on Pinus elliottii growth, N use efficiency, soil N2 O and CH4 emissions and C storage in a subtropical area of China. Pedosphere. 27(2): 248–261.

The role of planted forests in the global C cycle has gained increasing attention in many countries, as planted forests have the potential to sequester C in living vegetation and soil organic matter (P´erezCruzado et al., 2012). Due to increasing demands for timber, the area of planted forests has increased rapidly during the last decades, and wood supply (especially industrial roundwood) is shifting from natural forest to planted forest (FAO, 2010). China had an area of 62 × 106 ha of planted forest in 2008 (Zhang, 2006; SFA, 2010). Sixty three percent of the forest plantations are in South China (Ren et al., 2007; SFA, 2007; Ma et al., 2014). Short rotations, due to increased tim∗ Corresponding

author. E-mail: [email protected].

ber demands and intensive harvest, have led to high rates of nutrient removal (Laclau et al., 2003) and soil fertility decline (Fox, 2000; Chen et al., 2013). As a consequence of soil fertility decline, stand biomass increments decrease (Zhang et al., 2004, 2009). Zhang et al. (2009) reported that stand biomass increment declined by 24% from the first to second rotation, and by a further 40% from the second to third rotation in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations in Hunan Province, China. Both scientists and timber producers are concerned about sustaining the productivity of successive fast-growing plantations in subtropical area of China (Zhang et al., 2009).

BIOCHAR EFFECTS ON C AND N DYNAMICS

Biochar has been proposed as a soil amendment to improve soil properties and to abate climate change by sequestering C, because of biochar’s relative recalcitrance, and by reducing N2 O and CH4 emissions from soil (Robertson et al., 2012; Xie et al., 2013). The benefits of biochar to soil fertility include raising soil pH and cation exchange capacity (CEC) (Lehmann et al., 2003), improving soil physical structure (Chan et al., 2007) and providing nutrients for plant growth (Singh et al., 2010; Slavich et al., 2013). However, the effects of biochars on soil properties largely depend on biochars’ properties, which vary widely between different biochars, mainly due to variations in feedstock materials (Kookana et al., 2011; Alburquerque et al., 2014) and also pyrolysis conditions (Singh et al., 2012; Wang et al., 2013). Manure-derived biochar generally contains higher pH, higher CEC and higher levels of essential plant nutrients, such as organic N, soluble P and K (Shinogi et al., 2003), than plant-derived biochar (Singh et al., 2010). Previous studies showed that application of manure-derived biochar to soil improved field-saturated hydraulic conductivity, increased soil pH, total N (TN), total C (TC), exchangeable base cations and CEC (Uzoma et al., 2011), decreased soil exchangeable acidity (Yuan and Xu, 2012) and enhanced nutrient availability (Omil et al., 2013). It is, thus, expected that biochar derived from animal manures may have greater effects on improving soil fertility and plant growth, overcoming soil degradation caused by successive rotations. However, plant-derived biochars generally have higher TC than manure-derived biochar, and lower decomposition rates (Singh et al., 2010), so they may be more effective in enhancing soil C storage. On the other hand, some researches showed that biochars have potential to improve N fertilizer uptake in soils via decreasing NH3 volatilization (Steiner et al., 2010), decreasing NO− ere˜ na et al., 2013) and 3 leaching (G¨ changing bacterial abundance (Ball et al., 2010). However, the effect of different biochars on N use efficiency (NUE) is still argued. G¨ere˜ na et al. (2013) reported that addition of maize stover biochar to fertile soil in a temperate climate did not improve NUE, but Slavich et al. (2013) showed that feedlot manure biochar may improve NUE by 23%. Knowledges of the overall effects of manure- and plant-derived biochars on forest soil fertility, tree growth, fertilizer NUE, and C sequestration potential are still limited. In addition, biochar can affect soil physical and chemical properties, e.g., nutrient availability, pH, waterholding capacity and soil structure (Lehmann et al., 2003; Chan et al., 2007). However, the changes of soil properties vary between plant- and manure-derived

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biochars, which may affect soil N2 O and CH4 emissions differently (Malghani et al., 2013; Xie et al., 2013). Yu et al. (2013) reported that a forest soil treated with chicken manure biochar (pyrolysis at 540 ◦ C) significantly reduced the emission of CH4 at 35% and 60% water-filled pore space (WFPS) and increased emission of CH4 at 85% WFPS. Malghani et al. (2013) reported that corn silage biochar (slow pyrolysis at 500 ◦ C) addition (1%, weight/weight) had almost no impact on CH4 and N2 O emissions in deciduous forest soil. So far, there are some mechanisms that have been proposed to explain the effect of biochar on greenhouse gas (GHG) emissions from soil including soil pH change because of biochar alkalinity (Kookana et al., 2011), soil bulk density change because of biochar porosity (Yanai et al., 2007) and soil labile C and N changes because of soil high sorption ability and C content (Keith et al., 2011; Lin et al., 2012). Because of widely various properties of biochars which derived from different feedstocks, especially differences between plant- and manure-derived biochars, the effects of biochars on soil N2 O and CH4 emissions are controversial. However, most research on the effects of biochar on forest soil GHGs was conducted under incubation conditions (Malghani et al., 2013; Yu et al., 2013). The effects of biochar on forest soil GHGs under field condition have been poorly studied. Therefore, more research should be focused on the effects of plant- and manure-derived biochars on forest soil N2 O and CH4 emissions under field condition. This study aimed to investigate the effects of two contrasting biochars, pyrolyzed from sawdust and chicken manure and applied to an acidic forest soil in South China, on (i) soil fertility and planted forest growth, (ii) fertilizer NUE using the 15 N-labeling technique, (iii) soil N2 O and CH4 emissions and (iv) C storage in Pinus elliottii and soil. As manure-derived biochar contains higher levels of nutrient elements and plant-derived biochar contains higher organic C, it was hypothesized that chicken manure biochar had higher nutrient bioavailability, which benefited soil properties, fertilizer NUE and plant growth, and sawdust biochar could be more effective in increasing soil C storage in short term. MATERIALS AND METHODS Production of feedstocks and biochars The sawdust (< 2 mm) and chicken manure were collected from a wood-producing factory in Xiaoji Town, and Tianmu Livestock and Poultry Co. Ltd. in Shaobo Town, respectively, both in Jiangdu City, Ji-

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angsu Province of China. Before pyrolysis, chicken manure and sawdust were air-dried on a cement ground for 3 d, and then packed to a reactor. Biochars were produced by a step-wise procedure under limited-oxygen conditions using a patented slow-pyrolysis reactor (100 cm length × 100 cm width × 100 cm height) (China patent No. ZL200920232191.9). The pyrolysis chamber was flushed with N2 (3 L min−1 ). The temperature was set at 200 ◦ C initially, and then elevated gradually to 250, 300, 350 and 400 ◦ C. At each temperature (except for 400 ◦ C), the process was maintained for 1.5 h, and the temperature of 400 ◦ C was maintained for 10 h. After the reactor temperature was cooled to the air condition, the biochar was taken out. Moisture contents of the air-dried chicken manure and sawdust were analyzed by drying in an oven at 80 ◦ C for 12 h. Biochar was ground to pass through a 2-mm sieve for later use and analysis. Selected chemical properties of the biochars and feedstocks are listed in Table I. The pH values of the biochars were determined in a 20:1 (volume/weight) water-biochar ratio with a pH meter (PHS-3C, INESA Ltd., Shanghai, China). Biochar TC and TN contents were determined with an automated nitrogen-carbon analyzer (ANCA) (Sercon Ltd., Crewe, UK). After wet digestion of biochar with the mixture of HF and HClO4 , biochar total P (TP) was determined by the colorimetric method and biochar total K (TK) was determined with a flame photometer (Jackson, 1958). An aliquot of the digested sample was used to determine the con-

tents of metal elements in biochar with an inductively coupled plasma emission spectrometer (ICP, Optima 8000, PerkinElmer, Waltham, USA). The ash content of biochar was determined by combustion at 800 ◦ C in a muffle furnace. Site description and soil properties A field mesocosm experiment was carried out in a forest at Liujiazhan Town (116◦ 56′ E, 28◦ 12′ N), Yingtan City, Jiangxi Province, China. The site has a typical subtropical monsoon climate with a mean annual precipitation of 1 750 mm, a mean annual evaporation of 1 318 mm, a mean annual temperature of 17.7 ◦ C and an average non-frost period of 262 d (Qin et al., 2006), at an elevation of 42 m above sea level and an inclination of less than 5◦ . Soil was collected from an open land (about 120 m2 in area) in the forest to 100 cm depth at increments of 0–30, 30–50, 50–70 and 70–100 cm, after removing sparse grasses and shrubs. The soil, an acidic soil with a PH of 4.8, classified as an Ultisol (USDA, 1999), was derived from Quaternary red clay with dominant kaolinite minerals and contained 34.29% clay, 38.57% silt, and 27.14% sand. Selected chemical properties of the acidic soil are presented in Table I. Mesocosm experiment Mesocosms were used to study the impact of biochars on tree growth, fertilizer NUE and C storage of tree and soil and soil N2 O and CH4 emissions. The me-

TABLE I Properties of the acidic forest soil (0–30 cm), biochars, feedstocks and P. elliottii sapling used in this study Propertya)

Soil

Sawdust Sawdust biochar Chicken manure Chicken manure biochar P. elliottii sapling (aboveground)b)

RE (%) pH TC (g kg−1 ) Ash (g kg−1 ) TN (g kg−1 ) C/N ratio TP (g kg−1 ) TK (g kg−1 ) AN (g kg−1 ) AP (g kg−1 ) AK (g kg−1 ) Ca (g kg−1 ) Mg (g kg−1 ) Al (g kg−1 ) Cu (mg kg−1 ) Zn (mg kg−1 ) Mn (mg kg−1 ) Pb (mg kg−1 ) Cr (mg kg−1 )

4.8 4.84 – 0.55 8.9 0.24 8.32 0.078 0.001 0.033 – – – – – – – –

8.3 446 45.1 3.83 117 0.52 2.72 1.06 0.021 1.07 4.55 0.96 – 2.35 15.1 82.8 1.19 –

27.8 7.5 490 282 6.53 75 1.11 5.25 0.47 0.033 1.19 7.49 2.72 – 12.4 110 230 16.2 –

9.4 287 257 23.9 12 15.7 29.2 3.18 2.58 28.5 80.2 8.13 1.16 69.8 891 912 0.38 29.9

47.5 10.5 304 488 25.7 11.9 27.1 55.7 0.23 2.69 47.5 94.1 16.0 4.69 94.6 1 248 1 357 2.44 63.9

– 438 – 3.36 131 0.57 2.64 – – – – – – – – – – –

rate of feedstock to biochar (RE) = biochar weight ÷ dry feedstock weight × 100; TC = total C; TN = total N; TK = total K; AN = available N; AP = available P; AK = available K. b) P. elliottii saplings used in the experiment were 2 years old.

a) Conversion

BIOCHAR EFFECTS ON C AND N DYNAMICS

socosms were made from 2 cm thick polyvinyl chloride (PVC) and had inner dimensions of 100 cm length × 100 cm width × 120 cm height. The bottom of each mesocosm was sealed with a PVC plate. Three reinforcement frames of PVC (3 cm thick × 5 cm wide) were sealed around each mesocosm outside wall at 5, 60 and 120 cm from the top. The outside surfaces of each mesocosm were wrapped with polystyrene foam and aluminum foil for heat insulation. A water outlet with valve was installed on one sidewall, 10 cm above the bottom to prevent water logging in the mesocosm. The mesocosms were arranged according to row spacings of 2.5 m × 2.5 m (center to center of the mesocosms). Silica sand (0.5–2 mm), which was washed with 2 mol L−1 HCl and then tap water till no acid remained, was first filled to the mesocosm to 10 cm height. Then, the bottom three soil layers (70–100, 50– 70 and 30–50 cm) were filled to the mesocosm successively over the silica sand to achieve field bulk density of 1.45, 1.42 and 1.40 g cm−3 . Finally, the top 30-cm soil was mixed with other materials according to treatments and filled to the mesocosms. The top soil in all treatments was packed in the mesocosm to achieve a bulk density of 1.22 g cm−3 . The experiment consisted of a non-amended control (CK) and treatments of sawdust at 2.16 kg m−2 (SD), chicken manure at 1.26 kg m−2 (CM), sawdust biochar at 2.4 kg m−2 (SDB), chicken manure biochar at 2.4 kg m−2 (CMB), 15 N-fertilizer alone (10.23 atom% 15 N) (NF), sawdust biochar at 2.4 kg m−2 plus the 15 N-fertilizer (SDBN) and chicken manure biochar at 2.4 kg m−2 plus the 15 N-fertilizer (CMBN). 15 N-urea, superphosphate fertilizer (containing 12% of superphosphate) and potassium chloride fertilizer (containing 60% of potassium chloride) were applied at 10.7 g m−2 (equivalent to 5 g m−2 of N), 41.7 g m−2 (equivalent to 5 g m−2 of P2 O5 ) and 13.2 g m−2 (equivalent to 5 g m−2 of K2 O) in the NF, SDBN and CMBN treatments. As limited information on optimal biochar application rate was available, the biochar application rate of 2.4 kg m−2 chosen for this experiment was based on the results of an unpublished trial of wheat in the same soil. It was initially intended that the raw feedstocks would be applied at rates equivalent to the amounts of feedstocks used to make the biochars. The conversion rates of sawdust and chicken manure to biochar were 27.8% and 47.5%, respectively, by the biochar production technique. The corresponding feedstock amounts to make 2.4 kg biochar were 8.63 kg for sawdust and 5.05 kg for chicken manure. It was found that when 8.63 kg m−2 sawdust was mixed to 30 cm depth, the soil-sawdust mixture was

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too loose to support seedlings. Thus, the application rate was reduced to 1/4 of the originally designed 8.63 kg m−2 sawdust. Accordingly, chicken manure was adjusted to 1.26 kg m−2 . The treatments were replicated three times in a completely randomized design. Two 2-year-old P. elliottii saplings were transplanted to each mesocosm the day after packing the mesocosms (May 4, 2012). The heights (H) of the saplings ranged from 95 to 120 cm and diameters at 30 cm height (D30 ) from 1.4 to 1.9 cm. The saplings were watered with 2.5 L water after the trees were transplanted. In the following three weeks, the saplings in each mesocosm were watered with 2.5 L water once a week in addition to natural rainfall so as to ensure their survival. During the 12-month experiment, weeds were removed every two months. Fertilizers were applied in a circle band (5 cm width × 5 cm depth) with an inner circle radius of 10 cm around the trees on August 26, 2012. Tree growth parameter measurement The H and D30 of P. elliottii were measured from June 2012 to April 2013. Litterfall in each mesocosm was collected from the soil surface from June 2012 to April 2013, washed with deionized water to remove dust, dried at 80 ◦ C for 48 h in the oven, weighed, ground with mill and passed through a 0.25-mm sieve. Soil N2 O and CH4 flux measurement Gas samplings for soil N2 O and CH4 flux measurement were performed twice a month in the hightemperature period from June to November 2012 and once a month in the low-temperature period from December 2012 to April 2013, using the static opaque chamber technique. Samplings were done between 8:00 to 10:30 a.m. as the literature showed that gas flux during that time is a good approximation of the daily average (Zou et al., 2005). A PVC collar (inner dimensions: 50 cm length × 50 cm width × 15 cm height) with groove (5 cm width × 5 cm height) around the top side was inserted into the soil with a distance of 5 cm to the mesocosm sidewall, before the saplings were transplanted. A PVC top chamber (inner dimensions: 50 cm length × 50 cm width × 30 cm height), which was equipped with a battery-driven fan to ensure complete gas mixing and wrapped with sponge and aluminum foil to minimize air temperature change inside the chamber during the sampling period, was fitted into the groove filled with water to seal the chamber during gas sampling. Four gas samples were collected with a 30-mL plastic syringe at 0, 30, 60 and 90 min after chamber closure, with the fan running during the sam-

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pling period. The air temperature inside the chamber was recorded during each gas sampling. Gases were injected into pre-evacuated 20-mL glass vials fitted with butyl rubber stoppers. The N2 O and CH4 concentrations were analyzed with a gas chromatograph equipped with a flame ionization detector (FID) and an electron capture detector (ECD) (Varian 3380, Varian America Inc., Palo Alto, USA). The N2 O and CH4 fluxes were calculated from the slope of the plot of temporal changes in N2 O and CH4 concentrations in the chamber headspace at the average chamber temperature. Tree and soil analysis One tree (aboveground) from each mesocosm was harvested on April 26, 2013 after nearly one year of the experiment and divided into needle, branch, trunk and bark. Tree root was not included because it could not be extracted due to its entanglement with the other tree root in the mesocosms. The tree components were dried at 105 ◦ C for 0.5 h to deactivate enzymes, dried at 80 ◦ C for 48 h, and then weighed. A subsample of the tree components was ground to pass a 0.25-mm sieve. Total C and TN contents of tree and litterfall were determined with an automated nitrogen-carbon analyzer (ANCA) (SerCon Ltd., Crewe, UK) and 15 N isotopic compositions were analyzed using an ANCA coupled to a 20/20 isotope ratio mass spectrometer (SerCon Ltd., Crewe, UK). Tree TP and TK contents were determined by the colorimetric method and with a flame photometer, respectively, after wet digestion with the mixture of H2 SO4 and H2 O2 . For the treatments with fertilizer application (NF, SDBN and CMBN), two composite soil samples were taken from the fertilization and non-fertilization zones of each mesocosm, respectively, with a stainless steel soil core sampler on April 27, 2013. Composite samples were obtained by mixing three soil cores (0–30 cm). After visible plant residues were carefully removed from all soil samples, the soil samples from the fertilization zone were passed through a 2-mm sieve and stored in the laboratory at 4 ◦ C for the analysis of − soil NH+ 4 -N, NO3 -N, available P (AP) and available K (AK). The soil samples from the non-fertilization zone were air-dried, ground and passed through a 2mm sieve, and aliquots of soil samples were sieved through 0.25 mm for the analysis of soil pH, TC, TN, TP and TK. Soil pH was determined in a 2.5:1 watersoil slurry with a pH meter (PHS-3C, INESA Ltd., Shanghai, China). Ammonium N and NO− 3 -N were extracted with 2.0 mol L−1 KCl and determined by the continuous flow analytical system (Autoanalyzer III,

Bran Luebbe, Hamburg, Germany). Soil AP was extracted by the mixture of 0.025 mol L−1 HCl and 0.03 mol L−1 NH4 F (Bray, 1945) and soil AK was determined by the 1.0 mol L−1 CH3 COONH4 extraction method (Jones, 1973). Soil TP was determined by the colorimetric method after wet digestion with the mixture of H2 SO4 and HClO4 and soil TK was determined with a flame photometer after digestion with the mixture of HF and HClO4 (Jackson, 1958). Soil TC and TN were determined by an ANCA (Sercon Ltd., Crewe, UK). Data calculations Net primary production. Net primary production (NPP, g tree−1 year−1 ) of tree was defined as the increment of tree biomass plus litterfall. NPP = Biomassh − Biomassi + Biomass1

(1)

where Biomassh is the biomass of P. elliottii at harvest; Biomassi is the estimated initial biomass of P. elliottii at transplanting; and Biomassl is the biomass of litterfall during the experiment. Annual net C fixation. Annual net C fixation (ANCF, g tree−1 year−1 ) of tree was determined as: ANCF = Ch × Biomassh − Ci × Biomassi + C1 × Biomass1

(2)

where Ch , Ci and Cl are the TC contents of tree at harvest, P. elliottii sapling and litterfall, respectively. Ci was 438.2 g kg−1 . Fertilizer NUE. The amount of N in tree biomass that was derived from the labeled 15 N-urea (Ndff) was calculated by the following equation (Hood, 2001): Ndff = (atom%15 Nt − atom%15 Nc ) × TTN ÷ (atom%15 Nf − atom%15 Nc )

(3)

where atom%15 Nt and atom%15 Nc are the tree atom% 15 N in the treatment with 15 N-fertilizer alone (or biochar plus 15 N-fertilizer) and the control (or the treatment with biochar but without 15 N-fertilizer), respectively; atom%15 Nf is the urea atom% 15 N (10.23%); and TTN denotes the TN content of the tree. Fertilizer NUE (%) was then calculated by: NUE = Ndff/Nf × 100 where Nf is the total applied N in the

(4) 15

N-fertilizer.

Statistical analysis Covariance analysis was used to analyze the diffe-

BIOCHAR EFFECTS ON C AND N DYNAMICS

rences of P. elliottii sapling H and D30 between treatments. Statistical analyses of the results were performed with one-way analysis of variance (ANOVA) with least significant difference (LSD) tests to assess the effects of contrasting biochars on tree growth, NPP of tree, fertilizer NUE, soil N2 O and CH4 emissions and soil C storage. All the tests were performed using SPSS software (version 13.0). Differences were considered significant when P ≤ 0.05. RESULTS Influence of biochars on tree growth With the covariance analysis results, the D30 and H of P. elliottii saplings at transplanting showed no differences among all treatments (P > 0.05). After one year of the experiment, increments of tree D30 in the CM and CMBN treatments were 2.9 and 2.8 times those of CK, respectively, but the increment of D30 in the other treatments did not differ from that in CK (Fig. 1a). The increments of H in the SD, CM, SDB,

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CMB and CMBN treatments were higher than those in CK (P < 0.05) (Fig. 1b). However, applications of 15 Nfertilizer alone and sawdust biochar plus 15 N-fertilizer did not significantly affect tree height. Based on the D30 , H and biomass (Biomassh ) data, which were achieved by destructive harvest in April 2013, the relationships among D30 , H and Biomassh could be demonstrated as: Biomassh = 2 31.24D30 H + 35.92 (R2 = 0.88, n = 24, P < 0.001). With the data of D30 and H measured at transplanting, the original biomass of P. elliottii saplings were calculated (Table II). The biomass of the saplings has no significant difference among treatments (P > 0.05), except that the mean value in the SDBN treatment was higher than that in the CMBN treatment (P = 0.03) (Table II). The biomass of P. elliottii in the CM, CMB and CMBN treatments was higher than that of CK (P < 0.05) (Table II). Amendments with sawdust, sawdust biochar, 15 N-fertilizer alone and sawdust biochar plus 15 N-fertilizer showed no significant effects on P. elliottii biomass (P > 0.05) (Table II). Only sawdust application significantly increased annual litterfall when compared with CK (P = 0.02) (Table II). The NPP of P. elliottii differed in the range from 32.6 to 199.6 g tree−1 year−1 among all treatments. In the absence of fertilizer, the NPP values of P. elliottii in the CM and CMB treatments were 4.3 and 2.8 times that of CK, and the value in the SDB treatment showed a slight but non-significant decrease relative to CK (P > 0.05) (Table II). The NPP values of P. elliottii in the NF and SDBN treatments were higher than those in CK (P < 0.01) and the SDB (P < 0.01) treatment (Table II), respectively. The NPP in the CMBN treatment increased by more than 2-fold over that of CK, but showed no difference compared with the CMB treatment (P > 0.05) (Table II). Influence of biochars on soil properties, fertilizer NUE and tree nutrient elements

Fig. 1 Tree diameter (at 30 cm height above soil surface) (a) and height (b) dynamics of P. elliottii on the acidic forest soil in the non-amended of control (CK) and treatments of sawdust (SD), chicken manure (CM), sawdust biochar (SDB), chicken manure biochar (CMB), 15 N-fertilizer alone (NF), sawdust biochar plus 15 N-fertilizer (SDBN) and chicken manure biochar plus 15 N-fertilizer (CMBN). The arrow indicates the day of fertilizer application. Error bars indicate the pooled standard deviations (n = 24).

Because chicken manure biochar was applied at 2.4 kg m−2 , the application rates of TN, AN, AP and AK would be equivalent to 61.7 g m−2 , 0.55 g m−2 , 6.46 g m−2 and 114 g m−2 , respectively, in the CMB treatment (Table III). With chicken manure applied at 1.26 kg m−2 , the application rates of TN, AP and AK would be equivalent to 30.1, 3.25 and 35.9 g m−2 , respectively, in the CM treatment. The rates of AN, AP and AK added were equivalent to 1.1 g m−2 , 0.08 g m−2 and 2.86 g m−2 , respectively, with incorporation of sawdust biochar at 2.4 kg m−2 in the SDB treatment (Table III).

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TABLE II Aboveground biomass, litterfall biomass, estimated initial sapling biomass and net primary production (NPP) of P. elliottii on the acidic forest soil in the non-amended control (CK) and treatments of sawdust (SD), chicken manure (CM), sawdust biochar (SDB), chicken manure biochar (CMB), 15 N-fertilizer (NF), sawdust biochar plus 15 N-fertilizer (SDBN) and chicken manure biochar plus 15 N-fertilizer (CMBN) after one year of the experiment Treatment

Aboveground biomass

Litterfall biomass

Estimated initial sapling biomass

tree−1

CK SD CM SDB CMB NF SDBN CMBN

157 181 311 133 246 198 208 244

± ± ± ± ± ± ± ±

25a) deb)

7.1 10.1 7.7 8.1 8.5 8.0 5.7 5.5

33cde 79a 16e 14ab 31cd 36bcd 44ac

a) Mean ± standard deviation. b) Means with the same letter(s)

± ± ± ± ± ± ± ±

g 1.2bcd 1.1a 1.6bcd 1.7ab 0.8ba 1.1ba 1.7cd 1.1d

118 130 119 108 126 123 135 99

± ± ± ± ± ± ± ±

NPP g tree−1 year−1 46.1 ± 7.5de 61.0 ± 33.6cd 199.6 ± 81.8a 32.6 ± 9.0e 128.3 ± 13.4a 83.2 ± 10.3c 79.1 ± 12.6c 149.9 ± 41.1a

26ab 21ab 24ab 9ab 7ab 22ab 24a 8b

in the same column are not significantly different at P ≤ 0.05 (n = 3).

TABLE III Rates of total N (TN), available N (AN), total P (TP), available P (AP), total K (TK) and available K (AK) added in the nonamended control (CK) and treatments of sawdust (SD), chicken manure (CM), sawdust biochar (SDB), chicken manure biochar (CMB), 15 N-fertilizer (NF), sawdust biochar plus 15 N-fertilizer (SDBN) and chicken manure biochar plus 15 N-fertilizer (CMBN) Item

CK

SD

CM

SDB

CMB g

TN AN TP AP TK AK

0 0 0 0 0 0

8.27 2.29 1.12 0.05 5.88 2.31

30.10 4.01 19.80 3.25 36.80 35.90

15.70 1.13 2.66 0.08 12.60 2.86

NF

SDBNa)

CMBNa)

5 5 5 5 5 5

20.70 6.13 7.66 5.08 17.60 7.86

66.70 5.55 70.00 11.50 139.00 119.00

m−2 61.70 0.55 65.00 6.46 133.00 114.00

a) The

rates of AN, AP and AK added in the SDBN (or CMBN) treatment were calculated as the rates of AN, AP and AK added in the SDB (or CMB) treatment plus 5 g m−2 , respectively.

After one year of the experiment, for the soil from the non-fertilization zone, application of chicken manure biochar (CMB and CMBN treatments) increased soil pH, TC, TN and TP contents (Table IV), with no difference in soil TK showed, as compared with CK (P > 0.05) (Table IV). However, the SDB and SDBN treatments did not affect soil pH, TN and TP contents relative to CK (P > 0.05) (Table IV). Comparison of soil TC and C/N ratio in the SDB and SDBN treatments with those in CK revealed that sawdust biochar increased soil TC content by 64% and soil C/N ratio by 48% (Table IV). Application of fertilizer (NF, SDBN and CMBN treatments) increased soil NO− 3 -N content relative to CK (P < 0.01). Soil AN (NH+ -N and NO− 4 3 -N) contents in the NF and SDBN treatments were higher than those in the CMBN treatment (P < 0.05) (Table IV). Additionally, the contents of soil AP and AK in the CMB and CMBN treatments were much greater than those in CK (P < 0.001); however, the SDB and SDBN treatments did not affect soil AP and AK contents relative to CK (P > 0.05) (Table IV). Tree atom% 15 N in the NF, SDBN and CMBN

treatments increased significantly (P< 0.001) when compared with CK and the SDB and CMB treatments, respectively (Table V). Compared with the NF treatment, the CMBN treatment increased fertilizer NUE of tree (P = 0.06), while the SDBN treatment did not (P = 0.64) (Table V). The treatments of biochars without N fertilizer (SDB and CMB) reduced tree TN contents relative to CK; however, the treatments of biochars with N fertilizer (SDBN and CMBN) did not change tree TN content relative to CK (Table V). Application of chicken manure biochar (CMB and CMBN treatments) increased N uptake of P. elliottii relative to application of sawdust biochar (SDB and SDBN treatments) (P < 0.05) (Table V). Comparision of tree N uptake in the SDBN and CMBN treatments with those of the SDB and CMB treatments revealed that fertilizer N application increased N uptake of P. elliottii. Comparing biochar treatments (SDB and CMB treatments) with CK showed that the tree TP content and P uptake increased with application of chicken manure biochar (P < 0.001), but decreased with incorporation of saw-

4.6 ± 0.1b 6.52 ± 0.02c 0.45 ± 0.01c 14.6 ± 0.1a 4.31 ± 1.04d 0.16 ± 0.02e 0.18 ± 0.03d 0.74 ± 0.22c 8.02 ± 0.01c 37.5 ± 2.5d

4.5 ± 0.1b) bc) 5.12 ± 1.18d 0.53 ± 0.09bc 9.6 ± 0.6bc 8.41 ± 3.06abc 0.61 ± 0.09c 0.22 ± 0.01cd 0.65 ± 0.04c 8.38 ± 0.20ab 48.3 ± 14.4cd

pH TC (g kg−1 ) TN (g kg−1 ) C/N −1 ) NH+ 4 -N (mg kg −1 ) -N (mg kg NO− 3 TP (g kg−1 ) AP (mg kg−1 ) TK (g kg−1 ) AK (mg kg−1 )

4.6 ± 0.1b 5.22 ± 0.14d 0.59 ± 0.13b 9.3 ± 0.5bc 4.61 ± 0.33cd 1.06 ± 0.13b 0.32 ± 0.11bc 4.44 ± 3.78b 7.53 ± 0.34d 85.8 ± 11.3b

CM 4.7 ± 0.1b 8.19 ± 0.19a 0.55 ± 0.01b 14.9 ± 0.2a 6.51 ± 2.26bcd 0.28 ± 0.12de 0.25 ± 0.08cd 0.51 ± 0.20c 7.63 ± 0.34d 49.2 ± 3.8c

SDB 5.2 ± 0.3a 7.85 ± 0.38ab 0.90 ± 0.03a 8.8 ± 0.2cd 4.98 ± 2.11cd 0.53 ± 0.27cd 0.45 ± 0.06a 28.0 ± 12.25a 8.55 ± 0.10a 226.7 ± 14.2a

CMB 4.5 ± 0.2b 4.58 ± 0.05d 0.55 ± 0.03b 8.4 ± 0.6cd 12.71 ± 7.21ab 3.96 ± 2.15a 0.17 ± 0.06d 0.75 ± 0.39c 8.42 ± 0.16a 41.7 ± 6.3cd

NF 4.7 ± 0.1b 8.52 ± 0.48a 0.64 ± 0.09b 13.6 ± 2.7a 13.05 ± 6.69a 3.78 ± 2.59ab 0.22 ± 0.01cd 0.70 ± 0.14c 8.08 ± 0.05bc 42.5 ± 2.5d

SDBN

5.1 ± 0.1a 7.61 ± 1.06bc 0.87 ± 0.10a 8.7 ± 0.3cd 4.85 ± 0.74cd 1.14 ± 0.13b 0.38 ± 0.01ab 22.07 ± 1.92a 8.46 ± 0.14a 200.8 ± 9.5a

CMBN

0.37 – – 7.79 0.72 0.66 0.04 2.55 0.11

15 N

0.01b) cc)

0.58a 0.14de 0.05c 0.001b 0.23c 0.04c

±

± ± ± ± ± ±

– – – 6.11 0.55 0.52 0.02 2.01 0.04

SD

± ± ± ± ± ± 0.60b 0.24ef 0.03d 0.02bc 0.06d 0.08c

– – – 8.04 2.00 0.77 0.18 3.27 0.73

CM

± ± ± ± ± ± 0.15a 0.68a 0.05b 0.08a 0.24b 0.30a

0.37 – – 6.71 0.44 0.56 0.02 2.34 0.04

SDB

± ± ± ± ± ± 0.13b 0.09f 0.03d 0.01c 0.18c 0.04c

± 0.001c

0.37 – – 6.29 1.04 0.78 0.12 3.01 0.42

± ± ± ± ± ±

0.28b 0.05c 0.05b 0.02a 0.19b 0.01a

± 0.001c

CMB

b) Mean

= amount of N in the tree that was derived from the labeled 15 N-urea; TN = total N; TP = total P; TK = total K. ± standard deviation (n = 3). c) Means with the same lower letter(s) in the same row are not significantly different at P ≤ 0.05.

a) Ndff

Atom% Ndff (g tree−1 ) NUE (%) TN (g tree−1 ) N uptake (g tree−1 ) TP (g kg−1 ) P uptake (g tree−1 ) TK (g kg−1 ) K uptake (g tree−1 )

CK

Parametera)

3.90 0.57 22.7 8.04 1.08 0.56 0.04 2.20 0.12

NF ± ± ± ± ± ± ± ± ±

0.53b 0.15b 6.0b 1.31a 0.37bcd 0.10cd 0.02bc 0.47cd 0.09c

4.15 0.64 25.5 7.87 1.07 0.54 0.04 3.07 0.29

± ± ± ± ± ± ± ± ±

SDBN 0.56b 0.19b 7.7b 0.25a 0.17cd 0.06d 0.01b 0.45bc 0.04b

4.93 0.92 37.0 8.23 1.57 0.88 0.16 4.10 0.74

± ± ± ± ± ± ± ± ±

CMBN 0.26a 0.18a 7.2a 0.70a 0.25ab 0.01a 0.03a 0.52a 0.34a

Atom% 15 N, fertilizer N use efficiency (NUE), content and uptake of N, P and K in P. elliottii on the acidic forest soil in the non-amended control (CK) and treatments of sawdust (SD), chicken manure (CM), sawdust biochar (SDB), chicken manure biochar (CMB), 15 N-fertilizer (NF), sawdust biochar plus 15 N-fertilizer (SDBN) and chicken manure biochar plus 15 N-fertilizer (CMBN) after one year of experiment

TABLE V

b) Mean

= total C; TN = total N; TP = total P; AP = available P; TK = total K; AK = available K. ± standard deviation (n = 3). c) Means with same lower letter(s) in the same row are not significantly different at P ≤ 0.05.

a) TC

SD

CK

Propertya)

Selected properties of the acidic forest soil under P. elliottii in the non-amended control (CK) and treatments of sawdust (SD), chicken manure (CM), sawdust biochar (SDB), chicken manure biochar (CMB), 15 N-fertilizer (NF), sawdust biochar plus 15 N-fertilizer (SDBN) and chicken manure biochar plus 15 N-fertilizer (CMBN) after one year of experiment

TABLE IV

BIOCHAR EFFECTS ON C AND N DYNAMICS 255

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256

dust biochar (P < 0.05) (Table V). Uptake of P in the SDBN treatment was greater than that in the SDB treatment (P = 0.02), while P uptake in the CMBN treatment was not statistically different from that in the CMB treatment (P = 0.17) (Table V). The treatments of chicken manure biochar (CMB and CMBN treatments) increased TK content and K uptake of P. elliottii, but incorporation of sawdust biochar did not significantly change tree TK content and tree K uptake relative to CK (P > 0.05) (Table V). The SDBN treatment increased tree K uptake relative to CK and the SDB treatment (P < 0.05) (Table V). Soil N2 O and CH4 flux dynamics and cumulative emissions Although there was a tendency of greater N2 O emissions from the CM treatment in the first four weeks, N2 O emission and CH4 uptake showed no significant difference among all the treatments (P > 0.05) (Figs. 2 and 3), except that cumulative N2 O emission in the SDB treatment was lower than that in the CM treatment (P < 0.05). ANCF of P. elliottii and SOC dynamics The ANCF of P. elliottii in the CM and CMB treatments increased by 287% and 157% relative to that in the CK, respectively (Fig. 4). However, the AN-

CF in the SD and SDB treatments did not differ from that in CK (P > 0.05). Comparison of ANCF in the NF and SDBN treatments with CK and the SDB treatment showed that fertilizer application increased tree ANCF in the NF and SDBN treatments by 70% and 115%, respectively (Fig. 4). Incorporation of sawdust, sawdust biochar and chicken manure biochar rather than chicken manure increased SOC stocks after one year of the experiment (Table VI). The apparent C loss from sawdust biochar and chicken manure biochar (calculated as the difference between added biochar C and SOC increment) after one year was below 1.6%. However, the apparent C loss from sawdust and chicken manure after one year was 35% and 61%, respectively. DISCUSSION Dependence of plant growth response on biochars’ properties The different effects of sawdust biochar and chicken manure biochar on tree NPP were mainly due to the differences in nutrient content and availability between the biochars. As shown in Table I, chicken manure biochar contained higher levels of TN, AP and AK, but lower level of AN compared with sawdust biochar. Incorporation of chicken manure biochar at the rate of

Fig. 2 N2 O (a) and CH4 (b) flux dynamics in the acidic forest soil for the period from June 2012 to April 2013 under P. elliottii (no data were obtained in December 2013) in the non-amended control (CK) and treatments of sawdust (SD), chicken manure (CM), sawdust biochar (SDB) and chicken manure biochar (CMB). Error bars indicate the pooled standard deviations (n = 15).

BIOCHAR EFFECTS ON C AND N DYNAMICS

257

Fig. 3 Cumulative N2 O (a) and CH4 (b) emissions in the acidic forest soil from June 2012 to April 2013 under P. elliottii in the nonamended control (CK) and treatments of sawdust (SD), chicken manure (CM), sawdust biochar (SDB) and chicken manure biochar (CMB). Bars with the same lower letter(s) indicate no significant difference among different treatments at P ≤ 0.05. Error bars indicate standard deviations of means (n = 3).

Fig. 4 Annual net C fixation (ANCF) of P. elliottii on the acidic forest soil in the non-amended control (CK) and treatments of sawdust (SD), chicken manure (CM), sawdust biochar (SDB), chicken manure biochar (CMB), 15 N-fertilizer alone (NF), sawdust biochar plus 15 N-fertilizer (SDBN) and chicken manure biochar plus 15 N-fertilizer (CMBN) after one year of the experiment. Bars with the same letter(s) indicate no significant difference among different treatments at P ≤ 0.05. Error bars indicate standard deviations of means (n = 3).

2.4 kg m−2 increased soil TN, TP, AP and AK contents (Table IV). Although the AN content in chicken manure biochar was low, the N uptake of P. elliottii in the CMB treatment was higher than that in CK (Table V), demonstrating that N in chicken manure biochar may have become available for tree growth during the experiment. As N and P are two main elements limiting plant growth in subtropical regions (Walker and Syers, 1976; Cramer, 2010; Xie et al., 2013), this in-

creased supply of N and P contributed to the enhanced P. elliottii growth, indicating that the chicken manure biochar could play a role as fertilizer in infertile soil. Previous literature also reported an increase in plant production attributed to the increase of available nutrients when nutrient-rich biochar was applied (Lehmann et al., 2003; Asai et al., 2009). Although the rate of TN added was lower in the CM treatment than in the CMB treatment (Table III), the tree NPP showed no significant difference between the CM and CMB treatments (Table II) and the tree N uptake in the CM treatment was higher than that in the CMB treatment, indicating that the bioavailability of N in chicken manure decreased after pyrolysis; in other words, chicken manure biochar N appeared to be only partially bioavailable. Furthermore, with the assumption that tree N uptake was derived from mineralized chicken manure biochar, the ratio of mineralized N to applied N in the CMB treatment was just only about 2% after one year of the experiment. Obviously, the rate of N mineralization from chicken manure biochar was slow over this period. Cao and Harris (2010) and Knicker (2010) attributed the decrease of N bioavailability in biochar to the formation of recalcitrant N-heterocyclic aromatic structures such as pyridines and imidazoles during pyrolysis. Xie et al. (2013) demonstrated lower than 2% N bioavailability of wheat straw biochar by the 15 N labeling technique. By contrast, sawdust biochar contained much less TN, TP and TK than chicken manure biochar, which was commensurate with the levels in the feedstocks. The low rates of TN, TP and TK added (Table III) through sawdust biochar had little effect on

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TABLE VI Organic C stocks and budgets (0–30 cm) of the acidic forest soil under P. elliottii in the non-amended control (CK) and treatments of sawdust (SD), chicken manure (CM), sawdust biochar (SDB) and chicken manure biochar (CMB) after one year of the experiment Parameter

CK

SD

CM

SDB

CMB

1.77 ± 0.02 1.18 3.00 ± 0.07a 1.23 ± 0.07a

1.77 ± 0.02 0.73 2.82 ± 0.21b 1.04 ± 0.21a

m−2

Initial C stock C inputb) Final C stock C incrementd)

1.77 ± 0.02a) 0.00 1.87 ± 0.10dcc) 0.10 ± 0.10c

1.77 ± 0.02 0.96 2.39 ± 0.07b 0.62 ± 0.07b

kg 1.77 ± 0.02 0.36 1.91 ± 0.05c 0.14 ± 0.05c

± standard deviation (n = 3). input = biochar (or sawdust, chicken manure) amendment quantity × C content. c) Means with the same lower letter(s) in the same row are not significantly different at P ≤ 0.05. d) C increment = final C stock − initial C stock.

a) Mean b) C

soil TN, AP and AK contents. Low nutrient contents in sawdust biochar were probably the main reason for the little effect of the SDB treatment on tree growth. Another reason for little effect of sawdust biochar on tree growth may be due to the suppression of N mineralization from soil following sawdust biochar application, resulting in the limited supply of NH+ 4 -N and NO− -N for tree growth. The content of soil AN (NH+ 3 4− N and NO3 -N) in the SDB treatment (6.79 mg kg−1 ) was lower than that in CK (9.02 mg kg−1 ) after the one-year experiment. Dempster et al. (2012) also reported that Jarrah wood biochar decreased the soil net N mineralization and attributed the suppression of soil N mineralization to the negative priming effect of biochar addition on soil organic matter decomposition and the present of potentially toxic volatile organic compounds (such as benzene) in biochar. Therefore, the properties of biochars determined their effects on soil properties and tree growth. Chicken manure biochar supplied N, P and K for tree growth; however, the persistence of manure biochar supplying nutrients needs further investigation. The benefit of chicken manure biochar application to soil productivity was also due to factors such as increasing soil pH, besides the improved availability of nutrients in biochar. In the current study, the CMB and CMBN treatments increased soil pH, while the SDB and SDBN treatments did not, corresponding well with the higher pH of chicken manure biochar compared with sawdust biochar (Table I), which was supported by previous reports (Lehmann et al., 2003; Chan et al., 2008; Singh et al., 2010). Singh et al. (2010) reported that the relatively high pH of manurederived biochar could have resulted from the presence of greater quantities of calcite and salts of alkali and alkaline elements. Eucalyptus saligna wood biochar pyrolyzed at 400 ◦ C had higher total surface acidity (carboxyls + lactones + phenols + additional acidic

species) (6.07 mmolc g−1 C) and lower total surface basicity (0.38 mmolc g−1 C) than poultry litter biochar (400 ◦ C), which had surface acidity of 5.10 mmolc g−1 C and total surface basicity of 4.29 mmolc g−1 C. Due to high pH and the presence of calcite, chicken manure biochar has a high acid-neutralizing capacity. Consequently, chicken manure biochar could increase soil pH more effectively than sawdust biochar. Furthermore, the increase in soil pH may have affected nutrient availability. The availability of P is limited in acid soils due to adsorption to Al and Fe oxides, and exchangeable Al and exchangeable Fe decrease as pH increases (Yuan et al., 2011; Ch’ng et al., 2014). Therefore, it is likely that the increase in soil pH due to application of manure-derived biochar contributed to the increased P availability observed in the CMB and CMBN treatments (Table IV), as suggested by Uzoma et al. (2011). Thus, the enhanced growth of P. elliottii in the CMB and CMBN treatments was probably due to nutrient addition and enhanced nutrient availability resulting from application of nutrient-rich biochar with high liming capacity to the acidic soil of this study. Effects of biochars on fertilizer NUE Chicken manure biochar application increased urea NUE, while sawdust biochar had little effect on NUE (Table V). The different impacts of these two biochars on fertilizer NUE could be ascribed to their different properties. Uptake of N and P was both substantially higher in the CMBN treatment than in the NF and SDBN treatments. Chicken manure biochar increased soil AP (Table IV), relieving P deficiency, which could increase the tree’s demand for N. This was consistent with previous reports of increased fertilizer NUE observed in amendment of a Ferrosol and an Alfisol with manure-derived biochar (Chan et al., 2008; Slavich et al., 2013). As a result of increased N uptake by P. elli− ottii from fertilizer, soil NH+ 4 -N and NO3 -N contents

BIOCHAR EFFECTS ON C AND N DYNAMICS

in the CMBN treatment were lower than those in the NF and SDBN treatments (Table IV). However, little AP in sawdust biochar (Table I) resulted in little enhancement of P. elliottii growth, and thus the uptake of N from fertilizer was limited. Xie et al. (2013) and Zhu et al. (2014) also showed that wheat straw biochar had little effect on fertilizer NUE in a similar Ultisol. Therefore, variations of soil AP content caused by sawdust biochar and chicken manure biochar were probably one of the main factors that affected fertilizer NUE. Another explanation for the increased fertilizer NUE in the CMBN treatment could be the increase in soil pH. Uzoma et al. (2011) observed that an increase in soil pH following application of manure biochar promoted the uptake of fertilizer N. On the other hand, an increase in soil pH was concomitant with an increase in soil CEC (Singh et al., 2010; Song and Guo, 2012; Van Zwieten et al., 2013). As a result, NH3 loss may be decreased through adsorption of NH+ 4 to the exchange sites on the biochar surface (Jones et al., 2012; Song and Guo, 2012). The NH+ 4 adsorbed by the biochar could be available to the plant (TaghizadehToosi et al., 2011), and thus application of chicken manure biochar to soil could increase retention and uptake of urea N. The average uptake of N from non-fertilization zone was 0.51 g tree−1 in the NF treatment, lower than those in CK (0.72 g tree−1 ), the CMBN treatment (0.65 g tree−1 ), and the CMB treatment (1.04 g tree−1 ). This indicated that when fertilizer N was applied to soil, soil N mineralization (including N mineralization from chicken manure biochar) might decrease because P. elliottii preferred to take in NH+ 4 -N and/or NO− -N from fertilizer N directly. On the con3 trary, the average uptake of N from non-fertilization zone in the SDBN treatment (0.43 g tree−1 ) was not obviously different from that in the SDB treatment (0.44 g tree−1 ), but significantly lower than that in CK (0.72 g tree−1 ), showing that sawdust biochar might suppressed the N mineralization, and application of fertilizer had little effect on N mineralization of soil amended with sawdust biochar (including N mineralization from sawdust biochar). This was consistent with the finding of Dempster et al. (2012). The suppression of soil N mineralization may be attributed to the negative priming effect on the soil organic matter decomposition, which was caused by the constrained microbial activity with the presence of sawdust biochar. Dempster et al. (2012) reported that soil microbial biomass decreased with the application of Jarrah wood biochar. Furthermore, addition of fertilizer N may not alleviate

259

the constraint of microorganism activity as C bioavailability in sawdust biochar was very low. Effects of biochars on N2 O and CH4 emissions of soil and C storage of P. elliottii Cumulative N2 O emission and CH4 uptake of soil in the SDB and CMB treatments were not significantly different from those in CK (Fig. 3). However, expressing N2 O emission with respect to N added to soil revealed that the values of N2 O emission factor (N2 O-N emitted per unit N added) in the SDB (0.003 g N2 O-N g−1 N added) and CMB (0.004 g N2 O-N g−1 N added) treatments were lower than those in the SD (0.029 g N2 O-N g−1 N added) and CM (0.024 g N2 O-N g−1 N added) treatments, respectively. These results were consistent with the study by Van Zwieten et al. (2013), who showed that the N2 O emission factor decreased from 0.073 g N2 O-N g−1 N added for poultry litter applied at 1.2 kg m−2 to 0.011 g N2 O-N g−1 N added for poultry litter biochar applied at 1.0 kg m−2 over 57 d in a Ferrosol. This could be due to low mineral N in sawdust biochar and chicken manure biochar, as most N in the feedstock was converted to recalcitrant Nheterocyclic aromatic structures (Knicker, 2010). The N in chicken manure biochar may be released gradually, supporting tree growth, but further work is needed to elucidate the long-term impacts on forest soil N2 O emission and CH4 uptake when biochar is applied as an amendment. As expected, both the addition of biochars and unpyrolyzed organic amendments increased soil TC content (Table IV). However, from the view of net soil C dynamics, after one year, the 0–30 cm apparent C losses in the SD (35%) and CM (61%) treatments were higher than those in the SDB and CMB treatments, respectively, whose C losses were negligible (Table VI). These results were consistent with previous studies that showed a very slow mineralization rate for plant- or manure-derived biochar pyrolyzed under similar conditions (Singh et al., 2010; Bruun et al., 2012; Song and Guo, 2012; Slavich et al., 2013; Van Zwieten et al., 2013; Xie et al., 2013). It is well understood that most O and H from the feedstock are removed, and much of the labile C is converted to aromatics during pyrolysis (Cao et al., 2011; Bruun et al., 2012). Sawdust biochar amendment, due to the higher C content, increased soil TC content more than chicken manure biochar amendment at the same application rate. However, chicken manure biochar was more beneficial for tree C fixation. In order to assess the overall potential of these two kinds of biochars for climate change mitigation, it was essential to estimate the C bud-

260

get from biochar production to tree-soil ecosystem, including the C loss during pyrolysis and C changes in P. elliottii and soil. As P. elliottii is a long-lived plant, it is hard to assess the overall effects of plantand manure-derived biochars on the C sequestration potential of planted forest ecosystem with one-year data. Therefore, long-term experiments are needed. CONCLUSIONS The properties of biochar determined its effect on ecosystem functions. Chicken manure biochar significantly increased NPP of P. elliottii and fertilizer NUE compared with sawdust biochar. The sawdust biochar significantly increased soil TC content and the chicken manure biochar was more beneficial for tree C fixation. The higher improvement of soil productivity with chicken manure biochar was due to its higher nutrient contents and higher acid-neutralizing capacity than those of sawdust biochar. However, it is hard to assess the overall effects of these contrasting biochars on C sequestration potential in planted forest ecosystem in a short time. Therefore, further work needs to be done to investigate the long-term eco-functional effect of biochar amendment on planted forests. ACKNOWLEDGEMENT This study was supported by the National Natural Science Foundation of China (No. NFSC-41171191), the Special Agricultural Science and Technology Project of China (No. 201503137), the Science and Technology Supporting Project of China (No. 2013BAD11B01), the Knowledge Innovation Program of Chinese Academy of Sciences (No. KZCX2-EW-409), and the Science and Technology Supporting Project of Jiangsu Province, China (No. BE2013451). REFERENCES Alburquerque J A, Calero J M, Barr´ on V, Torrent J, del Campillo M C, Gallardo A, Villar R. 2014. Effects of biochars produced from different feedstocks on soil properties and sunflower growth. J Plant Nutr Soil Sci. 177: 16–25. Asai H, Samson B K, Stephan H M, Songyikhangsuthor K, Homma K, Kiyono Y, Inoue Y, Shiraiwa T, Horie T. 2009. Biochar amendment techniques for upland rice production in Northern Laos. 1. Soil physical properties, leaf SPAD and grain yield. Field Crop Res. 111: 81–84. Ball P N, Mackenzie M D, Deluca T H, Hollen W E. 2010. Wildfire and charcoal enhance nitrification and ammoniumoxidizing bacteria abundance in dry montane forest soils. J Environ Qual. 39: 1243–1253. Bray R H. 1945. Determination of total, organic, and available forms of phosphorus in soils. Soil Sci. 59: 39–45. Bruun E W, Ambus P, Egsgaard H, Hauggaard-Nielsen H. 2012. Effects of slow and fast pyrolysis biochar on soil C and N

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