Biochar soil nematode popul

Pedosphere 23(1): 98–103, 2013 ISSN 1002-0160/CN 32-1315/P c 2013 Soil Science Society of China

Published by Elsevier B.V. and Science Press

Soil Nematode Response to Biochar Addition in a Chinese Wheat Field∗1 ZHANG Xiao-Ke1 , LI Qi1 , LIANG Wen-Ju1,∗2 , ZHANG Min1 , BAO Xue-Lian1,3 and XIE Zu-Bin2 1 State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164 (China) 2 Jiangsu Biochar Engineering Center, State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China) 3 University of Chinese Academy of Sciences, Beijing 100049 (China)

(Received April 24, 2012; revised November 12, 2012)

ABSTRACT While studies have focused on the use of biochar as soil amendment, little attention has been paid to its effect on soil fauna. The biochar was produced from slow pyrolysis of wheat straw in the present study. Four treatments, no addition (CK) and three rates of biochar addition at 2 400 (B1), 12 000 (B5) and 48 000 kg ha−1 (B20), were investigated to assess the effect of biochar addition to soil on nematode abundance and diversity in a microcosm trial in China. The B5 and B20 application significantly increased the total organic carbon and the C/N ratio. No significant difference in total nematode abundance was found among the treatments. The biochar addition to the soil significantly increased the abundance of fungivores, and decreased that of plant parasites. The diversity of soil nematodes was significantly increased by B1 compared to CK. Nematode trophic groups were more effectively indicative to biochar addition than total abundance.

Key Words:

diversity, ecological indices, microcosm trial, nematode community, trophic groups

Citation: Zhang, X. K., Li, Q., Liang, W. J., Zhang, M., Bao, X. L. and Xie, Z. B. 2013. Soil nematode response to biochar addition in a Chinese wheat field. Pedosphere. 23(1): 98–103.

INTRODUCTION Biochar, the high carbon material produced from the slow pyrolysis of biomass, is a kind of new green biofuel. Biochar application to soils is being considered as a means to sequester carbon while concurrently improving soil functions and playing an important role in the global carbon cycle (Forbes et al., 2006). Till date, most studies have focused on the effect of biochar on soil amendment (Steinbeiss et al., 2009; Dias et al., 2010; Gaskin et al., 2010), with little emphasis on its biological effect. Although few studies (Verheijen et al., 2009; Atkinson et al., 2010) have indicated that biochar can promote the activity of micro-organisms, there is little evidence of its effect on soil fauna. Soil biota is important to the functioning of soils and provides many essential ecosystem services. Understanding the interactions between biochar as a soil amendment and soil biota is therefore vital (Verheijen et al., 2009).

Soil nematodes are the most numerous mesofauna ∗1 Supported

and occupy all consumer trophic levels within the soil food web (Fu et al., 2000; Biederman and Boutton, 2009). The abundance and diversity of soil nematodes are crucial in determining their contributions to soil processes and assessing ecosystem functions (Yeates et al., 2009). Variations in the occurrence and abundance of different trophic groups of nematodes are often associated with soil management practices, and may indicate changes in the soil food web structure (Freckman and Ettema, 1993). The free-living soil nematode population, which partly controls the microbial biomass through grazing on it, plays a key role in nutrient cycling (Steinberger and Loboda, 1991).

There is a paucity of research on the interaction of biochar with soil biota, with the exception of earthworms (Verheijen et al., 2009). Especially, few studies have investigated the effects of biochar addition on soil nematodes (Graber et al., 2011; Lehmann et al., 2011). The processes that influence the energy flow and organic matter within the soil will impinge on bacterial and fungal-based energy channels, which impact at hi-

by the National Basic Research Program (973 Program) of China (No. 2011CB100504), the Knowledge Innovation Program of Chinese Academy of Sciences (No. KZCX2-YW-Q1-07), and the Bluemoon Foundation, USA. ∗2 Corresponding author. E-mail: liangwj@iae.ac.cn.

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gher trophic levels (Atkinson et al., 2010). Therefore, the objective of this research was to determine the response of soil nematode communities to biochar addition in a wheat field, East China.

MATERIALS AND METHODS Microcosm trial A microcosm trial was conducted in a completely randomized design with three replications at the experimental station of Jiangdu City, Jiangsu Province of China (32◦ 35 N, 119◦ 42 E). Rice-wheat rotation is the typical cropping system in this area. The selected study site was a winter wheat (Triticum aestivum L.) field planted on November 20, 2009. The soil is classified as Stagnic Anthrosol (FAO/UNESCO classification) with 7.0 g kg−1 organic carbon, total nitrogen 0.8 g kg−1 , C/N ratio 8.5 and pH 8.0 (Zhang et al., 2010).

The trial was started on November 20, 2009, and microcosm pots (20 cm length × 15 cm width × 20 cm depth) were set in the field. Four treatments were carried out in microcosm pots as follows: no addition of biochar (CK), and the addition of biochar at 2 400 (B1), 12 000 (B5), and 48 000 kg ha−1 (B20). B1 contains approximately 1 250 kg C ha−1 . The quantity of biochar in B1 was equivalent to the biochar converted from all biomass harvested on each hectare. Before wheat was planted, the biochar with basic properties of 521.3 g kg−1 organic carbon, total nitrogen 7.2 g kg−1 , C/N ratio 72.4 and pH 9.9 was mixed into the soil of the microcosm pots (Zhang et al., 2010).

Biochar was produced under no-oxygen condition by a patent facility (China patent No. ZL200920232191.9) (Xie et al., 2010). The wheat straw was oven-dried for 12 h at 80 ◦ C, and then moved to the biochar reactor. The reactor was heated by a step-wise procedure. At first, the temperature was set at 200 ◦ C, then elevated to 250 ◦ C, 300 ◦ C, and finally to 400 ◦ C. At each temperature (except for 400 ◦ C), the process was maintained for 1.5 h. The whole process was stopped when no further smoke came out from the gas exit pipe.

Wheat was harvested on June 12, 2010. Five cores of soils were taken from 0–20 cm of each plot just before harvesting on June 10, 2010 and mixed as one sample, which was used for soil analysis and nematode determination.

Soil analysis and nematode determination Soil moisture (SM) was determined gravimetrically by drying samples at 105 ◦ C for 48 h. Soil pH was

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measured in a soil-water suspension (1:2.5, soil:water ratio). Soil organic carbon (SOC) (potassium dichromate heating method) and total nitrogen (TN) (Kjeldahl method) were determined (Bremner, 1996).

Nematodes were extracted from 50 g fresh soil by a modified cotton-wool filter method (Liang et al., 2009). Nematode populations are expressed as individuals per 100 g dry soil, and at least 100 nematodes from each sample were identified to genus level using an inverted compound microscope (Jairajpuri and Ahmad, 1992; Bongers, 1994; Ahmad and Jairajpuri, 2010). Soil nematodes were assigned to the following trophic groups characterized by feeding habits: bacterivores, fungivores, plant parasites and omnivorespredators (Steinberger and Loboda, 1991; Yeates et al., 1993). Ecological indices for soil nematodes were calculated: Shannon diversity (H ) (Shannon, 1948), dominance (λ), generic richness (GR), maturity index (MI) (excluding plant parasites), and the ratios of fungivores to bacterivores (F/B) (Bongers, 1990; Yeates and Bongers, 1999).

Statistical analysis Nematode abundances were ln(x + 1) transformed prior to statistical analysis. One-way ANOVA was used to determine the differences among biochar treatments. Mean separation was conducted based on least significant difference (LSD), and differences with P < 0.05 level was considered as statistically significant. All statistical analyses were performed by SPSS statistical software (SPSS Inc., Chicago, IL).

RESULTS AND DISCUSSION Soil properties Changes in soil chemical properties as a result of different rates of biochar application were measured at the end of the microcosm trial. No significant changes in soil pH and moisture were detected among different treatments (data not shown). The values of soil organic carbon, total nitrogen and C/N ratio increased with increasing addition of biochar (Fig. 1). Significant differences were found in soil organic carbon, total nitrogen and C/N ratio among different treatments (P < 0.01). Soil organic carbon and C/N ratio in B5 and B20 treatments and total nitrogen only in B20 treatment increased significantly compared to CK. Similarly, Zhang et al. (2010) found that the additions of biochar produced from wheat straw to soil increased soil organic carbon and nitrogen and caused significant fertility improvements. As reviewed in Atkinson et al.

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(2010), the highly porous structure and large surface area of most biochars provided refuge for beneficial soil micro-organisms such as mycorrhizae and bacteria, influenced the binding of important nutritive cations and anions, and enhanced the availability of macronutrients such as N.

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significant differences in total nematode abundance when comparing control and treatment (manure) in the ripening stage of maize. The biochar effect was not indicated by the total nematode abundance at the end of wheat growth period. It also perhaps suggested that short-term biochar application within only one growing season was not enough to affect total nematode abundance.

Composition of soil nematode community

Fig. 1 Soil organic carbon (SOC), total nitrogen (TN) and C/N ratio in different biochar addition treatments. Error bars represent the standard deviation of the mean (n = 3). Bars with the same letter in each soil property (SOC, TN or C/N ratio) indicate no significant difference at P < 0.05 by least significant difference (LSD). CK, B1, B5 and B20 represent no addition of biochar, and the addition of biochar at 2 400, 12 000 and 48 000 kg ha−1 , respectively.

Total nematode abundance No significant difference in total nematode abundance was found among different treatments (Fig. 2), which was similar with the report of Liang et al. (2009) about the effect of manure on total nematode abundance in a field experiment. They also mentioned no

Fig. 2 Responses of the total nematode and trophic group abundance to biochar addition. Error bars represent the standard error of the mean (n = 3). CK, B1, B5 and B20 represent no addition of biochar, and the addition of biochar at 2 400, 12 000 and 48 000 kg ha−1 , respectively.

Different trophic groups of soil nematodes responded differently to the biochar addition. No significant differences in the abundance of fungivores were found between the low rate (B1) and no addition of biochar (CK) (Fig. 2). The abundance of fungivores was significantly higher in B5 and B20 treatments than in CK (P < 0.05). Soil biochar incorporation has a positive impact on beneficial fungi (Atkinson et al., 2010), which would support more fungivorous nematodes. Enhanced nutrient (C or N) availability with biochar application was one of most important reasons for increasing fungi (Matsubara et al., 2002). Therefore, the responses of fungivores have been attributed to the increase of the food base and availability for microbivores with increasing biochar addition (Mahmood et al., 2003). However, no significant increase was found in the abundance of bacterivores. Dupont et al. (2009) showed that abundance of bacterial feeders did not respond significantly to crop residue (including wheat). No significant differences in omnivores-predators were found among different treatments. Similarly, omnivores-predators did not significantly respond to cover crop quality and quantity in the study of Dupont et al. (2009).

The abundance of plant parasites decreased significantly in the B5 and B20 treatments compared to CK (P < 0.05). Biochar application enhanced the progressive accumulation of soil organic matter (Atkinson et al., 2010), which increased food sources for microbes and then maintained the population of plant parasites below damaging levels through competition and antagonism between microbes and plant parasites (Hominick, 1999). The decrease in population of plant parasites has also been recorded with the application of animal manure, raw manure or green manure, which suggests that biochar has the potential to be an excellent soil ameliorant as other manures (Hayer, 2006). The accumulation of certain nitrogenous compounds (toxic for nematodes) produced during organic matter decomposition is often cited as a possible mechanism for reducing the levels of plant parasitic nematodes (Nahar et al., 2006).

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Thirty-six genera were identified under different biochar addition treatments (Table I). Among bacterivores, Heterocephalobus was found to be dominant (relative abundance > 10%) among all treatments and Chiloplacus in B20. Aphelenchoides, a dominant fungivore, was significantly higher in the biochar addition treatments (B1, B5 and B20) than CK (P < 0.05).

Dupont et al. (2009) found a significantly high population of Aphelenchoides in soil with residue of a high C/N ratio. High C/N ratios were also found in biochar addition treatments in our study. Tylenchus, a plant parasite, was the dominant genus in the no biochar treatment (CK), and Hirschmanniella in CK and B1. Hirschmanniella was also prevalent in the study of Li et al. (2009) about the effect of residue in-

corporation on soil nematodes in a wheat field, which proved that it might be associated with the wheat field.

Significantly high populations of Rhabdolaimus in B20 (P < 0.05) and Longidorella in CK (P < 0.01) were found. Nematode genera belonging to fungivores preferred biochar-enriched environment to get more microbial resource as food (Atkinson et al., 2010), while those belonging to plant parasitic group favored environment with no or low biochar to avoid the competition of microbes (Hominick, 1999).

Nematode ecological indices Significant differences in the values of H and F/B ratio were observed among different treatments (Table II). The ratios of F/B were significantly higher in the

TABLE I Relative abundance of nematode genera present in different biochar addition treatmentsa) Tropic group

Genus

Bacterivores

Acrobeloides Alaimus Chiloplacus Chromadorita Eucephalobus Heterocephalobus Leptolaimus Mesorhabditis Monhystera Panagrolaimus Plectus Rhabdolaimus Aphelenchoides Campydora Diphtherophora Ditylenchus Dorylaimoides Tylencholaimus Coslenchus Hirschmanniella Merlinius Paratylenchus Pratylenchus Psilenchus Rotylenchus Tylenchus Clarkus Dorylaimellus Epidorylaimus Eudorylaimus Longidorella Mesodorylaimus Microdorylaimus Nygolaimus Prodorylaimium Tobrilus

CK

B1

B5

B20

6.6±1.1 -c) 4.6±0.5 0.3±0.3 2.1±0.7 34.3±13.0 1.1±0.6 0.4±0.4 3.3±1.9 0.7±0.7 18.8±5.6 0.4±0.4 0.7±0.4 6.6±0.8 0.4±0.4 0.4±0.4 4.1±2.6 3.8±2.1 0.4±0.4 1.0±1.0 0.7±0.4 0.4±0.4 4.8±3.0 4.2±1.1

7.9±1.7 0.4±0.4 20.9±8.0 1.8±1.8 24.4±8.3 1.8±1.0 1.1±0.6 0.7±0.7 3.3±1.1 11.2±1.7 1.1±1.1 1.4±1.4 1.9±0.4 0.7±0.7 5.8±1.3 0.3±0.3 0.4±0.4 3.9±0.9 0.4±0.4 7.5±0.5 0.4±0.4 1.2±0.6 0.7±0.4 0.7±0.7

%

Fungivores

Plant parasites

Omnivores-predators

1.2±1.2b) 1.1±0.5 9.3±4.0 27.8±5.0 1.4±0.8 1.2±1.2 0.6±0.6 7.2±4.5 1.8±1.8 2.2±1.6 1.5±0.2 1.7±1.0 1.5±0.2 0.5±0.5 15.2±4.0 0.4±0.4 11.3±1.3 3.8±2.1 3.6±0.9 1.0±0.5 4.2±1.6 1.7±1.1

8.0±1.7 1.3±0.7 1.3±1.3 0.4±0.4 2.9±0.7 19.3±0.4 0.4±0.4 0.4±0.4 0.4±0.4 4.3±2.5 3.7±1.0 12.7±4.0 2.0±0.8 2.2±0.2 10.9±1.7 0.6±0.6 2.2±1.7 1.0±0.5 8.3±2.4 0.8±0.8 1.1±1.1 3.8±1.8 3.4±1.2 1.3±0.7 2.7±1.3 5.0±0.8

B1, B5 and B20 represent no addition of biochar, and the addition of biochar at 2 400, 12 000 and 48 000 kg ha −1 , respectively. error (n = 3). c) Not found. a) CK,

b) Mean±standard

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TABLE II Nematode ecological indicesa) in different biochar addition treatments Treatment

F/B ratio

H

λ

GR

MI

CK B1 B5 B20

0.08±0.00bb) 0.22±0.11a 0.21±0.02a 0.26±0.03a

2.08±0.12b 2.52±0.06a 2.20±0.18b 2.21±0.07b

0.18±0.03a 0.10±0.01a 0.19±0.07a 0.17±0.02a

3.24± 0.08a 3.95±0.42a 3.64±0.51a 3.21±0.14a

2.50±0.15a 2.36±0.01a 2.40±0.49a 2.35±0.05a

a) F/B ratio = ratio of fungivores to bacterivores; H = Shannon diversity; λ = dominance; GR = genera richness; MI = maturity index. b) Mean±standard deviation.

three biochar addition treatments than CK (P < 0.01).

F/B ratio was used as an indicator of the dominant decomposition pathway (Ruess, 2003) and clearly reflected the shift in prevalence of bacterial-feeding to fungal-feeding nematodes (Steel et al., 2010). The results in this study suggested that fungal decomposition pathways were relatively more important in the treatment with biochar addition. Ecosystems with fungaldominated soil communities may have higher C retention than soil communities dominated by bacterial pathways of decomposition due to differences in fungalmediated aggregate turnover (Six et al., 2006). However, supporting evidence from references was limited until now and more studies were needed to verify it.

The values of H were significantly higher in B1 than in CK, B5 and B20 (P < 0.01). The low biochar addition rate stimulated the diversity of soil nematode communities, but the high addition did not. No significant adverse effect on soil nematode diversity was exhibited at any level of biochar addition. No significant differences in λ, GR and MI were found among different treatments in our study. Nematode faunal analysis inferred by these ecological indices indicated that the soil nematode communities were relatively undisturbed or disturbed very little by the biochar addition treatments. We can conclude that no significant disturbance to soil food web was found, and biochar as compost manure with short-term addition was safe enough in view of biodiversity.

CONCLUSIONS Our microcosm trial showed that the higher rates of biochar application significantly increased soil organic carbon content and C/N ratio. No significant treatment effects were found on the total nematode abundance when short-term biochar addition was practiced.

The biochar addition to soil significantly increased the abundance of fungivores, but decreased that of plant parasites. The effect of biochar application was more pronounced on nematode trophic groups than on total abundance. Further studies are needed to determine

the long-term effect of biochar application on soil nematodes.

ACKNOWLEDGEMENT The authors wish to express their appreciation to Prof. W. AHMAD (Department of Zoology, Aligarh Muslim University, India) for the English proofreading.

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