The impact of sewage sludge compost on tree peony growth and soil microbiological, and biochemical properties

Chemosphere xxx (2013) xxx–xxx

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The impact of sewage sludge compost on tree peony growth and soil microbiological, and biochemical properties Dong Xue ⇑, Xiangdong Huang Department of Environmental Engineering and Chemistry, Luoyang Institute of Science and Technology, Luoyang 471023, China

h i g h l i g h t s  The effects of sludge compost on tree peony–soil ecosystems were studied.  Proper sludge compost improved soil microbiological and biochemical properties.  Proper sludge compost enhanced ornamental value of tree peony.  Sludge compost inhibited the yellow leaf disease of tree peony.

a r t i c l e

i n f o

Article history: Received 7 December 2012 Received in revised form 16 May 2013 Accepted 17 May 2013 Available online xxxx Keywords: Sludge compost Tree peony Microbial biomass Microbial activity Enzyme activity

a b s t r a c t In order to assess the suitability of sludge compost application for tree peony (Paeonia suffruticosa)–soil ecosystems, we determined soil microbial biomass C (Cmic), basal respiration (Rmic), enzyme activities, and tree peony growth parameters at 0–75% sludge compost amendment dosage. Soil Cmic, Rmic, Cmic as a percent of soil organic C, enzyme (invertase, urease, proteinase, phosphatase, polyphenoloxidase) activities, and plant height, flower diameter, and flower numbers per plant of tree peony significantly increased after sludge compost amendment; however, with the increasing sludge compost amendment dosage, a decreasing trend above 45% sludge compost amendment became apparent although soil organic C, total Kjeldahl N, and total P always increased with the sludge compost amendment. Soil metabolic quotient first showed a decreasing trend with the increasing sludge compost application in the range of 15–45%, and then an increasing trend from compost application of 45–75%, with the minimum found at compost application of 45%. As for the diseased plants, 50% of tree peony under the treatment without sludge compost amendment suffered from yellow leaf disease of tree peony, while no any disease was observed under the treatments with sludge compost application of 30–75%, which showed sludge compost application had significant suppressive effect on the yellow leaf disease of tree peony. This result convincingly demonstrated that 645% sludge compost application dosage can take advantage of beneficial effect on tree peony growth and tree peony–soil ecosystems. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction With the development of wastewater treatment industry, the production of municipal sewage sludge increased rapidly and has reached an enormous magnitude. Sewage sludge application on land was considered as a kind of economic and effective treatment method because it can recycle the nutrients such as organic matter, nitrogen and phosphorous contained in sludge for plant growth and improve soil physical properties (Casado-Vela et al., 2006; Kidd et al., 2007). However, the farming practice of sewage sludge is not exempt of threats to environment from their heavy metal and other harmful toxics such as toxic organics, pathogens and phytotoxic (Schnaak et al., 1997; Dai et al., 2007; Singh and Agra⇑ Corresponding author. Tel./fax: +86 (0)379 65928271. E-mail address: [email protected] (D. Xue).

wal, 2007). Many studies have shown that composting is an efficient way to stabilize the organic matter, eliminate harmful toxics, and reduce risks of heavy metals in sludge (Planquart et al., 1999; Korboulewsky et al., 2002). The impact of composted sewage sludge application on some soil–plant ecosystems of crops has been reported, which have shown that the response of plant and its soil property to composted sewage sludge was different between different plants and at different levels of composted sewage sludge amendments (Wei and Liu, 2005; Araújo et al., 2007; RocaPérez et al., 2009). Up to now, there are few available data about the impact of sewage sludge compost on perennial woody plants and assessing the optimum dose to be applied. Tree peony (Paeonia suffruticosa) is one of the most famous ornamental flowers, known as the queen of flowers, and planted throughout the country in China. In order to develop tourism and commercialization of tree peony, there are increasing planting

0045-6535/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2013.05.065

Please cite this article in press as: Xue, D., Huang, X. The impact of sewage sludge compost on tree peony growth and soil microbiological, and biochemical properties. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.05.065

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areas of tree peony in recent years in the world. Like many perennial woody flowers, fertilization is very important management measures with peony planting. Tree peony garden soils usually received three applications of fertilizer per year in order that peony flowers are big and colorful, at the same time, a large amount of fertilizer applications also undoubtedly causes the increase of tree peony planting cost. Soil biological and biochemical properties are increasingly recognized as important for assessing the sustainability of ecosystems. Soil microorganisms play a crucial role in nutrient cycling, energy flow and organic matter decomposition (Schutter et al., 2001; Bastida et al., 2008). Consequently, they have been widely recognized as integrative component of soil quality. Microbial biomass C (Cmic), basal respiration (Rmic), and enzyme activities have been employed in the national and international monitoring programs due to their great sensitivity to anthropogenic disturbance and environmental changes (Shen et al., 2005; Chen et al., 2008; Franco-Otero et al., 2012; Gong et al., 2012). Little is known about how composted sewage sludge application affects tree peony growth and its soil microbiological, and biochemical properties in tree peony–soil ecosystems. Therefore, the objectives of our study were to evaluate the effects of composted sewage sludge application on the growth of tree peony and their soil chemical, microbiological, and biochemical properties and identify the suitable application quantity of sludge compost for tree peony–soil ecosystems.

2. Materials and methods

Table 1 Physicochemical characteristics of the soil and sludge compost used in this study. Parameter

Soil

Sludge compost

pH EC (lS cm1) Organic C (g kg1) Total Kjeldahl N (g kg1) Total P (g kg1) Total Cu (mg kg1) Total Zn (mg kg1) Total Pb (mg kg1) Total Cd (mg kg1) Total Cr (mg kg1) Total Ni (mg kg1)

8.42–8.49 229 7.82 1.18 0.83 21.8 75.1 20.7 0.20 48.6 24.3

7.03–7.12 667 124 19.4 20.2 975 1350 186 7.61 288 129

2.2. Chemical analysis The samples of soil and sludge compost were air dried for chemical analysis by conventional methods (Sparks et al., 1996). Briefly, pH and electrical conductivity (EC) were determined on a suspension of samples in water (1:5 w/v) with a pH and EC meter. Total organic C (Org C) was determined by dichromate oxidation, and the total Kjeldahl N (TKN) was determined by Kjeldahl digestion and quantified using a continuous flow analyzer (Skalar, the Netherlands). Total P (TP) was determined at a wavelength of 880 nm by the phosphomolybdate colorimetric method. Total heavy metals were determined by digestion with mixture of nitric, sulphuric, and perchloric acid in the ratio of 5:1:1 (Allen et al., 1986), and then analyzed in a Perkin–Elmer AA300 atomic absorption spectrophotometer. Physicochemical characteristics of the soil and sludge compost used in this study are shown in Table 1.

2.1. Test materials and experimental design 2.3. Microbiological and biochemical assays The sewage sludge used for composting was collected from the wastewater treatment plant located in Luoyang city, China. Sewage sludge was composted in a forced ventilation system, on a pilot scale, using 70% sewage sludge and 30% maize straw by volume. The temperature of the compost remained above 55 °C for over a wk. After 45 d of composting, the sludge compost products presented loose structure, grayish brown, and fragrance like fresh clay. The soil used for pot experiments were cinnamon soil which were common soils locally. Soil and sludge compost were air dried in the shade, sieved through a 2-mm mesh, homogenized and mixed according to each treatment. Three-year-old tree peonies sapling of Luo Yang Hong used in pot experiments were provided by National Peony Garden of Luoyang, China. Luo Yang Hong were grown with six types of sludge compost treatments in round plastic pots (35 cm in top width and 40 cm in height) for the pot experiments (twenty replicates each treatment). The compositions and names of each treatment in the experiment were C0 (100% soil), C15 (15% sludge compost and 85% soil), C30 (30% sludge compost and 70% soil), C45 (45% sludge compost and 55% soil), C60 (60% sludge compost and 40% soil), and C75 (75% sludge compost and 25% soil). Planting experiment was performed at a greenhouse under natural light. The temperature was maintained at 14–16 °C in the daytime and 10–12 °C at night before flower bud appearance. After flower bud appearance, the daytime temperature was 20–25 °C and the nighttime temperature was 14–16 °C. The relative humidity throughout the experimental period was 60–85%. About 60 d after planting, tree peony flowers were in full bloom stage. At this time, all of the soil chemical, microbiological, and biochemical properties analyses were conducted, and moreover, tree peony growth parameters, plant height, flower diameter, flower numbers per plant, diseased plant rate, were observed and measured.

Cmic was determined by the chloroform fumigation–extraction method (Vance et al., 1987). The K2SO4-extracted C of both fumigated and unfumigated samples was analyzed using a total organic C analyzer (Shimazu, TOC-500, Chiba, Japan), and a KEC value of 0.45 was used to convert the measured flush of C to Cmic (Yao et al., 2003). Rmic was determined by measuring CO2 evolution. 20 g (oven-dry basis) of field-moist soil were incubated in 250 mL airtight glass vessels at 25 °C for 1 d. The CO2 produced from the soil was absorbed in NaOH and determined by titration with HCl. The metabolic quotient (qCO2) is defined as the ratio of Rmic to Cmic (Anderson and Domsch, 1986). Soil enzyme activities were determined using the methods described by Guan (1986). Catalase activity was determined by back-titrating residual H2O2 with KMnO4 in the presence of H2SO4. 5 g of soil sample were mixed with 40 mL distilled water and 5 mL 0.3% hydrogen peroxide solution. The mixture was incubated at 37 °C for 20 min and added 5 mL of 1.5 M sulfuric acid. After filtration, the mixture was titrated using a standard solution of 0.1 M KMnO4. Invertase activity was determined colorimetrically using 3, 5dinitrosalicylic acid. 5 g of soil sample were mixed with 15 mL of 8% sucrose solution, 5 mL of phosphate buffer (pH 5.5), and 5 drops of methylbenzene. The mixture was filtered immediately after incubation at 37 °C for 24 h. Then 1 mL of filtrate was put in 50 mL volumetric flask and added with 3 mL of 3, 5-dinitrosalicylic acid solution. The volumetric flask were heated in a boiling water bath for 5 min and then cooled with tap water for 3 min. Finally, the solution was diluted with distilled water to 50 mL and assayed colorimetrically at 508 nm. Urease activity was measured colorimetrically using indophenol blue. 5 g of soil sample were mixed with 1 mL of methylbenzene for 15 min, then added with 10 mL of 10% urea solution and

Please cite this article in press as: Xue, D., Huang, X. The impact of sewage sludge compost on tree peony growth and soil microbiological, and biochemical properties. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.05.065

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a

42

Plant height (cm)

b

b

35 c 28

c

d

21 14 7 0

Flower diameter (cm)

20

a b

16

b

b

c 12

d

8 4 0 15 a

Flower numbers per plant

20 mL of citrate buffer (pH 6.7). The mixture was filtered after incubation at 37 °C for 24 h. Next 4 mL of sodium phenolate solution and 3 mL of sodium hypochlorite solution were added to 3 mL of filtrate. After 20 min, the solutions were diluted with distilled water to 50 mL and the released ammonium was assayed colorimetrically at 578 nm. Proteinase activity was measured colorimetrically using ninhydrin. 4 g of soil sample were mixed with 20 mL of 1% casein solution prepared with phosphate buffer (0.2 M, pH 7.4) and 1 mL of methylbenzene. The mixture was incubated at 30 °C for 24 h, then 2 mL of 0.05 M sulphuric acid and 12 mL of 20% sodium sulfate solution were added. After centrifugation at 6000 rpm for 15 min, 2 mL of the supernate was placed at 50 mL volumetric flask and added with 1 mL of ninhydrin reagent (2 g of ninhydrin dissolved in 100 mL of acetone). The solution was heated in boiling water for 10 min and then cooled to room temperature. Finally, the solutions were adjusted to 50 mL with distilled water, then measured colorimetrically at 500 nm. Phosphatase activity was determined colorimetrically using disodium phenyl phosphate. 5 g of soil sample were mixed with 2.5 mL of methylbenzene for 15 min, then 20 mL of 0.5% disodium phenyl phosphate solution (prepared with pH 7.0 citrate buffer solution) was added. After shaking, the mixture was incubated at 37 °C for 24 h, added with 100 mL of 0.3% aluminum sulfate solution, and then filtered. Next, 3 mL of filtrate was added with 5 mL of boric acid buffer solution and 0.2 mL of 2, 6-dibromoquinone chloride solution. Finally, the solution was diluted with distilled water to 50 mL, and the released phenol was measured colorimetrically at 660 nm. Polyphenol oxidase activity was determined with iodine titrimetry method. 5 g of soil sample were mixed with 10 mL distilled water, 6 mL of 0.1% ascorbic acid, and 10 mL of 0.02 M catechol solution. The mixture was incubated in 30 °C water for 2 min, and 6 mL of 10% phosphoric acid was added. Next, the mixture was filtered after shaking. The filtrate was added with 1 mL of 1% starch solution, and titrated using a standard solution of 0.005 M iodine solution.

12

b

b 9

c c

6

d

3 0

Statistical procedures were carried out with the software package SPSS 16.0 for Windows. In order to test whether effects of the sludge compost applications on soil chemical, microbiological, and biochemical properties and the biological characteristics of tree peony were significant, means and least significant differences of 5% level were calculated by a one-way ANOVA. The principal component analysis (PCA) based on the data of soil chemical, microbiological, and biochemical properties and the biological characteristics of tree peony was used to comprehensive assess the suitable application quantity of sludge compost for tree peony–soil ecosystems. 3. Results 3.1. The biological characteristics of tree peony Plant height, flower diameter, and flower numbers per plant of tree peony were significantly higher in the treatments with sludge compost applications than in the corresponding control treatment, and moreover, significantly increased with the increasing sludge compost application dosage within the range of 15–45%, and then decreased from compost application dosage of 45–75% (Fig. 1). As for the diseased plants, 50% of peony plant under the treatment without amendment suffered from yellow leaf disease of peony, while no any disease was observed in the plants with compost

Diseased plant rate (%)

50

2.4. Statistics

40 30 20 10 0

C0

C15

C30

C45

C60

C75

Treatment Fig. 1. Effect of sludge compost on the plant height, flower diameter, flower numbers per plant, and diseased plant rate of tree peony. Different letters indicate significant difference of mean value.

application dosage of 30–75%. The results showed that sludge compost application had significant suppressive effect on the yellow leaf disease of peony.

3.2. Effect of sludge compost on soil chemical properties Soil pH decreased with increasing sludge compost application dosage (Table 2). EC, Org C, TKN, and TP of soil amended with sludge compost of 15–75% were 1.4–2.6, 2.0–9.3, 3.4–16, and 4.6–22 times, respectively, higher than those of the corresponding

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Table 2 Effect of sludge compost on soil physicochemical characteristics. Treatment

pH

EC (lS cm1)

Organic C (g kg1)

Total Kjeldahl N (g kg1)

Total P (g kg1)

C0 C15 C30 C45 C60 C75

8.21–8.54 7.67–7.96 7.35–7.71 7.21–7.36 7.10–7.27 6.97–7.07

213 ± 21e 290 ± 28d 336 ± 25cd 398 ± 31c 477 ± 22b 556 ± 34a

7.7 ± 1.1f 15.1 ± 1.4e 23.4 ± 1.7d 30.2 ± 1.2c 54.8 ± 2.2b 71.3 ± 2.8a

0.9 ± 0.6f 3.1 ± 0.7e 5.9 ± 0.6d 8.0 ± 0.8c 10.9 ± 1.1b 14.0 ± 1.2a

0.7 ± 0.4f 3.2 ± 0.5e 6.1 ± 0.7d 8.8 ± 0.6c 11.8 ± 0.8b 15.1 ± 1.3a

Different letters within each column indicate significant difference of mean value.

Table 3 Effect of sludge compost on soil microbial biomass C and basal respiration. Treatment

Cmic (lg C g1 soil)

Cmic/Corg (%)

Rmic (lg CO2 C g1 soil h1)

qCO2 (lg CO2 C mg1 Cmic h1)

C0 C15 C30 C45 C60 C75

73 ± 26d 229 ± 31c 485 ± 46b 773 ± 69a 496 ± 53b 283 ± 38c

0.9 ± 0.1d 1.5 ± 0.2c 2.1 ± 0.1b 2.6 ± 0.2a 0.9 ± 0.1d 0.4 ± 0.1e

0.7 ± 0.1d 2.0 ± 0.1c 3.0 ± 0.1b 3.5 ± 0.2a 3.2 ± 0.2ab 2.5 ± 0.1b

9.9 ± 0.4a 8.9 ± 0.2b 6.1 ± 0.4c 4.6 ± 0.2d 6.5 ± 0.5c 8.9 ± 0.4ab

Different letters within each column indicate significant difference of mean value.

control, and moreover, significantly increased with increasing sludge compost application dosage.

ment than that in the treatment without amendment, with the maximum at compost application dosage of 60%.

3.3. Effect of sludge compost on soil Cmic and Rmic

3.5. PCA of the soils with sludge compost application

Cmic increased significantly with sludge compost application dosage within the range of 15–45%, and then decreased from compost application dosage of 45–75% (Table 3). Sludge compost amendment increased Cmic by 3.1–11 times within application dosage of 15–75% as compared to the control (no amendment), with the maximum increased rates found at compost application dosage of 45%. Similarly, both the ratio of Cmic to soil Org C (Cmic/Corg) and Rmic first increased and then decreased with sludge compost application dosage, with the maximum at compost amendment of 45%. With respect to the effects of sludge compost application on qCO2, contrary change trend between the treatments was observed. The qCO2 first decreased and then increased with compost application dosage, with the minimum at compost application dosage of 45%.

The PCA revealed a significant effect of sludge compost application on tree peony–soil ecosystems (Fig. 2). The PCA showed that 96.9% of the total variance in the data set could be explained by the first principal component (PC1, accounting for 73.3% of the variance) and the second principal component (PC2, accounting for 23.6% of the variance). The change trends of the scores on PC1 and PC2 with the increasing sludge compost application dosage were different (Fig. 2a). Both the scores on PC1 and PC2 showed an increasing trend from 0% to 45% and then showed a decreasing trend from 45% to 75%. The factor loadings of PCA showed the PC1 had high factor loading for Cmic, Rmic, catalase, invertase, urease, proteinase, phosphatase, polyphenoloxidase, pH (negative), diseased plant rate (negative), qCO2 (negative), and plant height, flower diameter, and flower numbers per plant of tree peony (Fig. 2b), and the PC2 had high factor loading for Cmic/Corg, EC (negative), Org C (negative), TKN (negative), TP (negative). Comprehensive principal component was used to assess the suitable application quantity of sludge compost for tree peony–soil ecosystems (Fig. 2c). With the increasing sludge compost application dosage, an increasing trend within the range of 15–45% and then a decreasing trend within the range of 45–75% were found, with the maximum at compost application dosage of 45%. The results showed that the suitable application quantity of sludge compost for tree peony–soil ecosystems was 645%.

3.4. Effect of sludge compost on soil enzyme activities Invertase, urease, proteinase, phosphatase, and polyphenoloxidase took on a common characteristic, i.e., the five enzyme activities increased significantly with sludge compost application dosage within the range of 15–45%, and then decreased from compost application dosage of 45–75%, with the maximum at compost application dosage of 45% (Table 4). For catalase activity, it was significantly higher in all treatments with sludge compost amendTable 4 Effect of sludge compost on soil enzyme activities. Treatment

C0 C15 C30 C45 C60 C75

Catalase (mL (0.1 M KMnO4) g1 soil h1)

Invertase (mg glucose kg1 soil h1)

Urease

5.1 ± 0.3e 8.3 ± 0.5d 12.5 ± 0.4c 14.2 ± 0.6b 16.7 ± 0.9a 13.9 ± 0.5bc

437 ± 17e 513 ± 34d 625 ± 33c 804 ± 36a 716 ± 24b 531 ± 21d

12.3 ± 2.5d 33.6 ± 6.4c 57.1 ± 4.1b 84.9 ± 7.3a 65.4 ± 6.4b 41.5 ± 5.8c

ðmg NHþ 4 kg

1

soil h

1

Þ

Proteinase (mg tyrosine kg1 soil h1)

Phosphatase (mg phenol kg1 soil h1)

Polyphenoloxidase (mL (0.005 M I2) g1 soil h1)

15.2 ± 1.8d 32.7 ± 3.9c 54.6 ± 3.8b 87.4 ± 6.5a 65.1 ± 5.3b 20.8 ± 2.9cd

50.1 ± 3.7d 72.8 ± 6.3c 102.3 ± 8.1b 137.4 ± 9.9a 99.8 ± 8.4b 78.9 ± 5.2c

0.66 ± 0.05d 1.02 ± 0.08c 1.61 ± 0.18b 2.44 ± 0.29a 1.38 ± 0.10bc 0.81 ± 0.07cd

Different letters within each column indicate significant difference of mean value.

Please cite this article in press as: Xue, D., Huang, X. The impact of sewage sludge compost on tree peony growth and soil microbiological, and biochemical properties. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.05.065

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D. Xue, X. Huang / Chemosphere xxx (2013) xxx–xxx

(a)

(b) 1.5

3

C mic /C org

1

Polyphenoloxidase

C0

Proteinase

pH

0.5

C15

Microbial biomass C

C30

-1

PC2

PC2

Invertase

C45 C60

EC

C75

-3

-5 -8

Catalase

qCO 2

-0.5

Organic C

-1.5 -4

0

4

-1.5

8

-0.5

0.5

Total P Total Kjeldahl N

1.5

PC1

PC1

(c)

Phosphatase Urease

Basal respiration Flower numbers Plant height Flower diameter

Diseased plant rate

6

a b

b

CPC

2

C0

C15

C30

C45

-2

C75 c

d

-6

C60

e

Treatment Fig. 2. The scores of PC1 and PC2 (a), factor loadings (b), and comprehensive principal components (c) of principal component analysis based on biological characteristics of tree peony and soil chemical, microbiological, and biochemical properties. Different letters indicate significant difference of mean value.

4. Discussion The positive effect of sludge compost application on the growth of several other perennial woody plants has been demonstrated. For example, Song and Lee (2010) investigated the effects of sludge compost on sawtooth oak (Quercus acutissima) and Japanese red pine (Pinus densiflora), and found that the sludge compost application of 25% resulted in significant increases in both plant height and biomass, the N content of plant leaves, and chlorophyll content and photosynthetic rates of the plants. Our study showed that the sludge compost application dosage of 15–75% significantly increased plant height, flower diameter, and flower numbers per plant of tree peony compared to the control. However, the increased effect reached its maximum at the sludge compost application of 45% and then decreased with compost application dosage. The result might be attributed to the following reason. For the positive aspects, the sludge compost used in the study was near neutral in pH and had high contents of Org C, TKN and TP, consequently, the application of sludge compost resulted in near neutral soil pH, the increased supply of soil Org C, TKN, TP and the improvement of soil microbiological and biochemical properties, which were conducive to tree peony growth. As for the negative aspect, the sludge compost had high EC and heavy metals, and cause undesired increase in these substances in soil as a result of the application of sludge compost (Rigueiro-Rodríguez et al., 2012). The significantly higher promotion effect at the sludge compost application of 45% than that at other application dosage was possibly a result of a combination reflection of positive and negative aspects. The studies of Huang et al. (2012) demonstrated that sludge compost amendments can effectively suppress the Fusarium wilt of cucumber. Borrero et al. (2009) reported that some composts from agricultural industry waste were effective plant growth medium in suppressing carnation Fusarium wilt. Our results also

showed that sludge compost application had significant suppressive effect on the yellow leaf disease of peony. Yellow leaf disease of peony, which is a destructive disease in peony-cultivation areas, especially in those potted peony in greenhouse, can result in ornamental reduction and serious economic loss. Yellow leaf disease was observed on a variety of plant, the ambiguity regarding the etiology still prevails. It is considered that pathogenesis of yellow leaf disease may be the infection of mycoplasma and viruses, and may also be a lack of some nutrient elements in soil (Purushothama et al., 2007). At present, there is no effective and environmentally safe disease control method. Sludge compost characteristics are the possible reason for disease suppression ability on the yellow leaf disease of peony. Sludge compost after the composting processes of fermentation and decomposition contained useful microorganisms, antagonistic bacteria of plant disease, metabolic product of useful microorganisms and a variety of nutrition elements, so that it has suppressive effect on plant disease (CasadoVela et al., 2006; Huang et al., 2012). Soil Cmic was the living part of soil Org C, generally accounts for 1–4% of total soil Org C (Anderson and Domsch, 1989; Sparling, 1992). However, our study showed that the Cmic/Corg in the treatment with sludge compost application of 75% was less than 1%. It is generally accepted that a reasonably close, linear, and positive relationship exists between the Org C and Cmic, and the accumulation of soil Org C enhances both the Cmic and Cmic/Corg. The sewage sludge compost used in the present study had a high content of Org C, and as a result soil Org C always increased with the sludge compost amendment dosage (Table 2). However, we found that the Cmic and Cmic/Corg under the treatments of 60% and 75% sludge compost applications were lower than that under the treatments of 45% sludge compost applications, although the former had higher content of Org C. This result, together with the similar result showed by Rmic which indicates the capacity of total carbon turnover and soil total microbial activities, convincingly demonstrated

Please cite this article in press as: Xue, D., Huang, X. The impact of sewage sludge compost on tree peony growth and soil microbiological, and biochemical properties. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.05.065

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D. Xue, X. Huang / Chemosphere xxx (2013) xxx–xxx

that soil Org C available for microbes did not increase proportionately to the accumulation of soil Org C with the sludge compost amendment (Anderson and Domsch, 2010). Sludge compost also contains heavy metals which had more accumulations accompanied by more Org C under the treatment with higher sludge compost amendment dosage, so that the higher sludge compost amendment may cause environmental hazards (Gillett, 1992; Brookes, 1995) and the adverse effects on microorganisms. As a result, the microbes present under sludge compost amendment above the suitable application quantity metabolize very slowly, which leads to the low capacity of Org C mineralization. Our results also indicated that soil Cmic and Cmic/Corg responds more rapidly to changes resulting from sludge compost amendment than Org C, consequently, may be rapid markers of detecting changes in soil quality and gives early indication of soil pollution due to exogenous input. The qCO2 was often used in several investigations as an index of microbial stress (Anderson and Domsch, 1993; Fernandes et al., 2005), and considered to be higher under unfavorable conditions rather than favorable conditions (Anderson and Domsch, 1993; Hu et al., 2011). We observed that the qCO2 decreased with the increasing sludge compost application dosage in the range of 15– 45%, and then an increasing trend from compost application dosage of 45–75%. This may be due to ecological imbalance caused by heavy metals under the treatment with sludge compost application more than appropriate volume (Bardgett and Saggar, 1994; Fernandes et al., 2005). As a result, microbes divert more C to maintain respiration than to synthesize new microbial biomass during mineralization of organic matter (Anderson and Domsch, 2010; Franco-Otero et al., 2012). It was widely reported that enzyme activities are not only positively related to soil fertility but also sensitive to environmental pollution (Shen et al., 2005; Chen et al., 2008). In the present study, polyphenoloxidase, invertase, urease, proteinase, and phosphatase responded rapidly to changes resulting from sludge compost amendment, showed a significant increasing trend and then a significant decreasing trend with the increasing sludge compost application. This suggested that there is not only positive influence of the improved soil fertility but also negative influence of the increased EC and heavy metals on enzyme activities along with sludge compost amendment on tree peony–soils ecosystems. Catalase can catalyze the decomposition of hydrogen peroxide into oxygen and water and effectively prevent organisms from damage caused by reactive oxygen species produced in soil metabolic processes (Yao et al., 2006). There are many reports about the inhibition of soil pollution on catalase activity, which illustrated that the degree of inhibition varied with pollutant concentration (Kızılkaya et al., 2004; Liu et al., 2008). In our study, the significant stimulation effect of sludge compost application on catalase activity was found, and moreover, there was the maximum activity at sludge compost application dosage of 60%. The results indicated that the response of enzymes to environmental pollution depended on enzyme kinds, and catalase may be less sensitive to environmental stress than polyphenoloxidase, invertase, urease, proteinase, and phosphatase.

5. Conclusions Sludge compost application significantly affected soil chemical, microbiological and biochemical properties, and biological characteristics of tree peony. With the increasing sludge compost application dosage, soil Org C, TKN, and TP significantly increased; however, microbial biomass, microbial activity, enzyme activity, and biological characteristics of tree peony showed a common characteristic, namely, they first showed an increasing

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Please cite this article in press as: Xue, D., Huang, X. The impact of sewage sludge compost on tree peony growth and soil microbiological, and biochemical properties. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.05.065