Effects of the novel pyrimidynyloxybenzoic herbicide

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Oct 12, 2014 - microorganisms and its degradation in. Chinese soils. Zhiqiang Cai, Shanshan Li, Wenjie. Zhang, Jiangtao Ma, Jing Wang, Jinyan.
Effects of the novel pyrimidynyloxybenzoic herbicide ZJ0273 on enzyme activities, microorganisms and its degradation in Chinese soils Zhiqiang Cai, Shanshan Li, Wenjie Zhang, Jiangtao Ma, Jing Wang, Jinyan Cai & Guanghua Yang Environmental Science and Pollution Research ISSN 0944-1344 Volume 22 Number 6 Environ Sci Pollut Res (2015) 22:4425-4433 DOI 10.1007/s11356-014-3674-1

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Author's personal copy Environ Sci Pollut Res (2015) 22:4425–4433 DOI 10.1007/s11356-014-3674-1

RESEARCH ARTICLE

Effects of the novel pyrimidynyloxybenzoic herbicide ZJ0273 on enzyme activities, microorganisms and its degradation in Chinese soils Zhiqiang Cai & Shanshan Li & Wenjie Zhang & Jiangtao Ma & Jing Wang & Jinyan Cai & Guanghua Yang

Received: 15 July 2014 / Accepted: 29 September 2014 / Published online: 12 October 2014 # Springer-Verlag Berlin Heidelberg 2014

Abstract Enzyme activity and microbial population in soils have important roles in keeping soil fertility. ZJ0273 is a novel pyrimidynyloxybenzoic-based herbicide, which was recently developed in China. The effect of ZJ0273 on soil enzyme activity and microbial population in two different soils was investigated in this study for the first time. The protease activity was significantly inhibited by ZJ0273 and this inhibiting effect gradually weakened after 60-day incubation. The results also showed that ZJ0273 had different stimulating effects on the activities of dehydrogenase, urease, and catalase. Dehydrogenase was consistently stimulated by all the applied concentrations of ZJ0273. The stimulating effect on urease weakened after 60-day incubation. Catalase activity was subject to variations during the period of the experiments. The results of microbial population showed that the number of bacteria and actinomycetes increased in ZJ0273-treated soil compared with the control after 20 days of incubation, while fungal number decreased after only 10 days of incubation in soils. DT50 (half-life value) and k (degradation rate constant) of ZJ0273 in S1 (marine-fluvigenic yellow loamy soil) and S2 (Huangshi soil) were found 69.31 and 49.50 days and 0.010 and 0.014 day −1 , respectively.

Responsible editor: Zhihong Xu Z. Cai (*) : S. Li : W. Zhang : J. Ma : J. Wang : J. Cai : G. Yang Laboratory of Applied Microbiology, Changzhou University, Changzhou 213164, China e-mail: [email protected] Z. Cai e-mail: [email protected]

Keywords ZJ0273 . Soil enzyme . Herbicide . Microbial population . Degradation kinetics

Introduction Herbicides are usually applied for ensuring the crop production and yield in modern agriculture. The man-made herbicides can control weeds through their specific mechanisms, such as inhibiting enzyme activity and signal transduction pathway etc. However, herbicides are frequently detected in plants, soils, and groundwater, and herbicide application often leads to soil contamination of herbicide residues and can also affect the soil microbial communities by changing their number (Cycoń and Piotrowska-Seget 2007; Zhang et al. 2010a), overall microbial activity (Zabaloy et al. 2008), soil enzyme activity (Sannino and Gianfreda 2001), and diversity of soil microbial communities (Ratcliff et al. 2006; Zhang et al. 2010b; Mahía et al. 2011; Zabaloy et al. 2012). Soil organic matter decomposition is largely a biological process that occurs naturally. The decomposition speed is determined by soil microorganisms. Herbicide-induced changes in microbial metabolic activity, community structure, and enzyme activity can affect soil fertility, and some of the changes can be harmful to the sustainable development of crop productivity and also threaten human health through polluted food chains (Arias-Estevez et al. 2008; Walker et al 1997; Alexander 1977; Srinivasulu et al. 2012). The novel but widely used pyrimidynyloxybenzoic herbicide, propyl 4-(2-(4,6-demethoxypyrimidin-2yloxy)benzylamino) benzoate (ZJ0273), is a recently developed herbicide in China and can control weeds growing in oilseed rape crops, such as Chenopodium serotinum Linn., Sclerochloa kengiana (Ohwi) Tzvel, Alopecurus japonicus Steud., Ranunculus muricatus Thunb., Poa annua,

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Malachium aquaticum (L.) Fries, Alopecurus aequalis Sobol, and Capsella bursapastrois L. (Tang, et al. 2005). ZJ0273 can effectively eradicate many monocotyledonous and dicotyledonous weeds with an efficiency of 80–90 % (Lu et al. 2004; Tang et al. 2005). In 2007, ZJ0273 was applied to a planting area of almost 533,000 ha in China (Wang et al. 2009a; Cai et al. 2012). Recent studies have focused on ZJ0273 and its residue determination in soils and rapeseed (Yang et al. 2009; Han et al. 2009b), the formation of soil-bound residues (Wang et al. 2009a, 2013), absorption, translocation and residue in oilseed rape (Han et al. 2009a.), the kinetics of extractable and bound residues (Wang et al. 2009b), the transformation and fate characterization in aerobic and anaerobic soils (Wang et al. 2010, 2013; Cai et al. 2013a), the metabolism of ZJ0273 in oilseed rape and crickweed (Yue et al. 2012), and microbial degradation of ZJ0273 and its degradation pathway (Cai et al. 2012, 2013a, b). However, no data is available on the influence of ZJ0273 on enzyme activity and microorganism community in soils and it remains poorly understood until now. The present study aims to investigate the effect of ZJ0273 on the soil enzyme activity and microbial population in soils. In order to ascertain this impact, dehydorgenase, urease, protease, and catalase activities in soils, the bacterial, fungal, and actinomycic population were determined; moreover, the rate of ZJ0273 degradation in soils were also studied.

Materials and methods Herbicide and test soils ZJ0273 (formula weight, FW 423, Fig. 1) was synthesized at the Institute of Nuclear Agricultural Sciences, Zhejiang University (China) and Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences. HPLC grade methanol was purchased from TEDIA (OH, USA). All other reagents and common chemicals were of analytical grade and purchased from Sinopharm Chemical Reagent Company (Shanghai, China). Two different types of soils from different agricultural fields were used in this study, which were marine-fluvigenic yellow loamy soil (S1) and Huangshi soil (S2), respectively. The soil samples were taken from the surface zone (0 to 15 cm depth) by auger from 20 different positions over a 24,000-m2 area of the oil rape fields in Zhejiang and Jiangsu provinces, China. All the soil samples were air-dried, mixed, and passed through a 1-mm sieve. Their basic physicochemical characteristics were determined by previously reported methods (Gee and Bauder 1986) and listed in Table 1.

Environ Sci Pollut Res (2015) 22:4425–4433 Forced air inlet

OMe

MeO N

Forced air outlet

N

a

O

b

H N ZJ-0273

CO2Pr-n

Fig. 1 Chemical structural formula of ZJ0273 and experimental equipment for degradation of ZJ0273 in soil. a ZJ0273 (propyl 4-(2-(4,6demethoxy pyrimidin-2-yloxy)benzylamino)benzoate) molecular structure. b Equipment for monitoring degradation of ZJ-0273 in soil

Experimental design and soils incubation To study the effect of ZJ0273 on soil enzyme activity and soil microbial population in aerobic soils, 1 g of ZJ0273 was dissolved in 50 ml of methanol and added into the test soils. Each soil (400 g, air-dry weight) was transferred into a 500-ml flask with a rubber stopper and treated with ZJ0273 stock solution to give a final concentration (10, 50, and 100 mg kg−1 soil) and thoroughly mixed. The treated soil samples were left in a fume hood to allow the evaporation of methanol. Soil samples without herbicide served as controls. All the tests for each soil were conducted with three replicates. The soil moisture content was adjusted to about 60 % of the maximum water-holding capacity by adding MilliQ (MQ) water. During the incubation, the soil moisture content was maintained constant by weighing the flasks and correcting for any weight loss by adding MQ water. The incubation temperature was 30±2 °C. The flasks with soil samples were sealed and connected with a series of air-tight test tubes; a slow and continuous air flow was maintained (Fig. 1b). At different time intervals (5, 10, 20, 30, 45, 60, and 90 days after treatment), soil was sampled from the flask and was used for determining enzyme activity, microbial population, and the concentration of ZJ0273.

ZJ0273 extraction and analytical procedures At each sampling time, 10 g of soil sample was transferred into a centrifuge tube and consecutively extracted according to the reported methods (Mordaunt et al. 2005; Wang et al. 2009a; Cai et al. 2012, 2013a). The extraction procedure was employed with each subsequent solvent being less polar. ZJ0273 and its biodegradation intermediates were determined with an Agilent 1260 infinity high-performance liquid chromatography according the previous reported method (Cai et al. 2012, 2013a).

Author's personal copy Environ Sci Pollut Res (2015) 22:4425–4433 Table 1 Physico-chemical characteristics of the experimental soils

Characteristics

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Soil

Marine-fluvigenic yellow loamy soil (S1) Hangzhou, Zhejiang Province

Changzhou, Jiangsu Province

pH (H2O)

6.50

5.95

OMa (%) CEC b (cmol kg−1) Clay (%) Silt (%) Sand (%) Texture (%)

1.98 6.40

1.52 7.11

8.0 71.2 20.8 59.8 37.1 3.1 0.12 10.25 5.22

33.5 49.8 16.7 60.7 32.6 6.7 0.08 7.65 10.7

Location

a

Organic matter

b

Cation exchange capacity

0.09 mm

Total N (%) P (mg kg−1) K (g kg−1)

Enzyme activity in soils The short-term enzymatic activity of four hydrolases was analyzed for each soil: protease (EC 3.4.21.92), dehydrogenase (EC 1.1.1.1), urease (EC 3.5.1.5), and catalase (EC 1.11.1.6). Protease activity was determined using the method described by Lessard (2013) and Schinner (1996); (Lessard et al. 2013; Schinner et al. 1996). Two grams of fresh soil was mixed with 5 ml of 0.05 M TRIS buffer (pH 8.1) and 5 ml of 2 % w/v casein as substrate. The reaction system was incubated for 48 h at 30 °C. After incubation, the soil samples were mixed with 5 ml of 0.92 M trichloroacetic acid (Cl3CCOOH, TCA) to finish the reaction and centrifuged at 8000 rpm for 10 min, and the supernatant was quantitatively transferred to the test tube, where reactants (mixture of complexed alkali reagent and Folin Ciocalteu phenol reagent) were added to color the sample. The absorbance was read at 680 nm against the blank and converted in tyrosine concentration by the standard curve prepared with different standard solutions varying from 0 to 100 μg tyrosin ml−1. Dehydrogenase activity was measured according to the previous published method (Tabatabai 1994). Two grams of fresh soil was mixed fully with 1 ml of 2 % 2, 3, 5-triphenyl tetrazolium chloride (TTC) solution and 1 ml of deionized water. After 24 h of incubation at 37 °C, 10 ml of ethanol was added to each test tube and mixed thoroughly. The mixture solution was filtered through filter paper, and the concentration of triphenylformazan (TPF) was colored and determined at 485 nm by a spectrophotometer through the standard curve. Catalase activity was determined by back-titrating residual hydrogen peroxide (H2O2) with KMnO4 and was expressed as milligram of H2O2 consumption/gram of soil (Lu et al. 2014).

Huangshi soil (S2)

Two grams of soil sample was mixed fully with 20 ml of distilled water and 2 ml of 0.30 % H2O2 solution. The mixture was incubated at 37 °C, 120 rpm for 30 min. Then, 1.5 M H2SO4 was added to finish the reaction and titrated residual H2O2 with 0.02 M KMnO4 solution. Urease activity was assayed using the method described by May and Douglas (May and Douglas 1976). Five grams of dry soil sample was mixed with 5 ml of 10 % urea solution and 10 ml of 0.1 M citrate buffer (pH 6.7). The solution was incubated for 3 h at 37 °C. NH4+-H was determined at 578 nm using a spectrophotometer.

Soil microbial population determination Microbial population (heterotrophic bacteria, actinomycetes, and fungi) counting was assayed through most probable number method (MPN). Five replicate tubes of three consecutive tenfold serial dilutions of a microbial sample are cultured. Five grams of fresh soil sample was put into 250-ml flasks containing 45 ml of sterile 0.85 % NaCl solution, shaken for 20∼30 min at 200 rpm and stationed for 5 min. The suspension was diluted serially in sterile tubes containing 9 ml of sterile water. Beef extract peptone medium, Guze’a medium no. 1, and Martin medium were used for the enrichment of heterotrophic bacteria, actinomycetes, and fungi, respectively. The test tube was incubated at 30 °C for 36 h, 5 days, and 2 days for beef extract peptone medium, Guze’a medium no. 1, and Martin medium. The number of tubes showing microbial growth are scored (appropriate dilutions are such that growth is found in some, but not all tubes). The MPN table was used to calculate the number of microbial population in 1 g of soil sample.

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Statistical analysis and calculation The degradation of ZJ0273 in soils followed a first-order exponential decay model. The rate constant from the firstorder model was used to determine the DT50. DT50 (half-life value) was calculated by: −ln

ct ¼ kt c0

ct ¼ co e−kt

or

ð1Þ

where C0 is the initial concentration of ZJ0273 (mg kg−1 soil), Ct is the concentration of herbicide at time t, t is the incubation time (days), and k is the degradation rate constant of the herbicide (day−1). DT50 and DT90 were calculated as ln2/k and ln10/k, respectively. Descriptive statistics was applied and all data were averages.

Results and discussion Effect of ZJ0273 on soil enzyme activity Soil enzyme activities are sensitive indicators of response to environmental stress in natural system. Enzyme activities in

c

4.0 Control 10 ppm 50 ppm 100 ppm

3.5

Protease (mg tyrozine /g soil)

Protease activity Protease activity decreased in all herbicide-treated soils during the period of the experiment. Compared with the control, protease activity both decreased significantly after 10 days of incubation in S1 and S2. The value of protease activity in control soil samples was higher than that in herbicide-treated soil samples; the application of ZJ0273 can inhibit the protease activity in the order of 100 mg kg−1 soil>50 mg kg−1 soil>10 mg kg−1 soil. With the incubation time prolonged, protease activity gradually increased in the ZJ0273-treated soils. The activities of protease in S1 and S2 after 30 days of incubation reached higher levels and were found 2.54 and 1.90 mg tyrosine g−1 soil under the treatment of 50 mg kg−1 of ZJ0273, while protease activities in S1 and S2 were only 1.56 and 0.62 mg tyrosine g−1 soil under the treatment of 100 mg kg−1 of ZJ0273, respectively. The results showed that higher residue concentration of ZJ0173 could lead to relative low protease activity in both tested soils.

Dehydrogenase (mg TPF /g soil)

a

soil are important and support the biochemical processes. Herbicide application is generally expected to generate changes of enzyme activity in soils. The effects of ZJ0273 on the activities of protease, dehydrogenase, urease, and catalase are shown in Figs. 2 and 3.

3.0 2.5 2.0 1.5 1.0 0.5

Control 10 ppm 50 ppm 100 ppm

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0

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Catalase (ml, 0.02 M KMnO4 /g soil)

40

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Incubation days

d

Control 10 ppm 50 ppm 100 ppm

60

0

80

Incubation days

b 80 Urease ( g NH4-N / g soil)

2

Control 10 ppm 50 ppm 100 ppm

6

4

2

0

0 0

20

40

60

80

Incubation days

Fig. 2 Effects of ZJ0273 on soil S1 enzymatic activity for different incubation periods. a Soil protease activity; b soil dehydrogenase activity; c soil urease activity; d soil catalase activity. Control, 10, 50, and

0

20

40

60

80

Incubation days

100 ppm: soil spiked with ZJ0273, 0, 10, 50, and 100 mg kg−1, respectively. The error bars indicate standard deviations

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a

c

b

d

Fig. 3 Effects of ZJ0273 on soil S2 enzymatic activity for different incubation periods. a Soil protease activity; b soil dehydrogenase activity; c soil urease activity; d soil catalase activity

Dehydrogenase activity Dehydrogenase activity in S1 and S2 affected by ZJ0273 remained at a relatively high stable level during the period of the incubation. The value of dehydrogenase activity in the S1 and S2 after application ZJ0273 was higher than that in the control soil, and dehydrogenase activity increased from the stresses of 10, 50, and 100 mg kg−1 of ZJ0273. The results in Figs. 2 and 3 also showed that the stimulation effect by ZJ0273 was gradually weakened with increased concentration of ZJ0273 in S1 and S2, which means higher concentration of ZJ0273 may inhibit dehydrogenase activity in soils. Urease activity Urease activity in S1was slightly inhibited on day 10 and day 20 after treatment of 10, 50, and 100 mg kg−1 of ZJ0273; however, the urease activity was weakly increased from 30 days of incubation after application of ZJ0273, and then it returned to the control level after 60 days of incubation. While urease activity in S2 was stimulated to increase on day 10 after treatment of 10 mg kg−1 of ZJ0273, urease activity increased significantly. On day 20 treatment, urease activity in S1 after treatment of ZJ0273 was higher than the control and then it also returned to the control level after 60 days incubation. Catalase activity Catalase is a kind of oxidoreductase which can accelerate the degradation of hydrogen peroxide (H2O2) and protect organisms from H2O2 toxicity. Catalase activity

was stimulated to increase on day 20 treatment in S1 and on day 30 treatment in S2 of 50 and 100 mg kg−1 of ZJ0273; while under the condition of treatment of 10 mg kg−1 of ZJ0273, catalase activity remained almost the same level with the control samples. Catalase activity reached the highest and used 6.24 ml KMnO4 (0.02 M) on day 30 treatment of 50 mg kg−1 of ZJ0273, while it relatively decreased after treatment of 100 mg kg−1 of ZJ0273. The results also showed that the effect of ZJ0273 on catalase activity in S2 was subject to variations during the period of the experiment (Fig. 3). In this study, the activities of urease, protease, dehydrogenase, and catalase were chosen to investigate the effects of ZJ0273 on soils. These enzyme activities played significant roles in the transformation and degradation of organic pollutants in soils, including pesticide, herbicide, etc. (Zhang et al. 2014). On the whole, ZJ0273 can stimulate the activities of urease, dehydrogenase, and catalase under aerobic condition, while protease activity was inhibited under aerobic condition in S1 and S2. Protease activity has been reported to have implication with the biological capacity of soil enzymatic conversion of the relevant substrate (Burns 1982). Previous studies also showed that protease activity could be inhibited by herbicides such as butachlor (Rasool et al. 2014), glyphosate, and imazamox (Zulet et al. 2013). Dehydrogenase activity plays an important role since it indicates soil potential to

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have no effect or reduced effect on urease activity (Riah et al. 2014). The soil enzyme activity is the result of complex process of synthesis, persistence, stabilization, regulation, and catalytic behavior of the enzymes involved; therefore, response to an applied disturbance such as the presence of a herbicide will be a complex event (Rasool et al. 2014). The response of soil enzyme to an applied herbicide varied differently and cannot be predicted with certain model, because there are so many interactions in soils under different conditions. Our results showed that ZJ0273 seemed to influence the soil enzyme activity, which has potential implications for nutrient cycling.

fulfil specific biochemical reactions and maintains soil fertility, which is an indicator of soil biological activity (Burns 1982; Zhang et al. 2014). In this study, dehydrogenase was sensitive to ZJ0273, and its activity increased significantly during the experimental period. Similar studies reported that fomesafen, endosulfan, mancozeb, et al. seemed to stimulate dehydrogenase activity (Zhang et al. 2014; Riah et al. 2014), while majority of herbicide are either neutral toward this activity or they inhibit it (Riah et al. 2014). Urease can catalyze the hydrolysis of urea into carbon dioxide and ammonia and plays a very important role in the nitrogen cycle in soils. Many studies reported that herbicides seem to

400

Control 10 ppm 50 ppm 100 ppm

600 500

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0 0

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Incubation days

30

Control 10 ppm 50 ppm 100 ppm

300 200 100 0 0

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0 0

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0 0

f

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Control 10 ppm 50 ppm 100 ppm

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Incubation days

Fungal population (10 CFU/g soil, S2)

4

Fungal population (10 CFU/g soil, S1)

c

700

6

300

Bacterial population (10 CFU/g soil, S2)

Control 10 ppm 50 ppm 100 ppm

4

Actinomycic population (10 CFU/g soil, S1)

b

d 500

Actinomycic population (10 CFU/g soil, S2)

6

Bacterial population (10 CFU/g soil, S1)

a

10

0 0

20

40

60

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Incubation days

Fig. 4 Effects of ZJ0273 on soil microbial population for different incubation periods in soils S1 and S2. a Soil S1 bacterial population; b soil S1 actinomycic population; c soil S1 fungal population; d soil S2

10

0 0

20

40

60

80

Incubation days

bacterial population; e soil S2 actinomycic population; f soil S2 fungal population

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Fig. 5 Time curve of ZJ0273 degradation in soil. The concentration of ZJ0273 was monitored and the standard deviation was obtained from three independent repeated experiments

Effect of ZJ0273 on soil microbial population The results given in Fig. 4 showed the effects of ZJ0273 with different concentrations on the total numbers of bacteria, actinomycete, and fungi in soils. The bacteria number in S1 and S2 increased significantly after 20 days of treatment with 10 and 50 mg kg−1 soil of ZJ0273 compared with the control sample. While bacteria number was relatively lower in S1 and S2 after 20 days of treatment with 100 mg kg−1 soil of ZJ0273, numbers were found similar with the control, which showed that higher concentration of ZJ0273 can inhibit bacterial growth. On day 60 treatment, it increased significantly. The actinomycic number also significantly increased in S1 and S2, which was similar to the behavior of bacteria in soils. However, the cultivable fungal number significantly decreased under the treatment of different concentrations of ZJ0273 compared with the control after 10 days cultivation. And after 45 days treatment, the inhibitory effect by ZJ0273 decreased and disappeared, the number of fungi was not different from those of the control. Our results indicated that ZJ0273 had varying effects on soil microbial populations depending on ZJ0273 concentrations and incubation times. This variation is presumably due to the complicated degradation pathway of ZJ0273 and accumulation of ZJ0273 metabolites in soils. We have previously identified the ZJ0273 metabolites and proposed the degradation pathway of ZJ0273 in soils. Higher concentration of ZJ0273 leads to the accumulation of ZJ0273 important

Table 2 Degradation kinetic data of ZJ0273 in S1 and S2 (S1 Marine-fluvigenic yellow loamy soil; S2 Huangshi soil)

metabolite, (2-(4,6-dimethoxypyrimidin-2-yloxy) benzoic acid in soils (Cai et al. 2012, 2013a, b). It was reported that one of the ZJ0273 metabolites, (2-(4,6-dimethoxypyrimidin-2yloxy) benzoic acid, can inhibit the cell growth and degradation of ZJ0273 because (2-(4,6-dimethoxypyrimidin-2-yloxy) benzoic acid has efficient biological activity to inhibit the biosynthesis of branched-chain amino acids and it was also one of the acetolactate systhase inhibitors (Cai et al. 2012; 2013a, b). However, the effects of herbicide on soil microrganisms is governed not only by the chemical and physical properties of the herbicide itself but also by the soil type, soil properties, and prevailing environmental conditions (Riah et al. 2014). These results showed that a broad spectrum of analysis gives a better insight into the true effects of herbicides on soil microorganisms. However, the results in this study should be interpreted with caution since the interactions between other herbicides and biotic factors are very complex and many environmental factors modify the reaction of microbial populations to soil pollution (Cycoń and Piotrowska-Seget 2007; Cycon et al. 2013).

Degradation of ZJ0273 in soils The results of ZJ0273 degradation experiment and degradation kinetic data are shown in Fig. 5 and Table 2. The results showed that the degradation ratio of ZJ0273 increased rapidly in soils under the condition of 50 mg kg−1 of ZJ0273 treatment, up to 60.42 and 72.28 % after 90-day incubation in S1 and S2, respectively (Fig. 5). We have demonstrated in our previous work that the concentration of ZJ0273 remained almost unchanged in the sterilized soils after 90-day incubation, which showed that ZJ0273 photolysis in soils was negligible. Figures 3 and 4 showed the enzyme activity and microbial population in S1 and S2. In ZJ0273-treated soils, bacterial and actinomycic population and dehydorgenase, urease, and catalase activities were higher, while protease and fungal population were relatively lower than those in the control soils S1 and S2. The results illuminated that the microbial activity in soils leads to the concentration of ZJ0273 decrease and microorganism in soils plays the most important role in degradation of ZJ0273. The degradation kinetic data shown in Table 2 and indicates that the degradation process in experimental soils was characterized by rate constants of 0.010 and 0.014 days−1, following first-order kinetics. The half-life times of ZJ0273 (DT50, the time within

Soils

Regression equation

k (day−1)

R2

DT50 (day)

DT90 (day)

S1 S2

ln(ct/co)=−0.010t+3.8512 ln(ct/co)=−0.014t+3.8496

0.010 0.014

0.9186 0.9421

69.31 49.50

230.26 164.47

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which the initial ZJ0273 amounts were reduced by 50 %) were 69.31 and 49.50 days in S1 and S2, respectively (Table 2).

Conclusions Soil enzyme activity and microbial population have potential implications for nutrient cycling. ZJ0273 is a novel herbicide, and to the best of our knowledge, its effect on enzyme and microorganism in soils has not been investigated. The results in this study show that ZJ0273 can influence the soil enzyme activity and also affect microorganism growth and productivity in soils, which has a direct implication in the synthesis of these enzymes. We have demonstrated in this paper that ZJ0273 is able to inhibit the protease activity significantly and had different stimulating effects on the activities of dehydrogenase, urease, and catalase. ZJ0273 is able to stimulate the growth and productivity of bacteria and actinomycetes, while inhibited fungi in soils. These results indicated that ZJ0273 had varying effects on soil enzyme and microbial population; therefore, much care is required when applying ZJ0273 at the recommended doses to the soils in order to protect the soil microbial diversity and protect the soil health. Acknowledgments The research was financially funded by the grants “National Natural Science Foundation” (project no. 11275033) and the Talent Introduction Foundation of Changzhou University (no. ZMF13020003).

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