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Home , Anthrosol, Latosol, Soil respiration

Catena 87 (2011) 276–280

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Catena

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Long-term tillage effects on the distribution patterns of microbial and activities within aggregates

X. Jiang a,b,⁎, A.L. Wright b, J. Wang a,Z.Lia a College of Resources and Environment, Southwest University, 2 Tiansheng Road, Beibei, Chongqing, 400715, China b Everglades Research & Education Center, University of Florida, Belle Glade, FL 33430, USA article info abstract

Article history: The effects of tillage on the interaction between and microbial biomass vary spatially and Received 2 April 2011 temporally for different soil types and cropping systems. We assessed the relationship between soil structure Received in revised form 18 June 2011 induced by tillage and soil microbial activity at the level of soil aggregates. To this aim, organic C (OC), Accepted 20 June 2011 microbial biomass C (MBC) and were measured in water-stable aggregates (WSA) of different sizes from a subtropical rice soil under two tillage systems: conventional tillage (CT) and a combination of Keywords: ridge with no-tillage (RNT). Soil (0–20 cm) was fractionated into six different aggregate sizes (N4.76, 4.76– Soil structure – – – b Soil organic 2.0, 2.0 1.0, 1.0 0.25, 0.25 0.053, and 0.053 mm in diameter). Soil OC, MBC, respiration rate, and metabolic Metabolic quotient quotient were heterogeneously distributed among soil aggregates while the patterns of aggregate-size Respiration rate distribution were similar among properties, regardless of tillage system. The content of OC within WSA Soil tillage followed the sequence: medium-aggregates (1.0–0.25 mm and 1.0–2.0 mm)Nmacro-aggregates (4.76– 2.0 mm)Nmicro-aggregates (0.25–0.053 mm)Nlarge aggregates (N4.76 mm)Nsilt+ fractions (b0.053 mm). The highest levels of MBC were associated with the 1.0–2.0 mm aggregate size class. Significant differences in respiration rates were also observed among different sizes of WSA, and the highest

respiration rate was associated with 1.0–2.0 mm aggregates. The Cmic/Corg was greatest for the large- macroaggregates regardless of tillage regimes. This ratio decreased with aggregate size to 1.0–0.25 mm. Soil − 1 − 1 metabolic quotient (qCO2) ranged from 3.6 to 17.7 mg CO2 g MBC h . The distribution pattern of soil microbial biomass and activity was governed by aggregate size, whereas the tillage effect was not significant at the aggregate scale. Tillage regimes that contribute to greater aggregation, such as RNT, also improved soil microbial activity. Soil OC, MBC and respiration rate were at their highest levels for 1.0–2.0 mm aggregates, suggesting a higher biological activity at this aggregate size for the present . © 2011 Elsevier B.V. All rights reserved.

1. Introduction Agricultural is one of the most significant anthropogenic activities that alter soil characteristics, including Soil live in an ecosystem dominated by soil physical, chemical, and biological properties and processes. Previous particles which vary greatly in shape and size, and have complicated studies have shown that microbial biomass can be altered by spatial arrangements and composition (Dexter, 1988). The spatial changes in agricultural management practices (Angers et al., 1992; arrangement of solid particles results in a complex and discontin- Elfstrand et al., 2007; Frey et al, 2007; Govaerts et al., 2008; Jackson uous pattern of pore spaces of varying sizes and shapes filled with et al., 2003; Liebig et al., 2006; Lauber et al., 2008; Schutter and Dick, water or air (Chenu and Stotzky, 2002; Young and Ritz, 2000). Soil 2002; Visser and Parkinson, 1992; Yao et al., 2006). Conservation aggregates represent an ecological niche whose chemical and tillage is a widely adopted practice to improve sustainability of physical properties contribute to the heterogeneous distribution of agricultural and reduce input costs. However, differ- microorganisms among aggregates of different sizes (Young et al., encesinsoilstructureandfunctionoftendevelopasaresultof 2008). For example, microbial distribution patterns may be application of conventional tillage or reduce tillage regimes. influenced by pore size associated with particular aggregates, or Generally, microbial biomass is higher in under no tillage by differences in the clay and organic C content among aggregate- (NT) than conventional tillage (CT) management (Alvear et al., size classes (Van Gestel et al., 1996). 2005; Bausenwein et al., 2008; Feng et al., 2003; Kandeler et al., 1999; Spedding et al., 2004; von Lutzow et al., 2002). However, tillage effects on the distribution pattern of microorganisms ⁎ Corresponding author at: College of Resources and Environment, Southwest University, 2 Tiansheng Road, Beibei, Chongqing, 400715, China. associated with soil structure are not widely reported (Bronick E-mail address: [email protected] (X. Jiang). and Lal, 2005; Väisänen et al., 2005). Furthermore, results vary

0341-8162/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2011.06.011 X. Jiang et al. / Catena 87 (2011) 276–280 277 greatly due to changes in climate, , especially texture and 3. Results dominant mineralogy. The content and activity of microbial biomass can be higher in macroaggregates (Beauchamp and Seech, 1990; 3.1. Size distribution of water-stable aggregates Franzluebbers and Arshad, 1997; Gupta and Germuda, 1988; Lupwayi et al., 2001; Miller and Dick, 1995; Singh and Singh, The proportion of +clay (b0.053 mm) represented the 1995), but also concentrated in microaggregates (Jocteur et al., greatest fraction of whole soil for CT, while macro-aggregates of 1991; Kanazawa and Filip, 1986; Kandeler et al., 2000; Sessitsch et 4.76–2.0 mm represented the greatest fraction for RNT (Table 1). al., 2001; van Gestel et al., 1996). Approximately 13% of large aggregates are broken into smaller Further research is needed, however, to determine how tillage- aggregates (from the class of 4.76–2mmtotheoneb0.053 mm) by induced changes in the soil environment shape microbial biomass and tillage. No significant difference between tillage regimes occurred activity in agro-ecosystems (Bronick and Lal, 2005). The aim of the for other sizes of aggregates, indicating that CT disrupted soil present study was to evaluate soil microbial biomass and activities macroaggregates into microaggregates or individual particles. associated with soil aggregates under different tillage management in a sub-tropical purple rice soil to ascertain causative factors influencing the activity of soil microorganisms. 3.2. Organic C of soil aggregates

The OC content within water-stable aggregates ranged from 7.5 to 2. Materials and methods 32.2 g kg− 1 (Fig. 1). The size distribution patterns of OC were similar between RNT with the highest values were associated with medium- 2.1. Tillage systems and soil sampling aggregate (1.0–0.25 and 1.0–2.0 mm) fractions (32.2 and 21.9 g kg− 1 for RNT and CT, respectively) and the lowest with the silt+clay The experimental station is located in southwestern China (30° 26' fraction (9.0 and 7.5 g kg− 1 for RNT and CT, respectively). For both N, 106° 26' E). Annual mean temperature ranges between 14 and 19 °C tillage treatments, OC followed the sequence: medium-aggregates and mean rainfall between 1000 and 1400 mm. The field experiment (1.0–0.25 and 1.0–2.0 mm)Nmacro-aggregates (4.76–2.0 mm)N was established in 1990 on a hydargric (FAO/Unesco, 1988) micro-aggregates (0.25–0.053 mm)Nlarge aggregates (N 4.76 mm)N at Chongqing, southwest of China. Basic soil properties (0–20 cm) are: silt+clay fraction (b 0.053 mm) (p b0.05). −1 −1 pH (H2O)=7.1, organic C=21.7 g kg ,totalN=1.7gkg ,total Soil OC under RNT was significantly higher than under CT in most P=0.8 g kg−1, and total K=22.7g kg−1.Thefield was planted with aggregates from 0.053 to 4.76 mm. However, no effect occurred in the rape (Brassica napus L.) in winter and rice (Oryza sativa L.) in summer, smallest and largest aggregate sizes (Fig. 1). Organic C was≈11 g kg−1 with crop residues returned to the soil. in N4.76 mm aggregates and 8–9gkg−1 inb0.053 mm aggregates. Two tillage systems were compared: conventional tillage (CT) and a combination of ridge with no-tillage (RNT). Tillage treatments were described in detail by Jiang and Xie (2009).Briefly, for RNT, no Table 1 tillage was imposed on soil that was ridge tilled in 1990. Rape and Aggregate size distribution (%) of soils under RNT and CT. rice were planted on the top of the ridge and NT was employed since Tillage Aggregate size 1990. For CT, the soil was puddled and harrowed before rice (mm) seedlings were transplanted and after rice was harvested, and tilled N4.76 4.76–2.00 2.00–1.00 1.00–0.25 0.25–0.053 b0.053 again before rape planting. The size of the plots was 4×5 m2 and the RNT 8.1 a 37.8 a 5.2 a 4.1 a 26.0 a 18.8 b experiment was organized in a randomized complete block design CT 9.3 a 23.9 b 5.0 a 3.2 a 26.4 a 32.2 a (RCBD) with four replications. a fi b – Values with different letters in columns indicates signi cant differences (p 0.05). Five surface soil samples (0 20 cm) were collected from each b RNT, no-till treatment was imposed on the soil that was ridge tilled before the plot on October, 2008 (4 weeks after rape planting). Fractionation of experiment, and the ridges were kept intact since 1990; CT, conventional tillage. soil aggregates was achieved using a wet-sieving procedure (Wright and Upadhyaya, 1998; Chiu et al., 2006) with a small adaption. Field- moist soil was immersed in water on a set of five nested sieves (4.76, 2, 1, 0.25, and 0.053 mm) and shaken vertically 3 cm for 50 times 40 during a 2 min period. The aggregates retained on each sieve were RNT collected. The silt+clay fraction (b0.053 mm) was collected after CT

centrifugation. ) -1 30

2.3. Microbial and chemical analysis

Soil microbial biomass C was determined by fumigation 20 extraction (Anderson and Ingram, 1993; Vance et al., 1987)andK values of 2.64 was used for calculation of MBC (Vance et al., 1987). Soil organic C was determined by acid dichromate wet oxidation as described by Nelson and Sommers (1996). Soil respiration rate was 10 Soil total organic C (g kg assessed by measuring CO2 production by trapping respired CO2 in NaOH (Dahlin et al., 1997). All assays were performed in triplicate. Soil metabolic quotient was calculated as the soil respiration rate 0 divided by microbial biomass C (Anderson and Domsch, 1990; 4.76 4.76-2.0 2.0-1.0 1.0-0.25 0.25-0.053 0.053 Killham and Firestone, 1984). Data were subjected to ANOVA and Soil aggregate size (mm) mean values separated using Fisher's least significant difference b test at p 0.05. All statistical analyses were performed by SPSS Fig. 1. Soil total organic C associated with different sizes of aggregate under RNT and CT statistical package. (RNT, combines ridge with no-tillage; CT, conventional tillage). 278 X. Jiang et al. / Catena 87 (2011) 276–280

3.3. Microbial biomass C within soil aggregates rates occurred for micro-aggregates of 0.25–0.053 mm (2.5 and 3.3 mg −1 −1 CO2 kg h for RNT and CT, respectively). The distribution patterns of MBC associated with different sizes of aggregates under RNT and CT showed similar trends (Fig. 2). The 3.5. Ratio of soil MBC to soil OC within aggregates highest MBC was observed in the 1.0–2.0 mm fraction (1025 and 805 mg C kg− 1 for RNT and CT, respectively) and the lowest in the − Soil MBC represented 1.6–6.8% of total soil OC in the present study b0.053 mm fraction (390 and 251 mg C kg 1 for RNT and CT (Fig. 4). While significant differences of C /C occurred among respectively). It is interesting to note the sudden decrease of MBC mic org − different sizes of WSA for both tillage treatments, the size distribution values in 1–0.25 mm aggregates (511 and 353 mg C kg 1 for RNT and patterns were similar. The highest values corresponded to the largest CT, respectively). Statistical analysis showed that MBC was significant aggregates, N4.76 mm, (6.8 and 5.4% for RNT and CT, respectively) and higher for RNT than CT for all aggregate size fractions (pb0.05). the lowest to the aggregate size of 1.0–0.25 mm (1.6 and 1.7 for RNT and CT, respectively). 3.4. Respiration rate of soil aggregates

3.6. Microbial metabolic quotient (qCO2) within soil aggregates −1 −1 Soil respiration rate ranged from 2.5 to 12.1 mg CO2 kg h

(Fig. 3). Although soil respiration rates were heterogeneously distrib- Fig. 5 shows that qCO2 within soil aggregates ranged from 3.6 to − 1 − 1 uted within different sizes of WSA, similar trends in aggregate-size 17.7 mg CO2 g MBC h . Similar distribution patterns of microbial distribution were observed under RNT and CT. The highest respiration quotient associated different sizes of aggregates were observed for – rate occurred for 1.0 2.0 mm aggregates (10.0 and 12.1 mg CO2 RNT and CT. Higher levels of qCO2 were found for 1.0–0.25 mm, − − kg 1 h 1 for RNT and CT respectively), while the lowest respiration silt+clay fractions (b 0.053 mm) and 2.0–1.0 mm aggregates, while

1200 8 ) -1 RNT RNT CT CT 900 6 (%) org to C 600 4 mic

300 2 Ratio of C Soil microbial biomasskgSoil C (mg microbial C 0 4.76 4.76-2.0 2.0-1.0 1.0-0.25 0.25-0.053 0.053 0 4.76 4.76-2.0 2.0-1.0 1.0-0.25 0.25-0.053 0.053 Soil aggregate size (mm) Soil aggregate size (mm)

Fig. 2. Soil microbial biomass C associated with different sizes of aggregate under RNT and CT (RNT, combines ridge with no-tillage; CT, conventional tillage). Fig. 4. Ratio of soil microbial C to total organic C associated with different sizes of aggregate under RNT and CT (RNT, combines ridge with no-tillage; CT, conventional tillage).

15 ) ) -1 -1 20 soilh 12

-1 RNT RNT MBC h kg -1

CT 2 g

CT 2 15 9

10 6

5 3 Soil respiration rate (mg CO 0 0 4.76 4.76-2 2-1 1-0.25 0.25-0.053 0.053 4.76 4.76-2 2-1 1-0.25 0.25-0.053 0.053 Soil metabolic quotient (mg CO Soil aggregate size (mm) Soil aggregate size (mm)

Fig. 3. Soil respiration (CO2 production) associated with different sizes of aggregate Fig. 5. Soil metabolic quotient associated with different sizes of aggregate under RNT under RNT and CT (RNT, combines ridge with no-tillage; CT, conventional tillage). and CT (RNT, combines ridge with no-tillage; CT, conventional tillage). X. Jiang et al. / Catena 87 (2011) 276–280 279 the lowest levels were associated with 0.25–0.053 mm and 4.76– aggregates including both 2.0–1.0 mm and 1.0–0.25 mm size frac- 2.0 mm aggregates under RNT and CT, respectively. tions, and the highest levels of MBC were found for the 2.0–1.0 mm size fraction. However, MBC within 1.0–0.25 mm was at the second 4. Discussion lowest levels under CT and RNT. Present results clearly demonstrated

that Cmic/Corg was at the lowest levels for 1.0–0.25 mm aggregates for This work reports data on soil OC, MBC and respiration rate both CT and RNT. Greater biomass in microaggregates has also been associated with soil aggregates of different size under RNT and CT in a attributed to a larger percentage of clay in microaggregates (Van subtropical purple rice soil. While it was observed that OC, MBC, Gestel et al., 1996), but this seems unlikely in our study as MBC was respiration rate and qCO2 were heterogeneously distributed among quite low in the silt+clay fraction. Alternatively, it is possible that a soil aggregates of different sizes, their size-distribution patterns were substantial portion of the soil microbial biomass was disassociated similar between RNT and CT. The results indicated that the influence from the surface of aggregates, especially when ultra-sonication or of the aggregate size on the soil properties considered was not some chemicals were employed to disperse soil during the sieving affected by tillage. process in some studies (Ashman et al., 2003; Kandeler et al., 1999; The primary effect of tillage is to physically disturb the soil Van Gestel et al., 1996). A substantial portion of the soil microbial structure. Tillage usually disrupts soil aggregates and lowers TOC, biomass is thought to live on or near the aggregate surface (Oades, CEC, nutrients that contribute to aggregation (Filho et al., 2002; Jiang 1984), which may explain the high MBC in microaggregates if they and Xie, 2009; Jiang et al., 2011). The specific effect will depend originated on macroaggregate surfaces. largely on the disturbance that occurs at the spatial scale to which Consistent with our results, higher soil OC associated with the microorganisms are most sensitive (Young and Ritz, 2000). aggregates of 0.2–2.0 mm was observed earlier, and it was attributed Hernandez and Lopez (2002) reported that tillage had no significant to the non-active organic matter consisting mainly of residues effect on microbial biomass in soil microaggregates. Wright and (Kandeler et al., 1999; Schulten et al., 1993). However, when further Hons (2005) also reported that the tillage had no significant effects separating this soil into 0.25–1.0 and 1.0–2.0 mm fractions, significant on the distribution of TOC in soil aggregates through 20 years of differences were observed. The highest levels of MBC occurred for the long-term management, and the distribution of microbial biomass in 2.0–1.0 fraction while MBC was the second lowest for the 0.25–1.0 mm soil aggregates produced similar results (Elmholt et al., 2008). size fraction. Furthermore, soil respiration rate was also significantly According to a hierarchical model proposed by Tisdall and Oades higher for the 1.0–2.0 than 0.25–1.0 mm size fraction under both tillage (1982), the formation of soil micro- and macroaggregates are regimes. The basal respiration of the individual aggregate-size classes different, yet interrelated processes. Free primary particles and silt- reflects the overall activity of the microbial community (Miller and sized aggregates are bound together into micro-aggregates by Dick, 1995), which indicated there was a qualitative difference in persistent binding agents, oxides and highly disordered aluminosil- microbial communities between the 1.0–2.0 and 0.25–1.0 mm size icates. These stable micro-aggregates, in turn, are bound together into fractions. The lowest level of Cmic/Corg was associated with 1.0–0.25 mm macro-aggregates (N0.25 mm) by temporary (i.e. fungal hyphae and aggregates for both CT and RNT, which indicated the lowest substrate ) and transient (i.e., microbial- and plant-derived polysaccha- availability to microorganisms compared to other sizes of aggregates. rides) binding agents. Because of this hierarchical order of aggregates The highly complicated spatial arrangement and composition of the and their binding agents, the quantity and quality of readily solid particles results in heterogeneity of soil structure that may mineralizable organic matter may be different depending on the contribute to heterogeneous distribution of OC and microorganisms aggregate size. Secondly, the rate of O2 diffusion is directly related to among aggregates of different sizes. Therefore, heterogeneous distri- distance (aggregate radius), and O2 concentrations are assumed bution of OC may lead to “hot-spots” of aggregation (Bronick and Lal, different for different aggregate sizes (Kremen et al., 2005; Sexstone 2005). In the present study, soil OC, MBC and respiration rate were at et al., 1985). This rate of diffusion and O2 availability as affected by their highest levels in 1.0–2.0 mm aggregates, suggesting that tillage influences the soil respiration rate. Other evidence may microorganisms inside of these aggregates are the most biologically substantiate our speculation, such that similar patterns of soil pore- active in the present ecosystem. size distribution occurred under RNT and CT (Shi et al., 2008). The present results suggested that the size-distribution patterns of soil

TOC, MBC, qCO2 and respiration rate were governed by the size of 5. Conclusions aggregates, whereas tillage regimes that contribute to greater aggregation, such as RNT, affect soil microbial biomass and activity. Soil OC, MBC, respiration rate, and metabolic quotient were Microbial biomass C in all aggregate sizes was significantly higher heterogeneously distributed among soil aggregates while their size- under RNT than CT, which may imply that RNT was the ideal enhancer distribution patterns were similar between the two tillage systems of soil productivity for this subtropical rice ecosystem. considered. The distribution pattern of soil microbial biomass Heterogeneous distribution of microbial biomass has been associated with aggregates was likely governed by the size of reported (Beauchamp and Seech, 1990; Franzluebbers and Arshad, aggregates, whereas the tillage effect was not significant at the 1997; Gupta and Germuda, 1988; Miller and Dick, 1995; Roy and aggregate-size scale. Tillage regimes, such as RNT, that contribute to Singh, 1994). However, great variability of microbial biomass greater soil aggregation also will improve soil microbial activity to aid associated with aggregates was observed. For example, several studies in crop production. Heterogeneous distribution of OC and microbial reported that microbial biomass was higher in macroaggregates than biomass may lead to “hot-spots” of aggregation, and the present study microaggregates (Elliott, 1986; Franzluebbers and Arshad, 1997; suggests that microorganisms associated with 1.0–2.0 mm aggregates Jastrow et al., 1996; Lupwayi et al., 2001; Monreal and Kodama, 1997), are the most biologically active in the present ecosystem. while in other studies, higher microbial biomass levels and activities were observed in microaggregates (Kandeler et al., 2000: Mendes et al., 1999; Seech and Beauchamp, 1988; Sessitsch et al., 2001). These Acknowledgements quantitative differences in MBC among different sizes of soil aggregates are thought to be related to (Alvear We are grateful to the Natural Science Foundation of Chongqing, et al., 2005; Miller and Dick, 1995; Van Gestel et al., 1996;) and clay China (CSTC-2008BA1024) and Natural Science Foundation of China content (Alvear et al., 2005; Van Gestel et al., 1996). However, this (No. 40501033). We wish to acknowledge useful suggestions by the seems unlikely in our study. The highest OC was observed in medium- reviewers and the editor. 280 X. Jiang et al. / Catena 87 (2011) 276–280

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