Soil Science Society of America Journal 63:1825-1829 (1999)
© 1999 Soil Science Society of America
DIVISION S-6-SOIL & WATER MANAGEMENT & CONSERVATION
Changes in Aggregate Stability and Concentration of Glomalin during Tillage Management Transition
S.F. Wrighta,
J.L. Starrb and
I.C. Paltineanub
a USDA-ARS, Soil Microbial Systems Lab., Natural Resources Inst., Beltsville, MD 20705 USA
b Environmental Chemistry Lab., Natural Resources Inst., Beltsville, MD 20705 USA
swright{at}asrr.arsusda.gov
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ABSTRACT
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Improvement in structure of degraded soils or prevention of degradation of structure in healthy soils requires an understanding of processes contributing to aggregate stability. The impact of cropping systems on a specific molecule that contributes to aggregate stability is part of the process that has not been elucidated. The relationship between aggregate stability and glomalin, a glycoprotein produced by arbuscular mycorrhizal (AM) fungi, was studied during the first 3 yr in transition from plow tillage (PT) to no tillage (NT) maize (Zea mays L.). Results showed a high linear correlation
between glomalin concentration in aggregates and aggregate stability. Increases in both aggregate stability and glomalin were measurable from year to year in NT plots, but NT was significantly higher than PT after 2 or 3 yr (P < 0.05). Comparison of NT plots after 3 yr with nearby soil in grass cover indicated that there was 20% greater stability and 45% higher concentration of glomalin in the grass-covered soil. Comparison of PT and NT (3 yr) interrow samples with intrarow samples indicated that plant roots and NT management may have a synergistic effect on aggregate stabilization. These results show that cropping systems should be evaluated for the impact on production of glomalin by AM fungi.
Abbreviations: AM, arbuscular mycorrhizal fungi • EEG, easily extractable glomalin • IRTG, immunoreactive protein • NT, no tillage • PT, plow tillage • TG, total glomalin
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INTRODUCTION
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MANAGEMENT OF SOILS to improve soil quality involves an understanding of biological contributions leading to changes in stability and structure (Oades, 1993). Arbuscular mycorrhizal (AM) fungi have been linked to aggregation and aggregate stability of soils (Miller and Jastrow, 1992; Wright and Upadhyaya, 1998).
Improvement in the structure of a degraded soil to that of a grassland soil may take from 5 to 50 yr, depending upon the soil texture (Low, 1955). Cropping systems to maintain stability after degraded soils have been improved are needed for Conservation Reserve Program soils that are brought back into production.
Arbuscular mycorrhizal fungi produce copious amounts of an insoluble glycoprotein, glomalin (Wright et al., 1996; Wright and Upadhyaya, 1996, Wright et al., 1998). Solubilization of glomalin on hyphae requires 20 mM citrate and 121°C for 1 h. Hyphal glomalin is highly immunoreactive with monoclonal antibody 32B11 (Wright et al., 1996). Extraction procedures were developed for two fractions of glomalin from soil (Wright and Upadhyaya, 1996). The easily extractable fraction (20 mM citrate, pH 7.0, 121°C for 30 min) was more immunoreactive than total glomalin extracted with 50 mM citrate, pH 8.0, 121°C for 90 to 420 min. Concentration of easily extractable immunoreactive glomalin in a variety of soils is closely related to aggregate stability (Wright and Upadhyaya, 1998). We tested both total and easily extractable glomalin and the immunoreactive fraction of each for the relationship with aggregate stability on a single soil for this study. This information will help determine which fraction to use in future studies for treatment comparisons on a single soil.
To use glomalin concentration as a specific assessment of soil quality and management impacts on soil, it is necessary to relate concentrations of this molecule to increases in aggregate stability over time. This information will provide evidence that cropping systems should be evaluated for their impact on the activity of AM fungi. The objectives of this research were (i) to assess the impact of PT vs. NT maize on the production of the aggregate stabilizing glycoprotein, glomalin and (ii) to compare these results with production of glomalin under perennial grass cover.
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Materials and methods
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Treatments and Sampling Method
The experimental design was previously described by Starr and Paltineanu (1998) and McCarty et al. (1998). Plots were four tillage treatments of maize distributed over 26 plots on a Mattapex silt loam (fine-silty, mixed, mesic Aquic Hapludult with about 35% sand, 56% silt and 9% clay in the Ap horizon) in an incomplete block experimental design. Planting was directly over the previous year's row for Years 2 and 3. The experiment was initiated in 1993 when all plots were PT. Samples for this report were taken in May 1997 prior to planting. Treatments were continuous plow tillage for 4 yr (PT), and 1-, 2-, and 3-yr no tillage (NT) with six or seven replicate plots. In addition, samples were removed perpendicular to the intrarow sample site from four NT (3 yr) and PT traffic and nontraffic interrows.
Six samples of soil from tall fescue (Festuca aerundinacea Schreb.) buffer area surrounding the corn plots also were taken (one each from the top and bottom and two from each side of the rectangular experimental layout) (McCarty et al., 1998). The grass buffer area had not been disturbed for 
15 yr.
A shovel was used to remove soil to a depth of 10 cm. Each sample was divided at approximately the 5-cm level and the two depths were saved separately. All plots were sampled in the second of six rows.
Aggregate Stability
Samples (1 kg) were spread to a depth <1 cm, air dried for 48 h, and then sieved to remove the 1- to 2-mm aggregates. Stability of 4 g of 1- to 2-mm aggregates was tested within 2 wk of sampling. Aggregates were prewetted with deionized water by capillary action for 10 min and agitated for 5 min on 0.25-mm screens in deionized water with the wet-sieving apparatus described by Kemper and Rosenau (1986). Stability is reported as the percentage of aggregated soil remaining on the sieve after drying at 103°C. Initial weight of aggregates was corrected for the weight of coarse material >0.25 mm. Two replicates of each sample were tested.
Glomalin
Fractions of glomalin were extracted from 2 g of the 1- to 2-mm aggregates. The easily extractable glomalin fraction (Wright and Upadhyaya, 1996) was solubilized with 16 mL of 20 mM citrate, pH 7.0, at 121°C for 30 min. The supernatant containing solubilized glomalin was separated by centrifugation at 10000 x g for 10 min and decanted. The remaining material was subjected to two more extraction cycles to remove total glomalin with 16 mL of 50 mM citrate, pH 8.0, at 121°C for 90 min (Wright and Upadhyaya, 1996) for each extraction. Replicate samples were extracted. A 1-mL aliquot of easily extractable glomalin was set aside for protein and immunoreactive protein assays. The remainder of easily extractable glomalin was pooled with supernatants from the two 90-min extractions before measuring total and immunoreactive total glomalin. Material remaining after centrifugation and removal of solubilized glomalin was passed through a 0.25-mm sieve. Coarse material remaining on the sieve was washed with deionized water, dried at 103°C and weighed.
Protein and immunoreactive protein in the total and easily extractable fractions of glomalin were measured by methods previously described (Wright and Upadhyaya, 1996, 1998). Total glomalin (TG) and easily extractable glomalin (EEG) are based on the Bradford assay using bovine serum albumin standards. Immunoreactive protein in these fractions (IRTG and IREEG) is based on an enzyme-linked immunosorbent assay (ELISA) using monoclonal antibody 32Bll. Percentage immunoreactivity of a sample is obtained by comparing the assay values of 0.125 µg of sample with 0.125 µg of glomalin from an active culture (Wright and Upadhyaya, 1996, 1998). Replicate assays were performed on extracts from replicate subsamples. Assay values were extrapolated to milligrams per gram of soil with the total volume of liquid containing solubilized easily extractable or total glomalin and correcting the original weight for coarse material.
Statistical Analyses
Linear correlations and analysis of variance for means comparisons of interrow samples was analyzed by Statix (Analytical Software, Talahassee FL). Data from intrarow and grass samples were analyzed for differences in means at the 0.05 level for aggregate stability, TG, and IRTG by the general linear models (SAS Inst., Cary, NC).
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Results and discussion
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General Relationship between Glomalin and Soil Aggregate Stability
Aggregate stability was highest under continuous grass and lowest in the PT treatment in 0- to 5-cm samples (Table 1)
. Data show that the 0- to 5-cm samples from intrarow positions of NT had a greater response to the treatments than the corresponding 5- to 10-cm samples. Therefore, the relationship between aggregate stability and glomalin in the 0- to 5-cm samples was examined in detail. Table 2
shows correlation coefficients for aggregate stability, TG, IRTG, EEG, and IR EEG. All measures of glomalin are linearly correlated with aggregate stability and with each other. The linear relationship between TG and aggregate stability for all samples is shown in Fig. 1
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Table 1 Comparison of aggregate stability across treatments of no-till (N) and plow-till (PT) corn for intrarow samples at two soil depths
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Table 2 Correlation coefficients for aggregate stability and measures of glomalin: total (TG), immunoreactive total (IRTG), easily extractable (EEG) and immunoreactive easily extractable (IREEG)
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Fig. 1 Relationship between total glomalin and aggregate stability in 0- to 5-cm soil samples of plots in transition from plow tillage to no tillage. Samples are from the intrarow position of six or seven replicate plots of five treatments on the same soil. Treatments were continuous plow tillage, no tillage for 1, 2, and 3 yr, and continuous grass cover for about 15 yr
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Previous work (Wright and Upadhyaya, 1998) indicated that IREEG was more closely associated with aggregate stability across a number of different soils than the other fractions of glomalin. In this Mattapex soil it appears that both total and easily extractable glomalin are composed almost entirely of immunoreactive glomalin. Percentage immunoreactive protein in crude extracts of all samples ranged from 81 to 100%. The immunoreactive fraction is similar to native glomalin from fresh cultures of arbuscular mycorrhizae (Wright et al., 1996; unpublished data) and may be in a conformational state that results in glue-like properties. High immunoreactivity of extracts also provides additional evidence that glomalin is the major component of crude extracts (Wright et al., 1996; Wright and Upadhyaya, 1996), i.e., other proteins are either eliminated by the extraction conditions or are not present at high concentrations.
The concentration of glomalin in aggregates from the Mattapex soil is low compared with concentrations in other soils in the mid-Atlantic states (Wright and Upadhyaya, 1996, 1998). Mattapex values for TG ranged from 1.2 ± 0.1 for PT to 3.0 ± 0.3 for tall fescue. In other soils from the mid-Atlantic states bulk-soil TG values ranged from 4 to 15 mg/g soil (Wright and Upadhyaya, 1996). Thus, these aggregates of Mattapex soil have low concentrations of TG, but a large amount of TG is immunoreactive, as discussed above.
Changes in aggregate stability, TG, and IRTG during transition from PT to NT and comparison with undisturbed grass bordering the plots are shown as differences between means (Table 3)
. Significant differences in aggregate stability and glomalin occurred within 2 to 3 yr after initiation of NT treatments, but were not detectable over a time span of a single year. Aggregate stability and glomalin values after 3 yr of NT were still substantially lower than after 15 yr in undisturbed grass, but the maximum aggregate stability and level of glomalin in a cropped soil may be much lower than in an undisturbed grass area. It would be necessary to follow long-term comparisons or transitions to define the rate of increase, but 3 yr of data on this soil indicate linear increases for both TG and aggregate stability. McCarty et al. (1998) measured total N, organic C, active N, biomass N, and biomass C at depth intervals in these same plots. After 3 yr of transition, stratification of metabolically active pools of C and N was apparent, but total C and N pools did not show unequivocal changes. Soil organic matter, as a whole, is extremely difficult to study because it is a complex mixture of substances (Stevenson, 1994; Swift, 1996). However, our results indicate that evaluating cropping systems for glomalin provides a quantitative measure of a specific component of organic matter that increased over 3 yr and is related to increases in aggregate stability.
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Table 3 Differences between means of aggregate stability, total glomalin, and easily extractable glomalin over 3 yr of no-tillage treatments of corn compared with plow tillage and 15 yr of undisturbed grass (tall fescue) buffer area surrounding the corn plots. Means are for six or seven replicates. Corn plots were sampled at the intrarow positions, and all samples are from 0- to 5-cm soil depth
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Influence of Sample Site on Total Glomalin and Aggregate Stability under No Till and Plow Tillage Maize
Intrarow, interrow no traffic, and interrow traffic samples of NT (3 yr) compared with PT samples indicated that plant roots and no tillage may have a synergistic influence on stabilization of aggregates by glomalin (Fig. 2)
. Intrarow samples show (Fig. 2a) the strongest correlation
between TG and aggregate stability. After 3 yr of planting in the same row of NT treatments, aggregate stability was two times greater than for continuous PT. The nontraffic interrow samples showed more variation
and lower aggregate stability values (Fig. 2b). Traffic interrow samples (Fig. 2c) showed the same trends for a linear relationship between aggregate stability and glomalin
, but there was greater variability in the PT interrow than in the PT intrarow samples.
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Fig. 2 Relationship between glomalin and aggregate stability in intrarow samples, traffic and nontraffic interrow samples of plow-tilled, and no-tilled plots
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Total glomalin was significantly higher in the NT traffic interrow compared with no traffic interrow and intrarow samples (P < 0.01), but glomalin was not as closely related to aggregate stability as shown for intrarow samples not influenced by traffic (Fig. 1 and Fig. 2a). Aggregate stability as related to glomalin will require further investigation and larger sample numbers to determine the interactions among glomalin, tractor traffic, and sample distance from plants.
Thomas et al. (1993) reported higher aggregate stability in soil exposed to roots plus hyphae than hyphae alone in a pot culture experiment. Paltineanu et al. (1995) and Starr et al. (1996) reported twice as many roots in intrarow under NT than under PT in a 20-cm radius from the stems of corn plants. Also, Starr et al. (1995) reported higher values of soil bulk density at the 5-cm depth in traffic vs. nontraffic and intrarow positions regardless of NT or PT treatment. Significantly higher aggregate stability in intrarow NT samples compared with interrow samples may indicate additional rhizosphere influences on stability, such as a contribution of polysaccharides (Oades, 1984). Also, types of hyphae of AM fungi (Friese and Allen, 1991) may play different roles in production and sloughing of glomalin.
Other measures of bulk soil for mean diameter ranges of all aggregates along with glomalin concentration in the size fractions may help determine why 1- to 2-mm aggregates in traffic and nontraffic rows are not as closely related to glomalin concentration as are intrarow aggregates. Perhaps tractor traffic weakens larger aggregates by shearing.
Differences in aggregate stability for intrarow and interrow samples correspond to water infiltration. Ponded infiltration rates are higher in the intrarow positions than nontraffic and traffic locations (Starr et al., 1995). Also, Paltineanu and Starr (unpublished data) used capacitance probes and a monitoring system for real-time soil water dynamics on the same plots sampled for this report. Water penetrated to greater depths at the intrarow positions of both PT and NT than in the nontraffic and traffic positions. Water infiltration at the intrarow positions of NT was twice as high as corresponding positions in PT.
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Conclusions
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Improvement of structure of degraded soils or prevention of degradation of structure in healthy soils requires the understanding of processes contributing to aggregate stability, and the development of methods for evaluation of processes under different cropping systems. Our results showed the following.- There is a strong positive linear correlation
between total glomalin and aggregate stability for the Mattapex silt loam in the upper 0 to5 cm of soil under perennial grass, no-till, and plow-till corn.
- Despite improvement of aggregate stability over 3 yr of no-till, the values are still below those of samples from a nearby perennial grass.
- Sample site relative to distance from plant shoots or disturbance by tractor traffic has an impact on the relationship between aggregate stability and glomalin.
- The closest positive linear relationship
between aggregate stability and glomalin was obtained in the intrarow position.
- Influences of plant roots, soil moisture, and traffic on glomalin as related to aggregate stability need further study.
- For comparisons on a single soil type, it is probably necessary to measure only total glomalin and immunoreactive total glomalin.
Received for publication November 9, 1998.
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REFERENCES
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- Friese C.F., Allen M.F. The spread of VA mycorrhizal fungal hyphae in the soil: Inoculum types and external hyphal architecture. Mycologia 1991;83:409-418.[ISI]
- Kemper W.A., Rosenau R.C. Aggregate stability and size distribution. In: Klute A., ed. Methods of soil analysis: Part 1—Physical and mineralogical methods, 2nd ed Madison, WI: Agron. Monogr. 9. ASA and SSSA, 1986:425-442.
- Low A.J. Improvements in the structural state of soils under leys. J. Soil Sci. 1955;6:179-199.
- McCarty G.W., Lysenko N.N., Starr J.L. Short-term changes in organic carbon and nitrogen pools during tillage management transition. Soil Sci. Soc. Am. J. 1998;62:1564-1571.[Abstract/Free Full Text]
- Miller R.M., Jastrow J.D. The role of mycorrhizal fungi in soil conservation. In: Bethlenfalvay G.J., Linderman R.G., eds. Mycorrhizae in sustainable agriculture. CSSA, and SSSA, Madison, WI: ASA Spec. Publ. 54. ASA, 1992:29-44.
- Oades J.M. Soil organic matter and structural stability: mechanisms and implications for management. Plant Soil 1984;76:319-337.
- Oades J.M. The role of biology in the formation, stabilization and degradation of soil structure. Geoderma 1993;56:377-400.
- Paltineanu, C.I., J.L. Starr, and D.J. Timlin. 1995. Preferential water flow through corn canopy and soil surface. Agro. Abs. p. 194.
- Starr, J.L., D.R. Linden, S.D. Logson, and I.C. Paltineanu. 1996. The characteristics and temporal variability of infiltration as affected by macropores and plants. p. 150–170. In ARS Workshop on Real World Infiltration, Pingree Park, CO.
- Starr J.L., Paltineanu I.C. Soil water dynamics using multisensor capitance probes in nontraffic interrows of corn. Soil Sci. Soc. Am. J. 1998;26:114-122.
- Starr, J.L., I.C. Paltineanu, and D.J. Timlin. 1995. Temporal in situ changes of soil properties as affected by tillage, position and plants. p. 139–140. In Kearney Foundation. International Conference Proceedings, Davis, CA. Sept 1995. Kearney Foundation of Soil Science, Davis, CA.
- Stevenson F.J. Humus chemistry, 2nd edition New York: John Wiley & Sons, 1994.
- Swift R.S. Organic matter characterization. In: Sparks D.L., et al. , ed. Methods of soil analysis: Part 3—Chemical Methods. Madison, WI: SSSA and ASA, 1996:1011-1069 SSSA Book Ser. 5..
- Thomas R.S., Franson R.L., Bethlenfalvay G.J. Separation of vesicular-arbuscular mycorrhizal fungus and root effects on soil aggregation. Soil Sci. Soc. Am. J. 1993;57:77-81.[Abstract/Free Full Text]
- Wright S.F., Franke-Snyder M., Morton J.B., Upadhyaya A. Time-course study and partial characterization of a protein on hyphae of arbuscular mycorrhizal fungi during active colonization of roots. Plant Soil 1996;181:193-203.
- Wright S.F., Upadhyaya A. Extraction of an abundant and unusual protein from soil and comparison with hyphal protein of arbuscular mycorrhizal fungi. Soil Sci. 1996;161:575-586.
- Wright S.F., Upadhyaya A. A survey of soils for aggregate stability and glomalin, a glycoprotein produced by hyphae of arbuscular mycorrhizal mycorrhizal fungi. Plant Soil 1998;198:97-107.
- Wright S.F., Upadhyaya A., Buyer J.S. Comparison of N-linked oligosaccharides of glomalin from arbuscular mycorrhizal fungi and soils by capillary electrophoresis. Soil Biol. Biochem. 1998;30:1853-1857.
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ABSTRACT
INTRODUCTION
