Soil Physical, Microbial Enzyme, and Molecular Characterization of Native Prairie and Agricultural Ecosystems S.H. Anderson, R.J. Kremer, and N. Mungai Department of Soil, Environmental

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Soil Physical, Microbial Enzyme, and Molecular
Characterization of Native Prairie and
Agricultural EcosystemsS.H. Anderson, R.J.
Kremer, and N. MungaiDepartment of Soil,
Environmental Atmospheric Sciences, University
of MissouriUSDA-ARS Cropping Systems and Water
Quality Research Unit, Columbia, Missouri
Table 2. Soil physical and chemical properties.
Bulk Water-Stable Hydaulic Study
Site SOM Density Aggregates Conductivity Poro
sity g cm-3 mm h-1 m3
m-3 TP 7.0 0.83d 40.8a
671a 0.619a PF-NP 3.4 1.22ab 29.4b
243b 0.485cd PF-SL 3.8 1.12c
28.2b 222b 0.521b CRP 3.0 1.19b
30.6b 285b 0.497c RC 2.7 1.26a
3.8c 17.9c 0.473d Geometric
means Means within a column followed by the
same letter are not significantly different at
Plt0.05.

• Results
• Soil bulk density was 32 lower for the native
  prairie site (TP) compared to the sites with a
  history of tillage (RC, PF-NP, CRP Table 2).
• Water-stable aggregates were 10 times higher for
  the TP site compared to the RC site. The CRP
  and restored prairie sites had values at 72 of
  the TP site (Table 2).
• Saturated hydraulic conductivity values were
  over 35 times higher for the native prairie (TP)
  compared to the continuously cropped site (RC),
  and 2.5 times higher compared to the restored
  sites (PF-NP, PF- SL, CRP Table 2). This was
  attributed to the greater number of macropores
  (gt 1 mm in effective diameter) for the native
  prairie site.
• Soil enzyme activities were consistently highest
  for TP and PF-SL sites (Table 3), reflecting the
  close relationship of SOM levels with microbial
  activity.
• Enzyme activity values were generally lowest for
  soil under continuous cropping (RC) likely due
  to low SOM and water-stable aggregates (Table
  3).
• PF-NP soils were lower in dehydrogenase,
  glucosaminidase, and phosphatase, which may be a
  reflection of different microbial communities
  and possible different SOM quality.
• Soil DNA content agreed closely with other
  indicators of soil quality (SOM, glucosidase)
  that are associated with microbial activity.
• The site with the highest number of bands from
  molecular analysis of extracted soil DNA, TP
  with 20, appears to have the greatest bacterial
  diversity, while soil from RC with 10 bands had
  the lowest diversity. Soil from the PF and CRP
  sites had band numbers ranging from 12 to 16,
  suggesting that this intermediate level of
  diversity is a characteristic response of soil
  undergoing restoration to its original bacterial
  community.
• The relationship of soil organic matter (SOM) to
  biological activity is illustrated by strong
  correlations between soil DNA (representing the
  bacterial community) and water stable aggregates
  (r2 0.82) and glucosidase activity
  (representing SOM decomposition r2 0.83).

Introduction Evaluation of critical soil
properties is essential in assessing the
restoration of degraded prairies and old
cultivated fields to ecosystems that resemble
native prairies. Restoration and maintenance of
soil quality is highly dependent on organic
matter (SOM), an array of soil organisms and
biological activity, and improved physical
characteristics including water infiltration,
macroporosity, aggregate stability, and bulk
density. Soils managed under native ecosystems
relative to agricultural row crops often have
significant differences in soil physical and
microbial properties. Assessment of relationships
among these properties may provide useful
information in how the physical environment
affects microbial properties. Objective The
objective of this research was to quantify soil
physical properties and soil enzyme activity,
physiological and molecular characteristics for
native, restored, and cultivated prairies.
Table 1. Characteristics of ecosystems at study
sites. Study Site
Code Management System Vegetation Tucker
Prairie TP Uncultivated native Native, warm
season prairie. grasses and
forbs. Prairie Fork New PF-NP Row crops
until 1993, Little bluestem,
Prairie native grasses and side-oats
gramma, legumes since 1994. Indian
grass. Prairie Fork Siricea PF-SL Same as
PF-NP. Same as PF-NP with Lespedeza infes
tation of lespedeza. Centralia-CRP CRP
Managed as CRP since Cool season
grasses 1990, no fertility. and forage
legumes. Centralia-Row Crop RC Rotation since
1990, high Soybean (2003), fertility,
minimum tillage. corn (2004).
Table 3. Microbial enzyme activities and DNA
content for the sites. Dehydro- Glucos-
Soil Study Site genase aminidase Glucosidase
Phosphatase DNA mg tpf g-1 -------------- mg
r-nitrophenol g-1 soil -------------- mg
g-1 soil TP 320 a 160 a 350 a
1580 a 10.3 PF-NP 190 c 90 c 325 ab
640 cd 8.1 PF-SL 250 b 150 ab
300 bc 1180 b 7.4 CRP 260 b 130 b
290 c 710 c 8.2 RC 120 d 70 c
250 c 400 d 6.2 Means within a
column followed by the same letter are not
significantly different at Plt0.05.

• Materials and Methods
• Land treatments included native, uncultivated
  prairie with established warm-season grasses and
  forbs 10-yr-old restored prairie dominated by
  little bluestem (Schizachyrium scoparium),
  side-oats gramma (Bouteloua curtipendula), and
  Indian grass (Sorghastrum nutans) 10-yr-old
  restored prairie dominated by sericea lespedeza
  (Lespedeza cuneata) a 14-yr-old conservation
  reserve program site with cool-season grasses
  and low density forage legumes and a site under
  row crop production with the past 14 years under
  a corn (Zea mays)-soybean (Glycine max) rotation
  cropping system (Fig. 1, Table 1).
• Sampling sites were located on Mexico silt loam
  (fine, smectitic, mesic Aeric Vertic
  Epiaqualfs).
• Relatively undisturbed cores (7.62 cm by 7.62 cm
  ) were sampled from the 0 to 10 cm depth on 12
  May 2004 3 replicate locations with 5
  sub-samples per location.
• Samples were evaluated for physical properties
  bulk density, pore-size distributions, saturated
  hydraulic conductivity and water-stable
  aggregates.

• Materials and Methods (cont.)
• Additional soil samples were taken and essayed
  for energy transformation enzymes
  (dehyrogenase) nutrient mineralization enzymes
  for C (ß- glucosidase), P (alkaline
  phosphatases), and N (ß- glucosamidase) soil
  microbial diversity by a C substrate
  utilization assay and CO2 respiration.
• Total soil DNA was extracted, quantified, and
  subjected to amplification (polymerase chain
  reaction, PCR) with known, primer DNA to detect
  various bacterial genotypes. Different DNA
  sequence combinations resulting from PCR were
  separated on a gel matrix using electrophoresis,
  visualized as a series of bands distributed over
  the matrix. The series of bands obtained from
  separating the DNA fragments resulted in genetic
  profiles that characterized microbial
  communities.

Summary This research demonstrated that soil
measurements based on soil enzyme activity,
physiological and molecular characteristics, and
selected physical traits (water-stable
aggregation, saturated hydraulic conductivity)
differentiated soils managed as native prairie,
restored prairie, or cultivated land. Results
indicated that sites under restoration to prairie
vegetation are transitional between native
prairie and cultivated soils based on combined
physical and microbiological analyses. The use
of physiological and molecular analyses of
prairie soils yielded new insights on the complex
functional and structural diversity of their soil
bacterial communities, which contribute to the
biological characteristics of these soils.