Organic Matter

RCS01 Recovery and relative influence of root, microbial, and structural properties of soil on physically sequestered carbon stocks in restored grassland at Konza Prairie


Managing soil to sequester C can help mitigate increasing CO2 in the atmosphere. To maximize this ecosystem service, more knowledge of factors influencing C sequestration is needed. The objectives of this study were to (i) quantify recovery of the roots, microbial biomass and composition, and soil structure across a chronosequence of grassland restorations and (ii) use a structural equation model to develop a data-based hypothesis on the relative influence of physical and biological soil properties on the soil C aggregate fraction diagnostic of sequestered C. We hypothesized measured variables would recover with restoration age. Belowground plant biomass and tissue quality (C/N ratio), soil microbial biomass C, phospholipid fatty acid (PLFA) concentrations, soil structure, and soil C stocks in the bulk soil and each aggregate fraction were quantified from a cultivated field, prairies restored for 1 to 35-yr (n = 6), and a never-cultivated (native) prairie. Root biomass, microbial biomass C, arbuscular mycorrhizal fungi (AMF) PLFA biomass across the chronosequence increase to resemble native prairie following 35 yr of restoration. Many aspects of soil structure (i.e., bulk density, proportional mass of aggre- gate fractions, and aggregate mean weighted diameter) and the distribution C among soil fractions, including C in the micro-within-macro aggregate fraction (sequestered C), also became representative of native prairie within 35 yr of restoration. Total soil C stock and physically protected C increased at a similar rate (23 and 27 g C m-2 yr-1) respectively, across the chronosequence. After 35 yr of restoration, 50% of the total C pool was physically protected. The structural equation modeling developed by these data hypothesizes that microbial biomass C and AMF biomass (microbial composition) have the strongest causal influence on physically protected C. This model needs to be tested using independent sites to achieve greater inference.

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To quantify recovery of ecosystem properties with restoration and develop a multivariate hypothesis of C sequestration from physical protection using structural equation modeling.


Location of Sampling Stations (watershed name, or map with grid locations): A restoration chronosequence in the headquarters area was sampled; this consisted of an agricultural field next to the “Sequential Restoration Plots”, the first two sequences of the “Sequential Restoration Plots”, the “Konza Dominance Experiment”, the restoration next to the nature trail, the Gelroth property, and “Headquarters Prairie B” (native prairie reference).

Frequency of Sampling: One sampling in late August 2013.

Variable Measured: Soil aggregates, PLFA profiles, microbial biomass C, root biomass and quality.

Field Methods: Four plots were delineated in each field representing a different aged restoration. Two intact cores (5.5 cm dia., 10 cm deep) were collected per sampling plot.

Laboratory Methods (Procedures): Belowground biomass was handpicked from two composited intact cores (5.5 cm diameter to a depth of 10 cm) that were broken along planes of natural weakness until passing through an 8 mm sieve. Microbial biomass carbon was determined by the fumigation-extraction technique. Phospholipid fatty acids (PLFA) were extracted from subsamples of the intact soil cores that were frozen after sampling. Additional soil subsamples were slaked and wet sieved to separate aggregate fractions (large macroaggregates, small macroaggregates, microaggregates, and free silt/clay) by size. Intra-aggregate fractions [intra-aggregate coarse particulate organic matter (CPOM), intra-aggregate microaggregates, and Intra-aggregate silt/clay] were isolated by breaking aggregates with ball bearings on a shaker and wet sieving. Aggregate and intra-aggregate fractions used if there was a 95% recovery. Carbon content was determined from flash combustion of finely ground subsamples of soil fractions. The C:N ratio of intra-aggregate CPOM was also determined by flash combustion of a finely ground subsample of this fraction. Mean weight diameter was calculated from mass of aggregate fractions. Bulk density was determined from a core method with a 5.5 cm diameter core taken to a depth of 10 cm. Total C stock was determined by adding aggregate fractions.

Form of Data Output: Linear and non-linear regressions and a structural equation model were generated.

Quality Assurance: Data entry was checked for correctness.

Instrumentation: Flash 2000 CNHSO Elemental Analyzer (Thermo Scientific, Waltham, MA) solid phase column (0.50 g Si, Supelco, Inc. Bellefonte, PA) Shimadzu GC-2010 gas chromatograph with a flame ionization detector (Shimadzu Corp., Kyoto, Japan) and and Omegawax 320 col- umn: 30 m by 0.25 mm i.d., 0.25-mm film (polyethylene glycol phase) (Supelco, Belfonte, PA)

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