Vegetation can profoundly influence both the chemistry and biology of soils; altering soils in a way that enhances plant community resiliency to perturbation (Perry et al.1989). To a large degree, this finding explains why forests that have been disturbed by fire, disease, wind-throw, harvesting or other factors typically return to the same vegetative assemblage that was present before the disturbance. For instance comparative studies between grasslands and forests have shown large differences in soil chemistry (Göceoðlu, 1988; Hart et al., 1992; Popenoe et al., 1992; Ross et al., 1996; Yakimenko, 1997); litter decomposition rates (Hunt et al., 1988; Köchy and Wilson, 1997) and food web compositions (Hunt et al., 1987; Ingham at al., 1989).
The main objective of this study was to run a survey on the effects of different types of vegetation and rates of early succession on forest soil properties. In past studies, we had observed significant differences in soil properties in a chronosequence of post-clear-cut stands ranging in age from 5 to 40 years (seed data in study code SP07: “Disturbance effects on soil processes (stand age study))”. We found significant differences in soil properties between 5 year-year old stands and old-growth stands. The differences were essentially nonexistent after 40 years. We wanted to determine if we could detect differences in soils associated with different vegetation types (i.e. GRASS and FERN) as well as soils associated with stands with different rates of recovery after clear-cutting. The extreme on this continuum is the DEGRAD sites where essentially no conifers have become reestablished after harvest. The SLOW sites were those that did not have canopy closure after approximately 30 years and the FAST sites were ones that did.
The main focus of Synthesis Area “B” of LTER4 is early plant succession. Our study was designed to provide preliminary information about how the rate of early succession might impact soil processes. The current study was an important first step before conducting a much more comprehensive study of early succession sites conducted during 1998 and 1999. The results of this more recent study are reported in the data file entitled “Influence of coniferous tree invasion on forest meadow soil properties” (study code SP012). The current study also laid the groundwork for a data set entitled “Effects of bracken fern invasions on soil processes in clear-cut marginal sites” completed in 1997. In addition, it laid the groundwork for a 1998 study of forest meadow invasion by conifers in a data set entitled “Influence of coniferous tree invasion on forest meadow soil” (See SP016).
Sampling transects ran from old-growth (OG) forests into stands with different vegetation or were stand-alone transects within each vegetation type or successional type. Each transect was made up of 75 meter segments in both the OG and “treatment” stands. Soil samples and field observations were made at 5 meter-intervals along these segments.
At each sample location along these transects, a 4.7 x 10 cm soil core was taken for subsequent analysis. The samples were transported to the laboratory in an ice chest and subsequently stored at 15 degrees C until the initiation of analyses, usually within 16 h of their receipt. The following measurements were made in the field: litter depth, mineral soil respiration, soil and air temperature, light levels and ectomycorrhizal mat characteristics. Field (forest floor) respiration rates were measured with a nondispersive, infrared CO2 analyzer (Li-Cor, LI-6200). Measurements were made over a period of 1 min after the chamber gas reached ambient CO2 concentration. The instrument was calibrated on site against a known standard at each location. A Q10 adjustment was made for ambient soil temperature. Electronic thermometers calibrated at 0°C with ice water measured soil temperature. The temperature probes were inserted into the mineral soil to a depth of 10 cm.
The distribution of ectomycorrhizal mats was determined visually in the field by inspecting the relative abundance of mats in 4.7 x 10 cm cores. Two distinct mat types were scored: (1) mats similar to those of the genus Hysterangium and (2) mats similar to those of the genus Gautieria. This approach has been used successfully in the past to document ectomycorrhizal mat distribution patterns in coniferous forests of the Pacific Northwest (Griffiths et al. 1996).
In preparation for laboratory analyses, all soils were sieved through a 2-mm sieve.
Soil moisture was determined by drying duplicate 10 g field-moist sieved soils at 100 degrees C for at least 8 h. The percent soil moisture was calculated by dividing the difference between wet and dry samples and dividing that number by the dry wt., which was then multiplied by 100. Soil pH was measured in 1:10 (soil:distilled water) slurries of oven-dried (100 degrees C) soil. These slurries were shaken for 1 h prior to reading pH values with a Sigma model E4753 electrode. Soil organic matter was measured by loss-on-ignition at 550 degrees C for 6 h after oven drying at 100 degrees C. The dry mass of live roots within the cores was measured by removing by hand roots in cores that had been dried for 8 h at 100 degrees C.
Denitrification potential was measured using a method by Groffman and Tiedje (1989) as modified by us (Griffiths et al., 1998). Each reaction vessel (25-mL Erlenmeyer flask) contained 5 g of less than 2 mm, field-moist soil. Flasks were sealed with rubber serum bottle stoppers and purged with Ar to displace O2 in the headspace gas. After purging with Ar, 2 mL of a 1 mM solution of glucose and NO3- was added to each flask. Flasks were subsequently incubated at 25 degrees C for 1 h. This preincubation period was used because previous time-series experiments showed a lag in N2O production during this period. The same experiments have shown linear N2O production rates during the following 2-4 h (unpublished data). After the preincubation period, 0.5 mL of headspace gas was removed from the reaction vessel and injected into a gas chromatograph (GC) fitted with an electron capture detector (Hewlett Packard model 5890 GC, connected to a Hewlett Packard model 3396 integrator). The integrator was calibrated by the external calibration method with known gas standards. A second headspace N2O analysis was made after an additional 2-h incubation at 25 degrees C. The net N2O released over this 2-h period was used to estimate N2O production rates.
Laboratory respiration measurements were made on field-moist, sieved soils (4 g dry weight). These rates represent the basal respiration rate for soil microorganisms. Soils were brought to 75% moisture content by the addition of enough sterile deionized water to equal 3 g water per 25-mL Erlenmeyer flask. Once sealed with serum bottle stoppers, the flasks were incubated at 24 degrees C for 14 days after which headspace CO2 concentrations were measured using gas chromatography. This was a measure of labile soil carbon. The same GC and integrator as were used for this assay as that used to measure N2O, but in this case a flame ionization detector and a methanizer in series were used. Substrate induced respiration (SIR) was also measured in these soils. The reaction vessels were prepared as before except 0.1 mL of 1 M glucose solution was added to the reaction vessel and the assay for CO2 evolution rates were calculated from the difference between the headspace CO2 concentrations after the first h incubation and the concentration 2 h later. SIR was calculated by subtracting CO2 evolution rates without the glucose amendment from the rates in the presence of glucose.
Extractable ammonium was determined by shaking 10 g of field-moist soil with 50 mL 2 M KCl for 1 h (Keeney and Nelson 1982), adding 0.3 mL 10 M NaOH to the slurry, and measuring ammonium concentration with an Orion model 95-12 ammonium electrode (Orion Research Inc., Boston, MA). Mineralizable N was measured by the waterlogged technique of Keeney and Bremner (1966). For each analysis, 10 g of field-moist soil were added to 53 mL of distilled water in a 20 x 125 mm screw-cap test tube, and incubated at 40 degrees C for 7 d. Then 53 mL of 4 M KCl was added to the slurry, and ammonium concentration was determined with the ammonium electrode. Mineralizable N was calculated as the difference between initial and final ammonium concentrations.
Beta-glucosidase activity was determined by the spectrophotometric assay of Tabatabai and Bremmer (1969), as modified by Zou et al. (1992). One mL of 10 mM p-nitrophenyl b-D glucopyranoside substrate was added to duplicate 1-mL subsamples containing a soil slurry (1 gdw in 1 mL deionized H2O). The tubes were shaken and then placed with duplicate controls without substrate in a 30 degrees C water bath for 2 h. After incubating, 1 mL of 10 mM p-nitrophenyl b-D glucopyranoside was added to the controls, and all reactions were immediately stopped by the addition of 2 mL of 0.1 M tris[hydroxymethyl]aminomethane at pH 12.0. The mixtures were centrifuged for 5 min at 500 x g. From the supernatant, 0.2 mL was diluted with 2.0 mL deionized water. The optical density was measured at 410 nm, and a standard curve was prepared from 0.02 to 1.0 micro-mol/mL p-nitrophenol (pNP).
Griffiths, R.P., Homann, P.S., and Riley, R. (1998) Denitrification enzyme activity of Douglas-fir and red alder forest soils of the Pacific Northwest. Soil Biology and Biochemistry 30, 1147-1157.
Groffman, P.M., and Tiedje, J.M. 1989. Denitrification in north temperate forest soils: relationships between denitrification and environmental factors at the landscape scale. Soil Biology & Biochemistry 21, 621-626.
Keeney, D.R., and Nelson, D.W. 1982. Nitrogen-inorganic forms. In Methods of soil analysis. Edited by A.L. Page, R.H. Miller, and D.R. Keeney. American Society of Agronomy, Madison, Wis. pp. 643-698.
Zou, X., D. Binkley, and K. G. Doxtader. (1992) A new method for estimating gross phosphorus mineralization and immobilization rates in soils. Plant & Soil 147,243 - 2
References
Griffiths, R. P., Bradshaw, G. A., Marks, B., and G. W. Lienkaemper. 1996. Spatial distribution of ectomycorrhizal mats in coniferous forests of the Pacific Northwest, USA. Plant and Soil 180:147-158.
Ingham, E R., Coleman, D.C., and Moore, J.C. (1989) An analysis of food-web structure and function in a shortgrass prairie, a mountain meadow, and a lodgepole pine forest. Biology and Fertility of Soils 8, 29-37.
Perry, D.A., Amaranthus, M.P., Borchers, J.G., Borchers, S.L. and Brainerd, R.E. (1989) Bootstrapping in ecosystems Biological Science 39, 230-237.
Ross, D.J., Tate, K.R., and Feltham, C.W. (1996) Microbial biomass, and C and N mineralization, in litter and mineral oils of adjacent mountain ecosystems in the southern beech (Nothofagus) forest and a tussock grassland.
Yakimenko, E.Y. (1997) Soil comparative evolution under grasslands and woodlands in the forest zone of Russia. In Management of Carbon Sequestration in Soil, eds. R. Lal, J. K. Kimble, and B.A. Stewart, pp. 391-404. CRC Press, New York.
