Grantee Research Project Results
1999 Progress Report: Soil Enzyme Stability as an Ecosystem Indicator
EPA Grant Number: R826592Title: Soil Enzyme Stability as an Ecosystem Indicator
Investigators: Dick, Richard P.
Institution: Oregon State University
EPA Project Officer: Hahn, Intaek
Project Period: August 19, 1998 through August 18, 2000
Project Period Covered by this Report: August 19, 1998 through August 18, 1999
Project Amount: $196,806
RFA: Ecological Indicators (1998) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Aquatic Ecosystems
Objective:
The objectives of this project are to: (1) refine microwave enzyme stress test for maximum sensitivity in detecting soil management/stressors as a soil quality and ecosystem indicator; (2) determine temporal dynamics of selected soil enzyme activities and MWES across diverse agroecosystems; and (3) investigate the relationship of soil enzyme activities to other soil properties to develop conceptual models on the role of enzyme activity and stability to be an indicator of soil quality.Progress Summary:
Sustainability assessment of ecosystems is a national priority to assist land managers and policy makers in promoting long-term sustainability, yet quantifying environmental sustainability remains an elusive goal. One approach is to use the soil as an indicator of ecosystem "health." Soil enzyme activity assays are advantageous as a potential indicator because they are operationally practical, sensitive integrative "biological fingerprints" of past soil management, and apparently related to soil aggregation, linking enzymes with soil tilth. In the first year of the project, the initial screening of three promising soil enzyme assays as indicators were performed at three experimental sites in Oregon (located in divergent forest and agroecosystems), where detailed management history is known and soils vary widely in soil "health" (i.e., biological activity and organic matter content) because of past soil management. This included refinement of sample handling and lab protocols to increase sensitivity and reproducibility of the indicators. Samples were taken in early May, June, and September to assess the seasonal temporal variability of these indicators.
First, the forest soils generally have much higher activities than agricultural soils. This would fit as these agricultural soils are regularly disturbed, whereas forest soils, even with recent logging, would have had only surface disturbance once, and even then, there would not be tillage. If we look at within-site treatment effects, there is a very consistent pattern in the agricultural soils in that those receiving greater C inputs (as cover cropping manure, and green manure) have higher activities than the plots receiving lower C inputs. Across the agricultural soils, the biological measurements ergosterol, fungi biomass, and biomass C are very consistent with soil enzyme activities; however, bacterial counts show very few significant differences as a function of soil management in either forest or agricultural soils. This suggests that soil enzyme activities are good indicators of the soil biological component and are reflecing the differences due to fungal biomass.
Background Rationale. Soil is a vital natural resource that, on a human time scale, is nonrenewable. In the 1980s alone, 10 percent of the earth's vegetated land was severely degraded by soil erosion, pollution, cultivation, overgrazing, land clearing, and desertification. Since soil pedogenic processes occur over decadal, millennial, or longer periods, there is increasing concern about reversing the negative impacts of modern soil management. Parallel to this is the need to develop soil quality or "health" indices that are temporally sensitive to positive or negative effects of management on soils and reflect ecosystem health. Ecosystem managers and policymakers require such a tool to assist them in promoting the sustainability of agricultural and forest systems.
Historically, chemical and physical properties have been used as crude measures of soil productivity. Most notably, determination of soil organic matter has been related to general soil tilth but changes too slowly to be useful ecological indicator. There is growing evidence that soil biological parameters may have potential as early and sensitive indicators of soil ecological stress or restoration. Soil enzymes play an important role in soil microbial ecology by catalyzing innumerable reactions in soils, and have potential as an index of the effect of soil and ecosystem management on soil biology. Many enzyme assays are simple to run and are sensitive to temporal changes due to soil management.
Study Sites. Four forested sites on the humid westside of the Cascade Mountains, and two agricultural sites (one in western humid Willamette Valley, and one in semi-arid eastern Oregon) were sampled in April, June, and mid-September. The two agricultural sites are long-term research sites with statistically valid designs and replication (three to four replications at each site). The Residue Utilization Plot (RUP), Columbia Basin Plateau Research Center, Pendleton, OR is located in a semi-arid wheat region. This trial has a range of treatments that were begun in 1931 and include a steer manure, green manure, and series of inorganic N rate treatments (nearby is a plot with vegetation similar to native vegetation that has never been tilled). The second agricultural site is the Vegetable Crop Rotation/Cover Crop Study, Corvallis, Oregon. Located in a humid maritime of Western Oregon, this project represents the intensively managed vegetable systems of the region. Initiated in 1989, this trial is comparing conventional (vegetable-winter bare-ground fallow) and alternative vegetable systems that utilize winter cover crops.
The four forest long-term experimental sites are each side-by-side, paired comparisons of old growth timber (>100 year stand) versus recent clear cut (<3 year stand). This site is considered to have an RCB design, where each site is one block with two treatments. All sampling sites have been located and permanently recorded by global positioning systems technology.
Soil Sampling and Pretreatment Protocols. At each site, approximately 30 soil cores (0 to 15 cm depth in agricultural soils) (A horizon in forest soils-with the litter layer/O horizon not included in the sample) per treatment were bulked for each replication. Soil samples were stored in coolers, transported back to the lab at OSU, and within 24 h. Samples were homogenized, sieved, split with one-half being air-dried, and both air-dried and field moist samples being stored at 4 C. Field moist samples were used for biological parameters within time frames appropriate for each method. Air-dried samples were stored at 4 C and used for all enzyme assays.
At the agricultural research sites, samples were randomly taken within the center of the plots at each sampling period. The other sites have much larger plots or fields on the order of hectares, therefore sampling sites that have been previously sampled with legal location descriptions were used by randomly sampling an area with a radius of 5.6 m (0.01 ha) at each sampling period. There are five sampling pairs of points on a transect on each side of the line that divides the old growth from clear cut areas (10 sampling points per site).
Soil Enzyme Assay Results. Three enzyme assays were investigated to determine their effectiveness in reflecting soil management effects. -glucosidase, arylsulfatase, and FDA hydrolysis were studied because the assays are simple (i.e., potential for commercial scale), and consistently show soil management treatment effects. The microwave stress test was studied as an approach to develop a soil quality indicator of biological status that is relative and independent of soil type. The microwave enzyme stress (MWES) index is calculated as follows:
MWES Index = Activity of microwave treated soil / Control activity
Therefore, the range of values is from 0.0 to 1.0, with higher values having higher soil quality (i.e., greater potential to protect complexed abiontic soil enzymes).
The fall of 1998 and winter of 1999 were spent conducting detailed studies on microwave stress of -glucosidase activity as a function of soil management?trying to identify the best way to microwave the sample to best separate treatment effects. After investigating various pretreatments (water content, soil sample size) and microwave energy inputs, it was decided to microwave 10 g soil on watch glasses for 10 minutes at full power, with 65 mL water in the center of the microwave.
Although the data are still being analyzed and some of the laboratory work for the September sampling is still being completed, very consistent results with all three enzyme assays across all three sampling times are being found. The forest soils generally have much higher activities than agricultural soils. This makes sense, as these agricultural soils are regularly disturbed, whereas forest soils, even with recent logging would have only have had surface disturbance once, and even then there would not be tillage. Consequently, the assays are reflecting that forest soils have higher soil quality. Looking at within-site treatment effects, there is a very consistent pattern in the agricultural soils in that those receiving greater C inputs (as cover cropping, manure, and green manure) have higher activities than the plots receiving lower C inputs. The forest sites generally showed no differences between clear cuts and mature forest, except at two sites on arylsulfatase and one site on -glucosidase, where activities were higher in the mature forest stand.
Assessment of Other Soil Properties. In tandem with the enzyme assays, additional measurements were performed on soil samples. Soils from the first sampling period were characterized for the chemical properties total C and N, pH, texture, and bulk density. Other properties that were measured at all three sampling periods were: microbial biomass C (fumigation-incubation method); lab CO2 respiration; dissolved organic C; active and dead fungal and bacterial biomass by direct counts; ergosterol content (originates only from fungi); and aggregate stability by wet sieving. In addition, the metabolic quotient (mass CO2 evolved/unit biomass C [qCO2]) will be calculated. This measurement has been proposed as an indicator ecological stress.
Across the agricultural soils, the biological measurements ergosterol, fungi biomass, and biomass C are very consistent with soil enzyme activities; however, bacterial counts show very few significant differences as a function of soil management in either forest or agricultural soils. This suggests that soil enzyme activities are good indicators of the soil biological component and are reflecting the differences due to fungal biomass, and lends credence to the working hypothesis that soils of high quality are fungal-dominated. Fungal-dominated soils would confer greater soil quality in several ways. Most importantly, fungi are important in promoting aggregation, particularly the larger aggregates (>1 mm), by binding particles with their hyphae.
On the forest soils, differences in treatment effects (mature versus recent clear cut) are seen on fungal biomass and ergosterol (a compound unique to fungi), but enzyme activities are not reflecting these differences. As mentioned above, activities were generally much higher on forest soils than agricultural soils. It may be that these soils are already "saturated" with stabilized enzymes, and that enzyme assays run on air-dried soils (as was done to facilitate soil handling and enable commercial adoption) may not readily reflect the status of forest soils.
Future Activities:
Over the winter of 2000, data analysis and assessment of relative indices that include ratios (enzyme activity to total C, microbial biomass C, etc.,) will be done. Further refinement of the microwave stress test in preparation for the summer sampling period is anticipated. This coming year, the sites will be expanded to a wider range of soil types and soil management systems. To facilitate this, only one sampling will be conducted in June. More extensive sampling on forest soils is desirable to determine if the results seen in the first year are consistent at other sites.Journal Articles:
No journal articles submitted with this report: View all 8 publications for this projectSupplemental Keywords:
soil, ecological effects, enzymes, ecosystems, indicators, sustainable development, environmental chemistry, biology, measurement methods, analytical, pacific northwest, agriculture, forestry., RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Ecology, Ecosystem/Assessment/Indicators, Ecosystem Protection, Environmental Chemistry, Ecological Effects - Environmental Exposure & Risk, Agronomy, Geology, Ecological Indicators, ecological exposure, biogeochemical indicators, substrate catalysis, biomonitoring, ecosystem indicators, terrestrial, bioassay, environmental stress, soil enzyme, microwave enzyme stress test, agriculture ecosystemsProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.