Jonathan J. Halvorson

Soil properties and microbial activity across a 500 m elevation gradient in a semi-arid environment

If climate change causes the semi-arid shrub-steppe to become hotter and drier it may affect soil C and N cycling and precipitate changes in soil processes and microbial and plant community structure. This study was conducted, using an elevation gradient as an analog of climate change, to analyze climatic influence on soil microbial activity and soil properties. We collected soil from under cryptogamic crust and bunchgrass plants at 25 sites over a 500 m elevation transect in a shrub-steppe ecosystem located in eastern Washington State of the US. The samples were analyzed for several chemical and microbiological attributes including pH, microbial biomass and nitrification potential and the data grouped into five climate sites for statistical analysis. Soil pH decreased over the transect with higher pH values in the grass soil than the crust. In contrast soil electrical conductivity (EC) increased with increasing elevation as did both ammonium and nitrate. Ammonium and EC were greater in the crust soil than the grass soil but nitrate concentration was the same under both plant covers. Both total C and N amounts increased with elevation as did nitrification potential. Due to high sample spatial variability microbial biomass, respiration and N mineralization showed non-significant trends over the 500 m elevation transect. Using these measured gradient relationships the increase in temperature and decrease in precipitation that is expected in this shrub-steppe ecosystem over the next 100 years would eventually cause the pH to increase and the EC to decrease. Plants would become more sparse, nitrification potential would decrease and ammonium would increase. Total C, N and microbial biomass concentrations would begin decreasing and may shift the controlling factors of the ecosystem to abiotic factors. The changes in the cycling of N and to some extent C due to climate change could alter the microbial and plant community structure and function of this ecosystem and cause it to move in the direction of desertification.

Chicken manure biochar as liming and nutrient source for acid Appalachian soil.

Acid weathered soils often require lime and fertilizer application to overcome nutrient deficiencies and metal toxicity to increase soil productivity. Slow-pyrolysis chicken manure biochars, produced at 350 and 700°C with and without subsequent steam activation, were evaluated in an incubation study as soil amendments for a representative acid and highly weathered soil from Appalachia. Biochars were mixed at 5, 10, 20, and 40 g kg into a Gilpin soil (fine-loamy, mixed, active, mesic Typic Hapludult) and incubated in a climate-controlled chamber for 8 wk, along with a nonamended control and soil amended with agronomic dolomitic lime (AgLime). At the end of the incubation, soil pH, nutrient availability (by Mehlich-3 and ammonium bicarbonate diethylene triamine pentaacetic acid [AB-DTPA] extractions), and soil leachate composition were evaluated. Biochar effect on soil pH was process- and rate-dependent. Biochar increased soil pH from 4.8 to 6.6 at the high application rate (40 g kg), but was less effective than AgLime. Biochar produced at 350°C without activation had the least effect on soil pH. Biochar increased soil Mehlich-3 extractable micro- and macronutrients. On the basis of unit element applied, increase in pyrolysis temperature and biochar activation decreased availability of K, P, and S compared to nonactivated biochar produced at 350°C. Activated biochars reduced AB-DTPA extractable Al and Cd more than AgLime. Biochar did not increase NO in leachate, but increased dissolved organic carbon, total N and P, PO, SO, and K at high application rate (40 g kg). Risks of elevated levels of dissolved P may limit chicken manure biochar application rate. Applied at low rates, these biochars provide added nutritional value with low adverse impact on leachate composition.

Nitrogenase Activity, Nitrogen Fixation, and Nitrogen Inputs by Lupines at Mount St. Helens

We measured the timing and magnitude of nitrogenase activity and N2 fixation by lupines colonizing early successional volcanic sites at Mount St. Helens. Ni- trogenase activity (measured by acetylene reduction) in Lupinus lepidus growing at a py- roclastic site exhibited significant diurnal trends, with lowest ethylene evolution rates at night. Nitrogenase activity also followed seasonal trends, with high rates in June, very low levels in August, the dry warm part of the season, and a partial recovery of nitrogenase activity in September after precipitation resumed. A comparison of typical nitrogenase activities measured at several sites suggested that rates of N2 fixation were highest in L. lepidus growing at disturbed low N sites. Adult lupine C and N composition also varied during the growing season, with trends correlated with seasonal patterns of nitrogenase activity. Seasonal N2 fixation in L. lepidus and L. latifolius was measured using 15N isotope. Both species fixed ;60% of their N during the first season of growth with some evidence of preferential allocation to aboveground biomass. N fixation by Lupinus lepidus individuals was - 18.1 mg/g biomass or an average of 15.4 mg per plant, while L. latifolius fixed an average of 16.3 mg/g biomass, equivalent to 22.9 mg per plant. Average net C fixation during the same period was 355 and 589 mg per plant for L. lepidus and L. latifolius, respectively. Despite these rates, the current distribution of L. lepidus into a few, small patches that occupy < 1% of the surface area indicates that annual N inputs by lupines are <0.05 kg/ha and thus probably not the primary source of N input into developing Mount St. Helens pyroclastic sites except at a local scale.

Lupine Effects on Soil Development and Function During Early Primary Succession at Mount St. Helens

The pyroclastic flows of Mount St. Helens remain important to scientists seeking to understand the mechanisms of early succession. As in other primary-succession systems, biotic and abiotic development on these sites has been strongly influenced by legume colonists. Legumes are postulated to be critical contributors to nutrient pools during early succession, especially in infertile volcanic substrates, and are thought to facilitate colonization and growth of subsequent species that are limited by soil organic matter and by availability of critical nutrients such as nitrogen (Chapin et al. 1986; Franz 1986; Mooney et al. 1987; Vitousek et al. 1987; Chapin et al. 1994; Ritchie and Tilman 1995). Two species of lupines, broadleaf lupine (Lupinus latifolius), an upright deciduous species, and prairie lupine (Lupinus lepidus), a prostrate wintergreen species (Braatne and Chapin 1986;Braatne andBliss 1999),were among the initial colonists of cool mudflows (lahars) and pyroclastic deposits at Mount St. Helens. Photosynthesis, litter input, and symbiotic nitrogen fixation by lupines contributed to the formation of highly localized soil-resource islands, characterized by higher concentrations of carbon and nitrogen than in the surrounding soil, and supported larger and more diverse active populations of heterotrophic soil microorganisms in the soil (Halvorson et al. 1991b; Halvorson and Smith 1995). Lupines growing on pyroclastic deposits have influenced revegetation of the site by other plants (Morris and Wood 1989; del Moral and Bliss 1993; del Moral andWood 1993a,b; del Moral 1998), insect distributions (Fagan and Bishop 2000; Bishop 2002), soil resources, and microorganisms (Allen et al. 1984; Allen 1987, Carpenter et al. 1987; Halvorson et al. 1991b;Halvorson andSmith 1995; Titus and delMoral 1998b). This chapter summarizes research about the impacts of lupines on soil that in turn influenced plant and soil microbialcommunity development of Mount St. Helens pyroclastic deposits. The following sections provide conceptual frameworks for viewing succession as a belowground process, describe the rationale and analytical approach of lupine-soil research at the pyroclastic study site during the first 20 years after the eruption, summarize researchfindings, and suggest topics for future research.

Soil biology for resilient, healthy soil

What is a resilient, healthy soil? A resilient soil is capable of recovering from or adapting to stress, and the health of the living/biological component of the soil is crucial for soil resiliency. Soil health is tightly coupled with the concept of soil quality (table 1), and the terms are frequently used interchangeably. The living component of soil or soil biota represents a small fraction (<0.05% dry weight), but it is essential to many soil functions and overall soil quality. Some of these key functions or services for production agriculture are (1) nutrient provision and cycling, (2) pest and pathogen protection, (3) production of growth factors, (4) water availability, and (5) formation of stable aggregates to reduce the risks of soil erosion and increase water infiltration (table 2). Soil resources and their inherent biological communities are the foundation for agricultural production systems that sustain the human population. The rapidly increasing human population is expanding the demand for food, fiber, feed, and fuel, which is stretching the capacity of the soil resource and contributing to soil degradation. Soil degradation decreases a soils production capacity to directly supply human demands and decreases a soils functional capacity to perform numerous critical services, which…

Overwinter changes to near-surface bulk density, penetration resistance and infiltration rates in compacted soil

Abstract Previous studies at Yakima Training Center (YTC), in Washington State, suggest freeze-thaw (FT) cycles can ameliorate soil compacted by tracked military vehicles [J. Terramechanics 38 (2001) 133]. However, we know little about the short-term effects of soil freezing over a single winter. We measured bulk density (BD), soil penetration resistance (SPR), and steady-state runoff rates in soil newly tracked by an Abrams tank and in uncompacted soil, before and after a single winter at YTC. We similarly measured BD, SPR and saturated hydraulic conductivity (kfs) in simulated tank tracks at another site near Lind Washington. Average BD was significantly greater in tank ruts at YTC and in simulated tracks at the Lind site than in uncompacted soil soon after tracking and did not change significantly during the winter of 1997–1998. Measurements of SPR were strongly influenced by soil moisture. When soil was moist or tracks were newly formed, SPR was significantly higher in tank ruts than in uncompacted soil from the surface to a depth of about 10–15 cm. The greatest average SPR in compacted soil was observed between 4 and 6 cm depth. We observed less difference in SPR between tank ruts and uncompacted soil near-surface at YTC as the time after trafficking increased. We observed highest SPR ratios (compacted rut:undisturbed) in fresh tracks near the surface, with lower ratios associated with increasing track age or soil depth, indicating that some recovery had occurred at YTC near-surface. However, we did not observe a similar over-winter change in SPR profiles at the Lind site. Rainfall simulator data from YTC showed higher steady-state runoff rates in tank ruts than over uncompacted soil both before and after winter. However, more time was required to reach steady-state flow in tank ruts and the proportion of runoff was slightly lower in May 1998 than in August 1997. At the Lind site, kfs was lower in newly compacted soil than in one-year old compacted soil or uncompacted soil. Our data suggest that indices of water infiltration such as steady-state runoff rates or kfs, are more sensitive indicators of soil recovery after compaction than are BD or SPR.

Polyphenol–Aluminum Complex Formation: Implications for Aluminum Tolerance in Plants

Natural polyphenols may play an important role in aluminum detoxification in some plants. We examined the interaction between Al(3+) and the purified high molecular weight polyphenols pentagalloyl glucose (940 Da) and oenothein B (1568 Da), and the related compound methyl gallate (184 Da) at pH 4 and 6. We used spectrophotometric titration and chemometric modeling to determine stability constants and stoichiometries for the aluminum-phenol (AlL) complexes. The structures and spectral features of aluminum-methyl gallate complexes were evaluated with quantum chemical calculations. The high molecular weight polyphenols formed Al3L2 complexes with conditional stability constants (β) ∼ 1 × 10(23) at pH 6 and AlL complexes with β ∼ 1 × 10(5) at pH 4. Methyl gallate formed AlL complexes with β = 1 × 10(6) at pH 6 but did not complex aluminum at pH 4. At intermediate metal-to-polyphenol ratios, high molecular weight polyphenols formed insoluble Al complexes but methyl gallate complexes were soluble. The high molecular weight polyphenols have high affinities and solubility features that are favorable for a role in aluminum detoxification in the environment.

Soil microbial communities respond differently to three chemically defined polyphenols

High molecular weight polyphenols (e.g. tannins) that enter the soil may affect microbial populations, by serving as substrates for microbial respiration or by selecting for certain microbes. In this study we examined how three phenolic compounds that represent some environmentally widespread tannins or their constituent functional groups were respired by soil microorganisms and how the compounds affected the abundance and diversity of soil bacteria and archaea, including ammonia oxidizers. An acidic, silt loam soil from a pine forest was incubated for two weeks with the monomeric phenol methyl gallate, the small polyphenol epigallocatechin gallate, or the large polyphenol oenothein B. Respiration of the polyphenols during the incubation was measured using the Microresp™ system. After incubation, metabolic diversity was determined by community level physiological profiling (CLPP), and genetic diversity was determined using denaturing gradient gel electrophoresis (DGGE) analysis on DNA extracted from the soil samples. Total microbial populations and ammonia-oxidizing populations were measured using real time quantitative polymerase chain reaction (qPCR). Methyl gallate was respired more efficiently than the higher molecular weight tannins but not as efficiently as glucose. Methyl gallate and epigallocatechin gallate selected for genetically or physiologically unique populations compared to glucose. None of the polyphenols supported microbial growth, and none of the polyphenols affected ammonia-oxidizing bacterial populations or ammonia-oxidizing archaea. Additional studies using both a wider range of polyphenols and a wider range of soils and environments are needed to elucidate the role of polyphenols in determining soil microbiological diversity.

Metal mobilization in soil by two structurally defined polyphenols

Polyphenols including tannins comprise a large percentage of plant detritus such as leaf litter, and affect soil processes including metal dynamics. We tested the effects of tannins on soil metal mobilization by determining the binding stoichiometries of two model polyphenols to Al(III) and Fe(III) using micelle-mediated separation and inductively coupled plasma optical emission spectroscopy (ICP-OES). By fitting the data to the Langmuir model we found the higher molecular weight polyphenol (oenothein B) was able to bind more metal than the smaller polyphenol (epigallocatechin gallate, EGCg). For example, oenothein B bound 9.43 mol Fe mol(-1), while EGCg bound 4.41 mol of Fe mol(-1). Using the parameters from the binding model, we applied the Langmuir model for competitive binding to predict binding for mixtures of Al(III) and Fe(III). Using the parameters from the single metal experiments and information about polyphenol sorption to soils we built a model to predict metal mobilization from soils amended with polyphenols. We tested the model with three natural soils and found that it predicted mobilization of Fe and Al with r(2)=0.92 and r(2)=0.88, respectively. The amount of metal that was mobilized was directly proportional to the maximum amount of metal bound to the polyphenol. The secondary parameter in each model was the amount of weak organically chelated Fe or Al that was in the soil. This study provides the first compound-specific information about how natural polyphenols interact with metals in the environment. We propose a model that is applicable to developing phytochelation agents for metal detoxification, and we discuss how tannins may play a role in metal mobilization from soils.

Effects Of Freeze-Thaw Cycling On Soil Erosion

Landscapes evolve as a result of the interactions of topography, climate, hydrology, vegetation conditions, rock-weathering processes, soil conditions, sediment transport and deposition processes, and land use. An integral part of understanding and modeling that evolution must be a knowledge of the spatial and temporal dynamics in soil erodibility and runoff erosivity and how these dynamics affect the mechanics of soil erosion.