James A. Entry

Cellulose and lignin degradation in forest soils: Response to moisture, temperature, and acidity.

The concentration of lignin in plant tissue is a major factor controlling organic matter degradation rates in forest ecosystems. Microbial biomass and lignin and cellulose decomposition were measured for six weeks in forest soil microcosms in order to determine the influence of pH, moisture, and temperature on organic matter decomposition. Microbial biomass was determined by chloroform fumigation; lignin and cellulose decomposition were measured radiometrically. The experiment was designed as a Latin square with soils of pH of 4.5, 5.5, and 6.5 adjusted to 20, 40, or 60% moisture content, and incubated at temperatures of 4, 12, or 24°C. Microbial biomass and lignin and cellulose decomposition were not significantly affected by soil acidity. Microbial biomass was greater at higher soil moisture contents. Lignin and cellulose decomposition significantly increased at higher soil temperatures and moisture contents. Soil moisture was more important in affecting microbial biomass than either soil temperature or soil pH.

Comparison of direct vs fumigation incubation microbial biomass estimates from ectomycorrhizal mat and non-mat soils

Abstract Direct estimates of microbial biomass were compared to chloroform fumigation incubation estimates of microbial biomass using samples collected from mesic forest stands. Paired soil samples were collected from ectomycorrhizal mats, which contain visible amounts of fungal material, and from non-mat areas immediately adjacent to the mats but which contain no visible fungal material. As much as 30–50% of the dry wt of soil collected from ectomycorrhizal mats can be comprised of strictly fungal biomass. Direct estimates of microbial biomass from both mat and non-mat soils were 10–300 times higher than biomass estimates obtained using the fumigation incubation method. Fumigation incubation estimates of microbial biomass showed little seasonal variation, while direct estimates revealed that microbial biomass peaked during both the spring and fall when rainfall and temperatures were optimal and were lowest during the dry summer. We compared our values to ones reported for shortgrass prairies and in Jenkinsons original fumigation incubation paper. Fumigation incubation estimates indicated that microbial biomass carbon was the same in both prairie and forest soils, about 0.5 mg C g −1 soil. Direct estimates showed that microbial biomass was actually greater, by factors of 10–300, in these forest soils. Some forest soils, for which fumigation incubation indicated very low microbial biomass, contained visible amounts of fungal hyphae. Our conclusion is that fumigation incubation does not necessarily measure microbial biomass, and that the error can be extremely high when soils contain high quantities of fungal biomass.

Litter decomposition and nutrient release in ectomycorrhizal mat soils of a Douglas fir ecosystem

Abstract The ectomycorrhizal fungus Hysterangium setchellii (Fisher) forms extensive hyphal mats at the soil-litter interface with the roots of its host tree Douglas fir { Pseudotsuga menziesii [(Mirb.) Franco]}. Microbial biomass, needle decomposition rates, nutrient release from needles and exchangeable soil nutrients were measured in ectomycorrhizal mat soils and adjacent non-mat soils in a second-growth Douglas fir forest periodically throughout 1 yr. Microbial biomass and needle decomposition were 4.0 and 1.1 times higher, respectively, in mat soils than in adjacent non-mat soils during the year of sampling. After 1 yr of decomposition, needle litter concentrations of K and Mg decreased in both soil types, and release of both nutrients was greater in mats than in non-mat soils. Needle litter concentrations of Ca, Mn, Cu. Zn and Al increased during the year in both soil types, but nutrient absorption by needles tended to be highest in non-mat soils. Concentrations of N, P, Fe and B in needle litter did not change during the year, yet nearly twice as much N and P were released in mat soils compared to non-mat soils, suggesting either faster decomposition or nutrient import to mat soils. Soil solution concentrations of nh 4 , P, K, Mg and Zn measured by absorption onto ion-exchange resins, did not differ between mat and non-mat soils. Mat soils had higher concentrations of NO 3 , Fe, Cu and B but lower concentrations of Ca and Mn compared to non-mat soils. Nutrients released from the decomposing needles but not absorbed by ion-exchange resins must be rapidly removed from the soil solution either by plant roots, microbial tissue, saprophytic fungi or via ectomycorrhizal translocation to host trees. Our data suggest that the ectomycorrhizal fungus H. seichelli provides an improved microcnvironment for organic matter decomposition resulting in faster release of N, P, K, and Mg and more efficient removal of the nutrients from the soil solution.

Interactions between soil animals and ectomycorrhizal fungal mats

Estimates of microbial biomass were made for ectomycorrhizal fungal mats colonizing mineral soil in a 50–75-year-old Douglas-fir stand in western Oregon. The ectomycorrhizal fungal mats are from the basidiomycete, Hysterangium setchellii. Numbers and biomass of soil animals including microarthropods and nematodes were estimated for both fungal mat and non-mat areas. The mats generally showed a significantly greater microbial biomass and also greater numbers of soil microarthropods. Protozoans were also sampled and exhibited greater abundance in fungal mats for amoebae and ciliates, but not flagellates. We hypothesize that these mats represent a larger and more active microbial biomass, available as a soil-animal food resource. Fungal mats had greater concentrations of soil C and soil N, and soil respiration and enzyme activity rates were significantly greater in mat than non-mat soil.

The influence of nitrogen on atrazine and 2,4-dichlorophenoxyacetic acid mineralization in grassland soils

The influence of fertilizer N on the mineralization of atrazine [2-chloro-4(ethylamino)-6(isopropylamino)-s-triazine] and 2,4-D (2,4-dichlorophenoxyacetic acid) in soils was assessed in microcosms using radiometric techniques. N equivalent to 0, 250, and 500 kg N as NH4NO3 ha-1 was added to three grassland soils. Compared to the control, the 250- and 500-kg treatments suppressed mineralization of atrazine by 75 and 54%, respectively, and inhibited mineralization of 2,4-D by 89 and 30%, respectively. Active fungal biomass responded to the N treatments in an opposite manner to herbicide mineralization. Compared to the control, the 250- and 500-kg treatments increased the active fungal biomass by more than 300 and 30%, respectively. These results agree with other observations that N can suppress the decomposition of resistant compounds but stimulate the primary growth of fungi. The degree of suppression was not related to the amount of N added nor to the inherent soil N levels before treatment. The interaction between the N additions and the active fungal biomass in affecting herbicide mineralization suggests that N may alter microbial processes and their use of C sources and thus influence rates of herbicide degradation in the field.

90sr uptake by 'pinus ponderosa' and 'pinus radiata' seedlings inoculated with ectomycorrhizal fungi

Strontium-90 ((90)Sr) is a radionuclide characteristic of fallout from nuclear reactor accidents and nuclear weapons testing. Prior studies have shown that Pinus ponderosa and P. radiata seedlings can remove appreciable quantities of (90)Sr from soil and store it in plant tissue. In this study, we inoculated P. ponderosa and P. radiata seedlings with one of five isolates of ectomycorrhizal fungi. Inoculated and noninoculated (control) seedlings were compared for their ability to remove (90)Sr from an organic growth medium. Seedlings were grown in a growth chamber in glass tubes containing 165 cm(3) of sphagnum peat moss and perlite (1 : 1 (v/v)) and, except in the controls, the fungal inoculum. After 3 months, 5978 Bq of (90)Sr in 1 ml of sterile, distilled, deionized water was added. Seedlings were grown for an additional month and then harvested. P. ponderosa seedlings with ectomycorrhizae accumulated 3.0-6.0% of the (90)Sr; bioconcentration ratios (Bq (90)Sr cm(-3) plant tissue/Bq (90)Sr cm(-3) growth medium) ranged from 98-162. Ectomycorrhizal P. radiata seedlings accumulated 6.0-6.9% of the (90)Sr; bioconcentration ratios ranged from 88-133. Nonmycorrhizal P. ponderosa and P. radiata seedlings accumulated only 0.6 and 0.7% of the (90)Sr and had bioconcentration ratios of 28 and 27, respectively. Ectomycorrhizal P. ponderosa and P. radiata seedlings are able to remove 3-5 times more (90)Sr from contaminated soil than seedlings without ectomycorrhizae.

Influence of ectomycorrhizal mat soils on lignin and cellulose degradation

SummaryThe ectomycorrhizal fungus Hysterangium setchellii (Fisher) forms extensive hyphal mats at the soillitter interface with the roots of the host tree Douglas fir Pseudotsuga menziesii [(Mirb.) Franco]. Microbial biomass, and lignin and cellulose decomposition rates were measured seasonally for 1 year, using 14C techniques in ectomycorrhizal mat soils and adjacent non-mat soils in a second-growth Douglas fir forest. The microbial biomass and cellulose degradation rates were 3–6 times higher in ectomycorrhizal mat soils than in adjacent nonmat soils. Lignin degradation rates were higher in ectomycorrhizal mat soils than adjacent non-mat soils. Our data suggest that the ectomycorrhizal fungus H. setchellii provides a microenvironment with increased microbiological activity which results in faster lignin and cellulose decomposition.

Microbial biomass and nutrient concentrations in hyphal mats of the ectomycorrhizal fungus Hysterangium setchellii in a coniferous forest soil

Abstract In western Oregon, the calcium oxalate-producing ectomycorrhizal fungus Hysterangium setchellii (Fischer) forms a symbiotic relationship with Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] resulting in fungal mats that range from 1 to 1.5m dia and 7–10 cm thickness. Microbial biomass, extractable soil nutrients and nutrient concentration of hyphal tissue were measured in mat soils and adjacent non-mat soils. Extractable concentrations of N, P, K, Ca, Mg, AI, B, Cu, Fe, Mn and Zn were analyzed in H. setchellii hyphal tissue, mat soils, non-mat soils and mat soils with H. setchellii hyphae removed. Mierobial biomassand concentrations of most nutrients were greater in mat soils than in non-mat soils. Nutrients were incorporated primarily in the fungal tissue rather than on soil exchange sites. Extractable nutrients other than Cu were correlated with microbial biomass for combined data from mat and adjacent non-mat soils. Macronutrients other than N were positively correlated with Al + Fe concentration in mat soils, but showed negative correlations in the non-mat soils and in mat soils with hyphae removed. The inverse correlation of soil Al + Fe concentration to soil macronutrient concentration in non-mat soils may reflect greater leaching and lower retention of macronutrients in soils without H. setchellii mats. These results indicate that the ectomycorrhizal fungus H. setchellii is able to concentrate nutrients in hyphal tissue that are important to the growth and productivity of Douglas-fir forests.

Mineralization of atrazine and 2,4-d in soils inoculated with Phanerochaete chrysosporium and Trappea darkeri

Abstract Previous studies have shown that Phanerochaete chrysosporium and Trappea darkeri can degrade atrazine (2-chloro-4 [ethylamino]-6[isopropylamino]- s -triazine) and 2,4- d (2,4dichlorophenoxyacetic acid) in vitro. In this study radiometric techniques were used to measure the mineralization of atrazine and 2,4- d during each season in microcosms of forest soil, forest soil amended with wood chips, forest soil with wood chips inoculated with P. crysosporium , and forest soil with wood chips inoculated with T. darkeri . In the winter, atrazine or 2,4- d mineralization did not differ significantly among treatments. In spring, summer, and fall, soil amended with P. chrysosporitan mineralized more atrazine than all other treatments, but soil amended with T. darkeri -mineralized less atrazine than soil without amendments. In spring, summer, or fall, soil amended with either P. chrysosporium or T. darkeri mineralized more 2,4- d . Results of this study indicate that adding P. chrysosporium or T. darkeri to riparian forest soils via wood chips may increase the rate of degradation of some aromatic herbicides.

Microbial mineralization of atrazine and 2,4-dichlorophenoxyacetic acid in riparian pasture and forest soils

Microbial biomass and mineralization of atrazine [2-chloro-4(ethylamino)-6(isopropylamino)s-triazine] and 2,4-D (2,4-dichlorphenoxyacetic acid) were examined in the top 10 cm of riparian pasture soils and in the litter layer and top 10 cm of mineral soils of riparian forest ecosystems. The riparian forest litter had higher levels of active and total fungal biomass than forest or pasture mineral soils in winter, spring, and fall. Active bacterial biomass was higher in forest litter than in forest and pasture mineral soils in spring and autumn, and higher in forest mineral soils than in pasture soils in summer. Total bacterial biomass was higher in forest mineral soils than in pasture soils during all seasons. In spring, it was also higher in forest litter than in pasture soils. Atrazie and 2,4-D mineralization in pasture soils was exceeded by that in forest litter in spring and autumn and by that in forest mineral soils in summer and autumn. There was no correlation between either active or total fungal and bacterial biomass with pesticide degradation.