Enhancement of revegetation on construction fill by fertilizer and topsoil application: Effect on mycorrhizal infection

The influence of topsoil and fertilizer application on denuded road construction sites was evaluated to assess its contribution to improvement of vegetation re-establishment. the study sites were within a mixed hardwood and conifer forest on crushed, unweathered subsurface material with low fertility and low biological activity. Topsoils were removed from the site, stockpiled and reapplied to the site after construction. the effect of topsoil amendment on plant growth, soil fertility, mycorrhizal infection and an index of microbial biomass were measured in field and greenhouse experiments. Plant growth on the topsoil amended field plots were greatly increased relative to treatments with fertilizer but no topsoil. Three years after establishment, dry weight production on the plots without topsoil treatment was about 40 per cent of the plots treated with topsoil. Greenhouse experiments were designed to compare fresh, dried and stockpiled topsoil. These experiments indicated that storage of the harvested topsoil for five months in a stockpile had minor effects on plant growth, soil fertility, mycorrhizal infection and microbial biomass. Topsoil volumes had to exceed 20 per cent of the total soil volume to achieve statistically significant benefits and higher ratios showed greater benefit. the percentage of mycorrhizal infection was greatest in topsoil treatments without fertilizer. the addition of fertilizer increased growth but reduced the percentage of roots forming mycorrhizae. When the total weight of infected roots was calculated, however, infection was found to be greatest with a moderate level of fertilizer (equivalent to approximately 27 kg N ha⁻¹ and 39 kg P ha⁻¹), and was less in both higher fertilizer treatments and in unfertilized treatments. Topsoil amendment increased microbial biomass nitrogen but fertilizer treatment did not.     

Influences of a root-lesion nematode, Pratylenchus coffeae, and two arbuscular mycorrhizal fungi, Acaulospora mellea and Glomus clarum on coffee (Coffea arabica L.)

A greenhouse experiment was conducted to investigate the effects of a root-lesion nematode, Pratylenchus coffeae, two arbuscular mycorrhizal (AM) fungi, Acaulospora mellea and Glomus clarum, and timing of inoculation on the growth and nutrition of a nematode-susceptible Arabica coffee cultivar. The late AM inoculation (added simultaneously with nematodes) did not enhance coffee tolerance to P. coffeae. In the presence of P. coffeae, late-mycorrhizal plants were P deficient during the entire experiment and their foliar P concentration remained as low as that of non-mycorrhizal plants. After 7.5 months, nematodes decreased AM colonization of late-mycorrhizal plants by half and their biomass was only 20–30% that of the controls. In contrast, early AM inoculation (4 months before nematode inoculation) with either AM species improved the tolerance of coffee to P. coffeae. Root colonization by AM was not significantly reduced by P. coffeae. Despite higher densities of nematodes, root lesions were less numerous and more localized in early AM inoculated plants than in those of non-mycorrhizal plants. In the presence of P. coffeae, early AM-inoculated plants remained P sufficient and their biomass was still 75–80% that of their nematode-free controls. This study shows that in soils with low P levels, enhanced tolerance to P. coffeae seems limited to mycorrhizal coffee plants with well established AM symbiosis and improved P status. Received: 11 March 1997     

Carbon and nitrogen dynamics in a forest soil amended with purified tannins from different plant species

Tannins are purported to be an important factor controlling nitrogen cycling in forest ecosystems, and the ability of tannins to bind proteins in protein-tannin complexes is thought to be the primary mechanism responsible for these effects. In this study, we examined the influence of well-characterized tannins purified from five different plant species on C and N dynamics of a forest soil A horizon. Tannic acid, a commonly used and commercially available hydrolyzable tannin (HT), and cellulose were also included for comparison. With the exception of tannins from huckleberry (Vaccinium ovatum), the amendments increased respiration 1.4-4.0 fold, indicating that they were acting as a microbial C source. Tannic acid was significantly more labile than the five purified tannins examined in this study. All treatments decreased net N mineralization substantially, through greater N immobilization and decreased mineralization. The six tannins inhibited gross ammonification rates significantly more than cellulose. This suggests that added tannins had effects in addition to serving as an alternative C source. Tannins purified from Bishop pine (Pinus muricata) were the only tannins that significantly inhibited potential gross nitrification rates, however, rates were low even in the control soil making it difficult to detect any inhibition. Differences in tannin structure such as condensed versus HTs and the hydroxylation pattern of the condensed tannin B-ring likely explain differences observed among the tannin treatments. Contrary to other studies, we did not find that condensed tannins were more labile and less inhibitory than HTs, nor that shorter chained tannins were more labile than longer chained tannins. In addition to supporting the hypothesis that reduced N availability in the presence of tannins is caused by complexation reactions, our data suggests tannins act as a labile C source leading to increased N immobilization.     

A comparison of plant available nutrients on decomposed granite cut slopes and adjacent natural soils

Decomposed granite (DG) slopes are often difficult to revegetate after existing topsoil and vegetative cover have been removed. In this study, naturally vegetated soils and denuded DG cut slopes were evaluated to compare edaphic (soil-related) conditions that may differ between the vegetated and non-vegetated states. Potential plant nutrient deficiencies were evaluated by soil nutrient extraction, plant tissue analysis and by greenhouse bioassay methods. The DG cut slopes have approximately one-quarter to one-half the clay content, soil organic matter, water-holding capacity, and total and available nitrogen (N) of the adjacent natural soils. Soil extraction tests for phosphorus (P) availability gave variable results, but a growth response to P amendment was observed in a greenhouse bioassay. The native topsoils and the DG cut slope materials had non-limiting levels of pH, exchangeable Ca, Mg and K, and total P. Cation exchange capacity and sulfate–sulfur (S) were low but similar between the two soil groups. Principle nutrient limitations are interpreted to be N, P, and possibly S and boron (B), in order of decreasing severity. Based on these results, we conclude that the removal of humified soil organic matter on the cut slopes reduces plant growth directly by lowering several of these essential nutrients, and indirectly by decreasing the soil's water-retention and infiltration capacity. Soil organic matter is viewed as a critical factor and major contrast between barren and revegetated DG materials. © 1998 John Wiley & Sons, Ltd.     

Effects of solution pH,temperature, nitrate/ammonium ratios,and inhibitors on ammonium and nitrate uptake by Arabica coffee in short‐term solution culture

Solution pH, temperature, nitrate (NO₃ ^‐)/yammonium (NH₄ ⁺) ratios, and inhibitors effects on the NO₃ ^‐ and NH₄ ⁺ uptake rates of coffee (Coffea arabica L.) roots were investigated in short‐term solution culture. At intermediate pH values (4.25 to 5.75) typical of coffee soils, NH₄ ⁺ and NO₃ ^‐ uptake rates were similar and nearly independent of pH. Nitrate uptake varied more with temperature than did ammonium. Nitrate uptake increased from 0.05 to 1.01 μmol g^‐1 FWh^‐1 between 4 and 16°C, and increased three‐fold between 16 to 22°C. Between 4 to 22°C, NH₄ ⁺ uptake rate increased more gradually from 1.00 to 3.25 μmol g^‐1 FW h^‐1. In the 22–40°C temperature range, NH₄ ⁺ and NO₃ ^‐ uptake rates were similar (averaging 3.65 and 3.56 umol g^‐1 FW h^‐1, respectively). At concentrations ranging from 0.5 to 3 mM, NO₃ ^‐ did not influence NH₄ ⁺ uptake rate. However, NO₃ ^‐ uptake was significantly reduced when NH₄ ⁺ was present at 3 mM concentration. Most importantly, total uptake (NO₃ ^‐+NH₄ ⁺) at any NO₃ ^‐/NH₄ ⁺ ratio was higher than that of plants fed solely with either NH₄ ⁺ or NO₄ ^‐. Anaerobic conditions reduced NO₃ ^‐ and NH₄ ⁺ uptake rate by 50 and 30%, respectively, whereas dinitrophenol almost completely inhibited both NH₄ ⁺ and NO₃ ^‐ uptake. These results suggest that Arabica coffee is well adapted to acidic soil conditions and can utilize the seasonally prevalent forms of inorganic N. These observations can help optimizing coffee N nutrition by recommending cultural practices maintaining roots in the temperature range optimum for both NH₄ ⁺ and NO₃ ^‐ uptake, and by advising N fertilization resulting in a balanced soil inorganic N availability.     

Cadmium,copper, and zinc adsorption by a forest soil in the presence of sludge leachate

Samples from three genetic horizons of an acidic forest soil were equilibrated with solutions containing Cd, Cu, and Zn in the presence and absence of a municipal sewage sludge leachate. Copper adsorption was greater than Cd and Zn in all three horizons, while Cd and Zn adsorption was quite similar. Relative to a NaN0₃ background solution, sludge leachate reduced Cu adsorption in all horizons; however, in the presence of leachate Zn adsorption increased in the B2 and C horizons, while Cd adsorption decreased in the Al and was unaffected in the B2 and C horizons. Distribution coefficients generally increased as solution concentration and adsorption increased. In all horizons additions of Cd and Zn were able to reduce apparent surface charge. Copper not only reduced surface charge in the Al horizon, but caused a charge reversal in the 132 and C horizons. Adsorption data were best fit by linear or Freundlich equations. Differences in adsorption between sludge leachate and NaN0₃ solutions could not be explained simply by differences in metal activities as calculated using the GEOCHEM program. Competition from cations and organics present m the sludge leachate appears to contribute to lower metal adsorption.     

Hyphal-mediated transfer of nitrate,arsenic, cesium,rubidium, and strontium between arbuscular mycorrhizal forbs and grasses from a California oak woodland

Arbuscular mycorrhizal (AM) fungi colonize most plant species in the savannah/oak woodland ecosystem of the California Sierra Foothills. These fungi may form belowground linkages between plant root systems, potentially altering nutrient transfers. In a laboratory experiment with two-chambered pots where only AM fungal hyphae connected the chambers, we examined nutrient transfer between native plant species of grasses and forbs. Two separate chambers with plants were separated by a set of two stainless steel screens (25 μm mesh) separated by a 1 cm air gap. These screens successfully restricted root growth but allowed hyphal coverage (15–100% of the area) of the screens. Nutrient transfers were monitored by applying nitrogen (¹⁵N), arsenic (P analog), strontium (Ca analog), and cesium and rubidium (K analogs). The analogs and ¹⁵N were applied to leaves of donor plants for 48 h. We observed transfer of ¹⁵N, As, Cs, and Rb from donor shoots to receiver shoots. Element transfers were not correlated with receiver biomass or donor concentrations. Transfers varied among the elements and plant combinations. Both Rb and Cs (K analogs) had the same pattern of transfer. Nitrogen was transferred in greatest amounts and between forbs and grasses, and grasses acted as a stronger sink for N. Forbs were generally the stronger sink for As. Fungal hyphae facilitated transfer among forbs and grasses, suggesting that they have a key role in nutrient transfer in California oak woodlands.     

Chromate Generation by Chromate Depleted Subsurface Materials

Soluble chromate concentrations as high as 200 μg Cr L^-1 have been reported in water samples from monitoringwells tapping alluvial deposits allegedly contaminated bylaboratory waste as well as control wells off site andupgradient (shallow aquifer) near Davis California, U.S.A. In this report we present evidence that these Cr(VI) levelscould have been generated by geogenic processes rather thanby anthropogenic inputs. We tested the hypothesis thatnative Cr(III) has been and can be oxidized to chromate bynative manganese oxides. Twenty-three drill core samples(all unsaturated) were retrieved from depths varying from1.5 to 22.5 m in 6 different wells. Visible nodules ofMnO₂ were dispersed throughout many of the samples andcarbonates were also present. Sample pH values averagedabout 8.0 and organic C was mostly less than 1.0 g kg^-1. Total Mn and Cr averaged 835 and 191 mg kg^-1respectively. All samples had the capability to oxidizeadded Cr(III) to Cr(VI). To determine the inherent capabilityof the samples to produce Cr(VI) from native Cr(III), subsamples were extracted with 5 mM CaSO₄ plus 5 mM MgSO₄ until Cr(VI) was no longer detected. After freeze-drying, deionized-distilled water was added to theleached samples to approximately field capacity (0.03 MPa). Freeze drying did not generate Cr(VI). These samples wereincubated in polyethylene film bags at room temperature inthe dark. After 1 week incubation, water in the samples wasextracted by centrifugation and the extracts were analyzedfor Cr(VI). All of the samples generated Cr(VI), and theconcentrations in the extracts ranged from 20 to 100 μg Cr L^-1. Total chromium, endemic chromium VI and chromium VI generated in leached samples were not statistically different between samples from onsite and control samples taken offsite and upgradient in respect to the shallowest aquifer.     

Soil pH and the Activity of a Pelletized Nematophagous Fungus

ABSTRACT When formulated as assimilative hyphae in alginate pellets, the nematophagous fungus Hirsutella rhossiliensis was more active (i.e., parasitized more assay nematodes) in an acidic vineyard soil than in a neutral vineyard soil. To determine whether soil pH explained the difference, fungus activity was measured in soil from the neutral site that had been acidified (by adding sulfuric acid) and in soil from the acidic site that had been neutralized (by adding calcium hydroxide). As hypothesized, the activity of pelletized Hirsutella rhossiliensis was negatively correlated with soil pH. Maximum activity occurred at pH(calcium chloride) 4.5, and activity gradually declined to near zero as the pH increased to 6.5 and rapidly declined to near zero as the pH dropped below 4.0. Assays performed on leached soil samples indicated that the effects of sulfuric acid and calcium hydroxide were largely due to pH rather than to specific ions or osmotic potential. The effect of pH, however, was indirect. Heating the neutral soil to 60 degrees C for 2 h did not alter soil pH or electrical conductivity but increased fungus activity to levels equivalent to those in acidified soil. We conclude that, in these two soils, heat treatment or low soil pH suppresses soil organisms that otherwise interfere with growth of Hirsutella rhossiliensis from alginate pellets.