Luigi Badalucco

Effect of liming on some chemical, biochemical, and microbiological properties of acid soils under spruce (Picea abies L.)

SummarySoil pH, total organic C, total N, exchangeable Al, available P, CO2 evolution, microbial biomass C and N, phosphatase and dehydrogenase activities were determined in acid soils sampled under spruce subjected to acid deposition, before and after liming. A slight decrease in pH values was observed from the edge of a tree canopy to the base of the trunk in acid soils. Liming drastically reduced exchangeable Al and increased CO2 evolution, microbial biomass, and the metabolic quotient. The microbial biomass C to total organic C ratio increased after liming but did not reach 2%, the average value considered valid in soils where the C content is in equilibrium, that is when C inputs are equal to C outputs. The microbial biomass C:N ratio decreased after liming, thus indicating that bacteria became predominant over fungi when soil acidity decreased. Dehydrogenase activity but not phosphatase activity was increased by liming. The decrease in phosphatase activity was not completely related to the increase in available P, but was also dependent on microbial growth and the decrease in acid phosphatase, the predominant component of acid soils.

Biochemical characterization of soil organic compounds extracted by 0.5 m K2SO4 before and after chloroform fumigation

Abstract The organic C (EC), total N (EN), anthrone-, phenol- and orcinol-reactive C (ARC, PRC and ORC, respectively), ninhydrin-reactive N (NRN), Folin-Ciocalteus reagent-reactive C and N compounds (FRC and FRN) and deoxyribose containing compounds (diphenylamine-reactive compounds, DRC) extracted by 0.5 m K2SO4 before (non-fumigated extracts) and after (fumigated extracts) CHC13 fumigation were evaluated in 8 very different soils. All quantities were significantly linearly correlated between them and with total organic C (TOC) and total N (TN) as well. The frequency distribution of the significance levels passing from non-fumigated to fumigated extracts and γ-values (fumigated minus non-fumigated values for the same class of compounds) showed a shift towards the highest significances; this may indirectly confirm the action of chloroform in lysing soil microbial cells. The significance levels (P) of TOC correlated vs fumigated extracts were higher than vs non-fumigated extracts and γ -values, thus indicating a release of non-biomass C organic compounds after CHCl3 fumigation. Since TN vs fumigated extracts showed significance levels higher than non-fumigated extracts but equal to γ-values, any release of non-biomass N probably did not occur. These considerations were confirmed by multiple regression analysis when EC and EN (dependent variables) were reconstituted taking into account TOC and TN as additional independent variables, respectively. However, released non-biomass C organic compounds (likely sugars) compared to TOC were very low and could be considered to be negligible. A low release of ribose-containing compounds (ORC) occurred, thus indicating that the amount of RNA material released after CHCl3 exposure was negligible. Deoxyribose-containing compounds rendered extractable after CHCl3 fumigation were probably derived from bacterial plasmids rather than from bacterial and eukaryotic chromosomes. The possibility of characterizing soil microbial biomass C and N compounds by adopting suitable colorimetric methods, as demonstrated in this work, is a further advantage of the fumigation-extraction method when compared with the fumigation-incubation method.

Activity and degradation of streptomycin and cycloheximide in soil

Streptomycin and cycloheximide were added (3 and 2 mg g-1 dry soil, respectively) single and in combination to a forest soil to follow their possible degradation and their effects on soil mineralization-immobilization processes. After 0, 1, 2, 4, 7, and 10 days of incubation at 25°C and 60% water-holding capacity, measurements were taken of microbial biomass C and N, the evolution of CO2, exchangeable NHinf4sup+, 0.5M K2SO4-extractable organic C, and total N in both unfumigated and CHCl3-fumigated soil. The results indicated that during the first 2 days of incubation, soil microorganisms were killed by the antibiotics and/or by CHCl3 and used subsequently as a substrate by the survivors. Thereafter, surviving microorganisms probably also started to use biocidal molecules as an energy and nutrient source. The ratios of biomass C to biomass N and of CO2 evolved to net NHinf4sup+ produced indicated that both biocides had non-target effects for most of the incubation. Thus, streptomycin and cycloheximide are not suitable in determining the relative contribution from fungi and bacteria to mineralization-immobilization processes in soils.

Use of sonication for measuring acid phosphatase activity in soil

Extracellular enzymes in soil often occur in immobilised forms, a state that may alter their interactions with substrates in comparison with enzymes in the solution phase. Sonication was evaluated for its usefulness in studying immobilised acid phosphatase by dispersing soil aggregates. Factors affecting soil dispersion during ultrasound application were soil extraction ratio, total applied energy and power output ml−1 of sonicated soil slurry. For the clay loam soil used, optimal values for these variables were, respectively, 1:6 (w/v) and, at least, 1800 J ml−1 and 15 W ml−1. At the optimal sonication conditions for soil dispersion a substantial increase in phosphatase activity (up to 156% greater than the non-sonicated control) was induced by sonication. This increase in activity with sonication, which coincided with a release of soil chromophores, might be related to the exposure or release from aggregates of the extracellular enzyme fraction immobilised on humic colloids. Analysis of multiple regression between the phosphatase activity (dependent variable) and chromophore solubilisation and ATP release (independent variables) suggested the increased activity was from complexed enzymes that were released and not due to cell lysis. Soil treatment with sonication appeared to have liberated a large dormant portion of acid phosphatase activity. Coefficients of variation of the activity decreased greatly (from 20% in control soil to 4% as an average after sonication).

Synthesis and characterization of an acid phosphatase-polyresorcinol complex

Abstract A stable acid phosphatase-polyresorcinol complex, retaining about 90% of the original enzymatic activity, was synthesized in the presence of peroxidase. The complex was disturbed by chaotropic agents, as 4 M urea, indicating that the enzyme linked the phenolic moiety by non-covalent bonds. The immobilized phosphatase was more stable than the free enzyme towards pH, temperature and proteolysis: however, when added to soil, free and immobilized phosphatase showed comparable stability. It appears that the polymerization conditions used, favouring the interaction between enzyme and polyphenol through secondary linkages, give rise to a fully active complex resembling those which naturally generate in soil.

Microbial biomass and anthrone-reactive carbon in soils with different organic matter contents

Abstract The microbial biomass C (Cmic) was evaluated by the fumigation-extraction (FE) method in 23 different soils (8 forest soils subjected to acid deposition, 12 sampled from a long-term field experiment and 3 from other arable soils). The hexose microbial biomass C (ARC) was the anthrone-reactive C extracted by 0.5 M K2 SO4 from the 20 h fumigated soil less that extracted from the unfumigated soil. The ratio Cmic to ARC was always lower than 10:1, the average ratio biomass C to carbohydrate C usually observed in microbial cells. Also the significant correlation between ARC and total organic C (TOC) content seems to confirm a release of non-biomass anthrone-reactive C during the chloroform fumigation; however, this solubilization is lower than 0.2–0.4% of the TOC content of soils and it may be considered as negligible. The release of non-biomass anthrone-reactive C seems to be supported by the fact that Cmic values calculated by multiple regression, considering ARC and TOC/100 as independent variables, are closer to observed values than those calculated by the simple regression with either ARC or TOC values.

Do physical properties of soil affect chloroform efficiency in lysing microbial biomass

Abstract Evolution of CO 2 was measured during a 24 h CHCl 3 fumigation at 25°C in eight different soils ( CO 2 F ) The cumulative production of such CO 2 was always lower than that evolved under the same conditions by unfumigated soils ( CO 2 NF ). However, for five of the eight soils, CO 2 F accounted for more than 50% of CO 2 NF . Neither CO 2 F nor CO 2 NF were singly or multiply correlated to soil pH, water holding capacity, Hg porosity and carbonate content, i.e. chemico-physical variables that could influence the release of CO 2 from soil. Also other considerations suggest that abiological evolution of CO 2 was likely to be negligible; thus, both CO 2 F and CO 2 NF were mostly of biological origin and, probably, the biomass surviving chloroform exposure, or partially lysed, was substantial. The ratio CO 2 F to CO 2 NF was taken as an indirect physiological assessment of the efficiency of CHCl 3 in lysing microbial cells as, in principle, the lower CO 2 F compared to CO 2 NF the more efficient the chloroform fumigation. This ratio was significantly multiply correlated with several combinations of independent variables, including a wide range of soil physico-chemical properties (Hg porosity, storage porosity, water holding capacity, sand, silt, organic C and carbonate contents) related to soil structure. These significant correlations were functionally confirmed because the dynamics of the CO 2 F evolution during fumigation was related to the relative structural stability of the soils. Other correlations seemed to indicate that the positive relationships reported earlier between clay content and organic C made extractable by CHCl 3 ( E C : from which biomass C is calculated in the FE method for estimating soil microbial biomass) could be largely dependent on the relative ability of chloroform to permeate pores in different soils. It is highly probable that the efficiency of CHCl 3 in lysing microbial cells is strongly influenced by the soil structural properties. This could be one of the reasons why the calibration procedures for calculating K C and K EC generate quite dissimilar values.

Reversing agriculture from intensive to sustainable improves soil quality in a semiarid South Italian soil

Intensive agriculture (IA) is widespread in South Italy, although it requires frequent tillage, large amounts of fertilizers and irrigation water. We have assessed the efficacy of reversing IA to sustainable agriculture (SA) in recovering quality of a typical South Italy soil (Lithic Haploxeralf). This reversion, lasting from 2000 to 2007, replaced 75% of nutrients formerly supplied inorganically by farmyard manuring and reduced the tillage frequency. Several chemical and biochemical properties, functionally related to C and N mineralisation–immobilisation processes and to P and S nutrient cycles, were monitored annually from 2005 to 2007 in the spring. Reversing IA to SA decreased soil bulk density, almost doubled the soil organic matter (SOM) as favoured the immobilisation of C and N, increased most soil microbial indicators but decreased contents of nitrate, mineral N and K2SO4-extractable C. The K2SO4-extractable C/K2SO4-extractable organic N ratio suggested that substrate quality rather than the mass of readily available C and N affected biomass and activity of soil microflora. Also, the largely higher 10-day-evolved CO2–C-to-inorganic N ratio under SA than IA indicated that higher C mineralisation, associated with higher microbial biomass N immobilisation, occurred under SA than IA. Decreases in most soil enzyme activities under IA, compared to SA, were much higher than concomitant decreases in SOM content. Soil salinity and sodicity were always higher in IA than SA soil, although not critically high, likely due to the intensive inorganic fertilisation as irrigation waters were qualitatively and quantitatively the same between the two soils. Thus, we suggest that the cumulative small but long-term saline (osmotic) and sodic (dispersing) effects in IA soil decreased the microbial variables more than total organic C and increased soil bulk density.

CPMAS 13C NMR Characterization of Leaves and Litters from the Reafforestated Area of Mustigarufi in Sicily (Italy)

Reafforestation is generally based on the planting of exotic fast growing tree species suitable for adapting to even harsh environments. Once the introduced plants ameliorate soil conditions, they can be progressively replaced by au- tochthonous plant species. Reafforestation is applied worldwide. However, only few studies on the effect of reafforesta- tion on lands from Mediterranean regions are available. This paper reports the characterization by cross polarization 13 C NMR spectroscopy of fresh leaves and superficial litters from a reafforestated area in central Sicily (Italy). NMR assign- ment is attempted. A differentiation among the molecular systems within leaves and litters is also done on the basis of NMR assessment. Results showed that the main differences among the leaves of four forest trees (two eucalyptus spp., one cypress sp. and one pine sp.) occur in the distribution of the aromatic and alkyl carbons. In particular, the alkyl moie- ties in the eucalyptus spp. leaves were attributed to branched structures belonging to the eucalyptus oil, whereas linear fatty acids were more representetive in the NMR spectra of pine and cypress leaves. In addition, the aromatic carbons of the conifer leaves were assigned not only to lignin- and tannin-like structures, but also to common olefin carbons in un- saturated fatty acids and abietic acid-like systems. The spectra of the litters resembled, as expected, those of the leaves. However, the presence of very large carbohydrate NMR signals suggested that degradation processes were still ongoing in litters. A comparative evaluation of CPMAS 13 C NMR spectra was done by applying principal component analysis. This paper confirmed the suitability of CPMAS 13 C NMR spectroscopy in evaluating the differences among natural bio-masses

Microbial Inoculants on Woody Legumes to Recover a Municipal Landfill Site

Tree and shrubby legumes have great potential in degraded land rehabilitation because of their ability to form symbiotic associations with nitrogen fixing rhizobia and mycorrhizal fungi. Extensive soil disturbance reduces natural microbial propagules thus preventing the formation of beneficial plant-microbes symbiosis. Reintroduction of selected microbial symbionts may improve the recovery rate of disturbed ecosystems. We inoculated selected rhizobia and arbuscular mycorrhizal fungi on two woody legume species, the mediterranean shrub Spartium junceumL. and the exotic tree Acacia cyanophylla Lindl. in order to recover a sealed municipal landfill (Palermo, Sicily, Italy). Inoculated plants showed shoot growth parameters 2 to 12-fold higher than uninoculated plants. After transplanting on the municipal landfill site, inoculated plants showed no transplant shock and low mortality (6–15%). The chemical analysis of P and N plant content showed no differences between inoculated and uninoculated plants suggesting that a dilution effect occurred due to higher biomass production of the inoculated plants. The beneficial effects of mycorrhization and rhizobium inoculum on growth parameters were still detectable one year after transplanting in S. junceum.