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Chemical fertilizer application is a common agronomic practice to improve crop productivity and liming is often used to counteract the soil acidification caused by long-term fertilization; however, it is unclear whether liming will counteract the effect of long-term fertilization on soil bacterial community structure and its co-occurrence pattern. Here, we examined the influence of long-term fertilization (NPKS) and liming (L) on soil bacterial community structure and its co-occurrence networks by sequencing 16S rRNA gene amplicons. Our results showed that liming counteracted the influence of long-term fertilization on soil pH, but not on soluble organic carbon (SOC) and electrical conductivity (EC). Long-term fertilization affected the abundance of Acidobacteriia, Deltaproteobacteria and Gammaproteobacteria in the 0–10 cm soil, and that of Deltaproteobacteria, Gammaproteobacteria and Gemmatimonadetes in the 10–20 cm soil; whereas liming affected the abundance of Acidobacteriia, Gammaproteobacteria, and Chloracidobacteria in the 0–10 cm soil and that of Deltaproteobacteria in the 10–20 cm soil. The bacterial community structure in soils with the NPKS-L treatment was different from that with other treatments, and was mainly affected by SOC, EC, and NO 3 − concentration. The link numbers in bacterial co-occurrence networks were decreased by long-term fertilization or liming alone, but were increased by the NPKS-L treatment. Notwithstanding the fact that liming alleviates fertilization-induced soil acidification, this study indicates that liming did not counteract the effect of long-term fertilization on soil bacterial community structure and its co-occurrence pattern, hence cannot recuperate the soil microbial functionality that is changed by long-term fertilization. [ABSTRACT FROM AUTHOR]

Human-managed grasslands receive significant inputs of fertilizing materials, which can greatly influence soil biological processes associated with the cycling of nitrogen (N), including microbial nitrification. Here we specifically address how soil ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) respond to 23 years of different management practices in a permanent grassland experiment. We found that AOB amoA gene copy numbers were significantly higher in limed soils (associated with greater pH values) whereas AOA amoA gene copy numbers were higher in grazed grasslands. The chronic addition of inorganic N fertilizer in the form of ammonium nitrate (either applied alone or in combination with other macro-nutrients) greatly contributed to increase AOB abundance. Our study brings evidence of how soil-nitrifying communities can differently respond to the long-term effect of animal (i.e. rabbit) grazing and to repeated applications of nutrient (e.g. NH 4 NO 3 ) and non-nutrient (i.e. CaCO 3 ) fertilizing materials. [ABSTRACT FROM AUTHOR]

Full denitirifcation of NO 3 − to N 2 is most likely when soil pH is elevated and oxygen levels are low. In the period immediately following urine deposition, soil pH and dissolved organic carbon (DOC) concentrations rapidly increase, coupled with O 2 consumption - conditions conducive to denitrification and gaseous N-loss - yet the potential for rapid denitrification during this early period post urine deposition has received little attention. In addition, recent research has shown that the amount of DOC (and N) released as pH increases is affected by the valence of the accompanying base cation, with monovalent cations releasing more. Liming has been used to positively influence N 2 O/(N 2 O + N 2 ) ratios in the later stages of N-transformations post urine deposition, yet the relative amounts of DOC (and N) released is likely to be affected in the presence of divalent Ca 2+ potentially lowering N-transformation potential. Soil pH in anaerobic microcosms was adjusted to values between 4.5 and 9.5 using either Ca(OH) 2 as a liming agent, or KOH as an analog of urine derived NH 4 OH. After 16 h incubation, up to ∼6800 μg g −1 of DOC and ∼480 μg g −1 of dissolved organic nitrogen (DON) was solubilized by KOH amendment which was ∼10-fold higher than Ca(OH) 2 ammendment, while NH 4 + and NO 3 − increased to concentrations well above native soil concentrations. In Ca(OH) 2 amended microcosms, denitrification enzyme activity (DEA) assays produced a maximum of 875 ng N 2 O-N g −1 h −1 at pH 7.2 with respiration rates <10 μg CO 2 -C g −1 h −1 . In contrast, DEA and respiration continually climbed in KOH amended microcosms with rates up to 4798 ng N 2 O-N g −1 h −1 and 47 μg CO 2 -C g −1 h −1 at pH 8.7 and 8.9, respectively. By using KOH as proxy for NH 4 OH derived from urea hydrolysis, this research has shown that rapid denitrification could occur shortly after urine deposition along with substantial DOC and DON solubilisation and N-mineralisation. However, elevated soil pH combined with excess Ca 2+ from liming might actually suppress denitrification potential. We propose that excess Ca 2+ affects how soil microbes access and process DOC and DON at elevated pH, with Ca 2+ acting to stabilize DOC and DON. Our results emphasize that although liming promotes soil conditions conducive to denitrification, DEA can be markedly affected by base type and prevailing soil chemical conditions. [ABSTRACT FROM AUTHOR]

Soil pH plays a critical role in determining the overall rate of several important processes in the agricultural nitrogen cycle. During denitrification, the activity of nitrous oxide reductase (N 2 O-R) is reduced at low pH. This effect has led to suggestions that soil pH adjustment via liming to enhance the activity of this enzyme might be a viable agricultural greenhouse gas mitigation strategy by enhancing the reduction of N 2 O in the soil to climatically inert N 2 . We assessed the effect of liming on the apparent activity of N 2 O-R by measuring the denitrification end products, N 2 O and N 2 , in a series of short-term anaerobic incubations. We compared a weakly-buffered fluvial soil and a well-buffered, volcanic soil under different incubation temperatures and in the presence or absence of a ∼600 kg ha −1 cow urine-N amendment. Our results indicated that the liming effect was heavily modulated by soil type, temperature, and urine amendment. Liming (at rates of 1.5 and 3.0 t ha −1 for the volcanic soil and at rates of 5 and 10 t ha −1 for the fluvial soil) caused pH increases of between 0.43 and 1.25 pH units. The highest reductions in N 2 O in the fluvial soil occurred when the 1.5 t ha −1 rate was used in the fluvial soils under urine addition and at the higher temperature. The combined flux of N 2 O + N 2 did not change with liming. However, an interaction of soil type and urine amendment caused large differences in the partitioning of the denitrification end-products between N 2 O and N 2 – an effect that overwhelmed the relatively modest effects of liming. When the soils were amended with urine-N, the resulting denitrification gases from the volcanic soil were mostly in the form of N 2 O (60–77%), whereas in the fluvial soil the denitrification products were mostly in the form of N 2 and a much smaller portion were in the form of N 2 O (11–45%). Nevertheless, we found liming-induced enhancements of N 2 O-R of 15–20% (P < 0.05) in urine-amended, fluvial soil. We suggest some possible mechanisms that would explain such large differences in the N 2 O/(N 2 O + N 2 ) product ratio. [ABSTRACT FROM AUTHOR]

Abstract: During the last several decades, colonization of soil by exotic earthworms and their effects on soil properties and biodiversity have been reported in forests of North America. In some northern hardwood stands, acid soils or harsh climate may have prevented earthworm colonization. However, climatic change and the increasing use of liming to restore the vigor of declining sugar maple (Acer saccharum Marsh.) stands, situated on base-poor soils in USA and Canada, could make many of these sites more suitable for earthworm colonization. We tested survival and reproduction of two exotic earthworm species (Lumbricus terrestris and Amynthas hawayanus) in unlimed and limed soils at the northern limit of the northern hardwood forest distribution in Canada. Improving soil parameters of base-poor, acidic soils by liming positively influenced activity, survivability and reproductive output of L. terrestris in this northern hardwood forest. In contrast, the high mortality and low vigor of L. terrestris observed in the unlimed plots show that soils in this area with a pH of 4.3 are not favorable to this species. Our results suggest that A. hawayanus was very active prior to winter at both soil pHs, but was not able to complete its life cycle during one year at this latitude. Both earthworm species significantly reduced organic C and total N, and increased the C/N ratio of the forest floor. Given that forest liming activities are increasing in proximity to human activities, there is high probability that some earthworm species, such as L. terrestris, will invade limed northern hardwood forests in the next decades, with possible consequences for soil organic matter turnover, nutrient cycling and forest biodiversity and dynamics. [Copyright &y& Elsevier]

Abstract: Nitrous oxide (N2O) emissions in semi-arid regions are often greater following summer rainfall events when the soil is fallow, than in response to N fertiliser applications during crop growth. Nitrogen fertiliser management strategies are therefore likely to be ineffective at mitigating N2O emissions from these cropped agricultural soils. Here we examined the influence of raising soil pH on N2O emissions, nitrification rates, and both nitrifier and denitrifier populations following simulated summer rainfall events. The soil pH was raised by applying lime to a field site 12 months before conducting the laboratory experiment, resulting in soil of contrasting pH (4.21 or 6.34). Nitrous oxide emissions ranged from 0 when the soil was dry to 0.065 μg N2O–N g dry soil−1 h−1 following soil wetting; which was attributed to both denitrification and nitrification. Increasing soil pH only decreased N2O emissions when losses were associated with nitrification, and increased amoA gene copy numbers. We propose increasing soil pH as a strategy for decreasing soil N2O emissions from acidic soils following summer rainfall in semi-arid regions when emissions result from nitrification. [Copyright &y& Elsevier]

Arbuscular mycorrhizal fungi (AMF) are important in plant nutrient uptake, but their function is prone to environmental constraints including soil factors that may suppress AMF transfer of phosphorus (P) from the soil to the plant. The objective of this study was to disentangle the biotic and abiotic components of AMF-suppressive soils. Suppression was measured in terms of AMF-mediated plant uptake of 33P mixed into a patch of soil and treatments included soil sterilization, soil mixing, pH manipulation and inoculation with isolated soil fungi. The degree of suppression was compared to volatile organic compound (VOC) production by isolated fungi and to multi-element analysis of soils. For a selected suppressive soil, sterilization and soil mixing experiments confirmed a biotic component of suppression. A Fusarium isolate from that soil suppressed the AMF activity and produced greater amounts than other fungal isolates of the antimicrobial VOC trichodiene (a trichothecene toxin precursor), beta-chamigrene, alpha-cuprenene and p-xylene. These metabolites deserve further attention when unravelling the chemical background behind the suppression of AMF activity by soil microorganisms. For the abiotic component of suppression, soil liming and acidification experiments confirmed that suppression was strongest at low pH. The pH effect might be associated with changed availability of specific suppressive elements. Indeed 33P uptake from the soil patches correlated negatively to Al levels and Al toxicity seems to play a major role in the AMF suppressiveness at pH below 5.0–5.2. However, the documentation of a biotic component of suppression for both low and high pH soils leads to the conclusion that biotic and abiotic components of suppression may act in parallel in some soils. The current insight into the components of soil suppressiveness of the AMF activity aids to develop management practices that allow for optimization of AMF functionality. • In some soils, suppression of AMF activity had a biotic component. • A Fusarium isolate from a suppressive soil inhibited the AMF activity. • This isolate produced greater amounts of antimicrobial VOCs than other isolates. • AMF suppression increased at low pH across several soils. • For these soils, Al toxicity played a major role in suppressiveness at pH ≤ 5.0 [ABSTRACT FROM AUTHOR]

We combined microbial community phospholipid fatty acid (PLFA) analyses with an in situ stable isotope 13CO2 labelling approach to identify microbial groups actively involved in assimilation of root-derived C in limed grassland soils. We hypothesized that the application of lime would stimulate more rapid 13C assimilation and turnover in microbial PLFAs. Four and 8 d after label application, 18:1ω9, 18:2ω6,9 (fungal biomarkers) and 16:1ω7, 18:1ω7, 19:0cy (Gram-negative bacterial biomarkers) showed the most 13C enrichment and rapid turnover rates. This suggests that these microorganisms were assimilating recently-photosynthesized root C inputs to soils. Contrary to our hypothesis, liming did not affect assimilation or turnover rates of 13C-labelled C. 13C stable isotope pulse-labelling technique paired with analyses of PLFA microbial biomarkers shows promise for in situ investigations of microbial function in soils. [Copyright &y& Elsevier]

The application of lime in a mature Norway spruce (Picea abies [L.] Karst.) forest in southern Germany induced major changes in the activity of soil organisms and root growth. Since this may influence the chemical compostion of the soil organic matter (SOM) of the organic surface layer, its composition and changes due to the treatment were examined in this study. Fine roots of Norway spruce have a relatively low content of extractable lipids, a low alkyl C content (13C CPMAS NMR) and a high ratio of non-cellulosic to cellulosic carbohydrates (NC/CC, carbohydrate determination by MBTH and gas chromatography analyses) as compared to needles. Furthermore, they show high ratios of suberin/cutin compounds (thermally assisted hydrolysis and methylation, (THM)) and high ratios of eicosanic acid/phytadiene I in their lipid extracts (pyrolysis-GC/MS).Liming (4 t ha−1 dolomite) of a Norway spruce organic surface layer decreased the proportion of alkyl C, the alkyl C/O-alkyl C ratio, and the content of extractable lipids. The NC/CC ratio and the abundance of suberin relative to cutin components increased. The contribution of the chlorophyll component phytadiene I decreased in relation to eicosanic acid. These changes are attributed to increased fine root formation in the organic layer after liming. Furthermore, the presence of less degraded lignin (THM, peak ratio of 3,4-dimethoxybenzoic acid, methyl ester/3,4-dimethoxy-benzaldehyde) on the limed plot is explained by the increased input of relatively fresh fine root material. On the other hand, the decrease in the carbon-to-nitrogen ratio may be attributed to the higher microbial activity after liming. [Copyright &y& Elsevier]