Reduction In Microbial Biomass Research Articles

Comparative Assessment of the Activities of Acid and Alkaline Phosphatases in Spent Crankcase Oil-Polluted Soil Ecosystem

Assessment of the level of contamination from possible impact of spent crankcase oil on soil ecosystem is imperative for the determination of environmental acceptability. This study investigated this impact ex-situ using a culture-dependent approach to evaluate the total microbial counts; biochemical and physicochemical tools to determine the activities of their exudates (acid and alkaline phosphatases), total petroleum hydrocarbon (TPH) and pH as indices. The experiment demonstrated that at 1.5 – 3.5% contamination across days-zero to -28, spent crankcase oil stimulated significantly (p<0.05) the activity of alkaline phosphatase in a concentration and time dependent manner from 4.0 ± 0.03 to 8.0 ± 0.00Katal. Acid phosphatase suffered inhibition significantly (p<0.05) from 6.0 ± 0.05 to 2.8 ± 0.01Katal. The contamination significantly (p<0.05) increased the total petroleum hydrocarbon (TPH) across all the days relative to control and this lowered the pH from 5.9 ± 0.00 to 4.8 ± 0.00. An initial reduction in microbial biomass from 1.32 x 109 ± 0.00 to 3.48 x108 ± 0.00 cfu/g on week one, and induction of hydrocarbon-degrading organisms, (the hydrocarbonclastics), to 3.7 x 10¬¬8 ± 0.10cfu/g at 1.5 – 3.5% contamination overtime correlated with enzyme induction, and activity. Ecosystem dynamics and mineralization were impaired and disrupted and the entire soil biochemistry was altered.

Soil biomass-related enzyme activity indicates minimal functional changes after 16 years of persistent drought treatment in a Mediterranean holm oak forest

Long-term drought impacts soil microbial responses and enzymatic activity, affecting carbon budget and nutrient cycling in terrestrial ecosystems. We examined a Mediterranean holm oak forest subjected to 16 years of drought treatment to understand the effects on soil organic matter decomposition, nutrient cycling, and enzymatic activity. We compared potential and biomass-related (normalized to microbial biomass) soil enzyme activity with measurements taken 10 years earlier. Relationships between potential enzyme activity, soil moisture, temperature, nutrient availability, and plant/microbial activity were explored. The prolonged drought led to decreased potential activities of all enzymes, especially acid phosphatase, protease, and urease. However, biomass-related activities of protease, urease, and phosphatase were unaffected. Interestingly, biomass-related beta-glucosidase activity increased during dry seasons, indicating a functional adaptation for carbon acquisition during extreme dry conditions. The negative impact of drought on potential enzyme activity intensified over time, particularly during summer when drought intensity increased. Soil water availability, microbial biomass, and nutrient availability strongly influenced potential enzyme activity. Long-term drought and summer aridity led to increased substrate accumulation in the soil. However, no significant changes were observed in biomass-related activities of nitrogen and phosphorus-acquiring enzymes. This lack of change is likely attributed to a decrease in the absolute potential enzyme activity capacity, caused by a reduction in microbial biomass in drought-affected plots, thereby favoring substrate accumulation. Specific functional adaptations were observed, including increased carbon acquisition by soil microbes during extreme summer drought. Long-term water scarcity in water-limited ecosystems diminishes the system's capacity to acquire resources through enzyme production, impacting mineralization and nutrient dynamics. Future climate scenarios may entail reduced ecosystem-level mineralization, carbon and nitrogen shifts from plants to soil, compromising plant control over nutrients, and increasing the risk of resource loss through leaching and erosion.

Response and driving factors of soil enzyme activity related to acid rain: a meta-analysis.

As a global pollution, acid rain can significantly alter soil physicochemical and biochemical processes, but our knowledge of how acid rain affects soil enzyme activity is still limited. To quantify the overall magnitude and direction of the response of soil enzyme activity to acidrain, we conducted a linear mixed model-based meta-analysis of 40 articles. Our analysis revealed that acid rain decreased enzyme activity by an average of 4.87%. Soil dehydrogenase and protease activities were particularly sensitive to acid rain, with significant inhibitions observed. The effect of acid rain was moderated by acid rain intensity (i.e., H+ addition rate, total H+ added, and acid rain pH) and soil fraction (i.e., rhizosphere and bulk soil). Structural equation modelling further revealed that acid rain suppressed soil microbial biomass by acidifying the soil and that the reduction in microbial biomass directly led to the inhibition of enzyme activity in bulk soil. However, the enzyme activity in the rhizosphere soil was not affected by acid rain due to the rhizosphere effect, whichwas also not impacted by thedecreased soil pHinduced by acid rainin rhizosphere. Our study gives an insight into how bulk soil enzyme activity is impacted by acid rain and highlights the need to incorporate rhizosphere processes into acid rain-terrestrial ecosystem models.

Influences of lithium on soil microbial biomass, bacterial community structure, diversity, and function potential

Lithium is an emerging contaminant, but there is little knowledge about its influences on soil microbial ecosystem. In this work, soils were treated with 10 to 1280 mg/kg lithium (Li10 to Li1280), and then microbial biomass assay and bacterial 16S rRNA high-throughput sequencing analysis were conducted to investigate the influences of lithium on soil microbial biomass, bacterial community structure and diversity, and predicted function potential. The results showed that lithium generally decreased microbial biomass carbon and the count of culturable microbe colony, reflecting the reduction in microbial biomass. However, microbial biomass nitrogen increased. Meanwhile, lithium altered bacterial community composition, structure, and dominance. The abundance of phylum such as Proteobacteria and Acidobacteria respectively increased and reduced under lithium stress, while genus such as Adhaeribacter dominated in control group to Li320, and genus such as Lysobacter dominated in Li640, Li960, and Li1280. Then, higher lithium treatments consistently inhibited the bacterial richness, evenness, and diversity, and caused community dissimilarity between groups and significant down-regulation of predicted pathways. Finally, the LEfSe cladogram distinguished several indicator bacteria for different lithium levels. Overall, the influences of lithium on soil microbial community depended on its content, and microbial biomass and richness were sensitive to lower lithium, while higher lithium varied bacterial community and predicted function potential more significantly. This study will provide microbial insights into understanding lithium contamination.

Contrasting effects of maize litter and litter-derived biochar on the temperature sensitivity of paddy soil organic matter decomposition.

Organic matter input regulates the rate and temperature sensitivity (expressed as Q10) of soil organic matter (SOM) decomposition by changing microbial composition and activities. It remains unclear how the incorporation of litter-made biochar instead of litter affects the Q10 of SOM decomposition. Using a unique combination of two-and three-source partitioning methods (isotopic discrimination between C3/C4 pathways and 14C labeling), we investigated: (1) how maize litter versus litter-made biochar (of C4 origin) addition influenced the Q10 of SOM (C3 origin) under 10°C warming, and (2) how the litter or biochar amendments affected the Q10 of 14C-labeled fresh organic matter (FOM) after long-term incubation. Compared with biochar addition, litter increased the rates and Q10 of mass-specific respiration, SOM and FOM decomposition, as well as the contents of SOM-derived dissolved organic C (DOC) and total phospholipid fatty acids (PLFA). Litter-amended soils have much higher activities (Vmax) of β-glucosidase, N-acetyl-β-glucosaminidase, and leucine aminopeptidase, suggesting larger enzyme pools than in soils with biochar. The Q10 of enzyme Vmax (1.6–2.0) and Km (1.2–1.4) were similar between litter-and biochar-amended soils, and remained stable with warming. However, warming reduced microbial biomass (PLFA) and enzyme activity (Vmax), suggesting decreased enzyme production associated with smaller microbial biomass or faster enzyme turnover at higher temperatures. Reductions in PLFA content and enzyme Vmax due to warming were larger in litter-amended soils (by 31%) than in the control and biochar-amended soils (by 4–11%), implying the active litter-feeding microorganisms have a smaller degree of heat tolerance than the inactive microorganisms under biochar amendments. The reduction in enzyme activity (Vmax) by warming was lower in soils with biochar than in the control soil. Our modeling suggested that the higher Q10 in litter-amended soils was mainly caused by faster C loss under warming, linked to reductions in microbial biomass and growth efficiency, rather than the slightly increased SOM-originated substrate availability (DOC). Overall, using straw-made biochar instead of straw per se as a soil amendment lowers the Q10 of SOM and FOM by making microbial communities and enzyme pools more temperature-tolerant, and consequently reduces SOM losses under warming.

Toxicological Indices of Crude Oil-Polluted Soil Ecosystem

Assessment of the level of contaminations from possible impact of crude oil on soil ecosystem is imperative for the determination of environmental acceptability. This study investigated this impact ex-situ using a culture-dependent approach to evaluate the total microbial counts; physicochemical tools to determine the cation exchange capacity (CEC), metal leachates, exchangeable bases (Mg, Ca, Na and K), pH, total petroleum hydrocarbon (TPH) and the overall effects on plants as indices of toxicity. The experiment demonstrated that at 1.5 – 3.5% contamination across days-zero to -28, there was a significant (p<0.05) increase in total petroleum hydrocarbon (TPH) from 0.03 ± 0.00 to 0.07 ± 0.00 with increase in acidity from pH 5.2 ± 0.00 to 4.0 ± 0.00 and a reduction in cation exchange capacity (CEC) from 0.82 ± 0.05 to 0.70 ± 0.11mEq and exchangeable bases with an augmented increase in phytotoxic elements and metal leachates. A reduction in microbial biomass from control, 1.30 x 109, to 3.6 x 108 cfu on week one as contamination increased and induction of hydrocarbonclastic organisms thereafter across weeks two and four, 3.88 x 108 and 4.40 x 108 cfu respectively was an indication of a reduction in microbial diversity. Ecosystem dynamics and mineralization were impaired and disrupted and the entire soil biochemistry altered with adverse effects on plant health.

Deciphering soil bacterial community structure in subsidence area caused by underground coal mining in arid and semiarid area

Subsidence caused by underground coal mining results in soil degradation. However, little is known about bacterial community structure and its response to a 1-year-old coal mining subsidence area in arid and semiarid areas northwest China. Soil samples from 5 unexplored areas (MC, RC, YC, LC and ZC) and a 1-year-old subsidence area above a coal working face were collected and soil biogeochemical properties and bacterial community structure were determined. Results showed electrical conductivity (EC), soil water content (SWC), soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), dissolved organic carbon (DOC), available nitrogen (AN), available phosphorus (AP) and available potassium (AK) decreased with depth. The microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and the activity of β-1,4-glucosidase (BG), β-1,4-N-acetylglucosaminidase (NAG), alkaline phosphatase (PP) and catalase (CAT) were also reduced. The nutrients, BG, PP and MBC in subsidence of marginal zone of a coal working face were significantly lower than those in control, suggesting subsidence led to a loss in nutrients and a reduction in microbial biomass. High-throughput sequencing revealed that the Sphingomonas, Gemmatimonas, Pseudomonas and Gp6, involved in C and N nutrient cycles, were dominant in this region. The relative abundances of Sphingomonas, Pseudomonas and Arthrobacter were decreased in subsidence due to the nutrient leakage and microbial biomass reduction. The predicted abundances of genes for metabolisms of xenobiotics via cytochrome P450 pathways and nitrogen were low in marginal zone, while peroxidase was high, indicating low capacities of degrading for xenobiotics and polycyclic aromatic hydrocarbons (PAHs) occurred marginal zone, while resistance to hydrogen peroxide was strengthened. Redundancy analysis (RDA) revealed EC, SWC and soil depth governed bacterial community structure. Overall, subsidence caused losses in soil water, nutrients and microbial biomass, alteration of bacterial community structure, and ultimately reduced soil nutrient conversion. Therefore, the cracks in the subsidence area should be filled manually in time, especially in marginal zone.

Experimental warming and precipitation reduction affect the biomass of microbial communities in a Sphagnum peatland

Abstract Due to their unique flora, hydrology and environmental characteristics, peatlands are precious and specific habitats for microorganisms and microscopic animals. Their microbial network structure and their biomass are crucial for peatland carbon cycling, through primary production, as well as decomposition and mineralization of organic matter. Wetlands are one of the ecosystems most at risk from anthropogenic activities and climate change. Most recent scenarios of climate change for Central Europe predict an increase in air temperature and a decrease in annual precipitation. These changes may disturb the biodiversity of aquatic organisms, and the peat carbon sink. Considering the above climatic scenarios, we aimed to: i) assess the response of microbial community biomass to warming and reduced precipitation through the lens of a manipulative experiment in a peatland ecosystem ii) predict how global warming might affect microbial biodiversity on peatlands exposed to warmer temperatures and decreased precipitation conditions. Additionally, we wanted to identify ecological indicators of warming among microorganisms living in Sphagnum peatland. The result of a manipulative experiment carried out at Rzecin peatland (W Poland) suggested that the strongest reduction in microbial biomass was observed in heated plots and plots where heating was combined with a reduction of precipitation. The most pronounced changes were observed in the case of the very abundant mixotrophic testate amoeba Hyalosphenia papilio and cyanobacteria. Shifts in the Sphagnum microbial network can be used as an early warning indicator of peatland warming, especially a decrease in the biomass of important phototrophic microbes living on the Sphagnum capitula, e.g. Hyalosphenia papilio.

Heavy Metal Pollution in the Ganga River Enhances Carbon Storage Relative to Flux.

This study evaluated the relationships between metal pollution and carbon production at six sites along a 285km length of the Ganga River. Metal contaminated sites did show a significant reduction in microbial biomass, substrate induced respiration, fluorescein diacetate hydrolytic assay (FDAase) and β-D-glucosidase. Concordantly, despite a high concentration of total organic carbon at these sites, CO2 emission at the land-water interface remained low. We found a strong positive correlation between CO2 emission and TOC (r = 0.92; p < 0.001). However, this relationship weakens when the sum of total heavy metal (∑THM) exceed 400µgg-1. Also, CO2 emission did show a positive correlation (r = 0.85; p < 0.001) with FDAase. The study shows that metal accumulation in riverbed sediment could potentially lead to better carbon sequestration on account of reduced microbial/enzyme activities. This carries significance for riverine carbon budget and modeling.

Contrasting responses after fires of the source components of soil respiration and ecosystem respiration

Wildfire is an important ecological disturbance that can have cascading effects on ecosystem carbon (C) fluxes. Ecosystem respiration (ER) and soil respiration (SR) account for two of the largest terrestrial C fluxes to the atmosphere, and they play critical roles in regulating C–climate feedbacks. Here, the responses of ER, SR and their source components to experimental burning in a meadow grassland on the Tibetan Plateau were investigated. Fire treatment increased ER by 9% but decreased SR by 15%. The contrasting post‐fire responses of SR and ER can be explained by the behaviour of their source components; that is, fire increased aboveground plant respiration (Ragb) by 37%, but decreased heterotrophic respiration (HR) by 21%. Increases in ER and Ragb were mainly related to enhanced plant productivity, whereas smaller SR and HR were associated with reductions in microbial biomass and soil moisture. Accounting for the responses of ER, SR and their intrinsic components has advanced our understanding of how fire affects ecosystem C fluxes.Highlights Fire treatment increased ecosystem respiration (ER) and aboveground plant respiration. Fire treatment decreased soil respiration (SR) and heterotrophic respiration (HR). Increases in ER and aboveground plant respiration were related to plant productivity. Reductions in SR and HR were caused by the suppressed microbial activity.

Deprivation of root-derived resources affects microbial biomass but not community structure in litter and soil.

The input of plant leaf litter has been assumed to be the most important resource for soil organisms of forest ecosystems, but there is increasing evidence that root-derived resources may be more important. By trenching roots of trees in deciduous and coniferous forests, we cut-off the input of root-derived resources and investigated the response of microorganisms using substrate-induced respiration and phospholipid fatty acid (PLFA) analysis. After one and three years, root trenching strongly decreased microbial biomass and concentrations of PLFAs by about 20%, but the microbial community structure was little affected and the effects were similar in deciduous and coniferous forests. However, the reduction in microbial biomass varied between regions and was more pronounced in forests on limestone soils (Hainich) than in those on sandy soils (Schorfheide). Trenching also reduced microbial biomass in the litter layer but only in the Hainich after one year, whereas fungal and bacterial marker PLFAs as well as the fungal-to-plant marker ratio in litter were reduced in the Schorfheide both after one and three years. The pronounced differences between forests of the two regions suggest that root-derived resources are more important in fueling soil microorganisms of base-rich forests characterized by mull humus than in forests poor in base cations characterized by moder soils. The reduction in microbial biomass and changes in microbial community characteristics in the litter layer suggests that litter microorganisms do not exclusively rely on resources from decomposing litter but also from roots, i.e. from resources based on labile recently fixed carbon. Our results suggest that both bacteria and fungi heavily depend on root-derived resources with both suffering to a similar extent to deprivation of these resources. Further, the results indicate that the community structure of microorganisms is remarkably resistant to changes in resource supply and adapts quickly to new conditions irrespective of tree species composition and forest management.

Effect of Cultivation and Soil Tillage Systems on the Microbial Biomass in Castor Bean Crop at the Irecê Plateau, Bahia

Inadequate soil management alters the microbiological attributes of the soil, causing reduction in microbial biomass and activity. Microbial biomass is the living and active part of the soil and can serve as an indicator of changes in the quantity of due to changes in land use. This study aimed to evaluate the effect of intercropping and soil tillage systems on the microbial biomass in castor bean-based crop in the Irec&amp;ecirc; Plateau, Bahia, Brazil. The experiment was carried out on an eutrophic Haplic Cambisol with clay texture in the Mata Verde Farm of Alto do Quindinho, municipality of S&amp;atilde;o Gabriel, Irec&amp;ecirc; Plateau, Bahia, Brazil. Six intercropping systems were evaluated including solely castor bean (control) and castor bean intercropped with each of the castor bean cake, common bean, pigeon pea, corn, and gliricidia. Plowing + harrowing and subsoiling were the two soil tillage techniques associated to the intercropping systems. C and N contents in microbial biomass (Cmic and Nmic), soil basal respiration and metabolic quotient were determined in soil samples collected from the 0-10 and 10-30 cm layers. The different soil management systems influenced microbial biomass and activity, and the most suitable conditions for soil microbiota occurred in the soil tillage system with subsoiling. In the semi - arid condition, at 0-10 cm depth, the castor bean + castor bean cake crop system promoted an increase of Cmic content, and the castor + gliricidia system increased Nmic content, both under soil tillage with subsoiling.

Long-term nitrogen addition suppresses microbial degradation, enhances soil carbon storage, and alters the molecular composition of soil organic matter

Forest soil organic carbon (SOC) is one of the largest reservoirs of terrestrial carbon (C) and is a major component of the global C cycle. Yet there is still uncertainty regarding how ecosystems, and the SOC they store, will respond to changes due to anthropogenic processes. Current and future reactive nitrogen (N) deposition to forest soils may alter biogeochemical processes and shift both the quantity and quality of stored SOC. We studied SOC storage and molecular-level composition after 22 years of N additions (100 kg N ha−1 y−1) in a temperate deciduous forest. SOC storage in surface soils increased by 0.93 kg m−2 due to a decline in microbial biomass (phospholipid fatty acids) and litter decomposition. N additions resulted in the selective preservation of a range of plant-derived compounds including steroids, lignin-derived, cutin-derived, and suberin-derived compounds that have anti-microbial properties or are non-preferred microbial substrates. This overall shift in SOC composition suggests limited sustainability and a decline in soil health. The reduction in microbial biomass and increase in specific SOC components demonstrate that long-term N fertilization negatively alters fundamental C cycling in forest soils. This study also demonstrates unequivocally that anthropogenic impacts on C and N cycling in forests at the molecular-level must be considered more holistically.

Forest residue removal decreases soil quality and affects wood productivity even with high rates of fertilizer application

Forest residues are frequently used as energy sources by Brazilian forest companies. The removal of such residues is known to reduce wood productivity, especially when fertilizer application rate is low. This study aimed to evaluate after two forest rotations the effects of forest residue management on wood productivity when fertilizer is applied at a high rate; and the effect of timber harvest intensity on soil organic matter and microbial activity. We assessed tree growth, soil microbial biomass and activity, and we fractionated soil organic matter (SOM) via its oxidation resistance. These assessments were performed after conducting a field trial comparing harvest residue management over two successive rotations in the same plots. We found no significant effect of treatments on wood productivity when the residues were removed for the first time; however, wood productivity reduced by 15% during the second rotation with residue removal even with high rates of fertilizer application. Further, 40% reduction in microbial biomass and soil respiration was noted with forest residue removal. At the reestablishment time, the SOM in the top soil (0–0.05 m layer) was 25% lower at the site where the forest residues were removed, and this difference increased to 50% at 300 days after the reestablishment. This reduction was found mainly in the SOM labile fraction.

Effect of Soil Drying Intensity During an Experimental Drying-Rewetting Event on Nutrient Transformation and Microbial Community Composition

Abstract Soil drying-rewetting (DRW) events affect nutrient transformation and microbial community composition; however, little is known about the influence of drying intensity during the DRW events. Therefore, we analyzed soil nutrient composition and microbial communities with exposure to various drying intensities during an experimental drying-rewetting event, using a silt loam from a grassland of northern China, where the semi-arid climate exposes soils to a wide range of moisture conditions, and grasslands account for over 40% of the nation's land area. We also conducted a sterilization experiment to examine the contribution of soil microbes to nutrient pulses. Soil drying-rewetting decreased carbon (C) mineralization by 9%–27%. Both monosaccharide and mineral nitrogen (N) contents increased with higher drying intensities (drying to ≤ 10% gravimetric water content), with the increases being 204% and 110% with the highest drying intensity (drying to 2% gravimetric water content), respectively, whereas labile phosphorus (P) only increased (by 105%) with the highest drying intensity. Moreover, levels of microbial biomass C and N and dissolved organic N decreased with increasing drying intensity and were correlated with increases in dissolved organic C and mineral N, respectively, whereas the increases in labile P were not consistent with reductions in microbial biomass P. The sterilization experiment results indicated that microbes were primarily responsible for the C and N pulses, whereas non-microbial factors were the main contributors to the labile P pulses. Phospholipid fatty acid analysis indicated that soil microbes were highly resistant to drying-rewetting events and that drought-resistant groups were probably responsible for nutrient transformation. Therefore, the present study demonstrated that moderate soil drying during drying-rewetting events could improve the mineralization of N, but not P, and that different mechanisms were responsible for the C, N, and P pulses observed during drying-rewetting events.

Microbial Nonlinear Response to a Precipitation Gradient in the Northeastern Tibetan Plateau

The response of soil microbes to global warming, especially their response to precipitation, remains poorly known. The Tibetan Plateau is very sensitive to climate change. In particular, the northeastern margin of the Tibetan Plateau is an interesting area to test the response of soil microbial communities to precipitation, as there is a distinct gradient in annual precipitation from east to west. We collected soil samples along a precipitation gradient in arid and semi-arid areas of the northeastern Tibetan Plateau. Phospholipid fatty acid (PLFA) technology was used to analyze the microbial community structure and total microbial biomass. With declining precipitation, bacterial biomass decreased significantly, whereas fungal biomass did not show an obvious trend; this result indicates that bacteria are more sensitive to mean annual precipitation (MAP). Overall, the biomass of Gram-negative (G−) bacteria represented up to 82% of the total bacterial biomass. In the high (260–394 mm yr−1) MAP areas, bacterial biomass was mainly concentrated at the surface and decreased with increasing soil depth (0–40 cm). In contrast, in the low (36–260 mm yr−1) MAP areas, bacterial biomass was mainly concentrated in the deep soils. The mean annual precipitation was strongly correlated with soil microbial community in space, with microbial communities in the 0–10-cm soil depth most affected by precipitation. Groundwater may impact microbial communities in the 20–40-cm soil depth of this arid and semiarid region. The clustering of the microbial communities was significantly grouped according to the MAP gradient, revealing that MAP is a major driving force of microbial communities in this arid and semi-arid area. The decline in MAP led to a shift in the structure of the microbial community and an overall reduction in microbial biomass.

Biogas digestates affect crop P uptake and soil microbial community composition

Fermentation residues from biogas production are known as valuable organic fertilisers. This study deals with the effect of cattle slurry, co-digested cattle slurry, co-digested energy crops and mineral fertilisers on the activity and composition of soil microbiota. Furthermore, the effect of solid–liquid separation as a common pre-treatment of digestate was tested. The fertilising effects were analysed in an 8-week pot experiment on loamy sand using two crops, Amaranthus cruentus and Sorghum bicolor. Amaranth, as a crop with significantly higher P uptake, triggered stress for occurring soil microbes and thereby caused a reduction of microbial biomass C in the soil. Irrespective of the crop, microbial basal respiration and metabolic quotient were higher with the digestates than with the untreated slurry or the mineral treatments. Community level physiological profiles with MicroResp showed considerable differences among the treatments, with particularly strong effects of solid–liquid separation. Similar results were also found on a structural level (PCR-DGGE). Alkaline phosphatase gene analyses revealed high sensitivity to different fertilisation regimes.

Erratum to: Soil compaction and forest floor removal reduced microbial biomass and enzyme activities in a boreal aspen forest soil

Soil enzymes are linked to microbial functions and nutrient cycling in forest ecosystems and are considered sensitive to soil disturbances. We investigated the effects of severe soil compaction and whole-tree harvesting plus forest floor removal (referred to as FFR below, compared with stem-only harvesting) on available N, microbial biomass C (MBC), microbial biomass N (MBN), and microbial biomass P (MBP), and dehydrogenase, protease, and phosphatase activities in the forest floor and 0–10 cm mineral soil in a boreal aspen (Populus tremuloides Michx.) forest soil near Dawson Creek, British Columbia, Canada. In the forest floor, no soil compaction effects were observed for any of the soil microbial or enzyme activity parameters measured. In the mineral soil, compaction reduced available N, MBP, and acid phosphatase by 53, 47, and 48%, respectively, when forest floor was intact, and protease and alkaline phosphatase activities by 28 and 27%, respectively, regardless of FFR. Forest floor removal reduced available P, MBC, MBN, and protease and alkaline phosphatase activities by 38, 46, 49, 25, and 45%, respectively, regardless of soil compaction, and available N, MBP, and acid phosphatase activity by 52, 50, and 39%, respectively, in the noncompacted soil. Neither soil compaction nor FFR affected dehydrogenase activities. Reductions in microbial biomass and protease and phosphatase activities after compaction and FFR likely led to the reduced N and P availabilities in the soil. Our results indicate that microbial biomass and enzyme activities were sensitive to soil compaction and FFR and that such disturbances had negative consequences for forest soil N and P cycling and fertility.

Soil respiration is not limited by reductions in microbial biomass during long-term soil incubations

Declining rates of soil respiration are reliably observed during long-term laboratory incubations. However, the cause of this decline is uncertain. We explored different controls on soil respiration to elucidate the drivers of respiration rate declines during long-term soil incubations. Following a long-term (707day) incubation (30 °C) of soils from two sites (a cultivated and a forested plot at Kellogg Biological Station, Hickory Corners, MI, USA), soils were significantly depleted of both soil carbon and microbial biomass. To test the ability of these carbon- and biomass-depleted (“incubation-depleted”) soils to respire labile organic matter, we exposed soils to a second, 42day incubation (30 °C) with and without an addition of plant residues. We controlled for soil carbon and microbial biomass depletion by incubating field fresh (“fresh”) soils with and without an amendment of wheat and corn residues. Although respiration was consistently higher in the fresh versus incubation-depleted soil (2 and 1.2 times higher in the fresh cultivated and fresh forested soil, respectively), the ability to respire substrate did not differ between the fresh and incubation-depleted soils. Further, at the completion of the 42day incubation, levels of microbial biomass in the incubation-depleted soils remained unchanged, while levels of microbial biomass in the field-fresh soil declined to levels similar to that of the incubation-depleted soils. Extra-cellular enzyme pools in the incubation-depleted soils were sometimes slightly reduced and did not respond to addition of labile substrate and did not limit soil respiration. Our results support the idea that available soil organic matter, rather than a lack microbial biomass and extracellular enzymes, limits soil respiration over the course of long-term incubations. That decomposition of both wheat and corn straw residues did not change after major changes in the soil biomass during extended incubation supports the omission of biomass values from biogeochemical models.

Influence of gap size on carbon and nitrogen biogeochemical cycling in Northern hardwood forests of the Upper Peninsula, Michigan

The objective of this study is to determine the effect of treefall gap size on carbon and nitrogen biogeochemistry in the Northern hardwood forest. The size of the gap controls the microclimate, particularly solar radiation, soil temperature, and soil moisture, which can alter nutrient cycling. However, in Northern hardwood forests, our understanding of the relation between biogeochemistry and gap size is incomplete. Twelve natural treefall gaps ranging in size from 27 to 590 m2 and four control plots located under closed canopy were identified in Upper Michigan in May 2008. Concentrations of ammonium and nitrate were measured in throughfall and soil leachates; soil respiration rates were measured in soil; and nutrient pools were measured in vegetative biomass, forest floor (Oe, Oi horizons), mineral soil, and microbial biomass. Gap size was positively correlated with sapling biomass density and throughfall ammonium concentration but negatively correlated with microbial biomass, endomycorrhizal biomass, and soil respiration. Gap size was unrelated to all other parameters measured. The results of this study suggest that in the Northern hardwood forest, vegetative recovery and a reduction in microbial biomass may limit the influence larger gaps have on nutrient cycling.