Relative Contribution Of Fungi Research Articles

Relative contributions of fungi and bacteria to litter decomposition under low and high soil moisture in an Australian grassland

Fungi and bacteria differ in their sensitivity to soil moisture, but their activity and contributions to soil carbon (C) cycling under different soil moisture conditions remain unclear. We manipulated soil fungi and bacteria with the fungicide captan and bactericide bronopol, respectively, and examined their effect on C dynamics at low and high moisture levels (40 and 80 % water holding capacity) in a grassland soil over a 21-day incubation period in the laboratory. 13C-labeled ryegrass was added with and without biocide treatments to separate ryegrass from soil-derived C in respiration, dissolved organic C (DOC) and soil C. We also measured activities of four C-degrading enzymes. Soil total- and ryegrass-respiration rates and microbial biomass C (MBC) decreased, while ryegrass-derived C in DOC and soil increased with decreased soil moisture, suggesting reduced microbial activity with decreased soil moisture. Initially, ryegrass respiration rates were suppressed by both biocides and both soil moisture levels. However, at low soil moisture, ryegrass respiration no longer was suppressed by bronopol after eight days of incubation, but remained suppressed with captan, suggesting that with low moisture fungi played a more important role in decomposing ryegrass litter than bacteria. On the other hand, at high soil moisture, biocide effects on ryegrass respiration mostly disappeared after eight days, suggesting that more labile components of ryegrass litter were no longer present, and that the surviving microorganisms adapted similarly to decomposing the more recalcitrant litter. Bacteria preferred to decompose labile substrates early on during the incubation, and fungi played a greater role in decomposing more recalcitrant ryegrass left over in soil at the end of the incubation. At low moisture with captan, a reduction in oxidative enzyme production contributed to the increase in the hydrolytic:oxidative enzyme ratio, further indicating the importance of fungi for decomposing more recalcitrant substances under low moisture conditions.

Variation of microbial residue contribution to soil organic carbon sequestration following land use change in a subtropical karst region

Microbial residues are an important constituent of persistent soil organic carbon (SOC). Nevertheless, how microbial residue contribution to bulk SOC sequestration changes following land use conversion remains poorly understood. Here, we investigated the variation of soil microbial residue C and its contribution to SOC following conversion of maize-soybean field to mulberry, forage grass and sugarcane fields in southwest China, with forest used as reference. Microbial residue C contents were estimated based on microbial cell wall biomarker amino sugars. The contents of fungal, bacterial and total microbial residue C were lowest in the sugarcane, maize-soybean and mulberry fields, intermediate in the forage grass field and highest in the forest. Fungal to bacterial residue C ratios were comparable among the five land use types, implying that the relative contribution of fungi and bacteria residues to SOC sequestration remained unchanged. Conversion of maize-soybean field to mulberry and sugarcane fields had no significant effect on microbial residue contribution to SOC sequestration. Nevertheless, the contribution of total microbial residues to SOC sequestration was marginally (p < 0.1) and significantly (p < 0.05) higher, respectively, in the forage grass field and forest than in the maize-soybean field. Levels of SOC and living microbial biomass were the major factors determining the dynamics of microbial residue contents. Stoichiometric imbalance of carbon: nitrogen ratios between soil organic matter and microbial biomass (i.e., C:N imbalance) was found to negatively correlate with the contribution of microbial residues to SOC sequestration. Our results suggest that increase of C:N imbalance may explain lowered microbial residue contribution to SOC sequestration following land use change.

Relative Contribution of nirK- and nirS- Bacterial Denitrifiers as Well as Fungal Denitrifiers to Nitrous Oxide Production from Dairy Manure Compost.

The relative contribution of fungi, bacteria, and nirS and nirK denirifiers to nitrous oxide (N2O) emission with unknown isotopic signature from dairy manure compost was examined by selective inhibition techniques. Chloramphenicol (CHP), cycloheximide (CYH), and diethyl dithiocarbamate (DDTC) were used to suppress the activity of bacteria, fungi, and nirK-possessing denitrifiers, respectively. Produced N2O were surveyed to isotopocule analysis, and its 15N site preference (SP) and δ18O values were compared. Bacteria, fungi, nirS, and nirK gene abundances were compared by qPCR. The results showed that N2O production was strongly inhibited by CHP addition in surface pile samples (82.2%) as well as in nitrite-amended core samples (98.4%), while CYH addition did not inhibit the N2O production. N2O with unknown isotopic signature (SP = 15.3-16.2‰), accompanied by δ18O (19.0-26.8‰) values which were close to bacterial denitrification, was also suppressed by CHP and DDTC addition (95.3%) indicating that nirK denitrifiers were responsible for this N2O production despite being less abundant than nirS denitrifiers. Altogether, our results suggest that bacteria are important for N2O production with different SP values both from compost surface and pile core. However, further work is required to decipher whether N2O with unknown isotopic signature is mostly due to nirK denitrifiers that are taxonomically different from the SP-characterized strains and therefore have different SP values rather than also being interwoven with the contribution of the NO-detoxifying pathway and/or of co-denitrification.

Fungi-to-bacteria ratio in soils of European Russia

The selective inhibition technique by specific antibiotics (streptomycin, cycloheximide) applied to substrate-induced respiration (SIR) measurement was used to test the relative contribution of fungi to bacteria (F/B ratio) to the overall microflora-induced activity in soils of European Russia. Investigated soils covered a wide climatic transect and different ecosystem types including managed vs. natural ecosystems. Before direct comparison among sites, the antibiotic inhibition technique was optimized for soil characteristics. Once the optimal concentration was set, the combined effect of the two antibiotics resulted in average 60% inhibition of SIR. The analyzed sites (in total 47) including various biomes (tundra, middle taiga, southern taiga, subtaiga, dark coniferous forests outside the boreal region, steppe, mountain forests and arable sites), were characterized by a wide range of soil pHw (3.95–7.95), soil organic carbon (0.69–24.08%), soil microbial biomass carbon (149–5028 µg C g−1 soil) and soil basal respiration (0.24–8.28 µg CO2-C g−1 soil h−1). In all the analyzed sites, a predominance of fungal over bacteria activity was observed with F/B ratios always higher than one (4.9 on average). Natural sites were characterized by higher F/B ratios (on average 5.6) compared to agricultural ones (on average 3.5).

Secondary metabolites ofPinus halepensisalter decomposer organisms and litter decomposition during afforestation of abandoned agricultural zones

SummaryOver a century of agricultural abandonment across the Mediterranean region has favoured the installation of the pioneer expansionist species Aleppo pine (Pinus halepensisMiller). This species synthesizes a wide range of secondary metabolites that are partially released during needle decomposition, and which can thus affect the ‘brown food chain’. Litter decomposition is a key process connecting ecosystem structure and function, and involving microbial and faunal components.The goal of this study was to determine the effect of chemical compounds from Aleppo pine needles on the litter decomposition process along a gradient of Mediterranean forest secondary succession. Usingin situlitterbags, we compared the dynamics of decomposers, particularly the relative contributions of fungal and mesofauna biomass to litter mass loss (calculations based on the measured decomposer biomass, published fungal growth efficiency and mesofauna feeding rate), against the dynamics of secondary metabolites associated with decomposed needles in three successional stages (early, middle and late, i.e. pinewoods that were aged 10, 30 and over 60 years old).Our first key finding was that fungi accounted for the largest portion of overall litter mass loss (60–79%) and detritivorous mesofauna contributed to 8–12%. In the early stage of succession, fungal biomass after 6 months of decomposition was lower than in middle and late stages, and may be responsible for the delay in litter colonization by mesofauna. We linked this result to a clearly longer residence time for phenolic compounds in young pine forest, leading to an overall slowdown in the decomposition process.Synthesis. Litter phenolic content emerged as a key functional trait for predicting litter decomposition, delaying the colonization of litter by decomposers in Mediterranean forest ecosystems. Another key finding is that the relative contributions of fungi and detritivores to needle mass loss were different between the successional stages. From the food‐web perspective, the organic matter available for higher trophic levels thus remains unchanged beyond 30 years after pine colonization.

The significant contribution of fungi to soil N2O production across diverse ecosystems

Sporadic observations from pure culture study and direct soil measurement have indicated that fungi can substantially contribute to soil N2O production. Yet, it is still uncertain whether this fungal significance is a more general ecological phenomenon. In this study, relative contributions of fungi and bacteria to soil N2O production were examined in five ecosystems, including conventional farming (CON), integrated crop and livestock system (ICL), organic farming (ORG), plantation forestry (PF), and abandoned agriculture field subjected to natural succession (SUCC). Soil N2O production was measured at 90% water-filled pore space from antibiotic-free controls and soils amended with streptomycin, cycloheximide, or both. Streptomycin and cycloheximide additions significantly reduced soil N2O fluxes from the five systems, ranging from 31% to 54% and 40% to 51%, respectively. Fungi contributed more to soil N2O fluxes than bacteria in PF, whereas fungi and bacteria made comparable contributions in other four systems. Furthermore, soil pH was correlated positively with the percentage of bacterial contribution to soil N2O flux, but negatively with the percentage of fungal contribution to soil N2O flux as well as the ratio of fungal-to-bacterial contributions. Our results showed that fungi could potentially contribute to soil N2O production in diverse agroecosystems and their contribution might be more pronounced in the acidic plantation forestry.

Effect of inorganic nutrients on relative contributions of fungi and bacteria to carbon flow from submerged decomposing leaf litter.

The relative contributions of fungi and bacteria to carbon flow from submerged decaying plant litter at different levels of inorganic nutrients (N and P) were studied. We estimated leaf mass loss, fungal and bacterial biomass and production, and microbial respiration and constructed partial carbon budgets for red maple leaf disks precolonized in a stream and then incubated in laboratory microcosms at two levels of nutrients. Patterns of carbon flow for leaf disks colonized with the full microbial assemblage were compared with those colonized by bacteria but in which fungi were greatly reduced by placing leaf disks in colonization chambers sealed with membrane filters to exclude aquatic hyphomycete conidia but not bacterial cells. On leaves colonized by the full microbial assemblage, elevated nutrient concentrations stimulated fungi and bacteria to a similar degree. Peak fungal and bacterial biomass increased by factors of 3.9 and 4.0; cumulative production was 3.9 and 5.1 times higher in the high nutrient in comparison with the low nutrient treatment, respectively. Fungi dominated the total microbial biomass (98.4 to 99.8%) and cumulative production (97.3 and 96.5%), and the fungal yield coefficient exceeded that of bacteria by a factor of 36 and 27 in low- and high-nutrient treatments, respectively. Consequently, the dominant role of fungi in leaf decomposition did not change as a result of nutrient manipulation. Carbon budgets indicated that 8% of leaf carbon loss in the low-nutrient treatment and 17% in the high-nutrient treatment were channeled to microbial (essentially fungal) production. Nutrient enrichment had a positive effect on rate of leaf decomposition only in microcosms with full microbial assemblages. In treatments where fungal colonization was reduced, cumulative bacterial production did not change significantly at either nutrient level and leaf decomposition rate was negatively affected (high nutrients), suggesting that bacterial participation in carbon flow from decaying leaf litter is low regardless of the presence of fungi and nutrient availability. Moreover, 1.5 and 2.3 times higher yield coefficients of bacteria in the reduced fungal treatments at low and high nutrients, respectively (percentage of leaf carbon loss channeled to bacterial production), suggest that bacteria are subjected to strong competition with fungi for resources available in leaf litter.

Relative contributions of fungi and bacteria to soil carboxymethylcellulase activity

Relative contributions of fungi and bacteria to soil carboxymethylcellulase activity