Differential response of ectomycorrhizal and saprotrophic fungal mycelium from coniferous forest soils to selected monoterpenes

The mycelia of saprotrophic (SP) and ectomycorrhizal (ECM) fungi occur throughout the upper soil horizons in coniferous forests and could therefore be exposed to high concentrations of monoterpenes occurring in the needle litter of some tree species.Monoterpenes are mycotoxic and could potentially affect fungi that are exposed to them in the litter layers. In order to investigate whether monoterpenes typical of coniferous litters could influence fungal communities, we analysed the monoterpene content of freshly fallen needles of Pinus sylvestris, Picea abies and Picea sitchensis. The most abundant monoterpenes were found to be α-pinene, β-pinene and 3-carene. We evaluated the effects of these three monoterpene vapours on the biomass production of 23 SP isolates and 16 ECM isolates. Overall, 75% of ECM isolates and 26% of SP isolates were significantly inhibited by at least one of the monoterpene treatments and both intra- and inter-specific variations in response were observed.Monoterpene concentrations are highest in surface litters. The differential effects on fungal taxa may influence the spatial and temporal distribution of fungal community composition, indirectly affecting decomposition and nutrient cycling, the fundamental ecosystem processes in which fungi have a key role in coniferous forest soils.     

Indirect host effect on ectomycorrhizal fungi: Leaf fall and litter quality explain changes in fungal communities on the roots of co-occurring Mediterranean oaks

Host trees can modify their soil abiotic conditions through their leaf fall quality which in turn may influence the ectomycorrhizal (ECM) fungal community composition. We investigated this indirect interaction using a causal modelling approach. We identified ECM fungi on the roots of two coexisting oak species growing in two forests in southern Spain - Quercus suber (evergreen) and Quercus canariensis (winter deciduous)-using a PCR-based molecular method. We also analysed the leaf fall, litter and soil sampled beneath the tree canopies to determine the concentrations of key nutrients. The total mycorrhizal pool was comprised of 69 operational taxonomic units (OTUs). Tomentella and Russula were the most species-rich, frequent and abundant genera. ECM fungi with epigeous and resupinate fruiting bodies were found in 60% and 34% of the identified mycorrhizas, respectively. The calcium content of litter, which was significantly higher beneath the winter-deciduous oak species due to differences in leaf fall quality, was the most important variable for explaining ECM species distribution. The evaluation of alternative causal models by the d-sep method revealed that only those considering indirect leaf fall-mediated host effects statistically matched the observed covariation patterns between host, environment (litter, topsoil, subsoil) and fungal community variables.     

Volatile monoterpenes in soil atmosphere under birch and conifers: Effects on soil N transformations

The aim of this study was to examine the occurrence and concentrations of volatile organic compounds (VOCs), in particular, volatile monoterpenes, in soil atmosphere under silver birch (Betula pendula L.) and two conifers, Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.), and to determine the effects of the most relevant monoterpenes on transformations of soil N. The study site was a 70-year-old tree species experiment in Kivalo, northern Finland. VOCs were collected using two methods, passive air samplers and a chamber method. In soil atmosphere under spruce and especially under pine, the concentrations of monoterpenes were high, α- and β-pinene, Δ-3-carene and myrcene being the most abundant compounds, whereas concentrations of monoterpenes in soil atmosphere under birch were negligible. Samples of humus layer from the birch stand incubated in vitro and exposed to vapors from monoterpenes typical of coniferous forest soil showed decreased rates of net N mineralization but simultaneously increased rates of C mineralization. The response of soil microbial biomass C and N to different monoterpenes varied, but some monoterpenes considerably decreased soil microbial biomass. Altogether these results suggest that these compounds have negative effects on soil N transformations, but may serve as carbon and energy source for part of soil microbes.     

Effect of litter quality on its decomposition in broadleaf and coniferous forest

Recently there has been much interest in the effect of litter mixing as well as the effect of different forest habitats on the decomposition process. Our aim was to test two hypotheses: high quality litter promotes decomposition of poor quality litter, and litter decomposes faster in broadleaf than in coniferous forest. We conducted a litter mixing experiment using litterbags placed in two forest floors, in which treatments consisted of litter monocultures of each of two campy species (Castanopsis eyrei and Pinus massoniana), as well as mixtures of these two species. The results showed that C. eyrei leaves decomposed significantly faster in the coniferous habitat than in their native habitat. On the other hand, P. massoniana needles decomposed significantly faster in their native coniferous habitat than in the broadleaf habitat. In our experiment we found that the mixture had different effect on different quality litter. P. massoniana needles (poor quality) had a positive effect on the decomposition of C. eyrei leaves (high quality), while C. eyrei leaves had a negative effect on the decomposition of P. massoniana needles in the mixture case in both broadleaf and coniferous habitats. The diversity of the fungi identified from different litters varied among treatments and the mass loss was positively correlated with the Shannon–Weaver diversity index of fungi. It is suggested that fungi may be one of the major drivers to control the decomposition process.     

Distribution of monoterpenes between organic resources in upper soil horizons under monocultures of Picea abies, Picea sitchensis and Pinus sylvestris

The aim of this study was to compare the monoterpene content and distribution in litters and roots of three conifer species: Picea abies (L.) Karst, Picea sitchensis (Bong.) Carr. and Pinus sylvestris (L.). We analysed the monoterpene content of green needles, needle litter, F (fermentation) layer material and roots collected from monoculture plots. The rate of loss of monoterpenes from freshly fallen litter in the field was also studied at two monthly intervals over 10 months, to assess the length of time that monoterpenes entering the litter layer remain. Monoterpene analysis was carried out by extracting homogenised samples in hexane and identifying and quantifying the resulting monoterpenes using gas chromatography with flame ionisation detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS). Mean total monoterpene concentrations varied significantly between the three species examined (e.g. in freshly fallen litter 1531 ± 96, 100 ± 5 and 1175 ± 122 μg g⁻¹ d. wt for P. abies, P. sitchensis and P. sylvestris); each species had distinctive and consistent monoterpene profiles associated with each type of tissue, and total monoterpene concentrations in green needles varied between individual trees of the same species, particularly for P. sitchensis. A substantial proportion of the monoterpene content of green needles remained in the needles after litter fall for P. abies (42%), P. sitchensis (11%) and P. sylvestris (30%). Although rates of monoterpene loss from needle litters varied initially (P. sylvestris > P. abies > P. sitchensis), the majority of the monoterpene content was lost after 4-6 months. Maximum monoterpene emission rates from decaying litter were calculated of 39 (P. abies), 1.7 (P. sitchensis) and 39 μg m⁻² h⁻¹ (P. sylvestris). Monoterpene concentrations in F layer material were very low (<10 μg g⁻¹ d. wt). Roots, particularly in P. sylvestris, represented a significant pool of monoterpenes (185 ± 16, P. abies; 258 ± 54, P. sitchensis; 2133 ± 200 μg g⁻¹ d. wt, P. sylvestris). The monoterpene profile was similar between roots and litter of P. sylvestris (α-pinene most abundant), and for P. sitchensis, (limonene and α-pinene most abundant), although a different pattern was observed between needle litter (most abundant β-pinene) and roots (most abundant myrcene) of P. abies. The relatively high concentrations and different profiles of monoterpenes characterised in upper organic soil horizons here emphasise the need for their influence on soil ecological processes to be assessed.     

Do oribatid mites (Acari: Oribatida) show a higher preference for ubiquitous vs. specialized saprotrophic fungi from pine litter?

Previous studies of oribatid mite feeding preferences for different saprotrophic fungi were limited to ubiquitous fungal species, whereas saprophytes specialized to decompose particular substrates have been neglected. We examined the preference of seven oribatid mite species (Adoristes ovatus, Eniochthonius minutissimus, Eueremaeus silvestris, Nothrus silvestris, Oppiella subpectinata, Porobelba spinosa and Spatiodamaeus verticillipes) for nine autochthonous saprotrophic fungi from Scots pine litter (Pinus sylvestris). Among the fungal species offered were specific coniferous litter colonizers (Allantophomopsis lycopodina, Ceuthospora pinastri, Hormonema dematioides, Scleroconidioma sphagnicola, Verticicladium trifidum, Marasmius androsaceus and Sympodiella acicola) and two ubiquitous species (Cladosporium herbarum and Oidiodendron griseum). The fungi were inoculated on fragments of pine needles and offered simultaneously and separately to the mites. Our main hypothesis, that oribatid mites (usually occurring in more than one type of ecosystems) would prefer the ubiquitous fungal species rather than those specific to pine litter, was supported only partly. The ubiquitous C. herbarum was highly preferred by all studied mites, but most of them preferred one or more of the specialized fungi with similar intensity. The basidiomycete M. androsaceus along with sterile needles were consistently avoided by all mites in all experiments. Our results do not support the hypothesis, that the “true” fungivorous oribatid mites in traditional sense are more selective fungal feeders than are the “unspecialized” panphytophagous ones. We observed no gradation in preference of fungi for oribatid mites as a group, but rather a discontinuous and dynamic mosaic with particular mites preferring particular fungal species. This heterogeneous mosaic shapes the feeding niches occupied by particular oribatid mite species and probably reduces competition for food source among numerous species coexisting in a given habitat and time.     

Plant growth and nutrition in pine (Pinus thunbergii) seedlings and dehydrogenase and phosphatase activity of ectomycorrhizal root tips inoculated with seven individual ectomycorrhizal fungal species at high and low nitrogen conditions

We investigated the functions and ecological traits of seven individual ectomycorrhizal (ECM) fungal species derived from a Pinus thunbergii-dominated (nitrogen-poor) and a Robinia pseudoacacia-dominated (nitrogen-rich) area. P. thunbergii seedlings were inoculated with seven individual ECM fungal species and cultured under high nitrogen (nitrogen group) and low nitrogen (control group) conditions. Control seedlings were not inoculated with any ECM fungus. Seedlings harvested were examined for the numbers of non-mycorrhizal and ECM root tips, growth, nutrient status (nitrogen, phosphorus and carbon) and the activity of dehydrogenase and phosphomonoesterase in the root tips. The relationships among the growth, nutrient status and the enzymatic activity in the seedlings inoculated with each ECM fungal species were also analyzed by canonical discriminants. As the results, inoculation of ECM fungi made the plant growth significantly higher than those of non-inoculated seedlings. Plant growth significantly correlated with the phosphorus content, N:P ratio and phosphomonoesterase activity, especially in the nitrogen group. Dehydrogenase and phosphomonoesterase activities in the seedlings were higher when the ECM fungi from a nitrogen-rich area were inoculated than when those from a nitrogen-poor area were inoculated. The canonical discriminant analyses separated seedlings by inocula: no fungus, ECM fungi from a nitrogen-poor area, and those from a nitrogen-rich area. These results suggested the possibility that nitrogen deposition caused P shortage and the P absorbing ability was higher in the ECM fungi in nitrogen-rich forests than those in nitrogen-poor forests.     

Effects of collembolan grazing on nutrient release and respiration of a leaf litter inhabiting fungus

An attempt was made to assess the effect of grazing by Onychiurus subtenuis Folsom on nutrient release from and respiration of a sterile dark fungus using simple microcosms held under controlled laboratory conditions.The results showed that the fungus was very efficient in taking up all available soluble NO₃^? and PO₄^2? and that collembolan grazing had no effects in releasing these nutrients during the 10 day experiment. Significant increase in respiration of litter colonized by the fungus was observed following collembolan grazing, but this increase was attributed to the activity of bacteria and fungi tracked into the leaf litter systems by the Collembola.     

Elevated UV-B radiation modifies the extractability of carbohydrates from leaf litter of Quercus robur

We examined the influence of elevated UV-B radiation on the extractability of carbohydrates from leaf litter of Quercus robur. Saplings were exposed to a 30% elevation above the ambient level of erythemally weighted UV-B (280-315 nm) radiation for eight months at an outdoor facility. UV-B radiation was applied under arrays of fluorescent lamps filtered with cellulose diacetate, which transmitted both UV-B and UV-A (315-400 nm) radiation. Saplings were also exposed to elevated UV-A radiation under arrays of polyester-filtered lamps and to ambient radiation under arrays of non-energised lamps. Abscised leaves were collected, ground and sequentially treated with seven solvents in order to fractionate extractable carbohydrates based on the way in which they are held in the cell wall. Elevated UV-B radiation reduced the extractability of carbohydrates from cell walls of Q. robur. Sodium phosphate buffer at pH 7 extracted 10% less total carbohydrate from leaf material exposed during growth to elevated UV-B radiation under cellulose diacetate-filtered lamps than from leaf material grown under polyester-filtered and non-energised lamps. The cumulative amount of carbohydrate released by sequential extraction with phosphate buffer, CDTA, urea and sodium carbonate was between 5.1% and 7.8% lower from leaf material grown under cellulose diacetate-filtered lamps relative to that from leaves grown under non-energised lamps. Abscised leaves were also digested with Driselase, an enzyme mixture extracted from a basidiomycete fungus. No effects of elevated UV radiation were recorded on the amount of carbohydrate released by Driselase digestion. Regression analyses, using data from a previous field decomposition study, suggested that reduced availability of carbohydrates enhanced the colonisation of Q. robur litter by basidiomycete fungi, which then accelerated the decomposition rate of the litter in soil. We recommend that future studies into the effects of UV-B radiation on plant litter decomposition measure not only the concentrations of chemical constituents of litter, but also determine the availability of litter carbon sources to soil microbes, using methods similar to those used here.     

Effects of nitrogen addition and litter properties on litter decomposition and enzyme activities of individual fungi

Litter decomposition is an important process of C and N cycling in the soil. Variation in the response of litter decomposition to nitrogen (N) addition (positive, negative or neutral) has been observed in many field studies. However, mechanism about variability in individual fungal species response to N addition has not yet been well demonstrated in the literature. Therefore, the objective of this study was to investigate the effects of N addition and litter chemistry properties on litter decomposition and enzyme activities of individual fungi. Three fungal species (Penicillium, Aspergillus, and Trichoderma) were isolated from a subtropical mixed forest soil. An incubation experiment was conducted using the individual fungi with two types of litter (leaf of Pinus massoniana and needle of Cryptocarya chinensis) and different N addition levels (0, 50 and 100 for N-deficient treatments, and 500 and 1000 μg N for N-excessive treatments). Cumulative CO₂-C, enzyme activities, and lignin and cellulose loss were measured during the incubation period of 60 days. Litter decomposition and enzyme activities significantly varied with the fungal species, while the N addition and litter types greatly affected fungal enzyme activities. The N treatments significantly increased lignin-rich needle decomposition by lignocellulose decomposers (Penicillium and Aspergillus) but did not affect their leaf decomposition. On the contrary, The N treatments stimulated leaf decomposition by cellulolytic species (Trichoderma) but did not affect its needle decomposition. Correlation analysis showed that lignin in the litter was the key component to affect litter decomposition. Activities of N-acetyl-β-glucosaminidase and phenol oxidase were both positively correlated to litter decomposition. The fungi (Penicillium and Aspergillus) with higher production of N-acetyl-β-glucosaminidase showed higher litter decomposition ability. The low N addition levels stimulated Penicillium and Aspergillus litter decomposition, but they still required more N source (e.g., litter N source) to support decomposition. Depressed fungal litter N uptake (lower N-acetyl-β-glucosaminidase activities) only occurred at the highest N addition level. Litter decomposition of Trichoderma depended more on external N and its litter decomposition capability was the lowest among the three species.     

Effects of fungal inocula on the decomposition of lignin and structural polysaccharides in Pinus sylvestris litter

 Litter bags containing sterile Scots pine (Pinus sylvestris) needles (19.8% lignin, 26.5% cellulose and 0.34% N) were inoculated with two species of fungi in the laboratory and then placed in the litter layer of a pine plantation. Marasmius androsaceus, which can degrade lignocellulose, was initially displaced by other fungal colonisers and was not detected in the litter after 2–3 months; but was re-isolated from the needles after 12 months. Trichoderma viride, which is a cellulolytic species and also antagonistic to other fungi, dominated the litter throughout the experiment. The control litter was naturally colonised by litter fungi. After 12 months, mass losses were similar at 52% for M. androsaceus and 48% for T. viride, compared with 36% for the control litter colonised by a more complex fungal community. Lignin concentrations increased with time in control litter and with T. viride because mass losses of carbohydrates were greater than those of lignin. Litter inoculated with M. androsaceus showed significant lignin decomposition throughout the experiment but cellulose concentrations showed a proportional increase in the first 6 months, suggesting that the fungus was preferentially exploiting hemicellulose and non-structural carbohydrates. Analysis of TFA-extractable sugars (mainly from hemicellulose) and CuO-derived phenylpropanoid moieties from lignin confirmed the differential patterns of resource decomposition which were not evident from total mass losses. During the initial stages of decomposition, T. viride was as effective in utilising structural polysaccharides as the complex fungal community in the control litter. Furthermore, M. androsaceus not only exhibited unexpectedly low cellulolytic activity but also facilitated lignin depolymerisation after the fungus was no longer detectable in the litter. The pre-inoculation of litter with these two fungal species therefore affected the overall dynamics of decomposition at a biochemical level. This study illustrates the importance of understanding the effects and interactions of specific fungi, rather than assumptions about the functional competence of diverse communities, on the processes of litter decomposition. Received: 5 July 2000     

Production of lignocellulose-degrading enzymes and degradation of leaf litter by saprotrophic basidiomycetes isolated from a Quercus petraea forest

Due to the production of lignocellulose-degrading enzymes, saprotrophic basidiomycetes can significantly contribute to the turnover of soil organic matter. The production of lignin- and polysaccharide-degrading enzymes and changes of the chemical composition of litter were studied with three isolates from a Quercus petraea forest. These isolates were capable of fresh litter degradation and were identified as Gymnopus sp., Hypholoma fasciculare and Rhodocollybia butyracea. Within 12 weeks of incubation, H. fasciculare decomposed 23%, R. butyracea 32% and Gymnopus sp. 38% of the substrate dry mass. All fungi produced laccase and Mn-peroxidase (MnP) and none of them produced lignin peroxidase or other Mn-independent peroxidases. There was a clear distinction in the enzyme production pattern between R. butyracea or H. fasciculare compared to Gymnopus sp. The two former species caused the fastest mass loss during the initial phase of litter degradation, accompanied by the temporary production of laccase (and MnP in H. fasciculare) and also high production of hydrolytic enzymes that later decreased. In contrast, Gymnopus sp. showed a stable rate of litter mass loss over the whole incubation period with a later onset of ligninolytic enzyme production and a longer lasting production of both lignin and cellulose-degrading enzymes. The activity of endo-cleaving polysaccharide hydrolases in this fungus was relatively low but it produced the most cellobiose hydrolase. All fungi decreased the C/N ratio of the litter from 24 to 15-19 and Gymnopus sp. also caused a substantial decrease in the lignin content. Analytical pyrolysis mass spectrometry of litter decomposed by this fungus showed changes in the litter composition similar to those caused by white-rot fungi during wood decay. These changes were less pronounced in the case of H. fasciculare and R. butyracea. All fungi also changed the mean masses of humic acid and fulvic acid fractions isolated from degraded litter. The humic acid fraction after degradation by all three fungi contained more lignin and less carbohydrates. Compared to the decomposition by saprotrophic basidiomycetes, litter degradation in situ on the site of fungal isolation resulted in the relative enrichment of lignin and differences in lignin composition revealed by analytical pyrolysis. It can most probably be explained by the participation of non-basidiomycetous fungi and bacteria during natural litter decomposition.     

Low levels of nitrogen addition stimulate decomposition by boreal forest fungi

Climate warming and associated increases in nutrient mineralization may increase the availability of soil nitrogen (N) in high latitude ecosystems, such as boreal forests. These changes in N availability could feed back to affect the decomposition of litter and organic matter by soil microbes. Since fungi are important decomposers in boreal forest ecosystems, we conducted a 69-day incubation study to examine N constraints on fungal decomposition of organic substrates common in boreal ecosystems, including cellulose, lignin, spruce wood, spruce needle litter, and moss litter. We added 0, 20, or 200 μg N to vials containing 200 mg substrate in factorial combination with five fungal species isolated from boreal soil, including an Ascomycete, a Zygomycete, and three Basidiomycetes. We hypothesized that N addition would increase CO₂ mineralization from the substrates, particularly those with low N concentrations. In addition we predicted that Basidiomycetes would be more effective decomposers than the other fungi, but would respond weakly or negatively to N additions. In support of the first hypothesis, cumulative CO₂ mineralization increased from 635 ± 117 to 806 + 108 μg C across all fungal species and substrates in response to 20 μg added N; however, there was no significant increase at the highest level of N addition. The positive effect of N addition was only significant on cellulose and wood substrates which contained very little N. We also observed clear differences in the substrate preferences of the fungal species. The Zygomycete mineralized little CO₂ from any of the substrates, while the Basidiomycetes mineralized all of the substrates except spruce needles. However, the Ascomycete (Penicillium) was surprisingly efficient at mineralizing spruce wood and was the only species that substantially mineralized spruce litter. The activities of β-glucosidase and N-acetyl-glucosaminidase were strongly correlated with cumulative respiration (r = 0.78 and 0.74, respectively), and Penicillium was particularly effective at producing these enzymes. On moss litter, the different fungal species produced enzymes that targeted different chemical components. Overall, our results suggest that fungal species specialize on different organic substrates, and only respond to N addition on low N substrates, such as wood. Furthermore, the response to N addition is non-linear, with the greatest substrate mineralization at intermediate N levels.     

Improved zinc tolerance in Eucalyptus globulus inoculated with Glomus deserticola and Trametes versicolor or Coriolopsis rigida

The potential of interactions between saprophytic and arbuscular mycorrhizal (AM) fungi to improve Eucalyptus globulus grown in soil contaminated with Zn were investigated. The presence of 100 mg kg ⁻¹ Zn decreased the shoot and root dry weight of E. globulus colonized with Glomus deserticola less than in plants not colonized with AM. Zn also decreased the extent of root length colonization by AM and the AM fungus metabolic activity, measured as succinate dehydrogenase (SDH) activity of the fungal mycelium inside the E. globulus root. The saprophytic fungi Trametes versicolor and Coriolopsis rigida increased the shoot dry weight and the tolerance of E. globulus to Zn when these plants were AM-colonized. Both saprophytic fungi increased the percentage of AM root length colonization and elevated G. deserticola SDH activity in the presence of all Zn concentrations applied to the soil. In the presence of 500 and 1000 mg kg⁻¹ Zn, there were higher metal concentrations in roots and shoots of AM than in non-AM plants; furthermore, both saprophytic fungi increased Zn uptake by E. globulus colonized by G. deserticola. The higher root to shoot metal ratio observed in mycorrhizal E. globulus plants indicates that G. deserticola enhanced Zn uptake and accumulation in the root system, playing a filtering/sequestering role in the presence of Zn. However, saprophytic fungi did not increase the root to shoot Zn ratio in mycorrhizal E. globulus plants. The effect of the saprophytic fungi on the tolerance and the accumulation of Zn in E. globulus was mediated by its effect on the colonization and metabolic activity of the AM fungi.     

亚热带2种针叶林土壤碳氮磷储量及化学计量比对混交的响应

针叶林混交阔叶树是改善土壤肥力、增强林地养分循环的重要措施,而混交效应受到针叶树种自身特性的影响,马尾松(Pinus massoniana)和湿地松(P.elliottii)是亚热带地区广泛种植的针叶树种,但目前2种针叶林对阔叶树混交的响应特征还不清楚。选取马尾松、湿地松纯林以及木荷(Schima superba)补植后形成的马尾松—木荷和湿地松—木荷混交林为研究对象,采集剖面土壤样品,测定土壤容重、有机碳(OC)、全氮(TN)和全磷(TP)含量,计算碳氮磷储量及化学计量特征,比较不同森林类型间的异同。混交阔叶树显著增加了马尾松林0—60cm各土层OC含量,而湿地松纯林与其混交林间OC含量无显著差异。同时,混交增加了2种针叶林土壤TN含量。马尾松林混交后0—60cm土层碳储量显著增加95.8%,而混交阔叶树对湿地松林土壤碳储量无显著影响。混交阔叶树后马尾松和湿地松林0—60cm土壤总氮储量分别增加了15.8%和28.4%,但混交对土壤磷储量无显著影响。混交显著增加了马尾松林0—40cm各土层C/N,而降低了湿地松林0—10cm土层C/N。混交阔叶树后马尾松林0—20cm土层C/P和0—10cm土层N/P显著增加,而混交仅增加湿地林0—10cm土层N/P。混交阔叶树增加了针叶林土壤氮储量,但对磷储量无显著影响,同时混交改变了土壤碳氮磷生态化学计量特征。与湿地松林相比,马尾松林土壤养分含量、储量及其化学计量特征对混交的响应更敏感。     

Elevated CO<Subscript>2</Subscript> concentration affected pine and oak litter chemistry and the respiration and microbial biomass of soils amended with these litters

Elevated atmospheric CO₂ concentration ([CO₂]) may change litter chemistry which affects litter decomposability. This study investigated respiration and microbial biomass of soils amended with litter of Pinus densiflora (a coniferous species; pine) and Quercus variabilis (a deciduous species; oak) that were grown under different atmospheric [CO₂] and thus had different chemistry. Elevated [CO₂] increased lignin/N through increased lignin concentration and decreased N concentration. The CO₂ emission from the soils amended with litter produced under the same [CO₂] regime was greater for oak than pine litter, confirming that broadleaf litter with lower lignin decomposes faster than needle leaf litter. Within each species, however, soils amended with high lignin/N litter grown under elevated [CO₂] emitted more CO₂ than those with low lignin/N litter grown under ambient [CO₂]. Such contrasting effects of lignin/N on inter- and intra-species variations in litter decomposition should be ascribed to the effects of other litter chemistry variables including nonstructural carbohydrate, calcium and manganese as well as inhibitory effect of N on lignin decomposition. The microbial biomass was also higher in the soils amended with high lignin/N litter than those with low lignin/N litter probably due to low substrate use efficiency of lignin by microbes. Our study suggests that elevated [CO₂] increases lignin/N for both species, but increased lignin/N does not always reduce soil respiration and microbial biomass. Further study investigating a variety of tree species is required for more comprehensive understanding of inter- and intra-species variations of litter decomposition under elevated [CO₂].     

Dual Inoculation of Arbuscular Mycorrhizal and Phosphate Solubilizing Fungi Contributes in Sustainable Maintenance of Plant Health in Fly Ash Ponds

Fly ash is one of the residues produced during combustion of coal, and its disposal is a major environmental concern throughout coal-based power-generated counties. Deficiencies of essential nutrients, low soil microbial activity, and high-soluble salt concentrations of trace elements are some of the concerns for reclamation of fly ash ponds. The effect of fly-ash-adapted arbuscular mycorrhizal (AM) fungi and phosphate solubilizing fungus Aspergillus tubingensis was studied on the growth, nutrient, and metal uptake of bamboo (Dendrocalamus strictus) plants grown in fly ash. Co-inoculation of these fungi significantly increased the P (150%), K (67%), Ca (106%), and Mg (180%) in shoot tissues compared control plants. The Al and Fe content were significantly reduced (50% and 60%, respectively) due to the presence of AM fungi and A. tubingensis. The physicochemical and biochemical properties of fly ash were improved compared to those of individual inoculation and control. The results showed that combination of AM fungi and A. tubingensis elicited a synergetic effect by increasing plant growth and uptake of nutrients with reducing metal translocation.     

Feeding preferences of the collembolan Onychiurus sinensis for fungi colonizing holm oak litter (Quercus rotundifolia Lam.)

Ten fungi isolated from decaying holm oak leaves (Quercus rotundifolia Lam.) have been presented to the collembolan species Onychiurus sinensis (Hexapoda). The attractiveness and selectivity of the ten fungi was investigated taken into account the effect of the substrate on which the fungus was growing (malt-agar or litter) and the effect of fungal odour. Furthermore, moulting, growth, survival and reproduction of O. sinensis in the presence of each of the ten test fungi were studied. Mucor plumbeus and Trichothecium roseum were the most preferred whatever the culture substrate and their odour was the most attractive. Two fungi (Penicillium spinulosum and the Basidiomycete S41) attracted Collembola by their odour but were not preferred as food sources. The animals could survive and reproduce on a mono-diet of several of our test fungi, but not on the Basidiomycete S41 and on Trichoderma polysporum.     

Organic acid exudation by mycorrhizal Andropogon virginicus L. (broomsedge) roots in response to aluminum

Elevated aluminum (Al) availability limits plant growth on acidic soils. Although this element is found naturally in soils, acidic conditions create an environment where Al solubility increases and toxic forms of Al impact plant function. Plant resistance to Al is often attributed to organic acid exudation from plant roots and the chelation of cationic Al in the rhizosphere. The association of arbuscular mycorrhizal (AM) fungi with the roots of plants may alleviate Al toxicity by altering soil Al availability or plant exposure through the binding of Al to fungal structures or through the influence of fungi on exudation from roots. Diverse communities of AM fungi are found in soil ecosystems and research suggests that AM fungi exhibit functional diversity that may influence plant performance under varying edaphic environments. In the present study, we evaluated acidic isolates of six AM species in their responses to Al. Andropogon virginicus (broomsedge), a warm-season grass that commonly grows in a range of stressful environments including acidic soils, was used as a plant host for Acaulospora morrowiae, Glomus claroideum, Glomus clarum, Glomus etunicatum, Paraglomus brasilianum, and Scutellospora heterogama. Fungal spores were germinated and exposed to 0 or 100 μM Al on filter paper in sand culture or were grown and exposed to Al in sand culture in association with A. virginicus. Short- and long-term responses to Al were evaluated using direct measurements of fungal spore germination, hyphal elongation, and measurements of A. virginicus colonization and plant growth as a phytometer of AM function in symbio. Spore germination and hyphal elongation varied among AM species in response to Al, but patterns were not consistent with the influences of these AM species on A. virginicus under Al exposure. Exposure to Al did not influence colonization of roots, although large differences existed in colonization among fungal species. Plants colonized by G. clarum and S. heterogama exhibited the least reduction in growth when exposed to Al, produced the highest concentrations of Al-chelating organic acids, and had the lowest concentrations of free Al in their root zones. This pattern provides evidence that variation among AM fungi in Al resistance conferred to their plant hosts is associated with the exudation of Al-binding organic acids from roots and highlights the role that AM fungal diversity may play in plant performance in acidic soil environments.     

Site of leaf origin affects how mixed litter decomposes

Recent studies have demonstrated that mass loss, nutrient dynamics, and decomposer associations in leaf litter from a given plant species can differ when leaves of that species decay alone compared to when they decay mixed with other species’ leaves. Results of litter-mix experiments have been variable, however, making predictions of decomposition in mixtures difficult. It is not known, for example, whether interactions among litter types in litter mixes are similar across sites, even for litter mixtures containing the same plant species. To address this issue, we used reciprocal transplants of litter in compartmentalized litterbags to study decomposition of equal-mass litter mixtures of sugar maple (Acer saccharum Marshall) and red oak (Quercus rubra L.) at four forest sites in northwestern Connecticut. These species differ significantly in litter quality. Red oak always has higher lignin concentrations than maple, and here C:N is lower in oak leaves and litter, a pattern often observed when oak coexists with maple. Overall, we observed less mass loss and lower N accumulation in sugar maple and red oak litter mixtures than we predicted from observed dynamics in single-species litterbags. Whether these differences were significant or not depended on the site of origin of the leaves (P<0.02), but there was no significant interaction between sites of decay and the differences in observed and predicted decomposition (P>0.2) . Mixing of leaf litter types could have significant impacts on nutrient cycling in forests, but the extent of the impacts can vary among sites and depends on the origin of mixed leaves even when the species composition of mixes is constant.