We explore empirical and theoretical evidence for the functional significance of plant-litter diversity and the extraordinary high diversity of decomposer organisms in the process of litter ...decomposition and the consequences for biogeochemical cycles. Potential mechanisms for the frequently observed litter-diversity effects on mass loss and nitrogen dynamics include fungi-driven nutrient transfer among litter species, inhibition or stimulation of microorganisms by specific litter compounds, and positive feedback of soil fauna due to greater habitat and food diversity. Theory predicts positive effects of microbial diversity that result from functional niche complementarity, but the few existing experiments provide conflicting results. Microbial succession with shifting enzymatic capabilities enhances decomposition, whereas antagonistic interactions among fungi that compete for similar resources slow litter decay. Soil-fauna diversity manipulations indicate that the number of trophic levels, species identity, and the presence of keystone species have a strong impact on decomposition, whereas the importance of diversity within functional groups is not clear at present. In conclusion, litter species and decomposer diversity can significantly influence carbon and nutrient turnover rates; however, no general or predictable pattern has emerged. Proposed mechanisms for diversity effects need confirmation and a link to functional traits for a comprehensive understanding of how biodiversity interacts with decomposition processes and the consequences of ongoing biodiversity loss for ecosystem functioning.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, INZLJ, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK, ZRSKP
Polyethylene film is one of the most common types of recalcitrant plastic waste materials. Information regarding the fate of plastic films in soil is scarce compared to the fate of plastic films in ...aquatic environments. The aim of this study was to evaluate the effects of soil fauna and of impregnation of polyethylene films with oil on the colonization of low-density polyethylene films by prokaryotic communities. The field experiment was performed in a monsoon tropical forest (Vietnam). Polyethylene films were incubated in thermally pre-defaunated soil isolated from the surrounding soil by a stainless steel mesh. Three mesh sizes were used, allowing access to different size groups of soil fauna. The diversity, taxonomic structure and co-occurrence patterns in prokaryotic communities were studied using high-throughput sequencing of 16S rRNA gene libraries. The prokaryotic communities that formed on polyethylene films were slightly different from those inhabiting the surrounding soil. Contrary to our expectations, no difference in the diversity of prokaryotes was observed between microcosms with different mesh sizes. Oil impregnation also had only a minor influence on the prokaryotic community structure. Polyethylene films incubated in microcosms with soil appeared to be colonized by various consortia of prokaryotes as a barren and inert surface.
Display omitted
•The effects of soil fauna and oil impregnation on the prokaryotic colonization of polyethylene films were studied.•The field experiment was performed in a monsoon tropical forest (southern Vietnam).•Soil fauna activity did not affect the structure or diversity of prokaryotic communities on polyethylene films.•Polyethylene films appear to be colonized by various consortia of prokaryotes as a barren and inert surface.
Aims
Experimental data concerning possible trophic relationships between phorophytes and epiphytes are contradictory. Several studies have indirectly shown that epiphytes affect the nitrogen cycle in ...tropical forests, but the degree of interaction between nutrition cycles of epiphytes and phorophytes remains unclear. We hypothesised that, in the case of preferential usage of autochthonous sources, a correlation between isotopic composition of epiphytes and phorophytes would be observed, whereas no such correlation suggests mainly external (atmospheric) N sources.
Methods
To identify the trophic relationship between epiphytes and phorophytes, the isotopic composition of nitrogen was studied in soils, phorophytes, epiphytes, and canopy plants having access to autochthonous nitrogen, such as parasites, ground-rooted climbers, or carnivorous plants. The study was conducted in three habitats in southern Vietnam: a savanna-like forest on Phu Quoc Island, a montane forest in Bidoup and a lowland forest in Cat Tien.
Results
Isotopic composition of nitrogen was similar in different taxonomic and morphological groups of epiphytes. Indicating the dependence on wet atmospheric deposits, all epiphytes were 2–4‰ depleted in
15
N relative to phorophytes and canopy plants having access to autochthonous nitrogen. A correlation in nitrogen isotopic composition between phorophytes and epiphytes was observed in two of the three studied habitats (R
2
= 0.47 and 0.74 for Phu Quoc and Bidoup, respectively).
Conclusions
At the ecosystem level, the epiphytic community can have different degree of dependence on autochthonous and external nitrogen sources. Both, bulk δ
15
N values and the correlation between
15
N content of epiphytes and phorophytes can indicate a relative contribution of autochthonous and allochthonous nitrogen in the nutrition of epiphytic plants.
Many field and laboratory studies have demonstrated that the addition of easily available carbon can increase rates of decomposition of plant litter or humified soil organic matter, though opposite ...trends are also common. In boreal forests, a large part of labile carbon enters soil via tree roots and ectomycorrhizal (EM) network. The influence of increased C availability and the presence of EM roots on litter decomposition was studied in a long-term field experiment in a 50-year-old
Picea abies plantation. Litterbags containing litter of three species (
Populus tremula,
Quercus robur, or
P. abies) were buried to the depth of ca. 2.5
cm. The experiment was set up in a full-factorial design with carbon availability and presence of roots as factors. Carbon was added as an aqueous sucrose solution (50
g
C
m
−2) every second week during snow-free period. Spruce roots around and underneath experimental plots were cut once a month. Subsets of litterbags were analysed after 12, 21 and 24 months. The serial dilution technique was used to assess the fungal community composition. The addition of labile carbon led to a strong decrease in litter decomposition rates, associated with consistent shifts in the composition of saprotrophic microfungal communities, and to an increase in the overall density of culturable fungal species (
r-strategists), but not of specialized cellulolytic microfungi (
K-strategists), isolated on Hutchinson agar. Sucrose addition did not affect the number of species isolated but the dominance structure was shifted toward the domination of the 2–4 most abundant species. The presence of EM roots significantly reduced moisture content in decomposing litter but had only weak and inconsistent effect on the decomposition rates and on the community composition of saprotrophic microfungi; these effects did not depend on the level of carbon availability.
The development of stable isotope techniques is one of the main methodological advances in ecology of the last decades of the 20th century. Many biogeochemical processes are accompanied by changes in ...the ratio between stable isotopes of carbon and nitrogen ( super(12)C/ super(13)C and super(14)N/ super(15)N), which allows different ecosystem components and different ecosystems to be distinguished by their isotopic composition. Analysis of isotopic composition makes it possible to trace matter and energy flows through biological systems and to evaluate the rate of many ecological processes. The main concepts and methods of stable isotope ecology and patterns of stable isotope fractionation during organic matter decomposition are considered with special emphasis on the fractionation of isotopes in food chains and the use of stable isotope studies of trophic relationships between soil animals in the field.
► The addition of easily available C strongly decreases decomposition rates of plant litter. ► Possible mechanisms of negative priming are preferential utilization and catabolic repression. ► ...Disrupting of the mycelial connection decreases decomposition rates of N-poor litter. ► Disruption of mycelial connection does not necessary decrease the net N input into the litter.
The translocation of nutrients by networks of fungal hyphae is an important mechanism controlling decomposition rates of plant residues. We performed a 15-month long field experiment aiming to assess the effects of the C and N availability and the role of the mycelial connection between litter and underlying mineral soil on the decomposition rates and levels of enzyme activities in plant litter. Litterbags containing either N-rich litter of alder (
Alnus glutinosa) or N-poor litter of aspen (
Populus tremula) were exposed on top of A-horizon of forest soil. The experiment was set up in a full-factorial design with litter species, C and N availability, and presence of mycelial connection as factors. Labile C and N were added as sucrose and ammonium nitrate solutions in four combinations: −C−N, +C−N, −C+N and +C+N. To disrupt the mycelial connection between litter and soil half of the litterbags were slightly moved, whereas others were left untouched. All experimental manipulations were performed every ten days during snow-free period. At the natural levels of C and N availability, N-poor aspen litter, but not N-rich alder litter, accumulated significant amounts of N. The addition of easily available C decreased the activity of xylanase and phenoloxidase and reduced litter decomposition rates of aspen litter; in alder litter similar but less pronounced trends were also observed. The severance of the mycelial connection between plant litter and underlying soil generally decreased xylanase activity and decomposition rates of the N-limited litter, likely due to the reduced presence of basidiomycete fungi in the litterbags. This effect was not observed, if the N-limitation was artificially relieved by the addition of easily available N, likely due to the increased activity of bacteria and microfungi.
Even though Fusarium is an important genus of fungi, both phytopathogenic and toxigenic, that infects various cereals worldwide, the existing methods of Fusarium spp. suppression in agroecosystems ...are not sufficiently operative. On the other hand, being tightly linked to plant residues it its life cycle, Fusarium spp. could be expected to interact with detrital food webs. Over the past 30 years, 21 quantitative studies have been published on the effect of soil fauna on the abundance and pathogenicity of Fusarium species. In this paper, we summarize the available data on the trophic interactions between Fusarium species and soil organisms, particularly soil fauna.
On the average, Fusarium species are shown to be 2.4 times (95% CI, 1.3–4.4) more preferable as food source compared to other soil fungi for earthworms and 1.7 times (95% CI, 1.4–2.0) for collembolans. Compared to other species of soil fungi, feeding on Fusarium spp. increases the growth of soil fauna by 18.2% (95% CI, 12.4–24.1). Soil animals reduce the content of deoxynivalenol (DON) in Fusarium-infected wheat straw and soil by 24.3 mg kg−1 (95% CI, 18.0–30.6). Overall, soil fauna diminish the abundance of Fusarium species in experimental systems by 20.0% (95% CI, 9.9–30.1). Thus, our meta-analysis suggests that soil fauna is capable of suppressing the abundance of Fusarium spp. in arable ecosystems, while manipulating the structure of detrital food webs might be useful for affecting the soil phase of Fusarium species. However, a very limited array of potential biocontrol agents has been tested, with studies on the feeding interactions between Fusarium species and soil mites and nematodes being particularly scarce.
•Meta-analysis of interactions between soil fauna and Fusarium species was performed.•Feeding on Fusarium spp. increased the growth of soil fauna by 18.2%.•Soil fauna decreased the abundance of Fusarium spp. by 20.0%.•Fusarium spp. were 1.7 times more preferable for collembolans than other fungi.•Manipulating detrital food webs might be used to suppress the soil phase of Fusarium species.
In the Memory of Our Teacher Uvarov, A. V.; Tiunov, A. V.
Biology bulletin of the Russian Academy of Sciences,
09/2019, Letnik:
46, Številka:
5
Journal Article
Recenzirano
Students, colleagues, and friends of Bella Rafailovna Striganova as well as the Editorial Board of the journal
Biology Bulletin
, which she headed for many years, dedicate this issue of the journal ...to her memory. The subjects of the articles represent the most important areas of research for B.R. Striganova: regularities of geographic changes in taxonomic diversity, abundance, and landscape distribution of soil communities; trophic relations of pedobionts and zoomicrobial relationships; functioning of detrital food webs; the importance, conservation, and rational use of the biological diversity of natural systems; soil zoology and problems of the national economy; problems of evolutionary theory.
Activity of soil decomposer microorganisms is generally limited by carbon availability, but factors controlling saprophagous soil animals remain largely unknown. In contrast to microorganisms, ...animals are unable to exploit mineral nutrient pools. Therefore, it has been suggested that soil animals, and earthworms in particular, are limited by the availability of nitrogen. In contrast to this view, a strong increase in density and biomass of endogeic earthworms in response to labile organic carbon addition has been documented in field experiments. The hypothesis that the growth of endogeic earthworms is primarily limited by carbon availability was tested in a laboratory experiment lasting for 10 weeks. In addition, it was investigated whether the effects of earthworms on microbial activity and nutrient mineralization depend on the availability of carbon resources. We manipulated food availability to the endogeic earthworm species Octolasion tyrtaeum by using two soils with different organic matter content, providing access to different amounts of soil, and adding labile organic carbon (glucose) enriched in ¹³C.Glucose addition strongly increased the growth of O. tyrtaeum. From 8 to 17% of the total C in earthworm tissue was assimilated from the glucose added. Soil microbial biomass was not strongly affected by the addition of glucose, though basal respiration was significantly increased and up to 50% of the carbon added as glucose was incorporated into soil organic matter. The impact of earthworms on the mineralization and leaching of nitrogen depended on C availability. As expected, in C-limited soil, the presence of earthworms strongly increased nitrogen leaching. However, when C availability was increased by the addition of glucose, this pattern was reversed, i.e. the presence of O. tyrtaeum decreased nitrogen leaching and its availability to soil microflora. We conclude that irrespective of the total carbon content of soils, O. tyrtaeum was primarily limited by carbon, and that increased carbon availability allowed earthworms to be more effective in mobilizing N. The presence of earthworms increases C limitation of soil microorganisms, due to increased availability of N and P in earthworm casts or a direct depletion of easily available carbon resources by earthworms.
The number and taxonomic structure of the yeast complexes were investigated in the full profiles of the soddy-podzolic soil (Central Forest State Nature Biosphere Reserve), dark gray forest soil ...(Kaluzhskie Zaseki Reserve), and chernozem (Privolzhskaya Forest-Steppe Reserve). In all these soils, the number of yeasts was maximal (10
4
CFU/g) directly under the litter; it drastically decreased with the depth. However, at the depth of 120–160 cm, the number of yeasts significantly increased in all the soils; their maximum was found in the illuvial horizon of the soddy-podzolic soil. Such a statistically significant increase in the number of yeasts at a considerable depth was found for the first time. Different groups of yeasts were present in the yeast communities of different soils. The species structure of yeast communities changed little in each soil: the same species were isolated both from the soil surface and from the depth of more than 2 m. The results showed that yeasts could be used for soil bioindication on the basis of specific yeast complexes in the profiles of different soil types rather than individual indicative species.
