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H Ferris - One of the best experts on this subject based on the ideXlab platform.
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ecosystem services of the soil food web after long term application of agricultural management practices
Soil Biology & Biochemistry, 2017Co-Authors: Jeffrey P Mitchell, H Ferris, Xiaoke Zhang, Wenju LiangAbstract:Abstract The structure of soil nematode assemblages was assessed in field plots in the San Joaquin Valley of California which have 16-year management system histories. Attributes of the ecosystem functions of the assemblages were determined in laboratory studies. The four agricultural management systems were no tillage (minimum tillage) with cover crops in the intervals between economic crops, standard tillage with cover crops, minimum tillage without cover crops and standard tillage without cover crops. The economic crops were sorghum and garbanzo beans. A soil column system was used in laboratory studies to evaluate the nitrogen mineralization ecosystem service associated with nematode assemblages in soils from the four management systems compared to that in defaunated soil. In an additional comparison, defaunated soil was amended with mineral fertilizer solution for comparison with the mineralization service of the soil fauna. Management systems using cover crops, which created a continuity of both photosynthetic production and roots in the soil, strongly enhanced the nematode assemblages in the field soil. Management systems with cover crops had greater total abundance, measured as numbers, biomass and metabolic footprints, of nematodes, and also of the functional guilds of nematodes considered important in soil fertility and as prey for predators. Leachates from soil columns with intact nematode assemblages had greater total mineral nitrogen and supported greater plant growth than those from defaunated columns. Soil carbon levels in field plots were strongly affected by the management systems. The biomass and diversity-weighted footprint of Bacterivore and microbivore (Bacterivores plus fungivores) nematodes, in turn, were correlated with levels of soil carbon.
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structure functions and interguild relationships of the soil nematode assemblage in organic vegetable production
Applied Soil Ecology, 2012Co-Authors: H Ferris, Sara Sanchezmoreno, Eric B BrennanAbstract:Abstract The abundance and metabolic footprints of soil nematodes were quantified during four of eight years of an intensive organic vegetable production system. Treatment variables included cover crop mixtures and compost application rates. The abundances of Bacterivore and fungivore nematodes were enhanced by the annual use of winter cover crops but showed no relationship to the level of residual soil organic matter. Metabolic footprints, based on biomass and respiratory activity, were calculated for functional guilds and ecosystem services of the nematode assemblage. The enrichment footprint, representing the ecosystem service of nutrient mineralization, was related to the level of soil organic carbon. It was strongly related to the metabolic footprint of Bacterivore nematodes and both were enhanced in treatments that were cover cropped annually. Cover-cropped treatments also had a slightly higher herbivore footprint, suggesting support of some taxa of plant-feeding nematodes. The structure footprint, reflecting the metabolic activity of higher trophic level nematodes, including the predators of opportunistic species, did not differ among cover crop and compost amendment treatments. However, enrichment footprints were correlated with Bacterivore footprints, which represented the predominantly Bacterivore resources available to predators. Abundance of predators increased as a function of the abundance of those nematode prey that can be amplified by organic inputs. The functional connectance, represented by spatial co-location, between predators and amplifiable prey was greater in treatments with a greater abundance of predators. The functional connectance between predators and herbivore prey, representing a management target, was strongly related to the functional connectance between predators and amplifiable prey. We conclude that cover crops not only affect organisms at the entry level of the web but that resources are also transferred to higher trophic links which increases top-down pressure on plant-parasitic nematodes.
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soil management to enhance Bacterivore and fungivore nematode populations and their nitrogen mineralisation function
Applied Soil Ecology, 2004Co-Authors: H Ferris, Robert C Venette, Kate M ScowAbstract:We tested the hypotheses that management of the soil food web in the fall would enhance grazing on bacteria and fungi by microbivorous nematodes in the spring, consequently increasing N availability in cover-crop driven organic and low-input farming systems. The food web was manipulated by irrigating the dry soil of late summer and/or providing carbon sources. By creating conditions conducive for biological activity, we increased the abundance of Bacterivore and fungivore nematodes in the fall and the following spring. Greater biological activity in the soil enhanced concentrations of mineral N available to the subsequent summer tomato crop. Mineral N concentration in the spring was associated with abundance of Bacterivore nematodes, and with the corresponding Enrichment Index (EI) provided by nematode community analysis. Because environmental conditions that favour increase of Bacterivore nematodes probably also favour other microbial grazers, including protozoa, the abundance of Bacterivore nematodes may be an indicator of overall grazing activity and N mineralisation rates from soil fauna. Decomposition pathways in the spring, inferred from nematode bioindicators, were dominated by bacteria in plots that had been irrigated the previous fall while fungi were more prevalent in those that had not. The responses of omnivore and predator nematodes to our treatments were not consistent and there was no evidence that regulation of opportunist species by predators would be enhanced by the management practices imposed.
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structural and functional succession in the nematode fauna of a soil food web
Applied Soil Ecology, 2003Co-Authors: H Ferris, M M MatuteAbstract:Soil microplots were amended with organic materials of varying nature and complexity but providing similar amounts of carbon. Materials were either placed on the soil surface or incorporated. Unamended and mineral fertilizer control plots were established. Plots were maintained vegetation-free so that the food web activity was fueled by resident soil organic matter and the input material. Enrichment-opportunist Bacterivore nematodes increased rapidly in response to low C/N plant materials and, to a lesser extent, to more complex materials. General-opportunist Bacterivores increased in all plots, but at a slower rate. Fungivore nematodes also increased gradually in all plots but most rapidly in those amended with higher C/N and more complex materials. Indices derived from nematode faunal analysis suggested a constant rate of succession from enrichment-opportunist to general-opportunist Bacterivore guilds across all treatments, probably mediated by bacterial abundance and differences in life course characteristics of the respective taxa. The rate of succession from Bacterivore to fungivore nematodes was greatest in plots receiving high C/N materials. Succession to fungivory, presumably indicating a shift from bacterial to fungal decomposition channels, was slowest in those plots with a high level of organismal metabolic activity, as measured by soil respiration. The cumulative amounts of N mineralized in the plots were directly related to the enrichment index (EI), based on the abundance of opportunistic bacterial- and fungal-feeding nematodes. The amounts of mineralized N were inversely related to the slope of the channel index (CI), that is, the rate at which decomposition changed from bacterial to fungal. Maintenance of adequate soil fertility in systems driven by organic input may require maintenance of food web structure and function as indicated by high levels of enrichment-opportunist Bacterivore nematodes. That will require frequent supply of labile organic sources. Allowing food web succession to guilds that indicate lower mineralization potential will result in lower levels of soil fertility.
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structural and functional succession in the nematode fauna of a soil food web
Applied Soil Ecology, 2003Co-Authors: H Ferris, M M MatuteAbstract:Soil microplots were amended with organic materials of varying nature and complexity but providing similar amounts of carbon. Materials were either placed on the soil surface or incorporated. Unamended and mineral fertilizer control plots were established. Plots were maintained vegetation-free so that the food web activity was fueled by resident soil organic matter and the input material. Enrichment-opportunist Bacterivore nematodes increased rapidly in response to low C/N plant materials and, to a lesser extent, to more complex materials. General-opportunist Bacterivores increased in all plots, but at a slower rate. Fungivore nematodes also increased gradually in all plots but most rapidly in those amended with higher C/N and more complex materials. Indices derived from nematode faunal analysis suggested a constant rate of succession from enrichment-opportunist to general-opportunist Bacterivore guilds across all treatments, probably mediated by bacterial abundance and differences in life course characteristics of the respective taxa. The rate of succession from Bacterivore to fungivore nematodes was greatest in plots receiving high C/N materials. Succession to fungivory, presumably indicating a shift from bacterial to fungal decomposition channels, was slowest in those plots with a high level of organismal metabolic activity, as measured by soil respiration. The cumulative amounts of N mineralized in the plots were directly related to the enrichment index (EI), based on the abundance of opportunistic bacterial- and fungal-feeding nematodes. The amounts of mineralized N were inversely related to the slope of the channel index (CI), that is, the rate at which decomposition changed from bacterial to fungal. Maintenance of adequate soil fertility in systems driven by organic input may require maintenance of food web structure and function as indicated by high levels of enrichment-opportunist Bacterivore nematodes. That will require frequent supply of labile organic sources. Allowing food web succession to guilds that indicate lower mineralization potential will result in lower levels of soil fertility. © 2003 Elsevier Science B.V. All rights reserved.
Karel Šimek - One of the best experts on this subject based on the ideXlab platform.
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Ecological Traits of the Algae-Bearing Tetrahymena utriculariae (Ciliophora) from Traps of the Aquatic Carnivorous Plant Utricularia reflexa.
The Journal of eukaryotic microbiology, 2016Co-Authors: Karel Šimek, Gianna Pitsch, Michaela M. Salcher, Dagmara Sirová, Tanja Shabarova, Thomas PoschAbstract:Trap fluid of aquatic carnivorous plants of the genus Utricularia hosts specific microbiomes consisting of commensal pro- and eukaryotes of largely unknown ecology. We examined the characteristics and dynamics of bacteria and the three dominant eukaryotes, i.e. the algae-bearing ciliate Tetrahymena utriculariae (Ciliophora), a green flagellate Euglena agilis (Euglenophyta), and the alga Scenedesmus alternans (Chlorophyta), associated with the traps of Utricularia reflexa. Our study focused on ecological traits and life strategies of the highly abundant ciliate whose biomass by far exceeds that of other eukaryotes and bacteria independent of the trap age. The ciliate was the only Bacterivore in the traps, driving rapid turnover of bacterial standing stock. However, given the large size of the ciliate and the cell-specific uptake rates of bacteria we estimated that bacterivory alone would likely be insufficient to support its apparent rapid growth in traps. We suggest that mixotrophy based on algal symbionts contributes significantly to the diet and survival strategy of the ciliate in the extreme (anaerobic, low pH) trap-fluid environment. We propose a revised concept of major microbial interactions in the trap fluid where ciliate bacterivory plays a central role in regeneration of nutrients bound in rapidly growing bacterial biomass.
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spatio temporal patterns of bacterioplankton production and community composition related to phytoplankton composition and protistan bacterivory in a dam reservoir
Aquatic Microbial Ecology, 2008Co-Authors: Karel Šimek, Jan Jezbera, Karel Hornák, Josef Hejzlar, Jirri Nedoma, Petr Znachor, Jaromir SedaAbstract:Seasonal changes in the abundance and production of epilimnetic bacterioplankton, protistan abundance and bacterivory, and extracellular phytoplankton production (EPP) were stud- ied at 3 sampling stations (DAM, MIDDLE and RIVER) located along the longitudinal axis of the canyon-shaped, meso-eutrophic R ˇ imov reservoir (Czech Republic). We found that at the river inflow (RIVER) compared to lacustrine parts of the reservoir (MIDDLE and DAM), different sources of organic carbon and of bacterial mortality control bacterioplankton dynamics and community compo- sition. At the RIVER site, EPP accounted for a negligible part of bacterial carbon demand, thus indi- cating the prominent role of allochthonous sources of organic substrates in the river inflow. In addi- tion, protistan bacterivory removed there, on average, only 9% of bacterial production. In contrast, at the lacustrine MIDDLE and DAM stations, protistan bacterivory accounted for 47 and 78% of bacte- rial production, respectively. Moreover, at these stations EPP was an autochthonous source of organic carbon sufficient to meet bacterial carbon demand and EPP was tightly correlated with bacterial car- bon demand (DAM, r 2 = 0.589, p < 0.005; MIDDLE, r 2 = 0.716, p < 0.001). At the DAM site, we ana- lyzed changes in EPP in relationship to phytoplankton community dynamics and found that crypto- phytes were associated with EPP. Only 2 algal groups, cryptophytes in a spring-early-summer period and diatoms in a summer-fall period, clearly dominated the phytoplankton. Changes in phytoplank- ton composition were related to changes in bacterial community composition studied by means of group-specific rRNA-targeted oligonucleotide probes. A trend of increased proportions of certain bacterial groups, mainly of the genus-like R-BT065 subcluster of Betaproteobacteria, was detected for the periods of high EPP levels, dominated by cryptophytes. More than 52% of the seasonal vari- ability in the abundance of the R-BT065 cluster was explained by changing EPP levels that indicated a tight taxon-specific algal-bacterial relationship.
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prey selectivity of bacterivorous protists in different size fractions of reservoir water amended with nutrients
Environmental Microbiology, 2006Co-Authors: Karel Šimek, Jan Jezbera, Karel HorňakAbstract:An experiment designed to examine food preferences of heterotrophic nanoflagellates (HNF) grazing on bacterioplankton was performed in the freshwater Rimov reservoir (Czech Republic). Water samples were size-fractionated to obtain < 5 microm filtrate containing bacteria and HNF. To manipulate resource availability, < 5 microm treatments were incubated in dialysis bags submerged in the barrels filled with the unfiltered reservoir water amended with either orthophosphate or glucose or combination of both. We employed rRNA-targeted probes to assess HNF prey preferences by analysing bacterial prey in HNF food vacuoles compared with available bacteria. Actinobacteria (the HGC69a probe) were avoided by HNF in all treatments. Cytophaga-Flavobacterium-Bacteroidetes bacteria (the CF319a probe) were positively selected mainly in treatments in which bacteria were heavily grazed, the < 5 microm treatments, but this trend was less pronounced towards the end of the study. The members of a small subcluster of Betaproteobacteria (the R-BT065 probe) were mostly positively selected. The nutrient amendments differentially affected bacterioplankton dynamics in almost all treatments, and together with the size fractionation, altered HNF overall bacterivory as well as prey selection. Analyses of Bacterivores in unfiltered treatments allowed to detect the effect of different protists on shifts in HNF selectivity observed in < 5 microm compared with unfiltered treatments.
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influence of top down and bottom up manipulations on the r bt065 subcluster of β proteobacteria an abundant group in bacterioplankton of a freshwater reservoir
Applied and Environmental Microbiology, 2005Co-Authors: Karel Šimek, Jan Jezbera, Karel Hornák, Jirri Nedoma, Josep M Gasol, Michal Masin, Michael SchauerAbstract:´mov reservoir (Czech Republic). The effects of protistan grazing on BCC were examined using a size fractionation approach. Water from the dam area with only bacteria (<0.8 m), bacteria and heterotrophic nanoflagellates (<5 m), or whole water were incubated in situ inside dialysis bags. Top-down or predator manipulations (size fractionation) were also combined with bottom-up or resource manipulations, i.e., transplantation of samples to the middle and upper inflow parts of the reservoir with increased phosphorus availability. Significant genotypic shifts in BCC occurred with transplantation as indicated by denaturing gradient gel electrophoresis. Using different probes for fluorescence in situ hybridization, we found that 10 to 50% of total bacteria were members of the phylogenetically small cluster of -proteobacteria (targeted with the probe R-BT065). These rod-shaped cells of very uniform size were vulnerable to predation but very fast growing and responded markedly to the different experimental manipulations. In all the grazer-free treatments, the members of the R-BT065 cluster showed the highest net growth rates of all studied bacterial groups. Moreover, their relative abundance was highly correlated with bacterial bulk parameters and proportions of bacteria with high nucleic acid (HNA) content. In contrast, increasing protistan bacterivory yielded lower proportions of R-BT065-positive and HNA bacteria substituted by increasing proportions of the class Actinobacteria, which profited from the enhanced protistan bacterivory.
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Role of diatom-attached choanoflagellates of the genus Salpingoeca as pelagic Bacterivores
Aquatic Microbial Ecology, 2004Co-Authors: Karel Šimek, Jan Jezbera, Karel Hornák, Jaroslav Vrba, Jaromir SedaAbstract:We studied the ecological role of choanoflagellates of the genus Salpingoeca (possibly S. amphoridium) attached to the colonial diatoms Asterionella formosa and Fragilaria crotonensis in the Rˇ imov reservoir (South Bohemia). The choanoflagellate was found only on these 2 species of diatoms (0 to 35 choanoflagellate cells per diatom colony). It is clearly identifiable in natural samples, and is a highly efficient planktonic Bacterivore. In 2 field experiments (Expt 1 in June 2000 and Expt 2 in September 2002) we estimated in situ rates of bacterivory using fluorescently labeled bacteria (FLB) as tracers. There was a linear increase in the number of FLB per choanoflagellate during the first 30 min of incubation, with only 8 to 16% of individuals within the natural populations displaying no ingestion of FLB. Taxon-specific bacteria uptake rate of Salpingoeca spp. was 35 to 65 bacteria cell -1 h -1 . In Expt 2, by manipulating phosphorus (P) and organic carbon availability (glucose), we also examined how alga host and bacterial prey abundances can affect the dynamics of Salpingoeca and of other bacterivorous heterotrophic nanoflagellates (HNF). P additions increased the growth of F. crotonensis and subsequently also that of the attached Salpingoeca sp. In contrast, glucose addi- tion produced a marked development of small, free-swimming chrysomonads which competed with the choanoflagellate for the bacteria. Overall, across all experimental treatments Salpingoeca spp. grazing accounted for 11 to 64% of the total protistan grazing and for 6 to 49% of the daily removal rate of the bacterial standing stock. Our data indicate that given a sufficient abundance of suitable host algae, which possibly provide a refuge from potential grazers, and efficient grazing of free- swimming HNF by zooplankton, this single choanoflagellate taxon can temporarily constitute the most important pelagic Bacterivore in the reservoir.
Senyu Chen - One of the best experts on this subject based on the ideXlab platform.
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swine manure application enriches the soil food web in corn and soybean production
Journal of Nematology, 2019Co-Authors: Zane J Grabau, Jeffrey A Vetsch, Senyu ChenAbstract:: Strategies for managing plant-parasitic nematodes while promoting soil quality are needed in corn (Zea mays) and soybean (Glycine max) cropping systems. Therefore, a series of two-year experiments were conducted in Minnesota to determine the simple and interactive effects of manure or conventional fertilizer and short-term crop rotation on the nematode community, a sensitive indicator of soil ecology. The two-year crop sequences were Sus-Sus, Res-Sus, and Corn-Sus, where Sus and Res are soybean susceptible and resistant to Heterodera glycines (soybean cyst nematode: SCN), respectively. The fertilizer treatments were liquid swine manure, conventional phosphorus (P)-potassium (K) fertilizer, and no fertilizer. Crop sequence and fertilizer choice had individual main effects, but did not have an interactive effect on the nematode community. Swine manure affected the nematode community in ways that conventional PK fertilizer or no fertilizer did not, substantially enhancing populations of Bacterivores in colonizer-persister group 1, which are extreme enrichment opportunists. Manure application did not affect other groups of free-living nematodes and decreased nematode community diversity. Conventional PK fertilizer did not influence the nematode community compared with untreated control. The effects of short-term crop sequences were much less pronounced and consistent than manure application, but corn altered the environment to favor fungivores while soybean increased Bacterivore abundances. : Strategies for managing plant-parasitic nematodes while promoting soil quality are needed in corn (Zea mays) and soybean (Glycine max) cropping systems. Therefore, a series of two-year experiments were conducted in Minnesota to determine the simple and interactive effects of manure or conventional fertilizer and short-term crop rotation on the nematode community, a sensitive indicator of soil ecology. The two-year crop sequences were Sus-Sus, Res-Sus, and Corn-Sus, where Sus and Res are soybean susceptible and resistant to Heterodera glycines (soybean cyst nematode: SCN), respectively. The fertilizer treatments were liquid swine manure, conventional phosphorus (P)-potassium (K) fertilizer, and no fertilizer. Crop sequence and fertilizer choice had individual main effects, but did not have an interactive effect on the nematode community. Swine manure affected the nematode community in ways that conventional PK fertilizer or no fertilizer did not, substantially enhancing populations of Bacterivores in colonizer-persister group 1, which are extreme enrichment opportunists. Manure application did not affect other groups of free-living nematodes and decreased nematode community diversity. Conventional PK fertilizer did not influence the nematode community compared with untreated control. The effects of short-term crop sequences were much less pronounced and consistent than manure application, but corn altered the environment to favor fungivores while soybean increased Bacterivore abundances.
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swine manure nematicides and long term tillage change soil ecology in corn and soybean production
Agronomy Journal, 2018Co-Authors: Zane J Grabau, Jeffrey A Vetsch, Senyu ChenAbstract:Corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] are important crops and a major part of the US landscape. Soybean and corn production practices influence soil ecology, and good soil quality is essential for crop productivity. Fertilizer application, tillage, and pesticide application are foundational practices in these crops, and the nematode community is a useful indicator of changes in soil ecology. Therefore, the nematode community was assessed in a series of 2-yr experiments in corn and soybean production. Long-term conventional tillage and minimum tillage treatments were in place at the study site for 14 yr at the start of the study. Additional treatments were combinations of conventional fertilizers (N-P-K and N-P-K-S), liquid swine manure, and granular nematicide (aldicarb or terbufos). Manure application consistently and substantially increased Bacterivore abundances compared with conventional fertilizers or untreated control, with effects continuing over a year after application. Bacterivores are resource opportunists, so this indicates that manure application enriched the soil food web in ways that conventional fertilizers did not. Tillage also enriched the soil food web, based on increased Bacterivore and fungivore abundances, albeit inconsistently between rotations. Aldicarb nematicide was generally effective against plant-parasitic nematodes but also decreased abundances of nontarget free-living nematodes, albeit inconsistently. Omnivores and predators had relatively small abundances throughout the study, and neither tillage nor fertilizer application affected these nematodes. In summary, agricultural practices influenced soil ecology, and manure application had the strongest influence among the practices tested, shifting the food web to an enriched condition.
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influence of long term corn soybean crop sequences on soil ecology as indicated by the nematode community
Applied Soil Ecology, 2016Co-Authors: Zane J Grabau, Senyu ChenAbstract:Abstract In the Midwestern United States, corn–soybean rotation is an essential agricultural practice, but relatively little is known about the impact of different corn–soybean cropping sequences on soil ecology. A long-term research site in Waseca, Minnesota was established in 1982 to study corn–soybean rotation. At the site, various corn–soybean crop sequences can be compared each year including corn and soybean in 1 to 5 years of monoculture and continuous monoculture of each crop. Additionally, granular nematicides (terbufos or aldicarb) have been applied to half of each plot since 2010 to minimize nematode populations, particularly plant-parasitic nematodes, across crop sequences. The nematode community, a sensitive indicator of changes in soil ecology, was assessed at this site to determine the impact of corn–soybean crop sequences and nematicide application on the soil ecosystem. Nematicide application was effective against target nematodes, herbivores, but also impacted non-target nematodes and thus soil ecology. Nematicide application decreased fungivore and Bacterivore populations, diversity, and maturity; but significantly increased enrichment compared to no nematicide application. The nematode community and thus soil ecology was significantly different in corn compared to soybean cropping systems and changed most during initial years after switching crops. Cropping systems in corn supported significantly greater fungivore populations, fungal decomposition pathways, more diversity, and a more mature ecosystem compared to soybean systems. Soybean systems supported significantly greater Bacterivore populations and a more disturbed, enriched ecosystem. These differences between corn and soybean systems demonstrate that each crop has a distinct impact on the soil ecosystem.
T. E. Miller - One of the best experts on this subject based on the ideXlab platform.
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Modelling the relationship between a pitcher plant (Sarracenia purpurea) and its phytotelma community: mutualism or parasitism?
Functional Ecology, 2008Co-Authors: Nicolas Mouquet, Tanguy Daufresne, S. M. Gray, T. E. MillerAbstract:1. To improve our understanding of the relationship between the pitcher plant ( Sarracenia purpurea ) and the phytotelma community inhabiting its leaves we built an exploratory, mechanistic model based on stochiometric constraints on carbon and nitrogen associated with prey decomposition. 2. Our theoretical results suggest that the phytotelma community is acting as a mineralizing system producing nitrogen for the plant. This is confirmed by data collected in the field and in the literature, that show the amount of nitrogen produced by the decomposition of prey is sufficiently high to be considered as a major source of nitrogen for the plant. 3. In our model, nitrogen yield is higher if the phytotelma community is restricted to bacteria alone than when the full food web is present. Nitrogen availability is negatively affected by Bacterivores (rotifers and protozoa mostly) and positively affected by a cascading effect of mosquito larvae. 4. When sedimentation rate is high, mosquitoes have a global positive effect on nitrogen production because they indirectly reduce the amount of nitrogen lost through sedimentation more than they export nitrogen through pupation. On the other hand, when sedimentation rate is low there is a hump-shaped relationship between the uptake rate of Bacterivores by mosquito larvae and the nitrogen yield in the plant. 5. We conclude that plant–bacteria and plant–mosquito interactions are predominantly mutualistic, whereas plant–Bacterivore interactions are predominantly parasitic. Our work also illustrates how ecosystem properties (here nitrogen production by the phytotelma community) can be understood as a function of trophic complexity and can be seen as a product of selection at the scale of a community.
Wenju Liang - One of the best experts on this subject based on the ideXlab platform.
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ecosystem services of the soil food web after long term application of agricultural management practices
Soil Biology & Biochemistry, 2017Co-Authors: Jeffrey P Mitchell, H Ferris, Xiaoke Zhang, Wenju LiangAbstract:Abstract The structure of soil nematode assemblages was assessed in field plots in the San Joaquin Valley of California which have 16-year management system histories. Attributes of the ecosystem functions of the assemblages were determined in laboratory studies. The four agricultural management systems were no tillage (minimum tillage) with cover crops in the intervals between economic crops, standard tillage with cover crops, minimum tillage without cover crops and standard tillage without cover crops. The economic crops were sorghum and garbanzo beans. A soil column system was used in laboratory studies to evaluate the nitrogen mineralization ecosystem service associated with nematode assemblages in soils from the four management systems compared to that in defaunated soil. In an additional comparison, defaunated soil was amended with mineral fertilizer solution for comparison with the mineralization service of the soil fauna. Management systems using cover crops, which created a continuity of both photosynthetic production and roots in the soil, strongly enhanced the nematode assemblages in the field soil. Management systems with cover crops had greater total abundance, measured as numbers, biomass and metabolic footprints, of nematodes, and also of the functional guilds of nematodes considered important in soil fertility and as prey for predators. Leachates from soil columns with intact nematode assemblages had greater total mineral nitrogen and supported greater plant growth than those from defaunated columns. Soil carbon levels in field plots were strongly affected by the management systems. The biomass and diversity-weighted footprint of Bacterivore and microbivore (Bacterivores plus fungivores) nematodes, in turn, were correlated with levels of soil carbon.
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soil microbial food web responses to free air ozone enrichment can depend on the ozone tolerance of wheat cultivars
Soil Biology & Biochemistry, 2012Co-Authors: Qi Li, Xiaoke Zhang, Caiyan Lu, Yong Jiang, Wenju LiangAbstract:Soil processes are driven by soil organisms and their interactions with plants and soil abiotic conditions. Climate changes may directly or indirectly alter soil processes and the organisms mediating these processes. Although aboveground influences of ozone have been studied widely on agroecosystems, the effects on belowground processes are poorly understood. This study aimed to investigate the effects of elevated ozone concentration [O3] on the components of soil microbial food webs and compare their responses between ozone-sensitive and ozone-tolerant wheat cultivars. The responses of soil biota to elevated [O3] varied between the two wheat cultivars. Fungal PLFA and the fungi to bacteria ratio decreased following elevated [O3], especially in the rhizospheric soil of ozone-tolerant wheat. Nematode functional guilds were sensitive to elevated [O3] and cultivar effects. At wheat jointing stage, Bacterivores belonging to K-strategies decreased following elevated [O3], while fungivores exhibited a reverse trend. The abundance of flagellates decreased in ozone-tolerant wheat, but increased in ozone-sensitive wheat following elevated [O3]. However, an opposite trend was found in the Bacterivores belonging to r-strategies. In conclusion, wheat cultivars play an important role in determining the effects of elevated [O3] on soil food web. The responses of soil biota to elevated [O3] were greater in ozone-tolerant wheat than in ozone-sensitive wheat, which may in turn have influenced soil organic matter decomposition and nutrient turnover.
