Effects of Collembola on root properties of two competing ruderal plant species

Plant roots compete for nutrients mineralised by the decomposer community in soil. By affecting microbial biomass and activity Collembola influence the nutrient availability to plants. We investigated the effect of Collembola (Protaphorura fimata Gisin) on growth and competition between of two plant species, Cirsium arvense L (creeping thistle) and Epilobium adnatum Griseb. (square-stemmed willow herb), in a laboratory experiment. Two seedlings of each plant species were planted in rhizotrons either in combination or in monoculture (intra- and interspecific competition). Interspecific competition strongly reduced total biomass of C. arvense whereas E. adnatum suffered most from intraspecific competition. Collembola neither affected the competitive relationship of the two plant species nor shoot and root biomass. Although Collembola did not affect total root biomass they influenced root morphology of both plant species. Roots grew longer and thinner and had more root tips in presence of Collembola. Root elongation is generally ascribed to the exploitation of nutrient rich patches in soil. We hypothesise that changes in root morphology in presence of Collembola are due to Collembola-mediated changes in nutrient availability and distribution.     

Interactions between mycorrhizal fungi and Collembola: effects on root structure of competing plant species

Mycorrhizal fungi influence plant nutrition and therefore likely modify competition between plants. By affecting mycorrhiza formation and nutrient availability of plants, Collembola may influence competitive interactions of plant roots. We investigated the effect of Collembola (Protaphorura fimata Gisin), a mycorrhizal fungus (Glomus intraradices Schenck and Smith), and their interaction on plant growth and root structure of two plant species, Lolium perenne L. (perennial ryegrass) and Trifolium repens L. (white clover). In a laboratory experiment, two individuals of each plant species were grown either in monoculture or in competition to the respective other plant species. Overall, L. perenne built up more biomass than T. repens. The clover competed poorly with grass, whereas the L. perenne grew less in presence of conspecifics. In particular, presence of conspecifics in the grass and presence of grass in clover reduced shoot and root biomass, root length, number of root tips, and root volume. Collembola reduced shoot biomass in L. perenne, enhanced root length and number of root tips, but reduced root diameter and volume. The effects of Collembola on T. repens were less pronounced, but Collembola enhanced root length and number of root tips. In contrast to our hypothesis, changes in plant biomass and root structure in the presence of Collembola were not associated with a reduction in mycorrhizal formation. Presumably, Collembola affected root structure via changes in the amount of nutrients available and their spatial distribution.     

Above- and below-ground plant inputs both fuel soil food webs

Soil food webs depend almost exclusively on plant derived resources; however, it is still subject to debate how plants affect soil biota. We tested the effects on soil decomposers of three components of soil inputs of plant species identity: presence of live plants (representing rhizodeposits), identity of shoot litter input and identity of root litter input; using all combinations of these for Trifolium pratense and Plantago lanceolata. We assessed impacts on soil microorganisms, Collembola, Oribatida and earthworms in a full-factorial greenhouse experiment. Species identity of shoot litter input had greatest effect on decomposers, following by species identity of live plant. Microbial carbon use efficiency and Oribatida density were significantly higher in the presence of T. pratense shoot litter input than in that of P. lanceolata shoot litter input, while earthworm body mass ratio was significantly higher in the presence of P. lanceolata plants than in that of T. pratense plants. Oribatida density was at minimum in the presence of P. lanceolata plants, shoot and root litter input, resulting in a significant three-way interaction and pointing to the relevance of all investigated plant input pathways. Live plant identity effects were not due to differences in living root biomass among species and treatments. Detrimental P. lanceolata effects may have been due to significantly lower N concentrations than in T. pratense tissue. Our results indicate that both above- and below-ground plant inputs into soil determine the performance of decomposers, and thus suggest due consideration of both types of inputs fueling soil food webs in future studies.     

Contrasting effects of nitrogen limitation and amino acid imbalance on carbon and nitrogen turnover in three species of Collembola

Soil animal detritivores play an important role in facilitating decomposition processes but little information is available on how the quality of dietary resources affects their stoichiometry of carbon (C) nitrogen (N) and phosphorus (P), and turnover of C and N. This study investigated how a fungal diet, Fusarium culmorum, with a low N content and imbalanced amino acid (AA) composition affected the physiology of three soil-dwelling collembolans (Folsomia candida, Protaphorura fimata and Proisotoma minuta) in comparison to a control diet, Saccharomyces cerevisiae, with a high N content and balanced AA composition. We compared the elemental composition of animals, their growth rates and tissue replacement of C and N. We also measured the individual AA δ¹³C to investigate the extent that Collembola may rely on endogenous sources to compensate for scarcity of essential AAs. The results showed that animal's N content tracked closely the composition of their diets, decreasing from around 10 to 7% N from the high to low N diet. They also had a significant increase of C and a decrease of P. P. fimata was less affected than F. candida and P. minuta. The total incorporation of C and N in the animals due to growth and tissue replacement decreased from 11-17 to 6-12% DM d⁻¹ on the high and low N diet respectively with P. fimata experiencing the smallest change. Essential AAs δ¹³C did not always match perfectly between Collembola species and their diets; particularly on the low N diet. Isotope patterns of AAs indicate that bacteria may have been the alternative source of essential AAs. While the results of this study cannot be extrapolated directly to the dynamics of Collembola populations in the field, they serve to demonstrate their flexibility in adapting physiologically to the temporal and spatial patchiness of the soil environment.     

Collembola grazing on arbuscular mycorrhiza fungi modulates nutrient allocation in plants

Arbuscular mycorrhiza (AM) mycelia networks are important for nutrient allocation in many plants, but fungivorous soil invertebrates such as Collembola can modulate the symbiosis by grazing on the extra-radical mycelium (ERM). This study employs a dual biomarker approach with stable isotopes and fatty acids to disentangle trophic interactions of Collembola in a plant-fungal soil system with maize (Zea mays) and the AM fungus Glomus mosseae. To separate ERM and root mediated effects, root (RC) and hyphal compartments (HC) were used, and the latter was spiked with labeled ¹⁵N substrate. The euedaphic Collembola species Protaphorura fimata was introduced as the fungal and root grazer. Generally, the presence of Collembola in RC fostered biomass and phosphorous uptake in roots colonized with AM. Nitrogen transport from HC to RC was not altered, indicating that Collembola did not disrupt the ERM network via grazing. Collembola–fungus interactions fostered AM hyphal proliferation in HC, whereas in RC it induced a change from fungal senescence with build-up of storage reserves, to an active foraging phase. A distinct diet switch by Collembola between HC and RC indicated different ERM palatability meditated by the presence or absence of the host plant. Overall, Collembola grazing increased ERM nutrient sequestration, particularly phosphorus, and in turn plant performance. Collembola modified fungal phenology, favoring fungal colonization over reproductive phases. These trophic interactions were strongly determined by fungal life stage, with the establishment of a functional mycorrhiza as a crucial factor.     

Localisation of nitrate in the rhizosphere of biochar-amended soils

A wheat seedling rhizobox approach was used to differentiate between the rhizosphere and non-rhizosphere (bulk) soil amended with low and high rates of biochar (20 and 60 t ha⁻¹ vs. control). Nitrate (NO₃⁻) was added as the main nitrogen (N) source because emerging biochar research points to reduced NO₃⁻ loss through leaching and gaseous loss as nitrous oxide. The rhizosphere under the different treatments were distinct (P = 0.021), with greater soil-NO₃⁻ and biochar-NO₃⁻ contents in the high biochar treatment. Biochar addition increased wheat root length ratio (P = 0.053) and lowered root N uptake (P = 0.017), yet plant biomass and N content were similar between treatments. The results indicate localisation of NO₃⁻ within the rhizosphere of biochar-amended soils which has implications for NO₃⁻ loss and improved nitrogen use efficiency.     

Collembola switch diet in presence of plant roots thereby functioning as herbivores

Collembola are abundant and ubiquitous soil decomposers, being particularly active in the rhizosphere of plants where they are assumed to be attracted by high microbial activity and biomass. While feeding on root associated microorganisms or organic matter they may also ingest plant roots, e.g. particularly root hairs and fine roots. Employing stable isotope analysis we investigated Collembola (Protaphorura fimata Gisin) feeding preferences and types of ingested resources. We offered Collembola two resources with distinct isotope signatures: a C4 plant (Zea mays L.) planted in soil mixed with ¹⁵N labelled litter of Lolium perenne L. (C3 plant). We hypothesised that Collembola obtain their nutrients (C and N) from different resources, with their carbon being mainly derived from resources that are closely associated to the plant root, e.g. root exudates, causing enrichment in ¹³C in Collembola tissue, while the incorporated nitrogen originating from litter resources. In contrast to our hypothesis, stable isotope analysis suggests that in absence of plant roots Collembola derived both the incorporated C and N predominantly from litter whereas in presence of plant roots they switched diet and obtained both C and N almost exclusively from plant roots.The results indicate that Collembola in the rhizosphere of plants, being assumed to be mainly decomposers, in fact predominately live on plant resources, presumably fine roots or root hairs, i.e. are herbivorous rather than detritivorous or fungivorous. These findings have major implications on the view how plants respond to decomposers in the rhizosphere.     

Evaluation of pinewood biochar as a carrier of bacterial strain Enterobacter cloacae UW5 for soil inoculation

The large-scale production of biochar for carbon sequestration provides an opportunity for using these materials as inoculum carriers to deliver plant growth-promoting rhizobacteria (PGPR) into agricultural soils. Here, we evaluated the suitability of a biochar produced from pinewood pyrolyzed at 300 °C as a carrier for a well-studied PGPR strain, Enterobacter cloacae UW5. This strain was genetically modified to produce a green fluorescent protein marker that enabled tracking of the inoculum. Results from selective plate count assays and quantitative PCR (qPCR) confirmed that cell survival was slightly improved by addition of bacteria to soil using biochar as a carrier for the inoculant, as compared to soil directly inoculated. Total 16S rRNA genes were quantified using qPCR and DNA templates from the same soil treatments to distinguish the impact of biochar on total bacterial abundance from its influence on inoculum survival. Here total bacterial abundance was not influenced by biochar. All treatments resulted in bacterial colonization of roots at population densities of approximately 10⁵ CFU g⁻¹ root mass. Cucumber plants grown in the biochar amended soils had significantly greater biomass and root development than those planted in un-amended soil, regardless of the presence of inoculum. The ability of bacteria to colonize the plant roots and produce a plant growth hormone was not affected by biochar. However, UW5 inoculum did not promote root development in cucumber in any of the soils tested here. Overall, these experiments suggest that the 300 °C pine biochar is effective for evenly distributing inoculum into soil and promotes cucumber development in sandy loams.     

New trophic biomarkers for Collembola reared on algal diets

We used fatty acid (FA) analysis to investigate green algae and cyanobacteria as food sources for Collembola. We studied the effects of food quality on body mass and on neutral lipid (NLFA) and phospholipid (PLFA) fatty acid patterns of Collembola. Folsomia candida, Heteromurus nitidus and Protaphorura fimata were fed with common green algae (Chlorella vulgaris), filamentous soil algae (Klebsormidium flaccidum), cyanobacteria (Nostoc commune) and baker's yeast (Saccharomyces cerevisiae). Body mass of F. candida and H. nitidus was highest when reared on C. vulgaris and S. cerevisiae. P. fimata gained the most weight when fed baker's yeast. K. flaccidum and N. commune as resources resulted to low biomass in all Collembola. The four diets caused significant differences in the NLFA and PLFA composition of Collembola after six weeks of feeding. Two new trophic biomarker FAs indicating algal diets were assigned with 16:3ω3,6,9 and 16:2ω6,9, which were only present in NLFAs of Collembola consuming C. vulgaris and K. flaccidum. The amount of FAs from the ω7 family was high in Collembola lipids with cyanobacteria and yeast as food sources, whereas only trace amounts occurred in the NLFA fraction with algae as the resource. In summary, common soil algae and cyanobacteria differed in food quality for Collembola, depending on their growth form (unicellular versus filamentous) and/or secondary metabolites (e.g. cyanobacteria). The new FA biomarkers detected will allow further investigation of these trophic interactions under field conditions; for example, assessing the role of collembolan grazers in the formation of biological soil crusts.     

Influences of non-herbaceous biochar on arbuscular mycorrhizal fungal abundances in roots and soils: Results from growth-chamber and field experiments

Biochar holds promise as an amendment for soil quality improvement and sequestration of atmospheric carbon dioxide. However, knowledge of how biochar influences soil properties, especially soil microorganisms, is limited. Three separate studies were conducted, with two studies using Plantago lanceolata as the AMF hosting plant, and a third being conducted in the field. Each of the three studies employed a different soil type. Furthermore, a total of five different biochars, and ten different biochar application rates, were used across the three experiments. All experiments had the goal to examine biochar influences on arbuscular mycorrhizal fungal (AMF) abundance in roots and AMF abundance (hyphal lengths) in soils. AMF abundance was either decreased or remained unchanged across all biochar treatments. When AMF abundances decreased, significant changes in soil properties, primarily in soil P availability, were observed. Application of large quantities (2.0% and 4.0%, w/w) of a lodgepole pine biochar, led to significant declines in AMF abundance in roots of 58% and 73% respectively, but not in soils. These declines in AMF abundance were accompanied by significant declines (28% and 34%) in soil P availability. After addition of a peanut shell biochar produced at 360 °C, P increased by 101% while AMF root colonization and extraradical hyphal lengths deceased by 74% and 95% respectively. Field application of mango wood biochar at rates of 23.2 and 116.1 t C ha⁻¹ increased P availabilities by 163% and 208% respectively and decreased AMF abundances in soils by 43% and 77%. These findings may have implications for soil management where the goal is to increase the services provided by AMF.     

不同质地潮土施用小麦和玉米秸秆生物质炭对玉米养分吸收和根际土壤胞外酶活性的影响

  【目的】  生物质炭施用于农田土壤中能够改善土壤肥力,并提高作物生产力,而该效应受到土壤条件和生物质炭条件的限制。针对不同土壤条件探究适宜的生物质炭利用方式,对促进农业生产具有重要意义。  【方法】  采用盆栽试验,以壤质和粘质两种质地的潮土为研究对象,分别施用玉米秸秆炭(MBC)和小麦秸秆炭(WBC)两种生物质炭,并以不施用生物质炭的处理为对照(CK)。测定各处理玉米苗期生长、生理抗性和养分吸收差异,并分析各处理根际土壤理化性质和胞外酶等活性。  【结果】  1)与CK相比,壤质潮土中,WBC处理下玉米地上部生物量显著增加了43.7%,总根长显著增加34.3%,而MBC处理没有显著影响。粘质潮土中,WBC和MBC对玉米生物量和根系构型均影响较小。2) WBC和MBC在壤质和粘质潮土中显著降低了苗期玉米叶片中MDA含量,降低幅度在32.7%～55.3%,且两种生物质炭之间没有显著差异;粘质潮土中,MBC处理显著提高了玉米叶片超氧化物歧化酶(SOD)活性,壤质潮土中,WBC和MBC处理对SOD活性均没有显著影响。3)壤质潮土中,生物质炭对苗期玉米地上部氮含量没有显著影响,而对作物全磷和全钾含量有显著促进作用,WBC处理的地上部全磷和全钾含量分别比对照显著提高23.5%和28.7%,且显著高于MBC处理。在粘质潮土中,WBC和MBC处理对地上部全氮和全磷含量均没有显著影响,而MBC处理提高了全钾含量。4)在壤质和粘质潮土中施用生物质炭均改善了根际土壤理化性质。与对照相比,壤质潮土中MBC处理的土壤速效磷含量显著增加了25.4%;粘质潮土中WBC和MBC处理速效磷含量均显著增加了15.03%,并且显著提高了阳离子交换量(CEC)。生物质炭处理提高了根际土壤胞外酶活性,在粘质潮土中WBC和MBC处理的胞外酶活性没有显著差异,而在壤质潮土中WBC处理的酶活性高于MBC处理。  【结论】  施用生物质炭能够调控根际土壤酶活性,提高有效磷含量,改善玉米根系构型,提高苗期玉米养分吸收并增加生物量。生物质炭的施用效果在壤质潮土中比粘质潮土中更好,小麦秸秆炭效应优于玉米秸秆炭。     

The significant contribution of mycorrhizal fungi and earthworms to maize protection and phytoremediation in Cd-polluted soils

Mycorrhizal fungi and earthworms can individually or interactively influence plant growth and heavy metal uptake. The influence of earthworms and arbuscular mycorrhizal (AM) fungi either alone or in combination on maize (Zea mays L.) growth and cadmium (Cd) uptake was investigated in a calcareous soil artificially spiked with Cd. Soils were contaminated with Cd (10 and 20 mg Cd kg⁻¹), inoculated or un-inoculated with the epigeic earthworm Lumbricus rubellus and two AM fungal species (Rhizophagus irregularis and Funneliformis mosseae) for two months of growth under greenhouse conditions. Generally, earthworms alone increased both shoot P uptake and biomass but decreased shoot Cd concentration and root Cd uptake. AM fungi individually often increased total maize P uptake, declined shoot Cd concentration, and consequently produced higher total biomass. However, R. irregularis enhanced shoot Cd uptake at low Cd level and root Cd uptake at high Cd level. In plants inoculated with F. mosseae species, earthworms increased shoot biomass and Cd uptake, decreased root biomass and Cd uptake at all Cd levels, and increased shoot Cd concentration at low Cd level. In plants colonized by R. irregularis species, however, earthworm addition decreased maize biomass only at high Cd level and root Cd concentration and total maize Cd uptake at both Cd levels. Earthworm activity decreased Cd transfer from the soil to maize roots at low Cd level, but this was counterbalanced in the presence of F. mosseae. Mycorrhizal symbiosis significantly reduced the transfer of Cd from roots to shoots, independence of earthworm effect. Overall, it is concluded that L. rubellus and AM fungi, in particular F. mosseae isolate, improved maize tolerance to Cd toxicity both individually and interactively by increasing plant growth and P nutrition, and restricting Cd transfer to the aboveground biomass. Consequently, the single and interactive effects of the two soil organisms might potentially be important not only in protecting maize plants against Cd toxicity, but also in Cd phytostabilization in soils polluted by this highly toxic metal.     

Microbial mineralization of biochar and wheat straw mixture in soil: A short-term study

A short-term incubation study was carried out to investigate the effect of biochar addition to soil on CO₂ emissions, microbial biomass, soil soluble carbon (C) nitrogen (N) and nitrate–nitrogen (NO₃–N). Four soil treatments were investigated: soil only (control); soil + 5% biochar; soil + 0.5% wheat straw; soil + 5% biochar + 0.5% wheat straw. The biochar used was obtained from hardwood by pyrolysis at 500 °C. Periodic measurements of soil respiration, microbial biomass, soluble organic C, N and NO₃–N were performed throughout the experiment (84 days). Only 2.8% of the added biochar C was respired, whereas 56% of the added wheat straw C was decomposed. Total net CO₂ emitted by soil respiration suggested that wheat straw had no priming effect on biochar C decomposition. Moreover, wheat straw significantly increased microbial C and N and at the same time decreased soluble organic N. On the other hand, biochar did not influence microbial biomass nor soluble organic N. Thus it is possible to conclude that biochar was a very stable C source and could be an efficient, long-term strategy to sequester C in soils. Moreover, the addition of crop residues together with biochar could actively reduce the soil N leaching potential by means of N immobilization.     

Effects of temperature and life stage on the fatty acid composition of Collembola

Fatty acid (FA) analysis is used as a promising tool to investigate trophic interactions in soil food webs. The FA profile of neutral lipids in consumers is affected by the diet, and the occurrence and amount of certain FAs can reflect feeding strategies. We investigated the lipid composition of the Collembola Folsomia candida, Heteromurus nitidus and Protaphorura fimata with the fungus Chaetomium globosum as food source. The impact of environmental temperature and life stage was assessed, with special respect to linoleic acid (18:2ω6,9) as a marker FA for fungal feeding. In all Collembola species the ratio of C16/C18 in neutral lipid fatty acids (NLFAs) increased with decreasing temperature. In the NLFAs of F. candida and H. nitidus the Unsaturation Index and the amount of 18:2ω6,9 decreased with temperature, whereas in P. fimata effects were the opposite. The composition of phospholipid fatty acids (PLFAs) differed between species, but was little affected by temperature. The degree of unsaturation in NLFAs increased with the age of Collembola, mainly due to higher amounts of 18:2ω6,9 and a lower proportion of 18:1ω9. The biomarker linoleic acid represented over 20% of FAs in all fungal feeding Collembola. Despite considerable influence of temperature and life stage on its proportion, the amount was always higher than in individuals reared on other diets. This suggests that linoleic acid can serve as marker for fungal feeding independent of such physiological variations in Collembola.     

Effect of land-use and elevation on microbial biomass and water extractable carbon in soils of Mt. Kilimanjaro ecosystems

Microbial biomass carbon (MBC) and water-extractable organic carbon (WOC) – as sensitive and important parameters for soil fertility and C turnover – are strongly affected by land-use changes all over the world. These effects are particularly distinct upon conversion of natural to agricultural ecosystems due to very fast carbon (C) and nutrient cycles and high vulnerability, especially in the tropics. The objective of this study was to use the unique advantage of Mt. Kilimanjaro – altitudinal gradient leading to different tropical ecosystems but developed all on the same soil parent material – to investigate the effects of land-use change and elevation on MBC and WOC contents during a transition phase from dry to wet season. Down to a soil depth of 50 cm, we compared MBC and WOC contents of 2 natural (Ocotea and Podocarpus forest), 3 seminatural (lower montane forest, grassland, savannah), 1 sustainably used (homegarden) and 2 intensively used (maize field, coffee plantation) ecosystems on an elevation gradient from 950 to 2850 m a.s.l. Independent of land-use, both MBC and WOC strongly increased with elevation on Mt. Kilimanjaro corresponding to ecosystem productivity and biodiversity. Through the agricultural use of ecosystems MBC and WOC contents decreased – especially in surface layers – on average by 765 mg kg⁻¹ for MBC and 916 mg kg⁻¹ for WOC, compared to the respective natural ecosystems. The decrease with depth was highest for forests > grasslands > agroecosystems and also was positively correlated with elevation. We conclude that MBC and WOC contents in soils of Mt. Kilimanjaro ecosystems are highly sensitive to land-use changes, especially in topsoil. The MBC and WOC contents were considerably reduced even in sustainable agricultural systems. Since MBC and WOC are very fast reacting and sensitive C pools, we expect a decrease in other soil C pools accompanied by a strong decrease in fertility and productivity due to changes in land use from natural to agricultural ecosystems.     

Rice straw biochar amended soil improves wheat productivity and accumulated phosphorus in grain

Abstract

Biochar is a pyrolyzed biomass produced under limited oxygen or oxygen absent conditions. Few investigations have been conducted to determine the combined effect of biochar with chemical fertilizer on growth, yield and nutrient distribution pattern in root, shoot and grain in wheat as well as changes in soil physiochemical properties. This research was designed to study the combined effect of chemical fertilizer and rice straw-derived biochar on soil physio-chemical properties, growth, yield and nutrient distribution pattern within wheat plant tissue and grain. Results showed that rice straw biochar caused a significant decrease in soil pH and increase in soil organic matter as well as nutrients like total nitrogen (TN), potassium (K), magnesium (Mg) and boron (B) due to incubation. Result also showed that root biomass and straw did not differ between Bangladesh Agricultural Research Council (BARC) and ½ BARC?+?rice straw biochar treatment. Similarly, thousand grain weight and grain yield did not differ between the same treatments. The phosphorus concentration in wheat grain was highest in ½ BARC?+?rice straw biochar as compared to other treatments. The use of rice straw biochar in addition to the chemical fertilizers in wheat production systems is an economically feasible and practical nutrient management practice. Our findings urged that reduction of chemical fertilizer application is possible with supplementation of rice straw biochar.     

Nutrient availability and corn growth in a poultry litter biochar‐amended loam soil in a greenhouse experiment

Nutrient‐rich biochar produced from animal wastes, such as poultry litter, may increase plant growth and nutrient uptake although the role of direct and indirect mechanisms, such as stimulation of the activity of mycorrhizal fungi and plant infection, remains unclear. The effects of poultry litter biochar in combination with fertilizer on mycorrhizal infection, soil nutrient availability and corn (Zea mays L.) growth were investigated by growing corn in a loam soil in a greenhouse with biochar (0, 5 and 10 Mg/ha) and nitrogen (N) and phosphorus (P) fertilizer (0, half and full rates). Biochar did not affect microbial biomass C or N, mycorrhizal infection, or alkaline phosphomonoesterase activities, but acid phosphomonoesterase activities, water‐soluble P, Mehlich‐3 Mg, plant height, aboveground and root biomass, and root diameter were greater with 10 Mg/ha than with no biochar. Root length, volume, root tips and surface area were greatest in the fully fertilized soil receiving 10 Mg/ha biochar compared to all other treatments. The 10 Mg/ha biochar application may have improved plant access to soil nutrients by promoting plant growth and root structural features, rather than by enhancing mycorrhizal infection rates.     

Synergists and antagonists in the rhizosphere modulate microbial communities and growth of Quercus robur L.

The synergistic and antagonistic interactions among biotic components in the rhizosphere play a crucial role in plant defence against soil-borne pathogens. We investigated if the rhizosphere helper bacterium Streptomyces sp. AcH 505 (HB) indirectly protects the plant from the parasitic nematode Pratylenchus penetrans by modifying the rhizosphere microbial community structure and whether these interactions are dependent on the growth stage of oaks. Changes in the abundance of Streptomyces sp. AcH 505 and the phospholipid fatty acid (PLFA) composition of the rhizosphere soil as well as oak shoot and root biomass were assessed. Investigated were the bud resting stage A and the bud swelling stage B with maximal root elongation of oak microcuttings at two successive harvest times. The deleterious effect of P. penetrans on oak biomass was dependent on plant development, being limited to oak microcuttings growing at the stage B. In comparison to control and HB inoculated soils, shoot biomass decreased by about 33% and 41%, and root biomass by about 33 and 48%, respectively. The antagonistic effect of Streptomyces against the nematode was linked to shifts in the rhizosphere microbial community. The Streptomyces AcH505 strain promoted growth of oak microcuttings at bud swelling stage B during maximal root elongation and enhanced the abundance of saprophytic and ectomycorrhizal fungi in the rhizosphere by 158% with respect to controls. Our results highlight the importance of Streptomyces for counteracting the damage of nematodes and promoting plant growth in natural ecosystems such as forests.     

Nutrient uptake and growth of potato: Arbuscular mycorrhiza symbiosis interacts with quality and quantity of amended biochars

Aims : The aim of this study was to explore interactive effects between quality (types) and quantity (application rates) of biochar as well as of arbuscular mycorrhiza (AM) symbiosis on the growth of potato plants. Methods : A low P sandy loam soil was amended with 0%, 1.5%, or 2.5% (w/w) of either of 4 types of biochar, which were produced from wheat straw pellets (WSP) or miscanthus straw pellets (MSP) pyrolyzed at temperatures of either 550°C or 700°C. Potato plants grown in pots containing the soils or soil biochar mixture were inoculated with or without AM fungus (AMF), Rhizophagus irregularis. The experiment was carried out under fully irrigated semi‐field conditions and plants were harvested 101 days after planting. Results : Application of high temperature biochar decreased growth, biomass and tuber yield of potato plants, while the low temperature biochar had a similar effect on yield as plants grown without biochar amendment. Total biomass of potato plants were decreased with the increasing rate of biochar. Arbuscular mycorrhizal fungus inoculation stimulated the growth of potato plants in all organs, increased tuber biomass significantly in 1.5% MSP700 amended plants, and to a lesser degree for WSP700, MSP550, and WSP550. In addition, plant biomass gain was linearly related to N, P, and K uptake, the ratio of P to N in the leaf of plants indicated that all treatments were mainly P‐limited. A multiple linear regression using P uptake and biochar rate as independent variables explained 91% of the variation in total biomass. The single effect of AMF inoculation, type and rate of biochar affected plant N, P and K uptake similarly. While AMF inoculation significantly increased P uptake in potato plants grown in soil with WSP700 or MSP700 despite of the rate of biochar. In general, application of biochar significantly increased AMF root colonization of potato plants. Conclusions : The application of MSP550 at 1.5% combined with AMF stimulated growth of potato the most. Furthermore, the results indicated that the interactive effect of AMF inoculation, biochar type and application rate on potato growth to a large extent could be explained by effects on plant nutrient uptake.