Daily dynamics of greenhouse gas (GHG) emissions and cultivable bacterial populations have rarely been examined. The objectives were: (1) to investigate if dynamics of GHG emissions can be described ...by harmonics and are related to those of cultivable bacteria after soil disturbances in three grassland management systems; (2) to determine to which extent daily GHG emissions are related to environmental variables rather than disturbance events in two climate zones; and (3) to investigate differences in GHG emissions between organic and conventional tilled grassland versus no-till long-term grassland systems (OG, CG and LG, respectively). In replicated field experiments with OG, CG, and LG plots in the Netherlands and Russia, GHG (CO2, N2O and CH4) emissions and cultivable bacterial populations were measured daily during two one-month periods at each location. Tillage, fertilization, biomass incorporation and irrigation were considered disturbances. The dynamics were subjected to harmonics, cross-correlation, and canonical correspondence analyses (CCA). The dynamics of cultivable bacterial populations and GHG fluxes rarely reflected autonomous growth and death cycles of bacteria after a disturbance due to the overarching influences of environmental conditions, especially in spring. Thus, GHG emissions were influenced more by weather variables than by agronomic disturbances. This was confirmed by CCA. Cultivable bacterial populations were cross correlated with CO2 fluxes and sometimes N2O emissions, but generally not with CH4 fluxes. Average cultivable bacterial populations and CO2 emissions were highest in OG and lowest in LG; N2O emissions were mostly highest in CG and lowest in LG; and CH4 fluxes were frequently highest in OG and lowest in LG. Thus, although bacteria and GHG peaks were induced by disturbances, sometimes followed by autonomous oscillations due to growth and death cycles and associated cycles in nutrient and oxygen availability, the dynamics were mainly affected by environmental variables and long-term management, with the smallest GHG emissions from LG plots.
•Daily greenhouse gas (GHG) emissions were related to cultivable bacteria in grassland soils.•Despite irregular fluctuations, GHG oscillations occurred after some agronomic disturbances.•Cross correlations among CO2, N2O fluxes and cultivable bacteria suggested process sequences.•GHG emissions were influenced more by environmental variables than by agronomic disturbances.•GHG emissions mostly were high in organic, medium in conventional, and low in long-term plots.
•Fusarium wilt was suppressed more in organic than conventional greenhouse soil.•Suppression was related more to biological than chemical soil characteristics.•Microbial resistance and resilience ...after disturbance were greater in organic soil.•Microbial resistance and resilience can be used as soil health indicators.
Soil health has been associated with internal cycling of nutrients, microbial activity and diversity as well as root disease suppression, which are frequently greater in organically than in conventionally managed soils. Resistance and resilience, measured as amplitude and frequency of oscillations in bacterial communities after a disturbance, were suggested as integral indicators of soil health, but until now there is little proof for this hypothesis. In this study, resistance and resilience of microbial communities and 24 soil chemical and biological parameters were analyzed and correlated to suppression of flax wilt (caused by Fusarium oxysporum f.sp. lini) in three experiments. Soil samples were collected on three different dates from a recently converted organic greenhouse and a similar, neighboring greenhouse under conventional management. The dynamics of copiotrophic and oligotrophic bacteria after a disturbance were monitored, and the resistance and resilience were calculated. The organic soil showed significantly higher water-holding capacity, organic matter content, total C and N contents, C:N ratio of the small particulate organic matter fraction, microbial biomass carbon, oxygen uptake rate, copiotrophic and oligotrophic bacterial communities and suppression of flax wilt incidence. After incorporation of a grass–clover mixture in both soils, the densities of copiotrophic and oligotrophic bacteria oscillated over time. The relative amplitudes of the oscillations (in grass–clover amended over non-amended soil) and the frequencies of the oscillations of both trophic groups were lower for the organic soil, indicating that the resistance and resilience of the microbial community were greater in this soil. These results support the hypothesis that the bacterial response to a disturbance can serve as an integral indicator for soil health, including disease suppressiveness.
Nitrogen fixation (NF) of phototrophic communities was studied in a number of soda lakes with a wide range of salinity (25-400 g/l) located in Kulunda Steppe (Altai, Russia) during several summer ...seasons (2011-2016). The phototrophic communities were represented by the algal-bacterial Ctenocladus communities or cyanobacterial biofilms dominated by heterocystous and non-heterocystous cyanobacteria and purple sulfur bacteria Ectothiorhodospira sp. (up to 210 g/l) and endoevaporitic Euhalothece communities dominated by the extremely salt-tolerant unicellular cyanobacterium Euhalothece sp. and Ectothiorhodospira sp. (above 350 g/l). Salinity was the major factor influencing the composition and NF potential of the phototrophic communities. The communities dominated by vegetative heterocystous cyanobacteria exhibited light-independent NF at total salinity up to 60 g/l. The communities dominated by non-heterocystous cyanobacteria exhibited light-dependent NF in a range of 55-100 g/l, but it was significantly suppressed at 100 g/l. At 160-200 g/l the dark heterotrophic NF was a prevailing process if communities didn't contain Euhalothece sp. At salt-saturating ranges above 350 g/l, light-dependent NF associated with the Euhalothece communities was detected. A statistically significant positive correlation between the NF and diurnal light intensity was found in all samples of communities dominated by non-heterocystous cyanobacteria in contrast to communities dominated by heterocystous cyanobacteria with insignificant correlation coefficients.
Vaccinium
twig blight (caused by
Phomopsis vaccinii
, teleomorph
Diaporthe vaccinii
) is a major endemic disease on blueberries and cranberries in the Eastern and Northwestern USA and Canada. It has ...also been found in Europe, Chile and China. Publications on its occurrence in the USA and Canada indicate that the pathogen is limited to cool climates. Published data on worldwide occurrence were inventoried and supplemented with National Plant Diagnostic Network (NPDN) data in the USA. These occurrence and long-term climate data were entered in the niche models MaxEnt and Multi-Model Framework to predict the potential global distribution of the disease. Precipitation in the driest quarter and mean annual temperature contributed most to the prediction. The results indicate that
P. vaccinii
is not limited to cool climates, although the optimal annual average temperature is 10 °C according to the MaxEnt model. The models correctly predicted that the climate in the central and eastern USA and the west coast of the USA and Canada would be conducive to blueberry twig blight. Large areas in Europe, eastern Australia and New Zealand, and smaller areas in South America and East Asia would be conducive too. For the first time, the NPDN database was shown to be an important source of information for the prediction of the potential global distribution of a plant pathogen.
International trade in live plant materials has increased worldwide over the last four decades. This has led to a dramatic increase in the introduction, establishment and spread of non‐native plant ...pathogens. Regulatory authorities need advice on measures that may mitigate these adverse consequences of trade. Risk models may be used to underpin such advice. In this review, we give a systematic overview of the data needed for a quantitative risk model for Phomopsis vaccinii, which causes stem and fruit infections on Vaccinium species, and sometimes death, potentially also on native wild Vaccinium species in the EU. P. vaccinii is a quarantine organism worldwide, except for North America, where it is endemic. Despite extensive knowledge of the aetiology of the diseases caused by this pathogen and its taxonomy, quantitative data on transportation and detection of infected plants for planting and berries are scarce, and quantitative assessment of the future introduction, establishment and spread of P. vaccinii is difficult. Estimation of the potential impact of this pathogen in production fields and wild Vaccinium stands is even more difficult. P. vaccinii is not unique in this respect, and this review indicates the need for more and better quantitative data for assessment of the risks posed by newly introduced plant pathogens in areas where they are not endemic.
Overview of assessment for Diaporthe vaccinii.
Recently, regular oscillations in bacterial populations and growth rates of bacterial feeding nematodes (BFN) were shown to occur after addition of fresh organic matter to soil. This paper presents a ...model developed to investigate potential mechanisms of those oscillations, and whether they were initiated by bacteria–substrate interactions or by predatory regulation of bacteria. The model was also used to investigate mineral nitrogen release during short-term organic matter decomposition. Experimental data originated from several microcosm experiments with a sandy soil amended with clover–grass mixture. Numbers of bacteria and BFN, and nitrate and ammonium content in soil were measured daily during about a month, whereas protozoa were counted occasionally. A substrate-based food web model was constructed with 3 plant residue and 5 soil organic matter compartments, 3 trophic groups of bacteria (copiotrophic, oligotrophic and hydrolytic), and two predatory groups (BFN and protozoa). Both carbon and nitrogen flows between these compartments were modelled. Fluctuations in microbial populations in soil after plant residue incorporation could be reproduced with and without participation of predators. The first two peaks in bacterial numbers were mainly related to bacteria–substrate interactions, while predators (particularly protozoa) influenced bacterial dynamics during later stages of bacterial community development. Oligotrophic bacteria had a stabilizing effect on fluctuations of other trophic groups, and were the main source of nutrients for predators. A peak in soil ammonium occurred within 1 week after residue incorporation. Nitrate increased sigmoidally after a short lag phase. The final nitrate concentration was primarily determined by bacterial dynamics, and to a lesser extent by protozoa and nematodes. This model indicates the importance of substrate–consumer relations for regulation of populations at different trophic levels and nutrient release from fresh organic matter added to soil.
•Organic soil amendments in pots resulted in oscillations in bacteria and greenhouse gases (GHG).•Their ratios in amended/nonamended soils had smaller oscillations in ORG than CONV soil.•GHG ...emissions were higher from ORG than CONV soil in field experiments.•Despite irregular fluctuations in the field, GHG oscillations occurred after irrigation or rain.•Cross correlations showed logical sequences of microbial processes in pots but not in the field.
Organically managed (ORG) soil is often considered healthier than conventionally managed (CONV) soil, with greater resistance and resilience to disturbances, as evidenced by reduced oscillations in bacterial populations and activities. Greenhouse gas (GHG) fluxes are mediated by bacterial processes, but variations in GHG emissions have not been related to bacterial oscillations in soil. Two environmentally controlled and two field experiments were set up to compare oscillations in bacterial colony-forming-units (CFUs) and GHG (nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4)) fluxes after disturbances in ORG and CONV soils. Soil amendment with grass-clover (GC) or cattle manure (CM) resulted in peaks in N2O and CO2 emission, followed by CFUs. CH4 temporarily increased in GC- but decreased in CM-amended soil. Ratios of CFUs and GHGs in amended over nonamended soils oscillated during three weeks, mostly with lower frequencies and amplitudes in ORG soils. Fluctuations were more irregular in field soils, but significant oscillations were detected after irrigation or intensive rain in summer. Cross correlations between variables showed several significant sequences of microbial processes under controlled conditions but not in the field. Average GHG emissions were higher from ORG soil than CONV soil under these conditions, indicating that these have to be taken into consideration when estimating soil health.
Soil fertility in biologized crop rotations depends on the saturation of them with legumes and sideral crops, perennial grasses, the involvement of grain crops in the organic matter cycle. The crop ...rotation was studied: 1) four-field grain and steam: clean steam winter wheat chickpeas spring barley (control); 2) five-field grain and steam: occupied steam (clover green manure) winter wheat chickpeas spring barley mustard + clover; 3) seven-field grain and grass: occupied steam (green manure oats) winter wheat mustard chickpeas safflower dyeing spring barley sainfoin (hatcher field); 4) semi-field grass and grassland: occupied steam (phacelia green manure) winter wheat spring wheat chickpeas grain sorghum spring barley alfalfa (hatchery field). The highest balance of organic matter was ensured in a five-field grain-steam crop rotation with clover for green manure +1.92 t/ha, in this crop rotation the highest balance was observed for nitrogen +23.8 kg/ha and phosphorus +1.3 kg/ha, grain harvest from 1 ha of arable land 0.51 t/ha. The greatest balance of potassium was ensured in the seven-field grain and grass-crop rotation with facet on green manure +8.8 kg/ha. The highest humus balance was observed in a seven-field grain-grass-crop rotation with oats per green manure +0.12 t/ha.
The objectives of the research were to investigate short-term dynamics of bacterial populations in soil after a disturbance in the form of fresh organic matter incorporation and to investigate how ...these dynamics are linked to those of some environmental parameters. To reach these objectives, soil bacterial populations, mineral nitrogen, pH, and redox potential (ROP) were monitored daily for 1 month after incorporation of clover-grass (CG) plant material in microcosm experiments. Colony-forming units (CFUs) and direct microscopic counts of FDA-stained and FITC-stained bacteria increased immediately after incorporation of the plant material, dropped within 2 days, and fluctuated thereafter. Harmonics analysis demonstrated that there were significant wavelike fluctuations with three or four significant peaks within 1 month after incorporation of clover-grass material. Peaks in CFUs were 1-2 days ahead of those in direct counts. Ammonium (NH₄ concentrations increased from the start of the experiments until nitrification commenced. Nitrate (NO₃) concentrations dropped immediately after plant incorporation, and then rose monotonically until the end of the experiments. There were no wavelike fluctuations in NH₄ and NO₃ concentrations, so that bacterial fluctuations could not be attributed to alternating mineral N shortages and sufficiencies. pH levels rose and declined with NH₄ levels. ROP dropped shortly before NH₄ concentrations rose, and increased before NH₄ concentrations decreased; there were no regular fluctuations in ROP, so that temporary oxygen shortages may not have been responsible for the observed fluctuations in bacterial populations. Thus, for the first time, regular wavelike dynamics were demonstrated for bacterial populations after perturbation by addition of fresh organic matter to soil, and several potential reasons for the death phase of the fluctuations could be excluded from further consideration.
To determine if spatial variation in soluble carbon sources along the root coincides with different trophic groups of bacteria, copiotrophic and oligotrophic bacteria were enumerated from bulk soil ...and rhizosphere samples at 2 cm intervals along wheat roots 2, 3, and 4 week's after planting. There was a moderate rhizosphere effect in one experiment with soil rich in fresh plant debris, and a very pronounced rhizosphere effect in the second experiment with soil low in organic matter. We obtained wavelike patterns of both trophic groups of bacteria as well as water-soluble total organic carbon (TOC) along the whole root length (60 or 90 cm). TOC concentrations were maximal at the root tip and base and minimal in the middle part of the roots. Oscillations in populations of copiotrophic and oligotrophic bacteria had two maxima close to the root tip and at the root base, or three maxima close to the tip, in the middle section, and at the root base. The location and pattern of the waves in bacterial populations changed progressively from week to week and was not consistently correlated with TOC concentrations or the location of lateral root formation. Thus, the traditional view that patterns in bacterial numbers along the root directly reflect patterns in exudation and rhizodeposition from several fixed sources along the root may not be true. We attributed the observed wavelike patterns in bacterial populations to bacterial growth and death cycles (due to autolysis or grazing by predators). Considering the root tip as a moving nutrient source, temporal oscillations in bacterial populations at any location where the root tip passed would result in moving waves along the root. This change in concept about bacterial populations in the rhizosphere could have significant implications for plant growth promotion and bioremediation.
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