Absence Of Plants Research Articles

Removal of Nitrogen, Phosphates, and Chemical Oxygen Demand from Community Wastewater by Using Treatment Wetlands Planted with Ornamental Plants in Different Mineral Filter Media

This study aimed to explore the impact of various ornamental plants (Heliconia psittacorum, Etlingera elatior, Spatyphilum walisii) grown in different filter media (porous river rock (PR) and tepezyl (TZ)) on the removal of pollutants in vertical-subsurface-microcosm treatment wetlands (TWs). This study also sought to assess the adaptability of these plant species to TW conditions. Twenty-four microcosm systems were utilized, with twelve containing PR and twelve containing TZ as the filter media. Each porous media type had three units planted with each species, and three were left unplanted. Rural community wastewater was treated in the TWs. The results showed no significant differences in the effects of the porous media on pollutant removal performance (p > 0.05). However, it was noted that while both porous media were efficient, TZ, a residue of construction materials, is recommended for sites facing economic constraints. Additionally, the removal efficiency was found to be independent of the type of ornamental plant used (p > 0.05); however, the measured parameters varied with plant spp. The adaptation of the plants varied depending on the species. H. psittacorum grew faster and produced a larger number of flowers compared to the other species (20–22 cm). S. wallisii typically produced 7–8 flowers. E. elatior did not produce flowers, and some plants showed signs of slight disease and pests, with the leaves turning yellow. In terms of plant biomass, the type of porous media used did not have a significant effect on the production of above (p = 0.111) or below-ground biomass (p = 0.092). The removal percentages for COD in the presence and absence of plants were in the ranges of 64–77% and 27–27.7%, respectively. For TN, the numbers were 52–65% and 30–31.8%, and for N-NO3, they were 54–60% and 12–18%. N-NH4 saw removal rates of 67–71% and 28–33%, while P-PO4 saw removal rates of 60–72% and 22–25%. The difference in removal percentages between microcosms with and without plants ranged from 30 to 50%, underscoring the importance of plants in the bio-removal processes (phytoremediation). These results reveal that incorporating ornamental plants in TWs with TZ for wastewater in rural areas holds great promise for enhancing the visual appeal of these systems and ultimately gaining public approval. Our findings also enable us to offer recommendations for selecting suitable plants and substrates, as well as designing combinations for TWs.

Co‐occurring intertidal ecosystem engineers with opposing growth strategies show opposite responses to environmental gradients during establishment

Coastal vegetated ecosystems including mangroves, seagrasses, and salt marshes are often shaped by positive plant–environment feedbacks. Plants improve their own living conditions with increasing patch size and density by attenuating hydrodynamics and stabilizing sediments. As these habitat modifications are critical for survival and growth, the positive density‐dependent nature of these feedbacks can lead to establishment thresholds for young plants in absence of mature conspecifics. Although feedback strength is known to depend on hydrodynamic exposure and plant traits (e.g. stiff versus flexible stems), it remains unclear how 1) opposing morphological plant traits affect establishment in contrasting environments, and 2) whether trait plasticity influences establishment success. Here, we investigate this by transplanting two tidal species with opposing growing strategies – Spartina anglica forms tussocks of stiff stems while Zostera noltii forms patches of stress‐avoiding flexible shoots – from two different donor sites in eight experimental locations. Results show that the survival and growth of both species was most successful at field locations with diverging environmental characteristics, while overall survival was highest for Z. noltii. Mainly, S. anglica survival was highest at locations with high organic matter and silt content and higher elevation relative to the tidal amplitude. In contrast, Z. noltii survival was highest at locations with larger grainsize and lower relative elevations. Furthermore, despite initial differences in plant traits between the two donor sites of Z. noltii, we found no effects of donor origin. Contrastingly, we found a significant effect of donor origin on S. anglica growth, even though transplants from the two donor sites showed no initial trait differences. Collectively, these results suggest that the stress‐tolerance strategy of S. anglica hampers establishment in exposed conditions, whereas the stress‐avoiding Z. noltii appears to be more susceptible to stress from desiccation and silty sediments.

Nitrogen Fertilizers Affect Microbial Hitchhiking to the Plant Roots.

The phenomenon of microbial hitchhiking, where nonmotile microbes utilize transspecies motility to navigate within their environment, has been observed. However, the underlying factors driving microbial hitchhiking remain unclear. Our study explored how nitrogen fertilizers affect microbial hitchhiking in soil through an in situ planting experiment. We established twelve treatments encompassing the presence and absence of plants, the presence and absence of a filter membrane that is used to prevent hitchhiking, and three nitrogen levels. Results showed that nitrogen influenced bacterial diversity in all soils, an effect thwarted by filter membranes. In the presence of plants, nitrogen significantly affected the bacterial mobility, Bacillus abundance, and plant biomass, but these effects vanished when filters were used. The correlation between motile Bacillus and rhizosphere bacteria was strong without filters at the proper nitrogen levels but weakened with membrane treatments. Thus, plants and nitrogen together, not nitrogen alone, alter the soil microbiome via hitchhiking.

Species Diversity of Grasshopper (Orthoptera: Caelifera) at the Rehabilitation Zone of the Bonangan Block, Wonoasri Resort, Meru Betiri National Park

Grasshoppers (Caelifera) are herbivorous insects that act as first consumers in the food chain. Grasshoppers can detect the presence or absence of plants as a source of food and a place to live, as well as being an indicator of environmental recovery. This study aims to determine the diversity of grasshopper species in the rehabilitation zone of Bonangan Block, Resort Wonoasri Meru Betiri National Park. The sampling method used a structured roaming technique. The results obtained nine types of grasshoppers covering seven genera with a total of 228 individuals. The diversity index value obtained is 1.86. The conclusion of this study was that the composition of grasshoppers included nine types of grasshoppers found, namely Oxya sp., Catantops sp., Trilophidia sp. (1), Trilophidia sp. (2), Schistocerca sp., Acrida sp., Phlaeoba sp., Atractomorpha sp. (1) and Atractomorpha sp. (2). The value of the diversity index of grasshoppers is in the medium category with the diversity index value of 1.86.

Apparent surface conductance sensitivity to vapour pressure deficit in the absence of plants

Apparent surface conductance sensitivity to vapour pressure deficit in the absence of plants

Effect of nonbiodegradable microplastics on soil respiration and enzyme activity: A meta-analysis

Nonbiodegradable microplastics (MPs) are emerging contaminants in the environment and potentially threaten soil health. In recent years, the impact of MPs on soil ecology has attracted widespread attention, but the responses of soil respiration and enzyme activity to MPs exposure remain unclear. Here, a meta-analysis including 1980 observations was used to assess the effects of MPs on soil microbial activity. MPs exposure significantly (p < 0.05) increased soil respiration by 18.2 % but did not significantly (p > 0.05) affect soil enzyme activity; moreover, these effects varied with MP type, concentration, size, and exposure period. The amendment of polypropylene (PP) MP increased soil respiration and enzyme activity by 58.8 % and 10.2 %, respectively, whereas exposure to polyethylene terephthalate (PET), polyethylene (PE) and polystyrene (PS) MPs reduced soil enzyme activities by 13.0 %, 6.8 % and 5.0 %, respectively. The soil respiration was unaffected and increased when the MPs concentrations were below and above 5 %, respectively, whereas soil enzyme activity was stimulated and inhibited when the MPs concentrations were less and >10 %, respectively. The size of MPs only significantly (p < 0.05) affected the response of soil respiration to MPs, as small (<500 μm) and large (≥500 μm) sizes of MPs increased and reduced soil respiration by 53.4 % and 5.8 %, respectively. Short-term (≤30 days) exposure to MPs increased soil respiration by 50.2 %, whereas the presence of MPs inhibited soil enzyme activity by 3.3 % when the incubation period ranged from 30 to 100 days. In addition, MPs exposure significantly (p < 0.05) increased soil respiration by 77.9 % in alkaline soil (pH > 7.5) and by 41.6 % in the absence of plants. The amendment of MPs significantly (p < 0.05) increased and reduced soil enzyme activities in acidic and alkaline soils by 4.3 % and 5.5 %, respectively, and significantly (p < 0.05) improved soil enzyme activity by 4.5 % in the presence of plants. Specifically, MPs significantly (p < 0.05) increased the activities of acid phosphatase and fluorescein diacetate hydrolase by 8.3 % and 17.1 %, respectively, but did not significantly (p > 0.05) influence urease, β-glucosidase, and catalase activities. Overall, our results suggested that MPs have nonnegligible impacts on soil microbial activity, and it is urgently necessary to explore the long-term effects of MPs on soil ecology in the natural environment.

Salt-tolerant plant moderates the effect of salinity on soil organic carbon mineralization in a subtropical tidal wetland.

Although salinization is widely known to affect cycling of soil carbon (C) in tidal freshwater wetlands, the role of the presence or absence of plants in mediating the responses of soil organic carbon (SOC) mineralization to salinization is poorly understood. In this study, we translocated soils collected from a tidal freshwater wetland to sites with varying salinities along a subtropical estuarine gradient and established unplanted and planted (with the salt-tolerant plant Cyperus malaccensis Lam.) mesocosms at each site. We simultaneously investigated cumulative soil CO2 emissions, C-acquiring enzyme activities, availability of labile organic C (LOC), and structures of bacterial and fungal communities. Overall, in the planted mesocosm, the soil LOC content and the activities of β-1,4-glucosidase, cellobiohydrolase, phenol oxidase, and peroxidase increased with salinization. However, in the unplanted mesocosm, soil LOC content decreased with increasing salinity, whereas all the C-acquiring enzyme activities did not change. In addition, salinization favored the dominance of bacterial and fungal copiotrophs (e.g., γ-Proteobacteria, Bacteroidetes, Firmicutes, and Ascomycota) in the planted mesocosms. Contrarily, in the unplanted mesocosms salinization favored bacterial and fungal oligotrophs (e.g., α-Proteobacteria, Chloroflexi, Acidobacteria, and Basidiomycota). In both planted and unplanted mesocosms, cumulative soil CO2 emissions were affected by soil LOC content, activities of C-acquiring enzymes, and microbial C-use trophic strategies. Overall, cumulative soil CO2 emissions increased by 35% with increasing salinity in the planted mesocosm but decreased by 37% as salinity increased in the unplanted mesocosm. Our results demonstrate that the presence or absence of salt-tolerant plants can moderate the effect of salinity on SOC mineralization in tidal wetland soils. Future C prediction models should embed both planted and unplanted modules to accurately simulate cycling of soil C in tidal wetlands under sea level rise.

Sources of nitrous oxide and the fate of mineral nitrogen in subarctic permafrost peat soils

Abstract. Nitrous oxide (N2O) emissions from permafrost-affected terrestrial ecosystems have received little attention, largely because they have been thought to be negligible. Recent studies, however, have shown that there are habitats in the subarctic tundra emitting N2O at high rates, such as bare peat (BP) surfaces on permafrost peatlands. Nevertheless, the processes behind N2O production in these high-emission habitats are poorly understood. In this study, we established an in situ 15N-labeling experiment with two main objectives: (1) to partition the microbial sources of N2O emitted from BP surfaces on permafrost peatlands and (2) to study the fate of ammonium and nitrate in these soils and in adjacent vegetated peat (VP) surfaces showing low N2O emissions. Our results confirm the hypothesis that denitrification is mostly responsible for the high N2O emissions from BP. During the study period, denitrification contributed ∼ 79 % of the total N2O emissions from BP, whereas the contribution from ammonia oxidation was less (about 19 %). Both gross N mineralization and gross nitrification rates were higher in BP than in VP, with high C/N ratios and a low water content likely limiting N transformation processes and, consequently, N2O production in the latter soil type. Our results show that multiple factors contribute to high N2O production in BP surfaces on permafrost peatlands, with the most important factors being the absence of plants, an intermediate to high water content and a low C/N ratio, which all affect the mineral-N availability for soil microbes, including those producing N2O. The process understanding produced here is important for the development of process models that can be used to evaluate future permafrost–N feedbacks to the climate system.

Multiple Linear and Polynomial Models for Studying the Dynamics of the Soil Solution

The objective of the present work was to study the soil solution throughout time in pots under greenhouse conditions. The work consisted of monitoring the solution of calcareous soil and forest soil in the absence of plants, with different types of fertilization: treatment 1: absolute control (irrigation water); treatment 2: Steiner nutrient solution; treatment 3: solid fertilizers; and treatment 4: vermicompost tea (aqueous extract). The samples were collected weekly using lysimeters for 14 weeks. They were analyzed to determine the nitrate content, total nitrogen, calcium, potassium, magnesium, sodium, sulfur, zinc, boron, pH, electrical conductivity, and oxide-reduction potential. To understand the interactions between treatments, soil type, and time over ion behavior and availability, linear and polynomial models were used, selected by a cross-validation method, which resulted in robust models, where it was found that the pH behavior is associated with the type of fertilization and soil type, with the elapsed time being a nonsignificant factor. On the other hand, time influenced the dynamics of the remaining ions and their availability. It was found that the multiple polynomial model fit better for the variables: potassium, calcium, sodium (square degree), electrical conductivity, nitrates, sulfur (cubic degree), zinc, oxidation-reduction potential, nitrogen, magnesium, and boron (quartic degree).

A comparison between the characteristics of a biochar-NPK granule and a commercial NPK granule for application in the soil

Continual application of nitrogen (N), phosphorous (P) and potassium (K) fertilizer may not return a profit to farmers due to the costs of application and the loss of NPK from soil in various ways. Thus, a combination of NPK granule with a porous biochar (termed here as BNPK) appears to offer multiple benefits resulting from the excellent properties of biochar. Given the lack of information on the properties of NPK and BNPK fertilizers, it is necessary to investigate the characteristics of both to achieve a good understanding of why BNPK granule is superior to NPK granule. Therefore, this study aims to investigate the characteristics of a maize straw biochar mixed with NPK granule, before and after application to soil, and compare them to those for a commercial NPK granule. The BNPK granule, with a greater surface area and porosity, showed a higher capacity to store and donate electrons than the NPK granule. Relatively lower concentrations of Ca, P, K, Si and Mg were dissolved from the BNPK, indicating the ability of the BNPK granule to maintain these mineral elements and reduce dissolution rate. To study the nutrient storage mechanism of the BNPK granule in the soil, short- and long-term leaching experiments were conducted. During the experiments, organo-mineral clusters, comprising C, P, K, Si, Al and Fe, were formed on the surface and inside the biochar pores. However, BNPK was not effective in reducing N leaching, in the absence of plants, in a red chromosol soil.

Organic Fertilization of Growing Media: Response of N Mineralization to Temperature and Moisture

Managing plant fertilization is a major concern of greenhouse growers when it comes to sustainable production on growing media. Organic fertilization is popular, but more difficult to control since organic compounds first need to be mineralized by microbes. The objective of this study was to characterize the time course of N mineralization by different fertilizer–growing media pairs, in the absence of plants. Several incubations were carried out at four temperatures (4, 20, 28, and 40 °C) and three suction potentials (−3.2, −10, and −31.6 kPa) on four growing media under two organic fertilization conditions to study the dynamics of NH4+ and NO3− production. The results showed that the release of mineral N was strongly dependent on growing media, temperature, humidity, and fertilizer nature, varying from 10.7% to 71.3% of the N fertilizer applied. A temperature action law was established for the four growing media. The Q10 value of the growing media was 1.13, lower than the average Q10 value of arable soils. On the other hand, the specific behavior of the growing media did not yield a single humidity action law. Nevertheless, the nitrification process, evaluated by analyzing the ratio of NO3− to total mineral N, showed a humidity-dependent relationship common to the four growing media and comparable to admitted observations on soils. Nitrification was optimal when growing media humidity was higher than 0.46 v/v.

Cell-Wall-Degrading Enzymes-Related Genes Originating from Rhizoctonia solani Increase Sugar Beet Root Damage in the Presence of Leuconostoc mesenteroides.

Sugar beet crown and root rot caused by Rhizoctonia solani is a major yield constraint. Root rot is highly increased when R. solani and Leuconostoc mesenteroides co-infect roots. We hypothesized that the absence of plant cell-wall-degrading enzymes in L. mesenteroides and their supply by R. solani during close contact, causes increased damage. In planta root inoculation with or without cell-wall-degrading enzymes showed greater rot when L. mesenteroides was combined with cellulase (22 mm rot), polygalacturonase (47 mm), and pectin lyase (57 mm) versus these enzymes (0–26 mm), R. solani (20 mm), and L. mesenteroides (13 mm) individually. Carbohydrate analysis revealed increased simpler carbohydrates (namely glucose + galactose, and fructose) in the infected roots versus mock control, possibly due to the degradation of complex cell wall carbohydrates. Expression of R. solani cellulase, polygalacturonase, and pectin lyase genes during root infection corroborated well with the enzyme data. Global mRNAseq analysis identified candidate genes and highly co-expressed gene modules in all three organisms that might be critical in host plant defense and pathogenesis. Targeting R. solani cell-wall-degrading enzymes in the future could be an effective strategy to mitigate root damage during its interaction with L. mesenteroides.

From energy to (soil organic) matter.

In this concept paper, we propose a new view on soil organic matter (SOM) formation: microorganisms use most of the organics entering the soil as energy rather than as a source of carbon (C), while SOM accumulates as a residual by-product because the microbial energy investment in its decomposition exceeds the energy gain. During the initial stages of decomposition, the nominal oxidation state of C (NOSC) in remaining litter decreases, and the energy content increases. This reflects the rapid mineralization of available compounds with positive and neutral NOSC (carboxylic acids, sugars, some amino acids). Consequently, the NOSC of the remaining compounds drops to -0.3 units, and the oxidation rate decreases due to the residual relative accumulation of aromatic and aliphatic compounds (which are hydrolized later) and entombment of the necromass. Ultimately, incompletely decomposed plant residues will have 1%-2.5% more energy per C unit than the initial litter. The linear decrease in energy density of a broad range of organic substances by 106kJ mol-1 C per NOSC unit upon oxidation is supported by experimental data on litter decomposition. Preferential recycling of energy-rich reduced (lipids, aromatics, certain amino acids, amino sugars) and the microbial degradation of oxidized compounds (carboxylic acids) also energetically enrich SOM. Despite the high energy content, the availability of energy stored in SOM is lower than in litter. This explains why SOM is not fully mineralized (thermodynamically unfavorable), especially in the absence of plant C to provide new energy (e.g., in bare soil). Energy from litter activates decomposers to mine nutrients stored in SOM (the main ecological function of priming effects) because the nutrient content in SOM is 2-5 times higher than that of litter. This results in only 0.4%-5%year-1 of litter-derived C being sequestered in SOM, whereas SOM stores 1%-10%year-1 of the total litter-derived energy. Thus, the energy captured by photosynthesis is the main reason why microorganisms utilize organic matter, whereby SOM is merely a residual by-product of nutrient storage and a mediator of energy fluxes.

Aquatic macrophytes mitigate the short-term negative effects of silver nanoparticles on denitrification and greenhouse gas emissions in riparian soils

Silver nanoparticles (AgNPs) are increasingly released into the aquatic environments because of their extensive use in consumer products and industrial applications. Some researchers have explored the toxicity of AgNPs to nitrogen (N) and carbon (C) cycles, but little is known about the role of aquatic plants in regulating the impact of AgNPs on these biogeochemical processes and related microorganisms. Here, two 90-day pot experiments were conducted to determine the effect of AgNPs on denitrification rates and greenhouse gas emissions in riparian wetland soils, with or without emergent plants (Typha minima Funck). As a comparison, the toxicity of equal concentration of AgNO3 was also determined. The results showed that AgNPs released a great quantity of free Ag+, most of which was accumulated in soils, while little (less than 2%) was absorbed by plant shoots and roots. Both AgNPs and AgNO3 could increase the soil redox potential and affect the growth and nutrient (N and phosphorus) uptake of plants. In soils with plants, there was no significant difference in denitrification rates and emissions of N2O and CH4 between control and AgNPs or AgNO3 treatments at all tested concentrations (0.5, 1 and 10 mg kg−1). However, low levels of AgNPs (0.5 mg kg−1) significantly enhanced CO2 emission throughout the experiment. Interestingly, in the absence of plants, a high dosage (10 mg kg−1) of AgNPs generally inhibited soil denitrification and stimulated the emissions of CO2, CH4 and N2O in the short-term. Meanwhile, the abundance of key denitrifying genes (nirS and nirK) was significantly increased by exposure to 10 mg kg−1 AgNPs or AgNO3. Our results suggest that emergent plants can alleviate the short-term negative effects of AgNPs on N and C cycling processes in wetland soils through different pathways.

Influence of wheat crop on carbon and nitrogen mineralization dynamics after the application of livestock manures

The growing global demand for livestock products has increased the scale of livestock farming. The management and disposal of large quantities of manures has become a serious environmental challenge. At the same time, there is a need for providing nutrients to plants in a sustainable way, in particular nitrogen (N). In this sense, a better understanding of N availability from livestock manures when applied to the soil will help to improve their use as fertilizers. It was hypothesized that the mineralization dynamics of the manures might be different depending on their composition and the presence of wheat.This work is performed to evaluate the effect of cattle manure (CM), hen manure (HM), and dairy slurry (DS), at two N rates when wheat (Triticum aestivum L.) was grown or not (bare soil) on i) protease, amidase, and urease activities and ii) dissolved organic carbon (DOC) and mineral N dynamics in soil solutions. A pot experiment was carried out in a greenhouse¸ and CM, HM, and DS were applied at 170 and 340 kg N ha−1 rates in the presence or absence of plants. Soil cores and solution samples were taken throughout the wheat growing period. Protease and amidase activities were higher for CM and DS applied at the highest N rate, respectively. Urease activity increased when wheat was grown with the lower N rate in the three manures. The DS caused higher concentrations of DOC and ammonium the day after its application than when HM and CM were used. During the first month, the nitrate concentration increased and was highest with HM, followed by DS and CM. However, the nitrate concentrations decreased in the treatments with plants after tillering. Wheat N uptake at harvest was highest with HM, followed by DS and CM. Mineralization dynamics were different in the three manures, which implies that the application times must be different.

Description of Microbial Communities of Phosphate Mine Wastes in Morocco, a Semi-Arid Climate, Using High-Throughput Sequencing and Functional Prediction.

Soil microbiota are vital for successful revegetation, as they play a critical role in nutrient cycles, soil functions, and plant growth and health. A rehabilitation scenario of the abandoned Kettara mine (Morocco) includes covering acidic tailings with alkaline phosphate mine wastes to limit water infiltration and hence acid mine drainage. Revegetation of phosphate wastes is the final step to this rehabilitation plan. However, revegetation is hard on this type of waste in semi-arid areas and only a few plants managed to grow naturally after 5 years on the store-and-release cover. As we know that belowground biodiversity is a key component for aboveground functioning, we sought to know if any structural problem in phosphate waste communities could explain the almost absence of plants. To test this hypothesis, bacterial and archaeal communities present in these wastes were assessed by 16S rRNA metabarcoding. Exploration of taxonomic composition revealed a quite diversified community assigned to 19 Bacterial and two Archaeal phyla, similar to other studies, that do not appear to raise any particular issues of structural problems. The dominant sequences belonged to Proteobacteria, Bacteroidetes, Actinobacteria, and Gemmatimonadetes and to the genera Massilia, Sphingomonas, and Adhaeribacter. LEfSe analysis identified 19 key genera, and metagenomic functional prediction revealed a broader phylogenetic range of taxa than expected, with all identified genera possessing at least one plant growth-promoting trait. Around 47% of the sequences were also related to genera possessing strains that facilitate plant development under biotic and environmental stress conditions, such as drought and heat.

SOIL-INSECT toolbox: A new chamber for analysing the behaviour of herbivorous insects and tri-trophic interactions in soil

A chamber, named SOIL-INSECT toolbox, was developed to analyse the effect of various factors on the behaviour of soil-dwelling insects. It is equipped with sensors that continuously monitor the concentration of CO2 in the different compartments of the chamber without disturbing the air balance in the soil. The chamber can be adapted to study different stimuli, including volatile compounds, both in the presence and absence of plants. The chamber was tested using the larvae of Melolontha spp., which confirmed its suitability for carrying out complex studies on insect-insect and insect-plant-microbiome interactions in a complex environment such as soil. The results of behavioural experiments using L3 larvae of Melolontha spp. in sterilized and natural soils revealed that the soil condition affected the behaviour of the larvae, likely due to its effect on the soil microbiome and physico-chemical characteristics.

Repeated annual application of glyphosate reduces the abundance and alters the community structure of soil culturable pseudomonads in a temperate grassland

Grasslands include some of the most endangered and less protected ecosystems on the planet, such as the Pampa of South America. In the Flooding Pampa where native grasslands were not replaced by crops, glyphosate is frequently sprayed in late-summer every year to increase winter forage productivity for cattle without knowing the impacts on both aboveground and belowground grassland genetic resources. Here, we evaluated the effect of this practice on the abundance and community structure of members of the genus Pseudomonas, one of the most diverse bacterial taxa of the plant rhizosphere broadly recognized by their benefits on plant growth and protection, and on soil remediation. In a field experiment, we analyzed the impact of a single application or of a repeated annual application during 4 consecutive years of the recommended dose of commercial glyphosate (Glacoxan®, 3 l ha-1 and 1440 g active ingredient ha-1). In a greenhouse experiment, we tested whether exposure of bare soil to either commercially formulated or pure glyphosate has a direct impact on the resident pseudomonas community in the absence of plants. In the field, we found that the repeated annual herbicide application resulted in a reduction in the abundance and a shift in the community structure of culturable pseudomonads, with evidence of an enrichment of glyphosate-metabolizing lineages. On the other hand, a single application of glyphosate to bare soil under greenhouse conditions did not affect the abundance nor the community structure of pseudomonads. Considering that these plant-beneficial bacteria are natural inhabitants of the rhizosphere and that their fitness is promoted by plant root exudates, the observed alterations are most likely associated with the drop in the vegetation cover directly provoked by the effect of glyphosate. For the first time, we report on the consequences that a reiterated glyphosate application has on a diverse soil reservoir of bacteria that contributes to crucial ecosystem functions in a temperate natural grassland under animal production. Our findings strengthen the notion that this agronomical practice has an unavoidable imprint on non-target microorganisms that are relevant components of the plant-soil feedbacks and that may be instrumental for ecosystem restoration. We conclude that it is necessary to develop sustainable management practices to avoid affecting key functional microorganisms and exploit their contributions to society.

Effects of Association of Barley Plants with Hydrocarbon-Degrading Bacteria on the Content of Soluble Organic Compounds in Clean and Oil-Contaminated Sand.

Plant-bacteria consortia are more effective in bioremediation of petroleum contaminated soil than when either organism is used individually. The reason for this is that plant root exudates promote growth and activity of oil degrading bacteria. However, insufficient attention has been paid to the ability of bacteria to influence root exudation. Therefore, the influence of barley plants and/or bacterial inoculation (Pseudomonas hunanensis IB C7 and Enterobacter sp. UOM 3) on the content of organic acids, sugars and plant hormones in the eluate from clean and oil-polluted sand was studied separately or in combination. These strains are capable of oxidizing hydrocarbons and synthesizing auxins. Concentrations of organic acids and sugars were determined using capillary electrophoresis, and hormones by enzyme-linked immunosorbent assays. In the absence of plants, no sugars were detected in the sand, confirming that root exudates are their main source. Introducing bacteria into the sand increased total contents of organic compounds both in the presence and absence of oil. This increase could be related to the increase in auxin amounts in the sand eluate, as well as in plants. The results indicate that bacteria are able to increase the level of root exudation. Since auxins can promote root exudation, bacterial production of this hormone is likely responsible for increased concentrations of soluble organic compounds in the sand. Bacterial mediation of root exudation by affecting plant hormonal status should be considered when choosing microorganisms for phytoremediation.

An integrated dynamic model for evaluating the influence of ground to air heat transfer system on heating, cooling and CO2 supply in Greenhouses: Considering crop transpiration

Nowadays, one of the most important challenges in developing greenhouses is meeting their energy demand. The other challenge is the high water consumption of evaporative-cooling systems in arid and semi-arid regions. In this study, a integrated dynamic model is developed to determine the greenhouse relative humidity, carbon dioxide, and temperature, considering transpiration. The model is applied to a greenhouse utilizing a ground to air heat transfer system, located in the Alborz province of Iran and the results are validated with experimental data. Energy and water performance of the greenhouse are evaluated for the case study greenhouse. Then, the model is applied to a greenhouse (similar to the case study) in different climate zones of Iran to study the impact of climatic conditions on greenhouse performance. The results are presented for both cases of presence and absence of plant in greenhouses. Transpiration causes the heating/cooling demand of the greenhouse to increases/decreases by 17–40%/63–71% from climate 1 (cold and dry-humid climatic conditions) to climate 4 (mild and hot-humid climate regions). The water consumption of the evaporative-cooling system decreases by 17–49% from climate 1 to 4 when transpiration is taken into consideration.