Reduced Nitrogen Availability Research Articles

Strong regulation of nitrogen supply and demand in a key desert legume tree

High abundance of legumes in drylands suggests that symbiotic nitrogen fixation provides an advantage in water-limited environments. However, the interactive effect of nitrogen availability and water scarcity on the nitrogen fixation strategies of dryland legumes remain largely unexplained. We conducted two experiments to test the effects of nitrogen availability and drought on symbiotic nitrogen fixation in two drought-adapted Acacia tree species. Seedlings were grown under deficient and sufficient levels of nitrogen and with and without an imposed drought to test the effect of resource availability on nitrogen fixation and plant growth. We found that seedlings that grew in extreme deficiency of nitrogen reached a similar biomass as seedling that grew with a sufficient supply of nitrogen, showing a high nitrogen-use efficiency. Nitrogen fixation was strongly downregulated (reduction of 90% in biomass allocation to nodules) when plants received sufficient nitrogen supply. Under nitrogen deficiency, drought had a slight negative effect on nodule biomass and total biomass. Under sufficient nitrogen, drought reduced nitrogen availability enough to induce an increase in symbiotic nitrogen fixation in the risk-averse A. raddiana but not in the risk-taking A. tortilis. We conclude that strong regulation of nitrogen fixation together with low nitrogen demand, and flexible strategies of carbon and nitrogen allocation, increase the chance of legume tree survival and establishment in dry and unpredictable environments.

Hydrogen peroxide regulates the biosynthesis of phenolic compounds and antioxidant quality enhancement in lettuce under low nitrogen condition.

Reduced nitrogen availability is an efficient strategy for increasing the accumulation of phenolic compounds in vegetables, but related mechanisms remain unknown. Here, the production of hydrogen peroxide (H2O2) and its potential roles in regulating phenolic biosynthesis and enhancing the antioxidant quality of lettuce under low nitrogen (LN) conditions were investigated. The LN treatment caused a rapid production of H2O2, which effectively increased lettuce quality by enhancing the levels of phenolic compounds and other nutrients such as ascorbic acid, glutathione, soluble sugar, and soluble protein. The increased phenolic content was related to the higher expression levels of phenolic biosynthesis genes, including PAL, CHS, DFR, F35H, and UFGT, and higher photosynthetic capacity after H2O2 addition under LN conditions. However, these positive effects were suppressed by dimethylthiourea (DMTU), a scavenger of H2O2. These results suggest that H2O2 as an important signal molecular mediates the LN-caused phenolic accumulation and antioxidant quality enhancement in lettuce.

Management Effects on the Performance of Double Cropping Systems—Results from a Multi-Site Experiment

Traditional (silage) maize production often has negative side-effects related to unprotected soil surface. There are several possibilities to enhance system sustainability through reducing soil disturbance. However, implementation may be hindered due to reduced nitrogen availability and increased weed infestation, especially in organic agriculture. A field experiment to evaluate yield potential of 18 silage maize cropping systems under organic management was conducted at three distinct locations. Examined parameters were first crop, maize and total harvested dry matter yield (DMY), and maize dry matter content (DMC). Treatment factors included first crop (FC—winter pea, hairy vetch, and their mixtures with rye, control (SCS), management—incorporating FC use and tillage (double cropping system no-till (DCS NT), double cropping system reduced till (DCS RT), double cropped, mulched system terminated with roller-crimper (DCMS Roll), SCS control), fertilization, mechanical weed control—and row width (75 cm, 50 cm). A high variation among environments occurred, but similar patterns manifested across locations: Number of crops in the rotation had a high influence, followed by management and FC. Row width had only marginal and inconsistent effect. FC mixtures generally yielded higher than pure legumes. Maize DMY in DCS, DCMS was lower than or comparable to SCS. Maize DMC were environment-specifically below acceptable range, especially under DCMS. Total harvested DMY in DCS were similar to or greater than SCS. Results suggest differences from the optimization of farming operations for one (SCS) or two crops (DCS, DCMS) with strong effects at early maize development and on the length of season. FC use and tillage factors possibly altered the soil water, temperature, and mineralization dynamics, resulting in modified maize growth. DCS RT and DCMS Pure performed with the best maize yields, improved soil protection, and tillage reduction in the silage maize part of the rotation under organic management. However, alternative management systems, especially under DCS NT and DCMS (Mix) with studied maize maturity classes are less suited, particularly in cool and wet spring conditions, because of a potentially slower development of FC, a later establishment of maize plants and therefore, a shorter growing season for the maize crop.

Nitrogen use efficiency, rhizosphere bacterial community, and root metabolome reprogramming due to maize seed treatment with microbial biostimulants

Seed inoculation with beneficial microorganisms has gained importance as it has been proven to show biostimulant activity in plants, especially in terms of abiotic/biotic stress tolerance and plant growth promotion, representing a sustainable way to ensure yield stability under low input sustainable agriculture. Nevertheless, limited knowledge is available concerning the molecular and physiological processes underlying the root‐inoculant symbiosis or plant response at the root system level. Our work aimed to integrate the interrelationship between agronomic traits, rhizosphere microbial population and metabolic processes in roots, following seed treatment with either arbuscular mycorrhizal fungi (AMF) or Plant Growth‐Promoting Rhizobacteria (PGPR). To this aim, maize was grown under open field conditions with either optimal or reduced nitrogen availability. Both seed treatments increased nitrogen uptake efficiency under reduced nitrogen supply revealed some microbial community changes among treatments at root microbiome level and limited yield increases, while significant changes could be observed at metabolome level. Amino acid, lipid, flavone, lignan, and phenylpropanoid concentrations were mostly modulated. Integrative analysis of multi‐omics datasets (Multiple Co‐Inertia Analysis) highlighted a strong correlation between the metagenomics and the untargeted metabolomics datasets, suggesting a coordinate modulation of root physiological traits.

Metabolomics and Transcriptomics Integration of Early Response of Populus tomentosa to Reduced Nitrogen Availability.

Nitrogen (N) is one of the most crucial elements for plant growth and development. However, little is known about the metabolic regulation of trees under conditions of N deficiency. In this investigation, gas chromatography-mass spectrometry (GC-MS) was used to determine global changes in metabolites and regulatory pathways in Populus tomentosa. Thirty metabolites were found to be changed significantly under conditions of low-N stress. N deficiency resulted in increased levels of carbohydrates and decreases in amino acids and some alcohols, as well as some secondary metabolites. Furthermore, an RNA-sequencing (RNA-Seq) analysis was performed to characterize the transcriptomic profiles, and 1,662 differentially expressed genes were identified in P. tomentosa. Intriguingly, four pathways related to carbohydrate metabolism were enriched. Genes involved in the gibberellic acid and indole-3-acetic acid pathways were found to be responsive to low-N stress, and the contents of hormones were then validated by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS). Coordinated metabolomics and transcriptomics analysis revealed a pattern of co-expression of five pairs of metabolites and unigenes. Overall, our investigation showed that metabolism directly related to N deficiency was depressed, while some components of energy metabolism were increased. These observations provided insights into the metabolic and molecular mechanisms underlying the interactions of N and carbon in poplar.

Positive interactions occur between Phragmites australis lineages across short term experimental nutrient regimes

Land use changes and greater nitrogen input into waterways have facilitated the spread of an invasive Eurasian lineage of Phragmites australis across North America. Its establishment has led to decreases in wetland plant diversity, and displacement of a native American Phragmites lineage considered to be a low-nutrient specialist. We hypothesized that carbon-rich amendments that reduced nitrogen availability would competitively favor the native lineage and nitrogen additions would favor the invasive lineage. In the greenhouse we assessed competitive interactions between native and invasive lineages following sawdust (low nitrogen) and urea (high nitrogen) additions by measuring total biomass, chlorophyll fluorescence and evaluating biomass allocation. Sawdust additions did not limit invasive Phragmites growth, while urea increased aboveground biomass of both lineages. Unexpectedly, mixtures of native and invasive Phragmites produced more above and belowground biomass than monocultures. Our findings suggest that at the level examined in this study, carbon additions would not be an effective management tool to control invasive Phragmites or restore the native North American lineage, but that facilitation between native and invasive lineages could promote their coexistence across a range of nutrient availability. Our results also provide limited evidence that displacement of native Phragmites could be due to other factors such as disturbance rather than competitive exclusion.

Suppression of Cheatgrass by Perennial Bunchgrasses

Long-term control of the invasive annual grass cheatgrass is predicated on its biological suppression. Perennial grasses vary in their suppressive ability. We compared the ability of a non-native grass (“Hycrest” crested wheatgrass) and two native grasses (Snake River wheatgrass and bluebunch wheatgrass) to suppress cheatgrass. In a greenhouse in separate tubs, 5 replicates of each perennial grass were established for 96 d, on which two seeds of cheatgrass, 15 cm apart, were then sown in a semicircular pattern at distances of 10 cm, 30 cm, and 80 cm from the established perennial bunchgrasses. Water was not limiting. After 60 d growth, cheatgrass plants were harvested, dried, weight recorded, and tissue C and N quantified. Soil N availability was quantified at each location where cheatgrass was sown, both before sowing and after harvest. Relative to cheatgrass grown at 80 cm, all perennial grasses significantly reduced aboveground biomass at 30 cm (68% average reduction) and at 10 cm (98% average reduction). Sown at 10 cm from established perennial grasses, cheatgrass aboveground biomass was inversely related with perennial grass root mass per unit volume of soil. All cheatgrass sown at 10 cm from “Hycrest” crested wheatgrass died within 38 d. Before sowing of cheatgrass, soil 10 cm from established perennial grasses had significantly less mineral N than soil taken at 30 cm and 80 cm. Relative to cheatgrass tissue N for plants grown at 80 cm, cheatgrass nearest to the established perennial grasses contained significantly less tissue N. All perennial grasses inhibited the NO2− to NO3− nitrification step; for “Hycrest” crested wheatgrass, soil taken at 10 cm from the plant had a molar proportion of NO2− in the NO2− + NO3− pool of > 90%. In summary, a combination of reduced nitrogen availability, occupation of soil space by perennial roots, and attenuation of the nitrogen cycle all contributed to suppression of cheatgrass.

Septoria Leaf Blotch and Reduced Nitrogen Availability Alter WRKY Transcription Factor Expression in a Codependent Manner.

A major cause of yield loss in wheat worldwide is the fungal pathogen Zymoseptoria tritici, a hemibiotrophic fungus which causes Septoria leaf blotch, the most destructive wheat disease in Europe. Resistance in commercial wheat varieties is poor, however, a link between reduced nitrogen availability and increased Septoria tolerance has been observed. We have shown that Septoria load is not affected by nitrogen, whilst the fungus is in its first, symptomless stage of growth. This suggests that a link between nitrogen and Septoria is only present during the necrotrophic phase of Septoria infection. Quantitative real-time PCR data demonstrated that WRKYs, a superfamily of plant-specific transcription factors, are differentially expressed in response to both reduced nitrogen and Septoria. WRKY39 was downregulated over 30-fold in response to necrotrophic stage Septoria, whilst changes in the expression of WRKY68a during the late biotrophic phase were dependent on the concentration of nitrogen under which wheat is grown. WRKY68a may therefore mediate a link between nitrogen and Septoria. The potential remains to identify key regulators in the link between nitrogen and Septoria, and as such, elucidate molecular markers for wheat breeding, or targets for molecular-based breeding approaches.

Nitrogen limitation reveals large reserves in metabolic and translational capacities of yeast

Cells maintain reserves in their metabolic and translational capacities as a strategy to quickly respond to changing environments. Here we quantify these reserves by stepwise reducing nitrogen availability in yeast steady-state chemostat cultures, imposing severe restrictions on total cellular protein and transcript content. Combining multi-omics analysis with metabolic modeling, we find that seven metabolic superpathways maintain >50% metabolic capacity in reserve, with glucose metabolism maintaining >80% reserve capacity. Cells maintain >50% reserve in translational capacity for 2490 out of 3361 expressed genes (74%), with a disproportionately large reserve dedicated to translating metabolic proteins. Finally, ribosome reserves contain up to 30% sub-stoichiometric ribosomal proteins, with activation of reserve translational capacity associated with selective upregulation of 17 ribosomal proteins. Together, our dataset provides a quantitative link between yeast physiology and cellular economics, which could be leveraged in future cell engineering through targeted proteome streamlining.

Mineralization of Nitrogen in Soils with Application of Acid Whey at Different pH

Agro-industrial wastes are commonly used as nitrogen sources in agriculture, and its availability depends on the dynamics of nitrogen mineralization. The pH has great effects on soil nitrogen dynamics; thus, we hypothesized that the increase of pH would increase nitrogen mineralization and nitrification. The aim of this study was to evaluate the effects of pH and application of acid whey in nitrogen mineralization and nitrification rates using two types of soils, a hapludult and a eutrudox. In a completely randomized factorial design, N mineralization under different pH levels (4.5; 5.0; 5.5; 6.0; 6.5) was evaluated, with and without whey application, with an equivalent of 40 mg N dm−3. Soils were incubated for 182 days, and throughout this period, eleven evaluations were made to assess N mineralization over time. The hapludult soil had higher nitrate concentrations and the acid whey fertilization increased inorganic nitrogen in both soils. Soil pH did not influence inorganic nitrogen contents, but affected nitrification in both soils. Soil pH levels also resulted in variations on the constant of mineralization, a parameter related to mineralization speed, but without any strong trend. The application of acid whey displayed a satisfactory potential in relation to nitrogen incorporation in both tested soils. Soil pH around 4.5–5.5 is the optimum pH range, because it did not affect the nitrogen supply and decreases nitrification. Results demonstrate that soil pH can be used to avoid nitrification without reducing nitrogen availability to plants.

Burrowing Crabs Weaken Mutualism Between Foundation Species

Foundation species often interact with each other and co-create habitat upon which other species depend. Whether the presence of these facilitated species feeds back to mediate the growth and resilience of the foundation species themselves, and influence the strength of their interactions, remains poorly understood. In a 16-month field experiment in a southeastern US salt marsh, we tested how the overlapping presence of two foundation species, cordgrass (Spartina alterniflora) and ribbed mussels (Geukensia demissa), influences the abundance of facilitated species, specifically burrowing crabs (mainly Uca pugnax), and how crabs, in turn, affect each foundation species and their mutualistic interaction. Mussel aggregations enhanced crab abundance 3.9-fold, which in turn reduced both mussel and cordgrass growth and stifled cordgrass recovery after a simulated disturbance. Porewater and plant tissue analyses suggest crabs reduced cordgrass growth by reducing nitrogen availability, damaging roots, and potentially interfering with mussel deposition of nutrient-rich pseudofeces. A five-site field survey along 700 km southeastern US coastline revealed that cordgrass biomass and crab abundance are consistently higher in mussel aggregations. Furthermore, cordgrass biomass correlated negatively with crab abundance, supporting our experimental findings and the hypothesis that facilitated biota can negatively impact the foundation species upon which they depend. We anticipate that such negative, but non-lethal, feedbacks between foundation species and the biota they facilitate may be a common but overlooked phenomenon controlling foundation species growth and interactions in a wide range of ecosystems.

High pyrolysis temperature biochars reduce nitrogen availability and nitrous oxide emissions from an acid soil

AbstractBiochar–bioenergy coproduction from biomass pyrolysis has the potential to contribute to climate change mitigation. Biochar produced at various pyrolysis temperatures (<600°C) has been widely studied. However, the effect of biochars, produced at high pyrolysis temperature (≥600°C), on soil nitrogen (N) dynamics and nitrous oxide (N2O) emission is largely unknown. A pot trial was performed to examine the effect of high pyrolysis temperature (600, 700, 850 and 950°C) woody biochars on soil N dynamics, microbial gene abundance and N2O emissions with (+N) and without N (−N) fertilization from an acid soil. Results showed that all biochar treatments significantly lowered the N2O emissions in both fertilized and unfertilized regimes. However, the suppressive effect on N2O emission among different high pyrolysis temperatures was not statistically different. Biochar amendment significantly decreased the concentration of soil NH4+, and lower levels of soil NO3− were observed at the later stage of experiment. Under −N, plant biomass and N uptake were significantly lowered in all biochar treatments. Under +N, biochar addition significantly increased plant biomass, while only the 700°C biochar significantly increased N uptake. This suggests that single application of biochar could limit soil mineral N bioavailability and further decrease plant growth and N uptake in the plant–soil system. Biochar amendments tended to increase nitrous oxide reductase (nosZ) gene abundance, but this effect was only significant for biochar produced at 950°C under +N. In conclusion, high pyrolysis temperature biochars can be effectively used to reduce N2O emission, while increases in nosZ gene abundance and decreases in NH4+ and NO3− concentrations in the acid soil are likely to be responsible for the reduction in N2O emission. Thus, woody biochars as a by‐product produced at high pyrolysis temperature have the potential to mitigate soil N2O emission via modifying N transformation and further affect climate change.

Nitrous oxide emissions from Norway spruce forests on drained organic and mineral soil

Nitrous oxide (N2O) emissions from drained organic (Histosol) and mineral (Umbrisol) soils having a 60 year old Norway spruce (Picea abies (L.) Karst.) forest in a catchment in southwest Sweden were measured using static closed chambers every other week over 3 years (August 2010 – July 2013). High emissions were observed during the summer months for both sites, which were significantly higher for the drained organic soils compared to the mineral soils: average emissions of 49.0 ± 3.3 and 8.0 ± 3.3 μg N2O·m−2·h−1, respectively. As the experiment was designed to have similar forest and weather conditions for both sites, these were omitted as explanatory factors for the emission difference. Initially, the soil organic matter concentration (percent by mass) difference was thought to be the cause. However, the results found that the soil organic matter amount per square metre of top soil was similar at both sites, suggesting other possible explanations. We propose that the most plausible explanation is that higher tree growth and mycorrhizal nitrogen demand reduce nitrogen availability contributing to the lower N2O emissions from the mineral soil site.

Earlier springs are causing reduced nitrogen availability in North American eastern deciduous forests

There is wide agreement that anthropogenic climate warming has influenced the phenology of forests during the late twentieth and early twenty-first centuries(1,2). Longer growing seasons can lead to increased photosynthesis and productivity(3), which would represent a negative feedback to rising CO2 and consequently warming(4,5). Alternatively, increased demand for soil resources because of a longer photosynthetically active period in conjunction with other global change factors might exacerbate resource limitation(6,7), restricting forest productivity response to a longer growing season(8,9). In this case, increased springtime productivity has the potential to increase plant nitrogen limitation by increasing plant demand for nitrogen more than nitrogen supplies, or increasing early-season ecosystem nitrogen losses(10,11). Here we show that for 222 trees representing three species in eastern North America earlier spring phenology during the past 30 years has caused declines in nitrogen availability to trees by increasing demand for nitrogen relative to supply. The observed decline in nitrogen availability is not associated with reduced wood production, suggesting that other environmental changes such as increased atmospheric CO2 and water availability are likely to have overwhelmed reduced nitrogen availability. Given current trajectories of environmental changes, nitrogen limitation is likely to continue to increase for these forests, possibly further limiting carbon sequestration potential.

Agronomic characteristics of five different urban waste digestates

The use of digestate in agriculture is an efficient way to recycle materials and to decrease the use of mineral fertilizers. The agronomic characteristics of the digestates can promote plant growth and soil properties after digestate fertilization but also harmful effects can arise due to digestate quality, e.g. pH, organic matter and heavy metal content. The objective of this study was to evaluate the differences and similarities in agronomic characteristics and the value of five urban waste digestates from different biogas plants treating either food waste, organic fraction of organic solid waste or a mixture of waste-activated sludge and vegetable waste. The digestate agronomic characteristics were studied with chemical analyses and the availability of nutrients was also assessed with growth experiments and soil mineralization tests. All studied urban digestates produced 5–30% higher ryegrass yields compared to a control mineral fertilizer with a similar inorganic nitrogen concentration, while the feedstock source affected the agronomic value. Food waste and organic fraction of municipal solid waste digestates were characterized by high agronomic value due to the availability of nutrients and low heavy metal load. Waste-activated sludge as part of the feedstock mixture, however, increased the heavy metal content and reduced nitrogen availability to the plant, thus reducing the fertilizer value of the digestate.

Effects of nitrogen on growth and carbohydrate formation in Porphyridium cruentum

Abstract The microalga Porphyridium cruentum (Rhodophyta) has several industrial and pharmaceutical uses, especially for its polysaccharide production. This study aimed to investigate the influence of nitrogen levels as reflected by altered N:P ratios on the production and content of biomass and carbohydrate. N:P molar ratios were altered in batch cultures to range from 1.6 to 50 using the Redfield ratio of 1:16 as reference. Algal growth (estimated as final cell number, biomass concentration and maximum specific growth rate) was negatively affected at low N:P ratios. The optimal N:P ratio for growth was identified at 35–50, with specific growth rates of 0.19 day−1 and maximum cell concentrations of 59·108 cells L−1 and 1.2 g dry weight of biomass L−1. In addition, variation in cell size was seen. Cells with larger diameters were at higher N:P ratios and smaller cells at lower ratios. The cellular carbohydrate content increased under reduced nitrogen availability. However, because accumulation was moderate at the lowest N:P ratio, 0.4 g per g dry weight biomass compared to 0.24 at the Redfield ratio of 16:1, conditions for increased total carbohydrate formation were identified at the N:P ratios optimal for growth. Additionally, carbohydrates were largely accumulated in late exponential to stationary phase.

Elevated CO<sub>2</sub> concentrations alter nitrogen metabolism and accelerate senescence in sunflower (Helianthus annuus L.) plants

Elevated CO<sub>2</sub> concentrations were found to cause early senescence during leaf development in sunflower (Helianthus annuus L.) plants, probably by reducing nitrogen availability since key enzymes of nitrogen metabolism, including nitrate reductase (NR); glutamine synthetase (GS) and glutamate dehydrogenase (GDH), were affected. Elevated CO<sub>2</sub> concentrations significantly decreased the activity of nitrogen assimilation enzymes (NR and GS) and increased GDH deaminating activities. Moreover, they substantially rose the transcript levels of GS1 while lowering those of GS2. Increased atmospheric CO<sub>2</sub> concentrations doubled the CO<sub>2</sub> fixation and increased transpiration rates, although these parameters decreased during leaf ontogeny. It can be concluded that elevated atmospheric CO<sub>2</sub> concentrations alter enzymes involved in nitrogen metabolism at the transcriptional and post-transcriptional levels, thereby boosting mobilization of nitrogen in leaves and triggering early senescence in sunflower plants.

Natural Establishment of Specialist Plant Species after Topsoil Removal and Soil Perturbation in Degraded Calcareous Sandy Grassland

AbstractSpecialist plant species in calcareous sandy grasslands are threatened by acidification and high nutrient levels in the topsoil. We investigated whether topsoil removal and soil perturbation in degraded sandy grasslands could lead to establishment of specialist species belonging to the threatened xeric sand calcareous grassland habitat. Restoration actions performed in 2006 resulted in increased soil pH and reduced nitrogen availability. We found early colonisztion of the perennial key species Koeleria glauca after both deep perturbation and topsoil removal, and high seedling establishment in topsoil removal plots 5 and 6 years following the restoration treatment (2011–2012). After topsoil removal, overall vegetation composition in 2012 had developed toward the undegraded community, with target species accounting for 20% of the community after topsoil removal, compared to 30% in the undegraded vegetation, and less than 1% in untreated controls. Deep perturbation led to 7% target species, while there were almost no effects of shallow perturbation 6 years following treatment. These results demonstrate that topsoil removal can promote colonization of target species of calcareous sandy grassland and highlights the importance of considering the regeneration niche for target species when implementing restoration measures.

Nitrogen stable isotopes indicate differences in nitrogen cycling between two contrasting Jamaican montane forests

The aim of this study is to enhance our knowledge of nitrogen (N) cycling and N acquisition in tropical montane forests through analysis of stable N isotopes (δ15N). Leaves from eight common tree species, leaf litter, soils from three depths and roots were sampled from two contrasting montane forest types in Jamaica (mull ridge and mor ridge) and were analysed for δ15N. All foliar δ15N values were negative and varied among the tree species but were significantly more negative in the mor ridge forest (by about 2 ‰). δ15N of soils and roots were also more negative in mor ridge forests by about 3 ‰. Foliar δ15N values were closer to that of soil ammonium than soil nitrate suggesting that trees in these forests may have a preference for ammonium; this may explain the high losses of nitrate from similar tropical montane forests. There was no correlation between the rankings of foliar δ15N in the two forest types suggesting a changing uptake ratio of different N forms between forest types. These results indicate that N is found at low concentrations in this ecosystem and that there is a tighter N cycle in the mor ridge forest, confirmed by reduced nitrogen availability and lower rates of nitrification. Overall, soil or root δ15N values are more useful in assessing ecosystem N cycling patterns as different tree species showed differences in foliar δ15N between the two forest types.

Effects of the integrated use of effective micro-organisms, compost and mineral fertilizer on greenhouse-grown tomato

Effective microorganisms (EM), a commercial concoction of microbes that includes yeasts, fungi, bacteria and actinomycetes, have been found to be effective in enhancing crop growth by a number of scholars. The present study was carried out mainly to investigate the effects of effective micro-organisms on growth, yield and quality of tomato (Lycopersicon esculentum mill) grown under a controlled environment, along with selected soil properties. Treatments included: control, effective microorganisms, mineral fertilizer, effective microorganisms + mineral fertilizer, compost, compost + effective microorganisms, compost + mineral fertilizer and compost + mineral fertilizer + effective microorganisms. EM application had a negative effect on tomato leaf dry matter yield, number of leaves, number of trusses, fruit yield and number of fruits. The negative effects of EM were ascribed to nitrogen immobilization by the effective microorganisms that could have resulted in reduced nitrogen availability to plants. The lower number of fruits associated with EM application resulted in improved average fruit weight of tomatoes grown in the greenhouse, possibly as a result of more assimilates being partitioned to the few fruits formed. Key words: Tomato, compost, effective microorganisms (EM), mineral fertilizer, yield.