Exogenous Nutrients Research Articles

Exogenous nutrients and carbon resource change the responses of soil organic matter decomposition and nitrogen immobilization to nitrogen deposition.

It is unclear whether exogenous nutrients and carbon (C) additions alter substrate immobilization to deposited nitrogen (N) during decomposition. In this study, we used laboratory microcosm experiments and 15N isotope tracer techniques with five different treatments including N addition, N+non-N nutrients addition, N+C addition, N+non-N nutrients+C addition and control, to investigate the coupling effects of non-N nutrients, C addition and N deposition on forest floor decomposition in subtropical China. The results indicated that N deposition inhibited soil organic matter and litter decomposition by 66% and 38%, respectively. Soil immobilized 15N following N addition was lowest among treatments. Litter 15N immobilized following N addition was significantly higher and lower than that of combined treatments during the early and late decomposition stage, respectively. Both soil and litter extractable mineral N were lower in combined treatments than in N addition treatment. Since soil N immobilization and litter N release were respectively enhanced and inhibited with elevated non-N nutrient and C resources, it can be speculated that the N leaching due to N deposition decreases with increasing nutrient and C resources. This study should advance our understanding of how forests responds the elevated N deposition.

Attacking the supply wagons to starve cancer cells to death.

The constitutive anabolism of cancer cells not only supports proliferation but also addicts tumor cells to a steady influx of exogenous nutrients. Limiting access to metabolic substrates could be an effective and selective means to block cancer growth. In this review, we define the pathways by which cancer cells acquire the raw materials for anabolism, highlight the actionable proteins in each pathway, and discuss the status of therapeutic interventions that disrupt nutrient acquisition. Critical open questions to be answered before apical metabolic inhibitors can be successfully and safely deployed in the clinic are also outlined. In summary, recent studies provide strong support that substrate limitation is a powerful therapeutic strategy to effectively, and safely, starve cancer cells to death.

Arginine starvation in colorectal carcinoma cells: Sensing, impact on translation control and cell cycle distribution

Tumor cells rely on a continued exogenous nutrient supply in order to maintain a high proliferative activity. Although a strong dependence of some tumor types on exogenous arginine sources has been reported, the mechanisms of arginine sensing by tumor cells and the impact of changes in arginine availability on translation and cell cycle regulation are not fully understood. The results presented herein state that human colorectal carcinoma cells rapidly exhaust the internal arginine sources in the absence of exogenous arginine and repress global translation by activation of the GCN2-mediated pathway and inhibition of mTOR signaling. Tumor suppressor protein p53 activation and G1/G0 cell cycle arrest support cell survival upon prolonged arginine starvation. Cells with the mutant or deleted TP53 fail to stop cell cycle progression at defined cell cycle checkpoints which appears to be associated with reduced recovery after durable metabolic stress triggered by arginine withdrawal.

Limnological assessment of the meteo-hydrological and physicochemical factors for summer cyanobacterial blooms in a regulated river system

This study aimed to explain how the changes in certain hydrological, meteorological and physicochemical factors influence the cell density of the cyanobacteria Microcystis aeruginosa in the Nakdong River. Occurrence patterns of M. aeruginosa were analyzed between 1993 and 2010 (N =96) using a self-organizing map. The cell density of M. aeruginosa was sensitive to certain meteorological, hydrological and physicochemical factors. In addition, our clustering analysis results identified specific limnological features under different environmental conditions. Cluster 1 suggested that high rainfall and increased river flow, dam discharge, total phosphorous and phosphate concentrations were associated with low M. aeruginosa cell density (June–July; monsoon season). However, cluster 2 suggested low irradiance since water temperature decreases with irradiation time, and thus low M. aeruginosa cell density (April–June and after November). Finally, cluster 3 was indicative of high water temperature and irradiance, increased irradiation time, low phosphate and nitrate concentrations, and high M. aeruginosa cell density (August, after the monsoon season). Taken together, these results suggest that rainfall, river flow, water temperature and nutrient concentration (i.e. , phosphates and nitrates) were the primary factors that affected cyanobacterial bloom occurrence in the Nakdong River. M. aeruginosa blooms can be suppressed by employing an integrated water resource management program that accommodates meteo-hydrological factors along with the effective control of exogenous nutrient sources.

Spatio-temporal variation in phytoplankton community and its influencing factors in Danjiangkou Reservoir

为研究丹江口浮游植物的群落特征，探讨影响浮游植物时空分布的环境因子，于2014年5月-2015年4月对丹江口水库进行了为期1年的调查.此次调查共采集到浮游植物66种，隶属于7门21科38属.浮游植物全年平均生物量为0.35 mg/L，平均密度为9.08×10⁵ cells/L.优势种为脆杆藻、小环藻、直链藻和栅藻，其中脆杆藻所占比例最大，平均生物量为0.089 mg/L，占总生物量的25.43%.近些年丹江口水库营养水平的提高可能是脆杆藻生物量升高的主要原因.绿藻和蓝藻在夏季大量繁殖，硅藻为春、秋和冬季优势门类.汉江库区浮游植物生物量大于丹江库区，两个库区的浮游植物种类组成存在明显的差异，丹江库区优势门类为硅藻门，而汉江库区为绿藻门.浮游植物生物量与环境因子的相关分析表明，浮游植物生物量的主要影响因子是总磷浓度、pH值和溶解氧浓度.RDA分析表明，影响浮游植物组成的主要环境因子是溶解氧浓度、pH值、总磷浓度和水温.为控制浮游植物的生物量，防止其异常增殖造成水华，应严格控制外源营养盐特别是磷元素的输入.本研究可为丹江口水库的水质改善及富营养化防治提供一定的科学依据.;In order to explore the spatiotemporal variations in phytoplankton community and its influencing factors in Danjiangkou Reservoir, we conducted a one-year survey from May 2014 to April 2015. Sixty-six species, including 38 genera, 21 families and 7 phyla, were identified in the survey. The average biomass of phytoplankton is 0.35 mg/L, while the average density is 9.08×10⁵ cells/L. Dominant species are Fragilaria spp., Cyclotella spp., Melosira spp., and Scenedesmus spp.. Fragilaria spp. is the most dominant specie, and its average biomass is 0.089 mg/L, making up 25.43% of total biomass. In recent years, high level of nutrient may be the main cause of increasement in Fragilaria biomass in Danjiangkou Reservoir. Chlorophyta and cyanobacteria bloomed in summer, while diatom dominated in spring, autumn and winter. Total phytoplankton biomass in Han Reservoir is greater than that of Dan Reservoir. There were significant differences in phytoplankton composition between these two reservoirs. The dominant phylum of Dan Reservoir is Bacillariophyta, while the dominant phylum of Han Reservoir is Chlorophyta. There was significant correlation of the phytoplankton biomass with phosphorus, pH and dissolved oxygen, respectively. RDA analysis showed that the major environmental factors affecting phytoplankton community were dissolved oxygen, pH, phosphorus and temperature. For preventing the algae blooms, strict measures should be taken to control the input of exogenous nutrient especially phosphorus. This study provides scientific basis for water quality improvement and control of eutrophication at Danjiangkou Reservoir.

Lipid droplet dynamics during Schizosaccharomyces pombe sporulation and their role in spore survival.

ABSTRACTUpon nitrogen starvation, the fission yeast Schizosaccharomyces pombe forms dormant spores; however, the mechanisms by which a spore sustains life without access to exogenous nutrients remain unclear. Lipid droplets are reservoirs of neutral lipids that act as important cellular energy resources. Using live-cell imaging analysis, we found that the lipid droplets of mother cells redistribute to their nascent spores. Notably, this process was actin polymerization-dependent and facilitated by the leading edge proteins of the forespore membrane. Spores lacking triacylglycerol synthesis, which is essential for lipid droplet formation, failed to germinate. Our results suggest that the lipid droplets are important for the sustenance of life in spores.

Direct Production of Butanol and Ethanol from Cane Sugar Factory Wastewater and Cellulosic Ethanol Pilot Plant Wastewater by Clostridium Beijerinckii CG1

The ability of Clostridium beijerinckii CG1 to utilize sugar from cane sugar factory wastewater (CSFW) and cellulosic ethanol pilot plant wastewater (CEPW) as a renewable carbon source and complete fermentation medium to produce acetone-butanol-ethanol (ABE) was investigated. CSFW and CEPW were used as the unsupplemented culture media (50mL) for ABE production by C. beijerenckii CG1 fermentation in 100-mL serum bottles. No acetone was produced from fermentation of either CEPW or CSFW, in contrast to the small amount (20g L-1) produced from glucose in the last 24h of a 120h fermentation. The average ethanol, butanol and butyric acid production from CEPW (butanol 0.6g L-1, ethanol 0.4g L-1 and butyric acid 2.5g L-1) was higher than that from CSFW (butanol 0.3g L-1, ethanol 0.3g L-1 and butyric acid 0.9g L-1), but still less than that from glucose (butanol 1.87g L-1, ethanol 0.86g L-1 and butyric acid 6.47g L-1). However, the productivity rate in this 50-mL fermentation was three-fold higher with CSFW (0.06g L-1 h-1) than with CEPW (0.02g L-1 h-1). These results suggest that CSFW and CEPW can be applied as appropriate substrates to produce solvents by C. beijerinckii CG1 at a reasonable concentration without the need for additional exogenous nutrient supplements or pretreatment. The idea then being to consolidate the bioprocess for low-cost biofuel production.

Bioconversion of degraded husked sorghum grains to ethanol

AbstractEfficient starch saccharification is an essential step towards achieving improved ethanol yields by fermentation. Sorghum grains are important starch sources for bioconversion to ethanol. In the present study, disease degraded (spoilt) husked grains from Nigerian sorghum cultivars were obtained from field sites and subjected to bioprocessing to ethanol. The crude husked grains (comprising husks, spikelet, awn, rachis and pubescence materials) were hammer milled and each meal separately mashed with enzyme cocktails comprising amylase, glucanase and protease enzymes. The saccharified worts obtained were then fermented with the yeasts, Saccharomyces cerevisiae and Pichia stipitis (aka Scheffersomyces stipitis), without exogenous nutrient supplementation. Sugars liberated during mashing were determined and it was found that enzymatic hydrolysis of milled sorghum grains was effective in yielding favourable levels of fermentable sugars up to 70g sugar/100g substrate with one particular cultivar (KSV8). Ethanol and carbon dioxide production was measured from subsequent trial fermentations of the sorghum mash and it was found that S. cerevisiae produced ethanol levels equating to 420 L/t that compares very favourably with yields from wheat and barley. Our findings show that crude degraded sorghum grains represent favourable low-cost feedstocks for bioconversion to ethanol with reduced energy input and without additional costs for nutrient supplementation during fermentation. Consequently, our results suggest some economic benefits could be derived from spoilt or degraded sorghum grains.

Eps15 homology domain containing protein of Plasmodium falciparum (PfEHD) associates with endocytosis and vesicular trafficking towards neutral lipid storage site

The human malaria parasite, Plasmodium falciparum, takes up numerous host cytosolic components and exogenous nutrients through endocytosis during the intra-erythrocytic stages. Eps15 homology domain-containing proteins (EHDs) are conserved NTPases, which are implicated in membrane remodeling and regulation of specific endocytic transport steps in eukaryotic cells. In the present study, we have characterized the dynamin-like C-terminal Eps15 homology domain containing protein of P. falciparum (PfEHD). Using a GFP-targeting approach, we studied localization and trafficking of PfEHD in the parasite. The PfEHD-GFP fusion protein was found to be a membrane bound protein that associates with vesicular network in the parasite. Time-lapse microscopy studies showed that these vesicles originate at parasite plasma membrane, migrate through the parasite cytosol and culminate into a large multi-vesicular like structure near the food-vacuole. Co-staining of food vacuole membrane showed that the multi-vesicular structure is juxtaposed but outside the food vacuole. Labeling of parasites with neutral lipid specific dye, Nile Red, showed that this large structure is neutral lipid storage site in the parasites. Proteomic analysis identified endocytosis modulators as PfEHD associated proteins in the parasites. Treatment of parasites with endocytosis inhibitors obstructed the development of PfEHD-labeled vesicles and blocked their targeting to the lipid storage site. Overall, our data suggests that the PfEHD is involved in endocytosis and plays a role in the generation of endocytic vesicles at the parasite plasma membrane, that are subsequently targeted to the neutral lipid generation/storage site localized near the food vacuole.

EMBRYO DEVELOPMENT AND ENDOGENOUS NUTRIENT ABSORBTION OF SEA SILVER POMPANO FISH LARVAE FROM NATURAL SPAWN OF BROODSTSOCK, Trachinotus blocii, (LACEPEDE)

Silver pompano is a prospective high value commodity to be developed in mariculture. The aims of this research were to understand the development of embryo and absorption pattern of endogenous nutrient at the time of changing from using endogenous to exogenous nutrient. This research was conducted in Institute for Mariculture Research and Development, Gondol, Singaraja, Bali using fertilized eggs which were stocked in concrete tanks 3 m3, filled with 2 m3 of seawater, in a density of 25 eggs/l. Temperature at the time of hatching was 28-30oC. The observation of embryo development and its morphology was performed after hatching by collecting larvae as many as 10. Parameters measured were total length of larvae (TL), yolk sac volume (VK), oil globule volume (VM) and larvae development. The results showed that embryo of silver pompano had a normal development, consisted of several phases i.e., fertilized egg, cell division, neurola, gastrula, complete embryo and hatching as larvae. Newly hatched larvae had endogenous nutrient as yolk sac and oil globule with volume of 2.27.10-1 mm3 ± 0.06 and 5.57.10-1 mm3 ± 0.02, respectively. Yolk sac was completely absorbed after 35:30 to 46:30 hours and oil globule after 52:30 to 64:30 hours. Initial feeding was given when yolk sac was completely absorbed but before oil globule was completely absorbed. The average total length of larvae was 2.40 ± 0.10 mm. Keywords: embryo, larvae, absorption, yolk sac, silver pampano

EMBRYO DEVELOPMENT AND ENDOGENOUS NUTRIENT ABSORBTION OF SEA SILVER POMPANO FISH LARVAE FROM NATURAL SPAWN OF BROODSTSOCK, Trachinotus blocii, (LACEPEDE)

<p><em>Silver pompano is a prospective high value commodity to be developed in mariculture. The aims of this research were to understand the development of embryo and absorption pattern of endogenous nutrient at the time of changing from using endogenous to exogenous nutrient. This research was conducted in Institute for Mariculture Research and Development, Gondol, Singaraja, Bali using fertilized eggs which were stocked in concrete tanks 3 m<sup>3</sup>, filled with 2 m<sup>3 </sup>of seawater, in a density of 25 eggs/l. Temperature at the time of hatching was 28-30<sup>o</sup>C. The observation of embryo development and its morphology was performed after hatching by collecting larvae as many as 10. Parameters measured were total length of larvae (TL), yolk sac volume (VK), oil globule volume (VM) and larvae development. The results showed that embryo of silver pompano had a normal development, consisted of several phases i.e., fertilized egg, cell division, neurola, gastrula, complete embryo and hatching as larvae. Newly hatched larvae had endogenous nutrient as yolk sac and oil globule with volume of 2.27.10<sup>-1</sup> mm<sup>3</sup> ± 0.06 and 5.57.10<sup>-1</sup> mm<sup>3</sup> ± 0.02, respectively. Yolk sac was completely absorbed after 35:30 to 46:30 hours and oil globule after 52:30 to 64:30 hours. Initial feeding was given when yolk sac was completely absorbed but before oil globule was completely absorbed. The average total length of larvae was 2.40 ± 0.10 mm.</em></p> <p><em> </em></p> <strong><em>Keywords:</em></strong><em> embryo, larvae, absorption, yolk sac, silver pampano</em>

Diversity and Abundance of Soil Animals as Influenced by Long-Term Fertilization in Grey Desert Soil, China

The relationship between soil fauna and different fertilizer management practices is of growing concern. The aim of this research was to investigate the response of soil fauna to fertilization regimes, to explore the relationships among the community of soil animals, soil moisture and crop yields. The application of organic fertilizers (i.e., sheep manure or crop residues) increased crop yields and promoted the number of individuals and species of soil fauna owing to the exogenous organic matter that fertilizers provided for the survival and development of soil fauna. Furthermore, the treatments that applied sheep manure (i.e., sheep manure only or nitrogen, phosphorus, potassium and sheep manure plus) were significantly beneficial for increasing crop yields and diversity of soil fauna compared to treatments with crop residues returned (i.e., crop residues returned only or nitrogen, phosphorus, potassium and crop residues returned to the field) (p < 0.05) due to the response of soil fauna to diverse exogenous nutrients and the effect of soil fertility. Therefore, the finding that soil fauna abundance is significantly positively correlated with soil moisture and crop yield may mean the effects of fertilizer applications on soil animals were partly masked by the soil moisture and crop yield.

Differential contributions of endogenous and exogenous nutrients to egg components in wild Baltic Common Eiders (Somateria mollissima): A test of alternative stable isotope approaches

ABSTRACT The relative importance of nutrients derived from feeding on breeding vs. nonbreeding grounds to the formation of eggs is crucial for predicting how the breeding success of migrating birds responds to changes in food availability during any part of their annual cycle. Eiders have been considered a classical capital breeder, but this assumption has rarely been tested. The measurement of naturally occurring stable isotopes in egg components, together with those in endogenous and exogenous nutrient endpoints, allow the estimation of the relative sources of nutrients to eggs, but these mixing models rely critically on appropriate isotopic discrimination factors that link egg isotope values with their source. A recent captive study using Spectacled Eiders (Somateria fischeri) provided estimates of these isotopic discrimination factors for income breeding. We applied these discrimination factors for investigating nutrient allocation strategies in Common Eiders (Somateria mollisima) breeding in the nort...

Abstract B08: Kicking the addictions: Therapeutic strategies for NSCLC

Abstract The discovery of cancer cells' dependency on the self-cannibalization program autophagy has spawned the investigation of its efficacy as a therapeutic target. However, the use of lysomotropic agents to inhibit autophagy as single-agent therapeutics has proven less than optimal. Recent investigations into the design of sequential treatment strategies targeting pathways preferentially used by cancer cells have shown promise. This novel spin on personalized medicine seeks to exploit the kinetics and mechanisms by which cancer cells become dependent on proliferation and survival pathways. Oncogenic KRAS-driven non-small cell lung cancer (NSCLC) is known to depend on mTORC1-driven growth and autophagy for survival; such autophagy addiction is beneficial to cancer cells, as it eliminates the need for exogenous nutrient supplies. We aim to elucidate the mechanism and kinetics of autophagy addiction in NSCLC, in order to design sequential treatment strategies against this disease. Citation Format: Abigail R. Solitro, Jeffrey P. MacKeigan. Kicking the addictions: Therapeutic strategies for NSCLC. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr B08.

Aminoimidazole Carboxamide Ribotide Exerts Opposing Effects on Thiamine Synthesis in Salmonella enterica.

In Salmonella enterica, the thiamine biosynthetic intermediate 5-aminoimidazole ribotide (AIR) can be synthesized de novo independently of the early purine biosynthetic reactions. This secondary route to AIR synthesis is dependent on (i) 5-amino-4-imidazolecarboxamide ribotide (AICAR) accumulation, (ii) a functional phosphoribosylaminoimidazole-succinocarboxamide (SAICAR) synthetase (PurC; EC 6.3.2.6), and (iii) methionine and lysine in the growth medium. Studies presented here show that AICAR is a direct precursor to AIR in vivo. PurC-dependent conversion of AICAR to AIR was recreated in vitro. Physiological studies showed that exogenous nutrients (e.g., methionine and lysine) antagonize the inhibitory effects of AICAR on the ThiC reaction and decreased the cellular thiamine requirement. Finally, genetic results identified multiple loci that impacted the effect of AICAR on thiamine synthesis and implicated cellular aspartate levels in AICAR-dependent AIR synthesis. Together, the data here clarify the mechanism that allows conditional growth of a strain lacking the first five biosynthetic enzymes, and they provide additional insights into the complexity of the metabolic network and its plasticity. In bacteria, the pyrimidine moiety of thiamine is derived from aminoimidazole ribotide (AIR), an intermediate in purine biosynthesis. A previous study described conditions under which AIR synthesis is independent of purine biosynthesis. This work is an extension of that previous study and describes a new synthetic pathway to thiamine that depends on a novel thiamine precursor and a secondary activity of the biosynthetic enzyme PurC. These findings provide mechanistic details of redundancy in the synthesis of a metabolite that is essential for nucleotide and coenzyme biosynthesis. Metabolic modifications that allow the new pathway to function or enhance it are also described.

Strontium source and depth of uptake shifts with substrate age in semiarid ecosystems

AbstractWithout exogenous rock‐derived nutrient sources, terrestrial ecosystems may eventually regress or reach a terminal steady state, but the degree to which exogenous nutrient sources buffer or slow to a theoretical terminal steady state remains unclear. We used strontium isotope ratios (87Sr/86Sr) as a tracer and measured 87Sr/86Sr values in aeolian dust, soils, and vegetation across a well‐constrained 3 Myr semiarid substrate age gradient to determine (1) whether the contribution of atmospheric sources of rock‐derived nutrients to soil and vegetation pools varied with substrate age and (2) to determine if the depth of uptake varied with substrate age. We found that aeolian‐derived nutrients became increasingly important, contributing as much as 71% to plant‐available soil pools and tree (Pinus edulis) growth during the latter stages of ecosystem development in a semiarid climate. The depth of nutrient uptake increased on older substrates, demonstrating that trees in arid regions can acquire nutrients from greater depths as ecosystem development progresses presumably in response to nutrient depletion in the more weathered surface soils. Our results demonstrate that global and regional aeolian transport of nutrients to local ecosystems is a vital process for ecosystem development in arid regions. Furthermore, these aeolian nutrient inputs contribute to deep soil nutrient pools, which become increasingly important for maintaining plant productivity over long time scales.

Surviving the heat: heterogeneity of response in Saccharomyces cerevisiae provides insight into thermal damage to the membrane.

Environmental heat stress impacts on the physiology and viability of microbial cells with concomitant implications for microbial activity and diversity. Previously, it has been demonstrated that gradual heating of Saccharomyces cerevisiae induces a degree of thermal resistance, whereas a heat shock results in a high level of cell death. Here, we show that the impact of exogenous nutrients on acquisition of thermal resistance differs between strains.Using single-cell methods, we demonstrate the extent of heterogeneity of the heat-stress response within populations of yeast cells and the presence of subpopulations that are reversibly damaged by heat stress. Such cells represent potential for recovery of entire populations once stresses are removed. The results show that plasma membrane permeability and potential are key factors involved in cell survival, but thermal resistance is not related to homeoviscous adaptation of the plasma membrane. These results have implications for growth and regrowth of populations experiencing environmental heat stress and our understanding of impacts at the level of the single cell. Given the important role of microbes in biofuel production and bioremediation, a thorough understanding of the impact of stress responses of populations and individuals is highly desirable.

Symbiotic in vitro seed propagation of Dendrobium: fungal and bacterial partners and their influence on plant growth and development.

The genus Dendrobium is one of the largest genera of the Orchidaceae Juss. family, although some of its members are the most threatened today. The reason why many species face a vulnerable or endangered status is primarily because of anthropogenic interference in natural habitats and commercial overexploitation. The development and application of modern techniques and strategies directed towards in vitro propagation of orchids not only increases their number but also provides a viable means to conserve plants in an artificial environment, both in vitro and ex vitro, thus providing material for reintroduction. Dendrobium seed germination and propagation are challenging processes in vivo and in vitro, especially when the extreme specialization of these plants is considered: (1) their biotic relationships with pollinators and mycorrhizae; (2) adaptation to epiphytic or lithophytic life-styles; (3) fine-scale requirements for an optimal combination of nutrients, light, temperature, and pH. This review also aims to summarize the available data on symbiotic in vitro Dendrobium seed germination. The influence of abiotic factors as well as composition and amounts of different exogenous nutrient substances is examined. With a view to better understanding how to optimize and control in vitro symbiotic associations, a part of the review describes the strong biotic relations of Dendrobium with different associative microorganisms that form microbial communities with adult plants, and also influence symbiotic seed germination. The beneficial role of plant growth-promoting bacteria is also discussed.

The role of aquatic fungi in transformations of organic matter mediated by nutrients

Summary We assessed the key role of aquatic fungi in modifying coarse particulate organic matter (CPOM) by affecting its breakdown rate, nutrient concentration and conversion to fine particulate organic matter (FPOM). Overall, we hypothesised that fungal‐mediated conditioning and breakdown of CPOM would be accelerated when nutrient concentrations are increased and tested the degree to which fungi were critical to CPOM processing and to FPOM production by an invertebrate consumer. We manipulated the presence and absence of fungi, exogenous nutrients [nitrogen (N) and phosphorus (P)] and an invertebrate consumer in a full‐factorial laboratory experiment and quantified their effects on CPOM mass loss and nutrient concentration, and the quantity and nutrient concentration of FPOM produced during leaf breakdown. Mass of CPOM lost and the quantity of FPOM produced were highest in nutrient‐enriched treatments containing fungal decomposers. Across all treatments, FPOM produced was a constant proportion of CPOM lost (67%). Loss of CPOM due to shredders was highest at fungal biomass values >16 mg g dry mass−1, which occurred with nutrient enrichment. Nitrogen concentration in CPOM increased in treatments with nutrients and fungi, while CPOM P concentration was primarily affected by nutrients. In contrast, FPOM P concentration declined in treatments with fungi and nutrients, suggesting either sequestration via CPOM‐associated fungi or preferential assimilation by shredders. Nitrogen in FPOM increased with nutrients, but was unaffected by fungi. Our results indicate that aquatic fungi play a critical role in facilitating energy and nutrient flow through detrital pathways and that their ability to mediate organic matter transformations is significantly influenced by nutrient enrichment.

Olive leachates affect germination of Colletotrichum godetiae conidia and the development of appressoria

The effects of nutrients and microorganisms from olive carpospheres on germination of conidia and the development of appressoria of Colletotrichum godetiae were investigated. The final germination ratio was the result of a dynamic equilibrium between the positive action of nutrients and the negative competition of indigenous microorganisms. In contrast, formation of appressoria was greatly increased by microorganisms and reduced by nutrients. Removal of the microbial fraction from olive leachates rich in natural nutrients amplified the vegetative phase after conidium germination, resulting in increased germtube length, and delayed and reduced production of appressoria. Three exogenous nutrients (sucrose, asparagine and glycine) increased germination of conidia and reduced the formation of appressoria. These results provide evidence that nutrients and microorganisms of the olive carposphere play important roles in the infection processes of C. godetiae . Since appressoria are necessary for successful host infection, microorganisms may favour the penetration of C. godetiae by stimulating the production of appressoria, reducing saprophyitic pre-infectional mycelial growth and reducing duration of the critical moist period required for host penetration.