Nutrient Manipulation Research Articles

A Study on Dunaliella salina Under Selected Nutrient Manipulation with Reference to the Biomass, Lipid Content Along with Expression of ACCase and RuBisCO Genes

A Study on Dunaliella salina Under Selected Nutrient Manipulation with Reference to the Biomass, Lipid Content Along with Expression of ACCase and RuBisCO Genes

Responses of tree growth and biomass production to nutrient addition in a semi-deciduous tropical forest in Africa.

Experimental evidence of nutrient limitations on primary productivity in Afrotropical forests is rare and globally underrepresented yet are crucial for understanding constraints to terrestrial carbon uptake. In an ecosystem-scale nutrient manipulation experiment, we assessed the early responses of tree growth rates among different tree sizes, taxonomic species, and at a community level in a humid tropical forest in Uganda. Following a full factorial design, we established 32 (eight treatments × four replicates) experimental plots of 40 × 40 m each. We added nitrogen (N), phosphorus (P), potassium (K), their combinations (NP, NK, PK, and NPK), and control at the rates of 125 kg N ha-1 year-1 , 50 kg P ha-1 year-1 and 50 kgK ha-1 year-1 , split into four equal applications, and measured stem growth of more than 15,000 trees with diameter at breast height (dbh) ≥1cm. After 2 years, the response of tree stem growth to nutrient additions was dependent on tree sizes, species and leaf habit but not community wide. First, tree stem growth increased under N additions, primarily among medium-sized trees (10-30 cm dbh), and in trees of Lasiodiscus mildbraedii in the second year of the experiment. Second, K limitation was evident in semi-deciduous trees, which increased stem growth by 46% in +K than -K treatments, following a strong, prolonged dry season during the first year of the experiment. This highlights the key role of K in stomatal regulation and maintenance of water balance in trees, particularly under water-stressed conditions. Third, the role of P in promoting tree growth and carbon accumulation rates in this forest on highly weathered soils was rather not pronounced; nonetheless, mortality among saplings (1-5cm dbh) was reduced by 30% in +P than in -P treatments. Although stem growth responses to nutrient interaction effects were positive or negative (likely depending on nutrient combinations and climate variability), our results underscore the fact that, in a highly diverse forest ecosystem, multiple nutrients and not one single nutrient regulate tree growth and aboveground carbon uptake due to varying nutrient requirements and acquisition strategies of different tree sizes, species, and leaf habits.

Microtopographic variations in soil physico‐chemical properties in oldfield targeted for ecological restoration

AbstractMicrotopographic conditions affect patterns of soil physico‐chemical properties in oldfields targeted for passive ecological restoration. This study sampled soil at a microtopographic level in three oldfield sites targeted for ecological restoration to better understand changes in soil physico‐chemical properties of pH, P, N, C, K, Na, Ca, Mg, moisture, penetration resistance and water repellency. The study was conducted in oldfields located at Nanaga farm in the Eastern Cape Province of South Africa. Topsoil samples were collected over 3 months in two oldfield locations, namely furrows and ridges, and were compared to soils from adjacent reference sites. Results indicate that soil P, C and N were significantly higher in oldfield ridges and reference sites than in oldfield furrows. Throughout the three sampling months, soils from oldfield ridges were less compact and repellent as compared to soils from the oldfield furrows which were compact and wettable. The study concludes that the observed soil physico‐chemical differences between oldfield furrows and ridges were influenced by vegetation availability and microtopographic conditions between oldfield ridges and furrows. The study recommends that soil restoration initiatives (e.g. soil nutrient manipulation) in these oldfields should concentrate on improving the nutrient‐poor and compact furrows than ridges.

Nutrient supply controls the linkage between species abundance and ecological interactions in marine bacterial communities

Nutrient scarcity is pervasive for natural microbial communities, affecting species reproduction and co-existence. However, it remains unclear whether there are general rules of how microbial species abundances are shaped by biotic and abiotic factors. Here we show that the ribosomal RNA gene operon (rrn) copy number, a genomic trait related to bacterial growth rate and nutrient demand, decreases from the abundant to the rare biosphere in the nutrient-rich coastal sediment but exhibits the opposite pattern in the nutrient-scarce pelagic zone of the global ocean. Both patterns are underlain by positive correlations between community-level rrn copy number and nutrients. Furthermore, inter-species co-exclusion inferred by negative network associations is observed more in coastal sediment than in ocean water samples. Nutrient manipulation experiments yield effects of nutrient availability on rrn copy numbers and network associations that are consistent with our field observations. Based on these results, we propose a “hunger games” hypothesis to define microbial species abundance rules using the rrn copy number, ecological interaction, and nutrient availability.

Simulated hurricane-induced changes in light and nutrient regimes change seedling performance in Everglades forest-dominant species.

Wind damage from cyclones can devastate the forest canopy, altering environmental conditions in the understory that affect seedling growth and plant community regeneration. To investigate the impact of hurricane‐induced increases in light and soil nutrients as a result of canopy defoliation, we conducted a two‐way factorial light and nutrient manipulation in a shadehouse experiment. We measured seedling growth of the dominant canopy species in the four Everglades forest communities: pine rocklands (Pinus elliottii var densa), cypress domes (Taxodium distichum), hardwood hammocks, and tree islands (Quercus virginiana and Bursera simaruba). Light levels were full sun and 50% shade, and nutrient levels coupled with an additional set of individuals that were subjected to a treatment mimicking the sudden effects of canopy opening from hurricane‐induced defoliation and the corresponding nutrient pulse. Seedlings were measured weekly for height growth and photosynthesis, with seedlings being harvested after 16 weeks for biomass, leaf area, and leaf tissue N and 13C isotope ratio. Growth rates and biomass accumulation responded more to differences in soil nutrients than differences in light availability, with largest individuals being in the high nutrient treatments. For B. simaruba and P. elliottii, the highest photosynthetic rates occurred in the high light, high nutrient treatment, while T. distichum and Q. virginiana photosynthetic rates were highest in low light, high nutrient treatment. Tissue biomass allocation patterns remained similar across treatments, except for Q. virginiana, which altered above‐ and belowground biomass allocation to increase capture of limiting soil and light resources. In response to the hurricane simulation treatment, height growth increased rapidly for Q. virginiana and B. simaruba, with nonsignificant increases for the other two species. We show here that ultimately, hurricane‐adapted, tropical species may be more likely to recolonize the forest canopy following a large‐scale hurricane disturbance.

Considerations When Choosing High-Fat, High-Fructose, and High-Cholesterol Diets to Induce Experimental Nonalcoholic Fatty Liver Disease in Laboratory Animal Models.

ABSTRACTNonalcoholic fatty liver disease (NAFLD) is intricately linked to metabolic disease (including obesity, glucose intolerance, and insulin resistance) and encompasses a spectrum of disorders including steatosis, nonalcoholic steatohepatitis (NASH), and fibrosis. Rodents consuming high-fat (HF; ∼40 kcal% fat including fats containing higher concentrations of saturated and trans fats), high-fructose (HFr), and high-cholesterol (HC) diets display many clinically relevant characteristics of NASH, along with other metabolic disorders. C57BL/6 mice are the most commonly used animal model because they can develop significant metabolic disorders including severe NASH with fibrosis after months of feeding, but other models also are susceptible. The significant number of diets that contain these different factors (i.e., HF, HFr, and HC), either alone or in combination, makes the choice of diet difficult. This methodology review describes the efficacy of these nutrient manipulations on the NAFLD phenotype in mice, rats, guinea pigs, hamsters, and nonhuman primates.

226 Integrated Pork Production During a Global Pandemic: Impact on the Live Production Supply Chain, Feed Mills, & Nutrition

The global COVID-19 pandemic of 2020/2021 resulted in widespread impacts on the production & processing of animal proteins. Specifically, the U.S. pork industry was hit with multiple, long-term plant closures and slow-downs due to labor safety issues and availability, resulting in a backlog reaction felt throughout the live production supply-chain. Impact and timing differed by region and required variable strategies to address them. While some plants in the Western United States weren’t impacted until the latter stages of the pandemic and thus were attempting to add valuable liveweight, other regions, including the Midwest and Southeastern United States were experiencing moderate to severe reductions in processing capacity that created an accumulation of heavy animals and placed additional feed and ingredient demands on the feed mills. The backlog also reduced available space & disrupted the normal barn fill/empty cycles. While there was no way to prepare for these impacts, university & industry groups attempted to fill the knowledge gap with management and nutritional tools to address the issues of excess inventory, decreasing feed capacity, and supply-chain disruptions. Numerous approaches were employed, including altered grading strategies, sow breeding target reductions, double/triple stocking situations, and feed, ingredient, and nutrient manipulation meant to slow down growth rate and feed intake. Nutritional strategies included the feeding of low energy ingredients as well as low protein/high methionine diets designed to reduce the growth rate of both heavy and light animals. While several of these strategies resulted in moderate success, some resulted in additional issues including stress-related vices, ulcers, increased mortality, and sub-optimal carcass characteristics. Ultimately, continuous planning, coordination, and communication between the plants, feed mills, nutritionists, and production groups enabled a return to normalcy, and while we hope to never experience a pandemic again, we are left with knowledge that will improve the resilience of the U.S. pork industry.

Impacts of Nutritional Management During Early Postnatal Life on Long-Term Physiological and Productive Responses of Beef Cattle

Effective early postnatal nutritional management is a crucial component of livestock production systems, and nutrient manipulation during this period has been shown to exert long-term consequences on beef cattle growth and physiology. Metabolic imprinting defines these biological responses to a nutritional intervention early in life that permanently alter physiological outcomes later in life. Early weaning has been used to study metabolic imprinting effects, given that it allows for nutritional manipulation of animals at a young age. This practice has been shown to enhance carcass characteristics in feedlot cattle and accelerate reproductive development of females. Another strategy to study the effects of metabolic imprinting without the need for early weaning is to provide supplements via creep feeding. Providing creep feed to nursing cattle has resulted in transient and long-term alterations in cattle metabolism, contributing to increased reproductive performance of developing heifers and enhanced carcass quality of feeder cattle. Collectively, results described herein demonstrate nutrient manipulation during early postnatal life exerts long-term consequences on beef cattle productivity and may be a strategy to optimize production efficiency in beef cattle systems.

Response of water-bound fluxes of potassium, calcium, magnesium and sodium to nutrient additions in an Ecuadorian tropical montane forest

In the past two decades, the Amazon-exposed, tropical montane rain forests in south Ecuador experienced increasing deposition of reactive N mainly from Amazonian forest fires, episodic Ca and Mg inputs from Saharan dust, and a low but constant P deposition from unknown sources. To explore the response of this tropical, perhumid ecosystem to nutrient inputs, we established in 2007 a Nutrient Manipulation Experiment (NUMEX). Since 2008, we have applied 50 kg ha−1 year−1 of N as urea, 10 kg ha−1 year−1 of P as NaH2PO4·H2O, 50 kg ha−1 year−1 of N + 10 kg ha−1 year−1 of P and 10 kg ha−1 year−1 of Ca as CaCl2·H2O in a randomized block design at 2000 m a.s.l. in a natural forest of the south Ecuadorian Andes. Previous studies have shown that alkali and alkaline earth metals had beneficial effects on the functioning of N and P co-limited tropical forests occurring on acidic soils. Therefore, we determined the response of all major aqueous ecosystem fluxes of K, Ca, Mg and Na to nutrient amendments, to understand how increasing atmospheric deposition would affect their cycling in the future. Additions of N and P decreased K leaching from the organic layer and in the mineral soil, thus tightening K cycling. This suggests that increasing future N and P availability may result in K limitation in the long term. The leaching of Ca and Mg from the canopy increased in response to amendments of N and P and we observed an enhanced uptake of these nutrients also if Ca was amended alone. Although N was applied as urea, acidity of soil solutions and leaching of K, Ca, Mg and Na did not increase following separate N amendments. In spite of the acid soils and of its low cation-exchange competitivity, Na included in the P fertilizer was only partly leached from the organic layer. We suggest that it was probably required to cover an unmet Na demand of the soil fauna. Our results demonstrate the major role in the functioning of the tropical montane forests played by K, Ca and Mg as potential future growth-limiting elements and increasingly required nutrients in response to rising N and P availability, while they also support the importance of Na as a functional element in these ecosystems.

Nutrient limitations regulate soil greenhouse gas fluxes from tropical forests: evidence from an ecosystem-scale nutrient manipulation experiment in Uganda

Abstract. Soil macronutrient availability is one of the abiotic controls that alters the exchange of greenhouse gases (GHGs) between the soil and the atmosphere in tropical forests. However, evidence on the macronutrient regulation of soil GHG fluxes from central African tropical forests is still lacking, limiting our understanding of how these biomes could respond to potential future increases in nitrogen (N) and phosphorus (P) deposition. The aim of this study was to disentangle the regulation effect of soil nutrients on soil GHG fluxes from a Ugandan tropical forest reserve in the context of increasing N and P deposition. Therefore, a large-scale nutrient manipulation experiment (NME), based on 40 m×40 m plots with different nutrient addition treatments (N, P, N + P, and control), was established in the Budongo Central Forest Reserve. Soil carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes were measured monthly, using permanently installed static chambers, for 14 months. Total soil CO2 fluxes were partitioned into autotrophic and heterotrophic components through a root trenching treatment. In addition, soil temperature, soil water content, and nitrates were measured in parallel to GHG fluxes. N addition (N and N + P) resulted in significantly higher N2O fluxes in the transitory phase (0–28 d after fertilization; p<0.01) because N fertilization likely increased soil N beyond the microbial immobilization and plant nutritional demands, leaving the excess to be nitrified or denitrified. Prolonged N fertilization, however, did not elicit a significant response in background (measured more than 28 d after fertilization) N2O fluxes. P fertilization marginally and significantly increased transitory (p=0.05) and background (p=0.01) CH4 consumption, probably because it enhanced methanotrophic activity. The addition of N and P (N + P) resulted in larger CO2 fluxes in the transitory phase (p=0.01), suggesting a possible co-limitation of both N and P on soil respiration. Heterotrophic (microbial) CO2 effluxes were significantly higher than the autotrophic (root) CO2 effluxes (p<0.01) across all treatment plots, with microbes contributing about two-thirds of the total soil CO2 effluxes. However, neither heterotrophic nor autotrophic respiration significantly differed between treatments. The results from this study suggest that the feedback of tropical forests to the global soil GHG budget could be disproportionately altered by increases in N and P availability over these biomes.

Short-term microbial responses to soluble inorganic P input in a tropical lowland rain forest in Amazonia

In non-flooded lowland rain forests with low soil phosphorus (P) in parts of Amazonia, P cycling largely occurs via leaf litter recycling by arbuscular mycorrhizal (AM) fungal symbionts. Occasional high input of P into these ecosystems occurs during drought years with increased litterfall. As the length and frequency of drought events are projected to increase in the region, a single-dose nutrient addition experiment was carried out to test how this would impact P cycling. An application rate of 4 kg P ha–1 was used, which corresponds to twice the amount of litter-derived P in an average year. It was hypothesized that i) the added mineral P would be immobilized by soil microorganisms, leading to measurable increase in soil microbial biomass carbon (C) and P and ii) AM colonization rate would be reduced by the pulse in mineral P available for plant uptake. The results did not support either of our hypotheses. The addition of P did not have an effect on AM root colonization, nor was P immobilized by soil microbiota during the experimental period. The lack of a difference between the control and treatment at our study site could be attributed to the relatively low one-off dose of P applied that did not change either the colonization rate of roots by AM fungi or the amount of soil available labile P. To obtain a mechanistic understanding of the availability, capture, and use of P by plant-symbiont associations in tropical rain forest ecosystems, further integrated studies of the soil-plant system combining long-term nutrient manipulations, modeling, and experimental approaches are required.

Densidade e composição do banco de sementes do solo em ecossistema sucessional de floresta na Amazônia Oriental, Brasil

Na Amazônia, a agricultura itinerante garante a subsistência das comunidades tradicionais, porém, ocasiona intensos impactos ambientais. A restauração florestal com o monitoramento de indicadores, como o banco de sementes é indispensável, pois, fornece informações sobre as espécies viáveis para germinação em cenários de distúrbios ecossistêmicos. Objetivou-se, portanto, avaliar a composição e a densidade do banco de semente de uma floresta sucessional na Amazônia, submetida à manipulação de água e nutrientes há 12 anos. As coletas foram realizadas de maneira aleatória, com o auxílio de um amostrador vazado, em um fragmento florestal com três tratamentos (controle - CTL, remoção de serapilheira - REM e irrigação periódica- IRR). Encontramos 684 indivíduos e 32 espécies. A densidade de indivíduos variou de 820 ± 112 a 972 ± 394 ind m-2 para REM e CTL, enquanto a de espécies variou de 188 ± 48 a 216 ± 9,24 spp m-2 para CTL e REM, respectivamente. Os arbustos apresentaram a maior quantidade de indivíduos emergentes, e os cipós, a menor. Os maiores índices de Shannon-Weanver e Pielou foram observados no CTL. As espécies Vismia guianensis, Cecropia obtusa e Cyperus rotundus foram as mais frequentes em todos os tratamentos e as espécies pioneiras predominaram. A velocidade de emergência do tratamento REM foi inferior ao CTL, enquanto o tempo médio de emergência foi semelhante entre os tratamentos. A composição e densidade do banco de sementes não foram afetadas pelo efeito residual da manipulação de serapilheira. Apesar disso, os resultados foram ligeiramente superiores para o tratamento CTL.

Restoration benefits of soil nutrient manipulation and weeding in invaded dry and wet tropical ecosystems in Hawaiʻi

Reducing soil nutrient availability has been proposed as a strategy to favor native vs. non‐native invasive plant species and represents a potential alternative to traditional manual removal or chemical control methods. We implemented a field experiment in invaded dry and wet montane Hawaiian ecosystems to test responses of soil and dominant plant species to three soil nutrient treatments (Control = no nutrient manipulation; Carbon = C substrate added to reduce nutrients; Fertilizer = fertilizer added to increase nutrients) and two non‐native plant treatments (Weeds removed; Weeds present) in a fully factorial experiment in each ecosystem over 18 months. Carbon amendments reduced soil inorganic nutrient availability by 60–70% in dry shrubland and 30–50% in wet forest. Fertilizer amendments increased soil inorganic nutrient availability by >20‐fold. Altered nutrient availability did not impact gross mineralization or nitrification rates in either ecosystem. In dry shrubland, neither C amendments nor weed removal altered growth or reproduction, but fertilizer increased woody growth and forb/grass reproduction in both natives and non‐natives. In wet forest, weed removal but not C amendments increased growth and survival of native woody seedlings, while fertilizer decreased native seedling survival and increased non‐native woody seedling growth. Overall, growth and reproduction of native and non‐natives responded similarly to altered nutrient availability, indicating that for the tropical ecosystems and species examined, manipulating nutrient availability does not favor native versus non‐native invasive plants in the first 18 months. In contrast, weed removal had positive effects on native plant growth, likely mediated through changes in other resources.

Characterization of a newly isolated cyanobacterium Trichocoleus desertorum BERC08 as a potential feedstock for the algal biorefinery

Cyanobacteria have numerous biotechnological applications in the environment, industry, pharmaceutics, food, feed, and energy which is why future cascading biorefineries are believed to employ cyanobacteria as their feedstock. The present study evaluated the potential of a newly isolated cyanobacterium for its applications in the multiproduct biorefinery. Based on morphology and the gene sequence of 23S rRNA, the strain was identified as Trichocoleus desertorum. Various abiotic growth factors including light, pH, and nutrients were optimized to achieve enhanced biomass production using various wastewaters as low-cost growth media. Accordingly, a 2.24-fold to 6.97-fold higher biomass production (gL-1) and biomass productivity of 0.86 gL-1d-1 with a CO2 fixation rate of 1.576 gL-1d-1 was achieved when cultured in synthetic wastewater. Besides, the impact of wastewater cultivation was studied on the biosynthesis of valuable metabolites including proteins, carbohydrates, lipids, and pigments. Accordingly, the lipid content of the wastewater-cultivated strain was increased from 24 to 30%, and protein content was increased from 27 to 46%. The lipids were trans-esterified to biodiesel which was turned out to be good quality biodiesel, as revealed through GC-MS analysis. Additionally, the wastewater-cultivated strain produced 117.35 mgg-1 (11.73 % of the total dried biomass) of phycobilin in response to nutrient manipulation, where phycocyanin was shown to be the most prominent pigment with a yield of 94.7 mgg-1, which covered 80% of the total pigments. These remarkable features reflected the promising potential of this strain to be employed as a feedstock in the multiproduct biorefinery.

How Nitrogen and Phosphorus Availability Change Water Use Efficiency in a Mediterranean Savanna Ecosystem

AbstractNutrient availability, especially of nitrogen (N) and phosphorus (P), is of major importance for every organism and at a larger scale for ecosystem functioning and productivity. Changes in nutrient availability and potential stoichiometric imbalance due to anthropogenic nitrogen deposition might lead to nutrient deficiency or alter ecosystem functioning in various ways. In this study, we present 6 years (2014–2020) of flux‐, plant‐, and remote sensing data from a large‐scale nutrient manipulation experiment conducted in a Mediterranean savanna‐type ecosystem with an emphasis on the effects of N and P treatments on ecosystem‐scale water‐use efficiency (WUE) and related mechanisms. Two plots were fertilized with N (NT, 16.9 Ha) and N + P (NPT, 21.5 Ha), and a third unfertilized plot served as a control (CT). Fertilization had a strong impact on leaf nutrient stoichiometry only within the herbaceous layer with increased leaf N in both fertilized treatments and increased leaf P in NPT. Following fertilization, WUE in NT and NPT increased during the peak of growing season. While gross primary productivity similarly increased in NT and NPT, transpiration and surface conductance increased more in NT than in NPT. The results show that the NPT plot with higher nutrient availability, but more balanced N:P leaf stoichiometry had the highest WUE. On average, higher N availability resulted in a 40% increased leaf area index (LAI) in both fertilized treatments in the spring. Increased LAI reduced aerodynamic conductance and thus evaporation at both fertilized plots in the spring. Despite reduced evaporation, annual evapotranspiration increased by 10% (48.6 ± 28.3 kg H2O m−2), in the NT plot, while NPT remained similar to CT (−1%, −6.7 ± 12.2 kgH2O m−2). Potential causes for increased transpiration at NT could be increased root biomass and thus higher water uptake or rhizosphere priming to increase P‐mobilization through microbes. The annual net ecosystem exchange shifted from a carbon source in CT (75.0 ± 20.6 gC m−2) to carbon‐neutral in both fertilized treatments [−7.0 ± 18.5 gC m−2 (NT) 0.4 ± 22.6 gC m−2 (NPT)]. Our results show, that the N:P stoichiometric imbalance, resulting from N addition (without P), increases the WUE less than the addition of N + P, due to the strong increase in transpiration at NT, which indicates the importance of a balanced N and P content for WUE.

Soil gas probes for monitoring trace gas messengers of microbial activity

Soil microbes vigorously produce and consume gases that reflect active soil biogeochemical processes. Soil gas measurements are therefore a powerful tool to monitor microbial activity. Yet, the majority of soil gases lack non-disruptive subsurface measurement methods at spatiotemporal scales relevant to microbial processes and soil structure. To address this need, we developed a soil gas sampling system that uses novel diffusive soil probes and sample transfer approaches for high-resolution sampling from discrete subsurface regions. Probe sampling requires transferring soil gas samples to above-ground gas analyzers where concentrations and isotopologues are measured. Obtaining representative soil gas samples has historically required balancing disruption to soil gas composition with measurement frequency and analyzer volume demand. These considerations have limited attempts to quantify trace gas spatial concentration gradients and heterogeneity at scales relevant to the soil microbiome. Here, we describe our new flexible diffusive probe sampling system integrated with a modified, reduced volume trace gas analyzer and demonstrate its application for subsurface monitoring of biogeochemical cycling of nitrous oxide (N2O) and its site-specific isotopologues, methane, carbon dioxide, and nitric oxide in controlled soil columns. The sampling system observed reproducible responses of soil gas concentrations to manipulations of soil nutrients and redox state, providing a new window into the microbial response to these key environmental forcings. Using site-specific N2O isotopologues as indicators of microbial processes, we constrain the dynamics of in situ microbial activity. Unlocking trace gas messengers of microbial activity will complement -omics approaches, challenge subsurface models, and improve understanding of soil heterogeneity to disentangle interactive processes in the subsurface biome.

Elevated nutrients and herbivory negatively affect Dictyota growth dynamics

Caribbean coral reefs are experiencing a shift to algal dominance at the expense of stony corals. Determining the factors leading to algal phase shifts is crucial for assuring the survival of Caribbean coral reefs. In this study, factors controlling the growth of the abundant brown macroalgae Dictyota spp. were investigated by varying herbivory pressure (caging) and nutrients (fertilizer addition) on coral reefs near St. Thomas (US Virgin Islands). Experiment 1 measured Dictyota heights and percent cover at 3 sites (11-20 m depth) and showed no growth response to nutrient addition and a weak negative response to herbivory. To confirm results of Experiment 1, a caging and nutrient manipulation (Experiment 2) was conducted at one site (14 m depth) using the dependent variable Dictyota biomass. A strong negative response of growth to nutrient addition was shown, presumably because of nutrient inhibition, and an equally negative response to herbivory (loss of ~50% biomass over 21 d). The inhibitory effect of fertilization on growth was confirmed in a third experiment that showed increasing biomass loss over 4 treatment levels of increasing fertilizer addition (0 [ambient], 5, 10, 20 g). Overall, Dictyota was not nutrient limited at any sites, and was weakly controlled by herbivore populations. Factors responsible for Dictyota abundance on Caribbean reefs may reflect decreased herbivory caused by overfishing and reductions in coral cover and do not appear to be affected by recent changes in nitrogen or phosphorus load. This study reinforces the need for conservation and management of herbivores in coral reef ecosystems, to mitigate the effects from anthropogenic stressors.

A comparative assessment of growth, pigment and enhanced lipid production by two toxic freshwater cyanobacteria Anabaena circinalis FSS 124 and Cylindrospermopsis raciborskii FSS 127 under various combinations of nitrogen and phosphorous inputs.

Nitrogen and phosphorous are important nutritional regulators for the growth of cyanobacteria, thereby having a significant impact in bloom formation by toxic species. Usage of toxic cyanobacteria for increasing valuable metabolite production by nutrient manipulation is still unexplored. Hence, the current work is aimed to estimate and compare growth, pigment, and increased lipid production coupled with the identification of fatty acids between two toxic strains-Anabaena circinalis FSS 124 and Cylindrospermopsis raciborskii FSS 127 under various combinations of these two nutrients. Low level of nitrogen and phosphorous enhanced lipid content in both strains (˃ 20% and 30% respectively) and C. raciborskii, respectively. Lipid productivity in low phosphorous concentration (P0.5) was achieved significantly high in C. raciborskii. Similarly, a substantial amount of carotenoids was obtained at reduced nitrogen and phosphorous in C. raciborskii accompanied by lessened growth and Chl a concentration. Unlikely, enough biomass (˃ 2 g L-1) was produced at high nutrient levels in both species. Comparative statistical significance (p < 0.05) was found between two species regarding biomass production, chlorophyll concentration, lipid content, and productivity and between these factors in each species under both nutrient variations. FAME of Cylindrospermopsis is composed of saturated fatty acids (˃ 50%) and MUFA (˃ 25%) while Anabaena contains PUFA (˃ 21%) additionally. However, the study highlights C. raciborskii as potential lipid and carotenoid producer at nutrient stress and finds a novel way to utilize these cyanobacterial biomasses, which cause immense environmental hazards and life threats.

Soil C, N and P cycling enzyme responses to nutrient limitation under elevated CO2

Elevated CO2 (eCO2) can stimulate plant productivity and increase carbon (C) input to soils, but nutrient limitation restricts productivity. Despite phosphorus (P)-limited ecosystems increasing globally, it is unknown how nutrient cycling, particularly soil microbial extra cellular enzyme activity (EEA), will respond to eCO2 in such ecosystems. Long-term nutrient manipulation plots from adjacent P-limited acidic and limestone grasslands were exposed to eCO2 (600 ppm) provided by a mini-Free Air CO2 Enrichment system. P-limitation was alleviated (35 kg-P ha−1 y−1 (P35)), exacerbated (35 kg-N ha−1 y−1 (N35), 140 kg-N ha−1 y−1 (N140)), or maintained (control (P0N0)) for > 20 years. We measured EEAs of C-, N- and P-cycling enzymes (1,4-β-glucosidase, cellobiohydrolase, N-acetyl β-D-glucosaminidase, leucine aminopeptidase, and acid phosphatase) and compared C:N:P cycling enzyme ratios using a vector analysis. Potential acid phosphatase activity doubled under N additions relative to P0N0 and P35 treatments. Vector analysis revealed reduced C-cycling investment and increased P-cycling investment under eCO2. Vector angle significantly increased with P-limitation (P35 < P0N0 < N35 < N140) indicating relatively greater investment in P-cycling enzymes. The limestone grassland was more C limited than the acidic grassland, characterised by increased vector length, C:N and C:P enzyme ratios. The absence of interactions between grassland type and eCO2 or nutrient treatment for all enzyme indicators signaled consistent responses to changing P-limitation and eCO2 in both grasslands. Our findings suggest that eCO2 reduces C limitation, allowing increased investment in P- and N-cycle enzymes with implications for rates of nutrient cycling, potentially alleviating nutrient limitation of ecosystem productivity under eCO2.Graphic abstract

Systematic Investigation of the Effects of Macro-elements and Iron on Soybean Plant Response to Fusarium oxysporum Infection.

Nutrient manipulation is a promising strategy for controlling plant diseases in sustainable agriculture. Although many studies have investigated the relationships between certain elements and plant diseases, few have comprehensively explored how differing mineral nutrition levels might affect plant–fungal pathogen interactions, namely plant susceptibility and resistance. Here, we systematically explored the effects of the seven mineral elements that plants require in the greatest amounts for normal development on the susceptibility of soybean plants (Glycine max) to Fusarium oxysporum infection in controlled greenhouse conditions. Nitrogen (N) negligibly affected plant susceptibility to infection in the range 4 to 24 mM for both tested soybean cultivars. At relatively high concentrations, phosphorus (P) increased plant susceptibility to infection, which led to severely reduced shoot and root dry weights. Potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), and iron (Fe) induced plant resistance to infection as their concentrations were increased. For K and Ca, moderate concentrations had a positive effect on plant resistance to the pathogen, whereas relatively high doses of either element adversely affected plant growth and promoted disease symptoms. Further experiments were conducted, assessing disease suppression by selected combinations of macro-elements and Fe at screened concentrations, i.e., K (9 mM) plus Fe (0.2 mM), and S (4 mM) plus Fe (0.2 mM). The disease index was significantly reduced by the combination of K plus Fe. In conclusion, this systematic investigation of soybean plant responses to F. oxysporum infection provides a solid basis for future environmentally-friendly choices for application in soybean disease control programs.