How and why grasshopper community maturation rates are slowing on a North American tall grass prairie

Invertebrate growth rates have been changing in the Anthropocene. We examine rates of seasonal maturation in a grasshopper community that has been declining annually greater than 2% a year over 34 years. As this grassland has experienced a 1°C increase in temperature, higher plant biomass and lower nutrient densities, the community is maturing more slowly. Community maturation had a nutritional component: declining in years/watersheds with lower plant nitrogen. The effects of fire frequency were consistent with effects of plant nitrogen. Principal components analysis also suggests associated changes in species composition-declines in the densities of grass feeders were associated with declines in community maturation rates. We conclude that slowed maturation rates-a trend counteracted by frequent burning-likely contribute to long-term decline of this dominant herbivore.

Tipping cancer cells over the edge: the context-dependent cost of high ploidy

Tetraploidy is an aneuploidy-permissive condition that can fuel tumorgenesis. The tip-over hypothesis of cytotoxic therapy-sensitivity proposes that therapy is effective if it pushes a cell's aneuploidy above a viable tipping point. But elevated aneuploidy alone may not account for this tipping point. Tissue micro-environments (TMEs) that lack sufficient resources to support tetraploid cells can explain the fitness cost of aneuploidy. Raw materials needed to generate deoxynucleotides, the building blocks of DNA, are candidate rate-limiting factors for the evolution of high-ploidy cancer cells. Understanding the resource cost of high ploidy is key to uncover its therapeutic vulnerabilities across tissue sites with versatile energy supplies.

Update on Vascular Complications After Renal Transplantation

Renal transplant is the treatment of choice for endstage renal failure. Since the first successful kidney transplant in 1954, advances in immunosuppression, surgical techniques, and posttransplant medical care have drastically improved the outcomes of this procedure. Despite these advances, surgical complications after renal transplant remain a challenge that can result in serious morbidity, graft loss, and recipient mortality. A significant proportion of surgical complications will have a vascular origin. Some of these vascular complications can cause irreversible damage to the transplanted kidney unless they are identified and treated urgently. In this review, common vascular complications of renal transplant are discussed, with emphasis on their mode of presentation, diagnosis, current management, and outcomes. Such knowledge can be useful for transplant clinicians, for prompt diagnosis and appropriate management of these complications.

A consumer-driven recycling theory for the impact of large herbivores on terrestrial ecosystem stoichiometry

Biological control of nutrient cycles is well documented in aquatic ecosystems, where consumer-driven recycling by herbivores can significantly impact ecosystem stoichiometry. In contrast, little is known in terrestrial ecosystems, where there is evidence that herbivores can also impact ecosystem stoichiometry. I studied a stoichiometric model of the soil-plant-herbivore system. The model shows that herbivores influence the ecosystem stoichiometry mainly through the direct and indirect controls of ecosystem inputs and losses, in a more complex way than predicted by the classic consumer-driven recycling theory. Overall, it shows that herbivores affect nutrient ratios in terrestrial ecosystems mostly independently of their own stoichiometric ratios, and that their impact may be different in forest versus grassland. The results highlight the sensitivity of terrestrial ecosystems to elusive actors, negligible in biomass but capable of modifying nutrient loss rates with major impacts on nutrient cycles and ecosystem stoichiometry.

Foliar nutrient allocation patterns in Banksia attenuata and Banksia sessilis differing in growth rate and adaptation to low-phosphorus habitats

BACKGROUND AND AIMS

Phosphorus (P) and nitrogen (N) are essential nutrients that frequently limit primary productivity in terrestrial ecosystems. Efficient use of these nutrients is important for plants growing in nutrient-poor environments. Plants generally reduce foliar P concentration in response to low soil P availability. We aimed to assess ecophysiological mechanisms and adaptive strategies for efficient use of P in Banksia attenuata (Proteaceae), naturally occurring on deep sand, and B. sessilis, occurring on shallow sand over laterite or limestone, by comparing the allocation of P among foliar P fractions.

METHODS

We carried out pot experiments with slow-growing B. attenuata, which resprouts after fire, and faster growing opportunistic B. sessilis, which is killed by fire, on substrates with different P availability using a randomized complete block design. We measured leaf P and N concentrations, photosynthesis, leaf mass per area, relative growth rate and P allocated to major biochemical fractions in B. attenuata and B. sessilis.

KEY RESULTS

The two species had similarly low foliar total P concentrations, but distinct patterns of P allocation to P-containing fractions. The foliar total N concentration of B. sessilis was greater than that of B. attenuata on all substrates. The foliar total P and N concentrations in both species decreased with decreasing P availability. The relative growth rate of both species was positively correlated with concentrations of both foliar nucleic acid P and total N, but there was no correlation with other P fractions. Faster growing B. sessilis allocated more P to nucleic acids than B. attenuata did, but other fractions were similar.

CONCLUSIONS

The nutrient allocation patterns in faster growing opportunistic B. sessilis and slower growing B. attenuata revealed different strategies in response to soil P availability which matched their contrasting growth strategy.

Landscape Controls on Nutrient Stoichiometry Regulate Lake Primary Production at the Margin of the Greenland Ice Sheet

Global change is reshaping the physical environment and altering nutrient dynamics across the Arctic. These changes can affect the structure and function of biological communities and influence important climate-related feedbacks (for example, carbon (C) sequestration) in biogeochemical processing hot spots such as lakes. To understand how these ecosystems will respond in the future, this study examined recent (< 10 y) and long-term (1000 y) shifts in autotrophic production across paraglacial environmental gradients in SW Greenland. Contemporary lake temperatures and light levels increased with distance from the ice sheet, along with dissolved organic C (DOC) concentrations and total nitrogen:total phosphorus (TN:TP) ratios. Diatom production measured as biogenic silica accumulation rates (BSiARs) and diatom contribution to microbial communities declined across these gradients, while total production estimated using C accumulation rates and δ13C increased, indicating that autochthonous production and C burial are controlled by microbial competition and competitive displacement across physiochemical gradients in the region. Diatom production was generally low across lakes prior to the 1800’s AD but has risen 1.5–3× above background levels starting between 1750 and 1880 AD. These increases predate contemporary regional warming by 115–250 years, and temperature stimulation of primary production was inconsistent with paleorecords for ~ 90% of the last millennium. Instead, primary production appeared to be more strongly related to N and P availability, which differs considerably across the region due to lake landscape position, glacial activity and degree of atmospheric nutrient deposition. These results suggest that biological responses to enhanced nutrient supply could serve as important negative feedbacks to global change.

Effects of Epichloë sinensis Endophyte and Host Ecotype on Physiology of Festuca sinensis under Different Soil Moisture Conditions

This study explored the effects of the Epichloë sinensis endophyte on growth, photosynthesis, ionic content (K+ and Ca2+), phytohormones (abscisic acid-ABA, cytokinin-CTK, indolE-3-acetic acid-IAA, and gibberellin-GA), and elements-C, N, P (in the shoot and root) in two ecotypes of Festuca sinensis (ecotypes 111 and 141) under different soil water conditions (35% and 65% relative saturation moisture content (RSMC)). The results showed that 35% RSMC inhibited the plants' growth, and compared with 65% RSMC, there was a significant (p < 0.05) decrease in the growth and photosynthesis indices, the contents of CTK and GA, Ca2+ concentration, and the contents of C, N, and P (in both the aboveground and underground parts) under 35% RSMC. E. sinensis had beneficial effects on host growth and stress tolerance. Under both 35% and 65% RSMC, the presence of E. sinensis significantly (p < 0.05) increased host plant height, tiller number, root length, root volume, shoot dry weight, chlorophyll content, and the rate of photosynthesis of both ecotypes. Furthermore, the shoot C, N, and P contents in plants infected with E. sinensis (E+) from the two ecotypes, under both conditions of RSMC, were significantly (p < 0.05) higher than those in corresponding plants that were not infected with E. sinensis (E-). Under 35% RSMC, the contents of ABA, K+, Ca2+, and root P contents in E+ plants were significantly (p < 0.05) higher than those in corresponding E- plants in both ecotypes. However, under 65% RSMC, root C, N, and P contents in E+ plants of ecotype 111 and 141 were significantly (p < 0.05) higher than those in corresponding E- plants. In addition, the host ecotype also had effects on host growth and stress tolerance; the growth and photosynthetic indices of ecotype 141 were significantly (p < 0.05) higher than those of ecotype 111 under 35% RSMC, which suggested that ecotype 141 is more competitive than ecotype 111 under water deficiency conditions. These findings suggest that the endophyte improved the host plant resistance to water deficiency by maintaining the growth of the plant, improving photosynthesis, accumulating K+ and Ca2+, promoting nutrient absorption, and adjusting the metabolism of plant hormones.

Reintegrating Biology Through the Nexus of Energy, Information, and Matter

Information, energy, and matter are fundamental properties of all levels of biological organization, and life emerges from the continuous flux of matter, energy, and information. This perspective piece defines and explains each of the three pillars of this nexus. We propose that a quantitative characterization of the complex interconversions between matter, energy, and information that comprise this nexus will help us derive biological insights that connect phenomena across different levels of biological organization. We articulate examples from multiple biological scales that highlight how this nexus approach leads to a more complete understanding of the biological system. Metrics of energy, information, and matter can provide a common currency that helps link phenomena across levels of biological organization. The propagation of energy and information through levels of biological organization can result in emergent properties and system-wide changes that impact other hierarchical levels. Deeper consideration of measured imbalances in energy, information, and matter can help researchers identify key factors that influence system function at one scale, highlighting avenues to link phenomena across levels of biological organization and develop predictive models of biological systems.

Cellular costs underpin micronutrient limitation in phytoplankton

Micronutrients control phytoplankton growth in the ocean, influencing carbon export and fisheries. It is currently unclear how micronutrient scarcity affects cellular processes and how interdependence across micronutrients arises. We show that proximate causes of micronutrient growth limitation and interdependence are governed by cumulative cellular costs of acquiring and using micronutrients. Using a mechanistic proteomic allocation model of a polar diatom focused on iron and manganese, we demonstrate how cellular processes fundamentally underpin micronutrient limitation, and how they interact and compensate for each other to shape cellular elemental stoichiometry and resource interdependence. We coupled our model with metaproteomic and environmental data, yielding an approach for estimating biogeochemical metrics, including taxon-specific growth rates. Our results show that cumulative cellular costs govern how environmental conditions modify phytoplankton growth.

Ecological stoichiometric characteristics and influencing factors of carbon, nitrogen, and phosphorus in the leaves of Sophora alopecuroides L. in the Yili River Valley, Xinjiang

Background

Sophora alopecuroides L. (S. alopecuroides L.) is a perennial herb widely distributed throughout Xinjiang, China. It is characterized by its rapid diffusion ability.

Methods

To reveal the ecological mechanism of the rapid spread of S. alopecuroides, and to elucidate the ecological stoichiometric characteristics of C, N, and P (and the influencing factors) in the leaves of S. alopecuroides, leaves were sampled from four habitats—forest, roadside, farmland, and desert—across the Yili River Valley. The variation rules of the ecological stoichiometric characteristics of C, N, and P in the leaves of S. alopecuroides were analyzed. Correlations between the ecological stoichiometric characteristics of leaves and environmental factors were examined using redundancy analysis (RDA).

Results

(1) The C, N, and P contents of S. alopecuroides leaves were 391.30–533.10 g/kg, 8.90–43.14 g/kg, and 0.71–2.04 g/kg, respectively, and the C/N, C/P, and N/P ratios were 10.34–4.94, 209.05–698.73, and 10.78–31.43 respectively. (2) The C content and C/P ratio of S. alopecuroides leaves were the highest in the desert habitat, leaf N content and N/P ratio were the highest in the forest habitat, leaf P content was the highest in the farmland habitat, and the leaf C/N ratio was the highest in the roadside habitat. (3) RDA showed that available potassium (AK) and pH were the main factors affecting the ecological stoichiometric characteristics of S. alopecuroides leaves in Yili Valley (p ≤ 0.05), and these factors were positively correlated with C, N, P, and N/P, and negatively correlated with C/P and C/N. AK was the dominant factor that affected the P content of S. alopecuroides leaves, and appropriate reduction of K fertilizer would be conducive to restraining the spread of S. alopecuroides. Soil C, N, P, and K content, soil organic matter (OM), nitrate nitrogen (NO₃⁻-N), ammonium nitrogen (NH₄⁺-N), and AK had no significant effect on the ecological stoichiometric characteristics of leaves (p > 0.05).

Digestion Efficiency during Alkaline Persulfate Oxidation for Determination of Total Phosphorus Content of Biological Samples

Quantifying total phosphorus contents of organisms can elucidate their physiological condition and the nutrient cycles of ecosystems. Simple, brief, and safe persulfate oxidation methods have been used for total P determination, but oxidizing solutions of different compositions and volumes have been used. Two certified reference materials were used to evaluate digestion efficiencies of different solutions for this study. Although the phosphorus recoveries were low (<90%) without NaOH, phosphorus recoveries using the solution with 4% K2S2O8 and 0.15 M NaOH were complete. Results demonstrated that digestion efficiency depends on the K2S2O8 concentration and on the pH condition. Moreover, the phosphorus recoveries were achieved at >4 mL/mg solution/material ratios for both standard materials. Therefore, the author recommends using >4 mL of the 4% K2S2O8 solution with 0.15 M NaOH for sample materials of <1 mg to quantify the total phosphorus of biological samples.

Understanding the evolution of nutritive taste in animals: Insights from biological stoichiometry and nutritional geometry

A major conceptual gap in taste biology is the lack of a general framework for understanding the evolution of different taste modalities among animal species. We turn to two complementary nutritional frameworks, biological stoichiometry theory and nutritional geometry, to develop hypotheses for the evolution of different taste modalities in animals. We describe how the attractive tastes of Na-, Ca-, P-, N-, and C-containing compounds are consistent with principles of both frameworks based on their shared focus on nutritional imbalances and consumer homeostasis. Specifically, we suggest that the evolution of multiple nutritive taste modalities can be predicted by identifying individual elements that are typically more concentrated in the tissues of animals than plants. Additionally, we discuss how consumer homeostasis can inform our understanding of why some taste compounds (i.e., Na, Ca, and P salts) can be either attractive or aversive depending on concentration. We also discuss how these complementary frameworks can help to explain the evolutionary history of different taste modalities and improve our understanding of the mechanisms that lead to loss of taste capabilities in some animal lineages. The ideas presented here will stimulate research that bridges the fields of evolutionary biology, sensory biology, and ecology.

How and why plant ionomes vary across North American grasslands and its implications for herbivore abundance

Plant elemental content can vary up to 1,000-fold across grasslands, with implications for the herbivores the plants feed. We contrast the regulation, in grasses and forbs, of 12 elements essential to plants and animals (henceforth plant-essential), 7 essential to animals but not plants (animal-essential) and 6 with no known metabolic function (nonessential). Four hypotheses accounted for up to two thirds of the variation in grass and forb ionomes across 54 North American grasslands. Consistent with the supply-side hypothesis, the plant-essential ionome of both forbs and grasses tracked soil availability. Grass ionomes were more likely to harvest even nonessential elements like Cd and Sr. Consistent with the grazing hypothesis, cattle-grazed grasslands also accumulated a handful of metals like Cu and Cr. Consistent with the NP-catalysis hypothesis, increases in the macronutrients N and P in grasses were associated with higher densities of cofactors like Zn and Cu. The plant-essential elements of forbs, in contrast, consistently varied as per the nutrient-dilution hypothesis-there was a decrease in elemental parts per million with increasing local carbohydrate production. Combined, these data fit a working hypothesis that grasses maintain lower elemental densities and survive on nutrient-poor patches by opportunistically harvesting soil nutrients. In contrast, nutrient-rich forbs use episodes of high precipitation and temperature to build new carbohydrate biomass, raising leaves higher to compete for light, but diluting the nutrient content in every bite of tissue. Herbivores of forbs may thus be particularly prone to increases in pCO₂ via nutrient dilution.

Nutrient criteria to achieve New Zealand's riverine macroinvertebrate targets

Waterways worldwide are experiencing nutrient enrichment from population growth and intensive agriculture, and New Zealand is part of this global trend. Increasing fertilizer in New Zealand and intensive agriculture have driven substantial water quality declines over recent decades. A recent national directive has set environmental managers a range of riverine ecological targets, including three macroinvertebrate indicators, and requires nutrient criteria be set to support their achievement. To support these national aspirations, we use the minimization-of-mismatch analysis to derive potential nutrient criteria. Given that nutrient and macroinvertebrate monitoring often does not occur at the same sites, we compared nutrient criteria derived at sites where macroinvertebrates and nutrients are monitored concurrently with nutrient criteria derived at all macroinvertebrate monitoring sites and using modelled nutrients. To support all three macroinvertebrate targets, we suggest that suitable nutrient criteria would set median dissolved inorganic nitrogen concentrations at ~0.6 mg/L and median dissolved reactive phosphorus concentrations at ~0.02 mg/L. We recognize that deriving site-specific nutrient criteria requires the balancing of multiple values and consideration of multiple targets, and anticipate that criteria derived here will help and support these environmental goals.

How to Restore Invertebrate Diversity of Degraded Heathlands? A Case Study on the Reproductive Performance of the Field Cricket Gryllus campestris (L.)

Background

Nitrogen (NOx, NHy) and acidifying (NOx, NHy, SOx) deposition has reduced the biodiversity of European dry heathlands. Restoration efforts such as sod-cutting (removal of vegetation, litter and humus layer) often shifted these systems from N to P limitation and have had limited success in restoring the invertebrate community. Possible reasons for this include the unresolved acidification and a change in food plant stoichiometry. Here, we investigate how liming and P addition change food nutritional quality and their consequences for invertebrate performance.

Methods

We performed feeding experiments with field crickets (Gryllus campestris), using plant material collected from a full factorial field experiment with liming and P addition. We related female reproduction as measure of individual fitness to elemental ratios of plants fed to the crickets.

Results

P addition stimulated cricket daily reproduction and shortened their reproductive period, resulting in no difference in total reproduction. Liming greatly reduced both daily and total reproduction and resulted in more females cannibalizing on their male mates. Females that did so could partly offset the liming induced reduction in reproduction, suggesting dietary deficiency. P-addition improved food quality (lower N:P ratios) while liming led to skewed Mn:Mg and Fe:Mg ratios that compare unfavorably to ratios found in terrestrial invertebrates.

Conclusion

Increased plant N:P ratio following sod-cutting constrains the reproductive potential in Gryllus campestris in a non-linear way. Liming reduced nutritional quality, likely by inducing deficiencies in Fe or Mn.

Management Implications

High-impact restoration management practices such as sod cutting and liming cause new problems for invertebrates rooted in ecological stoichiometry. Since P-addition only partially offsets these negative effects, we instead advocate the use of less intensive N removal management and weaker buffering agents to reduce soil acidification. Furthermore, a reduction in N emission is paramount as it will remove the need for disruptive interventions.

Generalized Stoichiometry and Biogeochemistry for Astrobiological Applications

A central need in the field of astrobiology is generalized perspectives on life that make it possible to differentiate abiotic and biotic chemical systems McKay (2008). A key component of many past and future astrobiological measurements is the elemental ratio of various samples. Classic work on Earth's oceans has shown that life displays a striking regularity in the ratio of elements as originally characterized by Redfield (Redfield 1958; Geider and La Roche 2002; Eighty years of Redfield 2014). The body of work since the original observations has connected this ratio with basic ecological dynamics and cell physiology, while also documenting the range of elemental ratios found in a variety of environments. Several key questions remain in considering how to best apply this knowledge to astrobiological contexts: How can the observed variation of the elemental ratios be more formally systematized using basic biological physiology and ecological or environmental dynamics? How can these elemental ratios be generalized beyond the life that we have observed on our own planet? Here, we expand recently developed generalized physiological models (Kempes et al. 2012, 2016, 2017, 2019) to create a simple framework for predicting the variation of elemental ratios found in various environments. We then discuss further generalizing the physiology for astrobiological applications. Much of our theoretical treatment is designed for in situ measurements applicable to future planetary missions. We imagine scenarios where three measurements can be made-particle/cell sizes, particle/cell stoichiometry, and fluid or environmental stoichiometry-and develop our theory in connection with these often deployed measurements.

Differential effects of various reclamation treatments on soil characteristics: an experimental study of newly reclaimed tidal mudflats on the east China coast

Reclamation of coastal land is increasingly being used as a means of raising agricultural productivity and improving food security in China. Applications of organic and inorganic supplements on reclaimed soils can significantly adjust a range of soil properties, C, N, P content and stoichiometry, and extracellular enzyme activities. However, the linkages between soil C꞉N꞉P stoichiometry and extracellular enzyme activities following reclamation of coastal saline soil remain largely unclear. In this experimental study, treatments included control (CK), chicken manure (OM), polyacrylamide plus chicken manure (PAM+OM), straw mulching plus chicken manure (SM + OM), buried straw plus chicken manure (BS + OM), and bio-organic manure plus chicken manure (BM + OM) were conducted to explore the linkages between soil physicochemical characteristics in reclaimed soils under different treatments and to evaluate their impact on oat yield. Soils under all reclamation treatments exhibited higher moisture content and, with the exception of SM + OM, lower soil pH compared to the control. The reclamation treatments also significantly decreased soil bulk density (BD) and soil salt content (SSC), and increased soil organic carbon (SOC), total nitrogen (TN) and organic phosphorus (OP). Our study of soil C꞉N꞉P stoichiometry revealed that newly reclaimed soils in the study area are N limited. Additionally, soil invertase (INV), urease (URE) and alkaline phosphatase (ALP) activity under different reclamation treatments were significantly enhanced compared with CK in surface soil, while soil catalase (CAT) activity was observed to be much higher in BM + OM than in other treatments. Mean oat yields for each of the treatments were ranked as follows: BM + OM > SM + OM > PAM + OM > BS + OM > OM > CK treatment. Our results also indicate that TN (12.1% and 12.4%) was the main factor affecting URE and ALP, whereas BD (13.5%) and pH (8.5) were key factors affecting INV and CAT activity, respectively.

Bryophyte C:N:P stoichiometry, biogeochemical niches and elementome plasticity driven by environment and coexistence

Ecological stoichiometry and studies of biogeochemical niches have mainly focused on plankton and vascular plants, but the phenotypically closest modern relatives of early plants, bryophytes, have been largely neglected. We analysed C:N:P stoichiometries and elemental compositions (K, Na, Mg, Ca, S, Fe) of 35 widely distributed bryophyte species inhabiting springs. We estimated bryophyte C:N:P ratios and their biogeochemical niches, investigated how elementomes respond to the environment and determined whether they tend to diverge more for coexisting than non-coexisting individuals and species. The median C:N:P was 145:8:1, intermediate between Redfield's ratio for marine plankton and those for vascular plants. Biogeochemical niches were differentiated amongst species and were phylogenetically conserved. Differences in individual and species-specific elementomes increased with coexistence between species. Our results provide an evolutionary bridge between the ecological stoichiometries of algae and vascular plants and suggest that differences in elementomes could be used to understand community assemblages and functional diversity.

Evolution of eukaryotes as a story of survival and growth of mitochondrial DNA over two billion years

Mitochondria's significance in human diseases and in functioning, health and death of eukaryotic cell has been acknowledged widely. Yet our perspective in cell biology and evolution remains nucleocentric. Mitochondrial DNA, by virtue of its omnipresence and species-level conservation, is used as a barcode in animal taxonomy. This article analyses various levels of containment structures that enclose mitochondrial DNA and advocates a fresh perspective wherein evolution of organic structures of the eukarya domain seem to support and facilitate survival and proliferation of mitochondrial DNA by splitting containers as they age and by directing them along two distinct pathways: destruction of containers with more mutant mitochondrial DNA and rejuvenation of containers with less mutant mitochondrial DNA.

The maximum growth rate hypothesis is correct for eukaryotic photosynthetic organisms, but not cyanobacteria

The (maximum) growth rate (µ_max ) hypothesis predicts that cellular and tissue phosphorus (P) concentrations should increase with increasing growth rate, and RNA should also increase as most of the P is required to make ribosomes. Using published data, we show that though there is a strong positive relationship between the µ_max of all photosynthetic organisms and their P content (% dry weight), leading to a relatively constant P productivity, the relationship with RNA content is more complex. In eukaryotes there is a strong positive relationship between µ_max and RNA content expressed as % dry weight, and RNA constitutes a relatively constant 25% of total P. In prokaryotes the rRNA operon copy number is the important determinant of the amount of RNA present in the cell. The amount of phospholipid expressed as % dry weight increases with increasing µ_max in microalgae. The relative proportions of each of the five major P-containing constituents is remarkably constant, except that the proportion of RNA is greater and phospholipids smaller in prokaryotic than eukaryotic photosynthetic organisms. The effect of temperature differences between studies was minor. The evidence for and against P-containing constituents other than RNA being involved with ribosome synthesis and functioning is discussed.

Genome analysis of Plectus murrayi, a nematode from continental Antarctica

Plectus murrayi is one of the most common and locally abundant invertebrates of continental Antarctic ecosystems. Because it is readily cultured on artificial medium in the laboratory and highly tolerant to an extremely harsh environment, P. murrayi is emerging as a model organism for understanding the evolutionary origin and maintenance of adaptive responses to multiple environmental stressors, including freezing and desiccation. The de novo assembled genome of P. murrayi contains 225.741 million base pairs and a total of 14,689 predicted genes. Compared to Caenorhabditis elegans, the architectural components of P. murrayi are characterized by a lower number of protein-coding genes, fewer transposable elements, but more exons, than closely related taxa from less harsh environments. We compared the transcriptomes of lab-reared P. murrayi with wild-caught P. murrayi and found genes involved in growth and cellular processing were up-regulated in lab-cultured P. murrayi, while a few genes associated with cellular metabolism and freeze tolerance were expressed at relatively lower levels. Preliminary comparative genomic and transcriptomic analyses suggest that the observed constraints on P. murrayi genome architecture and functional gene expression, including genome decay and intron retention, may be an adaptive response to persisting in a biotically simplified, yet consistently physically harsh environment.

Stoichiometric niche, nutrient partitioning and resource allocation in a solitary bee are sex-specific and phosphorous is allocated mainly to the cocoon

Life histories of species may be shaped by nutritional limitations posed on populations. Yet, populations contain individuals that differ according to sex and life stage, each of which having different nutritional demands and experiencing specific limitations. We studied patterns of resource assimilation, allocation and excretion during the growth of the solitary bee Osmia bicornis (two sexes) under natural conditions. Adopting an ecological perspective, we assert that organisms ingest mutable organic molecules that are transformed during physiological processes and that the immutable atoms of the chemical elements composing these molecules may be allocated to specific functions, thereby influencing organismal fitness and life history. Therefore, using the framework of ecological stoichiometry, we investigated the multielemental (C, N, S, P, K, Na, Ca, Mg, Fe, Zn, Mn, Cu) compositions of six components of the bee elemental budget: food (pollen), eggs, pupae, adults, cocoons and excreta. The sexes differed fundamentally in the assimilation and allocation of acquired atoms, elemental phenotypes, and stoichiometric niches for all six components. Phosphorus, which supports larval growth, was allocated mainly (55-75%) to the cocoon after larval development was complete. Additionally, the majority (60-99%) of the Mn, Ca, Mg and Zn acquired during larval development was allocated to the cocoon, probably influencing bee fitness by conferring protection. We conclude that for holometabolous insects, considering only the chemical composition of the adult body within the context of nutritional ecology does not provide a complete picture. Low ratios of C to other nutrients, low N:P and high Na concentrations in excreta and cocoons may be important for local-scale nutrient cycling. Limited access to specific nutritional elements may hinder bee development in a sex-dependent manner, and N and P limitations, commonly considered elsewhere, may not play important roles in O. bicornis. Sexual dimorphism in nutritional limitations due to nutrient scarcity during the larval stage may influence bee population function and should be considered in bee conservation efforts.

A unified framework for herbivore-to-producer biomass ratio reveals the relative influence of four ecological factors

The biomass ratio of herbivores to primary producers reflects the structure of a community. Four primary factors have been proposed to affect this ratio, including production rate, defense traits and nutrient contents of producers, and predation by carnivores. However, identifying the joint effects of these factors across natural communities has been elusive, in part because of the lack of a framework for examining their effects simultaneously. Here, we develop a framework based on Lotka–Volterra equations for examining the effects of these factors on the biomass ratio. We then utilize it to test if these factors simultaneously affect the biomass ratio of freshwater plankton communities. We found that all four factors contributed significantly to the biomass ratio, with carnivore abundance having the greatest effect, followed by producer stoichiometric nutrient content. Thus, the present framework should be useful for examining the multiple factors shaping various types of communities, both aquatic and terrestrial.

Takehiro Kazama et al. develop a framework based on Lotka–Volterra models to identify the relative influences of production rate, defense traits, nutrient contents of producers, and predation, in affecting the biomass ratio of herbivores to primary producers in a community. They apply this framework to freshwater plankton systems and find that while all factors affect the biomass ratio, carnivore abundance has the greatest relative influence.

Quantitative genetics of phosphorus content in the freshwater herbivore, Daphnia pulicaria

Phosphorus (P) is essential for growth of all organisms, and P content is correlated with growth in most taxa. Although P content was initially considered to be a trait fixed at the species level, there is growing evidence for considerable intraspecific variation. Selection on such variation can thus alter the rates at which P fluxes through food webs. Nevertheless, prior work describing the sources and extent of intraspecific variation in P content were not genetically explicit, confounded by unknown genetic background and evolutionary history. We constructed an F2 recombinant population of the dominant freshwater grazer, Daphnia pulicaria to mitigate such issues. F2 recombinants exhibited considerable variation in growth rate, P content (0.49%-1.97%), P use efficiency (PUE; 51-208 mg biomass/mg P), and correlated traits such as hatching time of resting eggs, in common garden conditions. These results clearly demonstrate the scope of genetic recombination in generating variation in ecologically relevant traits. The absence of environmental selection is a likely component driving such variation not observed in natural settings. Although phosphoglucose isomerase (PGI) genotype was significantly associated with variation in hatching time of resting eggs, contrary to prior work with less rigorous designs, and allelic variation at the PGI locus did not explain variation in P content and PUE of Daphnia, indicating that such quantitative traits are under polygenic control. Together, these results suggest that although there is considerable genetic scope for variation in key ecologically relevant traits, such as P content and efficiency of P use, these traits are likely under strong stabilizing selection, most likely due to selection on growth rate and size. Importantly, our observations suggest that anthropogenic alterations to P supply due to eutrophication could alter selection on these traits, thereby rapidly altering the role Daphnia plays in the P cycle of lakes.

Dynamics in Stoichiometric Traits and Carbon, Nitrogen, and Phosphorus Pools across Three Different-Aged Picea asperata Mast. Plantations on the Eastern Tibet Plateau

Understanding the variations in soil and plants with stand aging is important for improving management measures to promote the sustainable development of plantations. However, few studies have been conducted on the dynamics of stoichiometric traits and carbon (C), nitrogen (N), and phosphorus (P) pools across Picea asperata Mast plantations of different ages in subalpine regions. In the present study, we examined the stoichiometric traits and C, N, and P stocks in different components of three different aged (22-, 32-, and 42-year-old) P. asperata plantations by plot-level inventories. We hypothesized that the stoichiometric traits in mineral soil could shape the corresponding stoichiometric traits in soil microbes, tree roots and foliage, and the C, N, and P stocks of the total P. asperata plantation ecosystem would increase with increasing stand age. Our results show that the N:P ratio in mineral soil was significantly correlated with that in tree foliage and herbs. Additionally, the C:N ratio and C:P ratio in mineral soil only correlated with the corresponding stoichiometric traits in soil microbes and forest floor, respectively. Both the fractions of microbial biomass C in soil organic C and microbial biomass N in soil total N decreased with increasing stand age. The C, N, and P stocks of the total ecosystem did not continuously increase across stand development. In particular, the P stock of the total ecosystem exhibited a trend of increasing first and then decreasing. The aboveground tree biomass C accounted for more than 55% of the total ecosystem C stock regardless of stand age. In contrast, mineral soil and forest floor were the major contributors to the total ecosystem N and P stocks in all stands. This study suggested that all three different stands were N limited, and the stoichiometric homeostasis in the roots of P. asperata was more stable than that in the foliage. In addition, the soil microbial community assembly may change with increasing stand age for P. asperata plantations in the subalpine region.

Experimental nitrogen and phosphorus enrichment stimulates multiple trophic levels of algal and detrital-based food webs: a global meta-analysis from streams and rivers

Anthropogenic increases in nitrogen (N) and phosphorus (P) concentrations can strongly influence the structure and function of ecosystems. Even though lotic ecosystems receive cumulative inputs of nutrients applied to and deposited on land, no comprehensive assessment has quantified nutrient-enrichment effects within streams and rivers. We conducted a meta-analysis of published studies that experimentally increased concentrations of N and/or P in streams and rivers to examine how enrichment alters ecosystem structure (state: primary producer and consumer biomass and abundance) and function (rate: primary production, leaf breakdown rates, metabolism) at multiple trophic levels (primary producer, microbial heterotroph, primary and secondary consumers, and integrated ecosystem). Our synthesis included 184 studies, 885 experiments, and 3497 biotic responses to nutrient enrichment. We documented widespread increases in organismal biomass and abundance (mean response = +48%) and rates of ecosystem processes (+54%) to enrichment across multiple trophic levels, with no large differences in responses among trophic levels or between autotrophic or heterotrophic food-web pathways. Responses to nutrient enrichment varied with the nutrient added (N, P, or both) depending on rate versus state variable and experiment type, and were greater in flume and whole-stream experiments than in experiments using nutrient-diffusing substrata. Generally, nutrient-enrichment effects also increased with water temperature and light, and decreased under elevated ambient concentrations of inorganic N and/or P. Overall, increased concentrations of N and/or P altered multiple food-web pathways and trophic levels in lotic ecosystems. Our results indicate that preservation or restoration of biodiversity and ecosystem functions of streams and rivers requires management of nutrient inputs and consideration of multiple trophic pathways.

Stoichiometric variation within and between a terrestrial herbivorous and a semi-aquatic carnivorous mammal

BACKGROUND

The elemental composition of the mammalian body is widely believed to be more or less constant within and among species, yet reliable comparisons of elemental content are lacking. Here, we examine the elemental composition of two mammal species with different diet and provenance: terrestrial herbivorous Fallow deer (Dama dama) - collected from a single area - and semi-aquatic carnivorous Eurasian otter (Lutra lutra) - collected from different areas.

METHODS

We compared twelve elemental contents for twelve different body tissues and organs, for four tissue samples per species. Homogeneous samples were tested for twelve elemental contents using ICP-OES.

RESULTS

We found evidence for differences in elemental composition between species, between tissues, and between individuals. Herbivorous Fallow deer seemed more variable in its elemental composition compared to carnivorous Eurasian otter. The absolute concentration of some elements, e.g. Mn and Cu, showed differences between the species as well.

CONCLUSION

Since we found stoichiometric variation among the species, these findings question the widely held assumption that mammals are under relative tight stoichiometrically homeostatic control.

Intercropping Alters the Soil Microbial Diversity and Community to Facilitate Nitrogen Assimilation: A Potential Mechanism for Increasing Proso Millet Grain Yield

Intercropping of cereals and legumes has been used in modern agricultural systems, and the soil microorganisms associated with legumes play a vital role in organic matter decomposition and nitrogen (N) fixation. This study investigated the effect of intercropping on the rhizosphere soil microbial composition and structure and how this interaction affects N absorption and utilization by plants to improve crop productivity. Experiments were conducted to analyze the rhizosphere soil microbial diversity and the relationship between microbial composition and N assimilation by proso millet (Panicum miliaceum L.) and mung bean (Vigna radiata L.) from 2017 to 2019. Four different intercropping row arrangements were evaluated, and individual plantings of proso millet and mung bean were used as controls. Microbial diversity and community composition were determined through Illumina sequencing of 16S rRNA and internal transcribed spacer (ITS) genes. The results indicated that intercropping increased N levels in the soil-plant system and this alteration was strongly dependent on changes in the microbial (bacterial and fungal) diversities and communities. The increase in bacterial alpha diversity and changes in unique operational taxonomic unit (OTU) numbers increased the soil N availability and plant N accumulation. Certain bacterial taxa (such as Proteobacteria) and fungal taxa (such as Ascomycota) were significantly altered under intercropping and showed positive responses to increased N assimilation. The average grain yield of intercropped proso millet increased by 13.9-50.1% compared to that of monoculture proso millet. Our data clearly showed that intercropping proso millet with mung bean altered the rhizosphere soil microbial diversity and community composition; thus, this intercropping system represents a potential mechanism for promoting N assimilation and increasing grain yield.

Light and competition alter leaf stoichiometry of introduced species and native mangrove species

Ecological stoichiometry is the study of the balance of ecosystem energy and nutrient cycling, especially carbon (C), nitrogen (N), and phosphorus (P). C, N, and P are the key elements for plant growth and metabolism. Systematic research on leaf stoichiometry in mangrove forest ecosystems is still lacking. To understand the leaf stoichiometry of introduced species and native species in mangrove forests, we selected four species (one introduced species, Sonneratia apetala, and three native species, Avicennia marina, Aegiceras corniculatum, and Kandelia obovate) and measured leaf C, N, and P contents under different light conditions. The results showed that there were significant negative scaling relationships of leaf C versus N and C versus P but positive scaling relationships of leaf N versus P in the four mangrove species. Light and competition had significant effects on leaf stoichiometry, especially under the full light condition. S. apetala influenced leaf elements in a mixture with native species. Interspecific competition reduced leaf N and P contents in A. corniculatum and K. obovate but increased leaf N and P contents in A. marina. Leaf N and P contents of the four species showed similar responses to both intraspecific and interspecific competition. The ratio of leaf C:N:P (108:11:1) in the mangrove forests was lower than that in other ecosystems, and species with a higher growth rate had a higher leaf P content and lower N:P ratio, supporting the growth rate hypothesis. Leaf N:P was 11.04, indicating that there was N limitation in the mangrove forests. This systematic research of leaf stoichiometry of mangrove forests improves our understanding of mangrove growth and nutrient use strategies in response to different environmental stresses.

Mapping the Forage Nitrogen-Phosphorus Ratio Based on Sentinel-2 MSI Data and a Random Forest Algorithm in an Alpine Grassland Ecosystem of the Tibetan Plateau

Nondestructive and accurate estimating of the forage nitrogen–phosphorus (N:P) ratio is conducive to the real-time diagnosis of nutrient limitation and the formulation of a management scheme during the growth and development of forage. New-generation high-resolution remote sensors equipped with strategic red-edge wavebands offer opportunities and challenges for estimating and mapping forage N:P ratio in support of the sustainable utilization of alpine grassland resources. This study aims to detect the forage N:P ratio as an ecological indicator of grassland nutrient content by employing Sentinel-2 multispectral instrument (MSI) data and a random forest (RF) algorithm. The results showed that the estimation accuracy (R2) of the forage N:P ratio model established by combining the optimized spectral bands and vegetation indices (VIs) is 0.49 and 0.59 in the vigorous growth period (July) and the senescing period (November) of forage, respectively. Moreover, Sentinel-2 MSI B9 and B12 bands contributed greatly to the estimation of the forage N:P ratio, and the VIs (RECI2) constructed by B5 and B8A bands performed well in the estimation of the forage N:P ratio. Overall, it is promising to map the spatial distribution of the forage N:P ratio in alpine grassland using Sentinel-2 MSI data at regional scales. This study will be potentially beneficial in implementing precise positioning of vegetation nutrient deficiency and scientific fertilization management of grassland.

Animal body size distribution influences the ratios of nutrients supplied to plants

Nutrients released through herbivore feces have the potential to influence plant-available nutrients and affect primary productivity. However, herbivore species use nutrients in set stoichiometric ratios that vary with body size. Such differences in the ratios at which nutrients are used leads to differences in the ratios at which nutrients are deposited through feces. Thus, local environmental factors that affect the average body size of an herbivore community (such as predation risk and food availability) influence the ratios at which fecal nutrients are supplied to plants. Here, we assess the relationship between herbivore body size and the nitrogen-to-phosphorus ratios of herbivore feces. We examine how shifts in the average body size of an herbivore community alter the ratios at which nitrogen and phosphorus are supplied to plants and test whether such differences in the stoichiometry of nutrient supply propagate through plants. We show that dung from larger-bodied herbivores contain lower quantities of phosphorus per unit mass and were higher in N:P ratio. We demonstrate that spatial heterogeneity in visibility (a proxy for predation risk and/or food availability) and rainfall (a proxy for food availability), did not affect the overall amount of feces deposited but led to changes in the average body size of the defecating community. Feces deposited in areas of higher rainfall and reduced visibility originated from larger herbivores and were higher in N:P ratios. This indicates that processes that change the size distribution of herbivore communities, such as predation or size-biased extinction, have the potential to alter the nutrient landscape for plants.

Differential responses of macroinvertebrate ionomes across experimental N:P gradients in detritus-based headwater streams

Diverse global change processes are reshaping the biogeochemistry of stream ecosystems. Nutrient enrichment is a common stressor that can modify flows of biologically important elements such as carbon (C), nitrogen (N), and phosphorus (P) through stream foodwebs by altering the stoichiometric composition of stream organisms. However, enrichment effects on concentrations of other important essential and trace elements in stream taxa are less understood. We investigated shifts in macroinvertebrate ionomes in response to changes in coarse benthic organic matter (CBOM) stoichiometry following N and P enrichment of five detritus-based headwater streams. Concentrations of most elements (17/19) differed among three insect genera (Maccaffertium sp., Pycnopsyche spp., and Tallaperla spp.) prior to enrichment. Genus-specific changes in the body content of: P, magnesium, and sodium (Na) in Tallaperla; P, Na, and cadmium in Pycnopsyche; and P in Maccaffertium were also found across CBOM N:P gradients. These elements increased in Tallaperla but decreased in the other two taxa due to growth dilution at larger body sizes. Multivariate elemental differences were found across all taxa, and ionome-wide shifts with dietary N and P enrichment were also observed in Tallaperla and Pycnopsyche. Our results show that macroinvertebrates exhibit distinct differences in elemental composition beyond C, N, and P and that the ionomic composition of common stream taxa can vary with body size and N and P enrichment. Thus, bottom-up changes in N and P supplies could potentially influence the cycling of lesser studied biologically essential elements in aquatic environments by altering their relative proportions in animal tissues.

Response of Soil Microbial Community to C:N:P Stoichiometry along a Caragana korshinskii Restoration Gradient on the Loess Plateau, China

Soil microorganisms play crucial roles between plants and soil following afforestation. However, the relationship between the microbial community and carbon:nitrogen:phosphorus (C:N:P) stoichiometry in the plant–soil–microbe continuum remains unclear. In this study, we investigated this relationship by collecting plant and soil samples from Caragana korshinskii Kom. plantations with different years of afforestation (17-, 32-, and 42-year-old plantations), and from farmland. Illumina sequencing of the 16S rRNA and internal transcribed spacer (ITS) ribosomal RNA was used to examine the soil microbial community and the C, N, and P concentrations in plants, soil, and microbial biomass. Other soil characteristics were also measured. The results showed that the C and N concentrations in plants (leaves, herbs, and litter), soil, and microbial biomass increased as the vegetation restoration stage increased, but the P concentration in leaves and herbs slightly decreased. The C:P and N:P ratios in the plant–soil–microbe continuum substantially increased over time, particularly that of the microbial biomass. These results suggest that the unbalanced increase of C, N, and P following vegetation restoration may result in a P limitation in plant–soil systems. Moreover, bacterial and fungal alpha diversity significantly increased following afforestation. Afforestation had a greater impact on bacterial diversity (both alpha and beta diversity) than did fungal diversity. Among the dominant bacterial taxa, Proteobacteria increased significantly with afforestation time, whereas Actinobacteria decreased and Acidobacteria peaked in 32-year-old C. korshinskii plantations. However, there were no significant changes in the dominant fungal taxa. Collectively, we found that microbial diversity and dominant phyla were closely associated with the C:P and N:P ratios in the plant–soil–microbe continuum, particularly the N:P ratio. These results suggest that microbial diversity and composition may be limited by the imbalances of C, N, and especially P in afforested ecosystems, which provides evidence of linkages between microbial diversity and plant–soil systems in afforested ecosystems and could help in improving the predictions of sustainably restoring C. korshinskii plantations.

Effects of Stellera chamaejasme removal on the nutrient stoichiometry of S. chamaejasme-dominated grasslands in the Qinghai-Tibetan plateau

BACKGROUND

Stoichiometric relations drive powerful constraints in several fundamental ecosystem processes. However, limited studies have been conducted on the ecological stoichiometry of plants after the change of community composition induced by Stellera chamaejasme removal in alpine grassland in the Qinghai-Tibetan Plateau.

METHODS

We investigated the effects of S. chamaejasme removal on ecological stoichiometry by estimating the C:N:P stoichiometry in species, functional group and community levels of the ecosystem. The interactions between different species, functional groups and correlation with soil nutrient, responding to S. chamaejasme removal were also analyzed.

RESULTS

For the plants that became dominant after S. chamaejasme removal (SR), N content decreased and their C:N increased. S. chamaejasme removal significantly affected the nutrient stoichiometry of different functional groups. Specifically, Gramineae in the SR sites had decreased N content and N:P, and increased C:N; however, forbs had increased N content, C:P and N:P and decreased P content and C:N. At the community level, N content was lower and C:N higher in SR communities compared to CK. The N content of the plant community was positively correlated with soil total N content. S. chamaejasme removal could change the nutrient balance from species level, to functional group level, and to community level. Thus, supplementary measures might be cooperated with S. chamaejasme removal for the recovery of S. chamaejasme-dominated degraded grassland. These results provide insight into the role of S. chamaejasme in ecological protection and conservation, and the conclusions from this study could be used to develop effective and sustainable measures for S. chamaejasme control in the Qinghai-Tibetan Plateau.

Grazing resistance and poor food quality of a widespread mixotroph impair zooplankton secondary production

Growing evidence suggests that global climate change promotes the dominance of mixotrophic algae especially in oligotrophic aquatic ecosystems. While theory predicts that mixotrophy increases trophic transfer efficiency in aquatic food webs, deleterious effects of some mixotrophs on consumers have also been reported. Here, using a widespread mixotrophic algal genus Dinobryon, we aimed to quantify how colonial taxa contribute to secondary production in lakes. We, therefore, studied the dietary effects of Dinobryon divergens on Cladocera (Daphnia longispina) and Copepoda (Eudiaptomus gracilis), representing two main taxonomic and functional groups of zooplankton. In feeding experiments, we showed that Dinobryon was largely grazing resistant and even inhibited the uptake of the high-quality reference food in Daphnia. Eudiaptomus could to some extent compensate with selective feeding, but a negative long-term food quality effect was also evident. Besides, Eudiaptomus was more sensitive to the pure diet of Dinobryon than Daphnia. Low lipid content and high C:P elemental ratio further supported the low nutritional value of the mixotroph. In a stable isotope approach analysing a natural plankton community, we found further evidence that carbon of Dinobryon was not conveyed efficiently to zooplankton. Our results show that the increasing dominance of colonial mixotrophs can result in reduced dietary energy transfer to consumers at higher trophic levels. In a wider perspective, global climate change favours the dominance of some detrimental mixotrophic algae which may constrain pelagic trophic transfer efficiency in oligotrophic systems, similarly to cyanobacteria in eutrophic lakes.

Convergent nitrogen-phosphorus scaling relationships in different plant organs along an elevational gradient

A general relationship between the nitrogen (N) and phosphorus (P) content of all plant organs (e.g. leaf, stem, and root) is hypothesized to exist according to whole-plant economics spectrum (PES) theory, but the evidence supporting these expected patterns remains scarce. We measured the N and P content of the leaves, twigs and fine roots of 64 species in three different forest communities along an elevational gradient (evergreen broad-leaved forest, 1319 m a.s.l., coniferous and broad-leaved mixed forest, 1697 m a.s.l., and deciduous forest, 1818 m a.s.l.) in the Wuyishan National Nature Reserve, southeastern China. The scaling relationship between the N and P content and the linear regression relationship between the N:P ratio and N and P content were analysed. The leaf N and P content was significantly higher at the high-elevation site than at the low- or middle-elevation sites (P < 0.001). The N and P content followed a power-law relationship with similar scaling slopes between organs. The N (common slope, 1.13) and P (common slope, 1.03) content isometrically covaried among leaves, twigs and roots. The scaling exponents of the N-P relationship were not significantly different from 1.0 in all organs, with a common slope of 1.08. The scaling constants of N-P decreased significantly (P < 0.05) from the highest value in fine roots (β = 1.25), followed by leaves (β = 1.17), to the lowest value in twigs (β = 0.88). Standardized major axis (SMA) analyses and comparisons of 95 % confidence intervals also showed that the numerical values of the scaling slopes and the scaling constants did not differ regardless of elevation. The N content, but not the P content, accounted for a large proportion of the variation in the N:P ratio in leaves (N:P and N: r ² = 0.31, F = 33.36, P < 0.001) and fine roots (N:P and N: r ² = 0.15, F = 10.65, P < 0.05). In contrast, the N:P ratio was significantly related to both the N and P content in the twigs (N:P and N: r ² = 0.20, F = 17.86, P < 0.001; N:P and P: r ² = 0.34, F = 35.03, P < 0.001, respectively). Our results indicate that different organs of subtropical woody plants share a similar isometric scaling relationship between their N and P content, providing partial support for the PES hypothesis. Moreover, the effects of the N and P content on the N:P ratio differ between metabolic organs (leaves and fine roots) and structural organs (twigs), elucidating the stoichiometric regulatory mechanism of different organs.

Linkages between nutrient ratio and the microbial community in rhizosphere soil following fertilizer management

To unravel the linkages between ecological ratios (C:N:P) and the microbial community in rhizosphere soil in response to fertilizer management, soil samples were collected from a proso millet (Panicum miliaceum L.) field under different fertilizer management systems, including nitrogen fertilizer (NF), phosphorus fertilizer (PF), combined N and P (NP) fertilizer, and organic fertilizer (OF); no fertilizer (CK) was used as a control. Furthermore, 16S rRNA and ITS gene sequencing were applied to represent the bacterial and fungal diversity in the soil. Moreover, the elemental properties, including the carbon (C), nitrogen (N), and phosphorus (P) contents, in the microbial biomass and rhizosphere soil were evaluated. The results showed that the C, N, and P contents and microbial biomass (MBC, MBN and MBP, respectively) in the rhizosphere soil were augmented following fertilizer management. Increases in the alpha diversity indices (Shannon and Chao 1) of soil bacteria and fungi were observed in response to the fertilizers, and the responses were more closely related to the soil C:N and N:P ratios than to the C:P ratio. Additionally, with high relative abundances (>1%) across all soil samples, the composition of soil microbial phyla levels revealed different trends following fertilizer management. The abundances of Actinobacteria and Gemmatimonadetes increased, while the abundances of Acidobacteria and Nitrospirae decreased (P < 0.05) following fertilizer management. Among the fungal taxa, the abundances of Ascomycota and Mortierellomycota responded positively to fertilizer. These results were largely influenced by changes in the C:N and N:P ratios in both the soil and microbial biomass. Overall, significantly increased C:N and decreased N:P ratios in the soil reflected the N deficiency that would limit increased microbial biomass and diversity. Together, all of these results indicated that interactions between ecological ratios (C:N:P) and microbial community composition play vital roles in resource imbalance in dynamic environments. Thus, N status should be an important factor for sustainable agricultural management. Moreover, the synergistic effects were better with the combination of C, N, and P or with organic fertilizer than with C, N and P separately.

Quantifying nutrient throughput and DOM production by algae in continuous culture

Freshwater and marine algae can balance nutrient demand and availability by regulating uptake, accumulation and exudation. To obtain insight into these processes under nitrogen (N) and phosphorus (P) limitation, we reanalyze published data from continuous cultures of the chlorophyte Selenastrum minutum. Based on mass budgets, we argue that much of the non-limiting N and P had passed through the organisms and was present as dissolved organic phosphorus or nitrogen (DOP or DON). We construct a model that describes the production of biomass and dissolved organic matter (DOM) as a function of the growth rate. A fit of this model against the chemostat data suggests a high turnover of the non-limiting N and P: at the highest growth rates, N and P atoms spent on average only about 3 h inside an organism, before they were exuded as DON and DOP, respectively. This DOM exudation can explain the observed trends in the algal stoichiometric ratios as a function of the dilution rate. We discuss independent evidence from isotope experiments for this apparently wasteful behavior and we suggest experiments to quantify and characterize DON and DOP exudation further.