Nutrient Heterogeneity Research Articles

Disentangling effects of upslope runoff and sediment on soil nutrients on the hilly slopes of the Loess Plateau, China

Upslope runoff and sediment critically influence soil erosion, while their impact on the subsequent downslope nutrient distribution has not been examined, consequently hindering the exact assessment of the effects of erosion on soil biogeochemical cycles. Herein we selected two groups of wide and narrow slopes on the middle Loess Plateau, with each slope group including slopes with and without upslope runoff and sediment. For each slope, we collected soil samples from topsoil along the slope at different distances from the upper slope to the lower slope, and collected samples from depths of 0–60 cm at the upper, middle and lower positions of the slope. The contents of soil organic matter and nutrients were analysed. The purpose of this study was to disentangle the effects of upslope runoff and sediment on spatial distribution of soil nutrients on slopes of different widths. We showed that compared with slopes without upslope runoff and sediment, upslope runoff and sediment increased the content of most nutrients in topsoil on the wide slope, but had a contrasting effect on the narrow slope. Upslope runoff and sediment reduced the random spatial heterogeneity of soil nutrients on both the wide and narrow slopes, with greater effects observed on the narrow slope. The influence of upslope runoff and sediment on the profile distribution of soil nutrients varied with slope position and slope width, and was nutrient type-dependent. These results indicated that slope topographical conditions interact with upslope runoff and sediment in influencing vertical and horizontal patterns of soil nutrients on slopes.

CO2 elevation and nutrient patchiness interactively affect morphology, nitrogen uptake, partitioning and use efficiency of Nicotiana tabacum L. (tobacco) during anthesis

AbstractThe stimulation effect of elevated [CO2] (e[CO2]) on plant growth is modulated by nitrogen (N) availability, yet the mechanisms of this modulation under patchy N supply remain largely elusive. This study aimed to investigate the mechanisms by which patchy nutrient supply in the root‐zone influence on N uptake, partitioning and use efficiency of tobacco plants (Nicotiana tabacum L.) grown under e[CO2]. A split‐root pot experiment was conducted on tobacco plants grown at ambient (a[CO2], 400 μmol L−1) and e[CO2] (800 μmol L−1) conditions during anthesis. Plants were subjected to two fertilizer levels [0 and 113‐29‐214 (N‐P‐K) mg kg−1 soil] and three fertilization regimes (partial root‐zone fertilization, PRN, couple root‐zone fertilization, CRN and no fertilization, CK). Elevated [CO2] significantly decreased N concentrations in all tobacco organs, with the greatest reduction in leaves. Positive responses of tobacco biomass and NUE to e[CO2] were recorded, and a large amount of 15N labelled fertilizer‐N was partitioned to stems at the expense to leaves. Compared to the partially fertilized root, an equal N concentration was observed in the non‐fertilized root. In addition, compared with CRN, PRN increased the root exudates of sugar and organic acid; however, the increased root biomass by nutrient patchiness did not enhance plant total N uptake. Collectively, e[CO2] could sustain N assimilation and distribution of tobacco plants in response to natural heterogeneous nutrient available in the soil caused by patchy fertilization.

Grazing effects on shrub-induced resource islands and herbaceous vegetation heterogeneity in sagebrush-steppe communities

Spatial heterogeneity in plant communities promotes coexistence and diversity by providing a variety of niches for different species. In shrub-steppe communities, shrubs create distinct microsites under their canopies (canopy microsites) compared to areas between their canopies (interspace microsites). This creates spatial heterogeneity in soil nutrient availability and herbaceous vegetation. Grazing can influence spatial heterogeneity, but the effect of grazing on shrub-induced spatial heterogeneity is largely unknown. We investigated the long-term (+80 yrs.) effects of moderate grazing by cattle on sagebrush ( Artemisia )-induced spatial heterogeneity in soil nutrients, herbaceous vegetation, and ground cover in sagebrush-bunchgrass steppe communities at eight sites in southeastern Oregon. Each site consisted of a long-term grazing exclosure and an adjacent grazed area. Almost all measured herbaceous vegetation (cover, density, diversity, and evenness) and ground cover variables differed between canopy and interspace microsites. Grazing did not influence the effects of microsites on most measured herbaceous vegetation characteristics and ground cover variables. Available soil nutrients were not influenced by grazing, but the majority differed between microsites. The limited effect of moderate grazing on shrub-induced spatial heterogeneity provides evidence that sagebrush exerts a strong influence on patterns of soil nutrients and herbaceous vegetation in sagebrush-bunchgrass communities. These results also demonstrate that moderate grazing by cattle can be compatible with maintaining spatial heterogeneity within shrub-steppe communities. In these ecosystems, maintaining and restoring shrubs is critical to promoting spatial heterogeneity, thereby encouraging coexistence and diversity.

Effects of temporal heterogeneity in nutrient supply on intra- and inter-genet competition of a clonal herb

Nutrients are often released heterogeneously over time (e.g., in pulses) in natural habitats. Different genotypes of the same plant species may vary in their responses to temporal nutrient heterogeneity so that temporal nutrient heterogeneity may influence intraspecific interactions. To test effects of temporal nutrient heterogeneity on intra-genet (competition between ramets of the same genotype) and inter-genet competition (competition between ramets of different genotypes), we conducted a greenhouse experiment with five genotypes of the clonal herb Hydrocotyle vulgaris. We grew one ramet (no competition), two ramets of the same genotype or two ramets of different genotypes in a pot and supplied the pot with the same total amount of nutrients either homogeneously or heterogeneously. Results showed that temporal nutrient heterogeneity affected the growth and biomass allocation of some genotypes, but had no impact on those of other genotypes of H. vulgaris. These suggested that responses to temporal nutrient heterogeneity were different between genotypes of H. vulgaris. Temporal nutrient heterogeneity had little effect on intra-genet competition of H. vulgaris likely because ramets of the same genotype did not differ in their responses to temporal nutrient heterogeneity. However, temporal nutrient heterogeneity increased the competitive ability of the genotype of H. vulgaris with higher plant productivity. We conclude that temporal nutrient heterogeneity can influence intraspecific interactions of the clonal plant H. vulgaris by altering inter-genet competition, and this effect may further change population dynamics of the plant.

Spatial heterogeneity of soil nutrients in Yili River Valley.

Soil nutrients are a vital reference index of soil fertility and are essential in studying spatial variability for the development of land resources. The traditional statistical methods including correlation analysis and geostatistical analysis, were used to explore the spatial variability of nutrients and its influencing factors in the Yili River Valley. The results showed that soil total potassium (STK) had a weak variation, soil organic carbon (SOC), soil total nitrogen (STN) and soil total phosphorus (STP) showed a moderate degree of variation. Correlation analysis showed that SOC had a significant correlation with STN, STP, STK, silt, soil water content (SWC), Cos a and altitude (p < 0.01). In contrast, negative correlations were found between the SOC and sand, soil bulk density (SBD) and pH (p < 0.01), the same as STN. STP had a significant correlation with STK, silt (p < 0.01) and Cos a (p < 0.05), whereas negative correlations were found between the STP, sand and SBD (p < 0.01). STK had a significant correlation with silt, whereas negative correlations were found between the STK, sand and SBD. Ordinary Kriging interpolation showed that the distribution of SOC and STN had a high value in the northeast, northwest and southeast, and a low value in the central and southwest. STP was high in the northwest and southeast and low in the northeast and southwest. STK was high in the northwest and northeast and low in the central and southeast regions. This is helpful for the rational exploitation of land resources in ecological economy development in the Yili River Basin.

Visualising long distance sugar transport in fungi using infrared fluorescence scanning imaging

Mycelia of saprotrophic basidiomycetes can cover large areas in nature that are typified by their heterogeneous nutrient availability. This heterogeneity is overcome by long distance transport of nutrients within the hyphal network to sites where they are needed. It is therefore key to be able to study nutrient transport and its underlying mechanisms. An IRDye-conjugate was used for the first time for imaging transport in fungi. A method was set up for time-lapse, high spatial resolution infrared imaging of IRDye-labelled deoxyglucose (IRDye-DG) in Schizophyllum commune and Agaricus bisporus. Scanning imaging visualised the tracer in individual hyphae as well as deeper tissues in mushrooms (mm-cm depth). The advantage of using fluorescence scanning imaging of IRDye in contrast to radiolabelled tracers studies, is that a higher spatial resolution and higher sensitivity (244 fg/ml) can be obtained. Moreover, it has a large field of view (25 × 25 cm) compared to microscopy (µm-mm range), allowing relatively fast and detailed imaging of large dimension samples.

Accumulation in nutrient acquisition strategies of arbuscular mycorrhizal fungi and plant roots in poor and heterogeneous soils of karst shrub ecosystems

BackgroundArbuscular mycorrhizal (AM) fungi and roots play important roles in plant nutrient acquisition, especially in nutrient poor and heterogeneous soils. However, whether an accumulation strategy of AM fungi and root exists in such soils of karst shrubland ecosystems remains unclear. Root traits related to nutrient acquisition (root biomass, AM colonisation, root acid phosphatase activity and N2 fixation) were measured in two N2-fixing plants (i.e. Albizia odoratissima (Linn. f.) Benth. and Cajanus cajan (Linn.) Millsp.) that were grown in heterogeneous or homogeneous nutrient (ammonium) soil with and without AM fungi inoculation.ResultsBoth of these plants had higher AM colonisation, root biomass and relative growth rate (RGR), but lower N2 fixation and root acid phosphatase activity in the rhizosphere in the heterogeneous soil environment, than that in the homogeneous soil environment. Plants grown in the AM fungi-inoculated heterogeneous soil environment had increased root biomass and root acid phosphatase activity compared with those grown in soil without inoculation. AM colonisation was negatively correlated with the N2 fixation rate of A. odoratissima, while it was not significantly correlated with the root phosphatase activity.ConclusionsOur results indicated that enhanced AM symbiosis and root biomass increased the absorptive surfaces for nutrient acquisition, highlighting the accumulation strategies of AM and root traits for plant nutrient acquisition in nutrient poor and heterogeneous soils of the karst shrubland ecosystem.

Differentiated impacts of the feeding-habits of three ant species on carbon mineralization in tropical forest soils

Ants affect carbon mineralization probably through their modifications on spatiotemporal heterogeneity in soil nutrients. However, it is still unclear whether the impacts of belowground-nesting ants on carbon mineralization varied with species. For this study, three belowground-nesting ants (i.e., honeydew harvester Pheidole capellini, predatory Odontoponera transversa, and saprophagous Pheidologeton affinis) were considered to identify the effects on soil carbon mineralization in the tropical Xishuangbanna (Yunnan, southern China). P. capellini had the greatest carbon mineralization (1.9 times) in the nest soils compared with control soils, followed by O. transversa (1.5 times) and P. affinis (1.3 times). Ants had different modifications on the changes of carbon mineralization as well as soil nutrient availability. The highest increased levels (24.7–298.5%) of carbon and nitrogen pools were observed in P. capellini nests compared with control soils. Soil carbon and nitrogen pools together affected soil carbon mineralization dynamics. Total organic carbon, microbial biomass carbon, and readily oxidizable carbon were the key factors regulating soil organic carbon mineralization, followed by total, ammonium and dissolved nitrogen. Our results suggested that carbon mineralization differed among ant species, which was tightly linked with the effects of different feeding guilds on nutrient availability in tropical forest soils.

Optimal foraging strategies in varying nutrient heterogeneity: responses of a stoloniferous clonal plant to patch pattern, size and quality

ABSTRACT Contrast and aggregation are two components of spatial heterogeneity. To precisely determine the influence of varying nutrient heterogeneity on the foraging behavior of clonal plants, we selected Potentilla anserina L. as the material and designed different patch patterns, sizes and qualities. In Experiment 1, compared with random and uniform patch patterns, aggregation increased ramet density and biomass accumulation at the patch scale, but not at the plot scale. This implies that the adaptive responses of clonal plants to nutrient heterogeneity depend on spatial scale. We further designed three levels of patch size with the same fertilizer concentration at the patch scale in Experiment 2, and four levels of patch quality with the same total amount of fertilizer at the plot scale in Experiment 3. Increased ramet density and stolon growth rate within small patches in Experiment 2 demonstrated effects of heterogeneity on plant foraging responses at the patch scale, while no difference was found in Experiment 3. This means that the influence of patch size on ramet establishment and residence time was alleviated by patch contrast at larger spatial scales. Hence, spatial scale is a key factor determining the interactions between heterogeneous ecosystem components.

Responses of soil nutrient contents and eco-stoichiometric characteristics to fiddler crab activities in coastal wetland of the yellow river delta

The four typical wetlands of Phragmites australis wetland (TPa), Tamarix chinensis wetland (Tc), Suaeda salsa wetland (Ss) and Spartina alterniflora wetland (Sa) in the Yellow River Delta were selected to clarify the spatial heterogeneity of soil nutrients and their ecological stoichiometric characteristics under fiddler crab activities. The results showed that soil particle size, soil salinity and pH in Tc, TPa and Ss were greatly changed by fiddler crab activities. The averaged contents of TOC and TN in wetlands with fiddler crab activities (FC) were higher than those in wetlands without fiddler crab activities (CK). The averaged NH4+-N contents of FC group in Tc, Ss and Sa were 93.42%, 52.14% and 20.05% higher than those of CK group (p<0.05), respectively. The averaged NO3−-N contents of Tc and Sa in FC group were 89.79% and 167.70% higher than those of CK group (p<0.01), respectively. The variation tendency of C/N and C/P in four wetland types were greatly similar with the TOC, and N/P was similar with TN. Multi-ANOVA results showed that soil carbon and nitrogen were significantly influenced by fiddler crab activities and wetland types (p<0.05). The PCA and RDA analysis results indicated that the bioturbation from fiddler crab made the influencing factors of nutrient elements diversified. The fiddler crab activities were favorable to the soil nutrients accumulation and could reduce the nitrogen limitation of coastal ecosystem. Our results should be of importance to insight the biogeochemical process of soil nutrient elements differentiation by fiddler crab activities in coastal wetlands.

Spatial heterogeneity of soil nutrients in black soil areas of Northeast China

AbstractExploring the distribution and evolution of soil nutrients, it is needed to maintain quality of land and ensure food production. Based on geostatistical theory, 1,054 soil sites were selected from the surface (0–20 cm) of the typical black soil area in Northeast China. The spatial structure of soil pH, alkali‐hydrolyzed N, effective P, and available K was investigated using Kriging and spatial statistics. The soils in the study area are acidic, alkali‐hydrolyzed N, effective P, and available K content at moderate to high levels. Coefficients of variation for various nutrients ranged from 5 to 80%, all showing moderate variation. The pH, alkali‐hydrolyzed N, effective P, and available K increased from South to North, the value of soil nutrients near the city were high. The results provide reference values for future work targeted at improving food security and reducing the effect on the environment.

Episodic shifts of phytoplankton community and biomass during a restricted summer coastal upwelling event off the Southeast China

Upwelling supports a diversity of organisms in marine ecosystems. Wind-driven upwelling occurs off the southeast China during summertime. Interannual variability in the intensity, extent and central location of this upwelling presented, resulting in spatial heterogeneity in surrounding environment. A restricted coastal upwelling event visible in satellite contours and concave isolines of temperature, phosphate and silicic acid was observed across a geographical area with weak intensity, accompanied by spatial heterogeneity of nutrients in June 2009. Peaks in depth-averaged chlorophyll a (Chl a, 0.62 and 0.83 mg/m3) and phytoplankton abundance (10.51 and 9.23 × 103 cells/L) in two patches near the upwelling center were consistently exhibited, with maxima at 10 m and 30 m, respectively. A total of 122 species from 41 genera of diatoms and 33 species in 14 genera of dinoflagellates were identified by the Utermöhl method, as well as 4 species in Cyanobacteria and Chrysophyta. Rhizosolenia alata was the most dominant species, followed by Thalassionema nitzschioides, Pseudonitzschia pungens, R. alata f. gracillima, T. frauenfeldii and Paralia sulcata. The restricted upwelling caused an upward transport of deep-water associated flora including Heterodinium blackmanii, Pyrocystis pseudonoctiluca, Ceratium gravidum and C. incisum to the surface, and the dispersal of dominant species across the surveyed area. Cluster analysis was performed across three phytoplankton assemblages in relation to upwelling intensity and continental influence. Redundancy and Spearman correlation analyses revealed that phytoplankton variability was mainly associated with phosphate. Furthermore, transect profiles of Chl a and phytoplankton abundance confirmed the origination of summer upwelling was the transportation of deep cold water in South China Sea to the surface layer along the coastline. These results indicate that the spatial variability of the phytoplankton community and biomass were highly controlled by the changes in upwelling location and intensity.

Community patch dynamics governs direct and indirect nutrient recycling by aggregated animals across spatial scales

AbstractAnimals can have pervasive effects on ecosystems as they modify their biogeochemical and physical environments. In particular, when animals occur in high densities these effects can result in dramatic changes in the physical environment and biogeochemical hotspots or hot moments. While most research to date has focused on the direct role of animals in biogeochemical cycles, few have examined how animals indirectly influence biogeochemical cycles across scales.Freshwater mussels occur as spatially heterogeneous, dense and species‐rich aggregations in many river ecosystems world‐wide. Here we examined how mussel communities (a) directly influence the flux of particulate and dissolved nutrients and (b) indirectly effect the flux of N2production, via denitrification, across a gradient of mussel biomass and differences in community composition at the patch‐ (0.25 m2) and stream reach‐scales (60–80 m).We combined measurements of ammonia (N) and soluble reactive phosphorous (P) excretion and C, N and P biodeposition rates for 10 species with biomass and distribution estimates for seven mixed‐species aggregations to quantify direct mussel contributions to biogeochemical cycling and the spatial heterogeneity of their impact. Additionally, we sampled sediments at a fine spatial scale to determine how mussel biomass and richness influence potential denitrification (indirect flux) rates at the patch‐ and reach‐scales.We predicted that increasing mussel biomass would lead to greater direct and indirect fluxes of nutrients, manifesting in heterogeneous nutrient redistribution within and among stream reaches. We also predicted that variation in community composition would result in differential nutrient excretion and egestion stoichiometries.Our results indicate that mussel aggregations directly influence soluble and particulate nutrient fluxes with community composition, particularly phylogenetic tribe composition, controlling the stoichiometry. Mussel aggregations also indirectly influenced nutrient fluxes as greater mussel biomass and species richness resulted in higher denitrification rates as mediated by their interactions with the sediments and enhancement of nutrient availability. Our results underscore the importance of patchy communities in acting as biogeochemical control points.A freePlain Language Summarycan be found within the Supporting Information of this article.

Effects of ungulate density and sociality on landscape heterogeneity: a mechanistic modeling approach

Animals can be important vectors of nutrient transfer within and across landscapes, with important implications for ecosystem productivity and composition. While it is presumed large ungulates are agents of nutrient dispersal via movement and activity, research analyzing their net effects on landscapes remains scarce. We present an individual‐based model that investigates how caribou affect the distribution of nutrients on a landscape through consumption only, as well through the cumulative effects of consumption and nutrient deposition (i.e. fecal waste and carcass deposition). We explored these dynamics in simulations that altered the context of environments, either initially containing heterogeneous or homogeneous nutrient distributions, animal densities and sociality of caribou behavior. In the consumption‐only simulations, caribou density and sociality created different patterns of heterogeneity at both the landscape and local scale depending on the initial landscape conditions. In these simulations, caribou populations crashed at high densities because the lack of animal deposition resulted in low resources across the landscape. This was not the case when considering the cumulative effects of consumption and deposition, indicating the return of nutrients from animals may be important for population stability. Additionally, in simulations considering the cumulative effects of caribou, increasing caribou density increased landscape heterogeneity irrespective of the initial condition (i.e. heterogeneous and homogeneous landscapes), and maintained or increased local heterogeneity in heterogeneous and homogenous landscape, respectively. Importantly, in all simulations the net impact of caribou at the individual patch level was extremely variable, suggesting that animal inputs are highly varied throughout the landscape. Our results indicate the movement of large ungulates such as caribou can increase the heterogeneity of available nutrients within a landscape and provide an important feedback for population stability. Thus, the loss of large ungulates from natural ecosystems via anthropogenic activity is likely to result in less heterogeneous natural landscapes.

Dual nutrient heterogeneity modes in a continuous flow photobioreactor for optimum nitrogen assimilation to produce microalgal biodiesel

The impact of different nitrogen sources on the microalga, Chlorella vulgaris, was studied in a newly developed microalgal-bacterial photobioreactor via a dual nutrient heterogeneity mode. The mechanisms of nitrogen transformation and valorisation were unveiled, and subsequently, optimized via dual nutrient heterogeneity feeding modes comprising of various NH4+-N and NO3−-N concentrations. The nitrogen-assimilation mechanism from the microalgal-bacterial consortium was found to reduce microalgal growth inhibition, stemming at high NH4+-N concentrations. Accordingly, the total nitrogen removal efficiency was enhanced from 40.91% to 96.38% accompanied with maximum microalgal biomass production of up to 792 mg/L at a balanced or higher NH4+-N loading from mixed nitrogen environment. The harvested microalgal biomass contained high lipid accumulation of approximately 30% when fed with optimum NH4+-N and NO3−-N loadings at 60 and 58 mg/d, respectively. At this mixed nitrogen species loadings, high unsaturated fatty acid methyl esters (FAME) were attained. Indeed, the major FAME species (97%–100%) fell within the C16-18 range, signifying biodiesel characteristics conformity to the requirements for quality biodiesel application. Therefore, the dual heterogeneity modes of balanced NH4+-N and NO3−-N loadings into photobioreactor could offer effective microalgal nitrogen assimilation for sustainable wastewater treatment and microalgae-based biodiesel production simultaneously.

The Response of Plants and Mycorrhizal Fungi to Nutritionally-Heterogeneous Environments Are Regulated by Nutrient Types and Plant Functional Groups.

Nutrient type and plant functional group are both important in influencing proliferation of roots or hyphae and their benefit to plant growth in nutritionally heterogeneous environments. However, the studies quantifying relative importance of roots vs. hyphae affecting the plant response to nutrient heterogeneity are lacking. Here, we used meta-analysis based on 879 observations from 66 published studies to evaluate response patterns of seven variables related to growth and morphological traits of plants and mycorrhizal fungi in nutritionally heterogeneous environments. We found that phosphorus [P] and organic fertilizer [OF] supply significantly increased shoot (+18.1 and +25.9%, respectively) and root biomass (+31.1 and +23.0%, respectively) and root foraging precision (+11.8 and +20.4%, respectively). However, there was no significant difference among functional groups of herbs (grasses, forbs, and legumes), between herbs and woody species, and between arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) tree species in the shoot, root and mycorrhizal fungi responses to nutrient heterogeneity, except for root biomass and root foraging precision among grasses, forbs, and legumes, and mycorrhizal hyphal foraging precision between AM and ECM tree species. Root diameter was uncorrelated with neither root foraging precision nor mycorrhizal hyphal foraging precision, regardless of mycorrhizal type or nutrient type. These results suggest that plant growth and foraging strategies are mainly influenced by nutrient type, among other factors including plant functional type and mycorrhizal type.

An examination of maximum legal application rates of dairy processing and associated STRUBIAS fertilising products in agriculture

The dairy industry produces vast quantities of dairy processing sludge (DPS), which can be processed further to develop second generation products such as struvite, biochars and ashes (collectively known as STRUBIAS). These bio-based fertilizers have heterogeneous nutrient and metal contents, resulting in a range of possible application rates. To avoid nutrient losses to water or bioaccumulation of metals in soil or crops, it is important that rates applied to land are safe and adhere to the maximum legal application rates similar to inorganic fertilizers. This study collected and analysed nutrient and metal content of all major DPS (n = 84) and DPS-derived STRUBIAS products (n = 10), and created an application calculator in MS Excel™ to provide guidance on maximum legal application rates for ryegrass and spring wheat across plant available phosphorus (P) deficient soil to P-excess soil. The sample analysis showed that raw DPS and DPS-derived STRUBIAS have high P contents ranging from 10.1 to 122 g kg−1. Nitrogen (N) in DPS was high, whereas N concentrations decreased in thermo-chemical STRUBIAS products (chars and ash) due to the high temperatures used in their formation. The heavy metal content of DPS and DPS-derived STRUBIAS was significantly lower than the EU imposed limits. Using the calculator, application rates of DPS and DPS-derived STRUBIAS materials (dry weight) ranged from 0 to 4.0 tonnes ha−1 y−1 for ryegrass and 0–4.5 tonnes ha−1 y−1 for spring wheat. The estimated heavy metal ingestion to soil annually by the application of the DPS and DPS-derived STRUBIAS products was lower than the EU guideline on soil metal accumulation. The calculator is adaptable for any bio-based fertilizer, soil and crop type, and future work should continue to characterise and incorporate new DPS and DPS-derived STRUBIAS products into the database presented in this paper. In addition, safe application rates pertaining to other regulated pollutants or emerging contaminants that may be identified in these products should be included. The fertilizer replacement value of these products, taken from long-term field studies, should be factored into application rates.

Divergent Patterns and Spatial Heterogeneity of Soil Nutrients in a Complex and Dynamic Savanna Landscape

AbstractMany grassy ecosystems around the world are experiencing woody encroachment. These woody encroachers often cause nutrient enrichment in the plant‐soil environment, potentially facilitating their growth and reproduction. However, studies of encroachment effects on nutrient distributions have been confined to a few major elements (e.g.,N, and P) and limited in spatial extent. We analyzed 19 elements in dominant plants and in georeferenced soils across a subtropical savanna landscape experiencing woody encroachment to quantify their spatial patterns and elucidate drivers responsible for these patterns. We found divergent patterns of spatial heterogeneity of these elements in surface soils across this complex landscape. Nutrient accumulation and redistribution underneath woody canopies occurred in a subset of elements (i.e., N, P, S, Ca, Cu, and Sr). Though some of these elements are not necessarily growth‐limiting, they do occur in higher concentrations in woody compared to herbaceous plants. Distributions of the other elements were closely related to spatial variation in soil pH, clay content, and slope rather than to woody encroachment. Our nuanced spatial sampling approach and analysis reveal significant variation in nutrient distributions in response to woody encroachment, and illustrate the role of landscape patterns in mediating ecosystem processes. These changes in the concentrations and distributions of key essential nutrients broaden our understanding of the biogeochemical consequences of woody encroachment, and provide new insights regarding the significance of long‐term vegetation dynamics in dryland ecosystems.

Biogeochemical and Hydrological Drivers of Heterogeneous Nutrient Exports From Subterranean Estuaries

Submarine groundwater discharge (SGD) to coastal zones contributes terrestrial freshwater and nutrients that may support harmful algal blooms (HABs). The magnitude of nutrient exports via SGD depends on volumes of fresh groundwater discharge, its chemical composition, and modifications by biogeochemical processing within subterranean estuaries. Thus, the ability to upscale SGD exports requires knowing the range of chemical composition of inland groundwater and how those compositions may be transformed as fresh and saltwater mix within subterranean estuaries. These processes may create heterogeneous magnitudes of solute exports, even at small spatial scales, and such heterogeneities have rarely been assessed for regional or global SGD nutrient export estimates. To evaluate heterogeneity in subterranean estuary processes and nutrient export, we collected seasonal pore water samples in 2015–2016 at three proximal (&amp;lt;20 km) subterranean estuary sites in Indian River Lagoon, FL. Sites have homogenous hydrogeological settings, but differ in land use and coastal features, and include a mangrove site, an urban site, and a site offshore of a natural wetland. All sites exhibit little variation through time in nutrient concentrations and modeled SGD rates. In contrast, each site exhibits significantly different nutrient concentrations of potential fresh groundwater sources, fresh groundwater discharge volumes, and nutrient transformations within subterranean estuaries. Groundwater specific discharge correlates with nutrient concentrations, suggesting that higher residence times in the subterranean estuary increase biogeochemical transformations that reduce anthropogenic nutrient loads but increase in situ nutrient sources derived from organic matter remineralization. The differences in transformations lead to SGD nutrient contributions that differ by orders of magnitude between sites and have N:P ratios that are greater than the Redfield ratio (15) for the mangrove (29) and urban sites (28), but less than the Redfield ratio for the wetland site (8). These results indicate that heterogeneity of both absolute and relative nutrient export via SGD complicates integration of nutrient fluxes across regional coastal zones and evaluations of its impacts to coastal ecosystems. A better understanding of the drivers of heterogeneity, including subterranean estuary processes, land use, coastal topography, and vegetation dynamics could improve assessments of regional nutrient loading and upscaling for estimates of global solute cycles.

Regulation of Eukaryote Metabolism: An Abstract Model Explaining the Warburg/Crabtree Effect

Adaptation of metabolism is a response of many eukaryotic cells to nutrient heterogeneity in the cell microenvironment. One of these adaptations is the shift from respiratory to fermentative metabolism, also called the Warburg/Crabtree effect. It is a response to a very high nutrient increase in the cell microenvironment, even in the presence of oxygen. Understanding whether this metabolic transition can result from basic regulation signals between components of the central carbon metabolism are the the core question of this work. We use an extension of the René Thomas modeling framework for representing the regulations between the main catabolic and anabolic pathways of eukaryotic cells, and formal methods for confronting models with known biological properties in different microenvironments. The formal model of the regulation of eukaryote metabolism defined and validated here reveals the conditions under which this metabolic phenotype switch occurs. It clearly proves that currently known regulating signals within the main components of central carbon metabolism can be sufficient to bring out the Warburg/Crabtree effect. Moreover, this model offers a general perspective of the regulation of the central carbon metabolism that can be used to study other biological questions.