Explore the vast range of titles available.

1. Territorial or resting behaviour of large herbivores can cause strong local deposits of dung, in different places than where they graze. Additionally, dung beetles and other macrodetritivores can subsequently affect local nutrient budgets through post-depositional re-dispersion of dung and accompanying nutrients. Such horizontal displacement of nutrients by animals has strong implications for savanna ecosystem functioning, but remains poorly studied as it is notoriously difficult to accurately map these flows and incredibly time-consuming. 2. In an African savanna, with alternating patches of lawn, bunch grasses and trees/shrubs, we undertook such effort and studied nutrient aggregation and redistribution by different large herbivore functional groups and dung beetles for a full growing season. We used movable cages to quantify herbivore consumption rates and measured nutrient return through biweekly dung counts. Furthermore, we estimated the offtake of nitrogen (N) and phosphorus (P) by the dominant megagrazer (white rhinoceros) to middens (dung deposition hotspots). Last, we experimentally measured the removal amount and movement paths of telocoprid dung beetles to quantify their nutrient redistribution effects. 3. Our estimates suggest white rhinoceros to cause a large export of nutrients from grazing areas towards middens resulting in negative nutrient budgets for both lawn and bunch grassland types. Mesograzers (50-600 kg) realized a net nitrogen input towards high forage quality lawn vegetation at the expense of lower quality bunch grasslands. Browsers caused a net flow from trees/shrubs towards grassland patches. 4. Interestingly, while the magnitude of our estimated flows of N consumption and return by large herbivores were rather similar, the P returns were about half of what has been consumed. This is in agreement with ecological stoichiometry theory that predicts that large herbivores should recycle more N than P, due to their relatively high P demand. Furthermore, dung-rolling beetles had a small, but significant, directed movement from lawn to bunch grassland vegetation. 5. Synthesis. We conclude that within-ecosystem nutrient redistributions by animals are important and approximately of the same order of magnitude as regional atmospheric nutrient in and outputs (e.g. fire emissions, atmospheric N deposition, biological N fixation), and hence are important for understanding savanna ecosystem functioning.

Animals play an important and sometimes overlooked role in nutrient cycling. The role of animals in nutrient cycling is spatially and temporally variable, but few studies have evaluated the long-term importance of animal-mediated nutrient cycling in meeting nutrient demand by primary producers. We quantified the proportion of phytoplankton nutrient (phosphorus, P) demand met by excretion by gizzard shad (Dorosoma cepedianum) in a eutrophic reservoir where this species dominates fish biomass. From 2000 to 2014, gizzard shad excretion supported a variable proportion of phytoplankton P demand, averaging 7–27% among years over the growing season (spring and summer). Temporal patterns emerged, as gizzard shad consistently supported a higher proportion of demand during summer (mean 31%) than spring (8%). In spring, the proportion of demand met from gizzard shad excretion was best predicted by gizzard shad population biomass, stream discharge, and temperature. In summer, this proportion was best predicted only by biomass of the young-of-year (YOY) gizzard shad. Thus, variation in YOY shad biomass significantly alters nutrient supply, and future studies should explore the long-term role of animal population dynamics in nutrient cycling. Our study shows that several years of data are needed to perform a critical evaluation of the importance of animals in meeting ecosystem nutrient demand.

Predators can alter nutrient cycles simply by inducing stress in prey. This stress accelerates prey’s protein catabolism, nitrogen waste production, and nitrogen cycling. Yet predators also reduce the feeding rates of their prey, inducing food deprivation that is expected to slow protein catabolism and nitrogen cycling. The physiology of prey under predation risk thus balances the influences of predation risk and food deprivation, and this balance is central to understanding the role of predators in nutrient cycles. We explored the separate and combined effects of predation risk and food deprivation on prey physiology and nutrient cycling by exposing guppies (Poecilia reticulata) to predation risk and food deprivation in a 2 × 2 design. We simulated predation risk using chemical cues from a natural predator of guppies, and we created food deprivation by rationing food availability. We measured guppy response as food consumption, growth, tissue energy density, tissue carbon:nitrogen, and nitrogen (N) excretion and assimilation. We found that N-linked physiological processes (N consumption, assimilation, excretion) were strongly affected by predation risk, independent of food consumption. Guppies excreted substantially less under predation risk than they did under food deprivation or control conditions. These results suggest that predation risk, per se, triggers physiological changes in guppies that increase N retention and decrease N excretion. We suggest that slower N metabolism under predation risk is an adaptive response that minimizes protein loss in the face of predictable, predator-induced food restriction. Notably, N metabolism shares common hormonal control with food seeking behavior, and we speculate that increased N retention is a direct and immediate result of reduced food seeking under predation risk. Contrary to predation-stress-based hypotheses for how predators affect nutrient cycling by prey, our result indicates that even short-term exposure to predators may decelerate, rather than accelerate, the speed of N cycling by suppressing N turnover by prey.

Phosphorus (P) limits plant productivity in high-elevation ecosystems, yet the microbial networks that mobilize P, including arbuscular mycorrhizal (AM) fungi and phosphorus-cycling bacteria (PCBs), remain under-characterized in these nutrient-poor soils. We show that across a 10,00-m elevation gradient, AM fungi and P-cycling gene assemblages shift predictably with pH, organic carbon, and phosphate availability. Higher elevations, with less available P, select for stress-tolerant AM fungal taxa and PCB strategies geared toward mineral solubilization, while low-elevation sites favor root colonization by AM fungi and organic P mineralization. These results suggest that nutrient limitation can constrain microbial community assembly in consistent ways across landscapes. High mountain soils are low in P and rely on a network of underground AM fungi and PCB to deliver nutrients to plants. This study shows how those underground relationships reorganize with elevation and how climate change could collapse long-standing microbial strategies by pushing high-elevation ecosystems toward lowland conditions. As soils warm and dry, the microbial scaffolding that supports alpine plant life may become increasingly unstable.

PurposeLithic soils (with lithic contact up to 50 cm deep) are common in global drylands. Historically, have been little studied over time and the natural and anthropogenic factors that affect the storage of carbon (C) and nitrogen (N) in this soil group are little known.MethodsWe used 118 lithic soil profiles to understand how climate (semi-arid and dry sub-humid), lithology, relief, and land-use (agriculture, pasture, secondary forest, and native forest) affect soil C and N stocks in drylands, northeastern Brazil.ResultsClimate did not affect C and N stocks in lithic soils. However, soils with sedimentary lithology showed, on average, 17.4 and 27.1% less C and 20.5 and 38.2% less N than soils under metamorphic and igneous lithology, respectively. Soils under wavy relief presented the highest C (30.5 ± 16.9 Mg ha−1) and N (2.7 ± 1.2 Mg ha−1) stocks, while those under flat relief presented the lowest values (19.6 ± 16.3 Mg C ha−1 and 2.1 ± 1.5 Mg N ha−1), because of more significant anthropic use in profiles under flat relief. In general, soils under pasture and agriculture showed, on average, 73.6% and 65.8% less C than soils under native forest and the natural recovery of C and N stocks in soils (areas under natural regeneration) was limited, because of lithic contact close to the surface.ConclusionWe concluded that lithology, relief, and land use were the main factors affecting the accumulation of C and N in lithic soils, northeastern Brazil. Our results may be useful for sustainable use of lithic soils in drylands according to their aptitude and support capacity.

This paper reports on patterns in plant-mediated processes that determine the rate of nutrient cycling in temperate fens and bogs. We linked leaf-level nutrient dynamics with leaf-litter decomposition and explored how the observed patterns were reflected in nutrient cycling at the ecosystem level. Comparisons were made among growth forms (evergreen and deciduous shrubs and trees, graminoids and Sphagnum mosses) and between mire types (fens and bogs). A literature review showed that the predominant growth form was more important as a determinant of leaf-level nutrient-use efficiency (NUE) than mire type (fen vs. bog). Evergreens had the highest N and P use efficiency. The growth form differences in NUE were mainly determined by differences in N and P concentrations in mature leaves and not by differences in resorption efficiency from senescing leaves. Sphagnum leaves had lower N and P concentrations than the other growth forms, but because of a lack of data on nutrient resorption efficiency the NUE of these mosses could not be calculated. Nitrogen use efficiency did not differ among fen and bog species, whereas bog species had a higher P use efficiency than fen species. However, a complete evaluation of mire-type or growth-form effects on NUE is only possible when data become available about nutrient resorption from senescing Sphagnum leaves. As leaf-level NUE is negatively correlated with leaf-litter nutrient concentrations, there is a direct link between NUE and litter decomposition rate. Rates of litter decomposition of Sphagnum mosses are lower than in the other growth forms, but there is still much speculation about possible reasons. The role of litter chemistry of Sphagnum mosses (including decay inhibitors and decay-resistant compounds) in decomposition especially warrants further study. The strongly deviating nutritional ecology of Sphagnum mosses clearly distinguishes fens and bogs from other ecosystems. Moreover, N and P concentrations in mature leaves from vascular plant species from fens and bogs are in almost all cases lower and leaf-level N use efficiency is higher than in species from other ecosystems, irrespective of the growth form considered. Both literature data and data from a comparative study on soil nutrient cycling in temperate fens and bogs in the United States (Maryland), The Netherlands, and Poland showed that nutrient mineralization did not differ clearly between fens and bogs. The comparative study further showed that cellulose decomposition in bogs was lower than in fens and that nutrient mineralization was higher in forested than in herbaceous mires. The occurrence of dominant growth forms was clearly related to soil nutrient-cycling processes, and observed patterns were in agreement with patterns in the components of NUE as found in the literature study. We conclude that a protocol with standardized procedures for measuring various nutrient-cycling process rates that is used by scientists in various wetland types and geographical regions is a useful tool for unravelling large-scale patterns in soil nutrient-cycling processes in wetlands and for linking plant-mediated nutrient dynamics with ecosystem nutrient-cycling processes.

Within‐stand nutrient cycling is dependent on many factors, including primary productivity, nutrient‐use efficiency, nutrient resorption, sclerophylly, decomposition, nutritional quality of plant tissue, and allocation to defense. The efficiency of these plant‐mediated processes depends on nutrient availability in the environment and inherent functional properties of plants. However, little is known about how nutrient availability will affect these processes in forested wetlands in the tropics. In a factorial experiment we fertilized 48 dwarfed Rhizophora mangle (red mangrove) trees along tidal‐elevation and water‐depth gradients at Twin Cays, a range of intertidal, peat‐based offshore mangrove islands in Belize, Central America. Initial results indicated that phosphorus (P) deficiency is a major factor limiting primary productivity. Phosphorus‐fertilized trees had a significant decrease in P‐use efficiency and P‐resorption efficiency, but a significant increase in nitrogen (N)‐use efficiency and N‐resorption efficiency in their leaves compared with controls and N‐fertilized trees. Sclerophylly decreased dramatically in P‐fertilized trees, while the nutritional quality of the plant tissue increased. Phosphorus fertilization did not affect P leaching from green leaves. We found no fertilizer effect on the decomposition rates of leaf tissue, possibly due to higher phenolic concentrations in the P‐fertilized trees compared with controls and N‐fertilized trees. However, belowground decomposition of cotton strips increased in the substrate associated with P‐fertilized trees. Environmental conditions related to position along a tidal gradient may be as important as nutrients in controlling belowground decomposition.

PurposeThe landfill soil microbes related to nutrient cycling, such as carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) cycling, are changed by continuous waste decomposition. Monitoring the changes that occur in CNPS functional genes in different types of landfill cover soils as a whole is vital to our understanding of microbial function in element cycling.Materials and methodsThe high-throughput quantitative polymerase chain reaction–based chip (HT-Q-PCR) method was used to explore differences in the abundance of 71 CNPS functional genes in cover soils (0–20 cm, 20–40 cm, and 40–60 cm) from two types of landfills (sanitary and non-sanitary) and to examine the soil pH and the concentrations of C, N, P, S, and 6 heavy metals.Results and discussionThe absolute abundances of CNPS functional genes varied greatly, with the highest gene abundance reaching 5.28 × 109 copies per gram of soil, and 11% (8/71) of the genes not detected. Among the detected genes, there was a much higher functional gene abundance in the sanitary landfill than in the non-sanitary landfill cover soils, and the difference in gene abundance became more significant with increasing sampling depth. In addition to landfill type and sampling depth, the soil pH, soil dissolved organic carbon (DOC), available N (AN), and available S (AS) correlated significantly to functional gene abundance. Conversely, soil heavy metals, such as Cu, Cd, Cr, Zn, and Ni, had no effects on functional gene abundance, which might be due to their low contents.ConclusionsOur results suggest that sanitary landfill increases soil CNPS gene abundance compared to that of non-sanitary landfill. The findings provide suggestions for landfill treatment and ecological protection, especially regarding vegetation restoration.

• Understanding how plant species influence soil nutrient cycling is a major theme in terrestrial ecosystem ecology. However, the prevailing paradigm has mostly focused on litter decomposition, while rhizosphere effects on soil organic matter (SOM) decomposition have attracted little attention. • Using a dual 13C/15N labeling approach in a ‘common garden’ glasshouse experiment, we investigated how the economic strategies of 12 grassland plant species (graminoids, forbs and legumes) drive soil nitrogen (N) cycling via rhizosphere processes, and how this in turn affects plant N acquisition and growth. • Acquisitive species with higher photosynthesis, carbon rhizodeposition and N uptake than conservative species induced a stronger acceleration of soil N cycling through rhizosphere priming of SOM decomposition. This allowed them to take up larger amounts of N and allocate it above ground to promote photosynthesis, thereby sustaining their faster growth. The N₂-fixation ability of legumes enhanced rhizosphere priming by promoting photosynthesis and rhizodeposition. • Our study demonstrates that the economic strategies of plant species regulate a plant–soil carbon–nitrogen feedback operating through the rhizosphere. These findings provide novel mechanistic insights into how plant species with contrasting economic strategies sustain their nutrition and growth through regulating the cycling of nutrients by soil microbes in their rhizosphere.

Bivalve molluscs are abundant in marine and freshwater ecosystems and perform important ecological functions. Bivalves have epifaunal or infaunal lifestyles but are largely filter feeders that couple the water column and benthos. Bivalve ecology is a large field of study, but few comparisons among aquatic ecosystems or lifestyles have been conducted. Bivalves impact nutrient cycling, create and modify habitat, and affect food webs directly (i.e., prey) and indirectly (i.e., movement of nutrients and energy). Materials accumulated in soft tissue and shells are used as environmental monitors. Freshwater mussel and oyster aggregations in rivers and estuaries are hot spots for biodiversity and biogeochemical transformations. Historically, human use includes food, tools, currency, and ornamentation. Bivalves provide direct benefits to modern cultures as food, building materials, and jewelry and provide indirect benefits by stabilizing shorelines and mitigating nutrient pollution. Research on bivalve-mediated ecological processes is diverse, and future synthesis will require collaboration across conventional disciplinary boundaries.