Indicators Of Nutrient Availability Research Articles

Leaf habit drives leaf nutrient resorption globally alongside nutrient availability and climate

Abstract. Nutrient resorption from senescing leaves can significantly affect ecosystem nutrient cycling, making it an essential process to better understand long-term plant productivity under environmental change that affects the balance between nutrient availability and demand. Although it is known that nutrient resorption rates vary strongly between different species and across environmental gradients, the underlying driving factors are insufficiently quantified. Here, we present an analysis of globally distributed observations of leaf nutrient resorption to investigate the factors driving resorption efficiencies for nitrogen (NRE) and phosphorus (PRE). Our results show that leaf structure and habit, together with indicators of nutrient availability, are the two most important factors driving spatial variation in NRE. Overall, we find higher NRE in deciduous plants (65.2 % ± 12.4 %, n=400) than in evergreen plants (57.9 % ± 11.4 %, n=551), likely associated with a higher share of metabolic N in leaves of deciduous plants. Tropical regions show the lowest resorption for N (NRE: 52.4 % ± 12.1 %), and tundra ecosystems in polar regions show the highest (NRE: 69.6 % ± 12.8 %). At the same time, the PRE is lowest in temperate regions (57.8 % ± 13.6 %) and highest in boreal regions (67.3 % ± 13.6 %). Soil clay content, N and P atmospheric deposition (globally available proxies for soil fertility), and mean annual precipitation (MAP) play an important role in this pattern. The statistical relationships developed in this analysis indicate the important role of leaf habit and type for nutrient cycling and guide improved representations of plant-internal nutrient recycling and nutrient conservation strategies in vegetation models.

Towards comparable assessment of the soil nutrient status across scales-Review and development of nutrient metrics.

Nutrient availability influences virtually every aspect of an ecosystem, and is a critical modifier of ecosystem responses to global change. Although this crucial role of nutrient availability in regulating ecosystem structure and functioning has been widely acknowledged, nutrients are still often neglected in observational and experimental synthesis studies due to difficulties in comparing the nutrient status across sites. In the current study, we explain different nutrient-related concepts and discuss the potential of soil-, plant- and remote sensing-based metrics to compare the nutrient status across space. Based on our review and additional analyses on a dataset of European, managed temperate and boreal forests (ICP [International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests] Forests dataset), we conclude that the use of plant- and remote sensing-based metrics that rely on tissue stoichiometry is limited due to their strong dependence on species identity. The potential use of other plant-based metrics such as Ellenberg indicator values and plant-functional traits is also discussed. We conclude from our analyses and review that soil-based metrics have the highest potential for successful intersite comparison of the nutrient status. As an example, we used and adjusted a soil-based metric, previously developed for conifer forests across Sweden, against the same ICP Forests data. We suggest that this adjusted and further adaptable metric, which included the organic carbon concentration in the upper 20cm of the soil (including the organic fermentation-humus [FH] layer), the C:N ratio and of the FH layer, can be used as a complementary tool along with other indicators of nutrient availability, to compare the background nutrient status across temperate and boreal forests dominated by spruce, pine or beech. Future collection and provision of harmonized soil data from observational and experimental sites is crucial for further testing and adjusting the metric.

The role of mixing in controlling resource availability and phytoplankton community composition

We investigate the role of mixing, through its effect on nutrient and light availability, as a driver of phytoplankton community composition in the context of Margalef’s mandala. Data on microstructure turbulence, irradiance, new nitrogen supply and phytoplankton composition were collected at 102 stations in three contrasting marine environments: the Galician coastal upwelling system of the northwest Iberian Peninsula, the northwestern Mediterranean, and the tropical and subtropical Atlantic, Pacific and Indian oceans. Photosynthetic pigments concentration and microscopic analysis allowed us to investigate the contribution of diatoms, dinoflagellates, pico- and nanoeukaryotes, and cyanobacteria to the phytoplankton community. Simple linear regression was used to assess the role of environmental factors on community composition, and environmental overlap among different phytoplankton groups was computed using nonparametric kernel density functions. Mixing and new nitrogen supply played an important role in controlling the phytoplankton community structure. At lower values of mixing and new nitrogen supply cyanobacteria dominated, pico- and nanoeukaryotes were dominant across a wide range of environmental conditions, and finally enhanced new nitrogen supply was favourable for diatoms and dinoflagellates. Dinoflagellates were prevalent at intermediate mixing levels, whereas diatoms spread across a wider range of mixing conditions. Occasional instances of enhanced diatom biomass were found under low mixing, associated with the high abundance of Hemiaulus hauckii co-occurring with high N2 fixation in subtropical regions, and with the formation of thin layers in the Galician coastal upwelling. Our results verify the Margalef’s mandala for the whole phytoplankton community, emphasizing the need to consider nutrient supply, rather than nutrient concentration, as an indicator of nutrient availability.

Groundwater shapes sediment biogeochemistry and microbial diversity in a submerged Great Lake sinkhole.

For a large part of earth's history, cyanobacterial mats thrived in low-oxygen conditions, yet our understanding of their ecological functioning is limited. Extant cyanobacterial mats provide windows into the putative functioning of ancient ecosystems, and they continue to mediate biogeochemical transformations and nutrient transport across the sediment-water interface in modern ecosystems. The structure and function of benthic mats are shaped by biogeochemical processes in underlying sediments. A modern cyanobacterial mat system in a submerged sinkhole of Lake Huron (LH) provides a unique opportunity to explore such sediment-mat interactions. In the Middle Island Sinkhole (MIS), seeping groundwater establishes a low-oxygen, sulfidic environment in which a microbial mat dominated by Phormidium and Planktothrix that is capable of both anoxygenic and oxygenic photosynthesis, as well as chemosynthesis, thrives. We explored the coupled microbial community composition and biogeochemical functioning of organic-rich, sulfidic sediments underlying the surface mat. Microbial communities were diverse and vertically stratified to 12cm sediment depth. In contrast to previous studies, which used low-throughput or shotgun metagenomic approaches, our high-throughput 16S rRNA gene sequencing approach revealed extensive diversity. This diversity was present within microbial groups, including putative sulfate-reducing taxa of Deltaproteobacteria, some of which exhibited differential abundance patterns in the mats and with depth in the underlying sediments. The biological and geochemical conditions in the MIS were distinctly different from those in typical LH sediments of comparable depth. We found evidence for active cycling of sulfur, methane, and nutrients leading to high concentrations of sulfide, ammonium, and phosphorus in sediments underlying cyanobacterial mats. Indicators of nutrient availability were significantly related to MIS microbial community composition, while LH communities were also shaped by indicators of subsurface groundwater influence. These results show that interactions between the mats and sediments are crucial for sustaining this hot spot of biological diversity and biogeochemical cycling.

Satellite views of Pacific chlorophyll variability: Comparisons to physical variability, local versus nonlocal influences and links to climate indices

Concurrent satellite-measured chlorophyll (CHL), sea surface temperature (SST), sea level anomaly (SLA) and model-derived wind vectors from the 13+ year SeaWiFS period September 1997–December 2010 quantify time and space patterns of phytoplankton variability and its links to physical forcing in the Pacific Ocean. The CHL fields are a metric of biological variability, SST represents vertical mixing and motion, often an indicator of nutrient availability in the upper ocean, SLA is a proxy for pycnocline depths and surface currents while vector winds represent surface forcing by the atmosphere and vertical motions driven by Ekman pumping. Dominant modes of variability are determined using empirical orthogonal functions (EOFs) applied to a nested set of domains for comparison: over the whole basin, over the equatorial corridor, over individual hemispheres at extra-tropical latitudes (>20°) and over eastern boundary current (EBC) upwelling regions. Strong symmetry exists between hemispheres and the EBC regions, both in seasonal and non-seasonal variability. Seasonal variability is strongest at mid latitudes but non-seasonal variability, our primary focus, is strongest along the equatorial corridor. Non-seasonal basin-scale variability is highly correlated with equatorial signals and the strongest signal across all regions in the study period is associated with the 1997–1999 ENSO cycle. Results quantify the magnitude and geographic pattern with which dominant basin-scale signals are expressed in extra-tropical regions and the EBC upwelling areas, stronger in the Humboldt Current than in the California Current. In both EBC regions, wind forcing has weaker connections to non-seasonal CHL variability than SST and SLA, especially at mid and lower latitudes. Satellite-derived dominant physical and biological patterns over the basin and each sub-region are compared to indices that track aspects of climate variability in the Pacific (the MEI, PDO and NPGO). We map and compare the local CHL footprint associated with each index and those of local wind stress curl, showing the dominance in most areas of the MEI and its similarity to the PDO. Principal estimator patterns quantify the linkage between dominant modes of forcing variability (wind, SLA and SST) and CHL response, comparing local interactions within EBC regions with those imposed by equatorial signals and mapping equatorial forcing on extra-tropical CHL variability.

Relationship between ammonia oxidizing bacteria and bioavailable nitrogen in harvested forest soils of central Alberta

Forest soils are commonly limited in nitrogen (N), and the removal of aboveground biomass in harvesting operations can exacerbate the problem. Thus, the soil organisms that facilitate the rate-limiting step in the N cycle, the oxidation of ammonium (NH 4 +), are of special interest in harvested environments. The objective of this study was to investigate the changes in ammonia oxidizing bacteria (AOB) communities that occurred in the years following clear cutting, and link those community shifts to availability of inorganic N forms NH 4 + and nitrate (NO 3 −). Genetic fingerprinting targeting the amoA gene coupled with denaturing gel gradient electrophoresis was carried out over two summers on forest floor (LFH) and mineral (Ae) soils of three similar cutblocks harvested during different years. In- situ NH 4 + and NO 3 − availability was measured over the growing seasons of 2009 and 2010, as well as a suite of physical soil characteristics. Results indicated that the AOB community composition differed in younger vs. older cutblocks, but not by soil horizon. The changes seen in the AOB paralleled the change in N bioavailability across sites, soil horizons, and sampling years, thus indicating that N bioavailability may be directly linked to AOB community composition. This link may provide the basis for the use of AOB as indicators of nutrient availability in the future.

Modelling above-ground herbage mass for a wide range of grassland community types

Whereas it is recognized that management of plant diversity can be the key to reconciling production and environmental aims, most grassland models are tailored for high-value grass species. We proposed to adapt a mono-specific grass model to take into account specific features of species-rich permanent grasslands, especially over the reproductive phase. To this end, we used the concept of plant functional type (PFT), i.e. the grouping of plant species according to plant traits determined by the response of plant species to different management practices (land use and fertilization) and characterizing of agronomic properties of the corresponding species. In the model, weather and nutrient availability act upon rates of biophysical processes (radiation capture and use, plant senescence). These rates are modified over times due to PFT-specific parameters determined experimentally which represent the different strategies of plant species regarding growth. The integration of these parameters into the model made it possible to predict herbage biomass accumulation rate under different management practices for a wide range of plant communities differing in their PFT composition. The model was evaluated in two steps, first by analyzing separately the effects of PFT and an indicator of nutrient availability on herbage accumulation and then by conducting a sensitivity analysis. It was validated using two independent datasets; a cutting experiment running over the whole growing season to examine the consistency of the model outputs under different cutting regimes, and a monitoring of meadows and pastures in spring over a whole growth cycle to assess the model’s ability to reproduce growth curves. Although a good fit was observed between the simulated and observed data, the few discrepancies noticed between field data and predicted values were attributed mainly to the potential presence of non-grass species. More specifically, we noticed that nutrient (mainly nitrogen) availability is the main driver of plant growth rate, and that PFT determines the times at which this rate changes in relation to the phenological characteristics of species present. We concluded that integration of the PFT concept into the initial mono-specific growth model is especially suited to evaluating the consequences of management practices on species-rich permanent grasslands to meet feed production targets.

Potential for Using Plant Xylem Sap to Evaluate Inorganic Nutrient Availability in Soil

The “extraction method” that is commonly used to evaluate the availability of nutrients in soil often involves complex, problematic and simultaneous assays of multiple components and comparisons of analytical values. In a previous paper using pot experiments of plants, we confirmed the possibility of using nutrient concentrations in the xylem sap of Luffa cylindrica Roem. seedlings as an indicator of nutrient availability in soil and suggested that the “xylem sap method,” might represent a solution of the above-mentioned problems and inaccuracies characteristic of chemical extraction. To determine whether a method enables to evaluate available nutrient contents in soil, the criterion should probably be that the relationship between the values obtained by that method and the amounts of nutrients absorbed by plants does not vary depending on the types of soil. In this regard, we compared the conventional extraction method with our proposed xylem sap method. In the present paper, we attempted to change the cation exchange capacity (CEC) in soil by the addition of zeolite and/or humic acid to soil to change the nutrient availability without changing the total quantity of nutrients in soil in the pots. Our results showed that the amounts of nutrients absorbed by plants changed under these treatments. However, in some cases, changes in the amounts of phosphorus, calcium, magnesium, and zinc obtained via different extractants did not correspond to the changes in the amounts of nutrients absorbed by the plants. Thus, the amounts of nutrients absorbed by the plants were compared with nutrient concentrations in the xylem sap and the amounts of nutrients inferred by each extractant to examine their relationship. A highly positive correlation was consistently found between the amounts of nutrients absorbed by the plants and their concentrations in the xylem sap for every nutrient. By contrast, there was a lower correlation for the extraction method with some extractants. For phosphorus in particular, no close correlation was obtained between the amounts of nutrients absorbed by the plants and the amounts extracted, regardless of the extractants. In the present study, because we attempted to change the nutrient availability by artificially controlling the soil CEC value, without changing the total amount of nutrients present in the culture medium, the changes in nutrient availability were not conspicuous. Thus, it is possible that the extraction method itself generates large errors for such small changes. Therefore, we concluded that the xylem sap method is superior to the extraction method, as an indicator of nutrient availability in soil, at least under the conditions of the present experiment.

MODEL FOR OPTIMIZING FERTILIZATION OF SUGAR BEET, WHEAT, AND MAIZE GROWN ON PSEUDOGLEY SOILS

ABSTRACT The selected pseudogley soils from Eastern Croatia were analyzed by the electro-ultrafiltration (EUF) method and by the standard soil analyses. Functional dependency was established among parameters of plant nutrient availability. The experimental computer model for the determination of nitrogen, phosphorus and potassium fertilization rates for sugar beet, wheat and maize was developed. The major feature of this model is the application of mathematical functions to adjust crop nutrient demand using (i) the soil nutrient content determined by the EUF method, (ii) the nutrient interactions, and (iii) other factors determining soil fertility. A model was supplemented with the concept of the nutrient potential as a valuable indicator of nutrient availability. The model allows determining optimal fertilization for a range of crops quickly and precisely.

Using porewater profiles to assess nutrient availability in seagrass-vegetated carbonate sediments

We measured porewater profiles of inorganic (NH + ,N O − (+NO − ), PO 3− 4 (here- after referred to as DIP)) and organic (DON, DOP) nutrients in seagrass-vegetated sediments at two sites in a shallow bay in Bermuda within close proximity (200 m) but subject to different nutrient loading. At both sites, total dissolved and inorganic nutrient concentrations were usually 1-2 orders of magnitude higher in the sediments than in the water column, with the exception of NO − . Organic N and P were significant components of the total dissolved nutrient pools both in the sediment porewater and in the overlying water column (up to 75% for DON and 40% for DOP), and may be important in meeting plant nutrient demands. We used two approaches to examine how well porewater nutrient concentrations reflected the relative availabilities of N and P for seagrasses: (1) a simple stoichiometric nutrient regeneration model based on the N:P ratio of decomposing organic matter and porewater NH + concentrations to predict porewater DIP, and (2) fitting of the porewater profiles to estimate rates of net nutrient production (or consumption), which reflects the balance between nutrient sources and sinks in the rhizosphere. The stoichiometric model indicated that sediment porewaters were depleted in P relative to N in the low-nutrient outer bay site, and enriched in P relative to N in the higher- nutrient inner bay site. These results are consistent with the mechanism of carbonate sediments in oligotrophic tropical environments being a strong sink for dissolved inorganic P and our previous work suggesting that nutrient enrichment causes P to become disproportionately more available than N. Net nutrient production rates of porewater P at both sites and N at the inner bay site were low (typically < 2%) relative to the nutrient demands of the seagrasses. The implications of the profile interpretation are two-fold: (1) the low rates of net nutrient production indicate diffusive losses from the root zone were insignificant and that nutrient turnover rates were high, except in the P-limited outer bay where N accumulated in sediment porewaters; and (2) because standing stock nutrient concentrations often represent a small fraction of the total nutrients cycled in the sediments, they are in many cases a poor indicator of nutrient availability. Based on our estimates of losses from the root zone, decomposition, and plant uptake we have constructed a rough budget for the cycling of P and N at our two sites.

Seasonal dynamics of epiphytic algal growth in a marsh pond: composition, metabolism, and nutrient availability

Seasonal growth and succession of epiphytic algae on artificial substrates in a marsh pond were related to nutrient levels (N, P, and Si) and to various physiological indicators of nutrient availability, including chlorophyll content, protein to carbohydrate and lipid ratio, Si debt, storage phosphate levels, alkaline phosphatase activity, and nitrogenase activity. Low standing crops in June and early July coincided with indications of deficiency in terms of chlorophyll a content and protein to carbohydrate and lipid ratios at chosen Scirpus and Potamogeton sites. Low available N may have been limiting growth. In July and August, when available N, P, and Si were low, there was evidence of Si limitation of diatom growth at both sites. Growth of heterocystous, N2-fixing. blue-green algae and high alkaline phosphatase activity occurred in July at the Potanwgeton site. Increased standing crop of epiphytic algae in September and October at the Scirpus site coincided with higher nutrient levels and an absence of deficiency symptoms. A delay in the standing crop increase at the Potamogeton site correlated with low nutrient levels and various physiological deficiency symptoms.