Nutrient content of the seagrass Thalassia testudinum reveals regional patterns of relative availability of nitrogen and phosphorus in the Florida Keys USA

Between 1992 and 2000, we sampled 504 randomly chosen locations in theFlorida Keys, Florida, USA, for the elemental content of green leaves of theseagrass Thalassia testudinum. Carbon content ranged from29.4–43.3% (dry weight), nitrogen content from 0.88–3.96%, andphosphorus content from 0.048–0.243%. N and P content of the samples werenot correlated, suggesting that the relative availability of N and P variedacross the sampling region. Spatial pattern in C:N indicated a decrease in Navailability from inshore waters to the reef tract 10 km offshore;in contrast, the pattern in C:P indicated an increase in P availability frominshore waters to the reef tract. The spatial pattern in N:P was used to definea P-limited region of seagrass beds in Florida Bay and near shore, and anN-limited region of seagrass beds offshore. The close juxtaposition ofN–and P-limited regions allows the possibility that N loading from thesuburban Florida Keys could influence the offshore, N-limited seagrass bedswithout impacting the more nearshore, P-limited seagrass beds. Carbonate - Nutrient lim

Responses of seagrass communities to fertilization along a gradient of relative availability of nitrogen and phosphorus in a carbonate environment

Patterns of relative nutrient availability in south Florida suggest spatial differences regarding the importance of nitrogen (N) and phosphorus (P) to benthic primary producers. We did a 14-month in situ fertilization experiment to test predictions of N and P limitation in the subtropical nearshore marine waters of the upper Florida Keys. Six sites were divided into two groups (nearshore, offshore) representing the endpoints of an N: P stoichiometric gradient. Twenty-four plots were established at each site with six replicates of each treatment (1N, 1P, 1N1P, control), for a total of 144 experimental plots. The responses of benthic communities to N and P enrichment varied appreciably between nearshore and offshore habitats. Offshore seagrass beds were strongly limited by nitrogen, and nearshore beds were affected by nitrogen and phosphorus. Nutrient addition at offshore sites increased the length and aboveground standing crop of the two seagrasses, Thalassia testudinum and Syringodium filiforme, and growth rates of T. testudinum. Nutrient addition at nearshore sites increased the relative abundance of macroalgae, epiphytes, and sediment microalgae. N limitation of seagrass in this carbonate system was clearly demonstrated. However, added phosphorus was retained in the system more effectively than N, suggesting that phosphorus might have important long-term effects on these benthic communities. The observed species-specific responses to nutrient enrichment underscores the need to monitor all primary producers when addressing questions of nutrient limitation and eutrophication in seagrass communities.

Half-degree gridded nitrogen and phosphorus fertilizer use for global agriculture production during 1900-2013

In addition to enhance agricultural productivity, synthetic nitrogen (N) and phosphorous (P) fertilizer application in croplands dramatically altered global nutrient budget, water quality, greenhouse gas balance, and their feedbacks to the climate system. However, due to the lack of geospatial fertilizer input data, current Earth system/land surface modeling studies have to ignore or use over-simplified data (e.g., static, spatially uniform fertilizer use) to characterize agricultural N and P input over decadal or century-long period. We therefore develop a global time-series gridded data of annual synthetic N and P fertilizer use rate in croplands, matched with HYDE 3,2 historical land use maps, at a resolution of 0.5º latitude by longitude during 1900-2013. Our data indicate N and P fertilizer use rates increased by approximately 8 times and 3 times, respectively, since the year 1961, when IFA (International Fertilizer Industry Association) and FAO (Food and Agricultural Organization) survey of country-level fertilizer input were available. Considering cropland expansion, increase of total fertilizer consumption amount is even larger. Hotspots of agricultural N fertilizer use shifted from the U.S. and Western Europe in the 1960s to East Asia in the early 21st century. P fertilizer input show the similar pattern with additional hotspot in Brazil. We find a global increase of fertilizer N/P ratio by 0.8 g N/g P per decade (p< 0.05) during 1961-2013, which may have important global implication of human impacts on agroecosystem functions in the long run. Our data can serve as one of critical input drivers for regional and global assessment on agricultural productivity, crop yield, agriculture-derived greenhouse gas balance, global nutrient budget, land-to-aquatic nutrient loss, and ecosystem feedback to the climate system.

The effect of a reduction of nitrogen and phosphorus to eutrophic and mesotrophic conditions towards silver nanoparticle (AgNP) on freshwater green algae species

We investigated the sensitivity of algae towards silver nanoparticles with OECD test medium and lower nutrient concentrations under standard test conditions to improve comparability and to exclude any other confounding factor aside nutrient levels. Two unicellular freshwater microalgae Desmodesmus subspicatus and Raphidocelis subcapitata were chosen due to their status as standard test organisms for the algae growth inhibition test and the response to changes in nutrient supply was compared. The original medium was used as the reference (standard). For the other four media, the amount of either nitrogen or phosphorus in the medium was lowered from half (50%) to one-fourth (25 %) of that of the OECD guideline, resulting in the following media: 50% N, 25% N, 50% P and 25% P medium. As test substance, the OECD reference material NM-300K was used. For this reason, the characterization of AgNP was done using DLS and Absorption spectra (UV/vis). Actual silver concentrations and ionic silver concentrations were measured at the highest test concentration used (100 µg Ag L-1) in R. subcapitata treatments only to reduce the number of samples. All tests were run according to the OECD guideline 201 with sterilized 50 mL cell culture flask. Each medium was tested using the test conditions for culturing with 3 replicates. Test concentrations for both algae species were 0, 25, 50 and 100 µg Ag L-1 for OECD, 50% P and 25% P while for both N reductions, the silver concentrations were 0, 10, 25 and 100 µg Ag L-1. Samples for determining the algal density were taken at every 24 h.

Bioremediation potential of the macroalga Gracilaria lemaneiformis (Rhodophyta) integrated into fed fish culture in coastal waters of north China

Fed fish farms produce large amounts of wastes, including dissolved inorganic nitrogen and phosphorus. In China, fish mariculture in coastal waters has been increasing since the last decade. However, there is no macroalgae commercially cultivated in north China in warm seasons. To exploit fish-farm nutrients as a resource input, and at the same time to reduce the risk of eutrophication, the high-temperature adapted red alga Gracilaria lemaneiformis (Bory) Dawson from south China was co-cultured with the fish Sebastodes fuscescens in north China in warm seasons. Growth and nutrient removal from fish culture water were investigated in laboratory conditions in order to evaluate the nutrient bioremediation capability of G. lemaneiformis. Feasibility of integrating the seaweed cultivation with the fed fish-cage aquaculture in coastal waters of north China was also investigated in field conditions. Laboratory seaweed/fish co-culture experiments showed that the seaweed was an efficient nutrient pump and could remove most nutrients from the system. Field cultivation trials showed that G. lemaneiformis grew very well in fish farming areas, at maximum growth rate of 11.03% day(-1). Mean C, N, and P contents in dry thalli cultured in Jiaozhou Bay were 28.9 +/- 1.1%, 4.17 +/- 0.11 % and 0.33 +/- 0.01 %, respectively. Mean N and P uptake rates of the thalli were estimated at 10.64 and 0.38 mu mol g(-1) dry weight h(-1), respectively. An extrapolation of the results showed that a 1-ha cultivation of the seaweed in coastal fish fanning waters would give an annual harvest of more than 70 t of fresh G. lemaneiformis, or 9 t dry materials; 2.5 t C would be produced, and simultaneously 0.22 t N and 0.03t P would be sequestered from the seawater by the seaweed. Results indicated that the seaweed is suitable as a good candidate for seaweed/fish integrated mariculture for bioremediation and economic diversification. The integration can benefit economy and environment in a sustainable manner in warm seasons in coastal waters of north China. (c) 2005 Elsevier B.V. All rights reserved.

Global transcriptional responses of the toxic cyanobacterium, Microcystis aeruginosa, to nitrogen stress, phosphorus stress, and growth on organic matter

Whole transcriptome shotgun sequencing (RNA-seq) was used to assess the transcriptomic response of the toxic cyanobacterium Microcystis aeruginosa during growth with low levels of dissolved inorganic nitrogen (low N), low levels of dissolved inorganic phosphorus (low P), and in the presence of high levels of high molecular weight dissolved organic matter (HMWDOM). Under low N, one third of the genome was differentially expressed, with significant increases in transcripts observed among genes within the nir operon, urea transport genes (urtBCDE), and amino acid transporters while significant decreases in transcripts were observed in genes related to photosynthesis. There was also a significant decrease in the transcription of the microcystin synthetase gene set under low N and a significant decrease in microcystin content per Microcystis cell demonstrating that N supply influences cellular toxicity. Under low P, 27% of the genome was differentially expressed. The Pho regulon was induced leading to large increases in transcript levels of the alkaline phosphatase phoX, the Pst transport system (pstABC), and the sphX gene, and transcripts of multiple sulfate transporter were also significantly more abundant. While the transcriptional response to growth on HMWDOM was smaller (5–22% of genes differentially expressed), transcripts of multiple genes specifically associated with the transport and degradation of organic compounds were significantly more abundant within HMWDOM treatments and thus may be recruited by Microcystis to utilize these substrates. Collectively, these findings provide a comprehensive understanding of the nutritional physiology of this toxic, bloom-forming cyanobacterium and the role of N in controlling microcystin synthesis.

Dynamics of Dissolved Forms of Carbon and Inorganic Nitrogen in Small Watersheds of the Coastal Atlantic Forest in Southeast Brazil

Based on the fact that streamwater quality reflects landscape conditions, the objectives of this study were: to investigate nitrogen (N), carbon (C), and major ion concentrations in six streams crossing minimally disturbed Atlantic Forest areas, with similar geomorphological characteristics; to determine N and C fluxes in one of these pristine streams (Indaia); and assess the impact of human activity on the biogeochemistry of two other streams in the same region, crossing urbanized areas. The distribution pattern of carbon and inorganic nitrogen dissolved forms, as well as the major ion and biogenic gas concentrations in the streamwater, was similar in pristine streams, indicating that the C and N dynamics were determined by influence of some factors, such as climate, atmospheric deposition, geology, soil type, and land covering, which were analogous in the forested watersheds. The urban streams were significantly different from the pristine streams, showing low dissolved oxygen concentrations, high respiration rates, and high concentrations of carbon dioxide, dissolved inorganic nitrogen, dissolved inorganic carbon, and major ion. These differences were attributed to anthropogenic impact on water quality, especially domestic sewage discharge. Additionally, in the Indaia stream, it was possible to observe the importance of rainfall over temporal dynamics of dissolved carbon forms, and also, the obtained specific flux of dissolved inorganic nitrogen was relatively elevated (approximately 11 kg ha(-1) year(-1)). These results reveal the influence of human activity over the biogeochemistry of coastal streams and also indicate the importance N export of Atlantic Forest to the ocean.

Seasonally aggregated values of dissolved inorganic phosphorus in soil solution of the Jena Experiment (Main Experiment, year 2006)

This data set contains measurements of inorganic phosphorus in samples of soil solution collected in 2006 from the main experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below) that have been aggregated to seasonal values. In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing. Glass suction plates with a diameter of 12 cm, 1 cm thickness and a pore size of 1-1.6 µm (UMS GmbH, Munich, Germany) were installed in April 2002 in depths of 10, 20, 30 and 60 cm to collect soil solution. Manual soil matric potential measurements were used to regulate the vacuum system. Manual soil matric potential measurements were used to regulate the vacuum system. The sampling bottles were continuously evacuated to a negative pressure between 50 and 350 mbar, such that the suction pressure was about 50 mbar above the actual soil water tension. Thus, only the soil leachate was collected. Cumulative soil solution was sampled biweekly and analyzed for dissolved inorganic P (PO4P). Here volume-weighted mean values are provided as aggregated seasonal values (spring = March to May, summer = June to August, fall = September to November, winter = December to February) for 2006 in spring. To calculate these values, the sampled volume of soil solution is used as weight for P concentrations of the respective sampling date. Inorganic phosphorus concentrations in the soil solution were measured photometrically with a continuous flow analyzer (CFA Autoanalyzer [Bran&Luebbe, Norderstedt, Germany]). Ammonium molybdate catalyzed by antimony tartrate reacts in an acidic medium with phosphate and forms a phospho-molybdic acid complex. Ascorbic acid reduces this complex to an intensely blue-colored complex. As the molybdic complex forms under strongly acidic conditions, we could not exclude the hydrolysis of labile organic P compounds in our samples. Furthermore, the molybdate reaction is not sensitive for condensed phosphates. The detection limits of both TDP and PO4P were 0.04 mg P l-1 (Autoanalyzer, Bran&Luebbe).

Seasonally aggregated values of dissolved inorganic phosphorus in soil solution of the Jena Experiment (Main Experiment, year 2004)

This data set contains measurements of inorganic phosphorus in samples of soil solution collected in 2004 from the main experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below) that have been aggregated to seasonal values. In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing. Glass suction plates with a diameter of 12 cm, 1 cm thickness and a pore size of 1-1.6 µm (UMS GmbH, Munich, Germany) were installed in April 2002 in depths of 10, 20, 30 and 60 cm to collect soil solution. Manual soil matric potential measurements were used to regulate the vacuum system. Manual soil matric potential measurements were used to regulate the vacuum system. The sampling bottles were continuously evacuated to a negative pressure between 50 and 350 mbar, such that the suction pressure was about 50 mbar above the actual soil water tension. Thus, only the soil leachate was collected. Cumulative soil solution was sampled biweekly and analyzed for dissolved inorganic P (PO4P). Here volume-weighted mean values are provided as aggregated seasonal values (spring = March to May, summer = June to August, fall = September to November, winter = December to February) for 2004 in spring, fall, and winter. To calculate these values, the sampled volume of soil solution is used as weight for P concentrations of the respective sampling date. Inorganic phosphorus concentrations in the soil solution were measured photometrically with a continuous flow analyzer (for samples collected until spring 2004: CFA SAN++, Skalar [Breda, The Netherlands]; for samples collected later: CFA Autoanalyzer [Bran&Luebbe, Norderstedt, Germany]). Ammonium molybdate catalyzed by antimony tartrate reacts in an acidic medium with phosphate and forms a phospho-molybdic acid complex. Ascorbic acid reduces this complex to an intensely blue-colored complex. As the molybdic complex forms under strongly acidic conditions, we could not exclude the hydrolysis of labile organic P compounds in our samples. Furthermore, the molybdate reaction is not sensitive for condensed phosphates. The detection limits of both TDP and PO4P were 0.02 mg P l-1 (CFA, Skalar) and 0.04 mg P l-1 (Autoanalyzer, Bran&Luebbe).