Different Approaches to Assessing Pollution Load: The Case of Nitrogen-Related Grey Water Footprint of Barley and Soybean in Argentina

Agriculture is among the main causes of water pollution. Currently, 75% of global anthropogenic nitrogen (N) loads come from leaching/runoff from cropland. The grey water footprint (GWF) is an indicator of water resource pollution, which allows for the evaluation and monitoring of pollutant loads (L) that can affect water. However, in the literature, there are different approaches to estimating L and thus contrasting GWF estimates: (A1) leaching/runoff fraction approach, (A2) surplus approach and (A3) soil nitrogen balance approach. This study compares these approaches for the first time to assess which one is best adapted to real crop production conditions and optimises GWF calculation. The three approaches are applied to assess N-related GWF in barley and soybean. For barley in 2019, A3 estimated a GWF value 285 to 196% higher than A1, while in 2020, the A3 estimate was 135 to 81% higher. Soybean did not produce a GWF due to the crop characteristics. A3 incorporated N partitioning within the agroecosystem and considered different N inputs beyond fertilization, improving the accuracy of L and GWF estimation. Providing robust GWF results to decision-makers may help to prevent or reduce the impacts of activities that threaten the world’s water ecosystems and supply.

Growth responses of Sorghum bicolor (L.) Moench to arbuscular mycorrhizal fungi under simulated nitrogen deposition

Anthropogenic nitrogen (N) deposition leads to a dramatically increase in biologically available N in many ecosystems, which can change the symbiotic relationship between AMF and host plants. However, how and to what extent exogenous N-induced AMF could affect plants remains poorly understood. In this work, mycorrhizal growth responses of Sorghum bicolor to AMF under simulated N deposition were conducted in a glasshouse experiment. Results demonstrated that AMF elevated the growth performance and nutrient uptake (N, P) of S. bicolor at almost all treatments, although mycorrhizal colonization decreased with N addition. In addition, mycorrhizal response (MR) showed identical trend of first fall and then increase, and the lowest value was at the N1 treatment. The present study provided the first pot-based evidence that AMF can alleviate the mischief induced by high N addition, implying that AMF has a considerable significance in the farmland ecosystem under anthropogenic N deposition. Bangladesh J. Bot. 50(3): 933-938, 2021 (September) Special

Nitrogen and Sulfur Additions Improved the Diversity of nirK- and nirS-Type Denitrifying Bacterial Communities of Farmland Soil

Anthropogenic nitrogen (N) and sulfur (S) deposition can change above- and belowground biodiversity, including soil microbial diversity. The diversity of denitrifying microorganisms is of great significance to the calculation of the global nitrogen cycle and nitrogen flux. For a long time, nirK and nirS have been used as the functional genes to study denitrifying microorganisms, and have gradually become molecular markers for studying the composition and diversity of denitrifying bacteria. Here, three-time exposures to N and S applications (7, 30, and 60 days), were independently established. Additionally, the abundance, diversity, and structure of nirK- and nirS-type denitrifying communities were examined by sequencing analyses in response to three treatments, namely, N and S (TN/S), sodium chloride (TNaCl) and deionized water (pH = 7.0) (CK). Our results suggest that TN/S led to higher electrical conductivity (EC), total nitrogen (TN), total organic carbon (TOC), nitrate nitrogen (NO3−-N), ammonium nitrogen (NH4+-N), and lower pH compared with TNaCl and CK, which affected the diversity of nirK- and nirS-type denitrifying bacterial communities. We also observed that the nirK-type denitrifying community demonstrated a higher sensitivity to N and S additions. Overall, our results are important for the understanding of nitrogen in soil and N2O emissions.

Ontogenetic δ15N Trends and Multidecadal Variability in Shells of the Bivalve Mollusk, Arctica islandica

Bulk stable nitrogen isotope values of the carbonate-bound organic matrix in bivalve shells (δ15NCBOM) are increasingly used to assess past food web dynamics, track anthropogenic nitrogen pollution and reconstruct hydrographic changes. However, it remains unresolved if the δ15NCBOM values are also affected by directed ontogenetic trends which can bias ecological and environmental interpretations. This very aspect is tested here with modern and fossil specimens of the long-lived ocean quahog, Arctica islandica, collected from different sites and water depths in the NE Atlantic Ocean. As demonstrated, δ15NCBOM values from the long chronologies show a general decrease through lifetime by −0.006‰ per year. The most likely reason for the observed δ15NCBOM decline is a change in the type of proteins synthesized at different stages of life, i.e., a gradual shift from proteins rich in strongly fractionating, trophic amino acids during youth toward proteins rich in source amino acids during adulthood. Aside from this ontogenetic trend, distinct seasonal to multidecadal δ15NCBOM variations (ca. 50 to 60 years; up to 2.90‰) were identified. Presumably, the latter were governed by fluctuations in nutrient supply mediated by the Atlantic Multidecadal Variation (AMV) and Atlantic Meridional Overturning Circulation (AMOC) combined with changes in nitrate utilization by photoautotrophs and associated Rayleigh fractionation processes. Findings underline the outstanding potential of bivalve shells in studies of trophic ecology, oceanography and pollution, but also highlight the need for compound-specific isotope analyses.