Effect of contrasting phosphorus levels on nitrous oxide and carbon dioxide emissions from temperate grassland soils

www.nature.com/scientificreports OPEN Effect of contrasting phosphorus levels on nitrous oxide and carbon dioxide emissions from temperate grassland soils Amanuel W. Gebremichael1*, David P. Wall1, Rosie M. O’Neill1,2, Dominika J. Krol1, Fiona Brennan1, Gary Lanigan1 & Karl G. Richards1* Agricultural practices such as repeated fertilization impact carbon (C), nitrogen (N) and phosphorus (P) cycling and their relationships in the plant–soil continuum, which could have important implications for the magnitude of greenhouse gas emissions. However, little is known about the effect of C and N additions under contrasting soil P availability status on nitrous oxide (N2O) and carbon dioxide (CO2) emissions. In this study, we conducted a field-based experiment that investigated the impact of long-term (23 years) P management (no (P0, 0 kg P ha−1), low (P15, 15 kg P ha−1) and high (P45, 45 kg P ha−1) P inputs) on N2O and CO2 emissions following two C + N application events in two managed grassland ecosystems with loam and sandy loam soils. The magnitude of fluxes varied between the soil P availability levels. Cumulative N2O emission was significantly higher in P0 soils (1.08 ± 0.09 g N2O-N m−2) than P45 soils (0.63 ± 0.03 g N2O-N m−2), with the loam soil (1.04 ± 0.04 g N2O-N m−2) producing significantly higher emissions than the sandy loam soil (0.88 ± 0.05 g N2O-N m−2). We conclude that P-limitation stimulates N2O emissions, whereas P-enrichment promotes soil respiration in these temperate grassland sites. Our findings inform effective nutrient management strategies underpinning optimized use of N and P inputs to agricultural soils as mitigation measures for both food security and reducing greenhouse gas emissions. Nitrous oxide (N2O) and carbon dioxide (CO2) are two of the main greenhouse gases (GHGs) emitted from agricultural soils. Nitrous oxide is a potent GHG with 298 times more global warming potential than CO2 and arises from application of organic and inorganic nitrogen to soil1. Further, carbon dioxide emitted from soil auto- and heterotrophic respiration represents an important flux component in the global carbon cycle between soil and the a tmosphere2. Grasslands constitute one of the dominant land uses in Europe, comprising 38% of agricultural land, and grassland management practices substantially contribute to GHG emissions3,4. Owing to their large capacity for storing soil organic carbon (SOC), grasslands play a significant role in mitigating climate change5. Intensively farmed grassland soils are routinely supplemented with nutrient inputs, such as nitrogen (N) and phosphorus (P), to increase herbage biomass production, as these nutrients support plant photosynthesis, protein synthesis, and energy transfer. Despite their importance, imbalanced use or availability of N and P may induce significant alterations in ecosystem structure and functioning, and thereby dynamics of carbon (C) and nitrogen cycles6. Long term and repeated fertilizer applications affect the C:N:P ratio and the cycling of these nutrient in agricultural soils through changes in microbial biomass and community c omposition7–10. Phosphorus and nitrogen fertilization have been found to impact mycorrhizal community and biomass7,11, plant species richness and diversity12 as well as root exudation and turnover13, all of which could influence C movement and plant–soil nutrient relations in ecosystems. Microorganisms can obtain C from organic material and mineralise it into simpler inorganic compounds to release essential nutrients, whose availability in soil limit successful plant and microbial growth. The availability of N and P relative to C (stoichiometric relationships) determines microbial mineralization or immobilization of these n utrients14,15 and may strongly affect C dynamics in an ecosystem. Studies suggest strong limitations of N and P on heterotrophic respiration indicating tight coupling of essential 1 Environmental Research Centre, Teagasc, Johnstown Castle, Co. Wexford, Ireland. 2University College Dublin, Belfield, Dublin 4, Dublin, Ireland. *email: ; Scientific Reports | (2022) 12:2602 | https://doi.org/10.1038/s41598-022-06661-2 1 Vol.:(0123456789) www.nature.com/scientificreports/ nutrients and c arbon16–18. Nitrous oxide is primarily produced through microbial nitrification and denitrification, and its production via these pathways are affected by microbial composition as well as the availability of soil mineral N and phosphate, C substrate, oxygen, soil moisture, pH, and soil t emperature17,19. While it is known that N fertilizer applications contribute to the formation of N2O4, there is a poor understanding of the interaction between soil nutrients and carbon availability, and their subsequent impact on N 2O and C O2 emissions in agricultural soils. Fertilizer-driven changes in managed grassland soils could have functional implications for the composition of arbuscular mycorrhizal fungi (AMF) and alter their symbiotic relationship with p lants15,20–22. This symbiotic relationship comprises of increased access to N and P facilitated by the AMF to the plant in return for C11,23. However, the extent to which N, P and C is exchanged could be influenced by an increasing use of N and P fertilizers. In a P-rich soil, N enrichment has been found to cause reduced allocation of photosynthates to mycorrhizae arbuscules, coils and extraradical h yphae23. In contrast, nitrogen enrichment of low P soils increased 23 C allocations to these s tructures . Thus, the availability of N relative to P in mycorrhizal system could affect the relationship between fungi and hosting plants and limit the ability of fungi to procure the elements. Lower P levels were associated with a significant increase of AMF colonization in a study conducted in the same experimental field of the current i nvestigation24. Contrasting presence of AMF in agricultural soils could have major implications for variable N 2O and C O2 formation and may result in different nutrient use of efficiency of plants. Bender et al.25 and Storer et al.26 showed reduced N 2O emissions in soils with abundant presence of fungi group, AMF, despite fungi are generally considered as a source of N 2O as they lack N2O r eductase27. In contrast to these findings, Okiobe et al.28 demonstrated promoted potential N 2O production as a result of decreased abundance of arbuscular mycorrhizal fungi. In a recent laboratory-based study, significantly higher N2O emission was observed in a P-limited soil than in a P-enriched soil following the same input of C and N in the two varying P-levels29. However, this relationship requires further investigation and verification under natural field conditions with plants present. Here we investigate the influence of N fertilizer addition and C availability on N2O and C O2 emissions across two agricultural soils with sandy loam (Site A) and loam (Site B) textures with differing soil P levels in eac (...truncated)