Dr Muhammad Riaz1,2, Dr.  Joerg Luster2, Dr.  Martin Ley2, Mrs. Anais Cattin2, Dr.  Pascal A.  Niklaus3, Dr. Andreas C.  Schomburg4, Dr. Claire Guenat5, Dr. Philip Brunner4, Dr. Moritz Lehmann6

1Department of Environmental Sciences & Engineering, Government College University Faisalabad, Faisalabad, Pakistan, 2Swiss Federal Research Institute WSL, Birmensdorf, Switzerland, 3University of Zurich, Zurich, Switzerland, 4University of Neuchâtel, Switzerland, 5EPFL, Lausanne, Switzerland, 6University of Basel, Switzerland

The relative effects of soil aggregation, plant-soil-earthworm interactions and litter accumulation on the emissions of nitrous oxide (N₂O) from floodplain soils were investigated in a restored section of the Thur River (NE Switzerland). We carried out a manipulation experiment in a frequently flooded and by Phalaris arundinacea dominated zone with loamy sand by comparing separated treatment plots: (i)  control, (ii) vegetaton free, (iii) reduced earthworm population, (iv) combination of (ii) and (iii). In the laboratory we performed a flooding experiment in mesocosms using silty-loamy soil from the Thur floodplains, applying the following treatments: (i) soil 250µm-4mm, (ii) (i) planted with salix viminalis, (iii) (i) mixed with willow leaves, (iv) to (vi) as (i) bis (iii) but soil < 250µm. In the laboratory experiment, the emission of N₂O during the hot moments after flooding was reduced in the planted treatment, very likely due to aeration of the rhizosphere via aerenchyma. In the field experiment, the vegetated plots emitted more N₂O under moist conditions and the hot moments after flooding occurred for a longer period. In this case, probably stimulation of microbial activity by root exudation is the dominant rhizosphere effect. Under dry conditions, the additional drying effect due to plant water uptake leads to lower N₂O emissions from plots with vegetation. According to the laboratory experiment, the formation of large aggregates increases the intensity of the hot moments during the drying phase after a flood probably due to the development of good conditions for coupled nitrification – denitrification. A local increase in litter-associated C availability appears to lead to a further increase of N²O production only under concurrent protection in large aggregates. Temporary lower emissions from field plots with earthworms suggest that in sandy soils the aeration effect of earthworm activity is larger than the one on aggregate formation.


Dr. Muhammad Riaz is working as an Associate Professor in the Department of Environmental Sciences & Engineering, Government College University Faisalabad (GCUF), Pakistan. He earned his PhD in Environmental Sciences from the University of York, UK. His research is mainly focused on soil biogeochemistry, CNP cycling in agroecosystems, biochar as a tool for soil C sequestration and soil quality management, and dynamics of soil organic matter cycling and recycling in semi-arid and arid agroecosystems.

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