Microbial Degradation of Plant Residues Rapidly Causes Long-Lasting Hypoxia in Soil upon Irrigation and Affects Leaching of Nitrogen and Metals

Abstract

With this study, we aim to relate the substrate quality of different organic materials derived from plant residues to the respiratory activity of soil microorganisms after amendment, the formation of oxygen gradients upon irrigation, and the leaching of macronutrients and metals in soil. Elemental analyses were performed to determine the chemical composition of wheat straw, green compost, and a biochar product, showing that carbon availability, C/N ratio, and metal contents varied markedly. Consequently, after application to well-aerated sandy loam soil at 1% w/w, only straw increased microbial activity substantially, and nitrate was depleted within one week. Upon intense irrigation of soil columns packed with differently amended soils, strong hypoxia formed only in straw–soil, where microbial oxygen demand for straw degradation was high. This was enhanced after the application of mineral fertilizers, and nitrate leaching was mitigated. With the decreasing redox potential in straw–soil, the leaching of Fe, Mn, Al, Ni, Co, and As was increased. However, nitrate from mineral fertilizer mitigated the reduction of redox potential and, thus, the leaching of these metals. Measuring oxygen at different depths revealed near anoxic conditions at −15 cm of straw–soil with NP-fertilizer applied within 12 h after the start of irrigation and remained for at least 60 h, while oxygen showed extensive fluctuations in the upper few centimeters. This study showed that organic soil amendments with high carbon availability induce microbial respiration to the extent that causes strong and long-lasting hypoxia upon irrigation, even in sandy soil, which leads to substantial effects on the mobility of nutrients and toxic metals. In contrast, organic soil amendments with low carbon availability did not cause such effects.

Fertilizer and cultivar affect the barley rhizobiome, while domestication age only affects growth at low nutrient levels

“…This may lead to either nutrient mineralisation or nutrient immobilisation depending on the C/N ratio of the organic fertilizer (Probert et al ., 2005). Further, increased microbiome activity may result in oxygen depletion (Siedt et al ., 2023) and/or production of toxic metabolites (Duke and Dayan, 2011). Thus, the intricate balance between these factors will determine the net effect of the organic fertilizer.…”

Looking for Resistance to Soft Rot Disease of Potatoes Facing Environmental Hypoxia

“…Also, plant susceptibility to biotic stress, such as pectinolytic bacteria (e.g., Pectobacterium carotovorum), can be induced by changes in plant gene expression, e.g., phenylalanine ammonia-lyase and extensions [83]. Since microbial metabolic activity in the soil can lead to root local hypoxia [84], plant pathogenic microorganisms can utilize this and compete for oxygen with their host, facilitating symptom development [80]. In this context, SRP, not only uses the decreased plant defenses [26,83,85,86] but also adapts their gene expression to hypoxic conditions to more effectively induce soft rot disease [25] (Figure 3).…”