Grass populations control nitrification in savanna soils

Abstract

Summary1. Nitrification plays a key role in the functioning of many natural ecosystems. It is directly involved in plant nitrogen nutrition and soil N losses through leaching and denitrification. The control of this process by plants is poorly understood, although modifications of nitrification would allow plants to manipulate competition for N and induce changes in ecosystem N balance. In a wet tropical savanna ecosystem (Lamto, Côte d'Ivoire), the soil N cycle is characterized by distinct high-and low-nitrification sites. Previous publications showed that nitrification was positively or negatively correlated with root densities of the dominant grass covering these sites. These contrasting sites were chosen to investigate the extent to which vegetation controls longterm nitrification. 2. In situ experimental plots were created where grass individuals originating from high-or low-nitrifying soils were transplanted into both soils. Nitrifying enzyme activity (NEA) was measured up to 24 months after transplanting. Grasses from both sites significantly modified NEA up to rates similar to those at their respective control sites. 3. The level of individual plant control (inhibition and stimulation) was correlated with grass biomass. The potential mechanisms of this control is discussed, along with its consequences for ecosystem N cycling (such as N losses), as the denitrifying enzyme activity (DEA) is much higher in the high-nitrification site. Such results suggest that plant species can have important consequences for N cycling at the population level.

Measurements of nitric oxide and ammonia soil fluxes from a wet savanna ecosystem site in West Africa during the DACCIWA field campaign

“…The Dahra site (Delon et al, 2017) also shows similar pH than our site (Table 5), while lower pH (acidic or near-neutral) was recorded at the sites of Lamto (Le Roux et al, 1995, Lata et al, 2004 and Agonkanmey (Barthes et al, 2004). Higher soil organic C and N over bare soil could be due to the fact that these bare soil patches experienced recent burning (Santín and Doerr, 2016).…”

Nitrification and denitrification in an alpine meadow soil of the eastern Tibetan Plateau

“…In July, soil temperature and moisture reached a maximum, which benefits soil N mineralization, and accordingly soil NH 4 ' Ã/N increased (Joergensen, 1990;Fisk et al, 1998). Also increases in plant biomass could potentially increase NH 4 ' Ã/N availability in soil through an increase of root-derived carbon (Lata et al, 2004). The decreases in soil NO 3 ( Ã/N during the growing season can be attributed to high rates of NO 3…”

Reducing nitrous oxide emissions by changing N fertiliser use from calcium ammonium nitrate (CAN) to urea based formulations

“…Natural suppression of soil nitrification by plants has also been observed in some ecosystems, and is referred to as biological nitrification inhibition (Subbarao et al, 2006). This natural inhibition is most likely an evolutionary adaptation to ensure conservation and efficient use of N in natural systems 7 which have low-N availability (Lata et al, 2004). There are two main categories of commercially available N stabilisers:…”