Obtainment of a carbon-13-, nitrogen-15-labelled burnt soil

Burning effects on the distribution of organic N compounds in a 15N labelled forest soil

“…This increase most likely occurred because several changes in SOM took place during the heating, including: (1) the selective destruction of the more easily decomposable SOM (González-Prieto et al, 1999); (2) the enrichment of more stable forms of N, which were more resistant to volatilization losses (Knicker et al, 1996) and to acid hydrolyses (Barriuso et al, 1987); (3) the increased formation of irreversible linkages of organic compounds with clay and Al and Fe oxides (Almendros et al, 1990 andFernández et al, 1997), making extraction by acid hydrolysis more difficult (Barriuso et al, 1987). The reactions discussed in the last two points were likely the causes for the increase in the absolute amount of NH-N, both endogenous and exogenous, after soil burning.…”

“…The 15 N tracer was introduced in the soil as ( 15 NH 4 ) 2 SO 4 (66 atom % 15 N), at a dose equivalent to 325 kg N ha -1 . To prevent soil surface acidification and to ensure a homogeneous labelling of the whole soil, the soil was put into the containers in five successive layers (4 cm thick), each receiving 6.66 g of ( 15 NH 4 ) 2 SO 4 dissolved in 2 l of distilled water, which was the amount necessary to bring the soil to the 75% of water holding capacity (González-Prieto et al, 1999). After that, the soil in each container was thoroughly mixed.…”

“…Sub-samples of dried soil (350 g) were placed on a stainless steel tray, forming a 1.5 cm layer, and were introduced into the furnace preheated to 385 ºC. Temperature in the soil layer (monitored with a thermocouple) reached 385 ºC after 25 min in the furnace; the soil was maintained at this temperature for 10 min and then replaced by a new soil sample previously prepared on another tray (González-Prieto et al, 1999).…”

“…To evaluate accurately the efficiency of these and other techniques for the post fire restoration of the N cycle, it is very useful to use isotopic tracers and, therefore, to obtain previously a 15 N labelled burnt soil (Villar et al, 1998 andGonzález-Prieto et al, 1999). Although it is usually overlooked, the introduction of 15 N into plants or soils during studies on N dynamics can lead to a non-uniform distribution of 15 N and 14 N among the different N fractions.…”

Use of 13C to monitor soil organic matter transformations caused by a simulated forest fire

“…[7][8][9][10][11] Obtaining 13 C-labelled soil is expensive and laborious. 12 In the present study, the use of a stable carbon isotope ( 13 C) as a SOM tracer will allow small changes in the C content of the diverse organic fractions to be monitored and will provide a quantitative and accurate estimation of the processes and SOM transformations that take place in the soil environment as a consequence of the burning. To carry out this research, a 13 C-labelled soil was used and the 13 C isotopic compositions of the different organic fractions were determined before and after a heating treatment.…”