Forest fire phosphorus
- Published: May 15, 2010
- Author: David Bradley
- Channels: NMR Knowledge Base
Phosphorus-31 NMR spectroscopy has been used to investigate the effects on the chemistry of phosphorus in soil as an indicator of nutritional quality for vegetation and tree growth following a forest fire.
María-Belén Turrion, Francisco Lafuente, María-José Aroca, Olga López, Rafael Mulas, and Cesar Ruipérez of the University of Valladolid, Palencia, Spain, have turned to NMR to help them investigate the long-term effects of fire on soil phosphorus (P) and to determine the efficiency of various procedures in extracting soil different forms of phosphorus.
Forest wild fires cause significant damage and loss of life. "They constitute one of the most serious environmental problems affecting semi-arid areas," say Turrion and colleagues. Despite the notion that a fire helps regenerate a forest, they generally cause destruction of vegetation cover and soil, and interfere with the delicate balance of the forest ecosystem functions, such as water supply maintenance, protection against soil erosion, and nutrient accumulation the team adds.
The researchers point out that during a forest fire, soil organic matter (SOM) is damaged as refractory and oxidation-resistant materials form that do not necessarily benefit the plant life of the forest. They added that in the Mediterranean regions, climatic conditions alternate between intense hot spells with high levels of solar radiation and drying and more temperate and wet periods, all of which affect the formation of stable SOM.
One of the important inorganic components of soil is phosphorus. Indeed, it is a limiting nutrient for plant growth. But, there is a dearth of information about how the chemistry of phosphorus in soil affected by forest fire changes. The mineralisation of organic matter and other effects of fire might lead to a loss of soluble forms of the element, but little is known about the processes. The team points out that shortfalls in extraction methods and analytical techniques are partly to blame.
They point out that 31P NMR spectroscopy has been used to study the influence of cultivation and fertilization on the composition of organic phosphorus in structural soil as well as looking at how land use, temperature and precipitation changes affect the phosphorus. Despite the obvious benefits they add that the technique has not been widely applied after forest fires.
The Spanish team has now used anion exchange membranes and: AEM-P and NaOH-EDTA chelation to extract phosphorus from soil and then applied 31P NMR to assess total organic and inorganic soil phosphorus. Samples were obtained from the Pinus pinaster forest located at Arenas de San Pedro (southern Avila, Spain) in a valley region located on the southern face of the Gredos Mountain foothills (Sistema Central) at specific depths of 0-20 mm, 20-50 mm, and 100-150 mm, two years after a fire in the burned area and in an adjacent unburned forest area.
They report in the journal Science of The Total Environment how fire increased the total nitrogen, organic carbon, total phosphorus, and organic and inorganic phosphorus content in the surface soil layer. They add that standard chemical analyses over-estimate the organic P fraction in the EDTA-NaOH extract when compared with determination by an ignition procedure. This was significant in the burned soil rather than the unburned soil samples. They add that fire-induced changes in the structure of soluble phosphorus saw an increase in orthophosphate-phosphorus and a decrease in monoester-phosphorus and DNA-phosphorus, although the same forms are present in burned and unburned samples.
The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.
NMR analysing phosphorus in the aftermath of a forest fire