Abstract:Water repellency (WR) is a property that has implications on the hydrologic balance in affected soils. In semi-arid areas where water supply is limited, even slight WR may play an important role in the infiltration and spatial distribution of precipitation into the soil. Acidic and sandy-textured soils have been demonstrated to be more prone to develop WR, but there are studies reporting water repellent properties in other soil types. In the present study we investigated soil WR under four plant species in a semi-arid area with a calcareous, medium-textured forest soil. For this purpose, 160 soil samples were taken at micro-sites under different species (Pinus halepensis, Quercus coccifera, Juniperus oxycedrus and Rosmarinus officinalis). Soil WR was measured with the water drop penetration time (WDPT) test on air-dried samples. Samples with WDPT > 5 s were classified as water repellent. WR was present in 20% of the samples, and its persistence ranged mainly between 10 and 30 s. Under P. halepensis and Q. coccifera, WR occurred more frequently (40 and 30%, respectively) than under J. oxycedrus and R. officinalis (only 5% in both cases). In order to know the causes of the difference in occurrence of WR under the selected species and to establish relationships, soil organic matter (SOM) content and pH were measured for a selection of 66 samples, including all 32 water repellent and 34 wettable samples selected from those taken under the four species (n D 66). A negative relationship between WR and pH was found for all species. Moreover, in the case of P. halepensis soil samples, a positive correlation between WR and SOM content was found. A discriminant analysis allowed for the distinction between water repellent and wettable conditions in calcareous soils, based on the information provided by pH, SOM content and vegetation type. Soil pH turned out to be the most important parameter for discrimination. The hydrological and ecological implications from these results are discussed with special focus on the areas in the region extensively afforested with P. halepensis.
Samples of a Mediterranean forest soil were exposed in a muffle furnace to seven temperatures (100–700°C) for 15 min to simulate different fire intensities. Heated soils were incubated for 100 days after re-inoculation with fresh unheated soil. Immediately after heating, the extractable organic C increased with the heating temperature, reaching a maximum at 400°C. This increase in extractable organic C and nutrients in soils heated below 400°C allowed a rapid recolonization of bacteria, increasing the basal respiration. During the 100-day incubation, the cumulative values of basal respiration and carbon mineralization rates generally followed a double exponential equation in unheated and heated samples. Heating at 200°C caused a reduction of 99.6% for fungi (measured as culturable fungal propagules), which showed lower recolonization capacity than that of bacteria. Heating also caused a decrease in the organic C content of the soils, especially for the highest temperatures. As a consequence, the microbial biomass carbon recovery was short lived in heated soils. The varied effects of heating and incubation on the inorganic and organic nitrogen changes, available nutrients and metabolic quotients are also discussed. This study demonstrates that changes in soils exposed to comparatively high temperatures (>500°C) have a particularly strong impact on microbial population.
Telephone:+61 3 9662 7644 (editorial enquiries) +61 3 9662 7668 (subscription enquiries and claims) Fax: +61 3 9662 7611 (editorial enquiries) +61 3 9662 7555 (subscription enquiries and claims) O r g a n i c m a t t e r a n d a g g r e g a t e s i n b u r n t s o i l s W F 0 2 0 2 0 J . Ma t a i x -S o l e r a , I . G ó m e z , J . N a v a r r o -P e d r e ñ o , C . G u e r r e r o a n d R . Mo r a l J . Ma t a i x -S o l e r a e t a l .Abstract. Three Mediterranean soils located in the north of the Province of Alicante (Spain) were studied for a year after a forest fire. The percentage of water-stable aggregates (between 0.2 and 4 mm) and organic matter content were measured. Microaggregates (< 0.2 mm) were observed using electron microscopy. The results showed the importance of type of forest fire on soil organic matter and aggregates. Soil structure was more affected by surface fire (which affects mainly brushwood and soil surface) than crown fire (which burns the tops of trees and some brushwood). Accumulation of organic matter from burnt trees and brushwood in areas affected by crown fire and alterations in organic matter content through the soil profile were observed. Surface forest fire affected soil structure more negatively than crown fire as observed using electron microscopy. Soils affected by surface fire may be more easily eroded and recovery of vegetation may be delayed because of effects on soil structure. Organic matter content through the soil profile comparing burnt and adjacent unburnt soil could be used to determine the type of fire.
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