Acidification effects on the plant-soil system: a case-study in grassland and heathland soils in the UK

Comunicación oral presentada en el Simposio sobre interacciones planta-suelo 25-26 February 2016, Madrid

Vegetation and soil properties are defined by both biotic and abiotic processes. Acidification effects on soil biochemical properties were studied, as pH is a key factor for soil nutrients´ availability and for the development of soil microbial communities. The long-term plant-soil system interaction was studied in two different ecosystems, grassland (pH 5.5) and heathland (pH 4.3), and in two experimental grasslands, one treated with ferrous sulphate (pH 5.5) and one treated with elemental sulphur (pH 4.9), where both treatments were applied 14 years ago. Grassland and both sulphurous treated soils were dominated by Poaceae species, 60%, while heathland soils presented 90% coverage of Ericaceae species (Diaz, Green & Tibbett 2008). Elemental sulphur treated soils presented a shift from Asteraceae and Fabaceae species, the second most dominant species in grassland, to Juncaceae, Ranunculaceae and Polygonaceae species. Soil acidification was effective in the long-term only in elemental sulphur treated soils, however acidification increased phosphorus concentrations in both treated soils. Acidification may have solubilised the rock phosphate bind in these soils releasing available phosphorus to the soils. Total carbon and microbial biomass carbon were positively correlated and both variables showed a marked peak in heathland soils, which were significantly different to the rest of the soils. Moreover, microbial respiration CO2 rates were also highest in heathland soils in comparison to the rest of the soils. Heathland soils may have the highest substrate availability which is favouring the microbial growth. The microbial activity in these heathland soils was high, enhancing rapid decomposition and nutrient availability. The mean metabolic quotient confirmed the low maintenance requirements of the microbial communities in heathland soils, and grassland soils also presented high carbon utilization efficiency. It is probable that microbial communities in ferrous sulphate and elemental sulphur treated soils were disturbed by acidification processes and, 14 years after treatment application, this disturbance is maintained and, consequently, these microbial communities have a higher energy demand. Heathland plots were dominated by fungal communities (PLFA 18:2ω6,9) while the rest of the soils were dominated by bacterial communities. The long-term acidification effect in elemental sulphur treated soils was detrimental to arbuscular mycorrhizal fungi development, which were significantly present in grassland and ferrous sulphate treated soils. In conclusion, acidification of the soil by sulphurous treatments was not maintained in the long-term, thereby preventing the shift from bacterial to fungal communities. However, acidification effects were responsible for the high phosphorus solubility in treated soils, enhancing the establishment of nutrient-rich plant species. Both sulphurous treated soil groups were not efficient in carbon utilisation, which was reflected in the low biomass production, which may indicate the developmental stage of these acidified soils.

Peer reviewed