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Prescribed burning has been readopted in the last decade in the Central Pyrenees to stop the regression of subalpine grasslands in favour of shrublands, dominated among others by Echinospartum horridum (Vahl) Rothm. Nevertheless, the effect of this practice on soil properties is uncertain. The aim of this work was to analyse the effects of these burnings on topsoil organic matter and biological properties. Soil sampling was carried out in an autumnal prescribed fire in Buisán (NE-Spain, November 2015). Topsoil was sampled at 0-1cm, 1-2cm and 2-3cm depth in triplicate just before (U), ~1h (B0), 6months (B6) and 12months (B12) after burning. We analysed soil total organic C (TOC), total nitrogen (TN), microbial biomass C (C), soil respiration (SR) and β-D-glucosidase activity. A maximum temperature of 438°C was recorded at soil surface while at 1cm depth only 31°C were reached. Burning significantly decreased TOC (-52%), TN (-44%), C (-57%), SR (-72%) and β-D-glucosidase (-66%) at 0-1cm depth while SR was also reduced (-45%) at 1-2cm depth. In B6 and B12, no significant changes in these properties were observed as compared to B0. It can be concluded that the impact of prescribed burning has been significant and sustained over time, although limited to the first two topsoil centimetres.

Lime-induced chlorosis (LIC) is an important abiotic constraint affecting the growth and yield of grapevines growing in calcareous soils in the Mediterranean region, and the sensory properties of the produced wine. In the work presented herein, the impact of LIC on the nutritional status and chlorophyll content was assessed for eleven varieties and a clone (Merlot, Pinot Noir, Cabernet Sauvignon, Tempranillo, Parraleta, Moristel, Aglianico, Macabeo, Sauvignon, Chardonnay, and Riesling), grafted to the same rootstock (1103 Paulsen). Macro- and micronutrient contents were determined in the fruit set and veraison stages by petiole analyses, while chlorophyll content in young leaves was monitored by SPAD. Significant differences were detected amongst varieties for all nutrients (including Fe), and inverse relationships between Fe and P contents in the petiole and chlorophyll concentration in the young leaves were found. Regarding LIC resistance, the Fe and chlorophyll contents suggest that Cabernet Sauvignon, Tempranillo and Aglianico varieties would show the best performance, while Sauvignon would be the least tolerant.

Soil organic matter, aggregation and water repellency are relevant interrelated soil properties that can be affected by fire. The aim of this work was to analyse the effects of shrub prescribed burning for pasture reclamation on the soil aggregate stability, organic carbon and water repellency of different soil depths and aggregate sizes in a subalpine environment. Soil samples were collected from an area treated by an autumnal lowintensity prescribed fire in the Central Pyrenees (NE-Spain) at 0-1, 1-2, 2-3 and 3-5 cm depths just before and ~1 hour, 6 months and 12 months after burning. Samples were separated as whole soil (<10 mm) and 6 sieve fractions, <0.25, 0.25-0.5, 0.5-1, 1-2, 2-4 and 4-10 mm. We analysed soil organic C (SOC), aggregate stability (AS) and soil water repellency (SWR). In the unburned samples, SOC and SWR were higher in the <0.25 to 2 mm sieve fractions than the 2 to 10 mm sieve fractions. Fire severely and significantly decreased the SOC content in the whole soil and the <0.25 mm fraction at 0-1 cm depth and in the 0.25-0.5 mm fraction at 0-2 cm depth. SWR was reduced by burning mainly at 0-1 cm depth for the whole soil and the <0.25 to 2 mm sieve fractions. Nevertheless, the AS of the 0.25-0.5 mm aggregates increased after fire, while the rest of the sieve fractions remained virtually unaffected. One year after the prescribed burning, SOC slightly increased and SWR recovered in the fire-affected fractions, while the AS for all aggregate sizes and depths showed a considerable decrease. The results suggest that the direct effects of burning are still present one year after burning, and the post-fire situation may pose an increased risk of soil loss. Furthermore, our results indicate that fine soil fractions are more likely to be affected by fire than coarser soil fractions and highly influence the whole soil behaviour.

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