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Positive interspecific plant–plant interactions in (semi-)arid ecosystems are crucial for supporting ecosystem diversity and stability, but how interactions respond to grazing combined with temporal variation in drought is poorly understood. In a semi-arid area in south-eastern Spain (Murcia region), we planted 1280 saplings of the palatable shrub Anthyllis cytisoides (beneficiary) under the canopy of the unpalatable shrub Artemisia herba-alba (nurse) or in open microsites between shrub patches. We applied four grazing treatments (no grazing, low goat grazing pressure, high goat grazing pressure and rabbit grazing) and two watering treatments. Sapling height and survival were followed for two consecutive years, during which one extreme drought event occurred. We analysed how grazing, watering and their combination affected nurse effects throughout the course of the study. Grazing and the drought event, but not watering, significantly altered the nurse effects. Under ungrazed conditions prior to the extreme drought event, nurse effects on sapling survival were neutral, whereas they were positive at rabbit-grazed plots. At low goat grazing, sapling growth was higher under nurse shrubs than in open microsites. However, after the extreme drought event, sapling survival was higher in open microsites at ungrazed plots, whereas at rabbit-grazed plots, nurse effects shifted from positive to neutral. Our findings highlight the importance of rabbit grazing in determining the direction of plant–plant interactions in arid ecosystems. Moreover, our findings support the idea that positive plant–plant interactions may wane under the combination of high grazing and drought stress. [ABSTRACT FROM AUTHOR]

Abstract: Long-term soil salinity data are required to properly manage saline habitats. This study presents easy procedures for comparing soil salinity profiles, which were used to assess four saline wetlands in NE Spain. Soil salinity measurements at sites where different halophytes were dominant were recorded throughout the year in 1979–1980 and 1999–2000, with additional measurements in 1985. Electrical conductivity of saturation extracts (ECe) and the concentrations of major ions were measured in four hundred soil samples. To confirm the consistency of the quality of the lab measurements, we used saturation percentage (SP) statistics and the relationships between ECe and both the cationic and the anionic concentrations in the extracts (R2 >97%), and the relationship with the EC of the extracts at a soil-to-water ratio of 1:5 by weight (EC 1:5). The ECe of the soil samples ranged from 4 to 114dSm−1, and the averages in the four wetlands (AN, PC, AL, and AG) were 38.6, 10.1, 22.3, and 68.5dSm−1, respectively. The median of the sodium adsorption ratio [SAR, (meqL−1)0.5] in the samples was 69, 126, 64, and 28, respectively. At AN, the maximum average ECe in the upper 100cm of the soil was 35.0dSm−1 for Artemisia herba-alba and 75.2dSm−1 for Suaeda vera; at PC, the maximum value was 19.3dSm−1 for Puccinellia festuciformis; and, at AL, it was 30.3dSm−1 for Salicornia ramosissima and 44.6dSm−1 for S. vera. At AG, the maximum average ECe was 69.2 for S. vera, and 85.2dSm−1 for Arthrocnemum macrostachyum. The ECe and SAR remained stable between the two sampling periods in three of the wetlands but, in AL, which was converted into a paddy, ECe was reduced from ~40dSm−1 to ~2dSm−1 and SAR was reduced from >77 to ~2. The presence of saline non-sodic and saline–sodic soils at nearby wetlands reflects the pedodiversity of the area. [Copyright &y& Elsevier]