Soil quality and mesofauna diversity relationship are modulated by woody species and seasonality in semiarid oak forest

Abstract

The relationships between woody species, soil biota activity and soil quality were largely ignored in semi-arid areas. This study evaluated the influence of life form and seasonal variation on the mesofauna activity and soil chemical and microbial properties under three tree species (Quercus brantii (QU), Acer monspessulanum (AC) and Pistacia atlantica (PI), and three shrub species (Crataegus puntica (CR), Amygdalus scoparia (AM) and Lonicera nummularifolia (LO)) in a semiarid oak forest in western Iran. Soils were sampled beneath each individual woody species in spring and winter. Soil chemical and biological properties and soil mesofauna diversity were measured and soil quality index (SQI) was produced. The comparison of soil chemical properties under tree and shrub species showed that only soil total nitrogen (Ntot), available potassium (Kava) and soil organic carbon (SOC) were significantly higher under trees than shrubs (respective mean values for spring: 0.31 vs 0.19%; 1304 vs 1103 mg/kg, 3.94 vs 3.16%). In contrast, all of the studied soil biological characteristics including microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), basal respiration (BR), and substrate induced respiration (SIR) were significantly higher under trees than under shrubs (respective mean values for spring in mg/kg soil/day: 603.5 vs 431.2, 49.6 vs 35, 46 vs 35 and 57.6 vs 36.5). Besides, we found clear seasonal and species effects for most soil properties. Values were higher in spring than in winter and were the most similar for QU and AC for tree species (especially due to the higher content of SOC and MBN under these species in spring) and for AM and LO for shrub species. The Shannon-Wiener diversity index and richness of the soil mesofauna were significantly higher under trees than under shrubs (respective mean values for spring: 1.59 vs 1.09 and 6.5 vs 3.8). The Shannon-Wiener diversity and richness indices for soil mesofauna were positively linearly related to the soil quality index (SQI) in spring and winter. These relationships were weaker in winter than in spring and showed an increase of both indices from shrubs (LO, AM and CR) with low SQI values to trees (QU and AC) with higher SQI values. Based on these results, we conclude that these indices can be used as efficient soil bioindicators which can be helpful in restoration or conservation projects in semi-arid areas.