Nutrient cycling and soil-related processes under different land covers of semi-arid rangeland ecosystems in northern Iran

Abstract

There are contrasting reports about whether and how land covers influence soil organic matter fractions and microbial activities. To the best of the authors’ knowledge, the relationship between above-ground plant cover and the nutrient cycling in semi-arid areas, which are often considered as especially fragile and sensitive ecosystems, are almost unknown. The purpose of this research was to evaluate the influence of different shrub and grasslands located in northern Iran on the fractions of soil particulate and dissolved organic matter, microbial/enzyme activities. In this study, a total of 15 soil samples (30 × 30 × 10 cm) from each vegetation type [i.e. (1) Crataegus microphylla C. Koch., (2) Berberis integerrima Bunge., (3) Ribes Uva – crispa L., (4) Prunus spinosa L., (5) rangeland cover with dominant Lecokia cretica (Lam.) DC., Orchis mascula L., Cardamine bulbifera (L.) Crantz, and (6) rangeland cover with the dominance of Fragaria vesca L.] were transferred to the laboratory. Berberis significantly increased soil particulate organic C (2.26 g kg−1), but the maximum particulate organic N (0.27 g kg−1) was found under the Cratagus plant type. Soil dissolved organic C content was found to be significantly higher under Berberis (38.08 mg kg−1) ≈ Cratagus (34.81 mg kg−1), whereas the soil dissolved organic N was enhanced in Cratagus (22.84 mg kg−1) land cover. Significantly higher values of basal and substrate induced respiration (0.27 and 1.22 mg CO2 g−1 day−1, respectively) were found under Berberis when compared with the other land covers. Soil microbial biomass C and P were found to be significantly higher under Cratagus (259.90 and 61.00 mg kg−1) and Berberis (273.72 and 54.80 mg kg−1), whereas microbial biomass of N was enhanced under Cratagus (36.88 mg kg−1) plant type. Soil urease (18.22 µg NH4+–N g−1 2 h−1), acid phosphatase (305.66 µg PNP g−1 h−1), arylsulfatase (90.60 µg PNP g−1 h−1), invertase (97.53 µg Glucose g−1 3 h−1), geometric mean (4.73) and Shannon's diversity index (0.15) of enzyme activities were significantly increased in the topsoil of Cratagus compared with the other vegetation types. Based on principal component analysis (PCA), Cratagus, Berberis, and Ribes enhanced soil organic matter fractions, microbial and enzyme activities and were related to higher amounts of soil moisture, pH, organic C, total N, available P, fulvic/humic acids, and root biomass. Pasture and Prunus decreased the fractions of organic matter and soil microbial activities and most often affected the stoichiometry of carbon sources. It was concluded that shrubs (especially Cratagus and Berberis) can play a crucial role in nutrient cycling and soil-related processes in semi-arid rangeland ecosystems.