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Karst is a widespread ecosystem with properties that affect the microbial activity and storage and cycling of soil organic carbon. The mechanisms underlying microbial resource availability in karst, which limit the microbial growth and activity in soil aggregates, remain largely unknown. We assessed the microbial resource limitations using exoenzymatic stoichiometry and key extracellular enzyme activities in bulk soil and aggregates in karst and non-karst forest soils. Soil organic carbon, total nitrogen, and microbial biomass carbon and nitrogen were significantly higher in bulk soil and the aggregate fractions in karst forests. However, the microbial biomass accumulation was higher in finer aggregates than in macroaggregate fractions. This may be attributed to the surface area of finer aggregates that increase the microbial C accumulation. In karst forests, the activity of extracellular enzymes β-d-glucosidase, β-N-acetylglucosaminidase, α-glucosidase, and α-d-1,4-cellobiosidase was two to three times higher in microaggregates (0.053–0.25 mm) and mineral fractions (<0.053 mm) than in macroaggregates. This coincided with the distribution of microbial biomass carbon and phosphorus in finer aggregate fractions. The microorganisms in bulk soil and aggregates in karst forests were largely co-limited by carbon and phosphorus and rarely by nitrogen and only by phosphorus in non-karst soils. The microbial phosphorus limitation in non-karst soils was alleviated in finer soil aggregates, while these fractions reflected slightly higher. microbial C limitations than bulk and other aggregates in karst forests. The patterns of microbial resource limitations in the bulk and aggregate fractions in karst ecosystems reflected the regulation of enzyme activity and soil organic carbon accumulation in finer aggregate fractions but not in other aggregates.

to follow up the effects of different doses of gamma ray on castor bean (Ricinus communis L.) grown on a sandy soil and irrigated with either fresh water or wastewater from El-Gabal El Asfar. Irradiation resulted in higher values of both fresh and dry weight of castor bean. This effect seemed more obvious by increasing the dose of gamma ray up to 50 Gy beyond which a gradual decrease occurred. Nitrogen, phosphorus and potassium contents in castor bean under the effect of gamma irradiation were arranged in the following descending order; 50Gy > 100Gy > 150Gy > 200Gy > 0 > 250Gy> 300 Gy. Nitrogen, phosphorus, potassium and oil contents in castor bean plants irrigated with wastewater were higher than the corresponding ones in plants irrigated with fresh water.

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