Effects of soil tillage and planting grass on arbuscular mycorrhizal fungal propagules and soil properties in citrus orchards in southeast China

Abstract

Arbuscular mycorrhizal (AM) fungi play important roles in plant nutrition and soil conservation. AM fungal activity and amount of glomalin (a glycoprotein derived from AM fungi) are influenced by a series of abiotic and biotic factors associated with changes in soil management. However, the informations concerning AM fungal activity, amount of glomalin-related soil protein (GRSP), and its relationship with soil fertility and enzyme activities are scarce in citrus orchards under different soil management systems. Accordingly, this paper reports the effects of tilling soil and planting grass on AM colonization; AM fungal propagules; the amount of GRSP and its relationship with soil chemicals including organic carbon, available nitrogen, Olsen phosphorus, and available potassium; the activity levels of soil enzymes like catalase, invertase, urease, and acid phosphatase in citrus (Citrus unshiu Marc. grafted on Poncirus trifoliata L. Raf.) orchards in southeast China. Measurements were conducted in the fifth year of an ongoing tillage and grass planting experiment on an Acrisol soil under one of three treatments: natural grass cover, sod culture with white clover, and clean tillage. Soils and roots were sampled in March, July, and November 2013, during the vigorous growth period of citrus trees. AM colonization, AM fungal propagules, and GRSP were significantly higher in both no-tillage and grass-planted orchards than in clean tillage orchards. Soil organic carbon, available nitrogen, and soil enzyme activities showed a similar trend. Principal component analysis revealed that tillage and grass planting dramatically affected soil conditions in citrus orchards. However, sod culture promoted citrus mycorrhizal colonization and available nitrogen in soil more effectively than did grass cover, whereas natural grass cover enhanced AM fungal propagules, soil organic carbon, and soil enzyme activities more effectively than did sod culture. Soil organic carbon, available nitrogen, and soil enzymes activities were significantly (P<0.05) correlated with AM fungal propagules or GRSP, suggesting that plentiful AM symbionts may help preserve soil quality, especially in grass-planted orchards.