Abstract
The arbuscular mycorrhizal (AM) status [total AM colonization (RLT), percentage of root length with arbuscules (RLA) and vesicles (RLV), spore density and hyphal length density], microbial populations and soil enzyme activities were investigated in citrus (Satsuma Mandarin grafted on Poncirus trifoliata L. Raf) orchards. Two types of no-tillage soil management, natural grass cover and use of herbicides, were employed in these orchards. The citrus AM colonization (37.26-70.09%) was high in all the experimental orchards sampled. The highest RLA (43.83%), spore density (384.63 spores/100 g soil), hyphal length density (4.09 m g–1 soil), rhizospheric microbial populations and enzyme activities were observed in the orchards with a natural grass cover, and the lowest values, except urease activity, were found in the orchards treated with herbicides. Spore density, hyphal length density, catalase activity and phosphatase activity varied notably between no-tillage/natural grass and no-tillage/herbicides treated orchards in the soil layers above 40 cm. A correlation analysis showed that the hyphal length density and organic matter were significantly positively correlated. Soil enzyme activities, except phosphatase, were strongly correlated with the bacteria populations. The data presented here demonstrates that the RLA, spore density, hyphal length density, rhizospheric microbe populations and enzyme activities were significantly better in the soil layers above 40 cm of orchards with a natural grass cover than herbicidetreated soils. So, the establishment of a natural grass cover benefits soil quality in citrus orchards in Southern China.
Highlights
Arbuscular mycorrhizal fungi (AMF) are ubiquitous components of most agroecosystems and inhabit both plant roots and surrounding soils
The results indicate that no significant (p > 0.05) relationships were found among the relationships between the total AM colonization (RLT) and the spore density (SD) or hyphal length density (HLD), and no significant (p > 0.05) relationship between the RLT and soil enzyme activities
All citrus rootstocks were heavily colonized by native AMF, and the RLT levels varied significantly in the citrus roots between the different soil layers, especially in the NH orchards
Summary
Arbuscular mycorrhizal fungi (AMF) are ubiquitous components of most agroecosystems and inhabit both plant roots and surrounding soils. The formation of the AM symbiosis can change the composition of the microbial community in the rhizospheric soil (Schreiner et al, 1997) and its activity (Olsson et al, 1996) This change might be a consequence of the competition for energy-rich carbon compounds (Christensen and Jakobsen, 1993) or to an indirect influence through the quantity and quality of plant root exudates and soil structure (Johansson et al, 2004)
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