Phosphorus Fractions and Arbuscular Mycorrhizal Fungi Communities in a Tropical Coarse-Textured Soil under Natural Forest and Para Rubber Ecosystems

Abstract

Soil phosphorus (P) plays an essential role in rubber tree plantations that are rapidly and extensively being established in Southeast Asia. However, available information is quite limited on soil P fractions and arbuscular mycorrhizal fungi (AMF) in the tropical region. Herein, we investigated P fractions and AMF community under natural forest and rubber plantations at different ages of 5 years, 11 years, and 22 years in tropical coarse-textured soils from Thailand. The studied loamy sand soils were acidic (pH=5.0-5.7) with low available P concentrations (1.73-6.48 mg/kg). Data on the P fractions data revealed that the labile P (water-extractable Pi and NaHCO3-extractable Pi) and moderately labile P (NaOH0.1-extractable Po and HCl-extractable Pi) pools in rubber-growing soils were higher than those in the natural forest soil. Elevated values of these properties were substantial with increasing stand ages. The rubber monocropping systems declined in the density and diversity of AMF spores compared to the natural forest site. Glomus badium, Rhizophagus fasciculatus, Acaulospora Laevis, and Ambispora appendiculata were the most dominant and tolerant AMF species across the rubber stands (>50% of the total species). The P fractions and AMF were correlated with soil labile-P forms. Soil labile and moderately P fractions were the important factors affecting the difference in AMF community. This study highlighted that long-term rubber plantations in tropical ecosystems promoted labile P fraction but demoted AMF density and diversity.