Geographic isolates of Glomus increase root growth and whole-plant transpiration of Citrus seedlings grown with high phosphorus

Four Glomus species/isolates from arid, semiarid and mesic areas were evaluated for their effects on growth and water use characteristics of young Citrus volkameriana ('Volkamer' lemon) under well-watered conditions, followed by three soil-drying episodes of increasing severity (soil moisture tensions of -0.02, -0.06, and -0.08 MPa) and recovery conditions. Arbuscular mycorrhizal (AM) plants were also compared to non-AM plants given extra phosphorus (P) fertilizer. AM plants and non-AM plants had similar shoot size (dry weight and canopy area), but all AM fungus treatments stimulated root growth (dry weight and length). Leaf P concentrations were 12-56% higher in AM plants than non-AM plants. Enhanced root growth was positively correlated with leaf P concentration. In general, AM plants had greater whole-plant transpiration than non-AM plants under well-watered conditions, under mild water stress and during recovery from moderate and severe soil drying. This suggests a faster recovery from moisture stress by AM plants. AM plants had lower leaf conductance than non-AM plants when exposed to severe soil drying. Although the greatest differences were between AM and non-AM plants, plants treated with Glomus isolates differed in colonization level, leaf P concentration, root length, transpiration flux and leaf conductance.