Nurse effects mediated by acid-tolerance of target species and arbuscular mycorrhizal colonization in an acid soil

Abstract

We tested whether a nurse-plant effect depends on target-seedling tolerance to soil acidity and arbuscular mycorrhizal fungi (AMF) in an acid soil. A mesocosm experiment was used to assess the acid-tolerance of the seedlings of four target species. Field experiment 1 tested the nurse effects of an adult plant (Lespedeza formosa) on germination rate, seedling survival rate, growth and AMF colonization rate of target seedlings growing in an acid soil. Field experiment 2 tested the influence of AMF root colonization on nurse-plant effects. Target species greatly varied in their tolerance to soil acidity while nurse-effect on target species were mediated by target species acid-tolerance and AMF root colonization. In field experiment 1, as expected, nurse-effect was positive for acid-sensitive species and negative for acid-tolerant species. While nurse plant presence facilitated the germination, survival, growth, and AMF colonization of the two acid-sensitive species it competed with the two acid-tolerant species. In field experiment 2, the nurse plant facilitated the growth of the acid-sensitive seedlings more under AMF not suppressed treatment than AMF suppressed treatment. For the acid-tolerant seedlings, however, the nurse plant reduced their growth under AMF not suppressed treatment, but did not affect their growth under AMF suppressed treatment. Nurse plant facilitated the acid-sensitive species in an acid soil, and the facilitation was enhanced by increasing AMF in the soil. These findings highlight how acid-tolerance of target species and AMF colonization mediates nurse plant facilitation and has important implications for the use of nurse plants in the restoration of acid soils ecosystems.