Difference in Phosphorus Acquisition Strategies of N2-Fixing Plants in Shrubland and Primary Forest Soils of the Karst Regions

Abstract

Phosphorus (P) acquisition strategies of plants to adapt to P limitation in primary forest ecosystems of karst regions remain unclear. Root phosphatase and arbuscular mycorrhizal (AM) fungi, involved in two common P acquisition strategies, were measured in two N2-fixing plants (Albiziaodoratissima and Cajanuscajan) growing in shrubland and primary forest soils with and without soil AM inoculation. Both plants cultivated in primary forest soils had lower AM colonisation and N2 fixation rates but higher root acid phosphatase activity in the rhizosphere when compared with those in shrubland soils. Plants in shrubland soils predominantly exploit P resources by stimulating AM colonisation of roots, but do so by enhancing root phosphatase activity in primary forest soils. AM colonisation in both N2-fixing plants was positively correlated with N2 fixation rates but negatively correlated with root acid phosphatase activity. Soil available P content was higher in both N2-fixing plants under soil inoculation with AM fungi than in the treatment without fungal inoculation; root and shoot P content did not vary significantly between treatments. AM fungi and phosphatase enzymes increase N2-fixing plants’ capacity to obtain soil P, thus contributing to the decrease in soil P limitation in karst ecosystems.