Interactive relationship between plant growth and soil chemical properties in a mangrove afforestation stand, Kiribati

Abstract

Purpose There is increased recognition of the importance of mangroves worldwide, with efforts being made to sustainably manage these ecosystems for forestry and fishery use. Although successive monitoring of mangrove growth after planting has been conducted in some afforestation stands, measurements of soil environmental changes accompanying the plant growth have not been made in most stands. In this study, we observed the interactive relationship between the growth of mangrove, Rhizophora stylosa, and soil chemical properties at an afforestation stand on Tarawa atoll, Kiribati.Methods We first estimated root biomass in the stand. Next, we measured the concentrations of dissolved phosphorus, nitrogen, and other ions (Br−, Ca2+, K+, Na+, Cl−, and SO42−) in soil pore water, as well as the isotopic ratio of leaf carbon and nitrogen in patches of different plant ages. Results Differences in salt stress among the patches were reflected in leaf δ13C, suggesting it would be a good indicator of the physiological response of mangrove plants to salinity. Estimated root biomass was positively related with phosphate and nitrate concentrations in soil pore water, indicating the formation of a rhizosphere environment with the occurrence of root–microorganism interactions. Leaf δ15N analysis suggested that the discrimination of nitrogen isotopes during nitrification and/or uptake of NH4+ and NO3− occurs in accordance with plant growth. Conclusions Our findings revealed the changes that occur in the chemical properties of mangrove leaves and soil pore water after mangrove plantation on a yearly basis, which can improve our understanding of environmental succession during the formation of mangrove ecosystems.