Native plants and nitrogen in agricultural landscapes of New Zealand

Abstract

Background and Aims: The Canterbury Plains of the South Island, New Zealand are being converted to intensive dairy farming; native vegetation now occupies < 0.5 % of the area. Reintroducing native species into nutrient-rich systems could provide economic, environmental and ecological benefits. However, native species are adapted to low nitrogen (N) environments. We aimed to determine the growth and N-uptake response of selected native species to elevated soil N loadings and elucidate the effect of these plants on the N speciation in soil. Methods: Plant growth, N-uptake, and N speciation in rhizosphere soil of selected native species and Lolium perenne (ryegrass, as reference) were measured in greenhouse and field trials. Results: At restoration sites, several native species had similar foliar N concentrations to ryegrass. Deciduous (and N-fixing) species had highest concentrations. There was significant inter-species variation in soil mineral N concentrations in native plant rhizospheres, differing substantially to the ryegrass root-zone. Pot trials revealed that native species tolerated high N-loadings, although there was a negligible growth response. Among the native plants, monocot species assimilated most N. However, total N assimilation by ryegrass would exceed native species at field productivity rates. Conclusions: Selected native plant species could contribute to the sustainable management of N in intensive agricultural landscapes.