Companion species mitigate nutrient constraints in high country grasslands in New Zealand

Background: Experimental work using pot trials and mesocosm studies has indicated that species combinations are more effective than single species mitigating the soil nutrient constraints that limit pasture productivity in New Zealand’s hill country, but there is little field evidence to support this. Aim: We question whether coexistence of species provides an opportunity to facilitate enhanced uptake and improved procurement of key soil nutrients in these mid-altitude grasslands. Methods: Native and exotic legumes and co-occurring plant species were sampled according to whether they were growing together in close proximity or in single species patches. Foliar concentrations of nutrients were compared. Results: Nutrient concentrations in a native broom, Carmichaelia petriei, were higher when it was growing in combination with native tussock grasses. Higher concentrations of eight nutrients were recorded in foliage of an exotic legume, Lotus pedunculatus, when it was growing with native grasses or within the acuminate foliage of Aciphylla aurea (golden spaniard). Foliar concentrations of only P and Mn were elevated in white clover (Trifolium repens) foliage when it was growing in combination with grasses. Conclusions: These findings point to mutual facilitation of nutrient uptake by combinations of species growing together. Some species that are less desirable from an agricultural perspective improve acquisition of soil nutrients by the plant community. Novel native species assemblages represent a potential opportunity to refine pasture management, facilitating optimal exploitation of nutrients. This could reduce fertiliser requirements and enhance and protect native biodiversity in pastoral grasslands