Effect of mānuka (Leptospermum scoparium) on nitrogen and Escherichia coli reductions in soils: a field experiment

Purpose Planting strategies can be effective mechanisms to reduce diffuse pollution from agricultural catchments reaching water bodies. Plants with antimicrobial properties such as mānuka (Leptospermum scoparium) demonstrated in controlled conditions the ability to inhibit nitrification and growth of pathogens in soils. This potential in a real on-farm setting was still to be investigated. Methods In a stock-excluded riparian area, planted with mānuka on a dry stock farm, synthetic excrement patches high in urea (950 kg N ha−1 equiv.) and Escherichia coli (7.9 × 109 cfu plant-1) underneath mānuka saplings and pasture were applied. Soil was sampled at three depths over 21 days after the excrement application and analysed for total C and N, inorganic N, pH, soil moisture and E. coli. Results There was no significant difference between the pasture and mānuka for total C and N, C:N ratio, and soil moisture. E. coli was only different between both at 20–30 cm deep. NO3− - N and NH4+ - N concentrations were significantly lower under mānuka compared to pasture for the upper two soil depths (NO3− - N: 109 mg kg−1 vs 205 mg kg−1 in the topsoil). Conclusions The results of this study indicate that mānuka may inhibit urease activity and nitrification and could reduce on-farm nitrate leaching, while also highlighting that field conditions make quantifying such phenomenon more complex.

Genome-wide patterns of genetic diversity, population structure and demographic history in mānuka (Leptospermum scoparium) grown on indigenous Māori land

Leptospermum scoparium J. R. Forst et G. Forst, known as mānuka by Māori, the indigenous people of Aotearoa (New Zealand), is a culturally and economically significant shrub species, native to New Zealand and Australia. Chemical, morphological and phylogenetic studies have indicated geographical variation of mānuka across its range in New Zealand, and genetic differentiation between New Zealand and Australia. We used pooled whole genome re-sequencing of 76 L. scoparium and outgroup populations from New Zealand and Australia to compile a dataset totalling ~2.5 million SNPs. We explored the genetic structure and relatedness of L. scoparium across New Zealand, and between populations in New Zealand and Australia, as well as the complex demographic history of this species. Our population genomic investigation suggests there are five geographically distinct mānuka gene pools within New Zealand, with evidence of gene flow occurring between these pools. Demographic modelling suggests three of these gene pools have undergone expansion events, whilst the evolutionary histories of the remaining two have been subjected to contractions. Furthermore, mānuka populations in New Zealand are genetically distinct from populations in Australia, with coalescent modelling suggesting these two clades diverged ~9 –12 million years ago. We discuss the evolutionary history of this species and the benefits of using pool-seq for such studies. Our research will support the management and conservation of mānuka by landowners, particularly Māori, and the development of a provenance story for the branding of mānuka based products.

Genome-wide patterns of genetic diversity, population structure and demographic history in mānuka (Leptospermum scoparium) grown on indigenous Māori land

Leptospermum scoparium J. R. Forst et G. Forst, known as mānuka by Māori, the indigenous people of Aotearoa (New Zealand), is a culturally and economically significant shrub species, native to New Zealand and Australia. Chemical, morphological and phylogenetic studies have indicated geographical variation of mānuka across its range in New Zealand, and genetic differentiation between New Zealand and Australia. We used pooled whole genome re-sequencing of 76 L. scoparium and outgroup populations from New Zealand and Australia to compile a dataset totalling ~2.5 million SNPs. We explored the genetic structure and relatedness of L. scoparium across New Zealand, and between populations in New Zealand and Australia, as well as the complex demographic history of this species. Our population genomic investigation suggests there are five geographically distinct mānuka gene pools within New Zealand, with evidence of gene flow occurring between these pools. Demographic modelling suggests three of these gene pools have undergone expansion events, whilst the evolutionary histories of the remaining two have been subjected to contractions. Furthermore, mānuka populations in New Zealand are genetically distinct from populations in Australia, with coalescent modelling suggesting these two clades diverged ~9 –12 million years ago. We discuss the evolutionary history of this species and the benefits of using pool-seq for such studies. Our research will support the management and conservation of mānuka by landowners, particularly Māori, and the development of a provenance story for the branding of mānuka based products.

Leptospermum scoparium (manuka).

A datasheet on Leptospermum scoparium covering, as an economically important tree, its taxonomy, importance, silviculture, distribution, biology and ecology, uses, products and pests.