Response of a pioneering species (Leptospermum scoparium J.E.Forst. & G.Forst.) to heterogeneity in a low-fertility soil

12 páginas.-- 6 figuras.-- 2 tablas.-- 35 referencis.-- The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fpls.2019.00093/full#supplementary-materialRoot foraging may increase plant nutrient acquisition at the cost of reducing the total volume of soil explored, thereby reducing the chance of the roots encountering additional patches. Patches in soil seldom contain just one nutrient: the patch may also have distinct textural, hydrological, and toxicological characteristics. We sought to determine the characteristics of root foraging by a pioneering species, Leptospermum scoparium, using pot trials and rhizobox experiments with patches of biosolids. The growth of L. scoparium was increased by <50 t/ha equiv. of biosolids but higher doses were inhibitory. Roots foraged patches of biosolids in a low-fertility soil. There was no evidence of chemotaxis, rather, the roots proliferated toward the patch of biosolids, following chemical gradients of nitrate. While the biosolids also contained high concentrations of other nutrients (P, K, and S), only significant chemical gradients of nitrate were found. Once the roots encountered a patch of biosolids, the growth of the plant increased to a level similar to plants growing in soil homogeneously mixed with biosolids or surface-applied biosolids. Our results indicate that roots forage nitrate, which is mobile in soil, and that gradients of nitrate may lead to patches containing other less mobile nutrients, such as phosphate or potassiumThis study was funded by the Centre for Integrated Biowaste Research which is supported by ESR Strategic Science Investment Funding from the Ministry of Business, Innovation and Employment, New Zealand. MG-G held a fellowship granted by Fundación Ramón Areces. EM thanks the financial support for her work at Lincoln University, New Zealand, from Program Salvador de Madariaga of the Spanish MECD.Peer reviewe

Mānuka (Leptospermum scoparium) roots forage biosolids in low fertility soil

Potentially, biosolids could be applied to low fertility or degraded soils to establish mānuka (Leptospermum scoparium), an economically important plant species used for honey and essential oil production. Given that this pioneering species is adapted to low-fertility soils, it is unclear whether it would respond positively to biosolids. We aimed to determine the growth, root morphology and elemental uptake of L. scoparium in contrasting soils amended with biosolids, distributed either homogeneously or heterogeneously. Pot and rhizobox experiments revealed that the roots of L. scoparium morphologically foraged patches of biosolids in soil. This finding is in contrast to previous reports that foraging is uncommon in plants adapted to low fertility soils. In a low-fertility sand, biosolids increased the growth 40-fold, irrespective of the distribution of biosolids. This increase was lower (60%) in an orthic brown soil. In the biosolids-amended soils, the foliar concentrations of N, P, K, S, Mg and Ca were above 2%, 1.5 g kg⁻¹, 0.8%, 2.0 g kg⁻¹, 1.7 mg kg⁻¹ and 0.8% respectively, which is within the range of concentrations found in native species in their natural habitat. In the control soils, foliar concentrations of N, P & S were significantly lower, indicating that these elements may be limiting. The maximum concentration of Mn (660 mg kg⁻¹), Zn (211 mg kg⁻¹), and Cd (1.5 mg kg⁻¹) in leaves of plants growing in biosolids-amended soil should not cause concern to plant health, but it should be taken into account for their potential effect on trophic networks. Further experiments should focus on the design of field-scale applications of biosolids for improving L. scoparium growth and determine the effect of biosolids distribution on nutrient losses

Chemical elements and the quality of mānuka (Leptospermum scoparium) honey

Soil properties in the foraging range of honeybees influence honey composition. We aimed to determine relationships between the antimicrobial properties of New Zealand mānuka (Leptospermum scoparium) honey and elemental concentrations in the honey, plants, and soils. We analyzed soils, plants, and fresh mānuka honey samples from the Wairarapa region of New Zealand for the chemical elements and the antimicrobial activity of the honey as indicated by methylglyoxal (MGO) and dihydroxyacetone (DHA). There were significant negative correlations between honey MGO and the concentrations of Mn, Cu, Mg, S, Na, Ba, K, Zn, and Al. These elements may provide a low-cost means of assessing mānuka honey quality. For individual elements, except for K, there were no correlations between the honeys, plants, and soils. Soil nitrate concentrations were negatively correlated with concentrations of MGO and DHA in the honey, which implies that soil fertility may be a determiner of mānuka honey quality

Risks and benefits of pasture irrigation using treated municipal effluent : A lysimeter case study, Canterbury, New Zealand

Compared to discharge into waterways, land application of treated municipal effluent (TME) can reduce the need for both inorganic fertilizers and irrigation. However, TME irrigation may result in the accumulation of phosphorus (P) or trace elements in soil, and increased salinity and sodicity, which could damage soil structure and reduce infiltration. TME irrigation can also result in groundwater contamination through nitrate leaching or surface water contamination through runoff. This study aimed to evaluate the effects of increasing TME irrigation rates on quantity and quality of leachate and pasture growth in a lysimeter experiment using a Fluvial Recent soil and a Fragic Pallic soil. Pasture growth in the lysimeters was up to 2.5-fold higher in the TME treatments compared to the non-irrigated treatments. There were no signs of toxicity or accumulation of B, Al, Cd, Cu, Fe, Mn, As, and Zn. TME significantly increased the concentration of P and Na in the pasture. Nitrogen leaching from the lysimeters was negligible (< 1 kg/ha⁻¹ equiv.) in all treatments, but mineral N accumulated in the soil profile of the highest application rate (1672 mm/yr). Although more P was added than removed in pasture, the rate of accumulation indicated that over a 50-year period, P will still be within the current New Zealand thresholds for grazed pastures. Sodium accumulated in the soil columns in all the TME treatments. The rate of accumulation was not proportional to the TME application rate, indicating that Na was moving down through the soil profile and leaching. Results indicate a low to moderate risk of sodicity in soil or toxicity in plants caused by Na

Phytoremediation of microbial contamination in soil by New Zealand native plants

Novel research has demonstrated that the roots of some bioactive plants - called pathogen phytoremediation plants - enhance die-off of pathogenic organisms in the soil. Strategic establishment of pathogen phytoremediation plants may reduce the transport of human pathogens to water sources. Such plantings could be used in riparian margins, as buffer strips to protect drinking water supplies, or block planting in ‘critical source areas’ of microbial contamination, such as grazing paddocks, organic waste – including sewage sludge - amended land, animal feedlots and housing facilities, and manure storage areas. This work aimed to investigate the antimicrobial activity of a range of New Zealand native plants known for their antimicrobial potential from previous research or through indigenous knowledge, and to assess if any of them could potentially be used for pathogen phytoremediation. Two laboratory screening experiments demonstrated the antimicrobial activity of Leptospermum scoparium, including the local variety swamp mānuka, Kunzea ericoides, Pseudowintera colorata, and Metrosideros robusta against three human pathogens and two indicator organisms. A greenhouse experiment showed a 90% reduction of Escherichia coli numbers in dairy shed effluent irrigated pots after 14 days in soils under swamp L. scoparium and M. robusta, compared with 45 days in soil under Lolium perenne. The pH in the soil under swamp L. scoparium and M. robusta was significantly lower than under L. perenne, which could partially explain the faster E. coli reduction