The phytoremediation potential of native plants on New Zealand dairy farms

Responses to Airborne Ozone and Soilborne Metal Pollution in Afforestation Plants with Different Life Forms

With the current increases in environmental stress, understanding species-specific responses to multiple stress agents is needed. This science is especially important for managing ecosystems that are already confronted with considerable pollution. In this study, responses to ozone (O3, ambient daily course values + 20 ppb) and mixed metal contamination in soils (MC, cadmium/copper/lead/zinc = 25/1100/2500/1600 mg kg-1), separately and in combination, were evaluated for three plant species (Picea abies, Acer pseudoplatanus, Tanacetum vulgare) with different life forms and ecological strategies. The two treatments elicited similar stress reactions, as shown by leaf functional traits, gas exchange, tannin, and nutrient markers, irrespective of the plant species and life form, whereas the reactions to the treatments differed in magnitude. Visible and microscopic injuries at the organ or cell level appeared along the penetration route of ozone and metal contamination. At the whole plant level, the MC treatment caused more severe injuries than the O3 treatment and few interactions were observed between the two stress factors. Picea trees, with a slow-return strategy, showed the highest stress tolerance in apparent relation to an enhancement of conservative traits and an exclusion of stress agents. The ruderal and more acquisitive Tanacetum forbs translocated large amounts of contaminants above ground, which may be of concern in a phytostabilisation context. The deciduous Acer trees-also with an acquisitive strategy-were most sensitive to both stress factors. Hence, species with slow-return strategies may be of particular interest for managing metal-polluted sites in the current context of multiple stressors and for safely confining soil contaminants below ground.

The Potential of Myrtaceae Species for the Phytomanagement of Treated Municipal Wastewater

The use of native plants in land application systems for treated municipal wastewater (TMW) can contribute to ecological restoration. However, research on the potential of native species to manage the nutrients and contaminants contained in TMW is scarce. At a 10-hectare field site irrigated with TMW at >4000 mm yr-1, we investigated the distribution of nutrients and trace elements in the soil-plant system, comparing the New Zealand native Myrtaceae species Leptosperum scoparium and Kunzea robusta with pasture. The results showed that plant growth did not correlate with TMW irrigation rates. L. scoparium and K. robusta had higher foliar trace element concentrations than pasture, but these were not correlated with TMW irrigation rates. The pasture accumulated more N and P (68 kg of N ha-1 yr-1 and 11 kg of P ha-1 yr-1) than the Myrtaceae species (0.6-17 kg of N ha-1 yr-1 and 0.06-1.8 kg of P ha-1 yr-1). Regular harvesting of the pasture would likely remove more N and P from the site than the Myrtaceae species. The results highlight the importance of adjusting TMW application rates to the soil-plant capacity, in which case, native plants could provide ecological or economic value to TMW-irrigated land.

Plant Species Complementarity in Low-Fertility Degraded Soil

The aim of this study was to investigate the compatibility of plants with contrasting root systems, in terms of procurement of limiting soil nutrients. Paired combinations of species of proteas and grasses were grown in a pot experiment using soil from a site with impoverished vegetation and degraded soil. The soil contained sufficient N but was low to deficient in P, Mn, S, Fe, and B. The uptake of chemical elements into the foliage differed significantly according to whether the plants were growing as single or mixed species. When two species of Grevillea and grasses with evolutionary origins in low fertility soils were growing together, there was an enhanced uptake of P and Mn, in one or both species, in addition to other elements that were in low concentrations in the experimental soil. In contrast to this, Protea neriifolia that probably originated from a more fertile soil procured lesser amounts of the six elements from the soil when growing together with grasses. Two grasses tolerant of less fertile soils (Dactylis glomerata and Poa cita) obtained more nutrients when they grew together with proteas; this was a much stronger neighbour effect than was measured in Lolium perenne which is better adapted to high fertility soils. The findings illustrate both the functional compatibility and competition for plant nutrients in mixed-species rhizospheres. Species combinations substantially increased the acquisition of key elements from the soil nutrient pool.

Effects of dominant plant growth on the nutrient composition and bacterial community structure of manganese residues

The rhizospheres of three dominant plant species (Miscanthus floridulus, Buddleja lindleyana, and Erigeron annuus) growing in manganese residue disposal sites in eastern Guizhou Province, China, were analyzed to study the effects of plant growth on the nutrient levels and bacterial community structure of two types of manganese residues. The results showed that the growth of the three species improved the nutritional composition of manganese residues; the available nitrogen (AN) contents of the manganese mine residue significantly increased by 29.56-60.78% while the available phosphorus (AP) contents of the electrolytic manganese residue significantly increased by 30.24-44.41% compared to those in unvegetated manganese residue. The diversity of the bacterial community in the manganese mine residue increased significantly due to plant growth. Proteobacteria, Acidobacteria, and Bacteroidetes were the dominant phyla in both manganese residues. Sphingomonas and GP6 were the dominant bacterial genera. The relative abundance of the Firmicutes phylum was significantly higher in the manganese mine residue than in the control and that of the Thiobacillus genus was lower, which indicated improvements in the microenvironment. Correlation analysis showed that OM and AN were the main nutrient factors affecting the bacterial community structure in the manganese mine residue.Novelty statement At present, research on the phytoremediation of manganese residue disposal sites focuses mostly on the investigation of different plant types and their heavy metal accumulation and transformation characteristics. However, comparative studies of the differences in growth matrix characteristics between plant growth areas and exposed areas are lacking. In addition, dominant plant species are regionally distributed. The previous studies were mostly concentrated in Chongqing, Guangxi, and Hunan in China. The eastern region of Guizhou Province is located in the "Manganese Triangle" area of China, where the manganese resources account for about 50% of the national total. There is no report on the phytoremediation of manganese residue disposal sites in this region. Therefore, the rhizospheres of three dominant plant species (Miscanthus floridulus, Buddleja lindleyana, and Erigeron annuus) growing in manganese residue disposal sites in eastern Guizhou Province, China, were analyzed to study the effects of plant growth on the nutrient levels and bacterial community structure of two types of manganese residues (manganese mine residue and electrolytic manganese residue). This study could provide useful theoretical information to benefit the ecological restoration of manganese residue disposal sites.

Vegetation Options for Increasing Resilience in Pastoral Hill Country

Steep, uncultivable hill country below 1,000 m comprises about 40% of New Zealand's land surface area. Hill country farmers require options to increase the resilience of their farms to climatic and economic extremes while addressing soil conservation and water quality issues. We profile and discuss two options that can assist in transforming hill country. The first comprises a simple approach to grazing management in hill country pastures to increase pasture resilience and the second approach focuses on including selected forage shrubs (and trees) to create grazed pasture-shrublands. Deferred grazing, the cessation of grazing from flowering until seed dispersal of the desirable species in a pasture, is an old practice which has novel applications to improve resilience of hill country farming systems. We draw on current research and practitioner experience to demonstrate the impact of deferred grazing on the resilience of the deferred pasture and the farm system. We propose that deferred grazing will: (i) increase resilience of a pasture by enabling it to better recover from biotic and abiotic stresses and (ii) reduce the risk of nutrient and sediment losses in hill country by increasing ground cover, rooting depth and soil structural stability. Introducing woody forage shrubs into hill country pastures is another option that can improve farm profitability and resilience to current and future economic and climatic variabilities. The extensive root networks of shrubs can increase soil structural stability and reduce the risk of soil erosion. In addition, shrubs can supply many other ecosystem services, such as forage and shelter for livestock. In this paper, we discuss: (i) the potential benefits of a grazed pasture-shrubland at farm, landscape and national scales; (ii) candidate woody exotic and indigenous forage species; and (iii) priorities for research.

Developing a Landscape Design Approach for the Sustainable Land Management of Hill Country Farms in New Zealand

Landscape modification associated with agricultural intensification has brought considerable challenges for the sustainable development of New Zealand hill country farms. Addressing these challenges requires an appropriate approach to support farmers and design a better landscape that can have beneficial environmental outcomes whilst ensuring continued profitability. In this paper we suggest using geodesign and theories drawn from landscape ecology to plan and design multifunctional landscapes that offer improved sustainability for hill country farm systems and landscapes in New Zealand. This approach suggests that better decisions can be made by considering the major landscape services that are, and could be, provided by the landscapes in which these farm systems are situated. These important services should be included in future landscape design of hill country by creating a patterning and configuration of landscape features that actively maintains or restores important landscape functioning. This will help to improve landscape health and promote landscape resilience in the face of climate change. Through illustrating the potential of this type of approach for wider adoption we believe that the proposed conceptual framework offers a valuable reference for sustainable farm system design that can make an important contribution to advancing environmental management globally as well as in New Zealand.

Potential Use of Biosolids to Reforest Degraded Areas with New Zealand Native Vegetation

Biosolids could potentially be used for reforestation of degraded soils in New Zealand with native vegetation. Many native plant species of New Zealand thrive in low-fertility soils, and there is scant knowledge about their nutrient requirements. Therefore, it is unclear whether they will respond positively to the addition of biosolids. We used a pot trial to determine the responses of 11 native plant species to biosolids addition (10% w/w, ∼90 Mg hm) on two distinct degraded soils, Lismore stony silt loam and a Kaikōura sand. We also intended to prove that the soil microbial activity improves with the addition of biosolids, depending on the plant species. All species grew better in Lismore stony silt loam than the Kaikōura sand. All species in the Lismore stony silt loam responded positively to biosolids. The response to biosolids addition in the Kaikōura sand was variable, with four species showing no improvement in growth when biosolids were added. The nutrient status (N, P, S, Cu, and Zn) of all species improved when the two soils were amended with biosolids. However, some plant species, especially Sol. ex Gaertn. and Raoul, showed concerning concentrations of Cd (up to 2.4 mg kg). Dehydrogenase activity of soils (indicator of soil microbial activity) increased in biosolids-amended soils, with a strong species effect. Future work should involve field trials to determine the effect of biosolids addition on the establishment of native plant communities.