Nicholas M. Dickinson

Pastoral grasslands in New Zealand's mountainous landscapes contribute substantially to a primarily agricultural national economy. This landscape supports mosaics of regenerating indigenous biodiversity among more productive naturalized exotic herbage, each raising fundamental ecological, agronomic, and environmental concerns. Our objective was to investigate whether increased or lesser attention to native plant assemblages in these vegetation mosaics significantly influences soil carbon (C) stocks. At mid‐altitudes below the original tree line, we compared paired plots of regenerating successional endemic myrtaceous woody shrub communities ( Kunzea ericoides , kānuka) with exotic pasture at comparable slopes and aspects. We also investigated native snow tussock grass communities, the dominant vegetation at higher altitudes bordering the original tree line. Soils beneath kānuka had significantly higher C concentrations, C stocks, and carbon:nitrogen (N) ratios than adjacent areas of pasture. Soil C stocks were 15.43% higher under kānuka than under adjacent pasture. The bases of snow tussocks were frequently raised 10–20 cm above the surrounding inter‐tussock land surface with a sparse vegetation cover that provides pathways for stock, making them more susceptible to soil erosion. Soil directly beneath the snow tussocks had significantly higher C, nitrogen, and phosphorus (P) in comparison with adjacent inter‐tussock spaces. Soil C stocks were 38.7% higher under snow tussock than in the adjacent inter‐tussock spaces. Our findings indicate that maintaining and enhancing endemic woody shrub and snow tussock assemblages is beneficial to productive and sustainable pasturage, while also playing a significant role in biodiversity conservation and climate change mitigation.

Some biostimulant products provide proven benefits to plant production, potentially offering more environmentally friendly, sustainable, and natural inputs into production systems. However, the transference and predictability of known benefits between different growth environments, application protocols, and management systems are fraught with difficulty. In this study, we carried out carefully controlled glasshouse and in vitro assays with applications of humic acids, protein hydrolysates, and seaweed extract to compare the variability of biostimulant effects and dosage-dependent variations across diverse conditions, encompassing a sufficient range to comprehensively assess their full spectrum of impacts. The results demonstrated a clear trend of dosage-dependent effects with each biostimulant exhibiting a significant growth-promoting effect within a critical concentration range, but detrimental effects when the concentration fell outside this range. While substantial growth-promoting effects were observed under glasshouse conditions, biostimulant applications tended to be more sensitive and generally led to negative impacts in sterilised conditions. The combined use of biostimulants mostly resulted in detrimental and toxicological responses with only two combined treatments showing marginal synergistic effects. The findings demonstrated a complex interplay between biostimulants and the growth conditions of plants. Lack of knowledge of the indirect effects of different growth media may result in negative impacts of biostimulant applications and combinations of products outside narrow critical concentration ranges.

Nutrient constraints in low-fertility soil were modified by different species combinations. Grass-clover assemblages benefited both species in terms of nutrient procurement. Interplay of competition and facilitation is demonstrated. An invasive weed removed essential nutrients from the grazing cycle. To investigate the interplay of competition and facilitation between plants in low-fertility pasture grasslands of New Zealand, we compared nutrient uptake and acquisition of key nutrients of three species from different functional groups. Combinations of Pilosella officinarum (mouse-eared hawk-weed, an invasive weed), Trifolium repens (white clover, a nitrogen fixer) and Dactylis glomerata (cocksfoot, a pasture grass) were planted into a soil with low-to-deficient concentrations of key nutrients. Highest yields were achieved by the grass growing alone but, when the clover and grass had grown together, there were complementary benefits in terms of procurement of a wide range of nutrients from soil despite lower root biomass. The invasive weed negated these benefits, and soil nutrients were exploited less efficiently when Pilosella had grown alone or in a mixture with the other species. Competition from the weed removed the benefits of grass-legume coexistence. These findings are interpreted to suggest that requirements for legumes to be the main source of nitrogen in pasture grasslands may be compromised unless competitive weeds are controlled to avoid disrupted procurement of key nutrients. It is likely these constraints to nutrient procurement would similarly impact conservation grasslands.

Rhizobial nitrogen fixation in legumes provides spillover benefits to neighbouring plants such as pasture grasses. Generally, it is understood to be unidirectional between plant functional groups, providing a benefit from legumes to grasses. We question whether bidirectional complementarity also exists in terms of exploiting the wider soil nutrient pool. We test this hypothesis using soil cores with their component vegetation assemblages sampled from a hill country pasture in South Island, New Zealand. The soil was deficient in key essential elements: P, S, B, Mo and Ni. Facilitation from grasses to clovers was evident; legume–grass mixtures procured more nutrients from the soil than when either species was growing alone. When grasses and clover grow together in unfertilized grassland, more nitrogen is procured by the plant community, and other limiting plant nutrients in the soil are better exploited. Coexistence with grasses is favourable to clovers in terms of soil biogeochemistry.

BackgroundExperimental work using pot trials and mesocosm studies has indicated that species combinations are more effective in mitigating the soil nutrient constraints that limit pasture productivity in New Zealand’s hill country, but there is little field evidence to support this.AimWe question whether coexistence of species provides an opportunity to facilitate enhanced uptake and improved procurement of key soil nutrients by assemblages of plants in these mid-altitude grasslands.MethodsNative 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.ResultsUptake of nutrients by a native broom,Carmichaelia petriei, was enhanced when it was growing in combination with native tussock grasses. Enhanced uptake of eight nutrients was recorded in foliage of an exotic legume,Lotus pedunculatus, when it was growing with native grasses or within the acuminate foliage ofAciphylla 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. Overall, mutual facilitation of nutrient uptake by combinations of species growing together was in evidence.ConclusionsSome species that are less desirable from an agricultural perspective may improve acquisition of soil nutrients by the plant community. Novel native species assemblages represent an opportunity to refine pasture management. Exploiting combinations of plant species that facilitate optimal exploitation of nutrients could reduce fertiliser requirements, enhancing and protecting biodiversity in pastoral grasslands.

Improved predictability of the effectiveness of biostimulant products is required before their wider acceptance by ornamental plant growers. We investigated the effects of three of the main groups of biostimulants (humic acids, protein hydrolysates, and seaweed extracts) under six fertilization levels, using Antirrhinum majus L. as a model ornamental plant to evaluate potential interactive effects on plant performance and growth substrate biological activity. Number of leaves increased in response to biostimulant application, but leaf area was generally reduced, especially in potting mix with lower fertility. Seaweed extract had beneficial effects on both shoot and root dry mass accumulation but was less beneficial than higher fertilizer rates. The beneficial effects of protein hydrolysates and humic acids were marginal and less predictable under our experimental conditions; humic acids showed particularly negative effects on root dry mass accumulation. All biostimulants showed negative impacts on substrate microbial activity, although Dehydrogenase Activity (DHA) was substantially higher under lower fertility. Extrapolation of the results of this study suggests that it is feasible to apply biostimulants, particularly seaweed extracts, to improve the overall growth performance of ornamental plants. However, it is essential to consider the nutrient status of growth medium if we are to leverage the biostimulant paradigm in the ornamental plant sector.

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.

Kānuka (Kunzea serotina, Myrtaceae) dryland shrubland communities of the lowland plains of South Island (Te Wai Pounamu), New Zealand (Aoteoroa), contain a ground cover largely consisting of mosses, predominantly Hypnum cupressiforme. There has been no previous study of the role of mosses in this threatened habitat which is currently being restored within a contemporary irrigated and intensively farmed landscape that may be incompatible with this component of the ecosystem. The aim of the present study was to investigate the influence of moss ground cover on hydrology, nitrogen (N) availability and vascular plant interactions, and in relation to nutrient spillover from adjacent farmland. Experimental work was a combination of glasshouse experiments and field‐based studies. Extremes of soil temperature and moisture were found to be mediated by the moss carpet, which also influenced N speciation; available N declined with moss depth. The moss layer decreased the amount of germination and establishment of vascular plants but, in some cases, enhanced their growth. Spillover of mineral nitrogen and phosphate from farmland enhanced invasion of exotic grasses which may have benefited from conditions provided by the moss carpet. Synthesis: We found the moss layer to be crucial to ecosystem functioning in these dry habitats with low nutrient substrate. However, when the moss layer is accompanied by nutrient spillover, it has the potential to increase exotic weed encroachment. Our results not only emphasize the importance of non‐vascular plant inclusion in restoration schemes but also highlights the importance of mitigating for nutrient spillover.