Native plants and nitrogen in agricultural landscapes of New Zealand

Abstract

Native vegetation of the Canterbury Plains of South Island in New Zealand has been heavily modified by agriculture and now occupies less than 0.5% of the total land area. With recent large-scale conversion to intensive dairy farming, restoration of native plants and biodiversity into a modern agricultural matrix creates a significant challenge. Native species are adapted to low nitrogen (N) environments but fertilizers and effluents have substantially raised soil N loadings. We investigated the interactions of selected native species to elevated soil N, using field studies and glasshouse-based nutrient trials. Growth and uptake of N by perennial ryegrass provided a reference. At restoration sites, several native species had similar foliar N concentrations to ryegrass. Deciduous and N-fixing species of tree had highest concentrations. There was significant inter-species variation in soil mineral N concentrations in native plant rhizospheres, differing substantially to the root zone of ryegrass. Pot trials revealed that native species tolerate high N-loadings (up to 1600 kg ha-1), although there was a negligible or no significant growth response. Among the native plants, monocots (tussock grass, sedge and NZ flax) assimilated most N, although total N assimilation by ryegrass would exceed that of native species at field productivity rates. Nevertheless, the deeper rhizospheres of native species may reduce nitrate leaching when planted on the margins of agricultural land or for effluent disposal. Selected native plant species could contribute to the sustainable management of N in intensive agricultural landscapes. Highlights:  Native species are tolerant to elevated soil N, with negligible growth response  Low-N adapted plants show species-specific traits that include luxury N uptake  Differences rhizosphere N pools exist between native species and with ryegrass  Planting natives may help to provide sustainable agricultural management of N

Plants for nitrogen management in riparian zones: A proposed trait‐based framework to select effective species

“…; Marden & Phillips ), as well as studies of plant N uptake and influence on rhizosphere soil (Franklin ; Franklin et al . ). Comparative data for growth rate, root density and depth were largely from plants excavated and measured after 5 years growth in alluvial soil (Marden et al .…”

“…; Franklin et al . ). Nitrogen content is an important factor influencing litter decomposition by soil microbes; leaves with high N content (low C:N and lignin:N ratios) tend to decompose faster returning more N to the soil (Table , Box 1; Cornwell et al .…”

“…) and glasshouse (Franklin et al . ) studies during periods of high plant growth. Data on root biomass and depth for a range of species can be found in online repositories such as the Biomass and Allometry Database for woody plants [BaAD] (Falster et al .…”

Nutrient‐enriched soils and native N‐fixing plants in New Zealand

“…Nutrient spillover has been shown to negatively impact and threaten the sustainability of fragments of native vegetation adjacent to farms ( Didham et al, ; Bowie et al, ). Native species appear to be tolerant of, but not particularly responsive to, elevated soil loadings of N and P. We have found that native plants assimilate large amounts of applied N into foliage as luxury uptake which may be an adaptation of native species to naturally low fertility soils ( Franklin et al, ). Aside from this research, we have little understanding of the compatibility of fertile soils for establishing and sustaining native vegetation in New Zealand.…”

N2O-reducing activity of soil amended with organic and inorganic enrichments under flooded conditions

“…The rate of denitrification and the relative proportions for NO, N 2 O, and N 2 produced depend on the complex interactions between soil properties, soil microorganisms, climatic factors and management practices (Bieganowski et al, 2013;Franklin et al, 2015;Liu et al, 2010;Stępniewski and Stępniewska, 2009;Włodarczyk et al, 2014). From an environmental perspective, a very important result is the N 2 O/N 2 +N 2 O ratio, which shows the N 2 O-reducing activity of soil (Yanai et al, 2008).…”