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

Abstract

Summary Restoring plants to the riparian zone is regarded as management best practice in river restoration and has the potential to reduce the impact of nitrogen (N) pollution on aquatic organisms and improve water quality for human use. Plant characteristics and the interplay of hydrology and biogeochemistry control N retention in the riparian zone. The balance between processes such as denitrification and plant assimilation determines riparian N retention. Plant traits are likely to mediate these N removal processes through variations in root form, growth character, foliage production (quantity, quality and rate of return to the soil) and by altering conditions in the rhizosphere soil. Vegetation can slow N transfer via direct plant uptake of N (during periods of rapid vegetation growth) and changes induced to soil hydrology, nutrient cycling and microbial activity, principally denitrification. Few studies have focused on species‐dependent effects on N movement through soil and across boundaries. We propose a new framework, based on a literature review of plant traits with respect to N cycling, which can be used to select plant species with traits likely to maximise N removal during transport through the riparian zone. In the proposed framework, inter‐specific differences in traits known to influence N mobility: root form, growth rate, foliar characteristics and rhizosphere processes, are used to describe species’ potential impact on N removal. Plant trait data may be drawn from studies outside the riparian zone; for example forest ecology, horticulture or forestry research, and candidate species are scored to predict N removal efficiency. We apply the framework to New Zealand's native riparian plant assemblages to demonstrate the trait‐based approach. This framework can guide restoration management decisions and investment in riparian revegetation in a manner that is not restricted to geographically specific or well‐studied species.

Plant Species Complementarity in Low-Fertility Degraded Soil

“…The findings of the present study illustrate functional compatibility as well as competition between plant rhizospheres for plant nutrients. Beneficial coexistence appears to be explained by the differences between the plant rhizospheres of different species which exploit different components of the soil nutrient pool [ 38 , 39 ]. This implies that the enhancement of species diversity, for example, beyond simply focusing on legumes and grasses in pasture agronomy [ 3 ], may be a better way to manage ecosystems, including production systems, with low-fertility or degraded soils.…”

Principal Threats to the Conservation of Running Water Habitats in the Continental Biogeographical Region of Central Europe

“…xx Naiman & Decamps 1997;Hermoso et al, 2018;Abell et al, 2019;Franklin et al, 2019;Wilk-Woźniak et al, 2019 Implement agricultural best management practices and good agricultural practices recognised on the national or international level (FAO, EU Nitrates Directive, etc. ); locationsome sub-catchments or even stream reaches may support higher priority freshwater biodiversity elements and ecosystem processes than others, but most terrestrial PAs have not been sited with these elements in mind…”

“…xxx xx xx Güsewell & Le Nédic 2004;Strayer, and Dudgeon 2010;Leyssen et al, 2014;Francis et al, 2019;Franklin et al, 2019;Harvey et al, 2019; Implement rational fisheries management;…”

High Maintenance of Rhizosphere Soil C and N Equilibrium Regardless of Plant Species or Species Traits

“…As well as being important in natural ecosystems, BNI is of applied interest. The introduction or selection-based improvement of this trait into commercial plant cultivars [e.g., (18,19)], addition of the trait through plantmicrobiome manipulation [e.g., (20)], or using non-agricultural plants within productive landscapes for protection of riparian zones or other sensitive areas [e.g., (21)] all offer opportunities to utilise BNI as a means for reducing nitrification rates within agroecosystems (16). Although this can be measured directly, with inhibitor-based assays on target microorganisms (22), BNI is often measured by inference through assessment of changes in potential nitrification rate (PNR) in soils [e.g., (23)] particularly in initial screening-based trials.…”