Effects of native plants on nitrogen cycling microorganisms in soil

<p dir="ltr">Plants modify the nitrogen (N) cycle in soil through plant N uptake, root exudation, and nitrification inhibition resulting from <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/root-exudate" target="_blank">root exudates</a> and changes to the <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/physicochemical-property" target="_blank">physicochemical properties</a> of soil. Plants with specific traits can be selected to manage N fluxes in the soil following the land application of N-rich wastes thereby reducing losses of N from these systems into the atmosphere (via nitrous oxide) and waterbodies (via nitrate). Previous work has shown that some New Zealand native myrtaceous species can reduce such losses more than other species, but the underlying mechanisms are unknown. It was hypothesized that lower N losses may result from the inhibition of nitrification and denitrification. We aimed to determine the effect of New Zealand native <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/plant-specie" target="_blank">plant species</a> on the abundance of nitrifying and denitrifying <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/micro-organism" target="_blank">microorganisms</a> in the soil using a pot experiment with five native plant species (<a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/carex" target="_blank"><i>Carex</i></a><i> </i><i>secta</i>, C<i>oprosma robusta</i>, <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/kunzea" target="_blank"><i>Kunzea</i></a><i> </i><i>robusta</i>, <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/leptospermum-scoparium" target="_blank"><i>Leptospermum scoparium</i></a>, and <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/metrosideros" target="_blank"><i>Metrosideros</i></a><i> </i><i>umbellata</i>) and exotic pasture (<a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/lolium-perenne" target="_blank"><i>Lolium perenne</i></a>). Half of the pots received fertilisation with N (urea), phosphorus, potassium, and sulphur, while the remainder were unfertilised controls. We quantified the abundance of bacteria, <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/archaea" target="_blank">archaea</a>, and the functional genes encoding <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/nitrite-reductase" target="_blank">nitrite reductase</a> (<i>nirK</i>, <i>nirS</i>), <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/nitrous-oxide" target="_blank">nitrous oxide</a> reductase (<i>nosZ</i>), and bacterial and archaeal <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/ammonia-monooxygenase" target="_blank">ammonia monooxygenase</a> (<i>amoA</i>) in the <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/rhizosphere" target="_blank">rhizosphere</a> of these plants. Results indicated that plant species had a significant effect on the abundance of <i>nosZ</i> and bacterial <i>amoA</i>. In fertilised soil, the abundance of bacterial <i>amoA</i> was lower under mono- than dicotyledonous species. Similarly, the chemical properties of the soil differed between these groups. Monocotyledonous species took up more N and had lower concentrations of mineral N in the rhizosphere. This indicates that the increased competition for N likely reduced the abundance of <i>amoA</i> and therefore nitrification and nitrate losses. The results support the utilisation of species selection to reduce N losses. In particular, monocotyledonous species may be planted in high-fertility environments to mitigate N contamination of ground- and surface water. Future work should determine the mechanisms of plant specific interaction with ammonia-oxidising bacteria, although plant uptake can explain some of the observed differences.</p>