AUTHOR=Jia Xuan , Huangfu Chaohe , Hui Dafeng 

TITLE=Nitrogen Uptake by Two Plants in Response to Plant Competition as Regulated by Neighbor Density

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.584370

DOI=10.3389/fpls.2020.584370

ISSN=1664-462X

ABSTRACT=<p>Plant species may acquire different forms of nitrogen (N) to reduce competition for the same resource, but how plants respond to neighbors with different densities in their N uptake is still poorly understood. We investigated the effects of competition regime on the uptake of different N forms by two hygrophytes, <italic>Carex thunbergii</italic> and <italic>Polygonum criopolitanum</italic>, by conducting a hydroponic test of excised roots and an <italic>in situ</italic> experiment in a subtropical wetland ecosystem. The two species were grown either in monocultures or mixtures with various neighbor densities. Root functional traits and N uptake rates of different N forms were measured. Our results showed that N uptake was mainly determined by N form, rather than species identity. Both species were able to use organic N sources, but they took up relatively more N supplied as NO<inline-formula><mml:math id="INEQ1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi /><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:math></inline-formula> than as NH<inline-formula><mml:math id="INEQ2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi /><mml:mn>4</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:math></inline-formula> or glycine, irrespective of competition treatments. Both species preferred NO<inline-formula><mml:math id="INEQ3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi /><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:msubsup></mml:math></inline-formula> when grown in monoculture, but in the presence of competitors, the preference of fast-growing <italic>C. thunbergii</italic> persisted while <italic>P. criopolitanum</italic> acquired more NH<inline-formula><mml:math id="INEQ4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi /><mml:mn>4</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:math></inline-formula> and glycine, with stronger responses being observed at the highest neighbor density. The hydroponic test suggested that these divergences in N acquisition between two species might be partially explained by different root functional traits. To be specific, N uptake rates were significantly positively correlated with root N concentration and specific root length, but negatively correlated with root dry matter content. Our results implicated that <italic>C. thunbergii</italic> has a competitive advantage with relatively more stable N acquisition strategy despite a lower N recovery than <italic>P. criopolitanum</italic>, whereas <italic>P. criopolitanum</italic> could avoid competition with <italic>C. thunbergii</italic> via a better access to organic N sources, partly mediated by competition regimes.</p>