Interactions between species change the uptake of ammonium and nitrate inAbies faxonianaandPicea asperata

Abstract

Plant nitrogen (N) uptake is affected by plant–plant interactions, but the mechanisms remain unknown. 15N-labeled technique was used in a pot experiment to analyze the uptake rate of ammonium (NH4+) and nitrate (NO3−) by Abies faxoniana and Picea asperata in single-plant mode, intraspecific and interspecific interactions. The results indicated that the effects of plant–plant interactions on N uptake rate depended on plant species and N forms. P. asperata had a higher N uptake rate of both N forms than A. faxoniana, and both species preferred NO3−. Compared with single-plant mode, intraspecific interaction increased NH4+ uptake for A. faxoniana but reduced that for P. asperata, while it did not change NO3− uptake for two species. The interspecific interaction enhanced N uptake of both N forms for A. faxoniana but did not affect the P. asperata, compared with single-plant mode. NH4+ and NO3− uptake rates for two species were regulated by root N concentration, root nitrate reductase activity, root vigor, soil pH, and soil N availability under plant–plant interactions. Decreased NH4+ uptake rate for P. asperata under intraspecific interaction was induced by lower root N concentration and nitrate reductase activity. The positive effects of interspecific interaction on N uptake for A. faxoniana could be determined mainly by positive rhizosphere effects, such as high soil pH. From the perspective of root-soil interactions, our study provides insight into how plant–plant interactions affect N uptake, which can help to understand species coexistence and biodiversity maintenance in forest ecosystems.

Plant–plant interactions affect seasonal nitrogen uptake of subalpine conifer seedlings by altering root traits and soil nitrogen availabilities

“…Here, we found that both species preferred to absorb NO 3 À -N across the two seasons and that the contribution of NO 3 À -N in organs and the whole plant was higher than NH 4 + -N (Figures 3, 6), which supported that conifers prefer NO 3 À than NH 4 + (Zhu et al, 2021;Hu et al, 2021a). The reasons are linked to high soil NO 3 À -N availability, solubility, and mobility, as well as an efficient NO 3 À -N translocation and the use of plants (Zhou et al, 2017;Zhu et al, 2021;Hu et al, 2021a). The consistency of seasonal N-uptake preference may be mainly attributed to the mobility and high availability of NO 3 À -N (Zhu et al, 2021).…”

“…On July and September 20, 2020, three replicates per treatment were randomly selected for labelling 15 N isotope tracers ( 15 NH 4 + or 15 NO 3 − ) and control, respectively (Figure 1b). The 15 N labelling process and the details of this experiment have been described by Hu et al (2021a). A labelling solution with 19 μmol mL −1 N containing 15 NH 4 Cl or K 15 NO 3 (99 atom%) was used.…”

“…Facilitative and neutral effects often exist in interspecific interactions, whereas competitive effects occur in intraspecific interactions because of highly similar resource demands and intense competition (Adler et al, 2018;Carmona et al, 2019). In support of this, Hu et al (2021a) reported that intraspecific interaction decreased the N uptake of Picea asperata, while interspecific interaction enhanced the N uptake of Abies faxoniana but did not affect the N uptake of P. asperata. The effects of plant-plant interactions on plant N uptake and preference vary with plant species (Song et al, 2017;Bueno et al, 2018;Guo et al, 2019).…”

“…Several recent studies have reported that plant N uptake is closely related to root traits and soil physicochemical properties (McCormack et al, 2017; Hu et al, 2021a; Zhou et al, 2021). Root morphological and physiological traits are highly related to N uptake and assimilation (Meng et al, 2016a; Legay et al, 2020).…”

“…For interspecific interaction, dominant plant species use the more abundant soil N source, whereas subordinate species absorb fewer N sources (Kahmen et al, 2006). As such, plants can alter root traits or soil properties to adapt to environments when interacting with heterospecific species (Turcotte & Levine, 2016; Hu et al, 2021a). In addition, soil N availabilities and enzyme activities vary seasonally (Wang et al, 2013; Zhang et al, 2017), which may lead to seasonal dynamics in plant N uptake.…”