Studies of NH₄⁺ and NO₃⁻ uptake ability of subalpine plants and resource‐use strategy identified by their functional traits

Abstract

The leaf economics spectrum (LES) is based on a suite of leaf traits related to plant functioning and ranges from resource‐conservative to resource‐acquisitive strategies. However, the relationships with root traits, and the associated belowground plant functioning such as N uptake, including nitrate (NO3−) and ammonium (NH4+), is still poorly known. Additionally, environmental variations occurring both in time and in space could uncouple LES from root traits. We explored, in subalpine grasslands, the relationships between leaf and root morphological traits for three dominant perennial grass species, and to what extent they contribute to the whole‐plant economics spectrum. We also investigated the link between this spectrum and NO3− and NH4+ uptake rates, as well as the variations of uptake across four grasslands differing by the land‐use history at peak biomass and in autumn. Although poorly correlated with leaf traits, root traits contributed to an economic spectrum at the whole plant level. Higher NH4+ and NO3− uptake abilities were associated with the resource‐acquisitive strategy. Nonetheless, NH4+ and NO3−‐uptake within species varied between land‐uses and with sampling time, suggesting that LES and plant traits are good, but still incomplete, descriptors of plant functioning. Although the NH4+:NO3− uptake ratio was different between plant species in our study, they all showed a preference for NH4+, and particularly the most conservative species. Soil environmental variations between grasslands and sampling times may also drive to some extent the NH4+ and NO3− uptake ability of species. Our results support the current efforts to build a more general framework including above‐ and below‐ground processes when studying plant community functioning.

Glacier forelands reveal fundamental plant and microbial controls on short‐term ecosystem nitrogen retention

“…This finding suggests that microbes were limited by nitrate and plants by ammonium, thus when more of these forms were present the added 15 N‐forms were diluted more, and microbial and root uptake of added 15 N was reduced through a saturation effect (Grassein et al., 2015). This is consistent with the knowledge that subalpine grassland plants, especially more conservative species, have higher ammonium than nitrate uptake rates (Legay et al., 2020), and suggests coordination between plant and microbial N uptake strategies beyond broad‐scale tissue N requirements, as has been found before (Moreau et al., 2015; Theodose et al., 1996).…”

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

“…The usage of excised root segments in hydroponic experiment allowed to characterize the physiological uptake for different N sources in the absence of interspecific competition and to test our hypothesis 1 ( Legay et al, 2020 ). The experiment consisted of culture of excised fine roots of two focal species in vials in a completely randomized factorial design considering two species and four N isotope labeled solutions.…”

“…In response to the environmental variation, plants have evolved various root functional traits in term of the N uptake capacity ( Hong et al, 2018 ). Among these, both fine root traits ( Legay et al, 2020 ) and their associated mycorrhizal fungi ( Liese et al, 2018 ) play crucial roles in soil N acquisition, facilitating species coexistence via promoting diversity of resource acquisition strategies ( Lambers et al, 2008 ; Zemunik et al, 2015 ). In the littoral zone of Shengjin Lake, approximately 17% of the total area consists of Carex meadow ( Cao and Fox, 2009 ) which was historically dominated by Polygonum criopolitanum one decade ago.…”

Tree species mixing causes a shift in fine‐root soil exploitation strategies across European forests

“…A high root N concentration is generally indicative of high root metabolic activity (Reich et al, 2008) and may positively relate to specific root-uptake activities (e.g. Legay et al, 2020). Also, a low RTD, reflecting low construction cost (Chen et al, 2018), may indicate a higher efficiency in conditions where the risk of root loss from herbivory and/or pathogens is not high.…”