Dynamic niche sharing in dry acidic grasslands -a 15N-labeling experiment

Abstract

In this study we investigated the temporal variability of N-source utilization of pioneer plant species in different early successional stages of dry acidic grasslands. Current theory states that plant species occupy distinct ecological niches and that there are species-specific, temporal N-uptake patterns.We hypothesized that small-scale dynamics in the natural habitat may affect niche differentiation among plant species. We investigated N-uptake patterns of two co-occurring plant species from different functional groups (Corynephorus canescens, Rumex acetosella) under natural conditions using 15 N-labeled nitrate and ammonium in three different early successional stages during early and late summer. We found (1) marked seasonal dynamics with respect to Nuptake and N-source partitioning, and (2) different uptake rates across successional stages but a similar N-form utilization of both species. Nitrate was the main N-source in the early and later successional stages, but a shift towards enhanced ammonium uptake occurred at the cryptogam stage in June. Both species increased N-uptake in the later successional stage in June, which was associated with increasing plant biomass in C. canescens, whereas R. acetosella showed no significant differences in plant biomass and root/shoot-ratio between successional stages. Ammonium uptake decreased in both species across all stages with increasing drought. Nevertheless, the peak time of N-uptake differed between the successional stages: in the early successional site, with the lowest soil N, plants were able to extend N-uptake into the drier season when uptake rates in the other successional stages had already declined markedly. Hence, we found a pronounced adjustment in the realized niches of co-occurring plant species with respect to N-uptake. Our results indicate that ecological niches can be highly dynamic and that niche sharing between plant species may occur instead of niche partitioning.

Community scale 15N isoscapes: tracing the spatial impact of an exotic N2‐fixing invader

“…Traditional approaches, which focus on plant-plant interactions are typically limited to comparing neighbouring individuals (e.g. Ludwig et al 2004;Stahl et al 2011). Indeed, until recently there have been only limited methods for detecting and quantifying processes within ecosystems in a spatially explicit manner and these methods required exhaustive sampling, which is costly and timeconsuming (Rietkerk et al 2002;Beever et al 2006).…”

“…Specifically, N‐source utilisation is a dynamic process, which can vary at small scales even within one plant community (e.g. Stahl et al. 2011).…”

“…Specifically, N-source utilisation is a dynamic process, which can vary at small scales even within one plant community (e.g. Stahl et al 2011). Natural abundance foliar d 15 N signatures can lend insight into the N-cycle (Dijkstra et al 2008;Kahmen et al 2008) and specifically, into the origin of plant nitrogen (e.g.…”

Water fluxes mediated by vegetation: emerging isotopic insights at the soil and atmosphere interfaces

“…At the same time, water controls nutrient abundance and uptake, as soil moisture facilitates decomposition by microorganisms and nutrients are generally taken up in solution. Therefore, water shortage can severely impact nutrient uptake, potentially leading to chronic stress symptoms in plants (Larcher, 2003), varying with species-and ecosystemspecific nutrient recycling mechanisms and seasonal uptake pattern (Stahl et al, 2011;Lang et al, 2016). Therefore, in order to understand how and why plants swiftly alter their water uptake distribution or redistribute water between soil layers (i.e.…”

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

“…Plant N uptake ability also varies during the growing season, with N uptake increasing (Stahl et al 2011) or decreasing (Jaeger et al 1999) depending on the ecosystems investigated. In the UU grassland, NH 4 + uptake was higher for all species during the autumn than during the summer, and the same was found for NO 3 uptake by B.…”