Marginal Calluna populations are more resistant to climate change, but not under high-nitrogen loads

Abstract

The dominant plant species of European heathlands Calluna vulgaris is considered vulnerable to drought and enhanced nitrogen (N) loads. However, impacts may vary across the distribution range of Calluna heathlands. We tested the hypothesis that Calluna of southern and eastern marginal populations (MP) are more resistant to drought events than plants of central populations (CP), and that this is mainly due to trait differences such as biomass allocation patterns. Furthermore, we hypothesised that N fertilisation can offset differences in drought susceptibility between CP and MP. We conducted a full-factorial 2-year greenhouse experiment with Calluna plants of CP and MP and quantified growth responses in terms of biomass production, allocation and tissue d 13 C signatures. Biomass production, shoot-root ratios and tissue d 13 C values of 1-year-old plants were higher for CP than for MP, indicating a higher drought susceptibility of CP. These trait differences were not observed for 2-year-old plants. N fertilisation increased shoot-root ratios of 1-and 2-year-old plants and across populations due to a stimulation of the aboveground biomass allocation. As a consequence, population-related differences in drought susceptibility were offset for N-fertilised plants. We concluded that Calluna plants originating from different populations developed adaptive traits to local climates, which determined their drought sensitivity. However, the higher drought resistance of MP can be attenuated by an N-induced increase in shoot-root ratios. This suggests that analyses on plant growth responses to global change should include multi-factor approaches with a focus on different populations throughout a species' distribution range.

Time- and age-related effects of experimentally simulated nitrogen deposition on the functioning of montane heathland ecosystems

“…ing, tissue and litter chemistry or plant susceptibility to biotic (e.g., pathogen or pests) and abiotic (e.g., frost or drought) stressors] (Bähring et al, 2017;Jones and Power, 2012;Marcos et al, 2003;Meyer-Grünefeldt et al, 2016;Southon et al, 2013;Taboada et al, 2016). Elevated N inputs stimulate N mineralization rates (Phoenix et al, 2012), resulting in increased soil extractable N-NH 4 + and N-NO 3 − (Boot et al, 2016;Song et al, 2017;Southon et al, 2013).…”

“…In contrast to north-western (e.g., Phoenix et al, 2012;Southon et al, 2012) and central European (e.g., Bähring et al, 2017;de Vries et al, 2009;Friedrich et al, 2011) Calluna-heathlands, to date, only one study has been developed on the time-scale and age-related effects of enhanced N deposition in montane Calluna-heathlands located at the southern-most limit of their distribution range (Cantabrian Mountains, NW Spain) (i.e., plant-herbivore-predator relationships: Taboada et al, 2016). This is despite these marginal southern Calluna-heathlands having been found to respond differently to global change drivers (such as N deposition) as compared to central European ones (Meyer-Grünefeldt et al, 2016). In this study, we evaluated the effects of different levels of experimentally simulated N deposi tion on the functioning of marginal montane Calluna-heathlands, mediated by the age of heathland vegetation resulting from management activities (prescribed burning), with particular attention being paid to the cumulative impact of N loading throughout time.…”

“…Calvo et al (2007) also found that the vegetation of Cantabrian montane heathlands is resilient to disturbances like N loading and intense management practices, recovering the pre-disturbed vegetation structure and composition. However, further long-term research is needed to fully understand the effects of chronic N deposition and its interactions with other episodic biotic and abiotic stressors (like insect pest outbreaks; Taboada et al, 2016) and global environmental change factors (Meyer-Grünefeldt et al, 2016) on the functioning of montane heathlands.…”

“…Ecosystems adapted to low levels of nutrient availability, such as heathlands dominated by the dwarf shrub Calluna vulgaris (L.) Hull (henceforth referred to as Calluna), are particularly sensitive to airborne N deposition (Cuesta et al, 2008;Fagúndez, 2013;Jones and Power, 2012;Meyer-Grünefeldt et al, 2016;Southon et al, 2012). Both field-scale surveys and N-manipulation experiments testing the effects of a variety of N-loading rates over different temporal scales have evidenced substantial N-driven changes in the composition, diversity and functioning of nutrient-poor Calluna-heathlands (e.g., Calvo et al, 2005Calvo et al, , 2007Friedrich et al, 2011;Power et al, 2006;Southon et al, 2013), threatening their persistence across Europe (Fagúndez, 2013).…”

Plant and vegetation functional responses to cumulative high nitrogen deposition in rear-edge heathlands

“…Within the broad distribution area of Calluna-heathlands across Europe, it is very likely that dominant Calluna plants from different locations have evolved particular adaptive traits to their local conditions (Loidi et al, 2010) and are, thus, differentially sensitive to environmental changes. To our knowledge, though, only one study (Meyer-Grünefeldt et al, 2016) has experimentally assessed how central and marginal Calluna plants responded to global change testing the single and combined effects of drought and N deposition. This study concluded that (1-2-year-old) plants from the southern-most limit of the Calluna-heathland ecosystem's distribution are better adapted to drought events than those from the centre of the range, except under elevated N availability.…”