Data from: Impacts of drought and nitrogen addition on Calluna-heathlands differ with plant life-history stage

1. Climate change and atmospheric deposition of nitrogen (N) affect the
biodiversity patterns and functions of ecosystems worldwide. While many
single-factor studies have quantified ecosystem responses to single global
change drivers, less is known about the interaction effects of these
drivers on ecosystem functions. 2. Here, we present the results of a
three-year field and a two-year greenhouse experiment, in which we
assessed responses of Calluna vulgaris-heathlands to the single and
combined effects of drought events (D) and N fertilisation (D: 25%
precipitation reduction in the field experiment and 20-50% soil water
content reduction in the greenhouse experiment; N fertilisation: 35 kg N
ha−1 yr−1). 3. We examined the effects of D and N treatments on growth
responses of the dominant dwarf shrub Calluna vulgaris (in terms of
biomass production and allocation, tissue δ13C signatures and C:N ratios)
in relation to two plant life-history stages and different ‘ecotypes’
(sub-Atlantic vs. subcontinental heathlands). 4. Plant responses varied
strongly with life-history stage, and the interaction of N and D showed
lower effects than would be expected based on additive responses to single
factors. While D treatments had no effects on Calluna in the building
phase (ca. ten-year-old plants), seedlings (particularly one-year-old
plants) were highly susceptible to drought. Differences in response
patterns were attributable to the high shoot-root ratios typical of young
Calluna plants. These ratios decreased with progressing life-history as a
result of increasing below-ground biomass investments. Below-ground
biomass production and shoot-root ratios differed between plants from the
different heathland sites. 5. Tissue δ13C signatures decreased and C:N
ratios increased with plant age as a result of decreasing evaporative
demands (per unit root biomass). N fertilisation increases the shoot-root
ratios and thereby the drought susceptibility of Calluna plants. 6.
Synthesis. Our findings suggest that plant responses to global change are
difficult to anticipate by means of single-factor studies or by focusing
on a single life-history stage. This highlights the need for global change
research to include multiple factors and life-history stages when
assessing an ecosystem's susceptibility to shifts in environmental
conditions.

Data field and
greenhouse experimentsThe excel file contains
the datasets from our field and greenhouse experiments for all response
variables and study years used in this publication: dry weight, shoot-root
ratios, C:N ratios and delta13C signatures for aboveground and belowground
biomass.Data.xlsx