Abstract
Global warming affects plant fitness through changes in functional traits and thereby ecosystem function. Wetlands are declining worldwide, and hence, ecosystem functions linked to wetlands are threatened. We use Caltha palustris “a common wetland plant” to study whether warming affects growth and reproduction differently depending on origin of source population, potentially affecting phenotypic response to local climate. We conducted a 2‐year in situ temperature manipulation experiment using clone pairs of C. palustris in four regions, along a 1300‐km latitudinal gradient of Sweden. Open‐top chambers were used to passively increase temperature, paired with controls. Growth and reproductive traits were measured from 320 plants (four regions × five sites × two treatments × eight plants) over two consecutive seasons to assess the effect of warming over time. We found that warming increased plant height, leaf area, number of leaves, and roots. High‐latitude populations responded more strongly to warming than low‐latitude populations, especially by increasing leaf area. Warming increased number of flowers in general, but only in the second year, while number of fruits increased in low‐latitude populations the first year. Prolonged warming leads to an increase in both number of leaves and flowers over time. While reproduction shows varying and regional responses to warming, impacts on plant growth, especially in high‐latitude populations, have more profound effects. Such effects could lead to changes in plant community composition with increased abundance of fast‐growing plants with larger leaves and more clones, affecting plant competition and ecological functions such as decomposition and nutrient retention. Effects of warming were highly context dependent; thus, we encourage further use of warming experiments to predict changes in growth, reproduction, and community composition across wetland types and climate gradients targeting different plant forms.
Highlights
Global warming is considered one of the major drivers of environmental change, threatening biodiversity, ecosystem function, and the delivery of ecosystem services
We found that the open-top chamber (OTC) treatment led to an increase in all growth-related traits but only significantly affected one of the three traits associated with reproduction, namely the number of flowers
The effect of the treatment increased with time for most of these traits and regions, except for Uppsala that showed a diverging pattern
Summary
Global warming is considered one of the major drivers of environmental change, threatening biodiversity, ecosystem function, and the delivery of ecosystem services. Investigating changes in growth and reproduction in plant community as well as for single species as a response to climate will enhance predicting changes in growth, reproduction, and community composition in different habitats and ecosystems and for different plant forms Such knowledge could underpin a better insight into changes in ecosystem function and services (Balvanera et al, 2006; Cardinale et al, 2012); for example, in wetlands, clonality and number of shoots may affect flow regulation through water holding capacity, and specific leaf area (SLA) may though decomposition and accumulation affect greenhouse gas emission and nutrient retention (Moor et al, 2017). The limited number of studies, as well as the range of effects on wetland plant species traits and community responses to climate warming, inhibits our ability to fully understand how ecosystems function and services will be affected. We hypothesized that the magnitude of the effect will be more pronounced for plants in northern latitudes, since temperature-related constraints on growth and reproduction will be eased and that warming effects will increase cumulatively over time
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