Effects of enhanced nitrogen inputs and climate warming on a forest understorey plant assessed by transplant experiments along a latitudinal gradient
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Global warming and enhanced nitrogen (N) inputs are two key global-change drivers affecting temperate forest ecosystems simultaneously. Interactive effects of multiple drivers might cause species responses to differ from those in single-factor experiments; therefore, there is an urgent need for more multi-factor studies. Here, we assessed the growth and reproductive performance of multiple populations of a widespread grass of deciduous forests (Milium effusum) sampled along a latitudinal gradient and subjected to experimental manipulations of temperature and nitrogen availability. Common garden transplant experiments along the latitudinal gradient were used to manipulate temperatures and combined with experimental N addition to assess intraspecific responses of the study species to global-change drivers as well as to determine local adaptation. The total biomass, number of seeds and seedling emergence time of M. effusum increased when transplanted in the southern common garden. Apart from effects on the seed mass, the species did not respond to N addition alone. Yet, interactive effects between warming and N addition were found: N addition led to increased biomass growth but only in the northern common garden. Significant home-site advantages were apparent, most likely because of increased mycorrhizal colonization of roots of local transplants. We show that multiple global-change drivers may alter dynamics in understorey communities of temperate forests. Our study reinforces the need to increase our understanding of plant responses to future environmental changes by expanding the multi-factor research framework.
KeywordsClimate change Common garden experiment Forest understorey Latitude Local adaptation Mycorrhiza Nitrogen deposition Deciduous forest
We thank the Research Foundation—Flanders (FWO) for funding the scientific research network FLEUR (http://www.fleur.ugent.be). Support for this work was provided by the Kempe Foundation, Petra and Karl Erik Hedborg Foundation, an EU Transnational Access Program ATANS Grant (Fp6 506004), FWO post-doctoral fellowships (to PDF and EDLP) and the Special Research Fund of Ghent University (to RG). We are also grateful to Anna Shevtsova, Bente Graae, Thilo Heinken, Sharon Stanton, An De Schrijver, Luc Willems, Greet De bruyn, Rob Dhondt, Emma Holmström and Eva Sorgeloos and the staff at the Abisko Scientific Research Station for discussions, accommodation, facilities and assistance with the field work.
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