Plant-Soil Interactions of Range-Expanding Plants
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Plant-soil plants interactions of range-expanding Invitation Plant-soil interactions of to attend the public defense of range-expanding plants my PhD thesis, entitled: Plant-soil interactions of range-expanding plants Friday 7th of December at 11:00 in the Aula of Wageningen University, General Foulkesweg 1, Wageningen Marta Manrubia Freixa Marta Manrubia Freixa [email protected] Paranymphs: Sigrid Dassen [email protected] Paolo di Lonardo [email protected] 2018 Marta Manrubia Freixa Plant-soil interactions of range-expanding plants Marta Manrubia Freixa Thesis committee Promotor Prof. Dr W. H. van der Putten Special Professor Functional Biodiversity, Wageningen University & Research Netherlands Institute of Ecology, Wageningen Co-promotor Dr G. F. Veen Junior Group Leader Netherlands Institute of Ecology, Wageningen Other members Prof. Dr G. B. De Deyn, Wageningen University & Research Dr M. te Beest, Utrecht University Prof. Dr J. H. C. Cornelissen, VU Amsterdam Dr E. J. Sayer, Lancaster University, UK This research was conducted under the auspices of the C.T. de Wit Graduate School for Production Ecology & Resource Conservation (PE&RC) Plant-soil interactions of range-expanding plants Marta Manrubia Freixa Thesis submitted in fulfilment of the requirements for the degree of doctor at Wageningen University by the authority of the Rector Magnificus, Prof. Dr A.P.J. Mol, in the presence of the Thesis Committee appointed by the Academic Board to be defended in public on Friday 7 December 2018 at 11 a.m. in the Aula. Marta Manrubia Freixa Plant-soil interactions of range-expanding plants 184 pages. PhD thesis, Wageningen University, Wageningen, The Netherlands (2018) With references, with summaries in English, Catalan and Dutch ISBN: 978-94-6343-531-4 DOI: https://doi.org/10.18174/462576 “Keep Ithaka always in your mind. Arriving there is what you’re destined for. But don’t hurry the journey at all. Better if it lasts for years, so you’re old by the time you reach the island, wealthy with all you’ve gained on the way, not expecting Ithaka to make you rich” Fragment of “Ithaka” by K.P. Kavafis Translated by E. Keeley Table of contents Chapter 1 General introduction 9 Chapter 2 Nutrient content in plants and soils of range-expanding plant 23 species in their original and expansion ranges compared to natives Chapter 3 Belowground consequences of intracontinental range-expanding 45 plants and related natives in novel environments Chapter 4 Rhizosphere and litter feedbacks to range-expanding plant species 77 and related natives Chapter 5 Soil functional responses to drought under range-expanding and 109 native plant communities Chapter 6 General discussion 137 List of references 149 Summary 163 Sumari 167 Samenvatting 172 Acknowledgements 176 About the author 180 List of publications 181 Graduate school training and courses 182 Chapter 1 General introduction 9 Chapter 1 Anthropogenic activities during the last century have had a profound impact on greenhouse gas balances at a global scale. One of the clearest consequences of the rapid increase of greenhouse gas emissions is the rise of the mean global temperature (IPCC 2014). Quite some plant species are responding to a warming climate by expanding their ranges to higher latitude and altitude regions within continents (Chen et al. 2011). Similarly to introduced exotic species that become invasive, the arrival of range-expanding plant species in recipient ecosystems may have consequences for the composition and functioning of ecological communities, both of native plant species and soil communities (Morriën et al. 2010). In this thesis, I study plant species that expand their range as a response to current global warming and I focus on how these species interact with the abiotic soil environment, the soil microbial communities, and how they influence soil community functioning compared to native plant species. I will especially focus on the impacts of range-expanding plant species on litter decomposition and soil nutrient cycling, which regulate ecosystem carbon balance and the provisioning of nutrients for plant growth. Climate change and plant responses Global biochemical cycles have been profoundly modified by human activities (Vitousek et al. 1997), with important consequences for the climate system. The concentration of carbon dioxide in the atmosphere has now increased by 40% with respect to pre-industrial times. The increase in greenhouse gas emissions, mainly derived from fossil fuel emissions, has triggered an increase on global average surface temperatures of 0.6oC over the 20th century (IPCC 2014). This temperature increase varies locally and has especially been prominent in areas of high latitudes (Fig. 1.1). All projected climate scenarios predict that global temperature will continue to rise during the 21st century, which may further increase carbon dioxide emission from natural ecosystems (Crowther et al. 2016). Plant species can respond to climate warming in different ways. Plants can undergo genetic and phenotypical adaptation induced by climate warming. Adaptation can result, for example, in phenological changes such as earlier flowering time, or longer growing season (Peñuelas and Filella 2001, Cleland et al. 2007). However, adaptation processes in the future may be critically limited by the rapid rates at which the climate changes and by decreased gene flow between fragmented habitats (Davis and Shaw 2001, Jump and Penuelas 2005). Thereby, climate warming can also lead to local extinctions of plant species 10 Introduction that are unable to adapt or disperse (Thomas et al. 2004). Wild plant species can also respond to a warming climate by expanding their ranges to higher latitude and altitude regions within continents (Parmesan and Yohe 2003, Lenoir et al. 2008, Chen et al. 2011). It has been estimated that the average distribution of species has shifted polewards at a rate of 16.9 km per decade (Chen et al. 2011). Due to the increase of temperature in areas of high latitude, especially in the northern Hemisphere (Fig. 1.1), habitats have become more suitable for thermophilic plant species. For example, in the Netherlands, the number of plant species from warmer climatic regions has increased substantially during the last decades (Tamis et al. 2005, NDFF 2018). Even though the introduction of some of these species may have been induced by human activity, natural range expansion and the spread of plant species is likely to be enabled by warming climate. Fig. 1.1. Map of the observed surface temperature change, from 1901 to 2012 (source: IPCC, 2014). Trends have been calculated where data availability permitted a robust estimate (i.e., only for grid boxes with greater than 70% complete records and more than 20% data availability in the first and last 10% of the time period), other areas are white. Grid boxes where the trend is significant, at the 10% level, are indicated by a + sign. Plant species that expand their range within continents establish in ecosystems outside their native range. Similarly, plant species that have been introduced to other continents also establish outside their native range. In the ecological literature, the latter are traditionally referred to as (introduced) exotic species (Keane and Crawley 2002). While it can be argued that plants that expand their range within a continent into previously un- colonized higher latitude areas are exotic species as well, I will refer to them as “range- 11 Chapter 1 expanders” in this thesis. In contrast, I will use the term exotic species to refer to studies that have investigated the causes and consequences of intercontinental plant introductions. Numerous studies have examined successfully established exotic plants that become invasive and induce important changes on the composition and functioning of the invaded ecosystems (Ehrenfeld 2010, Vilà et al. 2011, Pyšek et al. 2012). However, little is known about the manner that range-expanding plant species may affect the composition and functioning of ecosystems in the new range. Plant-soil interactions All plant species, including introduced exotic plants, can induce changes in the soil biotic and abiotic components that affect their own performance and the performance of subsequent plant generations (Wardle et al. 2004, Bezemer et al. 2006). This phenomenon is known as plant-soil feedback (Bever et al. 1997). Individual plants and soil communities interact with each other in a direct or indirect manner, and the outcome of these interactions can have positive, negative or neutral feedback effects to plants. According to the general framework proposed by Wardle et al. (2004), soil communities can affect plants in a direct manner when soil organisms associate with living plant roots or in an indirect manner when soil organisms that consume dead plant material provide the nutrients needed by plants to grow (Fig. 1.2). Mechanisms of direct plant-soil interactions include pathogenesis, herbivory or symbiotic-mutualistic relationships. The association of pathogens, herbivores and symbiotic mutualists with a host plant has immediate effects to its performance. In contrast, the soil decomposer subsystem transforms organic plant material into inorganic plant-available nutrients via litter decomposition, thereby affecting plant performance indirectly. Besides the strong influence of climatic conditions on decomposition processes, plant traits and soil decomposer communities have been shown to regulate decomposition rates in soil (Cornelissen