PhD Thesis

Plant growth responses to winter climate change: from amongand within-species variation to plant-soil interactions

Andrey Malyshev (01/2012-01/2015)

Support: Jürgen Kreyling, Gregor Aas, Bettina Engelbrecht

Winter climate change is a complex phenomenon, with snow depth, soil freezing dynamics, and variable air temperature all interacting to bring about differences in among- and within-species growth responses. The objective was to detect growth differences in the responses of species, ecotypes and plant functional groups to winter processes impacted by warmer temperatures. Therefore, experiments were carried out to simulate winter warming and to study its effects on cold acclimation and deacclimation, dormancy loss and frost tolerance. Amongspecies variation was then compared with within-species variation to determine if a species could be largely treated as a single response unit under different climatic extremes. Plant-soil interactions were also explored to gain a more complete understanding of factors directly impacting plant responses to winter warming. Three in situ experiments, simulating winter warming for different durations and at different amplitudes were conducted for this purpose. Two main questions were posed: (1) what generalities can be found among species- and ecotypespecific plant responses to winter warming simulated under different environmental conditions? (2) what is the role of within species variation in predicting plant responses to climate warming? Generalities were found among species (relating dormancy depth and its rate of decrease with the passing of winter), within species (latitudinal grass ecotypes showed similar north-south cold acclimation differences as previously shown in trees) and in plant-soil interactions (plant community composition played a major role in N uptake and leaching following prolonged warming and increased temperature variability). This shows that even with high ecotypic and species diversity, experimental biology can provide answers, which apply across species, functional types and experimental conditions. Across several tree species and grass ecotypes the sensitivity to changes in photoperiod was found to influence the effect of temperature on growth cessation and resumption. Photoperiod sensitivity is therefore an important characteristic of plants related to the ability to extend the growing season and resume growth during sudden midwinter warm spells. With respect to the novel comparison of within-species variation to among-species variation under stress, evidence was found against treating a species as a uniform unit, in terms of its climate change responses, across its distribution. Multiple implications and applications of high within-species variation are possible. Firstly, the ability of food crop species and species declining in abundance to adapt to warmer temperatures may be improved with assisted migration of better-adapted ecotypes. Secondly, incorporation of within-species variation into models should enable more accurate projections of species distribution changes. Thirdly, preventing extinction and conserving biodiversity can be supplemented by increasing the ecotypic diversity of an area. This way, potentially undesirable side effects from species introductions can be bypassed. For future experiments, this means that the factors which contribute to development of ecotypes should be researched further. Additionally, plant communities with varying degrees of ecotypic and species diversity should be compared in terms of their resilience to climate change impacts.