Growth and anatomical responses of perennial forbs to climate change

The recent, accelerating climate change increasingly affects the dynamics of herbaceous vegetation. While changes at the species, community and ecosystem level (e.g. productivity and competitive interactions, phenology, distribution ranges, etc.) have been widely documented for many regions in the world, a mechanistic basis for these changes is generally lacking. Why do some plant species cope better with a changing environment than others when migration cannot keep pace? Is it because of a greater phenotypic plasticity and/or genetic variability in species’ life history and structural traits? Or may some species be pre-adapted because of a specific growth strategy?

In this project I aim to fill parts of this gap by quantifying lifetime phenotypic plasticity in growth and functional anatomy of perennial dicotyledonous herbs with life spans of up to 50 years. To this end, the width of annual rings in the secondary root xylem is used as a proxy for annual vegetative growth (a method termed "herb-chronology"), with anatomical features such as vessel diameter and lignification patterns being used to estimate the magnitude of inter-and intra-annual functional responses to soil moisture availability over the life of the plant. In a field survey, phenotypic plasticity in these traits are assessed and compared among perennial forb species with contrasting growth strategies and across natural moisture gradients in several montane areas in the western USA, a region expected to be especially affected by climate change. A cross-environmental moisture manipulation experiment is performed to quantify plastic responses, thus calibrating the results from the field survey. One hypothesis to be tested is that plants growing under drier conditions will respond by forming narrower xylem vessels to prevent cavitations and producing more lignified xylem tissue to enhance mechanical support. The degree of plasticity in these and other traits across moisture gradients would be an indicator of pre-disposition to withstand future climate change.

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Development of ROXAS, a software tool for age-related growth and anatomical analysis in forbs and trees

To facilitate and improve the analysis of annual rings and anatomical structures in perennial forbs, I have developed an automated image analysis tool (ROXAS – Root Xylem Analysis System). While this first prototype version of ROXAS already proofed its efficiency and accuracy (cf. von Arx & Dietz, 2005), ROXAS has been significantly improved, meantime, particularly by adaptations to tree cores of hardwood, by implementing a mode for manual user corrections, and by widely enhancing the set of output parameters. Among these are number, width and area of annual rings, individual vessel size, position of individual vessels within annual rings, vessel density, conductive area, and many more. The current implementation of ROXAS is still coupled to Image-Pro Plus (Media Cybernetics, Silver Spring, MD, USA), a specialized but quite expensive image analysis package. Any user of ROXAS therefore needs Image-Pro Plus installed on his or her computer.

This project aims to implement ROXAS as a stand-alone application that may be distributed to interested researchers as a non-commercial tool, along with other improvements.