Ph.D. on Root dynamics and below ground carbon input in a changing climate

This Ph.D. project was started in January 2007 by Ph.D. student Marie Frost Arndal. The project is mainly linked to the WP3.1 and will focus on below-ground root production, input of root litter to the soil and root litter decay rate in response to simultaneous changes of temperature, precipitation and CO2 in a large-scale field experiment. Other areas will be studies of root competition and phosphatase activity.

Root dynamics and below ground carbon input in a changing climate
Temperature and precipitation are key factors for biological processes and climate change is therefore expected to change ecosystem processes and functioning. One of the main questions is if ecosystems respond as a sink or a source of atmospheric carbon. A substantial amount of carbon assimilated by plants is transported below-ground and transferred to the soil as root exudates, or used for production of roots. The flux of carbon to the soil is difficult to measure and thus root production, root litter production and root litter turn-over is a key constraint regarding assessment of ecosystem carbon balance in a changing climate.

Objective
The objective of the Ph.D. study is to examine below-ground root production, input of root litter to the soil and root litter decay rate in response to simultaneous changes of temperature, precipitation and CO2. Further the objective is to examine below-ground plant competition.

Methods
Several methods will be included for assessment of root production. Root biomass and root production will be measured by sequential sampling of root cores and in-growth cores. Initially soil cores to a depth of about 20 cm will be sampled and divided by horizons. Roots will be removed and the soil will be used for in-growth cores, which are placed in the field for one year. Soil and roots will be separated and analyzed for total root length, root diameter, and root surface using image analysis. Mini-rhizotrons are already applied to the field site. Underground videotaped images will be taken in the rhizotrons to determine root biomass and dynamics. Root decay rate will be assessed using litterbags and differences in root chemistry to climate change will be measured by NIR spectroscopy. The synthesis of whole ecosystem carbon balance will take place in collaboration with scientists working in other field.