What is needed to fulfill a research proposal that measurers water and carbon fluxes from a cell-perspective to landscape level?

In the fall of 2015, the Knut and Alice Wallenberg foundation granted 39 million SEK during five years to a research group at SLU in Umeå, in collaboration with researchers at Umeå and Helsinki University, to study the physiological and environmental drivers of carbon and water fluxes in forest ecosystems. This project is divided into five interrelated Branch-Points (BP) that spans the scale from leaf-level physiology to forest stand-level to better understand mechanisms influencing biomass production in boreal forests.

The five nodes compromise of:
(1) Separation of water loss from ecosystems into transpiration and evaporation, which in turn quantifies the amount of water used by trees for growth.

(2) Quantifying tree water-use-efficiency (WUE = photosynthesis/transpiration) and thus tree photosynthesis given direct measurements of tree transpiration in BP1.

(3) Assessing light-use-efficiency, which partitioning light energy capture by cholorphyll into photosynthesis (carbon gain) and photorespiration (carbon losses).

(4) Partitioning of total respiration between different respiration paths (normal and alternative respiration) which controls the efficiency of trees to produce biomass.

(5) Quantifying tree growth into above- (i.e., stem, shoot, leaf) and below-ground growth (roots and mycorrhiza) which controls how much of the total forest growth can be harvested for biomass.

This study will take advantage of the rich history of research, measurements and state-of-the-art infrastructure at Svartberget Research Station. Niles Hasselquist has initiated field measurements of tree transpiration using sap flow sensor to address question associated with BP1. Niles is one of many researchers that will be involved in the project.
Niles Hasselquist presents the project at one excursion in Svartberget.
Niles Hasselquist presents the project at one excursion in Svartberget.

Is it a detective’s examination of a complex water pipe system that you will study?

Yes, you might see it like that. On an overall level, we have relatively good knowledge about the processes driving fluxes of water and energy in, through and out from different forest ecosystems. By using variation in natural abundance stable isotopes, it is possible to get a better process-based understanding of the processes and pathways influencing the isotopic signature of carbon and oxygen among the different BP. This approach is unique in that it will allow us quantify both carbon and water fluxes at multiple spatial and temporal scales.

Why do you believe this synthesizing study is made now?

One aspect is definitely the recent technical advancement instruments that permits real time isotopic measurements in the field. The processes we want to capture are both fast and slow, so to capture them and determine their isotopic signature we need instruments that can make isotopic measurements in the field every second. To meet this requirement, we have acquired several field instruments to measure 18O and 13C in the field. One example of these instruments is an Areodye that measures the carbon isotopic signature (13C) of CO2 that is being exchange between the forested ecosystem and the atmosphere. 

Nuclear Magnetic Resonance (NMR) isotopomer measurements is another important resource in the project and studied in Branch-Point 3. Expertise on the topic is brought in by researchers from Umeå University. By NMR they analyze partitioning of C-13 between atoms in glucose-rings and hence gets information about photosynthesis and photorespiration. Using this technique it is possible to go back in time and analyze tree rings to better understand tree growth during other environmental conditions, e.g. under low atmospheric CO2 concentration. 
Tree core with annual rings which are used in the NMR study.
Tree core with annual rings which are used in the NMR study.

Natural conditions during long time – Need for field measurements

Partly what has made this study possible is the already established start-of-the-art infrastructure at Svartberget Research Station as well as it long history of measurements. Given the long-term measurements at the site, we have the unique opportunity to assess how natural increases in atmospheric CO2 concentrations influences numerous ecosystem processes, i.e., photosynthesis, forest productivity as well as stand-level transpiration and the important ramifications this may have for ecosystem hydrology and stream runoff.

Most of the research associated with the different BP will be conducted within Svartbergets basal infrastructure in SITES. Existing facilities, such as long-term monitoring stations, micrometeorological stations, soil water sampling facilities and stream water network will be used in combination with the ICOS-atmospheric tower. In Niles, BP 1 project, trees has been mounted with sap flow sensors in the close vicinity of the ICOS-tower. Measurements from the ICOS-tower are used to estimate evapotranspiration at a forest stand level, which will be used in combination with sap flow measurements to partition evapotranspiration into its different flux components, i.e., evaporation and transpiration.

You have just started, what have you initiated so far?

In June of this year, Niles with assistance from Pantana Tor-ngern at Chulalongkorn University, Bangkok, Thailand installed sap flow sensors on 60 trees. Each tree has two temperature sensors that are placed 10 cm apart which is connected to a logger cabinet. At the moment, we are measuring sap flux in both Scots pine and Norway Spruce trees ranging in size from 7 to 40 cm diameter-at-breast-height. We will continue to monitor sap flux in these trees for the length of the project period; during the next five years.
Sap flow sensors on spruces at Svartberget.
Sap flow sensors on spruces at Svartberget.
Title: Physiological Branch-Points with Ecosystem Consequences: Carbon and Water in Boreal Forests
Main applicant: Torgny Näsholm, SLU Umeå
Funding: 39.5 million SEK during five years
Funder: Knut and Alice Wallenberg Foundation
Niles Hasselquist, SLU Umeå
Svartberget Research station

Photos by Anders Esselin, Ida Taberman, Johannes Tiwari and Niles Hasselquist.

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