Department of Forest Sciences
P.O. Box 27
FI-00014 University of Helsinki
Forest Sciences Building
Latokartanonkaari 7, Viikki
Tel. +358 (0)9 191 58134
I am modeling the long distance transport in the xylem and phloem and their effect on tree structure, leaf gas exchange and growth. Water transport from soil to the leaves is crucial for tree performance as tree carbon assimilation is largely dependent on the supply of water to the leaves. At the same time the construction and maintenance of the water transport system, the xylem, requires a large proportion of the carbon assimilated by the tree so the structure of the xylem must be efficient. When water tension decreases too low due to excess transpiration and/or a drop is soil water potential xylem transport disrupts due to cavitation and leaf gas exchange must be limited by stomatal closure.
Phloem transports assimilate products from the leaves to the rest of the tree. Phloem transport in most plants takes place in the form of sugars forming viscous solutions at high concentrations and this poses a real problem for transport of sugars from the leaves. Hydraulic coupling to the xylem is significant from phloem point of view as the phloem draws its water from the xylem and any changes in xylem water potential will be reflected to the phloem and influence its function. Interactions between the xylem and phloem have also been demonstrated to be involved in the refilling of cavitated xylem conduits, phenomena of considerable eco-physiological importance which is still very weakly understood. We also hypothesize that leaf level control of gas-exchange is related to phloem transport of sugars from leaves to sugar sinks. Currently I am involved in the modelling of the physiology of cambial growth and linking it to transport of water and sugars to site of growth.
Publications in peer reviewed journals:
Hölttä T., Mäkinen H., Nöjd P., A. Mäkelä, E. Nikinmaa (2010). A physiological model of cambial growth. Tree Physiology 30, 1235-1252.
Jyske T., Hölttä T., Mäkinen H., Nöjd P., Lumme I., Spiecker H. (2010) The effect of artificially induced drought on radial increment and wood properties of Norway spruce. Tree Physiology 30: 103-105.
Mencuccini M., Hölttä, T. (2010). On light bulbs and marbles. Transfer times and teleconnections in plant fluid transport systems. New Phytologist 187, 888-891.
Sevanto S., Hölttä T., Nikinmaa E. (2009) The effects of heat storage during low flow rates on Granier –type sap flow sensors output. Acta Horticulturae. 846: VII International Workshop on Sap Flow.
Mencuccini M., Hölttä T. (2009) The significance of phloem transport for the speed of link between canopy photosynthesis and belowground respiration. New Phytologist. DOI: 10.1111/j.1469-8137.2009.03050.
Cochard H., Hernandez E., Herbette S., Hölttä T., Mencuccini M. (2009) The effects of sap ionic composition on xylem vulnerability to cavitation. Journal of Experimental Botany. doi:10.1093/jxb/erp298.
Hölttä T., Kolari P. (2009) Interpretation of stem CO2 efflux measurements. Tree Physiology. doi:10.1093/treephys/tpp073.
Hölttä T., Cochard H., Nikinmaa E. & Mencuccini M. (2009) Capacitive effect of cavitation in xylem conduits: results from a dynamic model. Plant, Cell & Environment 32, 10–21.
Cochard H., Hölttä T, Herbette S. Sylvain D., Mencuccini M. (2009) New Insights into the Mechanism of Water-Stress Induced Cavitation in Conifers. Plant Physiology. 151: 949-954.
Hölttä T., Mencuccini M. & Nikinmaa E. (2009) Linking phloem function to structure: Analysis with a coupled xylem–phloem transport model. Journal of Theoretical Biology 259, 325-337.
Hölttä T., Vesala T. and Nikinmaa E. (2007) A model of bubble growth leading to xylem conduit embolism. Journal of Theoretical Biology 249: 111-123.
Mencuccini M., Hölttä T., Giai P., Magnani F. (2007) Sanio’s laws revisited. Size-dependent changes in the xylem architecture of trees. Ecology Letters 10: 1084-1093.
Hölttä T., Vesala T., Sevanto S., Perämäki M. and Nikinmaa E. (2006) Modeling xylem and phloem water flows in trees according to cohesion theory and Münch hypothesis. Trees – Structure and Function. 20:67-78.
Hölttä T., Vesala T., Perämäki M. and Nikinmaa E. (2006). Refilling of embolised conduits as a consequence of ‘Münch water’ circulation. Functional Plant Biology 33: 949–959.
Hölttä T. Vesala T., Nikinmaa E., Perämäki M., Siivola E. and Mencuccini M. (2005) Field measurements of ultra-sonic acoustic emissions and diameter variations. A new insight into the relationship of xylem tensions and embolism. Tree Physiology 25: 237-243.
Sevanto S., Hölttä T., Hirsikko A., Vesala T. and Nikinmaa E. (2005) Thermal expansion of green wood: an analysis of temperature corrections for tree stem diameter variation measurements. Boreal Environmental Research 10: 437–445.
Sevanto S., Hölttä T., Markkanen T., Perämäki M., Nikinmaa E., Vesala T. (2005) Relationships between diurnal xylem diameter variation and environmental factors in Scots pine. Boreal Environment Research 10: 447–458.
Vesala T., Hölttä T., Perämäki M. and Nikinmaa E. (2003) Refilling of a hydraulically isolated embolised vessel: Model calculations. Annals of Botany. 91: 419-428.
Üllar Rannik, Nuria Altimir, Jukka Raittila, Tanja Suni, Anca Gaman, Tareq Hussein, Teemu Hölttä, Hannu Lassila, Maria Latokartano, Antti Lauri, Anas Natsheh, Tuukka Petäjä, Riikka Sorjamaa, Hanna Ylä-Mella, Petri Keronen, Frank Berninger, Timo Vesala, Pertti Hari, Markku Kulmala (2002) Fluxes of carbon dioxide and water vapour over Scots pine forest and clearing. Agricultural and Forest Met. 111 pp. 187-202.
Hölttä T., Vesala T., Perämäki M. and Nikinmaa E. (2002) Relationships between Embolism, Stem Water Tension, and Diameter Changes. Journal of Theoretical Biology 215: 23-38.
Accepted for publication in peer reviewed journals:
Sevanto S., Hölttä T., Holbrook N. (2010). Effects of the hydraulic coupling between xylem and phloem on diurnal phloem diameter variation. Plant Cell & Environment (accepted for publication)