Drs. Dr. Onno Muller

 

Since December 2005 Onno Muller started as a post-doc for 2 years at Tohoku University. He will continue his research focusing on the functional mechanisms explaining the distribution of broad-leaved evergreens.

Contact address:

dr. O. Muller
Tohoku University
Graduate School of Life Science
Aoba-ku, Sendai, 980-8578

JAPAN

tel: +81 (0)22 795 6698
fax: +81 (0)22 795 6699
email: onnomuller@hotmail.com


His PhD- thesis in PDF-format is available through the library of Utrecht University:
http://igitur-archive.library.uu.nl/dissertations/2005-1217-214555/index.htm

 

Background

I started my specialization in plant ecology in my master’s course for which I did three major researches. My first research involved the classification of a satellite image into a vegetation map based upon a field survey that we did in Turkey. Secondly I specialized in plant taxonomy of a neotropical plant family in which we unraveled one species complex. In this framework I went on an expedition in Guyana to collect specimen for the “Flora of the Guianas”. I did my third research, in Japan, as part of an exchange program. I investigated the photosynthetic characteristics in relation to nitrogen of several evergreen species for one year. This study gave such interesting and new results that I was invited to continue my research in Japan. This resulted in a PhD position at Tohoku University, under supervision of Tadaki Hirose and Kouki Hikosaka, and Utrecht University simultaneously.

PhD project: general outline (see for a short outline in Dutch a poster presented on UU-employee day 2005)

Functional mechanisms of evergreen leaves in a seasonal climate

Within my PhD research I focus on leaf traits of plants in the forest understory and their acclimation to temperature and/or light. In a temperate climate there are large changes in temperature over the year. The seasonal development and shedding of leaves of deciduous canopy trees has a large impact on the light environment in the understory. So naturally evergreen plants in the forest understory are exposed to large changes in temperature and light over the year.
From literature we knew that a plant can acclimate to different temperature and light conditions separately, but the question was: does it acclimate under natural conditions? I showed that for Aucuba japonica mainly temperature affects the organization of the photosynthetic apparatus, resulting in relatively more light utilization components than light harvesting components in the low temperature season. 1,a,b
I observed strong seasonal dynamics in leaf nitrogen content over the year with highest values in winter. With a simple model, using the relation between photosynthetic capacity and leaf nitrogen content at different temperature and light conditions during the year, I showed the adaptive significance of changes in leaf nitrogen content in terms of maximizing carbon gain per unit nitrogen. I found a good correlation between the calculated optimal nitrogen values and the observed values in the field. A,d
In a pot experiment I measured photosynthesis under controlled conditions and also determined leaf anatomy. I showed that evergreen leaves have relatively much vacant space along the surface area of the mesophyll cells in summer and that this space was occupied by chloroplasts at low temperature in winter. The leaf anatomical parameters, such as chloroplast volume and chloroplast area exposed to the intercellular space, proved well correlated with the leaf nitrogen content. e
Presently, to furher investigate the details of leaf anatomy, I grew three species that differ in natural leaf phenology in a climate chamber under high and low temperature and light conditions. Each of these species produces most leaves in summer but one (evergreen) species maintains these leaves through winter sometimes for more than 2 years; one species maintains the leaves till spring but it also makes new leaves in autumn, and another species sheds its leaves in autumn while simultaneously making new leaves for winter. I expected that temperature and light conditions determine their leaf anatomy. I measured photosynthetic rates at respective temperature and light conditions and presently analyze their leaf anatomy. I expect to prove that species that can maintain leaves in winter are more plastic in leaf anatomy than the species that make new leaves in autumn.
 

Ph.D. Dissertation:

Muller, O, 2005 Seasonal acclimation to light and temperature in an
evergreen understory shrub. Ph.D. dissertation, Utrecht University, 100 p.
http://igitur-archive.library.uu.nl/dissertations/2005-1217-214555/index.htm


Publications:

1) Muller O, Hikosaka K, Hirose T, Seasonal changes in light and temperature affect the balance between light harvesting and light utilisation components of photosynthesis in an evergreen understory shrub. Oecologia, 143:501-508 , 2005 [ Article (pdf 315kb) | Pictures ].
 

Proceedings:

A) Muller O, Hikosaka K, Anten NPR, Hirose T, Werger MJA , Optimal leaf nitrogen content of an evergreen understorey plant in a temperate climate. In: van der Est A, Bruce D (eds) Photosynthesis: Fundamental Aspects to Global Perspectives, Allen Press, Lawrence, KS, 2005, USA, pp. 636-638. [ Article (pdf 126kb)].

Hikosaka, K., Ishikawa, K., Borjigidai, A., Muller O., Onoda Y. 2006
Temperature acclimation of photosynthesis: mechanisms involved in the
changes in temperature dependence of photosynthetic rate. Journal of
Experimental Botany, JXB Advance Access DOI 10.1093/jxb/erj049.
 

Congresses and abstracts:

e) Muller O, Oguchi R, Hikosaka K, Anten NPR, Werger MJA, Hirose T, Does acclimation to seasonal changes in temperature and light need changes in leaf anatomy in evergreen leaves? Plant Frontier Meeting Abstracts: Phenotypic plasticity and the changing environment. J. Exp. Bot. 56 p. i1-i13, 2005
[ Poster (PDF 392kb) | Pictures ]

d) Muller O, Hikosaka K, Anten NPR, Werger MJA, Hirose T, Optimal leaf nitrogen content of an evergreen understorey plant in a temperate climate. 13th International congress of photosynthesis, Allen press, p. 508 2004
[ Poster (PDF 243kb) ]

c) Muller O, Hikosaka K, Hirose T, Does photosynthetic acclimation contribute to carbon gain under seasonal environment in the evergreen understorey shrub Aucuba japonica? The 50th Annual Meeting of the Ecological Society of Japan, p. 286, 2003 (poster presentation)

b) Muller O, Hikosaka K, Hirose T Werger MJA, Photosynthetic acclimation of an evergreen understory plant, Aucuba japonica, to seasonal environment in different light regimes. Proceedings of the VIII INTECOL International Congress of Ecology, p190, 2002 (oral presentation)

a) Muller O, Hikosaka K, Hirose T, Photosynthetic acclimation of an evergreen understory plant, Aucuba japonica, to seasonal environment in different light regimes. The 49th Annual Meeting of the Ecological Society of Japan, p 153, 2002 (oral presentation)