PHOTOSYNTHESIS OF MISTLETOES IN RELATION TO THEIR HOSTS AT VARIOUS SITES IN TROPICAL BRAZIL

Chlorophyll a fluorescence parameters showing the instantaneous perfor mance and carbon-isotope ratios reflecting long-term behaviour of leav es were determined for a large number of mistletoe/host-pairs in the c errado belt of Brazil. Study sites were a very exposed rupestrian fiel d, a semi-exposed savanna and a highly shaded gallery forest. The majo r question asked was if photosynthetic capacity of mistletoe leaves di ffered from that of the leaves of their respective hosts. It is shown that except for the very exposed rupestrian field site, photosynthetic capacity appeared to be similar in mistletoes and host leaves. The su perior behaviour of host leaves in the rupestrian field was due to par ticularly expressed sun-plant characteristics of the host. However, mi stletoes always had higher average stormatal conductances, lower leaf temperatures at similar or even higher irradiance and higher intercell ular CO2-partial pressures than hosts. Photosynthetic performance of m istletoe leaves was independent of whether a given mistletoe species p arasitized aluminium-accumulating or non-accumulating host species in the cerrados with their aluminium-rich soils.