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Förslaget inkom 2003-01-30

The relationship between plant growth, the microbial available phosphorous and the soil water content in tropical rain forest soils (Sabah, Malaysia).

Background of the project: Department of Forest Ecology (FE) and Sabah Forest Industries (SFI) of Sabah, Malaysia are jointly operating an environmental impact assessment research project on site effects of the conversion of tropical rain forest to fast growing forest plantation (for more information see http://www.sek.slu.se/~malm/Joint_projec.htm). During the more than ten years of cooperation, the working environment within the framework of the joint project have been a good growing ground for teaching and training. For higher education degrees, the project have resulted in one Malaysian taking a MSc and one Swede taking a PhD. Presently, a MSc training aiming at graduating two Malaysians is in operation. Malaysian officers, laboratory personnel and field conductors have undergone successive training mostly in Sabah, but also for shorter periods in Umeå. Since 1989 eleven Swedish students have made field studies of between 4 to 10 weeks at the research site. Seven of these students have done Minor field studies (MFS).

Background for this study: Phosphorus is the main limiting nutrient in many tropical forests, and the phosphorus availability of the trees is thought to be dependent on the microbial activity in the soil. It is established that the microbial activity is tightly linked to the water content of the soil. Because this relationship is unique to different methods of water measurements and in most cases to different soils, there have been large problems to assess the effect of different land use on the microbial activity and the phosphorus availability. So far, attempts to link soil chemistry and biological activity to plant growth have been disappointing. A recent study showed that the specific growth rate of the microbes in three tropical soils and one Swedish mor layer had remarkably similar response to water when water was measured as water potential, however not if other methods where used. It would be of great importance to establish if this result is possible to repeat on other soils and if it could be used to increase the precision of phosphorus measurements.

Methods: Different soils of different productivity and land use history are sampled in the field in Malaysia. A pot study of plant growth is initiated. Soil samples are brought to Sweden, adjusted to different water potentials, and thereafter analyzed for microbial available phosphorus in a respirometer.


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