Abstract:
Ecosystems worldwide face increasing nutrient depositions mainly caused by anthropogenic processes. In particular, tropical ecosystems react sensitively to altering nutrient supply. The deposition of nutrients might influence the nutrient cycles, primarily of N and P in tropical montane rainforests. Increased nutrient supply leads to an enhanced biomass production and therefore other nutrients become limited for plants and microorganisms.
For this reason, the aim of this thesis is to study the response of phosphatase activity (PA) on moderate fertilization along an altitudinal gradient in a tropical montane rainforest in South Ecuador. The experiment was conducted on the NUMEX study sites including three different elevation levels 1000, 2000 and 3000m a.s.l. The different plots were treated with N, P, N+P to simulate increased nutrient depositions and one control plot. Further, organic layer and mineral soil was sampled and phosphomono- and phosphodiesterase activity (PMEA and PDEA) were determined.
The N fertilized plots showed only small effects compared to the control; presumably due to low amounts of added fertilizer. PA in the P addition plots showed reduced activity compared to the control with significant results of PMEA in the organic layer of the study sites on 2000 and 3000m a.s.l. The reason might be sufficient quantities of inorganic P which suppresses the production of phosphatases. Further, PA in N+P plots showed lower PA compared to the control than in the P addition plots. This effect could be caused through the dominating inhibitory effect of P in contrast to the stimulating effect of N on PA. Altitudinal differences were observed comparing the control plots at different elevation levels (1000, 2000 and 3000m a.s.l.). The results for the organic layer showed increasing PA along the altitudinal gradient with the lowest PA at 1000m a.s.l. The findings are contrary to the present literature which states that lowland tropical forests are characterized by high decomposition rates coming up with high PA. The findings cannot support this hypothesis; therefore more research is needed in the studied area in South Ecuador.
