Environmental changes in biodiversity hotspot ecosystems of
South Ecuador: RESPonse and feedback effECTs (FOR2730)

Abstract:

Precipitation event samples and weekly based water samples from streams and soils were collected in a tropical montane cloud forest catchment for 2 years and analyzed for stable water isotopes in order to understand the effect of sampling frequency in the performance of three lumped-parameter distribution functions (exponential-piston flow, linear-piston flow and gamma) which were used to estimate mean transit times of waters. Precipitation data, used as input function for the models, were aggregated to daily, weekly, bi-weekly, monthly and bi-monthly sampling resolutions, while analyzed frequencies for outflows went from weekly to bi-monthly. By using different scenarios involving diverse sampling frequencies, this study reveals that the effect of lowering the sampling frequency depends on the water type. For soil waters, with transit times on the order of few weeks, there was a clear trend of over predictions. In contrast, the trend for stream waters, which have a more damped isotopic signal and mean transit times on the order of 2 to 4 years, was less clear and showed a dependence on the type of model used. The trade-off to coarse data resolutions could potentially lead to misleading conclusions on how water actually moves through the catchment, notwithstanding that these predictions could reach better fitting efficiencies, fewer uncertainties, errors and biases. For both water types an optimal sampling frequency seems to be 1 or at most 2 weeks. The results of our analyses provide information for the planning of future fieldwork in similar Andean or other catchments.

Abstract:

In a litterbag study in a tropical montane rainforest in Ecuador we assessed the impact of leaf litter species identity and richness on decomposition. We incubated leaf litter of six native tree species in monocultures and all possible two and four species combinations and analysed mass loss over a period of 24 months. Mass loss in monocultures averaged 30.7% after 6 month and differed significantly between species with variations being closely related to initial concentrations of lignin, Mg and P. At later harvests mass loss in monocultures averaged 54.5% but did not vary among leaf litter species and, unexpectedly, did not increase between 12 and 24 months suggesting that litter converged towards an extremely poor common quality retarding decomposition. After 6 months mass loss of leaf litter species was significantly faster in mixtures than in monocultures, resulting in synergistic non-additive mixture effects on decomposition, whereas at later harvests mass loss of component litter species was more variable and leaf litter mixture effects differed with species richness. Mass loss in the two species mixtures did not deviate from those predicted from monocultures, while we found antagonistic non-additive mixture effects in the four species mixtures. This suggests that litter species shared a poor common quality but different chemistry resulting in negative interactions in chemically diverse litter mixtures at later stages of decomposition. Overall, the results suggest that interspecific variations in diversity and composition of structural and secondary litter compounds rather than concentrations of individual litter compounds per se, control long term leaf litter decomposition in tropical montane rainforests. Plant species diversity thus appears to act as a major driver for decomposition processes in tropical montane rainforest ecosystems, highlighting the need for increasing plant conservation efforts to protect ecosystem functioning of this threatened biodiversity hotspot.

Abstract:

Large areas in the tropics receive elevated atmospheric nutrient inputs. Presently, little is known on how nitrogen (N) cycling in tropical montane forest soils will respond to such increased nutrient inputs. We assessed how gross rates of mineral N production (N mineralization and nitrification) and microbial N retention (NH4+ and NO3- immobilization and dissimilatory NO3- reduction to NH4+ [DNRA]) change with elevated N and phosphorus (P) inputs in montane forest soils at 1000-, 2000-, and 3000-m elevations in south Ecuador. At each elevation, four replicate plots (20320 m each) of control, N (added at 50 kg N ha-1yr-1), P (added at 10 kg P ha-1 yr-1), and combined N x P additions have been established since 2008. We measured gross N cycling rates in 2010 and 2011, using 15N pool dilution techniques with in situ incubation of intact soil cores taken from the top 5 cm of soil. In control plots, gross soil-N cycling rates decreased with increase in elevation, and microbial N retention was tightly coupled with mineral N production. At 1000 m and 2000 m, four-year N and combined N þ P additions increased gross mineral N production but decreased NH4+ and NO3- immobilization and DNRA compared to the control. At 3000 m, four-year N and combined N x P additions increased gross N mineralization rates and decreased DNRA compared to the control; although NH4+ and NO3- immobilization in the N and NxP plots were not different from the control, these were lower than their respective mineral N production. At all elevations, decreased microbial N retention was accompanied by decreased microbial biomass C and C:N ratio. P addition did not affect any of the soil-N cycling processes. Our results signified that four years of N addition, at a rate expected to occur at these sites, uncoupled the soil-N cycling processes, as indicated by decreased microbial N retention. This fast response of soil-N cycling processes across elevations implies that greater attention should be paid to the biological implications on montane forests of such uncoupled soil-N cycling.

Abstract:

Although often overlooked in forest research, the canopy can play an important role in forest nutrient cycling. Since the canopy is spatially isolated from the forest floor, nutrient cycling in the two areas may differ as terrestrial nutrients accumulate. We measured rates of free-living N2 fixation along an elevation gradient (1,000, 2,000 and 3,000 m) of tropical montane canopy soils, compared these to rates measured in the top 5 cm of forest floor soils (excluding fresh litter), and assessed the effects of elevated nutrient inputs to the forest floor. N2 fixation was measured using the acetylene reduction assay. Measurements occurred in the field, in the wet and dry seasons, using intact cores of soil. The forest floor had been fertilized biannually with moderate amounts of nitrogen (N) and phosphorus (P) for 4 years; treatments included control, N, P and N x P. N2 fixation rates exhibited little variation with Elevation but were higher in the dry season than the wet season. Fixation was inhibited in forest floor N plots compared to control and P plots, and stimulated in canopy P plots compared to control. At 2,000 m, the canopy contributed 12 % of measured canopy and forest floor N2 fixation (1.2 kg N ha-1 year-1). Results suggest that N2 fixation is an active process in canopy soils, which is variable across seasons and sensitive to changes in terrestrial nutrient availability. Long-term terrestrial accumulation of N and/or P has the potential to significantly change the dynamics of soil N cycling in these canopies.

Abstract:

Orchid mycorrhizal detection, based only on fungal isolation from roots, is biased due to difficulties in isolating the respec- tive fungi. Previous investigations have shown that mostly ascomycetes, housed in the sheltered compartment of the vela- men covering the roots of epiphytic orchids, are isolated on agar plates. Roots of 83 individual epiphytic orchid of Stelis hallii, S. superbiens, S. concinna, Stelis sp. and Pleurothallis lilijae were sampled in the Reserva Biológica San Francisco, Southern Ecuador. The velamen was partly removed and root tissue macerated and transferred to Petri dishes containing corn meal agar, malt extract agar and Melin Norkrans modified medium. DNA was extracted from the cultures and the 5.8S-ITS region and partial nrLSU sequenced. Phylogenetic analysis revealed members of 12 orders of ascomycetes associ- ated with the roots of these orchids, a much higher diversity than previously known. Twelve isolates were related to the Helotiales. Our results have uncovered some of the fungal diversity within the velamen of epiphytic orchids; fungi invading, most likely, from tree bark or humus accumulation close to the roots.