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

Abstract:

Anthropogenic atmospheric deposition can increase nutrient supply in the most remote ecosystems, potentially affecting soil biodiversity. Arbuscular mycorrhizal fungal (AMF) communities rapidly respond to simulated soil eutrophication in tropical forests. Yet the limited spatio-temporal extent of such manipulations, together with the often unrealistically high fertilization rates employed, impedes generalization of such responses. We sequenced mixed root AMF communities within a seven year-long fully factorial nitrogen (N) and phosphorus (P) addition experiment, replicated at three tropical montane forests in southern Ecuador with differing environmental characteristics. We hypothesized (i) strong shifts in community composition and species richness after long-term fertilization, (ii) site- and (iii) clade-specific responses to N versus P additions depending on local soil fertility and clade life history traits respectively. Fertilization consistently shifted AMF community composition across sites, but only reduced richness of Glomeraceae. Compositional changes were mainly driven by increases in P supply while richness reductions were observed only after combined N and P additions. We conclude that moderate increases of N and P exert a mild but consistent effect on tropical AMF communities. To predict the consequences of these shifts, current results need to be supplemented with experiments that characterize local species-specific AMF functionality.

Abstract:

The anthropogenic deposition of nitrogen (N) and phosphorus (P) into terrestrial ecosystems has an influence on the leaf morphology and leaf properties of vegetation as well as on interactions within an ecosystem. In this context, the increased availability of nutrients has an impact on herbivory. In addition to the availability of nutrients, sea level has also been shown to influence these parameters. The shown work deals with the quantification of herbivory under the influence of N- and P-fertilization and differences in certain leaf parameters (leaf area, specific leaf area, leaf toughness, leaf nitrogen content and leaf area loss) between three altitudinal levels (1000 m, 2000 m, 3000 m). The study area was located in a tropical mountain rainforest in Southern Ecuador. In a nutrient manipulation experiment (NUMEX) 48 plots within the study areas were fertilized with either N, P or NP twice a year. Per plot 50 leaves were collected, examined for various parameters and then subjected to a nutrient analysis. The aim of this study was to figure out to what extent sea level influences the leaf morphology, nitrogen content and the leaf area loss of the vegetation within the control areas and to what extent fertilization with nitrogen, phosphorus or both elements changes these leaf properties. Finally, it was investigated whether possible changes in feeding rates resulted from an increased leaf nitrogen content. Sea level had a major influence on leaf strength, which increased with increasing height gradients, and on the specific leaf area and the mean leaf area, which decreased with increasing sea level. Many of the values differed significantly between the altitudinal levels. This suggests that not only the soil becomes nutrient-poorer with rising sea level, but also that the mineralisation of the few available nutrients is slower than at lower altitudes. The climatic environmental conditions, which become more extreme as the sea level rises, also explain the changes in the leaf parameters mentioned. Fertilisation instead did not have an influence as strong as sea level on the studied parameters. There were hardly any significant differences between the plots with different fertilisation. Since tropical forests are considered nutrient-limited, the addition of nitrogen led to the formation of large and soft leaves, which was expected. The correlations between leaf nitrogen content and SLA or leaf strength were positive and significant. Leaf area loss did not correlate with nitrogen content, which was unexpected. This can be attributed to the fact that plants show highly species-specific reactions to nutrient availability, which manifest themselves in very different plastic changes in growth and defence mechanisms against herbivore species. In this work a strong influence of the sea level on the leaf parameters could be determined. An increasing influence of fertilization on the feeding rate of herbivorous species was not found.

Abstract:

The tropical Andes are one of the most biodiverse hotspots on earth. Though the nutrient-limited systems are affected by anthropogenic nutrient inputs due to industry and agriculture. The NuMEx (Nutrient Manipulation Experiment) project, which was set up in 2008 and is located in southern Ecuador and aims to find out about the consequences of nutrient pollution to herbivore and plant interaction. Therefore experimental plots at three different levels of elevation were fertilised with nitrogen and phosphorus. In this study, fresh leaf samples were collected in May 2018. Plant parameters like leaf area, specific leaf area, leaf toughness and nitrogen content were analysed. Herbivory was examined trough leaf area loss measurements. Changes in these parameters along an elevation gradient from 1000 to 3000 m were analysed. Moreover, the study focussed on the influence of the nutrient addition to the sensible tropical system. A significant influence of the elevation on most of the leaf morphology parameters was shown. Specific leaf area and leaf nitrogen content showed a significant decrease along the elevation gradient, while the leaves became tougher. The mean leaf area and the leaf area loss gained no significant results; however, the leaf area tended to be smaller within rising elevation. The leaf area loss was highest at 3000 m of elevation. All elevation outcomes, except for the leaf area loss, could be explained by the harsher climatic conditions at higher elevation levels and the relationship between nitrogen content and the leaf traits. Nutrient addition results on the leaf traits were less clear. Almost no significant influences could be measured. The leaf characteristics showed mostly a clear trend though, except for the leaf area. The leaf area partially increased (mostly under mixed nitrogen and phosphorus addition) and partially decreased (nitrogen treatment) due to the nutrient addition. Specific leaf area, leaf nitrogen content and leaf area loss mostly increased due to the nutrient addition, especially nitrogen and the mixed nitrogen and phosphorus sample contributed to the increase. Leaf toughness whereas decreased. The highest decrease was caused at the plots treated with the nitrogen and phosphorus mix. The results make clear that a high leaf nitrogen content correlates with soft leaves and a high specific leaf area. An analysis of the leaf area loss and the leaf nitrogen content yielded that also these traits are correlated.

Abstract:

Anthropogenic activities have produced changes in natural ecosystems worldwide. In tropical regions in South America, industrialization of cities and forest clearance via burning are the main activities releasing pollutants into the atmosphere and inducing changes in nutrient deposition patterns and climate of primary forests. Nitrogen (N) and phosphorus (P) are considered the main limiting nutrients of plant growth since their availability is vital for net primary productivity. Therefore, any change in N or P availability in soils would likely alter important mechanisms of forests dynamics such as growth and survival. Changes in soil pH (acidity), nutrient cycles and altered nutrient stocks affect N and P availability and affect various physiological processes of trees. Although low levels of nutrient deposition have been reported for montane forests in southern Ecuador (ca. 5 kg ha–1 for N, 0.49 kg ha–1 for P), even these levels are expected to lead to changes in forest structure and dynamics over the long term. The responsiveness of forest to changes in resource availability varies with forest age and successional status, as well as life stage of the plant. Young plants (tree seedlings) should be more responsive to changes in nutrient availability than mature forest trees. Further, any demographic response is more likely to be visible in seedlings before mature trees because of the more rapid dynamics of seedlings. Therefore, I studied the regeneration dynamics of montane forest to understand which nutrient-related processes are involved in the growth and establishment of seedlings at both the individual and community levels. The Ecuadorian NUtrient Manipulation EXperiment (NUMEX) has been designed to study the response of montane forest to moderate fertilization. The experiment has been set up over an elevation range across three main study sites (1000 m. a.s.l: Bombuscaro; 2000 m. a.s.l: San Francisco; 3000 m. a.s.l: Cajanuma) within the Podocarpus National Park and San Francisco Reserve. The factorial experiment consists of four blocks containing four experimental plots (N, P, NP and control) in every study site (16 plots per elevation). Fertilization has been done since 2008, adding moderate quantities of fertilizer (50 kg ha–1 y–1 of N and/or 10 kg ha–1 y–1 of P). Three different approaches were used to assess the seedling community and common species responses to fertilization. First, the seedling community was monitored in natural forest at 2000 m over three consecutive years (2011 – 2013). In 192 monitoring subplots (1m2 each) in San Francisco, all seedlings and saplings were mapped and tagged. Measurements of height, diameter, herbivory and leaf production were recorded for all individuals, and the number of recruited and dead seedlings was counted every year. Second, allocation patterns and stoichiometry of seedlings of the six most common species were determined across the elevation gradient. Naturally occurring seedlings of the following species were harvested: Clarisia racemosa and Pouteria torta in Bombuscaro, Graffenrieda emarginata and Palicourea angustifolia in San Francisco and Grafferieda harlingii and Hedyosmum purpuracens in Cajanuma. Morphology (biomass allocation, herbivory and foliar areas such as SLA, LAR and LA) and foliar stoichiometry (nutrient contents and N:P ratios) were recorded and analyzed. Third, a reciprocal transplantation experiment (STE) within the NUMEX experimental plots monitored seedlings of the most common species in Bombuscaro, (Pouteria torta), to assess specific responses in seedling performance over one year. These three levels of analysis showed differential responses of the species community and common species to fertilization. Contrary to lowland forests, the community seedlings in this montane forest showed a moderate response. The density of seedling individuals decreased following nutrient addition, as a result of lower recruitment in treatments plots, but mortality was unaffected. Consequently, density-dependent mechanisms activated by additional N uptake did not show evidence of being a main driver to changes in species density. The community of seedlings did not show significant growth in response to fertilization although seedlings were higher in the N treatment. However, N addition increased herbivory over all seedlings and plots, which could have masked other seedlings growth responses. Common species seem to be well adapted to the relatively poor soils since these species were not favored by nutrient addition showing no change in growth or leaf traits. Over the long-term, common species might lose their dominance by being less competitive than faster growing species. However, it would need a longer period of monitoring under continued fertilization to produce visible shifts in community composition. Species-specific responses are hard to determine in such species rich communities. Therefore, analyses of the six common species were conducted to complement the community-level study. Leaf morphology and foliar stoichiometry were assessed from harvested seedling from the experimental plots. Both N and P had effects on seedling traits, suggesting co-limitation of N and P in montane tree species in all elevations. However, foliar N:P ratios and the more frequently response to P addition indicated this nutrient might be more limiting than N along the gradient. Responsiveness of the studied species varied between the six species. Stronger foliar P concentration compared with N in all species but Pouteria torta suggested higher P consumption in montane forest species, similar to the responses of several other tropical plant species after P addition. Increased herbivory was only evident in the opposite responses of G. emarginata (N and N+P addition) and P. angustifolia (P addition) at 2000 m suggesting that plant selection by herbivores is driven by resource quality. Most of the species had higher belowground biomass in root fractions following fertilization, except for G. harlingii at 3000 m, the only species that showed significant increase in aboveground biomass after nutrient addition. Pouteria torta seedlings showed no significant changes in species performance after fertilization one year after establishment of the STE. Pouteria seems to be well-adapted to poor soils, since N and P addition did not alter foliar nutrient concentrations. Nevertheless, N and N+P addition significantly increased mortality and diameter growth rates. P addition resulted in higher leaf area loss and shifted carbon allocation to root growth. These responses indicated consequences in the competitive strength in the understory and recruitment success of Pouteria torta. However, the ambiguous response in some attributes (growth and herbivory) not related with mortality made it difficult to predict the future abundance of this species in long term. In conclusion, complementary studies demonstrated that specific nutrient limitation for N or P in montane species seem not to be a rule in rich species ecosystems although nutrient addition did alter some pattern of growth and survival. Thus, nutrient fertilization might affect various mechanisms and dynamics of plant communities, the balance of which will only play out over long time scales.

Abstract:

In times of climate change and devastation, the conservation of biodiversity is an important issue. The formation of a mycorrhiza plays a very important role. The arbuscular mycorrhiza is a mutualistic symbiosis between fungi and plant roots. The arbuscular mycorrhizal fungi represent a monophyletic group, the Glomeromycota, which probably have a common ancestor with the Asco-and Basidiomycota. The arbuscular mycorrhiza is characterized by an enormous spreading. It is found in all climates. The vast majority of tropical plants form an arbuscular mycorrhiza, including plants in the Páramo, a type of vegetation in the humid tropical high Andes of South America above the treeline. In this study, root material from the Páramo-vegetation in Cajanuma in South Ecuador was examined. The analysis can be divided into two parts, the morphological and genetic analyses. Concerning the morphology the root samples were analysed under the light microscope. In 16 of 20 samples colonization with arbuscular mycorrhizal fungi was detected. Exactly these 16 samples also showed fungi belonging to the group of dark sepatate endophytes (DSE) which are likely representatives of the Ascomycota. In the context of genetic analyses arbuscular mycorrhizal fungi have been analysed with molecular methods sequencing part of the 18S rDNA. For the identification of fungi, which do not belong to the Glomeromycota, a part of the ITS-region of the DNA has been studied and sequenced. The sequences of arbuscular mycorrhizal fungi belong to families of Glomeraceae and Acaulosporaceae. In comparison with other investigations it can be assumed that the Páramo in Cajanuma has its own AMF community. The sequences of the Ascomycota all belong to the order of the Helotiales. By comparing the results to other investigations it could be demonstrated, that the dark septate endophytes survive under several climatic conditions. Furthermore they probably play an important role in the supply of nutrients. In this work, the dark septate endophytes show a greater range of species than the arbuscular mycorrhizal fungi. That possibly indicates a higher diversity in the Ascomycota than in the Glomeroycota in the Páramo-vegetation in Cajanuma. In order to confirm this hypothesis, a far greater data base is required. This data base will be the key to maintaining biodiversity. It ensures a better understanding of fungi and their interactions. Through this understanding, new approaches to protect biodiversity can be created.