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

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:

Ecosystem services, provided from tropical forests, are indispensable for human beings. Coherencies in the system, their networks, drivers and various underlying pathways are not completely understood yet. Elucidation on directions of key nutrients and changes in organisms delivers the opportunity to get an overview about these relations. Leaf functional traits are one important component to uncover those cascades and organizations. With their fast respond to environmental conditions, changes can be detected. Since, tropical regions suffer from increasing atmospheric inputs of nitrogen (N) and phosphorus (P), it is a need to investigate these progressions and predict future scenarios. The alarming fact, that these anthropogenic caused input have unknown consequences for the structure and functioning of tropical forests leads to a crucial study topic. Furthermore, questions should be answered if these increased inputs have a comparable influence on different elevations, based on identification the limiting nutrients. To forecast these impacts the Nutrient Manipulation Experiment (NUMEX) has been conducted since 2008. It gained to show, that Neotropical montane forests respond rapidly to moderate nutrient additions of N (50 kg ha-1 yr-1) and P (10 kg ha-1 yr-1). Within the present study, the eight most abundant tree species from the NUMEX sites were analyzed to their leaf functional traits from three elevations (altitude above sea level) in an Ecuadorian montane forest. The premontane forest in Bombuscaro (1,000 m) contains the species Clarisia racemosa and Pouteria torta. Further, in San Francisco (2,000 m), Alchornea lojaensis, Graffenrieda emarginata, Hieronyma fendleri, and Myrcia sp., were selected. In Cajanuma (3,000 m), the upper montane forest contains Hedyosmum purpurascens and Weinmannia loxensis. The fertilization effects were calculated, using a mixed effect model, including study year and treatment as fixed effects and block and individual as random effects. The results show, that foliar N decrease over the years, whereas, Foliar P conversely increases. Further, the relation of nitrogen and phosphorus (N:P) is decreasing during the study years. Upwards trends for ?15N are best replicated for the San Francisco site. With the leaf trait nutrient resorption efficiency (NuR) for N and P a decline over the study years is proceeding. In addition, leaf area (LA) and specific leaf area (SLA) tend to decrease. In conclusive processes over the study years might be the result of microclimatic events. The sites differ in that San Francisco and Cajanuma respond more similar in some leaf functional traits, compared to them from Bombuscaro. It can be deduced that changes in the analyzed leaf traits over the last eight years between the sites and species are not significantly different. Summarizing, results represent the emphasis on the considerable influence of nutrient addition with notably changing foliar nutrient and show that the predicted nutrient deposition will probably change the ecosystem dynamics sustained.