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Response of water-bound fluxes of potassium, calcium, magnesium and sodium to nutrient additions in an Ecuadorian tropical montane forest
No full textCarbon Stable Isotope Ratio of Dissolved Organic Matter as a Tool To Identify Its Sources and Transformations in a Tropical Montane Forest in Ecuador
No full textSources and Sinks of N in Ecosystem Solutions Along the Water Path Through a Tropical Montane Forest in Ecuador Assessed With δ 15 N Values of Total Dissolved Nitrogen
No full textAbstract The globally increasing reactive N richness affects even remote ecosystems such as the tropical montane forests in Ecuador. We tested whether the δ 15 N values of total dissolved N (TDN), measured directly in solution with a TOC‐IRMS, can be used to help elucidate N sources and sinks along the water path and thus might be suitable for ecosystem monitoring. From 2013 to 2016, the δ 15 N values of TDN in bulk deposition showed the most pronounced temporal variation of all ecosystem solutions (δ 15 N values: 1.9–5.9‰). In throughfall (TF), TDN was on average 15 N‐depleted (−1.8 ± s.d. 0.4‰) relative to rainfall (3.4 ± 0.9‰), resulting from net retention of isotopically heavy N, mainly as NH 4 + . Simultaneously, N‐isotopically light NO 3 − ‐N and dissolved organic nitrogen (DON) with a δ 15 N value between NO 3 − ‐N and NH 4 + ‐N were leached from the canopy (leaves: −3.5 ± 0.5‰). The increasing δ 15 N values in the order, TF < stemflow (SF, 0.1 ± 0.6‰)< litter leachate (LL, 1.3 ± 0.7‰) concurred with an increasing DON contribution to TDN reflecting the δ 15 N value of the organic layer (1.9 ± 0.9‰). The lower δ 15 N value of the mineral soil solution at the 0.15 m soil depth (SS15, −1.5 ± 0.3‰) than in LL can be explained by the retention of DON and NH 4 + and the addition of NO 3 − from mineralization and nitrification. The increasing δ 15 N values in the order, SS15 < SS30 (−0.6 ± 0.2‰) < streamflow (ST, 0.5 ± 0.6‰) suggested gaseous N losses because of increasing denitrification. There was no seasonality of the δ 15 N values. Our results demonstrate that the δ 15 N values of TDN in ecosystem solutions help identify N sources and sinks in forest ecosystems.Plain Language Summary Many ecosystems experience increasing nitrogen availability because of nitrogen deposition from the atmosphere caused by human activities. The deposited nitrogen can produce a growth boost or be leached into groundwater and surface water. The stable isotope ratios of nitrogen (δ 15 N values) provide a tool to investigate into the consequences of increasing nitrogen availability. Here, we applied a new direct measurement method of δ 15 N values in total dissolved nitrogen of ecosystem solutions to follow sources and sinks of nitrogen in a tropical montane rain forest in Ecuador. We found that the isotopically heavy nitrogen input via rainfall is enriched by isotopically lighter nitrogen from plants and nitrogen turnover during the water passage through the canopy. Once, the solutions reach the mineral soil, dissolved organic nitrogen, which is comparatively rich in the heavy nitrogen isotope, is retained rendering the remaining nitrogen isotopically lighter. This process is reversed deeper in the soil by conversion of the nitrate to nitrogen gasses, which are depleted in the heavy nitrogen isotope and leave the ecosystem to the atmosphere. The direct measurement of δ 15 N values provides a tool to monitor the changing nitrogen cycle in ecosystems.Key Points Increasing δ 15 N values in total dissolved nitrogen from throughfall to litter leachate correlated with an increasing organic contribution The retention of N‐isotopically heavy dissolved organic nitrogen in the mineral topsoil decreased the δ 15 N values in mineral soil solutions Increasing δ 15 N values from the topsoil solution via the subsoil to the streamflow suggested gaseous N losses because of denitrificationDeutsche Forschungsgemeinschaft https://doi.org/10.13039/501100001659Secretaría de Educación Superior, Ciencia, Tecnología e Innovación https://doi.org/10.13039/50110000429
Response of element cycling and budgets to nutrient additions in a tropical montane forest of Ecuador
No full texthttp://dx.doi.org/10.13039/100019129 Ministerio del Ambiente, Agua y Transición Ecológicahttp://dx.doi.org/10.13039/501100001659 German Research Foundatio
Above‐ and belowground strategies of tropical montane tree species are coordinated and driven by small‐scale nitrogen availability
No full textAbstract
The question whether the strategies of above‐ and belowground plant organs are coordinated as predicted by the plant economics spectrum theory is still under debate. We aim to determine the leading dimensions of tree trait variation for above‐ and belowground functional traits, and test whether they represent spectra of adaptation along a soil fertility gradient in tropical Andean forests.
We measured leaf, stem and fine root functional traits, and individual‐level soil nutrient availability for 433 trees from 52 species at three elevations between 1000 and 3000 m a.s.l.
We found close coordination between above– and belowground functional traits related to the trade‐off between resource acquisition and conservation, whereas root diameter and specific root length formed an independent axis of covarying traits. The position of a tree species along the acquisition–conservation axis of the trait space was closely associated with local soil nitrogen, but not phosphorus, availability.
Our results imply that above‐ and belowground plant functional traits determine at which edaphic microhabitats coexisting tree species can grow, which is potentially crucial for understanding community assembly in species‐rich tropical montane forests.
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for this article on the Journal blog.Deutsche Forschungsgemeinschaft https://doi.org/10.13039/501100001659Alexander von Humboldt-Stiftung https://doi.org/10.13039/10000515
Nitrogen and phosphorus additions impact arbuscular mycorrhizal abundance and molecular diversity in a tropical montane forest
No full textIncreased nitrogen (N) depositions expected in the future endanger the diversity and stability of ecosystems primarily limited by N, but also often co-limited by other nutrients like phosphorus (P). In this context a nutrient manipulation experiment (NUMEX) was set up in a tropical montane rainforest in southern Ecuador, an area identified as biodiversity hotspot. We examined impacts of elevated N and P availability on arbuscular mycorrhizal fungi (AMF), a group of obligate biotrophic plant symbionts with an important role in soil nutrient cycles. We tested the hypothesis that increased nutrient availability will reduce AMF abundance, reduce species richness and shift the AMF community toward lineages previously shown to be favored by fertilized conditions. NUMEX was designed as a full factorial randomized block design. Soil cores were taken after 2 years of nutrient additions in plots located at 2000 m above sea level. Roots were extracted and intraradical AMF abundance determined microscopically; the AMF community was analyzed by 454-pyrosequencing targeting the large subunit rDNA. We identified 74 operational taxonomic units (OTUs) with a large proportion of Diversisporales. N additions provoked a significant decrease in intraradical abundance, whereas AMF richness was reduced significantly by N and P additions, with the strongest effect in the combined treatment (39% fewer OTUs), mainly influencing rare species. We identified a differential effect on phylogenetic groups, with Diversisporales richness mainly reduced by N additions in contrast to Glomerales highly significantly affected solely by P. Regarding AMF community structure, we observed a compositional shift when analyzing presence/absence data following P additions. In conclusion, N and P additions in this ecosystem affect AMF abundance, but especially AMF species richness; these changes might influence plant community composition and productivity and by that various ecosystem processes
Chlorine in plants and soils of a tropical lower montane forest in Ecuador: Development during two decades
No full textAbstract Aims Cl is a micronutrient mainly supplied via deposition of marine aerosols. We assessed the development of Cl concentrations and stocks in plants and soils of a tropical montane forest far from a downwind ocean during two decades (1998–2019). Methods We measured Cl concentrations in solid samples with a new combustion-based method. Results The Cl concentrations in leaves of 17 tree species ranged 0.04–1.6 g kg −1 . Three tree species showed Cl concentrations below the minimum requirement of 0.2 g kg −1 . Twigs had the largest Cl concentration of all plant compartments (2.1 ± SD1.5 g kg −1 ) and leaves the smallest. The Cl concentrations decreased from litterfall (0.52 ± 0.14) to the soil organic layer (0.12 ± 0.06), within the organic layer from top to bottom and further in the mineral soil (0.02–0.03) reflecting leaching losses and the retention of Cl in soil organic matter. The parent rocks (metamorphic sand to clay stone interlayering) contained 0.44 ± 0.20 g kg −1 Cl. The vegetation stored more Cl (28 ± 17 g m −2 ) than the organic layer (2.9 ± 3.1) and mineral soil (fine earth 0–1 m, 22 ± 8.6) together. One meter of rock contained up to 168 g m −2 Cl. Wood production took up 0.36 ± 0.24 g m −2 yr −1 Cl. Litterfall cycled 0.55 ± 0.17 g m −2 yr −1 Cl representing 86 ± 72% of the standing Cl stock in leaves (0.64 ± 0.50 g m −2 ). The leaching potential of Cl − from leaves was likely < 10% of the reported Cl − bulk deposition of 1.2 g m −2 yr −1 . There were no significant temporal trends of Cl concentrations in leaves, litterfall, organic layer, and mineral soil.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Karlsruher Institut für Technologie (KIT
Concentrations of total organic carbon, dissolved organic nitrogen, TOC/DON ratios, ammonium-nitrogen, nitrate-nitrogen, ammonium-N/nitrate-N ratios, and δ15 values of solution samples from a tropical montane forest in south Ecuador
No full textWe tested whether the δ15N values of total dissolved N (TDN), measured directly in solution with a TOC-IRMS, can be used to help elucidate N sources and sinks along the water path in a tropical montane forest in south Ecuador. The forest is located on the east-exposed slope of the eastern cordillera at 1850-2150 m above sea level and thus on the rim of the Amazon basin. We therefore collected rainfall, throughfall, stemflow, litter leachate, mineral soil solutions at the 0.15 and 0.30 m depths, streamflow, and fine litterfall samples in weekly resolution from January 2013 to December 2016. To obtain a sufficient N mass for the N isotope ratio analysis, we composited the weekly samples to quarterly ones. In addition to the ecosystem solutions, we also sampled leaves and roots of ten abundant tree species and horizons (the organic layer horizons Oi, Oe, Oa and the mineral soil horizons A and B) of 21 soil profiles. To assess a possible temporal change in the δ15N values of tree leaves, we analyzed a time series of two tree species (with five individuals per species) from 2008 to 2015. We determined the pH value, total organic C (TOC) and total N concentrations, and the δ15N values of total N in all samples. In the solutions, we additionally measured ammonium-N (NH4-N), nitrate-N (NO3-N), and dissolved organic N concentrations. Because of low N concentrations, δ15N values in rainfall and streamflow could not be measured in all samples. In such cases, we based the quarterly values on selected weekly samples that contained a TDN concentration of at least 1.4 mg/L. The δ15N values of total dissolved nitrogen changed markedly in the ecosystem solutions along the water path from rainfall through the forest to streamflow, which could be related to N sources, sinks, and transformations, while the temporal variation was less pronounced. The δ15N values of the solid phases helped in interpreting these changes. We conclude that the direct measurement of the δ15N values in TDN of ecosystem solutions provides a new straight-forward tool to detect changes in the N cycle of terrestrial ecosystems in high resolution
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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