Jahrestagung der Arbeitsgemeinschaft
Stabile Isotope e.V.
26.–29. September 2021 | TU Darmstadt
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Block 4.1: Ökosysteme
14:45 - 15:00
Orchid Cremastra appendiculata on the path to self-supply with changing fungal companion
1BayCEER – Laboratory of Isotope Biogeochemistry, University of Bayreuth, Bayreuth, Germany; 2Biology Department, National Museum of Natural Science, Taichung, Taiwan
Covering one achlorophyllous, leafless and three chlorophyllous, leafy species the orchid genus Cremastra from East Asia allows inference on the evolutionary development from autotrophy to mycoheterotrophy of plant lineages mycorrhizal with saprotrophic fungi (Ogura-Tsujita et al. 2021). Particularly, the chlorophyllous, terrestrial orchid Cremastra appendiculata is unique with respect to its fungal mycorrhiza partners. Rather specialized wood/litter-decaying saprotrophic fungi are known to induce seed germination in the initially mycoheterotrophic protocorm stage (Yagame et al. 2013), while adult individuals either exploit wood-decaying Psathyrellaceae being partially mycoheterotrophic (Suetsugu et al. 2021) or form mycorrhiza with fungi of the ubiquitous saprotrophic rhizoctonia group.
We examined how a change in fungal community and subterranean morphology accompanies a nutrition mode alteration during the life cycle of Cremastra appendiculata.
Trophic strategies were revealed by comparing different development stages of Cremastra appendiculata to surrounding autotrophic reference plants based on multi-element natural abundance stable isotope analyses (δ13C, δ15N, δ2H, δ18O) and total N concentrations. Here we present the first stable isotope patterns of tiny protocorms related to non-rhizoctonia saprotrophic fungal partners and 18O and 2H natural abundance isotopic signatures of fully mycoheterotrophic terrestrial orchid specimens associated with saprotrophic fungi. Mycorrhizal fungi in Cremastra appendiculata protocorms, rhizomes and roots of seedling, and roots of adult were determined using next generation DNA sequencing.
We identified saprotrophic non-rhizoctonia Psathyrellaceae as dominant mycorrhizal fungi in protocorm and seedling rhizomes, while roots of seedlings and mature Cremastra appendiculata were mainly colonizes with rhizoctonia fungi. Mature Cremastra appendiculata did not differ in isotopic signature from autotrophic reference plants suggesting a fully autotrophic nutrition mode. Characteristic of orchid specimens entirely relying on fungal nutrition, Cremastra appendiculata protocorms were enriched in 15N, 13C and 2H compared to reference plants. Seedlings with very early green leaves showed a dispersive, intermediate isotopic signature, underpinning their transitional nutrition mode and the differences in fungal community depending on their subterranean morphology.
In conclusion, chlorophyllous terrestrial orchid Cremastra appendiculata is a key species being able to feature both extremes on the continuous transition from autotrophy to mycoheterotrophy with changing fungal companion during its ontogenetic development. Our results on Cremastra appendiculata together with knowledge from recent literature (e.g. Suetsugu and Matsubayashi (2021)) suggest a high within-species variability in nutrition and fungal association depending on development stage and subterranean morphology of Cremastra appendiculata.
Ogura-Tsujita Y, Yukawa T, Kinoshita A. 2021. Evolutionary histories and mycorrhizal associations of mycoheterotrophic plants dependent on saprotrophic fungi. Journal of Plant Research 134: 19–41.
Suetsugu K, Haraguchi TF, Tayasu I. 2021. Novel mycorrhizal cheating in a green orchid: Cremastra appendiculata depends on carbon from deadwood through fungal associations. New Phytologist.
Suetsugu K, Matsubayashi J. 2021. Subterranean morphology modulates the degree of mycoheterotrophy in a green orchid Calypso bulbosa exploiting wood‐decaying fungi . Functional Ecology: 1–11.
Yagame T, Funabiki E, Nagasawa E, Fukiharu T, Iwase K. 2013. Identification and symbiotic ability of Psathyrellaceae fungi isolated from a photosynthetic orchid, Cremastra appendiculata (Orchidaceae). American Journal of Botany 100: 1823–1830.
15:00 - 15:15
Unravelling shoot:root drought responses in VOC emissions through 13C-pyruvate labelling
Chair of Ecosystem Physiology, Albert-Ludwigs-University of Freiburg, Germany
Plant shoots and roots reveal highly diverse and specialized metabolic adaptations to ensure plant survival above- and belowground while being faced by a multitude of external stressors. Plants hereby produce a plethora of biogenic volatile organic compounds (BVOCs) to communicate with their environment, e.g. to attract pollinators, repel herbivores or directly reduce effects of external stressors such as drought. Root and leaf metabolism are intertwined, with roots delivering minerals, nutrients and water, as well as carbohydrates to the leaves while receiving a multitude of metabolites from the leaves, including precursors for BVOC biosynthesis. Especially under drought stress, balanced resource allocation between leaves and roots is compromised. Even though many studies have focused on the complex dynamics of organ specific metabolome adaptations and changes in resource allocation under drought, little is known about metabolomic adjustments of BVOC biosynthesis of leaves relative to roots.
In our controlled climate chamber experiment, we aimed to unravel these dynamics by measuring compound-specific 13C-incorporation in BVOCs after position-specific ([1-13C]/[2-13C]-pyruvate) labelling of leaves and roots of potted, two-year old Fagus sylvatica and Picea abies saplings before and during drought stress, using flow-through chambers. BVOC emissions were measured online by PTR-TOF-MS in combination with GC-C-IRMS for further compound validation and 13C incorporation into specific monoterpenes. To quantify [1-13C]- and [2-13C]-pyruvate allocation into decarboxylation processes during primary and secondary metabolism, we used 13CO2 laser spectroscopy. Drought stress was determined by controlling soil moisture and measuring of plant physiological traits, such as leaf transpiration, assimilation rate and leaf water potential.
With this approach, we aim to identify active metabolic pathways responsible for BVOC biosynthesis in leaves and roots and how regulatory patterns changed due to drought. Considering our preliminary results, net CO2 assimilation, transpiration and respiration declined under drought. Overall BVOC composition and drought response, however, varied between organs in both species. Leaf emissions showed higher BVOC diversity even under drought. Monoterpene composition in leaves and roots of Fagus sylvatica differed and overall emissions were higher in roots. Contribution of de-novo synthesis of BVOCs in leaves was elevated due to storage depletion under drought in both species. Our results indicate major changes in BVOC emission pattern in leaves and roots under drought stress, providing first insights to elucidate drought-induced trade-offs in resource allocation into BVOCs above- and belowground.
15:15 - 15:30
Field 15N pool dilution approach to determine gross nitrification rate
Nitrification is the microbial oxidation of ammonium (NH4+) to nitrate (NO3–) and is one of the most important processes of the terrestrial nitrogen cycle. Nitrification is known to promote nitrogen leaching from soils as the less mobile cation ammonium (NH4+) is oxidized by nitrifiers to the mobile anion nitrate (NO3–). Additionally, nitrification promotes NO and N2O formation, directly as a by-product of nitrate formation and indirectly as a source of substrate for denitrification.
In numerous studies gross nitrification rates are determined using 15N pool dilution technique in laboratories, but only few field experiments with undisturbed soil structure were done. An appropriate in situ sprinkler method with a low irrigation rate and very even 15N-nitrate application was developed 2018 for sandy soils. The first test with a tracer solution confirmed that high amounts of the soil water can replaced from the top soil by applying a low irrigation rate by a special sprinkling device, and therefore all assumptions of the 15N-pool dilution technique can be fulfilled in the field by this method. Subsequently, the method was used to measure the small scale field heterogeneity (dm to m) and variability between field of gross nitrification at eight 3m*3m plots at sites with sandy soils (Fuhrberger Feld, northern Germany) in spring 2021. The results of the first application of the new method and der measurements in the Fuhrberger Feld will be shown. Different approaches to calculate the nitrification rates between two sampling dates t0 and t1 will be presented, and the heterogeneity of the nitrification rate will be discussed.
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