Both elevated atmospheric carbon dioxide (CO sub(2)) and nitrogen (N) deposition may induce changes in C:N ratios in plant tissues and mineral soil. However, the potential mechanisms driving the ...stoichiometric shifts remain elusive. In this study, we examined the responses of C:N ratios in both plant tissues and mineral soil to elevated CO sub(2) and N deposition using data extracted from 140 peer-reviewed publications. Our results indicated that C:N ratios in both plant tissues and mineral soil exhibited consistent increases under elevated CO sub(2) regimes whereas decreases in C:N ratios were observed in response to experimental N addition. Moreover, soil C:N ratio was less sensitive than plant C:N ratio to both global change scenarios. Our results also showed that the responses of stoichiometric ratios were highly variable among different studies. The changes in C:N ratio did not exhibit strong correlations with C dynamics but were negatively associated with corresponding changes in N content. These results suggest that N dynamics drive stoichiometric shifts in both plant tissues and mineral soil under both elevated CO sub(2) and N deposition scenarios.
Both elevated atmospheric carbon dioxide (CO.sub.2) and nitrogen (N) deposition may induce changes in C:N ratios in plant tissues and mineral soil. However, the potential mechanisms driving the ...stoichiometric shifts remain elusive. In this study, we examined the responses of C:N ratios in both plant tissues and mineral soil to elevated CO.sub.2 and N deposition using data extracted from 140 peer-reviewed publications. Our results indicated that C:N ratios in both plant tissues and mineral soil exhibited consistent increases under elevated CO.sub.2 regimes whereas decreases in C:N ratios were observed in response to experimental N addition. Moreover, soil C:N ratio was less sensitive than plant C:N ratio to both global change scenarios. Our results also showed that the responses of stoichiometric ratios were highly variable among different studies. The changes in C:N ratio did not exhibit strong correlations with C dynamics but were negatively associated with corresponding changes in N content. These results suggest that N dynamics drive stoichiometric shifts in both plant tissues and mineral soil under both elevated CO.sub.2 and N deposition scenarios. Keywords Carbon:nitrogen ratio* Global change * Mineral soil * Nitrogen deposition * Plant tissues * Stoichiometric shift * Terrestrial ecosystems
Permafrost thaw can alter the soil environment through changes in soil moisture, frequently resulting in soil saturation, a shift to anaerobic decomposition, and changes in the plant community. These ...changes, along with thawing of previously frozen organic material, can alter the form and magnitude of greenhouse gas production from permafrost ecosystems. We synthesized existing methane (CH sub(4)) and carbon dioxide (CO sub(2)) production measurements from anaerobic incubations of boreal and tundra soils from the geographic permafrost region to evaluate large-scale controls of anaerobic CO sub(2) and CH sub(4) production and compare the relative importance of landscape-level factors (e.g., vegetation type and landscape position), soil properties (e.g., pH, depth, and soil type), and soil environmental conditions (e.g., temperature and relative water table position). We found fivefold higher maximum CH sub(4) production per gram soil carbon from organic soils than mineral soils. Maximum CH sub(4) production from soils in the active layer (ground that thaws and refreezes annually) was nearly four times that of permafrost per gram soil carbon, and CH sub(4) production per gram soil carbon was two times greater from sites without permafrost than sites with permafrost. Maximum CH sub(4) and median anaerobic CO sub(2) production decreased with depth, while CO sub(2):CH sub(4) production increased with depth. Maximum CH sub(4) production was highest in soils with herbaceous vegetation and soils that were either consistently or periodically inundated. This synthesis identifies the need to consider biome, landscape position, and vascular/moss vegetation types when modeling CH sub(4) production in permafrost ecosystems and suggests the need for longer-term anaerobic incubations to fully capture CH sub(4) dynamics. Our results demonstrate that as climate warms in arctic and boreal regions, rates of anaerobic CO sub(2) and CH sub(4) production will increase, not only as a result of increased temperature, but also from shifts in vegetation and increased ground saturation that will accompany permafrost thaw.
Current and future warming of high-latitude ecosystems will play an important role in climate change through feedbacks to the global carbon cycle. This study compares 6 years of CO2 flux measurements ...in moist acidic tundra using autochambers and eddy covariance (Tower) approaches. We found that the tundra was an annual source of CO2 to the atmosphere as indicated by net ecosystem exchange using both methods with a combined mean of 105 ± 17 g CO2 C m-2 y-1 across methods and years (Tower 87 ± 17 and Autochamber 123 ± 14). The difference between methods was largest early in the observation period, with Autochambers indicated a greater CO2 source to the atmosphere. This discrepancy diminished through time, and in the final year the Autochambers measured a greater sink strength than tower. Active layer thickness was a significant driver of net ecosystem carbon exchange, gross ecosystem primary productivity, and Reco and could account for differences between Autochamber and Tower. The stronger source initially attributed lower summer season gross primary production (GPP) during the first 3 years, coupled with lower ecosystem respiration (Reco) during the first year. The combined suppression of GPP and Reco in the first year of Autochamber measurements could be the result of the experimental setup. Root damage associated with Autochamber soil collar installation may have lowered the plant community's capacity to fix C, but recovered within 3 years. While this ecosystem was a consistent CO2 sink during the summer, CO2 emissions during the nonsummer months offset summer CO2 uptake each year. Key Points Arctic tundra ecosystem is an annual net source of CO2 Winter CO2 release offsets growing season CO2 gain Active layer thickness is a significant driver of NEE, GPP, and Reco
The fossil record of Isopoda includes remains of presumed parasites. Among the fossils which have been discussed as potential parasites are those termed as Urda Münster, 1840. Some of these fossils ...have been discussed as possibly related to an extant group of parasites, Gnathiidae Leach, 1814. The type species of Urda – Urda rostrata Münster, 1840 – is herein interpreted as a close relative of the group Gnathiidae, based on the shared occurrence of a number of apomorphic features. This is with Urda punctata (Münster, 1842) herein being interpreted as a junior subjective synonym of U. rostrata. However, not all of the fossils associated with the name Urda can safely be identified as close relatives of Gnathiidae. Moreover, it is unclear whether the extinct species, which can be identified as close relatives of U. rostrata and Gnathiidae form a monophyletic group, as we could not identify an autapomorphy for a natural group Urda. A new species of close relatives of Urda rostrata and Gnathiidae – Urda buechneri n. sp. – is formally described based on μCT image data. Palaega suevica Reiff, 1936 and Palaega kessleri Reiff, 1936 are found to be subjective synonyms and are re-interpreted as Urda suevica n. comb. – a species closely related to U. rostrata. Due to the documented destruction of the holotype, a herein figured fossil specimen is designated as the neotype of Urda suevica. Palaega? stemmerbergensis Malzahn, 1968 is also interpreted as a close representative of U. rostrata and herein treated as Urda stemmerbergensis n. comb. Another already formally described species – Eobooralana rhodanica gen. et comb. nov. – is interpreted as a more distant relative, which is likely to be closer related to other extant species of Isopoda than those within Gnathiidae. For three species there are not enough characters preserved to interpret them as closely related to U. rostrata and Gnathiidae: Urda? liasica Frentzen, 1937 nom. dub. (type material destroyed, description insufficient for proper diagnosis), Urda? moravica Remeš, 1912 and Urda? zelandica Buckeridge and Johns, 1996.
El registro fósil de Isopoda incluye restos de posibles parásitos. Entre los fósiles que han sido discutidos como parásitos potenciales se encuentra Urda Münster, 1840. Algunos de estos fósiles han sido discutidos como posibles parientes de un grupo existente de parásitos, los Gnathiidae Leach, 1814. La especie tipo de Urda - Urda rostrata Münster, 1840 - es aquí interpretada como pariente cercano del grupo Gnathiidae, con base en la presencia común de un número de caracteres apomórficos. Esto incluye a Urda punctata (Münster, 1842) interpretada aquí como sinónimo junior subjetivo de U. rostrata. Sin embargo, no todos los fósiles asociados con el nombre Urda pueden ser indudablemente identificados como parientes cercanos a Gnathiidae. De manera adicional, no es aún claro si las expecies extintas, que podrían ser identificadas como cercanas a U. rostrata y Gnathiidae, forman un grupo monofilético, dado que no podemos identificar alguna autapomorfía para un grupo natural Urda. Una nueva especie de parientes cercanos a Urda rostrata y Gnathiidae - Urda buechneri n. sp. - es descrita formalmente con base en datos de imágenes μCT. Palaega suevica Reiff, 1936 y Palaega kessleri Reiff, 1936 son interpretados como sinónimos subjetivos y reinterpretados como Urda suevica n. comb. - como especies cercanamente relacionadas a U. rostrata. Debido a la documentada destrucción del holotipo, un ejemplar fósil aquí ilustrado, es designado como el neotipo de Urda suevica. Palaega? stemmerbergensis Malzahn, 1968 es también interpretada como como pariente cercano a U. rostrata y es tratada aquí como Urda stemmerbergensis n. comb. Otra especie ya descrita formalmente - Eobooralana rhodanica gen. et comb. nov. - es interpretada como un pariente más distante, quien probablemente se encuentra relacionada a otra especie viviente de Isopoda, que con los Gnathiidae. No existen caracteres suficientes preservados para tres especies, a fin de interpretarlas como cercanamente relacionadas a U. rostrata and Gnathiidae: Urda? liasica Frentzen, 1937 nom. dub. (material tipo destruído, descripción insuficiente para una adecuada diagnosis), Urda? moravica Remeš, 1912 y Urda? zelandica Buckeridge y Johns, 1996.
The fossil record of Isopoda includes remains of presumed parasites. Among the fossils which have been discussed as potential parasites are those termed as Urda Münster, 1840. Some of these fossils ...have been discussed as possibly related to an extant group of parasites, Gnathiidae Leach, 1814. The type species of Urda – Urda rostrata Münster, 1840 – is herein interpreted as a close relative of the group Gnathiidae, based on the shared occurrence of a number of apomorphic features. This is with Urda punctata (Münster, 1842) herein being interpreted as a junior subjective synonym of U. rostrata. However, not all of the fossils associated with the name Urda can safely be identified as close relatives of Gnathiidae. Moreover, it is unclear whether the extinct species, which can be identified as close relatives of U. rostrata and Gnathiidae form a monophyletic group, as we could not identify an autapomorphy for a natural group Urda. A new species of close relatives of Urda rostrata and Gnathiidae – Urda buechneri n. sp. – is formally described based on µCT image data. Palaega suevica Reiff, 1936 and Palaega kessleri Reiff, 1936 are found to be subjective synonyms and are re-interpreted as Urda suevica n. comb. – a species closely related to U. rostrata. Due to the documented destruction of the holotype, a herein figured fossil specimen is designated as the neotype of Urda suevica. Palaega? stemmerbergensis Malzahn, 1968 is also interpreted as a close representative of U. rostrata and herein treated as Urda stemmerbergensis n. comb. Another already formally described species – Eobooralana rhodanica gen. et comb. nov. – is interpreted as a more distant relative, which is likely to be closer related to other extant species of Isopoda than those within Gnathiidae. For three species there are not enough characters preserved to interpret them as closely related to U. rostrata and Gnathiidae: Urda? liasica Frentzen, 1937 nom. dub. (type material destroyed, description insufficient for proper diagnosis), Urda? moravica Remeš, 1912 and Urda? zelandica Buckeridge and Johns, 1996.
High latitude warming and permafrost thaw will expose vast stores of deep soil organic carbon (SOC) to decomposition. Thaw also changes water movement causing either wetter or drier soil. The fate of ...deep SOC under different thaw and moisture conditions is unclear. We measured weekly growing‐season δ13C of ecosystem respiration (Recoδ13C) across thaw and moisture conditions (Shallow‐Dry; Deep‐Dry; Deep‐Wet) in a soil warming manipulation. Deep SOC loss was inferred from known δ13C signatures of plant shoot, root, surface soil, and deep soil respiration. In addition, a 2‐year‐old vegetation removal treatment (No Veg) was used to isolate surface and deep SOC decomposition contributions to Reco. In No Veg, seasonal Recoδ13C indicated that deep SOC loss increased as the soil column thawed, while in vegetated areas, root contributions appeared to dominate Reco. The Recoδ13C differences between Shallow‐Dry and Deep‐Dry were significant but surprisingly small. This most likely suggests that, under dry conditions, soil warming stimulates root and surface SOC respiration with a negative 13C signature that opposes the more positive 13C signal from increased deep SOC respiration. In Deep‐Wet conditions, Recoδ13C suggests reduced deep SOC loss but could also reflect altered diffusion or methane (CH4) dynamics. Together, these results demonstrate that frequent Recoδ13C measurements can detect deep SOC loss and that plants confound the signal. In future studies, soil profile δ13C measurements, vegetation removal across thaw gradients, and isotopic effects of CH4 dynamics could further deconvolute deep SOC loss via surface Reco.
Plain Language Summary
Carbon (C) stored in permafrost soil is like a global savings account that keeps C out of the atmosphere. Arctic warming makes permafrost soil C vulnerable to microbial decomposition, and C released to the atmosphere would accelerate global warming. In this study we used 13C isotopes, which function like molecular fingerprints, to detect permafrost soil C decomposition from a soil warming experiment that doubled the thawed soil volume and changed soil moisture conditions. We found that permafrost soil C decomposition was best detected when vegetation was removed. Deeper thaw depth had only a small effect on isotopic signatures possibly because the signal from higher permafrost soil C decomposition was overwhelmed by a simultaneous increase in surface soil decomposition and respiration from plants. In wet areas, the isotopic signal changed which could imply reduced permafrost soil C decomposition. In wet areas, methane cycling might also change the isotope signature. We conclude that seasonal 13C sampling could be useful for detecting permafrost soil C decomposition if combined with measurements that can isolate contributions from surface soil, roots, and methane cycling. Developing methods that make it easier to assess permafrost soil C decomposition is critical for estimating the balance of our global C savings account.
Key Points
Vegetation removal shows deep soil C loss does increase with thaw, and plant contributions to Reco dilute delta13C signals from deep soil
Seasonal Reco delta13C suggests warming and permafrost thaw may stimulate deep soil respiration and also surface soil and plant respiration
Wet conditions may reduce deep soil C loss, with possible effects of altered diffusion dynamics and increased methane cycling on delta13C
PDF
