An official website of the United States government
Summary Steady‐state photosyntheticCO2responses (A/Cicurves) are used to assess environmental responses of photosynthetic traits and to predict future vegetative carbon uptake through modeling. The recent development of rapidA/Cicurves (RACiRs) permits faster assessment of these traits by continuously changing [CO2] around the leaf, and may reveal additional photosynthetic properties beyond what is practical or possible with steady‐state methods.Gas exchange necessarily incorporates photosynthesis and (photo)respiration. Each process was expected to respond on different timescales due to differences in metabolite compartmentation, biochemistry and diffusive pathways. We hypothesized that metabolic lags in photorespiration relative to photosynthesis/respiration andCO2diffusional limitations can be detected by varying the rate of change in [CO2] duringRACiR assays. We tested these hypotheses through modeling and experiments at ambient and 2% oxygen.Our data show that photorespiratory delays cause offsets in predictedCO2compensation points that are dependent on the rate of change in [CO2]. Diffusional limitations may reduce the rate of change in chloroplastic [CO2], causing a reduction in apparentRACiR slopes under highCO2ramp rates.MultirateRACiRs may prove useful in assessing diffusional limitations to gas exchange and photorespiratory rates.
more »
« less
Phylogenetic diversity in freshwater‐dwelling Isochrysidales haptophytes with implications for alkenone production
Abstract Members of the order Isochrysidales are unique among haptophyte lineages in being the exclusive producers of alkenones, long‐chain ketones that are commonly used for paleotemperature reconstructions. Alkenone‐producing haptophytes are divided into three major groups based largely on molecular ecological data: Group I is found in freshwater lakes, GroupIIcommonly occurs in brackish and coastal marine environments, and GroupIIIconsists of open ocean species. Each group has distinct alkenone distributions; however, only GroupsIIandIIIIsochrysidales currently have cultured representatives. The uncultured Group I Isochrysidales are distinguished geochemically by the presence of tri‐unsaturated alkenone isomers (C37:3bMe, C38:3bEt, C38:3bMe, C39:3bEt) present in water column and sediment samples, yet their genetic diversity, morphology, and environmental controls are largely unknown. Using small‐subunit (SSU) ribosomalRNA(rRNA) marker gene amplicon high‐throughput sequencing of environmental water column and sediment samples, we show that Group I is monophyletic with high phylogenetic diversity and contains a well‐supported clade separating the previously described “EV” clade from the “Greenland” clade. We infer the first partial large‐subunit (LSU)rRNAgene Group I sequence phylogeny, which uncovered additional well‐supported clades embedded within Group I. Relative to GroupII, Group I revealed higher levels of genetic diversity despite conservation of alkenone signatures and a closer evolutionary relationship with GroupIII. In Group I, the presence of the tri‐unsaturated alkenone isomers appears to be conserved, which is not the case for GroupII. This suggests differing environmental influences on Group I andIIand perhaps uncovers evolutionary constraints on alkenone biosynthesis.
more »
« less
- Award ID(s):
- 1762431
- PAR ID:
- 10461502
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Geobiology
- Volume:
- 17
- Issue:
- 3
- ISSN:
- 1472-4677
- Page Range / eLocation ID:
- p. 272-280
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
<bold>Summary</bold> Cytosolic calcium concentration ([Ca2+]cyt) and heterotrimeric G‐proteins are universal eukaryotic signaling elements. In plant guard cells, extracellular calcium (Cao) is as strong a stimulus for stomatal closure as the phytohormone abscisic acid (ABA), but underlying mechanisms remain elusive. Here, we report that the sole Arabidopsis heterotrimeric Gβ subunit,AGB1, is required for four guard cell Caoresponses: induction of stomatal closure; inhibition of stomatal opening; [Ca2+]cytoscillation; and inositol 1,4,5‐trisphosphate (InsP3) production. Stomata in wild‐type Arabidopsis (Col) and in mutants of the canonical Gα subunit,GPA1, showed inhibition of stomatal opening and promotion of stomatal closure by Cao. By contrast, stomatal movements ofagb1mutants andagb1/gpa1double‐mutants, as well as those of theagg1agg2 Gγ double‐mutant, were insensitive to Cao. These behaviors contrast withABA‐regulated stomatal movements, which involveGPA1 andAGB1/AGG3 dimers, illustrating differential partitioning of G‐protein subunits among stimuli with similar ultimate impacts, which may facilitate stimulus‐specific encoding.AGB1knockouts retained reactive oxygen species andNOproduction, but lostYC3.6‐detected [Ca2+]cytoscillations in response to Cao, initiating only a single [Ca2+]cytspike. Experimentally imposed [Ca2+]cytoscillations restored stomatal closure inagb1. Yeast two‐hybrid and bimolecular complementation fluorescence experiments revealed thatAGB1 interacts with phospholipase Cs (PLCs), and Caoinduced InsP3 production in Col but not inagb1. In sum, G‐protein signaling viaAGB1/AGG1/AGG2 is essential for Cao‐regulation of stomatal apertures, and stomatal movements in response to Caoapparently require Ca2+‐induced Ca2+release that is likely dependent on Gβγ interaction withPLCs leading to InsP3 production.more » « less
-
Abstract The springtime transition to regional‐scale onset of photosynthesis and net ecosystem carbon uptake in boreal and tundra ecosystems are linked to the soil freeze–thaw state. We present evidence from diagnostic and inversion models constrained by satellite fluorescence and airborneCO2from 2012 to 2014 indicating the timing and magnitude of spring carbon uptake in Alaska correlates with landscape thaw and ecoregion. Landscape thaw in boreal forests typically occurs in late April (DOY111 ± 7) with a 29 ± 6 day lag until photosynthetic onset. North Slope tundra thaws 3 weeks later (DOY133 ± 5) but experiences only a 20 ± 5 day lag until photosynthetic onset. These time lag differences reflect efficient cold season adaptation in tundra shrub and the longer dehardening period for boreal evergreens. Despite the short transition from thaw to photosynthetic onset in tundra, synchrony of tundra respiration with snow melt and landscape thaw delays the transition from net carbon loss (at photosynthetic onset) to net uptake by 13 ± 7 days, thus reducing the tundra net carbon uptake period. Two globalCO2inversions using aCASA‐GFEDmodel prior estimate earlier northern high latitude net carbon uptake compared to our regional inversion, which we attribute to (i) early photosynthetic‐onset model prior bias, (ii) inverse method (scaling factor + optimization window), and (iii) sparsity of available AlaskanCO2observations. Another global inversion with zero prior estimates the same timing for net carbon uptake as the regional model but smaller seasonal amplitude. The analysis of Alaskan eddy covariance observations confirms regional scale findings for tundra, but indicates that photosynthesis and net carbon uptake occur up to 1 month earlier in evergreens than captured by models orCO2inversions, with better correlation to above‐freezing air temperature than date of primary thaw. Further collection and analysis of boreal evergreen species over multiple years and at additional subarctic flux towers are critically needed.more » « less
-
Abstract Rich fens are common boreal ecosystems with distinct hydrology, biogeochemistry and ecology that influence their carbon (C) balance. We present growing season soil chamber methane emission (FCH4), ecosystem respiration (ER), net ecosystem exchange (NEE) and gross primary production (GPP) fluxes from a 9‐years water table manipulation experiment in an Alaskan rich fen. The study included major flood and drought years, where wetting and drying treatments further modified the severity of droughts. Results support previous findings from peatlands that drought causes reduced magnitude of growing seasonFCH4,GPPandNEE, thus reducing or reversing their C sink function. Experimentally exacerbated droughts further reduced the capacity for the fen to act as a C sink by causing shifts in vegetation and thus reducing magnitude of maximum growing seasonGPPin subsequent flood years by ~15% compared to control plots. Conversely, water table position had only a weak influence onER, but dominant contribution toERswitched from autotrophic respiration in wet years to heterotrophic in dry years. Droughts did not cause inter‐annual lag effects onERin this rich fen, as has been observed in several nutrient‐poor peatlands. WhileERwas dependent on soil temperatures at 2 cm depth,FCH4was linked to soil temperatures at 25 cm. Inter‐annual variability of deep soil temperatures was in turn dependent on wetness rather than air temperature, and higherFCH4in flooded years was thus equally due to increased methane production at depth and decreased methane oxidation near the surface. Short‐term fluctuations in wetness caused significant lag effects onFCH4, but droughts caused no inter‐annual lag effects onFCH4. Our results show that frequency and severity of droughts and floods can have characteristic effects on the exchange of greenhouse gases, and emphasize the need to project future hydrological regimes in rich fens.more » « less
-
ObjectiveTo elucidate the role of decorin, a small leucine‐rich proteoglycan, in the degradation of cartilage matrix during the progression of post‐traumatic osteoarthritis (OA). MethodsThree‐month–old decorin‐null (Dcn−/−) and inducible decorin‐knockout (DcniKO) mice were subjected to surgical destabilization of the medial meniscus (DMM) to induce post‐traumaticOA. TheOAphenotype that resulted was evaluated by assessing joint morphology and sulfated glycosaminoglycan (sGAG) staining via histological analysis (n = 6 mice per group), surface collagen fibril nanostructure via scanning electron microscopy (n = 4 mice per group), tissue modulus via atomic force microscopy–nanoindentation (n = 5 or more mice per group) and subchondral bone structure via micro–computed tomography (n = 5 mice per group). Femoral head cartilage explants from wild‐type and Dcn−/−mice were stimulated with the inflammatory cytokine interleukin‐1β (IL‐1β) in vitro (n = 6 mice per group). The resulting chondrocyte response toIL‐1β and release ofsGAGs were quantified. ResultsIn both Dcn−/−and DcniKOmice, the absence of decorin resulted in acceleratedsGAGloss and formation of highly aligned collagen fibrils on the cartilage surface relative to the control (P< 0.05). Also, Dcn−/−mice developed more salient osteophytes, illustrating more severeOA. In cartilage explants treated withIL‐1β, loss of decorin did not alter the expression of either anabolic or catabolic genes. However, a greater proportion ofsGAGs was released to the media from Dcn−/−mouse explants, in both live and devitalized conditions (P< 0.05). ConclusionIn post‐traumaticOA, decorin delays the loss of fragmented aggrecan and fibrillation of cartilage surface, and thus, plays a protective role in ameliorating cartilage degeneration.more » « less
