Growth Of Vascular Plants Research Articles

The dual effect of sand-covered biocrusts on annual plants: Increasing cover but reducing individual plant biomass and fecundity

It is generally accepted that biological soil crusts promote the growth of vascular plants. Nevertheless, contradictory results were recently found for annual plants in the extreme desert dunefield of the Negev (average precipitation of 95 mm) during extreme drought years, explained by the lower available water content (AWC) under the low-albedo biocrusted surfaces at the interdune (ID). Trying to assess whether the biomass and fecundity of the annual plants is higher at the non-crusted dune crest (CR) in comparison to ID also during years with near-average precipitation, surface stability, rain, AWC, fine (silt and clay) content (FC), and soil organic carbon (SOC) were measured in a pair of plots established in CR and ID in two dunes and interdunes. The research was conducted for three years (2009/2010, 2013/14 and 2014/15), having a mean precipitation of 109.4 mm. At the end of each winter, sampling of the annual plants (cover, density, species composition, biomass) took place at CR and ID at 30 cm-diameter miniplots (miniplot-scale), while the biomass and fecundity of 50 randomly-chosen individuals that abundantly inhabited both habitats during the same year were measured at parallel transects (individual plant-scale). Significantly higher cover and generally higher diversity characterized the plants at ID at the miniplot-scale, explained by the higher surface stability. Although characterized by lower FC and SOC, significantly higher biomass and fecundity characterized the individual plants at CR, explained by the higher AWC. Biocrusts were found to have a dual effect on the annual plants: positive due to increased surface stability (cover and for most years also diversity) at the miniplot-scale, and negative due to reduced AWC (low biomass and fecundity) at the individual plant-scale. The higher biomass and fecundity of the individual plants at CR point to the cardinal role played by water (rather than SOC) in this low-nutrient extreme desert. As far the annual plants are concerned, these findings also point at the fact that moderate crust destruction (such as by light trampling) may not necessarily be hazardous to the ecosystem, as it may increase fecundity and subsequently germination success.

Elevational changes in vascular plants richness, diversity, and distribution pattern in Abune Yosef mountain range, Northern Ethiopia

The aim of this research is to investigate the patterns of vascular plant species richness, diversity, and distribution along an elevation gradient in the Abune Yosef mountain range, Ethiopia. Preferential systematic sampling was employed to collect vegetation and environmental data along the elevation gradient. We found that plant species richness declines monotonically from low to high elevations. Specifically, vascular plant species richness and diversity were lower in the Afroalpine grassland (high elevation) than in the Dry evergreen Afromontane forest and Ericaceous forest (low elevations). In contrast, endemic vascular plant richness was significantly higher in the Afroalpine grassland than in the Dry evergreen Afromontane forest and Ericaceous forest. Elevation showed a significant impact on the richness, diversity, and endemism of vascular plants. According to Sørensen's coefficient, the similarity between Dry evergreen Afromontane forest and Ericaceous forest vegetation types is higher (32%) than the similarity between Ericaceous forest and Afroalpine grassland (18%). Only 5% similarity was recorded between the Dry evergreen Afromontane forest and Afroalpine grassland. Growth forms showed different elevational richness patterns. Trees and liana increased monotonically up to 3300 m. Shrub and herb richness patterns followed a hump-shaped and inverted hump-shaped pattern along the elevation gradient. The elevation patterns of vascular plant species richness, diversity, and growth form in the present study may be attributed to differences in management intensity, spatial heterogeneity, microclimatic variations, and anthropogenic disturbances.

Effects of native bryophytes on exotic grass invasion across an environmental gradient

AbstractUnderstanding the role of native biodiversity in controlling exotic species invasion is a critical goal in ecology. In terrestrial plant communities, most research has focused on the effects of native vascular plants on invasion by exotic vascular plants. However, in many ecosystems, native bryophytes and other non‐vascular plants are common and can affect the establishment, survival, and growth of vascular plants. A more complete picture of how native biodiversity affects exotic plant invasion demands that more studies measure the effects of native bryophytes on exotic vascular plants. Moreover, there is growing realization that the effects of native species on invaders can range from negative to positive and that a complete picture of interactions between native and exotic plants requires measuring interactions in multiple environments. We used both observational and experimental studies to quantify the effects of native bryophytes on vascular plants along a 200‐m environmental gradient in a coastal dune in northern California. We found a positive association between vascular plants and bryophytes across the environmental gradient. Our experiments with two exotic annual grass species showed the effects of bryophytes to be species‐specific and to vary with environmental context. Bryophytes facilitated the survival of one exotic grass species, Vulpia bromoides, at both ends of the environmental gradient. Bryophytes reduced the survival and inflorescence production of the other exotic grass, Bromus diandrus, at one end of the environmental gradient and had no effect at the other end. Our findings provide a test of the effects of native bryophytes on exotic vascular plant invasion and show that these effects can vary dramatically even across local environmental gradients.

Differences in the Cyanobacterial Community Composition of Biocrusts From the Drylands of Central Mexico. Are There Endemic Species?

In drylands worldwide, biocrusts, topsoil microbial communities, are prevalent, contributing to the biostabilization of soils and allowing the subsequent establishment and growth of vascular plants. In early successional biocrusts, cyanobacteria are the first dominant colonizers of bare ground, largely determining their functioning. However, there are large gaps in our knowledge of the cyanobacterial diversity in biocrusts, particularly in understudied geographic regions, such as the tropical latitudes. We analyzed the diversity of the cyanobacteria inhabiting the biocrusts of semideserts from Central Mexico in two localities belonging to the same desert system (Chihuahuan Desert) that are separated by a cordillera that crosses the center of Mexico. Morphological identification of the cyanobacteria was carried out after cultivation in parallel with the direct observation of the environmental samples and was supported by genetic characterization through analysis of the 16S rRNA gene of the isolated strains and by next-generation sequencing of the soil samples. Taxonomic assignment revealed a clear dominance of heterocystous cyanobacteria at one of the studied locations (Actopan, Hidalgo state). Although heterocystous forms were abundant at the other location (Atexcac, Puebla state), almost a third of the cyanobacterial phylotypes were represented by unicellular/colonial cyanobacteria, mostly Chroococcidiopsis spp. Only 28.4% of the phylotypes were found to be common to both soils. Most of the other taxa, however, were biocrust-type specific, and approximately 35% of the phylotypes were found to be unique to the soil they were collected in. In addition, differences in the abundances of the shared cyanobacteria between the locations were also found. These differences in the cyanobacterial distribution were supported by the distinct responses of the isolated strains representative of the sites to extreme heat and desiccation in bioassays. Some cyanobacteria with high abundance or only present at the hottest Actopan site, such as Scytonema hyalinum, Scytonema crispum, Nostoc commune, Nostoc sp., and Calothrix parietina, survived extreme heat and desiccation. However, Tolypothrix distorta and Chroococcidiopsis spp. were clearly sensitive to these extreme conditions in relation to their lower abundances at Actopan as opposed to Atexcac. Since novel biocrust-associated phylotypes were also found, the emergence of endemic cyanobacterial taxa is discussed.

Plant functional types and temperature control carbon input via roots in peatland soils

Northern peatlands store large amounts of soil organic carbon (C) that can be very sensitive to ongoing global warming. Recently it has been shown that temperature-enhanced growth of vascular plants in these typically moss-dominated ecosystems may promote microbial peat decomposition by increased C input via root exudates. To what extent different plant functional types (PFT) and soil temperature interact in controlling root C input is still unclear. In this study we explored how root C input is related to the presence of ericoid shrubs (shrubs) and graminoid sedges (sedges) by means of a factorial plant clipping experiment (= PFT effect) in two peatlands located at different altitude (= temperature effect). By selective clipping of shrub and sedge shoots in mixed vegetation at two Alpine peatland sites we interrupted the above- to belowground translocation of C, thus temporarily inhibiting root C release. Subsequent measurements of soil respiration, dissolved organic carbon (DOC) concentration and stable isotope composition (13C) of DOC in pore water were used as proxies to estimate the above- to belowground transfer of C by different PFT. We found that soil respiration rates and DOC concentrations temporarily decreased within 24 h after clipping, with the decrease in soil respiration being most pronounced at the 1.4 °C warmer peatland after clipping shrubs. The transient drop in DOC concentration coincided with a shift towards a heavier C isotope signature, indicating that the decrease was associated with inhibition of a light C source that we attribute to root exudates. Together these results imply that shrubs translocated more C into the peat than sedges, particularly at higher temperature. We showed that plant functional type and temperature interact in controlling root C input under field conditions in peatlands. Our results provide a mechanistic evidence that shrubs may potentially promote the release of stored soil C through root-derived C input.

Attack of Microcystis aeruginosa bloom on a Ceratophyllum submersum field: Ecotoxicological measurements in real environment with real microcystin exposure

Overproduction of toxic cyanobacteria is a type of harmful algal blooms (HABs). The heptapeptide microcystins (MCs) are one of the most common cyanotoxins. There is increasing research concerning the effects of MCs on growth and physiology of vascular plants, however there is a lack of studies on their direct effects on aquatic macrophytes in the real environment. Here we report the occurrence of a MC producing HAB in Lake Bárdos, Hungary in 2012 with harmful effects on cytological, histological and biochemical parameters of Ceratophyllum submersum (soft hornwort) plants naturally growing at the blooming site. Blue-Green Sinapis Test (BGST) showed high toxicity of HAB samples. Cell-free water samples contained a significant amount of MCs (7.31 ± 0.17 μg L−1) while C. submersum plants contained 1.01 ± 0.21 μg g DW−1 MCs. Plants showed significant increases of protein content and decreases of anthocyanin content and carotenoid/chlorophyll ratio, indicating physiological stress- as compared to plants from the control (MC free) sampling site of the same water body. Histological and cytological studies showed (i) radial swelling and the abnormal formation of lateral buds at the shoot tip leading to abnormal development; (ii) the fragmentation of nuclei as well as accumulation of phenolics in the nucleus indicating that the HAB induced cell death and stress reactions at the nuclear level. The most relevant effect was the increase of histone H3 phosphorylation in metaphase chromosomes: since MCs are strong inhibitors of protein phosphatases, this alteration is related to the biochemical targets of these toxins. The HAB decreased peroxidase activity, but increased nuclease and protease activities, showing the decreased capacity of plants to face biotic stress and as the cytological changes, the induction of cell death. This study is one of the first to show the complex harmful changes in aquatic plants that co-exist with HABs.

Road dust biases NDVI and alters edaphic properties in Alaskan arctic tundra

Increased road-building activity in the arctic has the potential to impact adjacent ecosystems. Roads in permafrost regions are often built atop insulative gravel pads that generate dust plumes, altering soil chemistry and ecosystem function of nearby tundra. Here, we measure edaphic and vegetation characteristics along transects of decreasing dust deposition perpendicular to the Dalton Highway in northern Alaska. We quantify the impact of dust deposition on normalized difference vegetation index (NDVI), a proxy for aboveground plant biomass. Deposition of calcium carbonate-rich dust declined from 1.625 grams m−2 day−1 immediately adjacent to the road, to negligible levels 625 meters away. Along these transects from the road, we found declines in soil moisture and temperature, thaw depth, shrub height, and foliar nitrogen content, indicating that tundra roads create corridors with edaphic conditions favorable to vascular plant growth. At sites nearest the road, dust deposited on leaf surfaces reduced measured NDVI values by 0.24 by blocking reflectance properties of the underlying leaves. Our findings on the impacts of roads and dust deposition on adjacent tundra may aid planning of future infrastructure projects. We caution that dust deposition may negatively bias NDVI-based estimates of plant biomass, especially where unpaved roads are common.

Assessment of arbuscular mycorrhizal fungal spore density and viability in soil stockpiles of South African opencast coal mines

The symbioses between arbuscular mycorrhizal (AM) fungi and plant roots is essential for nutrient uptake and growth of most vascular plants. Soil condition and management influence the density and viability of arbuscular mycorrhizal fungal (AMF) spores. In this study, AMF spore density and viability in soil stockpiles obtained from three opencast coal mines were assessed. Soil samples were randomly collected from stockpiles and an unmined site at depths of ≤20 cm (topsoil) and >20 cm (subsoil) for enumeration of AMF spores and a mycorrhizal trap culture experiment using maize (Zea mays). Roots of trap-plants were assessed for mycorrhization by classical staining as well as detection of nuclear rRNA gene of the Glomeromycota phylum. Number of AMF spores was highest in topsoil from the unmined site and was significantly (p < 0.05) influenced by site × sampling depth interaction. DNA-based detection revealed that AMF colonisation was mostly associated with topsoil than with subsoil. Five operational taxonomic units (OTUs)/ species related to Paraglomus were identified; however, some of the OTUs were phylogenetically distant from defined Paraglomus species on the basis of sequences in the GenBank database. Overall, results suggest that AMF spore density in stockpiles do not differ from an unmined site, but viability may be influenced by soil depth.

Elevated CO2 effects on nitrogen assimilation and growth of C3 vascular plants are similar regardless of N-form assimilated.

Atmospheric carbon dioxide concentration ([CO2]) increased from around 280 ppm in 1750 to 400 ppm in 2016 and is likely to continue to increase throughout this century. It has been argued that wheat, Arabidopsis, and C3 plants in general respond more positively to elevated atmospheric [CO2] under ammonium (NH4+) nutrition than under nitrate (NO3-) nutrition because elevated CO2 inhibits their photoreduction of NO3- and hence reduces their total plant nitrogen (N) assimilation and ultimately growth. Here, it is argued that the weight of evidence in the literature indicates that elevated atmospheric [CO2] does not inhibit NO3- assimilation and growth of C3 vascular plants. New data for common bean and wheat support this view and indicate that the effects of elevated atmospheric [CO2] on N assimilation and growth of C3 vascular plants will be similar regardless of the form of N assimilated.

Suppression of Arabidopsis GGLT1 affects growth by reducing the L-galactose content and borate cross-linking of rhamnogalacturonan-II.

SummaryBoron is a micronutrient that is required for the normal growth and development of vascular plants, but its precise functions remain a subject of debate. One established role for boron is in the cell wall where it forms a diester cross‐link between two monomers of the low‐abundance pectic polysaccharide rhamnogalacturonan‐II (RG‐II). The inability of RG‐II to properly assemble into a dimer results in the formation of cell walls with abnormal biochemical and biomechanical properties and has a severe impact on plant productivity. Here we describe the effects on RG‐II structure and cross‐linking and on the growth of plants in which the expression of a GDP‐sugar transporter (GONST3/GGLT1) has been reduced. In the GGLT1‐silenced plants the amount of L‐galactose in side‐chain A of RG‐II is reduced by up to 50%. This leads to a reduction in the extent of RG‐II cross‐linking in the cell walls as well as a reduction in the stability of the dimer in the presence of calcium chelators. The silenced plants have a dwarf phenotype, which is rescued by growth in the presence of increased amounts of boric acid. Similar to the mur1 mutant, which also disrupts RG‐II cross‐linking, GGLT1‐silenced plants display a loss of cell wall integrity under salt stress. We conclude that GGLT1 is probably the primary Golgi GDP‐L‐galactose transporter, and provides GDP‐L‐galactose for RG‐II biosynthesis. We propose that the L‐galactose residue is critical for RG‐II dimerization and for the stability of the borate cross‐link.

Warmer Temperatures Affect the in situ Freezing Resistance of the Antarctic Vascular Plants.

Although positive effects on growth and reproduction of Antarctic vascular plants have been reported under warmer temperatures, it could also increase the vulnerability of these plants to freezing. Thus, we assessed in situ whether warming decreases the freezing resistance of Colobanthus quitensis and Deschampsia antarctica, and we compared the level and mechanism of freezing resistance of these species in the field with previous reports conducted in lab conditions. We assessed the freezing resistance of C. quitensis and D. antarctica by determining their low temperature damage (LT50), ice nucleation temperature (NT) and freezing point (FP) in three sites of the King George Island. Plants were exposed during two growing seasons to a passive increase in the air temperature (+W). +W increased by 1K the mean air temperatures, but had smaller effects on freezing temperatures. Leaf temperature of both species was on average 1.7K warmer inside +W. Overall, warming decreased the freezing resistance of Antarctic species. The LT50 increased on average 2K for C. quitensis and 2.8K for D. antarctica. In contrast, NT and FP decreased on average c. 1K in leaves of warmed plants of both species. Our results showed an averaged LT50 of -15.3°C for C. quitensis, and of -22.8°C for D. antarctica, with freezing tolerance being the freezing resistance mechanism for both species. These results were partially consistent with previous reports, and likely explanations for such discrepancies were related with methodological differences among studies. Our work is the first study reporting the level and mechanisms of freezing resistance of Antarctic vascular plants measured in situ, and we demonstrated that although both plant species exhibited a great ability to cope with freezing temperatures during the growing season, their vulnerability to suffer freezing damage under a warming scenario increase although the magnitude of this response varied across sites and species. Hence, freezing damage should be considered when predicting changes in plant responses of C. quitensis and D. antarctica under future climate conditions of the Antarctic Peninsula.

The "isohydric trap": A proposed feedback between water shortage, stomatal regulation, and nutrient acquisition drives differential growth and survival of European pines under climatic dryness.

Climatic dryness imposes limitations on vascular plant growth by reducing stomatal conductance, thereby decreasing CO2 uptake and transpiration. Given that transpiration-driven water flow is required for nutrient uptake, climatic stress-induced nutrient deficit could be a key mechanism for decreased plant performance under prolonged drought. We propose the existence of an "isohydric trap," a dryness-induced detrimental feedback leading to nutrient deficit and stoichiometry imbalance in strict isohydric species. We tested this framework in a common garden experiment with 840 individuals of four ecologically contrasting European pines (Pinus halepensis, P.nigra, P.sylvestris, and P.uncinata) at a site with high temperature and low soil water availability. We measured growth, survival, photochemical efficiency, stem water potentials, leaf isotopic composition (δ13 C, δ18 O), and nutrient concentrations (C, N, P, K, Zn, Cu). After 2years, the Mediterranean species Pinus halepensis showed lower δ18 O and higher δ13 C values than the other species, indicating higher time-integrated transpiration and water-use efficiency (WUE), along with lower predawn and midday water potentials, higher photochemical efficiency, higher leaf P, and K concentrations, more balanced N:P and N:K ratios, and much greater dry-biomass (up to 63-fold) and survival (100%). Conversely, the more mesic mountain pine species showed higher leaf δ18 O and lower δ13 C, indicating lower transpiration and WUE, higher water potentials, severe P and K deficiencies and N:P and N:K imbalances, and poorer photochemical efficiency, growth, and survival. These results support our hypothesis that vascular plant species with tight stomatal regulation of transpiration can become trapped in a feedback cycle of nutrient deficit and imbalance that exacerbates the detrimental impacts of climatic dryness on performance. This overlooked feedback mechanism may hamper the ability of isohydric species to respond to ongoing global change, by aggravating the interactive impacts of stoichiometric imbalance and water stress caused by anthropogenic N deposition and hotter droughts, respectively.

Translational control of phloem development by RNA G-quadruplex-JULGI determines plant sink strength.

The emergence of a plant vascular system was a prerequisite for the colonization of land; however, it is unclear how the photosynthate transporting system was established during plant evolution. Here, we identify a novel translational regulatory module for phloem development involving the zinc-finger protein JULGI (JUL) and its targets, the 5' untranslated regions (UTRs) of the SUPPRESSOR OF MAX2 1-LIKE4/5 (SMXL4/5) mRNAs, which is exclusively conserved in vascular plants. JUL directly binds and induces an RNA G-quadruplex in the 5' UTR of SMXL4/5, which are key promoters of phloem differentiation. We show that RNA G-quadruplex formation suppresses SMXL4/5 translation and restricts phloem differentiation. In turn, JUL deficiency promotes phloem formation and strikingly increases sink strength per seed. We propose that the translational regulation by the JUL/5' UTR G-quadruplex module is a major determinant of phloem establishment, thereby determining carbon allocation to sink tissues, and that this mechanism was a key invention during the emergence of vascular plants.

Soil CO2 exchange controlled by the interaction of biocrust successional stage and environmental variables in two semiarid ecosystems

Biocrusts are a critical biological community that represents one of the most important photosynthetic biomass pools in dryland regions. Thus, they play an important role in CO2 fluxes in these regions, where water availability limits vascular plant growth and development. The effect of biocrusts on CO2 fluxes was expected to be controlled by the interplay of several environmental factors, as well as biocrust developmental stage and coverage. To test this hypothesis, we performed an in situ study during which we measured net CO2 fluxes and dark respiration over biocrusted soils at different successional stages in two semiarid ecosystems, where biocrusts are one of the main surface components. In addition, CO2 flux was measured in annual plants, which were an abundant interplant cover in one of the study sites during the measurement period. Field campaigns were conducted from early morning to dusk on selected days with different environmental conditions over the year. Gross photosynthesis was calculated from net CO2 flux and dark respiration.Biocrusts showed contrasting responses in CO2 exchange depending on environmental conditions during the day and the year and depending on biocrust developmental stage. CO2 flux in biocrusts was highly correlated with soil moisture, but also with photosynthetically active radiation and temperature. During dry soil periods, soils colonized by biocrusts had net CO2 fluxes close to zero, but after precipitation events (light or heavy) all the biocrust types began to photosynthesize. When the rainfall was right after an extended drought, the respiration by biocrusts themselves and underlying soil exceeded the biocrust gross photosynthesis, and consequently soils colonized by biocrusts behaved as CO2 sources. On the contrary, consecutive precipitation events and mild temperatures caused soil colonization by biocrusts to behave as CO2 sinks. Annual plants were measured during their senescence and acted as CO2 sources during all measurement campaigns. The time of day when the biocrusts showed net CO2 fixation depended on the interplay of humidity just above them, air temperature and photosynthetically active radiation. The biocrust type also significantly influenced CO2 fluxes in both semiarid ecosystems. In general, during wet periods, late successional biocrusts (i.e. lichens and mosses) had higher gross photosynthesis than early successional biocrusts (developed and incipient cyanobacteria crusts). Nevertheless, dark respiration from late successional biocrusts and underlying soils was also higher than from early successional biocrusts, so both biocrust types had similar net CO2 fluxes. These results highlight the importance of considering the whole soil profile under biocrusts with their associated microbial communities as well as the temporal variability of CO2 fluxes in soils covered by biocrusts in carbon balance studies in semiarid regions.

In situ warming in the Antarctic: effects on growth and photosynthesis in Antarctic vascular plants.

The Antarctic Peninsula has experienced a rapid warming in the last decades. Although recent climatic evidence supports a new tendency towards stabilization of temperatures, the impacts on the biosphere, and specifically on Antarctic plant species, remain unclear. We evaluated the insitu warming effects on photosynthesis, including the underlying diffusive, biochemical and anatomical determinants, and the relative growth of two Antarctic vascular species, Colobanthus quitensis and Deschampsia antarctica, using open top chambers (OTCs) and gas exchange measurements in the field. In C.quitensis, the photosynthetic response to warming relied on specific adjustments in the anatomical determinants of the leaf CO2 transfer, which enhanced mesophyll conductance and photosynthetic assimilation, thereby promoting higher leaf carbon gain and plant growth. These changes were accompanied by alterations in the leaf chemical composition. By contrast, D.antarctica showed no response to warming, with a lack of significant differences between plants grown inside OTCs and plants grown in the open field. Overall, the present results are the first reporting a contrasting effect of insitu warming on photosynthesis and its underlying determinants, of the two unique Antarctic vascular plant species, which could have direct consequences on their ecological success under future climate conditions.

Vascular plant‐mediated controls on atmospheric carbon assimilation and peat carbon decomposition under climate change

Climate change can alter peatland plant community composition by promoting the growth of vascular plants. How such vegetation change affects peatland carbon dynamics remains, however, unclear. In order to assess the effect of vegetation change on carbon uptake and release, we performed a vascular plant-removal experiment in two Sphagnum-dominated peatlands that represent contrasting stages of natural vegetation succession along a climatic gradient. Periodic measurements of net ecosystem CO2 exchange revealed that vascular plants play a crucial role in assuring the potential for net carbon uptake, particularly with a warmer climate. The presence of vascular plants, however, also increased ecosystem respiration, and by using the seasonal variation of respired CO2 radiocarbon (bomb-14 C) signature we demonstrate an enhanced heterotrophic decomposition of peat carbon due to rhizosphere priming. The observed rhizosphere priming of peat carbon decomposition was matched by more advanced humification of dissolved organic matter, which remained apparent beyond the plant growing season. Our results underline the relevance of rhizosphere priming in peatlands, especially when assessing the future carbon sink function of peatlands undergoing a shift in vegetation community composition in association with climate change.

Ligand-receptor co-evolution shaped the jasmonate pathway in land plants.

The phytohormone jasmonoyl-isoleucine (JA-Ile) regulates defense, growth and developmental responses in vascular plants. Bryophytes have conserved sequences for all JA-Ile signaling pathway components but lack JA-Ile. We show that, in spite of 450 million years of independent evolution, the JA-Ile receptor COI1 is functionally conserved between the bryophyte Marchantia polymorpha and the eudicot Arabidopsis thaliana but COI1 responds to different ligands in each species. We identified the ligand of Marchantia MpCOI1 as two isomeric forms of the JA-Ile precursor dinor-OPDA (dinor-cis-OPDA and dinor-iso-OPDA). We demonstrate that AtCOI1 functionally complements Mpcoi1 mutation and confers JA-Ile responsiveness and that a single-residue substitution in MpCOI1 is responsible for the evolutionary switch in ligand specificity. Our results identify the ancestral bioactive jasmonate and clarify its biosynthetic pathway, demonstrate the functional conservation of its signaling pathway, and show that JA-Ile and COI1 emergence in vascular plants required co-evolution of hormone biosynthetic complexity and receptor specificity.

Deviations on a theme: Peat patterning in sub-tropical landscapes

Patterned landscapes have long been a popular setting to test hypotheses about the effects of processes on ecosystem structure. The combination of scale-dependent and positive feedback theory is one of the most well-supported in current literature, each explaining separate aspects of patterned peatlands. These theories have been developed from dynamics in boreal peatlands and tested in boreal systems, but the mechanisms that control peat patterning in a sub-tropical system have yet to be acknowledged in theory. Statistical evidence for different mechanisms are present in the biophysical features of sub-tropical patterned peatlands, such as the ridge and slough landscape (RSL) within the greater Everglades wetland system. We use data from the RSL to test whether features of a sub-tropical, patterned peatland conform to positive and scale-dependent feedback patterning theories developed in boreal peatlands and use dynamic simulation to explain our results. The analysis of surface elements and nutrient differences within the RSL and our dynamic simulations indicate that positive and scale-dependent feedback may not be appropriate theories for sub-tropical peat patterning. Decomposition, rather than production, appears to be more important for abrupt microtopographical elevation differences, and differential nutrient concentrations are due to vegetation types, rather than increased evapotranspiration from greater vascular plant growth. Our model expands on the current theories for RSL maintenance, incorporating vegetation types and life history traits into differential peat deposition, which create the signature microtopographical differences found in the Everglades, and demonstrates that the underlying ecological patterning processes in sub-tropical peatlands are likely very different from boreal peatlands and require further discussion and study.

Coupled eco-hydrology and biogeochemistry algorithms enable the simulation of water table depth effects on boreal peatland net CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; exchange

Abstract. Water table depth (WTD) effects on net ecosystem CO2 exchange of boreal peatlands are largely mediated by hydrological effects on peat biogeochemistry and the ecophysiology of peatland vegetation. The lack of representation of these effects in carbon models currently limits our predictive capacity for changes in boreal peatland carbon deposits under potential future drier and warmer climates. We examined whether a process-level coupling of a prognostic WTD with (1) oxygen transport, which controls energy yields from microbial and root oxidation–reduction reactions, and (2) vascular and nonvascular plant water relations could explain mechanisms that control variations in net CO2 exchange of a boreal fen under contrasting WTD conditions, i.e., shallow vs. deep WTD. Such coupling of eco-hydrology and biogeochemistry algorithms in a process-based ecosystem model, ecosys, was tested against net ecosystem CO2 exchange measurements in a western Canadian boreal fen peatland over a period of drier-weather-driven gradual WTD drawdown. A May–October WTD drawdown of ∼ 0.25 m from 2004 to 2009 hastened oxygen transport to microbial and root surfaces, enabling greater microbial and root energy yields and peat and litter decomposition, which raised modeled ecosystem respiration (Re) by 0.26 µmol CO2 m−2 s−1 per 0.1 m of WTD drawdown. It also augmented nutrient mineralization, and hence root nutrient availability and uptake, which resulted in improved leaf nutrient (nitrogen) status that facilitated carboxylation and raised modeled vascular gross primary productivity (GPP) and plant growth. The increase in modeled vascular GPP exceeded declines in modeled nonvascular (moss) GPP due to greater shading from increased vascular plant growth and moss drying from near-surface peat desiccation, thereby causing a net increase in modeled growing season GPP by 0.39 µmol CO2 m−2 s−1 per 0.1 m of WTD drawdown. Similar increases in GPP and Re caused no significant WTD effects on modeled seasonal and interannual variations in net ecosystem productivity (NEP). These modeled trends were corroborated well by eddy covariance measured hourly net CO2 fluxes (modeled vs. measured: R2 ∼ 0.8, slopes ∼ 1 ± 0.1, intercepts ∼ 0.05 µmol m−2 s−1), hourly measured automated chamber net CO2 fluxes (modeled vs. measured: R2 ∼ 0.7, slopes ∼ 1 ± 0.1, intercepts ∼ 0.4 µmol m−2 s−1), and other biometric and laboratory measurements. Modeled drainage as an analog for WTD drawdown induced by climate-change-driven drying showed that this boreal peatland would switch from a large carbon sink (NEP ∼ 160 g C m−2 yr−1) to carbon neutrality (NEP ∼ 10 g C m−2 yr−1) should the water table deepen by a further ∼ 0.5 m. This decline in projected NEP indicated that a further WTD drawdown at this fen would eventually lead to a decline in GPP due to water limitation. Therefore, representing the effects of interactions among hydrology, biogeochemistry and plant physiological ecology on ecosystem carbon, water, and nutrient cycling in global carbon models would improve our predictive capacity for changes in boreal peatland carbon sequestration under changing climates.

The Emergence, Evolution, and Diversification of the miR390-TAS3-ARF Pathway in Land Plants.

In plants, miR390 directs the production of tasiRNAs from TRANS-ACTING SIRNA3 (TAS3) transcripts to regulate AUXIN RESPONSIVE FACTOR (ARF) genes, critical for auxin signaling; these tasiRNAs are known as tasiARFs. To understand the evolution of this miR390-TAS3-ARF pathway, we characterized homologs of these three genes from thousands of plant species, from bryophytes to angiosperms. We found the lower-stem region of MIR390 genes, critical for accurate DICER-LIKE1 processing, is conserved in sequence in seed plants. We propose a model for the transition of functional tasiRNA sequences in TAS3 genes occurred at the emergence of vascular plants, in which the two miR390 target sites of TAS3 genes showed distinct pairing patterns. Based on the cleavability of miR390 target sites and the distance between target site and tasiARF, we inferred a potential bidirectional processing mechanism exists for some TAS3 genes. We also demonstrated a tight mutual selection between tasiARF and its target genes and that ARGONAUTE7, the partner of miR390, was specified later than other factors in the pathway. All these data illuminate the evolutionary path of the miR390-TAS3-ARF pathway in land plants and demonstrate the significant variation that occurs in this functionally important and archetypal regulatory circuit.