Root evolution at the base of the lycophyte clade: insights from an Early Devonian lycophyte

Background and Aims The evolution of complex rooting systems during the Devonian had significant impacts on global terrestrial ecosystems and the evolution of plant body plans. However, detailed understanding of the pathways of root evolution and the architecture of early rooting systems is currently lacking. We describe the architecture and resolve the structural homology of the rooting system of an Early Devonian basal lycophyte. Insights gained from these fossils are used to address lycophyte root evolution and homology.Methods Plant fossils are preserved as carbonaceous compressions at Cottonwood Canyon (Wyoming), in the Lochkovian–Pragian (∼411 Ma; Early Devonian) Beartooth Butte Formation. We analysed 177 rock specimens and documented morphology, cuticular anatomy and structural relationships, as well as stratigraphic position and taphonomic conditions.Key Results The rooting system of the Cottonwood Canyon lycophyte is composed of modified stems that bear fine, dichotomously branching lateral roots. These modified stems, referred to as root-bearing axes, are produced at branching points of the above-ground shoot system. Root-bearing axes preserved in growth position exhibit evidence of positive gravitropism, whereas the lateral roots extend horizontally. Consistent recurrence of these features in successive populations of the plant preserved in situ demonstrates that they represent constitutive structural traits and not opportunistic responses of a flexible developmental programme.Conclusions This is the oldest direct evidence for a rooting system preserved in growth position. These rooting systems, which can be traced to a parent plant, include some of the earliest roots known to date and demonstrate that substantial plant–substrate interactions were under way by Early Devonian time. The morphological relationships between stems, root-bearing axes and roots corroborate evidence that positive gravitropism and root identity were evolutionarily uncoupled in lycophytes, and challenge the hypothesis that roots evolved from branches of the above-ground axial system, suggesting instead that lycophyte roots arose as a novel organ.     

Terminal processes of serotonin neurons in the caudal spinal cord of the molly,Poecilia latipinna,project to the leptomeninges and urophysis

Summary The caudal neurosecretory complex of poeciliids has previously been shown to be innervated by extranuclear and intrinsic serotonergic projections. In the present study, immunohistochemical techniques were used to characterize fibers originating from serotonin neurons intrinsic to the caudal spinal cord. Bipolar and multipolar neurons were oriented ventromedially, and contained numerous large granular vesicles. Three types of serotonergic fibers were distinguished based on their distribution and morphology. Intrinsic Type-A fibers branched into varicose segments near the ventrolateral surface of the spinal cord and contacted the basal lamina beneath the leptomeninges. Type-B fibers coursed longitudinally to enter the urophysis, where they diverged and terminated around fenestrated capillaries. Labelled vesicles in Type-A and Type-B terminals were the same size as those in labelled cells and in unlabelled neurosecretory terminals in the urophysis. Type-C small varicose fibers branched within the neuropil of the caudal neurosecretory complex. Serotonin may be secreted into the submeningeal cerebrospinal fluid, the urophysis, and the caudal vein by Type-A and Type-B fibers, whereas, Type-C fibers may be processes of serotonergic interneurons in the neuroendocrine nucleus. The possibility that urotensins I and II or arginine vasotocin were colocalized in the processes of the intrinsic serotonin neurons was investigated immunohistochemically. The negative results of these experiments suggest that serotonin-containing neurons may represent a neurochemically distinct subpopulation in the caudal neurosecretory complex.     

Jurassic Petrified Filician Plants from the Rajmahal Hills, India

Three types of petrified filician rhizomes and their associatedpetioles and roots from the Rajmahal Hills, Bihar, India aredescribed. Two rhizomes possess protostelic vasculature withmesarch protoxylem elements and exarch protoxylem points. Theformer are gleicheniaceous while the latter is described asa schizaeaceous rhizome. The associated petioles possess typicalgleicheniaceous anatomy while the roots show variations in thestructure of epiblema and cortex. filician fossils, Jurassic, Actinostelopteris pakurense, Gleichenia sonajoriense, Solenostelopteris jurassica, Gleichenioamyelon diarcha, Filicoamyelon cryptogrammoides Filicoamyelon actinostachyoides     

Early Jurassic flora from South Primorye,Far East,Russia

A unique Early Jurassic flora from the Schitukhe Formation of South Primorye, Russia is further studied, with newly collected materials. The flora is composed of over 50 taxa. It is dominated by ferns (Dipteridaceae, Marattiaceae, etc.), cycads (Pterophyllum, Nilssonia, Ctenis, Taeniopteris, etc.), conifers (Cycadocarpidium, Podozamites, etc.), and other seasonally deciduous gymnosperms (Czekanowskiales, Ginkgoales, etc.), showing a special flora living in an ecotone zone between the Palaeofloristic realms of Siberian Flora and Euro-Sinian Flora in the East Asia during the early Early Jurassic. The flora is compared with its coeval floras from China and Japan. A new species Cycadocarpidium pacificum n. sp. is reported. The age of the Schitukhe flora is constrained by the marine mollusca fossils yielded in the sandwich marine beds of the Schitukhe Formation, as the Hettangian–Sinemurian.     

Physiological and morphological characterization of olfactory descending interneurons of the male silkworm moth, Bombyx mori

In order to understand the neural mechanisms of pheromone-oriented walking in male silkworm moths, Bombyxmori, we have characterized olfactory responses and three-dimensional structure of two clusters (Group-I, Group-II) of descending interneurons in the brain by intracellular recording and staining with lucifer yellow. Neurons were imaged with laser-scanning confocal microscopy. Group-I and Group-II descending interneurons were classified into three morphological types, respectively. In response to the sex pheromone, bombykol, Type-A Group-I descending interneurons showed characteristic flipflopping activity. The Group-I descending interneurons had dendritic arborizations in the lateral accessory lobe and varicose profiles in the posterior-lateral part of the suboesophageal ganglion where the dendritic arborizations of a neck motor neuron (i.e., cv1 NMN) reside. Other types of Group-I descending interneurons exhibited long-lasting suppression of firing. The pheromonal responses of Group-II descending interneurons fell into two classes: brief excitation and brief inhibition. Type-A Group-II descending interneurons showing brief excitation had blebby processes in the posterior-lateral part of the suboesophageal ganglion. Type-B and Type-C Group-II descending interneurons did not have varicose profiles there. Therefore, the neck motor neuron regulating head turning, which accompanies the pheromone-oriented walking, may be controlled by these two types, flipflop and phasic excitation, of descending activity patterns. Accepted: 2 November 1998     

Heavy metal bioaccumulation by the organs of Phragmites australis (common reed) and their potential use as contamination indicators

The concentrations of heavy metals in the roots, rhizomes, stems and leaves of the aquatic macrophyte Phragmites australis (common reed), and in the corresponding water and sediment samples from the mouth area of the Imera Meridionale River (Sicily, Italy), were investigated to ascertain whether plant organs are characterized by differential accumulation, and to test the suitability of the various organs for heavy metal biomonitoring of water and soil. Heavy metals considered were Cd, Cr, Cu, Hg, Mn, Ni, Pb, Zn. Results showed that belowground organs were the primary areas of metal accumulation. In particular, metal concentrations in plant organs decreased in the order of root > rhizome ≥ leaf > stem. All four organs showed significant differences in concentration for Cr, Hg, Mn, Zn, thus suggesting low mobility from roots to rhizomes and to aboveground organs. Although the organs followed different decreasing trends of metal concentration, the trend Mn > Zn > Pb > Cu was found in each plant organ. Mn showed the highest concentrations in all organs whereas the lowest concentrations regarded Cd and Cr in the belowground and aboveground organs, respectively. The toxic threshold was exceeded by Cr in roots, rhizomes and leaves, Mn in roots and leaves, Ni in roots. The highest average concentrations were found as follows: Cd, Hg, Pb, Zn in root, Cr, Mn, Ni in sediment, Cu in water. Positive linear relationships were found between heavy metal concentrations in all plant organs and those in water and sediment, thus indicating the potential use of such organs for pollution monitoring of water and sediment. Advantages of using plant species as biomonitors, especially Phragmites australis, were also discussed.     

Biomass partitioning and water content relationships at the branch and whole-plant levels and as a function of plant size in Elaeagnus mollis populations in Shanxi, North China

Understanding of the biomass (dry weight) allocation and water relations in populations will provide useful information on the growth patterns and resource-allocation dynamics. By destructive sampling, foliage, branch and root biomass were measured in the endangered shrub Elaeagnus mollis populations growing in Shanxi province, North China. Biomass partitioning and water content relationships were compared at the branch and whole-plant levels, and as a function of basal diameter (plant size). The biomass was mainly distributed in the bigger branches at the branch level, and in the branch wood at the whole-plant level, and branch biomass (but not foliage or root biomass) increases significantly with increasing basal diameter. As a result, branch wood became the major biomass pool, even though considerable biomass was also allocated to the roots. However, the relative water content decreased from the periphery of the crown to the interior of the shrub at the branch level, and from the aboveground to the belowground at the whole-plant level though no significant variation among foliage, branches, and roots. Yet it increased significantly for the whole-plant with increasing basal diameter. The ratio of belowground to aboveground biomass was smaller than 1.0, even as a function of basal diameter. These growth responses indicated a strong adaptation to the shrub’s growing conditions. Biomass was primarily allocated above the ground and the aboveground components grew faster than the belowground one.     

Native and exotic foundation grasses differ in traits and responses to belowground tri-trophic interactions

A plant’s growth and fitness are influenced by species interactions, including those belowground. In primary successional systems, belowground organisms are known to have particularly important control over plant growth. Exotic plant invasions in these and other habitats may in part be explained by altered associations with belowground organisms compared to native plants. We investigated the growth responses of two foundation grasses on Great Lakes sand dunes, the native grass Ammophila breviligulata and the exotic grass Leymus arenarius, to two groups of soil organisms with important roles in dune succession: arbuscular mycorrhizal fungi (AMF) and plant-parasitic nematodes (PPN). We manipulated the presence/absence of two generalist belowground species known to occur in Great Lakes dunes, Rhizophagus intraradices (AMF) and Pratylenchus penetrans (PPN) in a factorial greenhouse experiment and assessed the biomass production and root architectural traits of the plants. There were clear differences in growth and above- and belowground architecture between Ammophila and Leymus, with Leymus plants being bigger, taller, and having longer roots than Ammophila. Inoculation with Rhizophagus increased above- and belowground biomass production by ~32% for both plant species. Inoculation with Pratylenchus decreased aboveground biomass production by ~36% for both plant species. However belowground, the exotic Leymus was significantly more resistant to PPN than the native Ammophila, and gained more benefits from AMF in belowground tri-trophic interactions than Ammophila. Overall, our results indicate that differences in plant architecture coupled with altered belowground interactions with AMF and PPN have the potential to promote exotic plant invasion.     

Effects of fire,mowing and nitrogen addition on root characteristics in tall-grass prairie

Abstract. Root harvests and root windows were used to study the influence of fire, mowing and nitrogen additions on root lengths, biomass, and nitrogen content in tall-grass prairie. Four years of nitrogen additions (10 g m² yr^?1) increased below-ground mass by 15 % and nitrogen concentration in that mass by 77 %. In general, live roots and rhizomes exhibited greater increases in nitrogen concentrations than detrital roots and rhizomes. After four years of treatment, live roots and rhizomes immobilized an additional 1.5 to 5 g/m² of nitrogen, depending upon specific treatment, while dead roots and rhizomes immobilized an additional 3 to 3.5 g/m². Average root growth parameters, as measured with root windows, were positively correlated with above-ground peak foliage biomass; however, the only significant correlation was between average new root growth and above-ground peak foliage biomass (r = 0.73, p ≤ 0.04). Root growth and decay, as measured by annual mean values for eight root windows over a four year interval, were insensitive to climatic and treatment effects.     

Persistent anthropogenic legacies structure depth dependence of regenerating rooting systems and their functions

Biotically-mediated weathering helps to shape Earth’s surface. For example, plants expend carbon (C) to mobilize nutrients in forms whose relative abundances vary with depth. It thus is likely that trees’ nutrient acquisition strategies—their investment in rooting systems and exudates—may function differently following disturbance-induced changes in depth of rooting zones and soil nutrient stocks. These changes may persist across centuries. We test the hypothesis that plant C allocation for nutrient acquisition is depth dependent as a function of rooting system development and relative abundances of organic vs. mineral nutrient stocks. We further posit that patterns of belowground C allocation to nutrient acquisition reveal anthropogenic signatures through many decades of forest regeneration. To test this idea, we examined fine root abundances and rooting system C in organic acid exudates and exo-enzymes in tandem with depth distributions of organically- and mineral-bound P stocks. Our design permitted us to estimate C tradeoffs between organic vs. mineral nutrient benefits in paired forests with many similar aboveground traits but different ages: post-agricultural mixed-pine forests and older reference hardwoods. Fine roots were more abundant throughout the upper 2 m in reference forest soils than in regenerating stands. Rooting systems in all forests exhibited depth-dependent C allocations to nutrient acquisition reflecting relative abundances of organic vs. mineral bound P stocks. Further, organic vs. mineral stocks underwent redistribution with historic land use, producing distinct ecosystem nutritional economies. In reference forests, rooting systems are allocating C to relatively deep fine roots and low-C exudation strategies that can increase mobility of mineral-bound P stocks. Regenerating forests exhibit relatively shallower fine root distributions and more diverse exudation strategies reflecting more variable nutrient stocks. We observed these disparities in rooting systems’ depth and nutritional mechanisms even though the regenerating forests have attained aboveground biomass stocks similar to those in reference hardwood forests. These distinctions offer plausible belowground mechanisms for observations of continued C sink strength in relatively old forests, and have implications for soil C fates and soil development on timescales relevant to human lifetimes. As such, depth-dependent nutrient returns on plant C investments represent a subtle but consequential signal of the Anthropocene.

     

Plant-dominated assemblage and invertebrates from the Lower Cenomanian of Jaunay-Clan,western France

Two fossil localities are reported on the “LGV SEA” railroad from the Lower Cenomanian of Jaunay-Clan (JC), near Poitiers, western France. The laminated mudstones yielded plant fossils including ferns (Cladophlebis, Osmundophyllum, Ruffordia goeppertii, Sphenopteris), conifers (Brachyphyllum, Dammarophyllum, Pagiophyllum), and terrestrial and aquatic freshwater angiosperms (Eucalyptolaurus depreii, Ploufolia). They are associated with a coleopteran insect that shows systematic affinities to the modern subfamily Chrysomelinae (Chrysomelidae). This assemblage suggests connections with arborescent vegetation growing in calm freshwater environment. Brackish to marine invertebrates also occur and include a dakoticancroid crab (Brachyura, Podotremata, Dakoticancroidea) and a few bivalves (Brachidontes). They suggest brackish episodes during pond sedimentation in a coastal environment. Lastly, vertebrates are represented by an isolated feather.     

Growth rates,biomass and distribution of selected woody plant roots in Burkea africana-Ochna pulchra savanna

Woody plants in an African Burkea africana-Ochna pulchra savanna on deep sandy soil were found to have characteristically bimorphic root systems. The shallow lateral root component was often well developed and roots extended up to seven times the extent of the plant canopy in several species. Exponential tapering of lateral roots was found in Terminalia sericea. The wide-ranging roots, together with the high degree of multispecies root system interpenetration, result in the so-called, open grassy areas in the savanna mosaic often containing a competitively significant woody plant component. Root systems of Ochna pulchra were found to be relatively specialized and included: negatively geotropic, superficial roots; sinker roots to bedrock; high suckering response to damage in roots; belowground lignotuber-type organs; and sustained subterranean interconnections between some aboveground stems. These features are likely to contribute substantially to the resilience of this plant species to various climatic and veld management stress factors. Root/shoot mass ratios averaged unity but depended on plant size and aboveground growth form in Ochna pulchra. The dependence of these ratios on sizes of plant also applied to plant clones. Initiation of root tip growth occurred in early summer in one year and late spring in another. Main root tip growth occurred in late summer and early autumn, well after completion of most growth of leafy shoots in spring. It is suggested that some active uptake of water and nutrients by non-extending roots allows this form of phased growth in the plant. In an analysis of the seasonal growth of individual root tip systems, it was clear that transitory states of rest occur in fine root development but that these are far more frequent in the branching (and hence proliferation) of roots than in the continuing development of any root axis.Nomenclature follows the present system of the Botanical Research Institute, Pretoria, and the Flora of Southern Africa.I thank M.D. Panagos, P.S. Carr and J. Steyn for assistance at various stages of this work.     

毛脉酸模的组织培养及植株再生

以毛脉酸模下胚轴和幼苗根茎为外植体,以MS为基本培养基,与不同浓度比例的6-BA和2,4-D等植物生长调节剂进行毛脉酸模组织培养的研究。结果表明,毛脉酸模幼苗根茎是诱导丛生芽的最佳材料,诱导丛生芽产生的最佳培养基为MS+6-BA 3.0 mg·L^-1+2,4-D 0.1 mg·L^-1,诱导率为81.2%;生根培养基为无激素的MS培养基,生根率可达92%,在此条件下生根迅速,可获得完整植株;组培苗经过炼苗移栽后成活率可达80%。     

Floral determination in axillary buds of Nicotiana silvestris

At anthesis of the terminal flower the developmental fates of axillary buds of the long-day plant Nicotiana silvestris were assessed in situ and in isolation. The in situ developmental fate was assessed by decapitating the plant above the bud in question and letting the bud mature. The developmental fate of isolated buds was assessed by removing the bud from the main axis, rooting it, and letting it mature. The number of nodes below the terminal flower of the mature shoot was indicative of the developmental fate of the bud. Terminal meristems of rooted axillary buds exhibited two patterns of development: (1) Their developmental fate was the same as that of in situ buds at the same node or (2) their developmental fate was the same as that of seed-derived plants. For example, terminal meristems of rooted buds from the fourth node below the inflorescence produced either 15 to 19 nodes or 36 to 40 nodes. In situ fourth buds produced 12 to 14 nodes while seed-derived plants produced 33 to 39 nodes. Terminal meristems of rooted axillary buds that exhibited the same developmental fate as that of in situ buds were determined for floral development. Although determined buds produced a terminal flower, all but one had abnormal inflorescences. That is, in the place of floral branches determined buds produced vegetative branches. Four buds that were not determined for floral development had their shoot tips rooted each time the plant bolted. Only when the plants were allowed to grow without being rerooted did they flower. These results indicate that roots may prevent and/or destabilize floral determination in N. silvestris.     

Deep rooting and global change facilitate spread of invasive grass

Abiotic global change factors, such as rising atmospheric CO₂, and biotic factors, such as exotic plant invasion, interact to alter the function of terrestrial ecosystems. An invasive lineage of the common reed, Phragmites australis, was introduced to North America over a century ago, but the belowground mechanisms underlying Phragmites invasion and persistence in natural systems remain poorly studied. For instance, Phragmites has a nitrogen (N) demand higher than native plant communities in many of the ecosystems it invades, but the source of the additional N is not clear. We exposed introduced Phragmites and native plant assemblages, containing Spartina patens and Schoenoplectus americanus, to factorial treatments of CO₂ (ambient or +300 ppm), N (0 or 25 g m^?2 year^?1), and hydroperiod (4 levels), and focused our analysis on changes in root productivity as a function of depth and evaluated the effects of introduced Phragmites on soil organic matter mineralization. We report that non-native invasive Phragmites exhibited a deeper rooting profile than native marsh species under all experimental treatments, and also enhanced soil organic matter decomposition. Moreover, exposure to elevated atmospheric CO₂ induced a sharp increase in deep root production in the invasive plant. We propose that niche separation accomplished through deeper rooting profiles circumvents nutrient competition where native species have relatively shallow root depth distributions; deep roots provide access to nutrient-rich porewater; and deep roots further increase nutrient availability by enhancing soil organic matter decomposition. We expect that rising CO₂ will magnify these effects in deep-rooting invasive plants that compete using a tree-like strategy against native herbaceous plants, promoting establishment and invasion through niche separation.     

Presence and Possible Mode of Action of a Proteinaceous Gonadotropin-like Growth Regulating Factor in Plant Systems

Antiserum to human chorionic gonadotropin (HCG) caused marked inhibition of adventitious rooting of Begonia semperflorens and Chrysanthemum morifolium stem cuttings. Immuno-absorption of crude protein extract from chrysanthemum foliage through a column of polymerized and unsolubilized HCG antibodies resulted in a significant reduction in adventitious root promoting activity of the extract. These results are discussed in the light of a hypothesis that an endogenous protein growth regulating substance which immunologically resembles HCG exists in plant systems. Further experimentation with HCG suggests that its mode of action is possibly via the regulation of peroxidase enzymatic control of auxin levels.     

A soil-free root observation system for the study of root-microorganism interactions in maize

Background and aims

The root surface of a plant usually exceeds the leaf area and is constantly exposed to a variety of soil-borne microorganisms. Root pathogens and pests, as well as belowground interactions with beneficial microbes, can significantly influence a plants' performance. Unfortunately, the analysis of these interactions is often limited because of the arduous task of accessing roots growing in soil. Here, we present a soil-free root observation system (SF-ROBS) designed to grow maize (Zea mays) plants and to study root interactions with either beneficial or pathogenic microbes.

Methods

The SF-ROBS consists of pouches lined with wet filter paper supplying nutrient solution.

Results

The aspect of maize grown in the SF-ROBS was similar to soil-grown maize; the plant growth was similar for the shoot but different for the roots (biomass and length increased in the SF-ROBS). SF-ROBS-grown roots were successfully inoculated with the hemi-biotrophic maize fungal pathogen Colletotrichum graminicola and the beneficial rhizobacteria Pseudomonas putida KT2440. Thus, the SF-ROBS is a system suitable to study two major belowground phenomena, namely root fungal defense reactions and interactions of roots with beneficial soil-borne bacteria.

Conclusions

This system contributes to a better understanding of belowground plant microbe interactions in maize and most likely also in other crops.     

Quality and decomposition in soil of rhizome, root and senescent leaf from Miscanthus x giganteus, as affected by harvest date and N fertilization

To predict the environmental benefits of energy crop production and use, the nature and fate of biomass residues in the soil need to be quantified. Our objective was to quantify Miscanthus x giganteus biomass recycling to soil and to assess how harvesting time and N fertilization affect their characteristics and subsequent biodegradability. The quantification of aerial and belowground biomass and their sampling were performed on 2- and 3-year-old Miscanthus stands, either fertilized with 120 kg N ha^?1 year^?1 or not fertilized, in autumn (maximal biomass production) and winter (maturity). Plant biomass was chemically characterized (total sugars, Klason lignin, C/N) and incubated in optimum decomposition conditions (15°C, ?80 kPa) for 263 days, for C and N mineralization. Accumulation of carbon in rhizomes and roots was 7.5 to 10 t C ha^?1 and represented about 50% of total plant biomass C. Senescent leaves represented about 1.5 t C ha^?1 year^?1. All residues, especially the roots, had high lignin contents, while the rhizomes also had a high soluble content due to their nutrient storage function. The C mineralization rates were closely related to the chemical characteristics of the residue, higher sugar and lower lignin contents leading to faster decomposition, as observed for rhizomes.