Root uptake and translocation of radiocaesium from agricultural soils by various plant species

Plant uptake of radiocaesium from soil is an important pathway for the entry of this pollutant into the human food chain and so contributes to any assessment of the radiation dose following contamination. Large differences in soil–plant transfer factors have been reported for plant species grown on the same soils. Few studies have attempted to distinguish between differences in root uptake and root-to-shoot translocation. We have investigated the root uptake of radiocaesium from artificially contaminated soils and the subsequent translocation to shoots for various plant species grown on three agricultural soils. The effects of short contact times and potassium starvation or enrichment have been studied. The Cs adsorption properties of rhizosphere soils have been compared with those of the initial soils. The proportion of activity removed from soil is largely soil dependent. Root uptake properties have less effect, but appear to be species determined, and not influenced by soil properties. Differences in soil-to-shoot transfer factor arise from species-dependent differences in root-to-shoot translocation. Root-to-shoot activity ratios are not soil dependent. There was little effect of soil potassium status. Root action slightly enhanced Cs adsorption on one soil, probably due to mineral weathering associated with the release of nonexchangeable potassium.     

Genotypic effects in phytoavailability of radiocaesium are pronounced at low K intensities in soil

The differences in radiocaesium uptake between species were analysed in a series of solution culture and pot trials. Since radiocaesium uptake is very sensitive to the solution potassium (K) concentration, it was hypothesised that species depleting K in the rhizosphere to a larger extent, will have a higher radiocaesium uptake. Five species (bean, lettuce, winter barley, ryegrass and bentgrass) were grown for 18–21 days in nutrient solution spiked with ¹³⁷Cs and at 4 K concentrations between 0.025 and 1.0 mM. Shoot ¹³⁷Cs activities all decreased between 17- and 81-fold with increasing K supply. Shoot ¹³⁷Cs activities were 4-fold different between species at the lowest K supply and 3.4-fold different at high K supply. The same five species were grown in two ¹³⁴Cs spiked soils with contrasting exchangeable K but similar clay content. Shoot ¹³⁴Cs activities were up to 19-fold higher in the soil with lowest exchangeable K. Differences in shoot activity concentrations between the species were only 4.5-fold in the high K soil, but were 15-fold in the low K soil. Bulk soil solution ¹³⁴Cs and K concentration data were combined with radiocaesium uptake characteristics measured in solution culture to predict radiocaesium uptake from soil. Predictions were within 1.6-fold of observations in the high K soil but largely underestimated ¹³⁴Cs uptake in lettuce, ryegrass and barley in the low K soil. A solute transport model was used to estimate K and radiocaesium concentrations in the rhizosphere. These calculations confirmed the assumption that higher radiocaesium uptake is found for species that deplete K in the rhizosphere to a larger extent.     

Relative contributions of soil chemistry, plant physiology and rhizosphere induced changes in speciation on Ni accumulation in plant shoots

The aim of this study is to rank the relative importance of soil properties, root uptake and root-to-shoot redistribution on the transfer of the trace element nickel from soil to the shoots of non hyperaccumulatings plants. Two contrasting soils and seven plant species have been studied using the radioactive isotope, ⁶³Ni. Shoots and roots were analysed separately and the specific activity of each plant has been measured. The isotopic exchange properties of rhizosphere soil where compared with control non rhizosphere soil. Possible changes in Ni speciation in the rhizosphere have been assessed by comparing the isotopic exchange properties of the rhizosphere and control soil and by comparing the specific activities of Ni in each plant. The capacity of soil to immobilise added radiotracer largely determines root uptake, leading to between a 4- and 40-fold difference between soils for a given species. The redistribution of nickel from roots to shoots was fairly constant for plants grown on the rendzina, but varied strongly between species for the acid soil. This variation enhanced the contrast between species of the soil-to-shoot transfer factor. Root action significantly enhanced immobilisation of added nickel in an acid soil due to the modification of speciation of initially non exchangeable soil nickel, but had little effect on a neutral rendzina. Changes in rhizosphere pH were similar on the two soils. In the acid soil, these pH changes were accompanied by changes in Ni speciation but a causative link has not been established. In the neutral soil pH changes may have modified root uptake properties.     

Radiocaesium in an organic soil and the effect of treatment with the fungicide ‘Captan’

Soil fungi accumulate radiocaesium from contaminated soil and it has been hypothesised that this may alter the plant availability and movement of the radionuclide in soil. The effect of twice-monthly addition of an aqueous suspension of the fungicide ‘Captan’ on the changes in a peaty podzol soil at 2 sites, contaminated 2 or 3 years earlier by the injection of ¹³⁴Cs, has been quantified. The sites had different soil acidity and vegetation cover. The less acid soil (pH_water 5.0) had been improved by the addition of lime and fertilizer and was reseeded with grass and clover. The more acid soil (pH_water 3.8) was under hill grasses, herbs and heather. On both sites the addition of fungicide did not alter the amount or concentration of radiocaesium in plant material sampled monthly or the depth distribution of radiocaesium in the soil profile. The concentration of the fungal constituent, ergosterol, in the soil, measured monthly, was unaffected by the fungicide treatment but evidence was obtained from a pot experiment to show that ergosterol decomposes slowly in cold, wet soils. On the more acid soil, two weeks after the last application of fungicide, there was a decline in active fungi as measured by fluorescein diacetate staining. Chloroform fumigation of the more acid soil resulted in a small increase in the amount of ¹³⁴Cs exchangeable with 1 M ammonium acetate. Radiocaesium in seven different fungi grown in pure culture was found to be almost entirely extractable (> 95%) with 1 M ammonium acetate. Another, Amanita rubescens, showed some retention and 88% was extractable. These findings do not preclude the fungal biomass as an important soil component controlling plant availability of radiocaesium from acid, organic soils by maintaining radiocaesium in a biological cycle, but make it unlikely that any fixation by fungi in a chemical sense is involved.     

Recent 14C-labelled assimilate allocation to Scots pine seedling root and mycorrhizosphere compartments developed on reconstructed podzol humus,E- and B- mineral horizons

In northern boreal forests, podzolic soils prevail that comprise of a distinct upper organic humus/mor (O) horizon that is supported by underlying eluvial (E) and illuvial (B) mineral horizons. The dominant tree species, Scots pine (Pinus sylvestris L.), is known to be highly dependent on root symbiosis with ectomycorrhizal fungi that develop in constituent podzol horizons for growth in these nutrient limited soils. The aim of this microcosm-based study was a quantification of photosynthetically fixed ¹⁴C allocation, following standard pulse-feeding of 7-month-old Scots pine seedling shoots, to respective root and mycorrhizosphere compartments that developed in the reconstructed podzol (O, E and B) profile. Biomass of roots and mycorrhizas decreased with increasing soil depth but no soil origin, control forest vs. clear-cut area, related differences were observed. Similarly, no major soil origin- or podzol horizon-related differences in categorised ectomycorrhizal morphotypes and number of mycorrhizas, in relation to pooled root and mycorrhiza biomass, were detected. However, the total recovery of ¹⁴C-label was significantly higher in clear-cut soil microcosms compared to control counterparts. A significant finding was equivalent ¹⁴C-carbon allocation to roots and ectomycorrhizas in all three major, organic and mineral, podzol profile horizons studied. These carbon allocation data provide additional support for direct (or indirect) roles of roots and symbiotic mycorrhizal fungi in mineral weathering and biodegradation of organic ligands that are central for plant acquisition of growth limiting nutrients and the podzolization process in boreal forest ecosystems.     

Extraradical mycelium of the arbuscular mycorrhizal fungus Glomus lamellosum can take up,accumulate and translocate radiocaesium under root-organ culture conditions

Radiocaesium enters the food chain when plants absorb it from soil, in a process that is strongly dependent on soil properties and plant and microbial species. Among the microbial species, arbuscular mycorrhizal (AM) fungi are obligate symbionts that colonize the root cortex of many plants and develop an extraradical mycelial (ERM) network that ramifies in the soil. Despite the well-known involvement of this ERM network in mineral nutrition and uptake of some heavy metals, only limited data are available on its role in radiocaesium transport in plants. We used root-organ culture to demonstrate that the ERM of the AM fungus Glomus lamellosum can take up, possibly accumulate and unambiguously translocate radiocaesium from a 137Cs-labelled synthetic root-free compartment to a root compartment and within the roots. The accumulation of 137Cs by hyphae in the root-free compartment may be explained by sequestration in the hyphae or by a bottleneck effect resulting from a limited number of hyphae crossing the partition between the two compartments. Uptake and translocation resulted from the incorporation of 137Cs into the fungal hyphae, as no 137Cs was detected in mycorrhizal roots treated with formaldehyde. The importance of the translocation process was indicated by the correlation between 137Cs measured in the roots and the total hyphal length connecting the roots with the labelled compartment. 137Cs may be translocated via a tubular vacuolar system or by cytoplasmic streaming per se.     

Association of the Plant-beneficial Fungus Verticillium lecanii with Soybean Roots and Rhizosphere

Colonization of soybean roots by the biocontrol fungus Verticillium lecanii was studied in vitro and in situ. For in vitro experiments, V. lecanii was applied to soybean root tip explant cultures. Four weeks after inoculation, the fungus grew externally on at least half of the roots (all treatments combined), colonizing 31% to 71% of root length (treatment means). However, when a potato dextrose agar plug was available as a nutrient source for the fungus, root tips inoculated soon after transfer were not colonized by V. lecanii unless Heterodera glycines was present. Scanning electron microscopy of colonized roots from in vitro cultures revealed a close fungus-root association, including fungal penetration of root cells in some specimens. In the greenhouse, soybeans in sandy soil and in loamy sand soil were treated with V. lecanii applied in alginate prills. The fungus was detected at greater depths from the sandy soil than from the loamy sand soil treatment, but fungus population numbers were small and variable in both soils. Root box studies coupled with image processing analysis of the spatial distribution of V. lecanii in sandy soil supported these findings. Verticillium lecanii was detected randomly in the rhizosphere and soil of root boxes, and was rarely extensively distributed. These in vitro and in situ experiments indicate that V. lecanii can grow in association with soybean roots but is a poor colonizer of soybean rhizosphere in the soil environment.     

Direct isolation of tobacco necrosis virus from soils

Summary In TNV-bearing soils, the virus occurred adsorbed to soil colloids in low levels. By direct assay, the TNV could be more readily isolated from the rhizosphere of naturally infected cluster bean plants. The level of reaction of the TNV isolated from the rhizosphere soil was the same as TNV-D (cb isolate) in precipitin ring tests with antisera against TNV-A and TNV-D. The phenomenon of release of TNV from the infected roots into the soil and adsorption of TNV particles to colloidal particles in the soil are discussed from the point of ecology and stability of TNV in soils.     

Water-soluble carbon in roots of rape and barley: impacts on labile soil organic carbon, arylsulphatase activity and sulphur mineralization

Investigating the impact of plant species on sulphur (S) availability in the rhizosphere soil is agronomically important to optimize S fertilization. Bulk, rhizosphere soils and the roots of field-grown rape and barley were sampled 7 times (every fortnight), from March to June, at plant maturity. Root carbon (C) and nitrogen (N) in water extract, along with soil SO₄²⁻-S, labile soil organic-C (HWC) and -N (HWN) in hot water extract, as well as soil arylsulphatase activity were then monitored. The average concentrations of both HWC and HWN were observed in the following decreasing order: rape rhizosphere soil >barley rhizosphere soil >bulk soil. In parallel, the average contents of water extractable-C and -N in rape roots were higher than those in barley roots. These results suggest that soil C and N contents in hot water extract (including rhizodeposition) were correlated with C and N released by roots. Great ARS activities found in rape rhizosphere soil were accompanied by great SO₄²⁻-S mineralization over time. Finally, bulk and rhizosphere soils of rape and barley were pooled from the seven samplings and incubated with the corresponding pooled root water-soluble C of both plant species and glucose-C. After 1 and 9 weeks, a greater net S mineralization (gross mineralization - immobilization) was observed with rape root water-soluble C than with barley root water-soluble C and glucose-C. Conjointly, we found a higher average value of ARS activity in rape rhizosphere than in barley rhizosphere soil. Our findings suggest that plant species, via their rhizodeposition, determine the dynamic of S in soil.     

重金属在根际中的化学行为——Ⅱ.土壤中吸附态铜解吸的根际效应

用第四纪红壤性水稻土(QP)、淀浆白土(WP)、第四纪红土(QR)和赤红壤(LR)研究了土壤中吸附态铜的解吸的根际效应。结果表明,吸附态铜可分为0.1M KNO_3解吸的易解吸态铜和0.1MHCl解吸的难解吸态铜。随吸附量增加,易解吸态铜百分数增加,而难解吸态铜百分数下降。易解吸态铜在根际土中的量小于非根际土中的量,各土壤的根际效应依次为:QP>WP>LR>QR;其平均解吸百分数则为:QR>LR>WP>QP。难解吸态铜的量为根际土大于非根际土,各土壤的根际效应为:WP>LR>QP>QR,其平均解吸百分数依次为QP>WP>LR>QR。根际中铜吸附的增加主要是因为难解吸态铜的增加。     

Dynamics of phosphorus in the rhizosphere of maize and rape grown on synthetic,phosphated calcite and goethite

In calcareous soils the dynamics of phosphorus is controlled by calcite and iron oxides such as goethite which strongly retain P and consequently maintain low P concentrations in soil solution. Plants can drastically change chemical conditions in the rhizosphere, in particular by releasing H⁺ or OH⁻ or by excreting organic anions. By modifying the dissolution/precipitation and desorption/adsorption equilibria, roots can influence the mobility of soil P. The aim of this work was to test whether H⁺ or OH⁻ release can induce the mobilization of P in the rhizosphere of maize and rape supplied with NO₃-N or NH₄-N and grown on synthetic phosphated calcite or goethite as sole source of P. With P-calcite, the mobilization of P was generally related to the acidification of the rhizosphere. With P-goethite, rhizosphere acidification induced some increase of DTPA-extractable Fe and hence dissolution of goethite. Rhizosphere P was concomitantly depleted but the mechanisms involved are less clear. The difference in behavior of the two species is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

磷酸盐在土壤中的竞争吸附与解吸机制

本文概述了近年来国内外有关磷酸盐的竞争吸附与解吸的研究成果。土壤中许多阴离子都能与磷竞争吸附点位,使得磷的吸附下降。有机质可促进或抑制磷的吸附,pH是影响竞争吸附的主要因子。磷被吸附后大多固持在表面而难于解吸,往往呈现明显的滞后现象。通常只有拟物理吸附的磷能被解吸,化学吸附的磷因与表面金属离子作用形成双齿配位而极难被淋洗下来。解吸受多种因素的影响,其中解吸剂的类型是主要因子之一。     

不同类型沙地上差巴嘎蒿细根的分布状态

 以生长于流动沙地和固定沙地上,处于植被演替不同阶段的半灌木差巴嘎蒿(Artemisia halodendron)种群为对象,用土钻取样法研究了生长季（2000年）降雨期前后差巴嘎蒿的根系随土壤深度的分布、生长动态及其与根际土壤含水量的动态关系,观察到：1)降雨期前各土层的根际土壤含水量随深度的增加而升高,增加的幅度为流动沙地>固定沙地;降雨期后根际土壤含水量随深度的增加而减少,减少的幅度为固定沙地>流动沙地。2)表土层（0～15 cm）中差巴嘎蒿的主根分布量在流动沙地显著高于固定沙地。3)降雨期前,差巴嘎蒿细根(直径<1 mm)分布比例在两种不同类型沙地上的差异表现为:在土层0～45cm中固定沙地(84.9%)极显著高于流动沙地(61.9%),而在深土层（>45 cm）中流动沙地（38.1%）显著高于固定沙地（22%）;降雨期后,不论是在固定沙地还是流动沙地细根多集中于0～15 cm的表土层中,流动沙地的细根分布比例由降雨期前33%增至降雨期后的78%,固定沙地由降雨期前的49%增至降雨期后的63%。表明流动沙地差巴嘎蒿种群细根的生长比固定沙地活跃,能够在生长季降雨期后迅速调整细根的分布比例,使细根分布适应降雨期后浅层土壤含水量高的特点。固定沙地的细根分布难以迅速适应土壤水分的变化,不利于差巴嘎蒿对水分的吸收,成为种群衰退的一个重要因素。     

胡桃揪、落叶松纯林及其混交林根际土壤有效磷特性的研究

用剥落分离采集胡桃揪（Juglans mandshurica）、落叶松（Larix gmelinii）纯林及其混交林根际与非根际土壤并分析有效P含量特性。结果表明,落叶松纯林根际土有效P含量较非根际土高出55．8％,而胡桃揪纯林根际土有效P含量较其纯林仅高10．1％,表现出落叶松根第泽根际P较强的活化能力。树种混交后,借助落叶松根系的作用使混交林中胡桃揪根际土有效P含量较其纯林高出45．2％,通过P的吸附／解吸及无机P分级等方面,对落叶松根际土壤有效P含量较高的原因进行了分析。     

Fate of polycyclic aromatic hydrocarbons (PAH) in the rhizosphere and mycorrhizosphere of ryegrass

Polycyclic aromatic hydrocarbons (PAH) can be degraded in the rhizosphere but may also interact with vegetation by accumulation in plant tissues or adsorption on root surface. Previous studies have shown that arbuscular mycorrhizal (AM) fungi contribute to the establishment and maintenance of plants in a PAH contaminated soil. We investigated the fate of PAH in the rhizosphere and mycorrhizosphere including biodegradation, uptake and adsorption. Experiments were conducted with ryegrass inoculated or not with Glomus mosseae P2 (BEG 69) and cultivated in pots filled with soil spiked with 5 g kg⁻¹ of anthracene or with 1 g kg⁻¹ of a mixture of 8 PAH in a growth chamber. PAH were extracted from root surfaces, root and shoot tissue and rhizosphere soil and were analysed by GC-MS. In both experiments, 0.006 – 0.11‰ of the initial extractable PAH concentration were adsorbed to roots, 0.003 – 0.16‰ were found in root tissue, 0.001‰ in shoot tissue and 36 – 66% were dissipated, suggesting that the major part of PAH dissipation in rhizosphere soil was due to biodegradation or biotransformation. With mycorrhizal plants, anthracene and PAH were less adsorbed to roots and shoot tissue concentrations were lower than with non mycorrhizal plants, which could contribute to explain the beneficial effect of AM fungi on plant survival in PAH contaminated soils. This revised version was published online in June 2006 with corrections to the Cover Date.     

Soil types with different texture affects development of Rhizoctonia root rot of wheat seedlings

The effect of different soil textures, sandy (97.5% sand, 1.6% silt, 0.9% clay), loamy sand (77% sand, 11% silt, 12% clay) and a sandy clay loam (69% sand, 7% silt, 24% clay), on root rot of wheat caused by Rhizoctonia solani Kühn Anastomosis Group (AG) 8 was studied under glasshouse conditions. The reduction in root and shoot biomass following inoculation with AG-8 was greater in sand than in loamy sand or sandy clay loam. Dry root weight of wheat in the sand, loamy sand and sandy clay loam soils infested with AG-8 was 91%, 55% and 28% less than in control uninfested soils. There was greater moisture retention in the loamy sand and sandy clay loam soils as compared to the sand in the upper 10–20 cm. Root penetration resistance was greater in loamy sand and sandy clay loam than in sand. Root growth in the uninfested soil column was faster in the sand than in the loamy sand and sandy clay loam soils, the roots in the sandy soil being thinner than in the other two soils. Radial spread of the pathogen in these soils in seedling trays was twice as fast in the sand in comparison to the loamy sand which in turn was more than twice that in the sandy clay loam soil. There was no evidence that differences among soils in pathogenicity or soil spread of the pathogen was related to their nutrient status. This behaviour may be related to the severity of the disease in fields with sandy soils as compared to those with loam or clay soils. This revised version was published online in June 2006 with corrections to the Cover Date.     

Post-fire transformation of microbial communities and invertebrate complexes in the pine forest soils,Central Siberia

We studied post-fire transformations in functional characteristics of soil microbial communities and invertebrate complexes in the central-taiga pine forests of Central Siberia. The study revealed that fires of any severity reduce the density and diversity of soil invertebrates and adversely affect the structure and functioning of the sandy podzol microbial complexes. Post-fire recovery of the density and structure of soil invertebrate complexes and the functioning of sandy podzol microbial communities depend on fire duration and severity, as well as dynamics of hydrothermal and trophic properties of the pine forest soils.     

Soil physical strength rather than excess ethylene reduces root elongation of Eucalyptus seedlings in mechanically impeded sandy soils

Seedling establishment in heavily compact soils is hampered by poor root growth caused by soil chemical or physical factors. This study aims to determine the role of ethylene in regulating root elongation through mechanically impeded sandy soils using Eucalyptus todtiana F. Muell seedlings. Concentrations of ethephon (1, 10, and 100???M) were added to non-compact soils, and endogenous ethylene production from seedling roots was compared to ethylene production of roots grown in physically compacted field soils (98.6?% sand). The ethylene-inhibitor 3,5-diiodo-4-hydroxybenzoic acid (DIHB) (0.1???M) was included for each treatment to counteract the negative effects of excess ethylene or compact soils on root elongation. Root elongation was reduced in high ethylene soils by 49?% and high bulk density soils by 44?%. Root ethylene production increased ninefold in roots grown in the high ethylene environment (100???M), but decreased 80?% in compact soils. The use of DIHB did not alter root length and produced varying results with respect to ethylene production, suggesting an interaction effect involving high amounts of soil ethylene. While ethylene regulates root growth, the physical strength of sandy soils is the major factor limiting root elongation in mechanically impeded soils.     

Short rotation coppice as alternative land use for Chernobyl-contaminated areas of Belarus

Field experiments were conducted in the Chernobyl-affected area to assess if short rotation coppice (SRC) for energy production is a feasible alternative for contaminated land. Four willow clones were planted on sandy and peaty soil and the radiocaesium (137Cs) and radiostrontium (90Sr) transfer factors (TF) and yield relevant parameters were recorded during four growing seasons. The 137Cs and 90Sr soil-to-willow wood TF on sandy soil (second growing season) were on average 1.40+/-1.06 x 10(-3) m2 kg(-1) and 130+/-74 x 10(-3) m2 kg(-1), respectively. The 137Cs TF recorded for the peaty soil (fourth growing season or end of the first rotation cycle) was on average 5.17+/-1.59 x 10(-3) m2 kg(-1). The 90Sr-TF was on average 2.61+/-0.44 x 10(-3) m2 kg(-1). No significant differences between clones for the 137Cs and 90Sr-TF were observed. Given the high TFs and the high deposition levels, Belarus exemption levels for fuel wood were highly exceeded. The annual average biomass production for one rotation cycle on the peaty soil ranged from 7.8 to 16.0 t ha(-1) y(-1) for one of the clones, comparable with average annual yield figures obtained for western Europe. On the sandy soils, first-year yields were 0.25 t ha(-1) y(-1). These soils are not suitable for SRC production and should better be dedicated to pine forests or drought-resistant grasses.     

Bioavailability of soil inorganic P in the rhizosphere as affected by root-induced chemical changes: a review

In most soils, inorganic phosphorus occurs at fairly low concentrations in the soil solution whilst a large proportion of it is more or less strongly held by diverse soil minerals. Phosphate ions can indeed be adsorbed onto positively charged minerals such as Fe and Al oxides. Phosphate (P) ions can also form a range of minerals in combination with metals such as Ca, Fe and Al. These adsorption/desorption and precipitation/dissolution equilibria control the concentration of P in the soil solution and, thereby, both its chemical mobility and bioavailability. Apart from the concentration of P ions, the major factors that determine those equilibria as well as the speciation of soil P are (i) the pH, (ii) the concentrations of anions that compete with P ions for ligand exchange reactions and (iii) the concentrations of metals (Ca, Fe and Al) that can coprecipitate with P ions. The chemical conditions of the rhizosphere are known to considerably differ from those of the bulk soil, as a consequence of a range of processes that are induced either directly by the activity of plant roots or by the activity of rhizosphere microflora. The aim of this paper is to give an overview of those chemical processes that are directly induced by plant roots and which can affect the concentration of P in the soil solution and, ultimately, the bioavailability of soil inorganic P to plants. Amongst these, the uptake activity of plant roots should be taken into account in the first place. A second group of activities which is of major concern with respect to P bioavailability are those processes that can affect soil pH, such as proton/bicarbonate release (anion/cation balance) and gaseous (O₂/CO₂) exchanges. Thirdly, the release of root exudates such as organic ligands is another activity of the root that can alter the concentration of P in the soil solution. These various processes and their relative contributions to the changes in the bioavailability of soil inorganic P that can occur in the rhizosphere can considerably vary with (i) plant species, (ii) plant nutritional status and (iii) ambient soil conditions, as will be stressed in this paper. Their possible implications for the understanding and management of P nutrition of plants will be briefly addressed and discussed.