Changed Clonal Growth Form Induced by Sand Burial Facilitates the Acclimation of Carex brevicuspis to Competition

Both competition and burial are important factors that influence plant growth and structuring plant communities. Competition intensity may decline with increased burial stress. However, experimental evidence is scarce. The aim of this study was to elucidate the role of burial stress in influencing plant competition by investigating biomass accumulation, biomass allocation, and clonal growth performance of Carex brevicuspis, one of the dominant species in the Dongting Lake wetland in China. The experiment was conducted with two typical wetland species, C. brevicuspis (target plant) and Polygonum hydropiper (neighbor plant), in a target-neighbor design containing three densities (0, 199, and 398 neighbor plants m-2) and two burial depths (0 and 12 cm). The biomass accumulation of C. brevicuspis decreased with increment of P. hydropiper density in the 0 cm burial treatment. However, in the 12 cm burial treatment, biomass accumulation of C. brevicuspis did not change under medium and high P. hydropiper densities. The relative neighbor effect index (RNE) increased with enhancement of P. hydropiper density but decreased with increasing burial depth. The shoot mass fraction decreased with P. hydropiper density in the 12 cm burial treatments, but the root mass fraction was only affected by burial depth. However, the rhizome mass fraction increased with both P. hydropiper density and burial depth. The number of ramets decreased with increasing P. hydropiper density. With increasing burial depth and density, the proportion of spreading ramets increased from 34.23% to 80.44%, whereas that of clumping ramets decreased from 65.77% to 19.56%. Moreover, increased P. hydropiper density and burial depth led to greater spacer length. These data indicate that the competitive effect of P. hydropiper on C. brevicuspis was reduced by sand burial, which was reflected by different patterns of biomass accumulation and RNE at the two burial depth treatments. A change from a phalanx to a guerrilla growth form and spacer elongation induced by sand burial helped C. brevicuspis to acclimate to competition.     

Nuclear DNA content variation of three Miscanthus species in China

In order to estimate the variation in nuclear genome size in Miscanthus, flow cytometry of nuclei stained by propidium iodide was carried out using 36 populations of three Miscanthus species: M. lutarioriparius, M. sacchariflorus and M. sinensis, which were sampled from cold northern to warm and humid southern and central China, as well as near the sea level in eastern China to mountains in western China. The DNA content of diploid was 4.37 ± 0.02 pg/2C in M. lutarioriparius, 4.37 ± 0.01 pg/2C in M. sacchariflorus, and 5.37 ± 0.03 pg/2C in M. sinensis, respectively. There was no intraspecific variation in the three Miscanthus species at the diploid level, suggesting that the genome size was stable within species and the diverse environments did not induce variation in genome size at the diploid level. However, tetraploid populations were found in M. lutarioriparius and M. sacchariflorus, and their genome sizes were 8.56 and 8.54 pg, respectively, which are lower than expected values (8.74 pg), indicating the genome downsizing after polyploidization in the genus. Our results showed that the plant height of M. lutarioriparius was the highest one among the three species and the species was more closely related to M. sacchariflorus than M. sinensis. The intra-species genomic variation and inter-species differentiation in Miscanthus species provide important genetic and genomic information for the development of Miscanthus, especially for the endemic species, M. lutarioriparius, (together with Miscanthus × giganteus) which are now emerging as a key bio-energy crop because of their high yields and strong adaptability.     

Growth responses and non-structural carbohydrates in three wetland macrophyte species following submergence and de-submergence

We investigated the responses of growth and non-structural carbohydrates to submergence and de-submergence in three wetland macrophyte species. Survival rate, recovery ability, and soluble sugar and starch contents of flood-tolerant Polygonum hydropiper and of flood-sensitive Phalaris arundinacea and Carex argyi from Dongting Lake wetlands were investigated after 20, 40, and 60 days of complete submergence without light and 10 days after de-submergence. Plant dry weight and soluble sugar and starch contents decreased in all species during the submergence period. The decreases were slowest in P. hydropiper, intermediate in C. argyi, and most rapid in P. arundinacea. After 60 days of submergence, survival rates were 100, 50, and 0 % in P. hydropiper, C. argyi, and P. arundinacea, respectively. After recovery, plant dry weight increased in P. hydropiper and in C. argyi, but decreased in P. arundinacea. Compared to pre-submergence, soluble sugar contents generally increased and then remained relatively constant after recovery in all species, while starch content increased in P. hydropiper and decreased in P. arundinacea with increasing submergence time. For C. argyi, starch content decreased after recovery from the 20-day submergence, but increased after recovery from the 40- and 60-day submergences. These data illustrate mechanisms behind the flood tolerance of P. hydropiper and the sensitivity to flooding in P. arundinacea and C. argyi. These mechanisms include lower consumption and quicker accumulation of non-structural carbohydrates in flood-tolerant plants.     

Expression analysis of dehydrin multigene family across tolerant and susceptible barley (Hordeum vulgare L.) genotypes in response to terminal drought stress

Dehydrins are one of the characteristic families of plant proteins that usually accumulate in response to drought. In the present study, gene expressions of dehydrin multigene family (13 genes) were examined in flag leaves of tolerant (Yousef) and susceptible (Moroco) barley varieties under terminal drought to characterize the involvement of dehydrins in the adaptive processes. The stomatal conductance, RWC, and Chl a, b contents had more reduction in Moroco than the Yousef which has more elevated osmotic adjustment. Drought stress increased significantly MDA and electrolyte leakage levels, but greater in Moroco, indicating a poor protection of cell and cytoplasmic membrane in this variety. Yousef variety had no reduction in grain yield under drought condition. Five genes (Dhn1, Dhn3, Dhn5, Dhn7 and Dhn9) were exclusively induced in Yousef under drought stress. In the stress condition, relative gene expression of Dhn3, Dhn9 had the direct correlations (P < 0.05) with Chl a, b contents, osmotic adjustment, stomatal conductance, plant biomass and grain yield, and the negative correlations (P < 0.05) with MDA and electrolyte leakage levels. The results supported the impending functional roles of dehydrin K_n and particularly Y_nSK_n types in dehydration tolerance of barley during the reproductive stage.     

Plant regeneration from the embryogenic calli of five major Miscanthus species, the non-food biomass crops

With the growing shortage of oil, coal, and other traditional fossil fuels, scientists in various fields have been looking for new fuel sources to solve the energy crisis. The genus Miscanthus is an ideal biofuel crop due to its rapid vegetative growth and its potential for high biomass yields. Plant regeneration through somatic embryogenesis is a viable method to achieve large-scale production of plant biomass. Callus induction from immature inflorescences of five Miscanthus species was performed on two different media, and the relative rates of callus proliferation were calculated. The highest multiplication coefficient, 3.92, was obtained with M. sacchariflorus ssp. lutarioriparius when the concentration of 2,4-dichlorophenoxyacetic acid (2,4-D) in the medium was 4.0 mg/L, and this species also performed the best at the induction phase. The proliferation coefficient for M. floridulus increased to 3.19 when the concentration of 2,4-D was decreased from 4.0 to 2.0 mg/L. When the concentration of 2,4-D was 2.0 mg/L, the proliferation coefficient for M. sinensis was 2.47. In M. sacchariflorus, the proliferation coefficients were 2.89 and 2.49 for the lower and higher concentrations of 2,4-D, respectively. The multiplication coefficient of M. x giganteus was 2.60 on medium containing 4.0 mg/L 2,4-D. Three different regeneration media were tested to induce shoots in vitro. M. floridulus and M. sacchariflorus regenerated shoots at 100% frequency in three different regeneration media. The regeneration rate for M. sacchariflorus ssp. lutarioriparius reached 99.0% on medium containing 4.0 mg/L?N ⁶ -Benzylaminopurine (6-BA) and 0.1 mg/L α-Naphthaleneacetic acid (NAA). The best regeneration rate of M. sinensis was 35.2% using 2.0 mg/L 6-BA and 0.3 mg/L NAA, whereas the regeneration rate of M. x giganteus was 57.4% on medium supplemented with 3.0 mg/L 6-BA and 0.2 mg/L NAA. The in vitro-derived plantlets of all five species had 100% rooting rates on basal MS medium without supplementation. The survival rates of plantlets were above 90% for each species when subsequently grown outdoors.     

Shoot organogenesis in three Miscanthus species and evaluation for genetic uniformity using AFLP analysis

A simple, efficient protocol for direct in vitro shoot organogenesis and regeneration was established for three species of Miscanthus including two clones of Miscanthus x giganteus, one clone of M. sinensis and one clone of M. sacchariflorus. Shoots were induced from the axillary nodes of both M. x giganteus and M. sacchariflorus and from apical meristems of both M. sinensis and M. sacchariflorus. A tillering method was used to accelerate shoot proliferation. Shoots were rooted in a wet perlite substrate in pots in the greenhouse. Subsequently, rooted plants were transferred to the field. The genetic uniformity of regenerated plants was evaluated using amplified fragment length polymorphism analysis and compared to that of rhizome-propagated plants. A total of 33,443 fragments were generated, representing 869 markers. There were 21 fragments (0.06 % of the fragments) or 19 markers (2.19 % of the markers) that were polymorphic, and almost all of these were singletons. The three species showed similar polymorphisms. Genetic variability was also found in the rhizome-propagated plants, sometimes at a higher rate than in the in vitro culture, indicating that the genetic uniformity was not altered by the protocol. This protocol may help breeders produce new clones of Miscanthus in the future.     

Heavy metal-induced oxidative damage is reduced by β-estradiol application in lentil seedlings

The protective effect of β-estradiol (E) application against heavy metal (HM) toxicity in lentil (Lens culinaris) seedlings was investigated. Seeds were treated with distilled water (control) or aqueous solutions of 100 μM CdCl₂, 200 μM CuCl₂ and 1 μM E singly or in combinations (1 μM E+100 μM CdCl₂ and 1 μM E+200 μM CuCl₂). HM treatments resulted in increase in the activities of antioxidative enzymes, including superoxide dismutase (SOD), catalase (CAT), guaicol peroxidase and ascorbate peroxidase. In a similar manner, Cd and Cu affected significantly oxidative injury indicators measured as electrolyte leakage (electrical conductivity of germination medium), lipoxygenase (LOX) activity and contents of malondialdehyde (MDA; lipoperoxidation marker), carbonyl groups (protein oxidation marker) and hydrogen peroxide (a reactive oxygen species). However, E was effective in reducing HM-induced toxicity. The steroid (1) alleviated HM-induced increase in the electrolyte leakage, LOX activity and contents of MDA, carbonyl and H₂O₂ and (2) improved the activities of SOD and CAT, but not the peroxidase ones, as compared to treatments with HM singly. In addition, E application prevented HM-induced decrease in dry weight production, but did not reduce the accumulation of Cd and Cu in tissues. Results of the present study suggest that E is able to protect lentil from HM-induced oxidative damage most likely by avoidance of H₂O₂ generation and improving antioxidative enzyme activities and, thereby, decreasing oxidative stress injury, but not by reducing Cd and Cu uptake.     

Responses of antioxidant defenses and membrane damage to drought stress in fruit bodies of Auricularia auricula-judae

Fruit bodies of Auricularia auricula-judae are often subjected to drought stress and became dormant. The responses of antioxidant defenses and membrane damage to drought stress were investigated in this study. Picked fruit bodies were exposed to sunlight and dehydrated naturally and samples were collected at different levels of water loss (0, 10, 30, 50, and 70 %) for determination of electrolyte leakage (EL); contents of malondialdehyde (MDA), ascorbic acid (AsA) and reduced glutathione (GSH); and activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). Results showed that membrane permeability (assessed by EL) and membrane lipid peroxidation (MDA content) remained unchanged at all levels of water loss studied. Contents of AsA and GSH showed no change at 0, 10 and 30 % of water loss, however, both of them increased significantly at 50 and 70 % of water loss. SOD activity significantly increased with the rising of water loss from 0 to 30 %, reached the peak at 30 and 50 % of water loss, and then significantly decreased at 70 % of water loss. A gradual increase in POD and CAT activities was observed when water loss rose from 0 to 50 %. As water loss went up to 70 %, POD activity remained the same as that at 50 %, but CAT activity decreased. The results indicate that the increased activities of enzymatic antioxidants (SOD, CAT and POD) and contents of non-enzymatic antioxidants (AsA and GSH) in fruit bodies of A. auricula-judae can effectively scavenge reactive oxygen species, cause no damage to cell membranes as demonstrated by the unchanged EL and MDA content, and contribute to dormancy under drought stress.     

Molecular evidence for a natural diploid hybrid between <Emphasis Type="Italic">Miscanthus</Emphasis><Emphasis Type="Italic">sinensis</Emphasis> (Poaceae) and <Emphasis Type="Italic">M. sacchariflorus</Emphasis>

The hybrid origin of Miscanthus purpurascens has previously been proposed, primarily because of its intermediate morphology. In this study, phylogenies based on the DNA sequences from the internal transcribed spacer region of nuclear ribosomal DNA (nrDNA ITS), on the DNA sequences of the trnL intron and trnL-F intergenic spacer of chloroplast DNA, and on amplified fragment length polymorphism (AFLP) fingerprinting confirm that M. purpurascens originated through homoploid hybridization between M. sinensis and M. sacchariflorus. Two different types of ITS sequences were identified from almost all plants of M. purpurascens. One type was found to be closely related to M. sinensis and the other to M. sacchariflorus. Miscanthus purpurascens was found to possess many M. sinensis- and M. sacchariflorus-specific AFLP bands but no band specific to itself. Clustering with the Unweighted Pair Group Method with Arithmetic Mean and principal coordinate analysis based on the AFLP data also demonstrated that M. purpurascens is an approximate intermediate of the two species. In addition, M. purpurascens has the plastid genome of M. sinensis or M. sacchariflorus, suggesting that either species could be its maternal parent. All specimens of M. purpurascens and its coexisting parental species are identified as diploids (2n = 2x = 38). Possible mechanisms of natural hybridization, hybrid status, chloroplast DNA recombination, and evolutionary implications of this hybridization are also discussed.     

Effect of Coronatine on Antioxidant Enzyme Response of Chickpea Roots to Combination of PEG-Induced Osmotic Stress and Heat Stress

Abiotic stresses, such as high temperature and drought, are major limiting factors of crop production and growth. Coronatine (COR), a structural and functional analog of jasmonates, is suggested to have a role in abiotic stress tolerance. The aim of our study was to examine whether pretreatment with COR enhances the tolerance of chickpea (Cicer arietinum L. cv ICC 4958) roots to PEG-induced osmotic stress, heat stress, and their combination. Therefore, seedlings raised hydroponically in a growth chamber for 15 days were pretreated with or without COR at 0.01 μM for 24 h and then exposed to 6 % PEG 6000-induced osmotic stress or heat (starting at 35 °C and then gradually increased 1 °C every 15 min and kept at 44 °C for 1 h) stress for 3 days. After different treatment periods, the changes in relative growth rate (RGR); malondialdehyde (MDA), proline (Pro), and hydrogen peroxide (H₂O₂) contents; and the activities of antioxidant enzymes/isoenzymes in roots of chickpea seedlings with or without 0.01 μM COR application were studied. RGR in roots was increased by COR application. Under all stress conditions, H₂O₂, MDA, and Pro levels increased sharply, but pretreatment with COR significantly reduced them. Moreover, COR increased the activities of H₂O₂ scavenger enzymes such as catalase (CAT) under heat stress, ascorbate peroxidase (POX) under PEG stress, and CAT and POX under combined stresses. Therefore, COR might alleviate adverse effects of PEG stress and heat stress and combined stresses on roots of chickpea by reduction of H₂O₂ production, enhancing or keeping the existent activity of antioxidant enzymes, thereby preventing membrane peroxidation.     

Morphological responses to different flooding regimes in Carex brevicuspis

Water regime can be described by the depth, duration, frequency, and timing and predictability of flooded and dry phases. Despite growing recognition of the importance of water regimes in the regulation of plant growth and distribution, which components of water regimes that determine plant growth are not well known. To identify the causative components, 72 ramets of Carex brevicuspis were grown under six different water regime treatments (treatment A: constant 0 cm water level; treatment B: constant 30 cm water level; treatment C: 0 cm water level to 30 cm water level for 30 days, repeated 2 times; treatment D: 30 cm water level to 0 cm water level for 30 days, repeated 2 times; treatment E: 0 cm water level to 30 cm water level for 5 days, repeated 12 times; and treatment F: 30 cm water level to 0 cm water level for 5 days, repeated 12 times). Biomass accumulation, below:above ground biomass ratio, number of ramets, and proportions of spreading and clumping ramet were assessed. Biomass accumulation decreased only in relation to length of flooding. The highest biomass accumulation occurred in the 120‐day + 0 cm water level treatment, it was intermediate in the four 60 day + 30 cm water level treatments, and lowest in the 120 day + 30 cm water level treatment. Likewise, the below:above ground ratio decreased only with increasing length of flooding. Ramet number was highest in the 120 day + 0 cm water level treatment, intermediate in the four 60 day + 30 cm water level treatments, and lowest in the 120 day + 30 cm water level treatment. The proportion of spreading ramets increased from 28.0% in the 120 day + 0 cm water level treatment to 76.4% in the 120 day + 30 cm water level treatment. These data suggest that the growth of C. brevicuspis was only limited by the duration of flooding. Reduction of the below:above ground ratio and change from phalanx to guerrilla growth form are effective strategies for C. brevicuspis to acclimate to flooding stress, because they allow the plant to grow above the water surface and escape from anoxic conditions. Our study provides experimental information on the role of different components of water regimes in regulating plant growth, and may assist in protection and restoration of the C. brevicuspis community.     

Response of three arid zone floodplain plant species to inundation

For species to persist on floodplains and in temporary wetlands in arid climates, where large and unpredictable water level fluctuations are common, at least one life history stage must be able to survive inundation. We investigated the survival and performance (RGR, total biomass and above-to-belowground biomass (A:B)) of three common and often coexisting arid zone floodplain species: Xanthium strumarium, Cyperus gymnocaulos and Ludwigia peploides. Observations suggested the species had different responses to inundation, which was tested in a controlled pond experiment. Plants were held at three elevations (+ 10 cm, ? 20 and ? 70 cm) and subjected to three hydrological regimes (static 90 cm, 1 and 5 cm day^?1 inundation) for 16 weeks. Xanthium strumarium died when completely inundated for longer than 4 weeks but when partially flooded survived, showed lower growth rates, increased A:B and produced adventitious roots. C. gymnocaulos showed reduced growth rates when partially flooded and senesced to rhizomes when completely inundated for longer than 4 weeks, which re-sprouted after inundation pressure was removed. L. peploides responded positively to flooding with increased A:B and the production of adventitious roots. The species exhibited three contrasting responses to inundation, which do not necessarily fit neatly within existing water regime functional classification frameworks.     

Morphological responses of two plant species from different elevations in the Dongting Lake wetlands,China, to variation in water levels

The vegetation of wetlands show strong zonation patterns, but the mechanisms determining these patterns are not fully understood. In the present study, growth and morphological responses to a water level gradient (–20 cm (i.e. water level 20 cm below soil surface), –10 cm, 0 cm, 10 cm, 20 cm) were compared between a higher elevation plant (Imperata cylindrica) and a lower elevation plant (Carex brevicuspis) in the Dongting Lake wetlands of China. For both species, the aboveground, belowground, and total biomass were greater at –10 cm than at any other water level.. However, when the water level increased from –10 cm to 0 cm, there was a greater decrease in the biomass of I. cylindrica than in that of C. brevicuspis. Plant height, tiller number, leaf length, leaf width and leaf area showed greater variation along the water level gradient in I. cylindrica than in C. brevicuspis. Generally, with increasing water level, root length, rhizome number, and adventitious root biomass and number all decreased in I. cylindrica. However, in C. brevicuspis, neither the rhizome number nor the primary adventitious root biomass differed significantly among the five water levels. These results indicate that I. cylindrica have a lower tolerance for flooding and higher water sensitivity than C. brevicuspis and these differences may explain why I. cylindrica is found at relatively higher elevations that are not prone to flooding, while C. brevicuspis is found at comparatively lower elevations in the Dongting Lake wetlands.     

Physiological and Biochemical Responses Reveal the Drought Tolerance Efficacy of the Halophyte Salicornia brachiata

The drought tolerance of Salicornia brachiata seedlings was assessed by monitoring growth, nutrient uptake, electrolyte leakage, lipid peroxidation, and biochemical responses under drought conditions simulated with 0, 10, 20, and 30 % polyethylene glycol (PEG 6000). After 7 days of drought induction, plants were harvested for measurement of various parameters. The biomass decreased and the plant height remained unchanged with PEG treatment. The total plant water content (TWC%) decreased by 11 % at the highest concentration of PEG (30 %). The electrolyte leakage and lipid peroxidation of shoots increased by 17 and 5 %, respectively, in 30 % PEG-treated plants. K⁺ and Ca²⁺ contents of shoots increased in a dose-dependent manner. However, in roots K⁺ content decreased and Ca²⁺ content remained unaffected by PEG treatment. Mg²⁺ content increased at high concentrations of PEG (20–30 %) in shoots and decreased at the highest concentration of PEG (30 %) in roots. Total free amino acids, proline, and polyphenol contents increased progressively with increase in severity of the drought stress. Total sugar content and reducing sugar content increased in 10 and 20 % PEG-treated plants and decreased in 30 % PEG-treated plants. Our results suggest that proline and other free amino acids, sugars, and polyphenols are the main compatible solutes in S. brachiata for maintenance of osmotic balance, protection of cellular macromolecules, detoxification of the cells, and scavenging of free radicals under drought stress. A greater accumulation of compatible solutes also facilitates the maintenance of nutrient uptake and adequate tissue water status and protection of membranes under drought conditions in S. brachiata. The results from the present study suggest that S. brachiata can be used for restoration of arid and semiarid lands of coastal ecosystems.     

Relative growth rate,biomass partitioning and nutrient allocation in seedlings of two threatened trees grown under different light conditions

The present study investigates the variation in the relative growth, biomass and nutrient allocation in two threatened tree species viz. Magnolia punduana Hook.f. & Th. and Elaeocarpus prunifolius Wall. ex Müll. Berol. grown under three different levels of irradiance. The irradiance ranged between 1 and 12 mol m^?2 d^?1. Results showed that the highest relative growth rate (RGR) was achieved under the intermediate light treatment for both the species (mean: 0.005 mg mg^?1 d^?1). The growth response coefficient (GRC) model revealed that net assimilation rate (NAR) was the factor driving the RGR in both species. A significant positive correlation was found between NAR and RGR (R² = 0.33, p = 0.000) whereas specific leaf area (SLA) and leaf mass fraction (LMF) was negatively correlated to RGR. Overall, multiple regression of the studied species based on the independent variables viz. NAR, SLA, and LMF showed a significant relation with RGR (F(3,50,53 = 13.001, p = 0.000, R² = 0.43). The biomass distribution in the studied species is in agreement with the “balanced-growth hypothesis” where high irradiance increased allocation to below ground biomass fraction and decreased irradiance increased allocation to the above ground fraction. The highest nitrogen concentration in leaves was observed under the intermediate light treatment. Overall seedlings growth under intermediate light had a higher mean RGR indicating the species' preference for partial light conditions. Long-term experiments under varied light conditions as in the present study would provide useful insight into plant growth strategies in varied environmental conditions.     

Involvement of Carbohydrates in Response to Preconditioning Flooding in Two Clones of <Emphasis Type="Italic">Populus deltoides</Emphasis> Marsh. × <Emphasis Type="Italic">P.</Emphasis> <Emphasis Type="Italic">nigra</Emphasis> L.

Poplar, a fast-growing species widely used outside its original area of distribution, was evaluated in the present study to verify its tolerance and hardening to waterlogging in anticipation of its implementation in rehabilitation practices for marginal lands subjected to flooding. Three water regimes were applied to the plants, grown in pots, with two clones (I-488 and D-64) with different sensitivities to flooding. These plants included a lot consisting of control plants (C), which were irrigated with good drainage, a non-preconditioned lot (NPr), and a third lot that was preconditioned to flooding (Pr). Furthermore, flooding was imposed on NPr and Pr plants by submerging pots up to 5 cm above the collar for 60 days followed by a 40-day recovery period. At the end of these two periods, shoot dry mass, foliar concentrations of certain ions, soluble sugars, starch and proline, and the relative electrolyte leakage were evaluated. The preconditioning treatment conferred different degrees of hardness on the treated plants compared with NPr plants. Our results revealed that high carbohydrate availability (soluble sugars and starch) is suggested to participate in sustaining membrane integrity which may affect the recuperative potential of Pr plants, notably those of clone I-488, from flooding damage.     

Reciprocal grafting between clones with contrasting drought tolerance suggests a key role of abscisic acid in coffee acclimation to drought stress

The role of abscisic acid (ABA) in drought tolerance of Coffea canephora is unknown. To determine whether ABA is associated with drought tolerance and if the use of tolerant rootstocks could increase ABA and drought tolerance, we performed reciprocal grafting experiments between clones with contrasting tolerance to drought (clone 109, sensitive; and clone 120, tolerant). Plants were grown in large (120 L) pots in a greenhouse and subjected to drought stress by withholding irrigation. The non-grafted 120 plants and graft treatments with 120 as a rootstock showed a slower reduction of predawn leaf water potential (Ψ_pd) and a lower negative carbon isotopic composition ratio compared with the other grafting combinations in response to drought. The same 120 graft treatments also showed higher leaf ABA concentrations, lower levels of electrolyte leakage, and lower activities of ascorbate peroxidase and catalase under moderate (Ψ_pd?=???1.0 or ??1.5 MPa) and severe (Ψ_pd?=???3.0 MPa) drought. Root ABA concentrations were higher in plants with the 120 rootstocks regardless of watering regime. The 120 shoots could also contribute to drought tolerance because treatment with 120/109 rootstock/scion combination showed postponed dehydration, higher leaf ABA concentration, and lower leaf electrolyte leakage compared with the sensitive clone. We conclude that both the shoot and root systems of the tolerant clone can increase the concentrations of ABA in leaves in response to drought. This further suggests that ABA is associated with a delayed onset of severe water deficit and decreased oxidative damage in C. canephora.     

Miscanthus sacchariflorus – biofuel parent or new weed?

The perennial grass triploid Miscanthus × giganteus is a promising renewable bioenergy feedstock in the United States and Europe. Originating from eastern Asia, this species is a sterile hybrid cross between M. sinensis and M. sacchariflorus. While research has begun to examine the impacts of M. sinensis and triploid M. × giganteus on the landscape, M. sacchariflorus has been largely overlooked in the peer‐reviewed literature. This review article discusses the origin, uses, distribution, and invasive potential of M. sacchariflorus. M. sacchariflorus is capable of producing high yields (10.7 t DM ha^?1 yr^?1), generally does not reproduce by seed, and can be challenging to establish due to poor cold tolerance, likely due to the limited germplasm used in evaluations. However, M. sacchariflorus has abundant and aggressively spreading rhizomes, which underscores its invasive risk. In the United States, it is listed as escaped from cultivation in at least eight states, primarily in the Midwest, although it is likely that not all populations have been reported. As such, it is essential to generate a comprehensive dataset of all known M. sacchariflorus populations and monitor any continued spread of this species.     

Determinants of change in subtropical tree diameter growth with ontogenetic stage

We evaluated the degree to which relative growth rate (RGR) of saplings and large trees is related to seven functional traits that describe physiological behavior and soil environmental factors related to topography and fertility for 57 subtropical tree species in Dinghushan, China. The mean values of functional traits and soil environmental factors for each species that were related to RGR varied with ontogenetic stage. Sapling RGR showed greater relationships with functional traits than large-tree RGR, whereas large-tree RGR was more associated with soil environment than was sapling RGR. The strongest single predictors of RGR were wood density for saplings and slope aspect for large trees. The stepwise regression model for large trees accounted for a larger proportion of variability (R ² = 0.95) in RGR than the model for saplings (R ² = 0.55). Functional diversity analysis revealed that the process of habitat filtering likely contributes to the substantial changes in regulation of RGR as communities transition from saplings to large trees.