DW In Shoots Research Articles

Plant Factories Are Heating Up: Hunting for the Best Combination of Light Intensity, Air Temperature and Root-Zone Temperature in Lettuce Production.

This study analyzed interactions among photon flux density (PPFD), air temperature, root-zone temperature for growth of lettuce with non-limiting water, nutrient, and CO2 concentration. We measured growth parameters in 48 combinations of a PPFD of 200, 400, and 750 μmol m–2 s–1 (16 h daylength), with air and root-zone temperatures of 20, 24, 28, and 32°C. Lettuce (Lactuca sativa cv. Batavia Othilie) was grown for four cycles (29 days after transplanting). Eight combinations with low root-zone (20 and 24°C), high air temperature (28 and 32°C) and high PPFD (400 and 750 μmol m–2 s–1) resulted in an excessive incidence of tip-burn and were not included in further analysis. Dry mass increased with increasing photon flux to a PPFD of 750 μmol m–2 s–1. The photon conversion efficiency (both dry and fresh weight) decreased with increasing photon flux: 29, 27, and 21 g FW shoot and 1.01, 0.87, and 0.76 g DW shoot per mol incident light at 200, 400, and 750 μmol m–2 s–1, respectively, averaged over all temperature combinations, following a concurrent decrease in specific leaf area (SLA). The highest efficiency was achieved at 200 μmol m–2 s–1, 24°C air temperature and 28°C root-zone temperature: 44 g FW and 1.23 g DW per mol incident light. The effect of air temperature on fresh yield was linked to all leaf expansion processes. SLA, shoot mass allocation and water content of leaves showed the same trend for air temperature with a maximum around 24°C. The effect of root temperature was less prominent with an optimum around 28°C in nearly all conditions. With this combination of temperatures, market size (fresh weight shoot = 250 g) was achieved in 26, 20, and 18 days, at 200, 400, and 750 μmol m–2 s–1, respectively, with a corresponding shoot dry matter content of 2.6, 3.8, and 4.2%. In conclusion, three factors determine the “optimal” PPFD: capital and operational costs of light intensity vs the value of reducing cropping time, and the market value of higher dry matter contents.

Assessment the copper-induced changes in antioxidant defense mechanisms and copper phytoremediation potential of common mullein (Verbascum thapsus L.).

In this research, the Cu phytoremediation capacity of common mullein (Verbascum thapsus L.) was evaluated concerning plant growth, antioxidant enzymes, and photosynthetic activities. Plants were subjected to five Cu concentrations (0, 125, 250, 375, and 500 mg/L) under the hydroponic conditions for 2 weeks. The results showed that at 125 mg/L, root and shoot biomass and chlorophylls remained the same as that of the control and then declined with increasing concentrations of Cu, when compared with control. The carotenoid contents remained unchanged up to 250 mg/L compared with control and then dropped with raising Cu dose. The raising of antioxidant enzymes activity reflected the occurrence of stress due to Cu exposure as manifested by increased MDA and ion leakage level. However, increased antioxidant enzymes may be associated with the tolerance capacity of V. thapsus to protect the plant from oxidative damage. Except for the highest concentration (500 mg/L), Cu accumulation in the roots and shoots all increased significantly with increasing Cu concentration, and the Cu accumulation in shoots was greater than roots. The Cu accumulation reached its maximum level at 375 mg/L Cu concentration, with 492.8 and 447.3 mg/kg DW in shoots and roots, respectively, which is highly greater than the threshold value for a Cu (hyper)accumulator plant. The extraction coefficient (EC) close to 1, and translocation factor (TF) > 1 from 125 to 375 mg/L Cu, suggested that V. thapsus could be used as a viable plant species for Cu phytoextraction.

Screening of Chinese mustard (Brassica juncea L.) cultivars for the phytoremediation of Cd and Zn based on the plant physiological mechanisms

Brassica juncea L. is an attractive species in PTMs contaminated soil remediation ascribing to its high tolerance under stress and great accumulation capacity of metals. To identify the potential Cd/Zn accumulators from numerous different Chinese mustard cultivars for practical phytoremediation is a promising strategy in China. In present work, a pot experiment involving elevated Cd/Zn concentrations was performed among 21 cultivars. Regarding physiological and biochemical indicators under Cd/Zn stress, principal component analysis and cluster analysis were used for cultivar tolerance evaluation and classification. Results showed that BJ (Bao Jie, var. involutus) cultivar was distinguished as a potential phytoremediation candidate comparing with other cultivars. Moreover, BJ accumulated the maximum Cd content of 63.85 and 77.29 mg kg−1 DW in shoots and roots, respectively, and the maximum Zn uptake by BJ were 6693 and 4777 mg kg−1 DW in shoots and roots, respectively. Accordingly, BJ had the highest Cd/Zn tolerance, remarkable accumulation and translocation capacity (accumulation factor (AF) > 1 for Cd and Zn; translocation factor (TF) > 0.8 for Cd and TF > 1 for Zn). In addition, the superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities of the mustard increased initially under low Cd/Zn stress as compared to the control and then declined dramatically with the increasing metals exposure concentration. Therefore, the antioxidant enzymes may play a protective role against reactive oxygen species (ROS) under low Cd/Zn stress, whereas the defense system might be collapsed under relatively high Cd/Zn stress. Furthermore, the enhanced Cd/Zn exposure led to an increase in malondialdehyde (MDA) content in the mustard cultivars, indicating that Cd/Zn had induced more severe oxidative stress and higher degree of lipid peroxidation had occurred. The present investigation results indicated that BJ (Bao Jie, var. involutus), as a native cultivar, can be further applied in the field trials of phytoremediation practices in contaminated soil.

Plant growth regulator interactions in physiological processes for controlling plant regeneration and in vitro development of Tulbaghia simmleri

The endogenous auxin and cytokinin contents of in vitro regenerated Tulbaghia simmleri maintained on applied plant growth regulators in Murashige and Skoog (MS) medium were investigated using UHPLC–MS analysis. The highest number of shoots (27.6 per leaf) were produced in MS medium supplemented with 2.5 μM thidiazuron. A higher number of these shoots were rooted with 10 μM 6-(2-hydroxy-3-methylbenzylamino) purine (PI-55, cytokinin antagonist). Production of somatic embryos (SEs: 16.4–4.6, globular to cotyledonary stages) improved significantly with liquid MS medium containing 2.5 μM picloram, 2.5 μM phloroglucinol (PG) and 1.5 μM gibberellic acid or 1.5 μM PI-55 and 1.0 μM trans-zeatin. SEs (torpedo and cotyledonary stages) germinated (100%) in plant growth regulator free MS medium. The plantlets were acclimatized and all survived in the greenhouse. Higher levels of endogenous auxin, 2-oxindole-3-acetic acid (oxIAA, 371.52 pmol/g DW) and indole-3-acetylaspartate (IAAsp, 141.56 pmol/g DW) were detected in shoots from PG treatments. The roots of garden-grown mother plants possessed the highest level of indole-3-acetic acid (IAA, 630.54 pmol/g DW) and oxIAA (515.26 pmol/g DW). Cytokinins [CKs: trans-zeatin-O-glucoside (tZOG), cis-zeatin (cZ) and N6-isopentenyladenosine-5′-monophosphate (iPRMP)] levels were relatively high in shoots and roots of plantlets in vitro. However, PI-55 treatments influenced the development of plantlets promoting a higher biosynthesis level of iPRMP (418.06 pmol/g DW in root) and cZRMP (904.61 pmol/g DW in roots and 1427.83 pmol/g DW in shoots). The presented protocols offer organogenesis and somatic organogenesis systems for rapid plant regeneration of T. simmleri. In addition, the importance of exogenous and endogenous hormonal effects on in vitro plant growth and development as well as endogenous hormone metabolism signalling and transport related to the physiological processes of CK metabolism and transport are illustrated for in vitro development of T. simmleri.

Effects of Pinching Treatment on Harvest Term and Plant Growth in Processing Tomato

The effects of pinching treatments carried out at the 3- and 6-true-leaf stages on harvest term and plant growth in processing tomato ‘Shuho’ (Solanum lycopersicum L.) were examined. Weekly yields in the 3- and 6-true-leaf pinching treatments were increased compared with those in the untreated control at 1 and 2 wk after the start of harvest, respectively. There were no differences among all treatments in yield, fruit weight, fruit number, or marketable fruit ratio. However, the fruit set ratio in the 3-true-leaf pinching treatment was increased more than those in the other treatments. The flowering periods in the pinching treatment groups were shorter than those of the control. The number of flowers per lateral shoot in the pinching treatment groups was greater than that in the control. DW in the lateral shoots in the 3-true-leaf pinching treatment was significantly greater than that in other treatment groups. The distribution of nitrogen and calcium in the lateral shoots in the 3-true-leaf pinching trea...

Arsenic toxicity in rice (Oryza sativa L.) is influenced by sulfur supply: Impact on the expression of transporters and thiol metabolism

Arsenic (As) is a non-essential element whose entry into rice grains is an issue of public concern. The need, therefore, exists to understand the regulatory mechanisms of As accumulation and distribution patterns in plants. This study analyzed the effect of sulfur (S) supply on As accumulation and distribution in rice (Oryza sativa L. var. IR64) plants. Nine day old seedlings were grown in 0.798mM S (Normal S), 0.2mM S (Low S) and 0.003mM S (Zero S) for 7days and then subjected to AsIII (20μM) exposure for 7–15days. The concentration of As varied significantly in different S treatments with a consistent trend of decrease in As concentration in depleted S supply treatments on both 7days and 15days. Arsenic concentration declined from 726μgg−1 DW to 537μgg−1 DW in roots and from 29μgg−1 DW to 8μgg−1 DW in shoots at 7days, and from 1536μgg−1 DW to 1062 in roots and from 58μgg−1 DW to 16μgg−1 DW in shoots at 15days, when S supply declined from normal to zero. The subcellular distribution of As was also found to vary with alteration in S supply and also differentially in shoot and root. In general, an up-regulation of sulfate transporters of groups 1 and 2 was observed while As transporters (Lsi1 and Lsi2) were down-regulated in response to As exposure to maintain sulfate and to regulate As levels. In spite of S depletion, an increase in cysteine, glutathione (GSH) and phytochelatin (PC) levels was observed upon As exposure. However, some negative impact of S depletion and As could be seen on the growth of plants. The study concluded that even in conditions of decreased S availability, plants continue to rely on thiol metabolism to tackle As levels and its toxicity effectively and altered subcellular distribution of As contributes only partially.

Analysis of Triticum aestivum seedling response to the excess of zinc.

The effects of 50 and 300 mg L−1 Zn2+ (50 Zn and 300 Zn) were investigated in Triticum aestivum (cv. Żura) grown hydroponically for 7 days. Although wheat treated with 50 Zn took up relatively high amount of the metal (8,943 and 1,503 mg kg−1 DW in roots and shoots, respectively), none of the morphological and cytological parameters were changed. After 300 Zn, the metal concentration increased to 32,205 and 5,553 mg kg−1 DW in roots and shoots, respectively. It was connected with the depletion of shoot and root growth, their fresh and dry weight, water content and mitotic index of root meristematic cells. Microelement contents (Cu, Mn and Fe) after 50 Zn were changed only in roots, while 300 Zn disturbed ion balance in whole plants. The most evident ultrastructural alterations of root meristematic cells caused by both tested Zn2+ doses included increased vacuolization, accumulation of granular deposits inside vacuoles and cell wall thickening. The effect of 300 Zn on root cell ultrastructure was greater that of 50 Zn. The majority of mitochondria had condensed matrix and swollen cristae, plastids contained plastoglobuli, nucleoli were ring-shaped, thinned down cytoplasm with lipid droplets and swollen endoplasmic reticulum cisternae appeared. In mesophyll cells, 50 Zn caused slight reorganization of chloroplast thylakoids and formation of condensed mitochondria. Three hundred Zn triggered more extensive, but not degenerative, changes: plasmolysis of some cells; chloroplasts with protrusions, changed thylakoid organisation and often large starch grains; irregular, condensed mitochondria. The results indicate that T. aestivum cv. Żura is relatively tolerant to Zn stress.

Influence of sodium salicylate on rosmarinic acid, carnosol and carnosic acid accumulation by Salvia officinalis L. shoots grown in vitro.

To evaluate sodium salicylate (NaSA) as an elicitor of rosmarinic acid (RA) and phenolic diterpenes, carnosol (C) and carnosic acid (CA) production, in a culture of Salvia officinalis shoots. In sage shoots grown in vitro, 28 polyphenolic compounds (phenolic acids, flavonoids, and phenolic diterpenes) were identified. In shoots treated for 1 week with increasing NaSA concentrations, the content of C increased from 2.3 in control to 5.7 mg g(-1) DW in shoots treated with 500 µM NaSA. In shoots that were recovered on basal medium for 3 weeks, the maximal amount of C (14 mg/g(-1) DW) was with 150 µM NaSA treatment. In treated and recovered shoots, the increase in C was accompanied with a decrease in CA, resulting in 1.9-fold increase in the C/CA ratio. Accumulation of RA was not affected by the NaSA treatment. However, elicitation by NaSA was accompanied with growth retardation. NaSA can improve C production in sage shoot culture, probably by stimulating the conversion of CA to C.

Effects of warming on annual production and nutrient‐use efficiency of aquatic mosses in a high Arctic lake

Summary Primary production in Arctic and Antarctic lakes is typically dominated by benthic photosynthetic organisms. These include aquatic mosses that can be very abundant although they must be able to tolerate extreme seasonal climatic variation in irradiance and temperature. Climate change is expected to cause increased nutrient run‐off and to prolong ice and snow cover on Arctic lakes. Despite the substantial role that aquatic mosses play in Arctic and Antarctic lakes, our study is the first of its kind to study the in situ growth and nutrient‐use efficiency of an Arctic aquatic moss, Drepanocladus trifarius, and how the net production of this species is coupled with a range of climatic factors undergoing change. Here, we verify the use of growth segments as a technique to record historic growth. We then used the method to reconstruct the growth of D. trifarius by comparing in situ measured growth with that determined from growth segments after one year's growth in a high Arctic lake. Finally, we determined nutrient‐use efficiency, resorption efficiency and resorption proficiency by measuring the tissue nutrient content in different annual growth segments. The observed annual mean production of D. trifarius was about 2–3 mg DW shoot−1 year−1 expressed as biomass increase and 10–30 mm shoot−1 year−1 expressed as length increase, while the age of most shoots was 7–10 years. About 90% of the variation in annual net production was explained by between‐year variability in snow prolongation and net radiation in June. The low tissue‐N (1.05%DW) and tissue‐P (0.081%DW) contents found in D. trifarius suggest that its growth in Lake Sommerfuglesø is limited by the availability of N and P during summer when the availability of light is sufficient for extensive growth of this species. P resorption was 43% in D. trifarius, whereas no N resorption was recorded, and P proficiency ranged between 0.02 and 0.04% DW, which is comparable to the concentrations measured in other plant types under P limitation, suggesting that P resorption is an advantageous trait for the existence of moss in this oligotrophic environment. Our results suggest that predicted prolongation of snow cover and consequent decrease in net radiation in lakes will decrease annual net primary production. Our results also suggest that species able to exploit elevated nutrient contents have an advantage in more nutrient‐rich lakes in future and indicate that dominance patterns may change. We therefore foresee that climate change will have dramatic effects on the annual net production of mosses and thus whole lake primary production in Lake Sommerfuglesø and similar lake types dominated by mosses in the high Arctic.

Effect of Inorganic and Organic Germanium Treatments on the Growth of Lettuce (Lactuca sativa)

Germanium (Ge) is a rare heavy metal and is known to toxic to plants at high level. However, there is little evidence about the Ge effect on plant growth. Here, we investigated the effect of inorganic (GeO2) and organic (Ge-132) germanium on lettuce growth by treatment with various concentrations of GeO2 and Ge-132. Under GeO2 treatment, lettuce growth was not much inhibited at 2.5 mg/L concentration and then significantly inhibited at 5 mg/L concentration. However, under Ge-132 treatment, lettuce growth was not much inhibited by concentrations up to 10 mg/L. Relative fresh weight of lettuce at 2.5, 5, 10 and 25 mg/L concentrations was 99, 76, 65 and 35% in GeO2 treatments and was 105, 99, 97 and 75% in Ge-132 treatments, respectively. In GeO2 treatments, Ge was highly accumulated in the roots at concentration below 10 mg/L and in the shoots at concentration above 25 mg/L. However, Ge was primarily accumulated in the roots at all Ge-132 concentrations. Accumulated Ge amounts of plants under GeO2 treatment were 0.72 mg/ g DW in roots and 0.27 mg/ g DW in shoots at a 10 mg/L concentration. At a 50 mg/L concentration of GeO2, the Ge content was 0.77 mg/g DW in roots and 1.58 mg/g DW in shoots, respectively. Based on our results, inorganic germanium is more toxic for lettuce growth than organic germanium. Upper critical toxic levels for lettuce growth were 2.5 to 5 mg/L concentrations in GeO2 treatments and 10 to 25 mg/L concentration in Ge-132 treatments, respectively.

Ultrastructural changes, zinc hyperaccumulation and its relation with antioxidants in two ecotypes of Sedum alfredii Hance.

Zn phytotoxicity and its possible detoxifying responses in two ecotypes of Sedum alfredii Hance, i.e. hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) were investigated. HE grew better with high Zn concentrations of 29.11gkg(-1) DW in shoots when exposed to 500microM Zn2+. Toxicity symptoms caused by Zn in root cells of both ecotypes mainly included plasmolysis, disruption of plasma membranes and increased cell vacuolation. At high supplied Zn concentration, chloroplasts suffered from structural disorganization in both ecotypes. Zn-induced hydrogen peroxide (H2O2) and superoxide radical (O(2)-) productions in leaves were determined by a histochemical method, which revealed that Zn stress may have involved NADPH oxidase, protein phosphatases and intracellular Ca2+ to activate the reactive oxygen species production. Inhibition of glutathione synthesis may have led to increased H2O2 and O(2)- accumulations in leaves of HE. In response to higher Zn concentrations, ascorbic acid significantly increased in both ecotypes and levels of glutathione increased in both leaves and roots of HE and in roots of NHE without any change in the leaves of NHE. The enzymatic activities like those of superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), guaiacol peroxidase (GPX, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and glutathione reductase (GR, EC 1.6.4.2) in leaves of HE were all enhanced at supplied Zn concentration of 500microM, which may account for its better growth.

Effects of chelates on plants and soil microbial community: Comparison of EDTA and EDDS for lead phytoextraction

Most studies on chelate-induced phytoextraction have focused on EDTA-mediated Pb phytoextraction. But EDTA and the formed EDTA–Pb complexes have low biodegradability and high solubility in soil, resulting in an elevated risk of adverse environmental effects. EDDS is an easily biodegradable chelating agent that has recently been proposed as an environmentally sound alternative to EDTA. Consequently, a greenhouse experiment, using a completely randomized factorial design with four replications, was carried out to compare the potential of EDTA and EDDS for chelate-induced Pb phytoextraction with Cynara cardunculus, as well as to investigate the toxicity of these two chelates to both cardoon plants and soil microorganisms. The effects of chelate addition on soil microbial communities were studied through the determination of a variety of biological indicators of soil quality such as soil enzyme activities, basal and substrate-induced respiration, potentially mineralizable nitrogen, and community level physiological profiles. EDTA was much more efficient than EDDS for the enhancement of root Pb uptake and root-to-shoot Pb translocation. In a soil polluted with 5000 mg Pb kg − 1 , as a result of the addition of 1 g EDTA kg − 1 soil, a value of 1332 mg Pb kg − 1 DW shoot was obtained. EDDS application resulted in a shoot Pb accumulation of only 310 mg kg − 1 DW. Plants treated with EDDS showed lower values of biomass than those treated with EDTA. EDDS proved to be rapidly degraded, and less toxic to the soil microbial community in control non-polluted soils. Pb-polluted EDDS-treated soils showed significantly higher values of basal and substrate-induced respiration than those treated with EDTA. Although EDDS had a lower capacity to enhance Pb phytoextraction than EDTA, it has the advantage of rapid biodegradation.

Seasonal variation in morphology, growth and reproduction of Zostera caespitosa on the southern coast of Korea

Seasonal dynamics of Zostera caespitosa Miki were monthly monitored in Jangmok Bay of Geoje Island, Korea by examining morphometrics, reproductive phenology, leaf productivity and environmental factors from July 2001 to July 2002. Shoot size and weight reached to maximum values during summer, but the number of leaves per shoot did not exhibit a clear seasonal pattern. The leaf area was approximately 2-fold greater in summer in during winter, which was mainly due to the increase in shoot length. Flowering shoot appeared in early March, and developed into fruits in early May. By the end of May, all reproductive shoots bore mature fruits. Leaf growth exhibited a seasonal pattern, ranging from 1.5 mg DW shoot −1 d −1 in November to 16.3 mg DW shoot −1 d −1 in June. The leaf plastochrone intervals varied from 12.5 days in May to 37.5 days in November. The mean lifetime of leaves was 99.1 days and the annual leaf turnover was estimated to be 3.7 times per year. This study indicated that the growth and flowering phenology of Z. caespitosa was strongly coupled to seasonal light conditions.

Productivity aspects of three tropical seagrass species in areas of different nutrient levels in Kenya

Previous work conducted in two seagrass areas of different nutrient status, along the Kenyan coast, has shown that the seagrasses were characterised by differences in the species composition and biomass of epiphytic algae. This study was undertaken to evaluate the productivity patterns of the seagrass species growing in these same sites. Studies were made on Thalassodendron ciliatum (Forskål) den Hartog, Thalassia hemprichii (Ehrenberg) Aschers and Cymodocea rotundata Ehrenberg and Hempr. ex Ascherson growing in the lagoons of Nyali and Vipingo, along the Kenyan coast, during the South East (SE) and North East (NE) monsoon periods. The results of this study revealed differences in the levels of nitrate within the water column, with Vipingo having lower levels of around 4 μM during the low tide period of the SE monsoon while nitrate levels in Nyali reached levels of 16 μM during the same period. Of the three seagrass species studied, C. rotundata had the highest shoot densities in both sites. The shoot densities of C. rotundata reached levels of 1300 shoots m −2 compared to an average of 600 shoots m −2 for both T. ciliatum and T. hemprichii. The stems of T. ciliatum were found to be 200 mm long in Nyali whereas those in Vipingo were 80 mm in length. Of the three seagrasses T. ciliatum and T. hemprichii showed significant differences in total leaf growth between the two sites. However, of these two species, only T. hemprichii showed distinct differences in leaf production and biomass when the two sites were compared. Leaves of T. hemprichii showed growth rates of 0.008 g dw shoot −1 day −1 in Nyali while the growth rate in Vipingo was 0.004 g dw shoot −1 day −1. Leaf production rates were approximately 0.005 g dw shoot −1 day −1 for T. ciliatum in both Nyali and Vipingo and that of C. rotundata was approximately 0.0015 g dw shoot −1 day −1 in the two sites. This suggests that of the three species studied, T. hemprichii may have been influenced by the nutrient input in Nyali. The abundance of epiphytes on the stems of T. ciliatum was higher in Nyali during both seasons; therefore we suggest that although the composition of epiphytic species is the main indicator of nutrient enrichment in these areas the enhanced productivity of T. hemprichii may be another indicator of the nutrient status of these study sites.

Morpho-chronological variations and primary production in Posidonia sea grass from Western Australia

The occurrence of morpho-chronological variations was demonstrated in three Australian species of phanerogams, Posidonia australis, Posidonia coriacea and Posidonia sinuosa, which are found living around Rottnest Island (Western Australia). Three chronological parameters were identified: the thickness of dead sheaths, the internodal distance and the regular presence of floral stalk remains. The foliar primary production for these three species, as estimated using the lepidochronology method, is very high since values of 1374, 1811 and 678 mg dw shoot−1 y−1 were recorded, respectively. Rhizome production values range from 70·6 and 376·7 mg dw shoot−1 y−1 for Posidonia coriacea and Posidonia australis respectively. The results obtained are very encouraging and confirm that these morpho-chronological variations are particularly well developed for the genus Posidonia.

Genotypic Differences in Effects of Cadmium Exposure on Plant Growth and Contents of Cadmium and Elements in 14 Cultivars of Bai Cai

Fourteen cultivars of bai cai (Brassica campestris L. ssp. chinensis var. communis) were grown in the nutrient solutions containing 0–0.5 μg mL−1 of cadmium (Cd) to investigate genotypic differences in the effects of Cd exposure on the plant growth and uptake and distribution of Cd in bai cai plants. The Cd exposure significantly reduced the dry and fresh weights of roots and shoots, the dry weight ratio of shoot/root (S/R), total biomass, and chlorophyll content (SPAD value). Cd concentrations in bai cai ranged from 13.3 to 74.9 μg g−1 DW in shoots and from 163.1 to 574.7 μg g−1 DW in roots under Cd exposure, respectively. The considerable genotypic differences of Cd concentrations and accumulations in both shoots and roots were observed among 14 bai cai cultivars. Moreover, Cd mainly accumulated in the roots. Cd also caused the changes of uptake and distribution of nutrients in bai cai and under the influence of cadmium, the concentration of potassium (K) decreased in shoot and increased in root. However, the concentrations of magnesium (Mg), phosphorus (P), manganese (Mn), boron (B), and iron (Fe) increased in shoots and decreased in roots. In addition, Cd exposure resulted in an increase in calcium (Ca), sulphur (S), and zinc (Zn) concentrations in both shoots and roots but had no significant effects on the whole uptake of the examined mineral nutrients except for S.

Genotypic Differences in Effects of Cadmium Exposure on Plant Growth and Contents of Cadmium and Elements in 14 Cultivars of Bai Cai

Abstract Fourteen cultivars of bai cai (Brassica campestris L. ssp. chinensis var. communis) were grown in the nutrient solutions containing 0–0.5 μg mL−1 of cadmium (Cd) to investigate genotypic differences in the effects of Cd exposure on the plant growth and uptake and distribution of Cd in bai cai plants. The Cd exposure significantly reduced the dry and fresh weights of roots and shoots, the dry weight ratio of shoot/root (S/R), total biomass, and chlorophyll content (SPAD value). Cd concentrations in bai cai ranged from 13.3 to 74.9 μg g−1 DW in shoots and from 163.1 to 574.7 μg g−1 DW in roots under Cd exposure, respectively. The considerable genotypic differences of Cd concentrations and accumulations in both shoots and roots were observed among 14 bai cai cultivars. Moreover, Cd mainly accumulated in the roots. Cd also caused the changes of uptake and distribution of nutrients in bai cai and under the influence of cadmium, the concentration of potassium (K) decreased in shoot and increased in root. However, the concentrations of magnesium (Mg), phosphorus (P), manganese (Mn), boron (B), and iron (Fe) increased in shoots and decreased in roots. In addition, Cd exposure resulted in an increase in calcium (Ca), sulphur (S), and zinc (Zn) concentrations in both shoots and roots but had no significant effects on the whole uptake of the examined mineral nutrients except for S.

Carbon and nitrogen translocation between seagrass ramets

The spatial scale and the magnitude of carbon and nitrogen translocation was examined in 5 tropical (Cymodocea serrulata, Halophila stipulacea, Halodule uninervis, Thalassodendron cilia- tum, Thalassia hemprichii) and 3 temperate (Cymodocea nodosa, Posidonia oceanica, Zostera noltii) seagrass species using 13 Carbon ( 13 C) and 15 Nitrogen ( 15 N) as tracers in experiments conducted in situ. Seagrass leaf and rhizome production during the study period varied from <0.001 to 0.015 g DW shoot -1 d -1 and 0.002 to 0.017 g DW rhizome apex -1 d -1 , respectively. Based on measured leaf and rhi- zome growth rates, the demand of resources for leaf production varied from 0.19 to 4.99 mgC shoot -1 d -1 , and from 0.01 to 0.24 mgN shoot -1 d -1 , while the demand for rhizome production varied from 0.62 to 5.57 mgC rhizome apex -1 d -1 and from 0.02 to 0.12 mgN rhizome apex -1 d -1 . Seagrass leaves incor- porated the isotopes at rates ranging from 0.04 to 0.63 µg 13 C g DW -1 h -1 , and <0.01 to 0.35 µg 15 N g DW -1 h -1 . After 4 d, all incubated shoots had shared part of the incorporated 13 C and 15 N with ram- ets placed at maximum distances ranging from 2.7 (H. stipulacea) to 81 cm (C. nodosa), indicating that seagrass clonal integration may be maintained between 1.6 d (H. stipulacea) and 5.4 yr (P. ocean- ica). Resource translocation within seagrass clones was stimulated towards horizontal rhizome apices. Seagrass ramets, in 4 d, shared with their neighbours between 0.37 and 390 µg 13 C and between 0.02 and 178 µg 15 N. During the study period, resource translocation would supply <5% and up to 40% of the leaf carbon and nitrogen required by a neighbouring developing ramet, respec- tively, and <5% and up to 36% of the carbon and nitrogen required for rhizome growth; provided that the incorporated resources over 1 d were mobilised at similar rates over 4 d. These results con- clusively demonstrate physiological integration between seagrass ramets, and that resource translo- cation may be an important mechanism for young seagrass ramets to acquire resources and for sea- grass clones to expand and persist.

Leaf growth response to simulated herbivory: a comparison among seagrass species

We examined in seven seagrass species the response of the leaf growth rate per shoot (mg DW shoot −1 day −1) to a gradient of herbivory simulated by leaf clipping. The clipping procedure was intended to mimic the removal by herbivores which only consume the leaves of a single shoot at every feeding attack and which do not feed over the same shoots selectively (i.e., most poikilotherm vertebrate and invertebrate herbivores). We tested whether (1) this defoliation procedure does not normally depress shoot leaf growth rates (i.e., the occurrence of compensatory leaf growth), and (2) whether leaf nutrient content, relative leaf growth rate, average distance between consecutive short shoots and rhizome diameter influence the response of the leaf growth rate per shoot to a gradient of defoliation. The leaf growth rate per shoot varied among clipping treatments in nine of the 15 populations treated (ANOVA, p<0.05) and meta-analyses techniques revealed a significant overall variation ( χ 2 test, p<0.001) when all the populations were considered in concert. The leaf growth rate per shoot was persistently depressed in all the clipping treatments only in one of the 15 populations treated, with only three more populations showing depressed leaf growth under some treatments (Tukey HSD test, p<0.05). The response of the leaf growth rate to clipping intensity, which was analysed on a per shoot basis (i.e. relationship between the leaf growth rate per shoot and clipping intensity on the shoot) was significant only for four populations, although meta-analyses revealed a tendency towards a general significance. None of the seagrass properties considered was related to the response of leaf growth to clipping intensity. Our results stress the remarkable variability seagrass leaf growth may exhibit under single events of defoliation on scattered shoots. Furthermore, because leaf growth rates are rarely depressed, these results suggest that most poikilotherm vertebrate and invertebrate herbivores, which typically remove <30% of leaf production, have a modest impact on the depression of leaf growth rates through removal of photosynthetic tissue.

Herbivory on the seagrass Cymodocea nodosa (Ucria) Ascherson in contrasting Spanish Mediterranean habitats

We assess the magnitude and variability of herbivory (i.e. leaf consumption and sloughing caused by herbivore bites) on the seagrass Cymodocea nodosa along the Spanish Mediterranean coast and test the hypothesis that this is higher in meadows growing in sheltered bays than in exposed, open zones. Total leaf loss by herbivores varied by about three orders of magnitude along the Spanish Mediterranean coast, from < 1 to 130 mg DW shoot −1 yr −1. These differences were paralleled by a great variation in the fraction of leaf production lost by herbivores, which ranged from < 1 to about 50%. Most (75%) of the populations, however, supported modest losses of leaf production (< 10%). A significant fraction (30%) of the variance in herbivory was explained by meadow exposure, the meadows growing in sheltered bays suffering about five times the losses encountered in open sites. These results suggest that the trophic importance of C. nodosa as a food resource for herbivores, and the role of herbivores on the control of the seagrass production, increases notably from exposed to sheltered meadows in the Spanish Mediterranean and point to the importance of considering the degree of exposure when addressing herbivory on other seagrass species.