Influence of zinc and manganese enrichments on growth, biosorption and photosynthetic efficiency of Chlorella sp

Treating biosolids from industrial, urban, and agricultural plants produces high amounts of water. After organic pollutants and non-essential heavy metals have been removed, these wastewaters are still rich in trace elements such as zinc (Zn), copper, or manganese (Mn) and have high conductivity and extremely variable pH. In this study, an isolated Chlorella sp. strain was grown for 21 days in nutrient solutions enriched with known amounts of Zn or Mn to obtain concentrations three (4.0 mg L−1)- and six (1.0 mg L−1)-fold higher than the basal medium levels, respectively, and over the limits permitted in aquatic environments. The green alga exhibited high tolerance to Zn and Mn, with the maximum abatement of Zn (28–30%) and Mn (60–63.5%) after 14 and 7 days of culture, respectively. Mn stimulated the growth rate and biomass production of Chlorella, which showed the highest carbon levels just in the first week. In both treatments, the nitrogen and protein contents remarkably increased. The photosynthetic pigments increased until the 14th day, with a higher extent in the Zn-enriched solution. An increasing photochemical efficiency was observed after 7 days of treatment, when the microalgae grown in Zn- and Mn-enriched solutions showed a slightly higher maximum photochemical efficiency than control. The autotrophic and controlled growth system adopted was designed to monitor the dynamic balance of Zn and Mn contents in the solutions and in the algal biomass. This system has proved to be useful in identifying the optimal nutritional conditions of the microalgae, along with the optimal temporal patterns of both metal biosorption capacity for water remediation and element bioaccumulation in the algal biomass

Phloem sap and leaf δ13C, carbohydrates, and amino acid concentrations in Eucalyptus globulus change systematically according to flooding and water deficit treatment

Phloem is a central conduit for the distribution of photoassimilate, nutrients, and signals among plant organs. A revised technique was used to collect phloem sap from small woody plants in order to assess changes in composition induced by water deficit and flooding. Bled phloem sap δ13C and sugar concentrations were compared to δ13C of bulk material, soluble carbon extracts, and the neutral sugar fraction from leaves. Amino acid composition and inorganic ions of the phloem sap was also analysed. Quantitative, systematic changes were detected in phloem sap composition and δ13C in response to altered water availability. Phloem sap δ13C was more sensitive to changes of water availability than the δ13C of bulk leaf, the soluble carbon fraction, and the neutral soluble fraction of leaves. Changes in water availability also resulted in significant changes in phloem sugar (sucrose and raffinose), inorganic nutrient (potassium), and amino acid (phenylalanine) concentrations with important implications for the maintenance of phloem function and biomass partitioning. The differences in carbohydrate and amino acid composition as well as the δ13C in the phloem, along with a new model system for phloem research, offer an improved understanding of the phloem-mediated signal, nutrient, and photoassimilate transduction in relation to water availability

Variability in the carbon isotopic composition of foliage carbon pools (soluble carbohydrates, waxes) and respiration fluxes in southeastern U.S. pine forests

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): G02009, doi:10.1029/2011JG001867.We measured the δ13C of assimilated carbon (foliage organic matter (δCOM), soluble carbohydrates (δCSC), and waxes (δCW)) and respiratory carbon (foliage (δCFR), soil (δCSR) and ecosystem 13CO2 (δCER)) for two years at adjacent ecosystems in the southeastern U.S.: a regenerated 32 m tall mature Pinus palustris forest, and a mid-rotation 13 m tall Pinus elliottii stand. Carbon pools and foliage respiration in P. palustris were isotopically enriched by 2‰ relative to P. elliottii. Despite this enrichment, mean δCER values of the two sites were nearly identical. No temporal trends were apparent in δCSC, δCFR, δCSR and δCER. In contrast, δCOM and δCW at both sites declined by approximately 2‰ over the study. This appears to reflect the adjustment in the δ13C of carbon storage reserves used for biosynthesis as the trees recovered from a severe drought prior to our study. Unexpectedly, the rate of δ13C decrease in the secondary C32–36 n-alkanoic acid wax molecular cluster was twice that observed for δCOM and the predominant C22–26 compound cluster, and provides new evidence for parallel but separate wax chain elongation systems utilizing different carbon precursor pools in these species. δCFR and δCER were consistently enriched relative to assimilated carbon but, in contrast to previous studies, showed limited variations in response to changes in vapor pressure deficit (D). This limited variability in respiratory fluxes and δCSC may be due to the shallow water table as well as the deep taproots of pines, which limit fluctuations in photosynthetic discrimination arising from changes in D.This work was supported by a NSF grants DEB-0343604, DEB-0344562 and DEB-0552202, and DOE grant DE-FC02-06ER64156/06-SC-NICCR-1063.2012-10-1

The College News, 1923-01-24, Vol. 09, No. 13

Bryn Mawr College student newspaper. Merged with The Haverford News in 1968 to form the Bi-college News (with various titles from 1968 on). Published weekly (except holidays) during the academic year

The effect of transient and continuous drought on yield,photosynthesis and carbon isotope discrimination in sugar beet (Beta vulgaris L.)

Stable carbon isotope discrimination (Δ13C), photosynthetic performance (A), dry matter accumulation (DW), and sucrose yield (Ys) of sugar beet were evaluated in a glasshouse experiment under transient (TS) and permanent (PS) water stress. A was significantly reduced under drought, to an extent depending on stress duration. The reduced A was strictly associated with a low DW and Ys, the later being 42% lower in PS than control plants (C). Restoring water steeply increased A and the associated leaf traits (RWC, leaf water potential etc.), but the increase of Ys was negligible. Therefore, the negative effects of severe water stress in the early growth period, though reversible on gas-exchange and most leaf traits, can drastically reduce Ys of sugar beet. Furthermore, A seems not to be effective in predicting sucrose accumulation, although it was very effective in detecting the occurrence of plant water stress. The A/C i model was used to assess the photosynthetic adjustments to continuous or transient drought by calculating the photosynthetic parameters Vcmax and Jmax and then compared with Δ 13C. Mesophyll conductance (gm) was estimated by comparing Δ13C measured on soluble sugars and gas-exchange data. This approach confirmed the expectation that gm was limiting A and that there was a significant drop in [CO2] from the substomatal cavities and the chloroplast stroma both in favourable and drought conditions. Therefore, the carbon concentration at the carboxylation site was overestimated by 25-35% by conventional gasexchange measurements, and Vcmax was consistently underestimated when gm was not taken into account, especially under severe drought. Root Δ13C was found to be strictly related to sucrose content (brix%), Ys and root dry weight, and this was especially clear when Δ13C was measured on bulk dry matter. By contrast, leaf Δ13C measured in soluble sugars (Δs) and bulk dry matter (Δdm) were found to correlate weakly to brix% and yield, and this was not surprising as the integration time-scale of leaf Δs and Δdm were found to be shorter than that of root Δ13C in bulk dry matter. The effect of water stress on diffusive and biochemical limitations with different integration times ranged from 1 d (leaf Δs) to more than 1 month (root Δdm)

The gibberellin-deficient dwarf2 mutant of sunflower shows a high constitutive level of jasmonic and salicylic acids and an elevated energy dissipation capacity in well-watered and drought conditions

Understanding the role of a low gibberellin (GA) level in counteracting water stress is crucial to improve crop productivity under future climate change scenarios. To date, there have been only a few studies on the physiological characterisation of severe dwarf mutants with deficient GA biosynthesis grown in soil subject to water shortage. Moreover, it is not yet clear whether already in well-watered conditions, the strong reduction in GA observed in these genotypes directly and/or indirectly affects photosynthetic performance, the content of stress-related hormones and the expression of genes associated with chloroplast functions that could contribute to confer tolerance to subsequent stress events. The drought tolerance responses of the sunflower mutant dwarf2 (dw2), deficient in GAs, were studied in both detached leaves left to dehydrate and in potted plants by watering interruption. In the absence of stress, dw2 plants showed higher constitutive endogenous levels of salicylic and jasmonic acids compared with wild type (WT) plants, together with thicker and less expanded leaves, lower stomatal conductance, higher photochemistry activity of photosystem II and higher photosynthetic capacity per unit leaf area. During water deprivation, dw2 plants maintained a better leaf water status and photosynthetic performance compared with WT plants, associated with a peculiar pattern of transcription for genes related to energy conversion processes. The drought tolerance of dw2 plants appeared to be related to the combination of several structural, photosynthetic and hormonal features together with the up-regulation of genes encoding proteins related to Rubisco subunits and photosystem II repair cycle, avoiding photoinhibition and photodamages to the photosynthetic apparatu