Nitrogen-induced variations in leaf gas exchange of spring triticale under field conditions

Nitrogen (N) is the key factor limiting photosynthetic processes and crop yield. Little is known about the response of leaf gas exchange of spring triticale (Triticosecale Wittm.) to N supply. The effect of N fertilizers on different gas exchange variables, i.e., photosynthetic rate (A), transpiration rate (E), stomatal conductance (g _s), instantaneous water use efficiency (WUE) and maximum quantum yield of photosystem II (PSII) (F _v/F _m), chlorophyll index (SPAD, soil–plant analysis development), and the relationship of these variables with yield were studied in spring triticale grown under field conditions. Six treatments of N—0, 90, 180, 90 + 30, 90 + 30 + 30 kg ha^?1 (applied as ammonium nitrate, AN) and one treatment of N 90 + 30 + 30 kg ha^?1 (applied as urea ammonium nitrate solution, UAN) were compared. The analysis of variance showed that throughout the triticale growing season, N fertilization had significant effects on A, WUE, g _s and SPAD. On average, N fertilizer application increased A values by 14–70%. E and F _v/F _m values were not influenced by N fertilization levels. The effect of growth stage and year on gas exchange variables and F _v/F _m and SPAD was found to be significant. At different growth stages, A values varied and maximum ones were reached at BBCH 31–33 (decimal code system of growth stages) and BBCH 59. With aging, values of A decreased independently of N fertilization level. The gas exchange variables were equally affected by both fertilizer forms. The interplay among grain yield, leaf gas exchange variables, F _v/F _m and SPAD of spring triticale was estimated. The statistical analysis showed that grain yield positively and significantly correlated with A and SPAD values throughout the growing season.     

Nutrient allocation and photochemical responses of <Emphasis Type="Italic">Populus</Emphasis> × <Emphasis Type="Italic">canadensis</Emphasis> ‘Neva’ to nitrogen fertilization and exogenous <Emphasis Type="Italic">Rhizophagus irregularis</Emphasis> inoculation

Arbuscular mycorrhizal fungi (AMF) can promote plant growth performance, but their effectiveness varies depending on soil nitrogen (N) availability. To clarify the effectiveness of exogenous AMF along an N-fertilization gradient (0, 2, 10, 20, and 30 mM), the impacts of exogenous Rhizophagus irregularis and N on the growth, photochemical activity, and nutritional status of Populus?×?canadensis ‘Neva’ in natural soil were evaluated in a pot experiment. The results showed that the 10 mM N level was the optimal fertilization regime with the highest promotion effect on plant growth and the maximum quantum yield of photosystem II (PSII) (F_v/F_m). Excess N (20 and 30 mM) fertilization reduced the actual quantum yield of PSII (ФPSII) and the F_v/F_m of the plants. Regardless of the N availability, inoculated plants exhibited greater F_v/F_m values than did non-inoculated plants. The biomass of inoculated plants was significantly higher compared with the control under low N levels (0 and 2 mM). Under high N levels, inoculated plants showed significant increases in ФPSII. Moreover, the nutrient imbalance of plants inoculated with exogenous R. irregularis was eased by increasing P, Fe, Mn and Cu uptake in roots and higher P, Ca, Mg, Fe, Mn and Zn concentrations in leaves. Moreover, the F_v/F_m and ФPSII exhibited positive correlations with P, Ca, Mg and Zn concentrations in leaves. In conclusion, inoculation with exogenous R. irregularis can benefit plant fitness by improving the photochemical capacity and nutrient composition of poplar under different N levels.     

Physiological and Biochemical Mechanisms Preventing Cd Toxicity in the New Hyperaccumulator <Emphasis Type="Italic">Abelmoschus manihot</Emphasis>

Abelmoschus manihot, an ornamental plant, was examined for phytoremediation purposes in accordance with the ability to accumulate cadmium and physiological mechanisms of cadmium tolerance. A net photosynthetic rate (A _N) glasshouse experiment for 60 days was conducted to investigate the influence of different cadmium amounts (0–100 mg kg^?1) on the growth, biomass, photosynthetic performance, reactive oxygen species (ROS) production, antioxidative enzyme activities, Cd uptake and accumulation of A. manihot. Exposure to cadmium enhanced plant growth even at 100 mg kg^?1, without showing symptoms of visible damage. The cadmium concentration of shoots (stems or leaves) and roots was more than the critical value of 100 mg kg^?1 and reached 126.17, 185.26 and 210.24 mg kg^?1, respectively. BCF values of A. manihot plants exceeded the reference value 1.0 for all the Cd treatments, and TF values were greater than 1 at 15–60 mg kg^?1 Cd treatment. The results also showed that cadmium concentrations of 60 mg kg^?1 or less induced a significant enhancement in plant net photosynthetic rate (A _N), stomatal conductance (G _s), transpiration rate (T _r), photosynthetic pigments and F _v/F _m. These parameters were slightly decreased at the higher concentration (100 mg kg^?1). The ROS production (O₂ ^?, H₂O₂) and antioxidative response including SOD, CAT and POD were significantly enhanced by increasing cadmium. These results suggest that A. manihot can be considered as a Cd-hyperaccumulator and the hormetic effects may be taken into consideration in remediation of Cd contamination soil.     

Evaluation of growth and phycobiliprotein composition of cyanobacteria isolates cultivated in different nitrogen sources

Phycobiliproteins, light-harvesting pigments found in cyanobacteria and in some eukaryotic algae, have numerous commercial applications in food, cosmetic, and pharmaceutical industries. Colorant production from cyanobacteria offers advantages over their production from higher plants, as cyanobacteria have fast growth rate and high photosynthetic efficiency and require less space. In this study, three cyanobacteria strains were studied for phycobiliprotein production and the influence of sodium nitrate, potassium nitrate and ammonium chloride on the growth and phycobiliprotein composition of the strains were evaluated. In the batch culture period of 12 days, Phormidium sp. and Pseudoscillatoria sp. were able to utilize all tested nitrogen sources; however, ammonium chloride was the best nitrogen source for both strains to achieve maximum growth rate μ?=?0.284?±?0.03 and μ?=?0.274?±?0.13 day^?1, chlorophyll a 16.2?±? 0.5 and 12.2?±? 0.2 mg L^?1, and phycobiliprotein contents 19.38?±?0.09 and 19.99?±?0.14% of dry weight, whereas, for Arthrospira platensis, the highest growth rate of μ?=?0.304?±?0.0 day^?1, chlorophyll a 19.1?±?0.5 mg L^?1, and phycobiliprotein content of 22.27?±?0.21% of dry weight were achieved with sodium nitrate. The phycocyanin from the lyophilized cyanobacterial biomass was extracted using calcium chloride and food grade purity (A₆₂₀/A₂₈₀ ratio >?0.7) was achieved. Furthermore, phycocyanin was purified using two-step chromatographic method and the analytical grade purity (A₆₂₀/A₂₈₀ ratio >?4) was attained. SDS-PAGE demonstrated the purity and presence of two bands corresponding to α- and β-subunits of the C-phycocyanin. The results showed that Phormidium sp. and Pseudoscillatoria sp. could be good candidates for phycocyanin production.     

Carbon Dioxide and Methane Fluxes From Tree Stems,Coarse Woody Debris,and Soils in an Upland Temperate Forest

Forest soils and canopies are major components of ecosystem CO₂ and CH₄ fluxes. In contrast, less is known about coarse woody debris and living tree stems, both of which function as active surfaces for CO₂ and CH₄ fluxes. We measured CO₂ and CH₄ fluxes from soils, coarse woody debris, and tree stems over the growing season in an upland temperate forest. Soils were CO₂ sources (4.58 ± 2.46 µmol m^?2 s^?1, mean ± 1 SD) and net sinks of CH₄ (?2.17 ± 1.60 nmol m^?2 s^?1). Coarse woody debris was a CO₂ source (4.23 ± 3.42 µmol m^?2 s^?1) and net CH₄ sink, but with large uncertainty (?0.27 ± 1.04 nmol m^?2 s^?1) and with substantial differences depending on wood decay status. Stems were CO₂ sources (1.93 ± 1.63 µmol m^?2 s^?1), but also net CH₄ sources (up to 0.98 nmol m^?2 s^?1), with a mean of 0.11 ± 0.21 nmol m^?2 s^?1 and significant differences depending on tree species. Stems of N. sylvatica, F. grandifolia, and L. tulipifera consistently emitted CH₄, whereas stems of A. rubrum, B. lenta, and Q. spp. were intermittent sources. Coarse woody debris and stems accounted for 35% of total measured CO₂ fluxes, whereas CH₄ emissions from living stems offset net soil and CWD CH₄ uptake by 3.5%. Our results demonstrate the importance of CH₄ emissions from living stems in upland forests and the need to consider multiple forest components to understand and interpret ecosystem CO₂ and CH₄ dynamics.     

Ammonium,nitrate, and urea play different roles for lipid accumulation in the nervonic acid—producing microalgae <Emphasis Type="Italic">Mychonastes afer</Emphasis> HSO-3-1

Producing valuable coproducts from oleaginous microalgae is an option to reduce the total cost of biofuel production. Here, the influence of nitrogen sources on biomass yield and lipid accumulation of a newly identified oleaginous green microalgal strain, Mychonastes afer HSO-3-1, was evaluated. Carbon assimilation and the following lipid biosynthesis of M. afer were inhibited to some extent under weak acidic conditions (6 < pH < 7) and any of the tested nitrogen source. The highest lipid productivity of 50.7 mg L^?1 day^?1 was achieved with a 17.6 mM nitrogen supplement in the form of urea. The cell polar lipid content was significantly higher than triacylglycerol (TAG), and saturated palmitic acid (C16:0) occupied a dominant position in the fatty acid profiles while culturing M. afer in acidic medium with NH₄ ⁺ as the nitrogen source. Under neutral conditions, the lipid productivities of M. afer cultivated in media containing 17.6 mM of NaNO₃, NH₄Cl, and NH₄NO₃ were 76.2, 77.5, and 79.0 mg L^?1 day^?1, respectively. The greatest TAG content (58.56%) of total lipids was obtained when NaNO₃ was used as the nitrogen source. There was no significant difference in the fatty acid composition of M. afer cells when they were cultivated in neutral media supplemented with NaNO₃, urea, NH₄Cl, and NH₄NO₃. Therefore, NH₄ ⁺ was not a suitable nitrogen source for M. afer cultivation due to the additional labor, working procedures, and alkali required to adjust the medium pH. Considering that using urea as nitrogen source could reduce the cost of nutrient salts substantially and urea can be taken up and utilized by most microalgae, it is a preferred nitrogen source. The major properties of biodiesel derived from M. afer HSO-3-1 met biodiesel quality, and nervonic acid concentrations remained at approximately 3.0% of total fatty acids.     

Effects of 28-homobrassinoloid on key physiological attributes of <Emphasis Type="Italic">Solanum lycopersicum</Emphasis> seedlings under cadmium stress: Photosynthesis and nitrogen metabolism

Heavy metal accumulation due to environmental pollution, especially in agricultural ecosystem can cause serious deterioration of crop yield and quality. In present study we assessed the effect of exogenous 28-homobrassinoloid (HBL; 10^?8 M) on growth, photosynthesis, indices of chlorophyll a fluorescence and nitrogen metabolism in Solanum lycopersicum seedlings grown under two doses (Cd₁: 3 mg kg^?1 sand and Cd₂: 9 mg kg^?1 sand) of cadmium. Accumulation of Cd in root tissues was considerably higher than shoot hence, Cd declined the growth, pigment contents, and photosynthetic O₂ yield in its concentration dependent manner. Chlorophyll a fluorescence due to Cd stress was negatively affected as shown by decreased Q_A ^? reoxidation kinetics: φP₀, ψ₀, φE₀ and PI__ABS and increased energy flux parameters: ABS/RC, TR₀/RC, ET₀/RC and DI₀/RC. HBL application under Cd stress improved the photochemistry of photosystem II (PS II) by affecting these parameters positively. Treatment of Cd in test seedlings resulted into significant decrease in nitrate reductase, nitrite reductase, glutamine synthetase and glutamate synthase activities, and induced enhancing effect on ammonium content and glutamate dehydrogenase activity. Exogenous HBL treatment alleviated the negative effect of Cd on growth, photosynthesis, contents of protein, carbohydrate and inorganic nitrogen and nitrogen assimilating enzymes. The data indicate that exogenous HBL protects the test seedlings during the early growth phase against Cd phytotoxicity by regulating Cd accumulation in tissues and two key metabolic processes; photosynthesis and nitrogen metabolism.     

Effect of short-term heat exposure on physiological traits of indica rice at grain-filling stage

Heat stress impacts the quantity and quality of rice grains, particularly during grain-filling stage needed for grain development. In this study, the effect of short heat stress (42 °C, 30 min) on indica rice plants at the grain-filling stage (dough grain stage) was found by determining their physiological and growth traits F_v/F_m, ?F/F_m′, chlorophyll content, leaf water potential (LWP), membrane stability, relative leaf area (RLA), relative plant height (RPH), total grain weight per panicle (TGW) and 1000 GW. Thai economic rice cvs. KDML105 and Pathumthani 1 (PTT1) were compared to the heat-tolerant rice cultivars N22 and Dular and to the heat-sensitive rice cultivar IR64. The results showed that short heat stress exhibited effects on physiology and growth greater than the control (35 °C, 30 min) by reducing of F_v/F_m, ?F/F_m′, chlorophyll content, LWP, membrane stability and RLA. This result impacted the TGW and 1000 GW. A higher reduction of physiological traits was shown in IR64, followed by KDML105. In contrast, N22 and Dular were minimally affected by heat stress and were able to adapt and recover based on their grain weight that exhibited less of an effect. PTT1 was also impacted by heat stress similarly to Dular. Thus, short heat stress affected the physiological parameters of five rice cultivars at the dough grain stage. In addition, the five indica rice cultivars were classified into three groups: (1) the heat-tolerant group (N22, Dular and PTT1), (2) the moderately heat-tolerant group (KDML105), and (3) the heat-sensitive group (IR64) by PC-ORD program at 50% of similarity of the 13 physiological traits.     

Short-term effects of crop rotation,residue management,and soil water on carbon mineralization in a tropical cropping system

The purpose of this study was to investigate the short-term effects of maize (Zea mays)-fallow rotation, residue management, and soil water on carbon mineralization in a tropical cropping system in Ghana. After 15 months of the trial, maize–legume rotation treatments had significantly (P?C ₀ (μg CO₂–C g^?1) than maize–elephant grass (Pennisetum purpureum) rotations. The C ₀ for maize–grass rotation treatments was significantly related to the biomass input (r?=?0.95; P?=?0.05), but that for the maize–legume rotation was not. The soil carbon mineralization rate constant, k (per day), was also significantly related to the rotation treatments (P?k values for maize–grass and maize–legume rotation treatments were 0.025 and 0.036 day^?1 respectively. The initial carbon mineralization rate, m ₀ (μg CO₂–C g^?1 day ^?1), was significantly (P?θ. The m ₀ ranged from 3.88 to 18.67 and from 2.30 to 15.35 μg CO₂–C g^?1 day^?1 for maize–legume and maize–grass rotation treatments, respectively, when the soil water varied from 28% to 95% field capacity (FC). A simple soil water content (θ)-based factor, f _w, formulated as: \(f_{\text{w}} = \left[ {\frac{{\theta - \theta _{\text{d}} }}{{\theta _{{\text{FC}}} - \theta _{\text{d}} }}} \right]\), where θ _d and θ _FC were the air-dry and field capacity soil water content, respectively, adequately described the variation of the m ₀ with respect to soil water (R ²?=?0.91; RMSE?=?1.6). Such a simple relationship could be useful for SOC modeling under variable soil water conditions.     

Photosynthetic capacity of the capsule wall and its contribution to carbon fixation and seed yield in castor (<Emphasis Type="Italic">Ricinus communis</Emphasis> L.)

Defoliation occurs in castor due to several reasons, but the crop has propensity to compensate for the seed yield. Photosynthetic efficiency in terms of functional (gas exchange and chlorophyll fluorescence) and structural characteristics (photosynthetic pigment profiles and anatomical properties) of castor capsule walls under light- and dark-adapted conditions was compared with that of leaves. Capsule wall showed high intrinsic efficiency of photosystem II (F _v/F _m, 0.82) which was comparable to leaves (F _v/F _m, 0.80). With increasing photon flux densities (PFD), actual quantum yields and photochemical quenching coefficients of the capsule walls were similar to that in leaves, while electron transport rates reached a maximum corresponding to about 118 % of the leaves. However, maximum net photosynthetic rate of the capsule walls (2.60 µmol CO₂ m^?2 s^?1) was less than one-fourth of the leaves (15.67 µmol CO₂ m^?2 s^?1) at the CO₂ concentration of 400 µmol mol^?1, and the difference was attributed to about 80 % lower stomatal density and the 75 % lower total chlorophyll content of capsule walls than the leaves. Furthermore, seed weight in dark-adapted capsules was 2.70–12.42 % less as compared to the capsules developed under light. The results indicate that castor capsule walls are photosynthetically active (about 15–30 % of the leaves) and contribute significantly to carbon fixation and seed yield accounting for 10 % photoassimilates towards seed weight.     

Toxin Gene Contents and Activity of <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> Strains Against Two Sugarcane Borer Species, <Emphasis Type="Italic">Diatraea saccharalis</Emphasis> (F.) and <Emphasis Type="Italic">D. flavipennella</Emphasis> (Box)

Bacillus thuringiensis (Berliner) bears essential characteristics in the control of insect pests, such as its unique mode of action, which confers specificity and selectivity. This study assessed cry gene contents from Bt strains and their entomotoxicity against Diatraea saccharalis (F.) and Diatraea flavipennella (Box) (Lepidoptera: Crambidae). Bioassays with Bt strains were performed against neonates to evaluate their lethal and sublethal activities and were further analyzed by PCR, using primers to identify toxin genes. For D. saccharalis and D. flavipennella, 16 and 18 strains showed over 30% larval mortality in the 7th day, respectively. The LC₅₀ values of strains for D. saccharalis varied from 0.08 × 10⁵ (LIIT-0105) to 4104 × 10⁵ (LIIT-2707) spores + crystals mL^?1. For D. flavipennella, the LC₅₀ values of strains varied from 0.40 × 10⁵ (LIIT-2707) to 542 × 10⁵ (LIIT-2109) spores + crystals mL^?1. For the LIIT-0105 strain, which was the most toxic to D. saccharalis, the genes cry1Aa, cry1Ab, cry1Ac, cry1B, cry1C, cry1D, cry1F, cry1I, cry2Aa, cry2Ab, cry8, and cry9C were detected, whereas for the strain LIIT-2707, which was the most toxic to D. flavipennella, detected genes were cry1Aa, cry1Ab, cry1Ac, cry1B, cry1D, cry1F, cry1I, cry2Aa, cry2Ab, and cry9. The toxicity data and toxin gene content in these strains of Bt suggest a great variability of activity with potential to be used in the development of novel biopesticides or as source of resistance genes that can be expressed in plants to control pests.     

Intrapopulation heterogeneity of the fluorescence parameters of the marine plankton alga <Emphasis Type="Italic">Thalassiosira weissflogii</Emphasis> at various nitrogen levels

Fluorescence of the marine alga Thalassiosira weissflogii (Grunow) Fryxell et Hasle with open (F _o ) and closed (F _m ) reaction centers of photosystem 2 (PS 2) and its relative variable fluorescence (F _v/F _m ) were measured at various levels of inorganic nitrogen. A significant heterogeneity of the population in terms of these parameters was revealed. Some cells within the population were more sensitive to nitrogen deficiency, and their photosynthetic apparatus was disrupted to a greater extent. The cells within a population also differed in terms of their ability to recover after incubation at low nitrogen levels. Enhancement of nitrogen deficiency resulted in an increase in the variability of the F _o and F _v/F _m values of the cells. Fluorescence variability decreased at a less pronounced deficiency. Fluorescence variability should be taken into consideration in the studies concerning responses of algae to changes in nutrient contents.     

Nitrogen Metabolism Genes from Temperate Marine Sediments

In this study, we analysed metagenomes along with biogeochemical profiles from Skagerrak (SK) and Bothnian Bay (BB) sediments, to trace the prevailing nitrogen pathways. NO₃ ^? was present in the top 5 cm below the sediment-water interface at both sites. NH₄ ⁺ increased with depth below 5 cm where it overlapped with the NO₃ ^? zone. Steady-state modelling of NO₃ ^? and NH₄ ⁺ porewater profiles indicates zones of net nitrogen species transformations. Bacterial protease and hydratase genes appeared to make up the bulk of total ammonification genes. Genes involved in ammonia oxidation (amo, hao), denitrification (nir, nor), dissimilatory NO₃ ^? reduction to NH₄ ⁺ (nfr and otr) and in both of the latter two pathways (nar, nap) were also present. Results show ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) are similarly abundant in both sediments. Also, denitrification genes appeared more abundant than DNRA genes. 16S rRNA gene analysis showed that the relative abundance of the nitrifying group Nitrosopumilales and other groups involved in nitrification and denitrification (Nitrobacter, Nitrosomonas, Nitrospira, Nitrosococcus and Nitrosomonas) appeared less abundant in SK sediments compared to BB sediments. Beggiatoa and Thiothrix 16S rRNA genes were also present, suggesting chemolithoautotrophic NO₃ ^? reduction to NO₂ ^? or NH₄ ⁺ as a possible pathway. Our results show the metabolic potential for ammonification, nitrification, DNRA and denitrification activities in North Sea and Baltic Sea sediments.     

Impacts of enhanced UVB radiation on photosynthetic characteristics of the marine diatom <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis> (Bacillariophyceae,Heterokontophyta)

Solar ultraviolet B (UVB) irradiance at the Earth’s surface is increasing due to anthropogenic influences. To evaluate the effects of enhanced UVB radiation on photosynthetic characteristics of the marine diatom Phaeodactylum tricornutum, the species was exposed to four levels of UVB radiation, 0, 0.25, 0.75, and 1.50 KJ m^?2 day^?1 for 7 days. Effects of UVB stress on net photosynthetic rate, net respiration rate, variable chlorophyll (Chl) fluorescence parameters, Chl a and carotenoid contents, and UV-absorbing compounds (UVACs) were investigated. Results showed that there were no significant differences in terms of net respiration rate or maximal photochemical efficiency of photosystem II (F_v/F_m) between the treatments in the short or long term. However, enhanced UVB radiation at an intensity of 0.16 W m^?2 had a negative effect on the net photosynthetic rate, electron transport rate, and on the pathway of excess energy dissipation over the short term (1 to 5 days). Carotenoid and UVACs content increased under UVB radiation. Photosynthetic parameters were unaffected by UVB radiation on the seventh day indicating that P. tricornutum can adapt to UVB radiation in the long term. Results of the present study indicate that there is a dynamic balance between damage and adaptation in microalgae that enables them to adapt to UVB-induced photosystem alterations during both short-term and long-term exposure.     

Effects of nitrogen and phosphorus imbalance on photosynthetic traits of poplar Oxford clone under ozone pollution

Ozone (O₃) pollution and the availability of nitrogen (N) and phosphorus (P) in the soil both affect plant photosynthesis and chlorophyll (Chl) content, but the interaction of O₃ and nutrition is unclear. We postulated that the nutritional condition changes plant photosynthetic responses to O₃. An O₃-sensitive poplar clone (Oxford) was subject to two N levels (N0, 0 kg N ha^??1; N80, 80 kg N ha^??1), two P levels (P0, 0 kg P ha^??1; P80, 80 kg P ha^??1) and three levels of O₃ exposure (ambient concentration, AA; 1.5?×?AA; 2.0?×?AA) over a growing season in an O₃ free air controlled exposure (FACE) facility. The daily change of leaf gas exchange and dark respiration (R_d) were investigated at mid-summer (August). Chl a fluorescence was measured three times in July, August and September. At the end of the growing season, Chl content was measured. It was found that Chl content, the maximum quantum yield (F_v/F_m), Chl a fluorescence performance index (PI) and gas exchange were negatively affected by elevated O₃. Phosphorus may mitigate the O₃-induced reduction of the ratio of photosynthesis to stomatal conductance, while it exacerbated the O₃-induced loss of F_v/F_m. Nitrogen alleviated negative effects of O₃ on F_v/F_m and PI in July. Ozone-induced loss of net photosynthetic rate was mitigated by N in medium O₃ exposure (1.5?×?AA). However, such a mitigation effect was not observed in the higher O₃ level (2.0?×?AA). Nitrogen addition exacerbated O₃-induced increase of R_d suggesting an increased respiratory carbon loss in the presence of O₃ and N. This may result in a further reduction of the net carbon gain for poplars exposed to O₃.     

Sap flow of the southern conifer, <Emphasis Type="Italic">Agathis australis</Emphasis> during wet and dry summers

Key message

Analysis of sap flux density during drought suggests that the large sapwood and rooting volumes of larger trees provide a buffer against drying soil.

Abstract

The southern conifer Agathis australis is amongst the largest and longest-lived trees in the world. We measured sap flux densities (F _d) in kauri trees with a DBH range of 20–176 cm to explore differences in responses of trees of different sizes to seasonal conditions and summer drought. F _d was consistently higher in larger trees than smaller trees. Peak F _d was 20 and 8 g m^?2 s^?1 for trees of diameters of 176 and 20 cm, respectively, during the wet summer. Multiple regression analysis revealed photosynthetically active radiation (PAR) and vapour pressure deficit (D) were the main drivers of F _d. During drought, larger trees were more responsive to D whilst smaller trees were more responsive to soil drying. Our largest tree had a sapwood area of 3,600 cm². Preliminary analysis suggests stem water storage provides a buffer against drying soil in larger trees. Furthermore, F _d of smaller trees had higher R ² values for soil moisture at 30 and 60 cm depth than soil moisture at 10 cm depth (R ² = 0.68–0.97 and 0.55–0.67, respectively) suggesting that deeper soil moisture is more important for these trees. Larger trees did not show a relationship between F _d and soil moisture, suggesting they were accessing soil water deeper than 60 cm. These results suggest that larger trees may be better prepared for increasing frequency and intensity of summer droughts due to deeper roots and/or larger stem water storage capacity.

     

Changes in growth and composition of the marine microalgae <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis> and <Emphasis Type="Italic">Nannochloropsis salina</Emphasis> in response to changing sodium bicarbonate concentrations

Oils, carbohydrates, and fats generated by microalgae are being refined in an effort to produce biofuels. The research presented here examines two marine microalgae, Nannochloropsis salina (green alga) and Phaeodactylum tricornutum (diatom), when grown with 0 (no addition), 0.5, 1.0, 2.0, and 5.0 g L^?1 NaHCO₃ added to an f/2 medium during the growth phase (GP) and a nutrient induced (nitrate limitation) lipid formation phase (LP). We hypothesize that the addition of NaHCO₃ is a sustainable and practical strategy to increase cellular density and concentrations of lipids in microalgae as well as the rate of lipid accumulation. In N. salina, final cell densities were significantly (p?<?0.05) higher in the NaHCO₃-treated cells than the control while in P. tricornutum the cell densities were higher with >[NaHCO₃] during the GP. During the LP, cell densities were generally higher in the NaHCO₃-treated cells compared with controls. F _V/F _M (efficiency of photosystem II) patterns paralleled those for cell density with generally higher values with higher concentrations of NaHCO₃ and significantly different values between controls and 5.0 g L^?1 NaHCO₃ at the end of the GP (p?<?0.05). F _V/F _M was variable between treatments in P. tricornutum (0.3–0.65) but less so in N. salina for (0.5–0.7) regardless of [NaHCO₃]. The lipid index (measured with Nile red), used as a proxy for triacylglycerides (TAGs), was 10.2?±?6.5 and 4.4?±?2.9 (fluorescence units/OD cells ×1000) for N. salina and P. tricornutum, respectively, at the end of the GP. At the end of the LP, the lipid index was eight and four times higher than during the GP in the corresponding 5.0 g L^?1 NaHCO₃ treatments, revealing that N. salina was accumulating more lipid than P. tricornutum. Dry weights essentially doubled during LP compared with GP for N. salina; this was not the case for P. tricornutum. In general, the percentage of ash in dry weights was significantly higher in the LP relative to the corresponding GP treatments for P. tricornutum; this was not the case for N. salina. During the LP, there was also less soluble protein in N. salina compared to GP; differences were not significant in cells growing with 2.0 or 5.0 g L^?1 NaHCO₃. In P. tricornutum, faster growing cells had more soluble protein during the GP and LP; differences between treatments were significant. P. tricornutum generally accumulated significantly more crude protein than N. salina at higher [NaHCO₃]; there was three times more crude protein in the highest NaHCO₃ (5.0 g L^?1) treatment compared with the controls. C:N ratios (mol:mol) were similar across treatments during GP: 7.03?±?0.12 and 10.16?±?0.41 for N. salina and P. tricornutum, respectively. Further, C:N ratios increased with increasing [NaHCO₃] during LP. Species-specific fatty acid methyl ester (FAMEs) profiles were observed. While C16:0 was lower in P. tricornutum compared to N. salina, the diatom produced more C16:1 and C14 but not C18:3. Monounsaturated fatty acids (MUFA) significantly increased in N. salina in the LP compared to GP and in response to increasing [NaHCO₃] (t tests; p?<?0.05). Saturated fatty acids (SFA) responded similarly but to a lesser degree. There were more polyunsaturated fatty acids (PUFA) in N. salina than MUFAs or SFAs. In P. tricornutum, there were generally more SFAs, MUFAs and PUFAs in P. tricornutum during LP than GP in the corresponding NaHCO₃ treatments. These findings reveal the importance of considering NaHCO₃ as a supplemental carbon source in the culturing marine phytoplankton in large-scale production for biofuels.     

Bioregulators protected photosynthetic machinery by inducing expression of photorespiratory genes under water stress in chickpea

Globally, water deficit is one of the major constraints in chickpea (Cicer arietinum L.) production due to substantial reduction in photosynthesis. Photorespiration often enhances under stress thereby protecting the photosynthetic apparatus from photoinhibition. Application of bioregulators is an alternative to counter adverse effects of water stress. Thus, in order to analyze the role of bioregulators in protecting the photosynthetic machinery under water stress, we performed an experiment with two contrasting chickpea varieties, i.e., Pusa 362 (Desi type) and Pusa 1108 (Kabuli type). Water deficit stress was imposed at the vegetative stage by withholding water. Just prior to exposure to water stress, plants were pretreated with thiourea (1,000 mg L^?1), benzyladenine (40 mg L^?1), and thidiazuron (10 mg L^?1). Imposed water deficit decreased relative water content (RWC), photosynthetic rate (P_N), quantum efficiency of PSII (F_v/F_m), and enhanced lipid peroxidation (LPO). However, bioregulator application maintained higher RWC, P_N, F_v/F_m, and lowered LPO under water stress. Expression of Rubisco large subunit gene (RbcL) was low under water stress both in the Kabuli and Desi type. However, bioregulators strongly induced its expression. Although poor expression of two important photorespiratory genes, i.e., glycolate oxidase and glycine decarboxylase H subunit, was observed in Desi chickpea under imposed stress, bioregulators in general and cytokinins in particular strongly induced their expression. This depicts that the application of bioregulators protected the photosynthetic machinery by inducing the expression of RbcL and photorespiratory genes during water deficit stress.     

Optimization of continuous-flow solid-phase denitrification via coupling carriers in enhancing simultaneous removal of nitrogen and organics for agricultural runoff purification

Coupling of biodegradable corncob and plastic carrier was optimized in continuous-flow solid-phase denitrification systems for enhancing simultaneously removal of nitrogen and organics in agricultural runoff. In compared with preposition of plastic carriers and mixed distribution method, it was demonstrated that the preposition of corncobs simultaneously enhanced nitrate (6.64 ± 1.35 mg L^?1 day ^?1) and organics removal (6.33 ± 1.44 mg L^?1 day^?1) at a hydraulic retention time (HRT) of 6 h. The operation performance could be further enhanced with extension of HRT to 12 h. The dominant genera found in corncob were denitrifiers for nitrate reduction (Bosea, Simplicispira, Desulfovibrio, Klebsiella, etc.) and fermentative bacteria (Pleomorphomonas, Actinotalea, Opitutus, Cellulomonas, Bacteroides, etc.) responsible for corncob degrading to simple organics for other denitrifiers. However, much lower and different denitrifiers abundances (Bradyrhizobium, Acinetobacter, Bacillus, etc.) exhibited on plastic filler than those of corncob. It well explained that the biofilm on plastic carrier was mainly related with organics removal while the biofilm on corncobs inclined to effectively remove nitrate, and simultaneous removal of nitrogen and organics could be achieved in coupling carriers system with preposition of biodegradable corncob.     

Mixotrophic cultivation of <Emphasis Type="Italic">Chlorococcum</Emphasis> sp. under non-controlled conditions using a digestate from pig manure within a biorefinery

A number of business opportunities may arise from microalgae and wastewater treatment becoming an integrated system, as biofuels and high-added value products could be obtained simultaneously. This study, performed under controlled and non-controlled conditions, aimed at cultivating Chlorococcum sp. using a digestate from pig manure as culture medium and assessing its growth and biochemical composition for further applications. Under controlled conditions, cultures of Chlorococcum sp. were established testing various digestate dilutions (v/v). It was found that all tested dilutions (up to 8% v/v) promoted a higher biomass density, compared to the control culture in modified Bold’s Basal Medium (modified BBM). Under non-controlled conditions, it was found that the biomass productivity using the digestate diluted 5.6% v/v (23.4 mg L^?1 day^?1) was statistically similar to the one obtained using modified BBM (26.4 mg L^?1 day^?1). The volatile fatty acids contained in the digestate might have allowed mixotrophic growth for Chlorococcum sp. The intracellular lipid content in Chlorococcum sp. remained constant throughout the experiments in both, treatment and control cultures, while carbohydrates increased from 20 to 45% of the cell dry weight in the treatment and from 20 to 42% in the control one. It was concluded that conditions of nitrogen starvation and fluctuating irradiance and temperature benefit carbohydrate accumulation in this strain, since intracellular carbohydrate content increased nearly two-fold during this period. Additionally, the obtained biomass has the potential to be used as feedstock for bioethanol production. This system can meet the concept of a microalgae-based biorefinery, in which biofuels and high-added value products are produced from microalgae and wastewater.