Jens Dyckmans

Nitrogen nutrition and water stress effects on leaf photosynthetic gas exchange and water use efficiency in winter wheat

The responses of gas exchange and water use efficiency to nitrogen nutrition for winter wheat were investigated under well-watered and drought conditions. The photosynthetic gas exchange parameters of winter wheat are remarkably improved by water and nitrogen nutrition and the regulative capability of nitrogen nutrition is influenced by water status. The effects of nitrogen nutrition on photosynthetic characteristics and on the limited factors to photosynthesis are not identical under different water status. Intrinsic water use efficiency (WUE(i)) of the plants at the high-N nutrition was decreased by a larger value than that of the plants in the low-N treatment due to a larger decrease in photosynthetic rate than in transpiration rate. Carbon isotope composition of plant material (delta(p)) is increased by the increase of drought intensity. The delta(p) at a given level of C(i)/C(a) is reduced by nitrogen deficiency. Leaf carbon isotope discrimination (Delta) is increased by the increase of nitrogen nutrition and decreased by the increase of drought intensity. Transpirational water use efficiency (WUE(t)) is negatively correlated with Delta in both nitrogen supply treatments and increased with the nitrogen supply.

Effects of Nitrogen Nutrition and Water Deficit on Net Photosynthetic Rate and Chlorophyll Fluorescence in Winter Wheat

Summary The responses of photosynthetic gas exchange and Chi fluorescence to nitrogen nutrition were studied under well-watered and drought conditions in winter wheat leaves. Nitrogen deficiency and water deficit strongly reduced the photosynthetic activity at light saturation level. For the well-watered treatment, the net photosynthetic rate was stimulated in the high-N (15 mmol/L N) plants as compared with the low-N (1.5 mmol/L N) plants and leaf conductance for water vapour was lower in the high-N than in the low-N treatment. As drought progressed, the net photosynthetic rate was significantly inhibited in the high-N plants as compared with the low-N plants. However, no significant nitrogen effect was noticed for net photosynthetic rate and leaf conductance for water vapour. The quantum yield of photochemical efficiency of PS II ( Fv/Fm ) determined on the youngest fully expanded leaf was unaffected by water stress, but it was lower for the low-N than for the high-N treatment. Nitrogen deficiency resulted in a decrease in the total Chi content and an inaease in the Chi a/b ratio; however, no difference was observed between the water treatments. During steady-state photosynthesis, the values of photochemical quenching decreased with increasing water stress in all treatments. For plants grown at low nitrogen nutrition photochemical quenching was higher than that for plants receiving high-N nutrition. The values of non-photochemical quenching decreased with increasing water stress in all treatments. Nitrogen deficiency and water stress decreased the efficiency of the PS II ( Fv/Fo ) and the efficiency of potential photosynthetic quantum conversion ( Fd/Fs ) of leaves significantly.

Interaction of Osmotic Adjustment and Photosynthesis in Winter Wheat Under Soil Drought

Summary The relationship between photosynthesis and osmotic adjustment in winter wheat ( Triticum aestivum L.) was studied in a controlled growth chamber under soil drought conditions. Leaf water potential, osmotic potential at full turgor, photosynthetic gas exchange, and chlorophyll fluorescence of plants under both control and stressed conditions were evaluated. Under a gradual drying process of soil water, the variability in the capacity of osmotic adjustment was observed, but not for a fast drying process of soil water. The plants that experienced the gradual drying process exhibited higher net photosynthetic gas exchange than those that experienced the fast drying process at a low water potential. Photosynthetic capacity of plants in the gradual drying process was greater than those in the fast drying process at low water potential. The data indicate that osmotic adjustment allows for maintenance of photosynthesis by stomatal adjustment and photosynthetic apparatus adjustment at low water potential.

Soil water uptake by trees using water stable isotopes (δ2H and δ18O)−a method test regarding soil moisture, texture and carbonate

AimsStable isotopes of oxygen and hydrogen are often used to determine plant water uptake depths. We investigated whether and to what extend soil moisture, clay content, and soil calcium carbonate influences the water isotopic composition.MethodsIn the laboratory, dried soil samples varying in clay content were rewetted with different amounts of water of known isotopic composition. Further, we removed soil carbonate from a subset of samples prior to rewetting. Water was extracted from samples via cryogenic vacuum extraction and analysed by mass spectrometry.ResultsThe isotopic composition of extracted soil water was similarly depleted in both 18O and 2H with decreasing soil moisture and increasing clay and carbonate content. Soil carbonate changed the δ18O composition while δ2H was not affected.ConclusionsOur results indicate that soil carbonate can cause artifacts for 18O isotopic composition of soil water. At low soil moisture and high carbonate content this could lead to conflicting results for δ18O and δ2H in plant water uptake studies.

A modification of a method to determine adenosine nucleotides in forest organic layers and mineral soils by ion-paired reversed-phase high-performance liquid chromatography

Abstract In the past, difficulties in the determination of microbial adenylate in forest soils were due to acidity of soils and high humus content. Therefore, a method was developed that allows separation of adenylates from impurities on high-performance liquid chromatography and quantitative extraction from soil. For extraction, samples were stirred with dimethyl sulfoxide and a 0.01 M Na3PO4/0.02 M EDTA buffer (adjusted to pH 12) was added. An aliquot of soil suspension was mixed with an equal volume of nucleotide releasing reagent and then sonified. The suspension was passed through a membrane filter (45 μm). The extracts were reacted with chloroacetaldehyde at pH 3.5 to form the fluorescent 1,N6-etheno-derivatives for fluorometric determination. The separation of the 1,N6-etheno-adenylates (e-adenylates) was performed using a reversed-phase high-performance liquid chromatography. The adenylate derivatives were eluted on a ODS column with 0.05 M ammonium acetate, 1.0 mM EDTA and 0.4 mM tetrabutylammonium hydrogen sulfate (pH 6.3) mixed with methanol (water phase–methanol 89.5:10.5 v/v) as a mobile phase. Column temperature was set to 26–28°C. For quantitative determination, the fluorometric emission was measured at 410 nm with 280 nm as excitation wavelength. This procedure resulted in recovery rates of 91%, 91% and 93% for added AMP, ADP and ATP, respectively in acidic soils as well as in clay rich soils and organic layers. The soil microbial adenylate can be determined with an accuracy of 10%.

Determination of fungal activity in modified wood by means of micro-calorimetry and determination of total esterase activity.

Beech and pine wood blocks were treated with 1,3-dimethylol-4,5-dihydroxyethylen urea (DMDHEU) to increasing weight percent gains (WPG). The resistance of the treated specimens against Trametes versicolor and Coniophora puteana, determined as mass loss, increased with increasing WPG of DMDHEU. Metabolic activity of the fungi in the wood blocks was assessed as total esterase activity (TEA) based on the hydrolysis of fluorescein diacetate and as heat or energy production determined by isothermal micro-calorimetry. Both methods revealed that the fungal activity was related with the WPG and the mass loss caused by the fungi. Still, fungal activity was detected even in wood blocks of the highest WPG and showed that the treatment was not toxic to the fungi. Energy production showed a higher consistency with the mass loss after decay than TEA; higher mass loss was more stringently reflected by higher heat production rate. Heat production did not proceed linearly, possibly due to the inhibition of fungal activity by an excess of carbon dioxide.

Interlaboratory assessment of nitrous oxide isotopomer analysis by isotope ratio mass spectrometry and laser spectroscopy: current status and perspectives.

RATIONALE In recent years, research and applications of the N2O site-specific nitrogen isotope composition have advanced, reflecting awareness of the contribution of N2O to the anthropogenic greenhouse effect, and leading to significant progress in instrument development. Further dissemination of N2O isotopomer analysis, however, is hampered by a lack of internationally agreed gaseous N2O reference materials and an uncertain compatibility of different laboratories and analytical techniques. METHODS In a first comparison approach, eleven laboratories were each provided with N2O at tropospheric mole fractions (target gas T) and two reference gases (REF1 and REF2). The laboratories analysed all gases, applying their specific analytical routines. Compatibility of laboratories was assessed based on N2O isotopocule data for T, REF1 and REF2. Results for T were then standardised using REF1 and REF2 to evaluate the potential of N2O reference materials for improving compatibility between laboratories. RESULTS Compatibility between laboratories depended on the analytical technique: isotope ratio mass spectrometry (IRMS) results showed better compatibility for δ(15)N values, while the performance of laser spectroscopy was superior with respect to N2O site preference. This comparison, however, is restricted by the small number of participating laboratories applying laser spectroscopy. Offset and two-point calibration correction of the N2O isotopomer data significantly improved the consistency of position-dependent nitrogen isotope data while the effect on δ(15)N values was only minor. CONCLUSIONS The study reveals that for future research on N2O isotopocules, standardisation against N2O reference material is essential to improve interlaboratory compatibility. For atmospheric monitoring activities, we suggest N2O in whole air as a unifying scale anchor.

Long‐term effects on soil microbial properties of heavy metals from industrial exhaust deposition

Soil samples were taken at 0-10 cm and 10-20 cm depth from 7 clay-marsh sites used as grassland close to Nordenham in the north of Lower Saxony, Germany. The sites had been contaminated by deposition of heavy metals from industrial exhausts, the level of contamination varying according to their distances from a lead factory. The soils were analyzed to assess the depth-specific effects of NH 4 NO 3 extractable and total amounts of Zn, Pb, and Cu on basal respiration, adenylates, ergosterol, and biomass C estimated by fumigation extraction (FE) and substrate-induced respiration (SIR). Most of the chemical and biological properties studied decreased with depth, but depth-specific differences in the relationships between these properties rarely occurred. The biomass C/soil organic C ratio was at a relatively high level, but most consistently reflected pollution as a decrease with increasing heavy metal load, independently of the method used for biomass C estimation. However, the SIR estimates were on average 44 % lower than those of FE, mainly due to pH effects. The metabolic quotient SIR- q CO 2 increased with increasing NH 4 NO 3 extractable and total heavy metal contents, but also with decreasing pH, whereas the FE- q CO 2 remained unaffected by heavy metals and pH. The ATP/FE-biomass C ratio was on average 8.2 μmol g -1 and negatively affected by soil pH, but also by total Zn, NH 4 NO 3 extractable Zn and Cu. The ergosterol/FE-biomass C ratio was on average 0.29 %, i.e. at a very low level, and increased with increasing heavy metal content. This indicates a change in the community structure towards fungi.

Slurry 15NH4-N recovery in herbage and soil: effects of application method and timing.

The effects of slurry application method and weather conditions after application on ammonia volatilisation are well documented, however, the effect on slurry N recovery in herbage is less evident due to large variability of results. The objective of this field experiment was to determine the recovery of cattle slurry NH4-N in herbage and soil in the year of application as affected by application method (trailing shoe versus broadcast) and season of application (spring versus summer), using 15N as a tracer. In 2007 and 2008, 15N enriched slurry was applied on grassland plots. N recovery in herbage and soil during the year of application was determined. Both spring and trailing shoe application resulted in significantly higher herbage DM yields, N uptake and an increased recovery of 15NH4-N in herbage. Additionally, the recovery of slurry 15NH4-N in the soil at the end of the growing season was increased. Spring and trailing shoe application reduced the losses of slurry 15NH4-N by on average 14 and 18 percentage points, respectively, which corresponded closely to ammonia volatilisation as predicted by the ALFAM model. It was concluded that slurry N recovery in temperate pasture systems can be increased by adjusting the slurry application method or timing.

Combined 13C and 15N isotope analysis on small samples using a near‐conventional elemental analyzer/isotope ratio mass spectrometer setup

RATIONALE A high sensitivity elemental analyzer/isotope ratio mass spectrometer setup was developed to allow analysis of (13)C and (15)N isotopic composition on microgram amounts of C and N, respectively. METHODS Increased sensitivity of a conventional elemental analyzer equipped with a low blank autosampler was obtained by decreased carrier gas flow of 35 mL/min. The diameters of the oxidation and reduction reactors and water trap were reduced to 7.8, 7.8 and 4 mm i.d., respectively, to obtain sharp sample peaks in the mass spectrometer. To increase the lifetime of the reduction reactor, a 1:1 He/O2 mixture was used as oxidizing agent in the elemental analyzer. RESULTS Sample amounts of 0.6 µg N and 1 µg C were sufficient for accurate isotopic analysis with <1 ‰ standard error after blank correction. One major advantage of the setup is the easy switching between conventional EA and μEA as only consumable parts need to be exchanged. CONCLUSIONS The proposed setup proved to be suitable to analyze minute amounts of C and N in one analytical run simultaneously.