Differences between wheat cultivars in acquisition and utilization of phosphorus

In an attempt to evaluate whether breeding and selection for high yielding capacity changed the P requirement of modem wheat cultivars. the response of two wheat cultivars to different levels of P supply was investigated. A traditional cultivar (‘Peragis’) and a modern spring-wheat cultivar (‘Cosir’) were cultivated in a C-loess low in available P and high in CaCO₃ in 120 cm high PVC tubes. In addition and for comparison, nutrient solution experiments were also conducted. Shoot growth, root growth. P uptake. P translocation and P distribution within the shoot at different developmental stages were compared. The grain yield of the modern cultivar ‘Cosir’ was higher at limiting and non-limiting P supply and. therefore, this cultivar can be considered as more P-efficient than the traditional cultivar. Grain yield reduction at low P supply was mainly due to an inhibition of tillering and thus lower number of ears per plant, whereas the number of grains per ear was hardly affected. Reduced tillering at low P supply could not be related to P concentrations in the shoot meristematic tissues which were generally much higher than in other plant tissues and kept at an elevated level even at limiting P supply. Root branching (1^st order laterals) was reduced at limiting P supply in ‘Cosir’ but not in ‘Peragis’ which, generally, had lower numbers of laterals at the beginning of tillering. From the results it can be concluded that the main factors contributing to the higher P efficiency of the modern cultivar ‘Cosir’ are (i) efficient use of assimilates for root-growth characteristics which enhance P acquisition: enhanced root branching and thus smaller mean root diameter and longer root hairs, (ii) an efficient P uptake system, (iii) efficient remobilization of P from vegetative plant organs to the grains, and most importantly (iv) lower P requirement for grain yield formation because of lower ear number per plant but higher grain number per ear.     

Oxygen profiles and methane turnover in a flooded rice microcosm

Summary Dissolved O₂ was depleted within the top 3.5-mm surface layer of flooded rice soil microcosms without plants. In planted microcosms, however, O₂ was detectable down to at least 40 mm in depth. O₂ concentrations in the uppermost soil layers of microcosms with rice plants were higher in the light than in the dark, indicating O₂ production by photosynthesis. The CH₄ emission rates were nearly identical for illuminated and for darkened microcosms, demonstrating that the photosynthetically produced O₂ did not increase CH₄ oxidation in the rhizosphere. In contrast, CH₄ emission rates increased when the microcosms were incubated under an N₂ atmosphere, indicating that transport of O₂ from the atmosphere into the rhizosphere was important for CH₄ oxidation. CH₄ emission under air accounted for only 10%–20% of the cumulative CH₄ production determined in cores taken from the microcosms. Apparently, 80%–90% of the CH₄ produced was oxidized in the rhizosphere and thus was not emitted.     

Root growth and N‐uptake activity of oilseed rape (Brassica napus L.) cultivars differing in nitrogen efficiency

Nitrate‐N uptake from soil depends on root growth and uptake activity. However, under field conditions N‐uptake activity is difficult to estimate from soil‐N depletion due to different loss pathways. We modified the current mesh‐bag method to estimate nitrate‐N‐uptake activity and root growth of two oilseed‐rape cultivars differing in N‐uptake efficiency. N‐efficient cultivar (cv.) ‘Apex' and N‐inefficient cv. ‘Capitol' were grown in a field experiment on a silty clayey gleyic fluvisol near Göttingen, northern Germany, and fertilized with 0 (N₀) and 227 (N₂₂₇) kg N ha^–1. In February 2002, PVC tubes with a diameter of 50 mm were installed between plant rows at 0–0.3 and 0–0.6 m soil depth with an angle of 45°. At the beginning of shooting, beginning of flowering, and at seed filling, the PVC tubes were substituted by PVC tubes (compartments) of the same diameter, but with an open window at the upper side either at a soil depth of 0–0.3 or 0.3–0.6 m allowing roots to grow into the tubes. Anion‐exchange resin at the bottom of the compartment allowed estimation of nitrate leaching. The compartments were then filled with root‐free soil which was amended with or without 90 mg N (kg soil)^–1. The newly developed roots and nitrate‐N depletion were estimated in the compartments after the installing period (21 d at shooting stage and 16 d both at flowering and grain‐filling stages). Nitrate‐N depletion was estimated from the difference between NO ‐N contents of compartments containing roots and control compartments (windows closed with a membrane) containing no roots. The amount of nitrate leached from the compartments was quantified from the resin and has been taken into consideration in the calculation of the N depletion. The amount of N depleted from the compartments significantly correlated with root‐length density. Suboptimal N application to the crop reduced total biomass and seed‐yield formation substantially (24% and 38% for ‘Apex’ and ‘Capitol’, respectively). At the shooting stage, there were no differences in root production and N depletion from the compartments by the two cultivars between N₀ and N₂₂₇. But at flowering and seed‐filling stages, higher root production and accordingly higher N depletion was observed at N₀ compared to N₂₂₇. Towards later growth stages, the newly developed roots were characterized by a reduction of root diameter and a shift towards the deeper soil layer (0.3–0.6m). At low but not at high N supply, the N‐efficient cv. ‘Apex’ exhibited higher root growth and accordingly depleted nitrate‐N more effectively than the N‐inefficient cv. ‘Capitol’, especially during the reproductive growth phase. The calculated nitrate‐N‐uptake rate per unit root length was maximal at flowering (for the low N supply) but showed no difference between the two cultivars. This indicated that the higher N‐uptake efficiency of cv. ‘Apex’ was due to higher root growth rather than higher uptake per unit of root length.     

Impact of litter quality on mineralization processes in managed and abandoned pasture soils in Southern Ecuador

Tropical regions are currently undergoing remarkable rates of land use change accompanied by altered litter inputs to soil. In vast areas of Southern Ecuador forests are clear cut and converted for use as cattle pastures. Frequently these pasture sites are invaded by bracken fern, when bracken becomes dominant pasture productivity decreases and the sites are abandoned. In the present study implications of invasive bracken on soil biogeochemical properties were investigated. Soil samples (0-5 cm) were taken from an active pasture with Setaria sphacelata as predominant grass and from an abandoned pasture overgrown by bracken. Grass (C₄ plant) and bracken (C₃ plant) litter, differing in C:N ratio (33 and 77, respectively) and lignin content (Klason-lignin: 18% and 45%, respectively), were incubated in soils of their corresponding sites and vice versa for 28 days at 22 °C. Unamended microcosms containing only the respective soil or litter were taken as controls. During incubation the amount of CO₂ and its δ¹³C-signature were determined at different time intervals. Additionally, the soil microbial community structure (PLFA-analysis) as well as the concentrations of KCl-extractable C and N were monitored. The comparison between the control soils of active and abandoned pasture sites showed that the massive displacement of Setaria-grass by bracken after pasture abandonment was characterized by decreased pH values accompanied by decreased amounts of readily available organic carbon and nitrogen, a lower microbial biomass and decreased activity as well as a higher relative abundance of actinomycetes. The δ¹³C-signature of CO₂ indicated a preferential mineralization of grass-derived organic carbon in pasture control soils. In soils amended with grass litter the mineralization of soil organic matter was retarded (negative priming effect) and also a preferential utilization of easily available organic substances derived from the grass litter was evident. Compared to the other treatments, the pasture soil amended with grass litter showed an opposite shift in the microbial community structure towards a lower relative abundance of fungi. After addition of bracken litter to the abandoned pasture soil a positive priming effect seemed to be supported by an N limitation at the end of incubation. This was accompanied by an increase in the ratio of Gram-positive to Gram-negative bacterial PLFA marker. The differences in litter quality between grass and bracken are important triggers of changes in soil biogeochemical and soil microbial properties after land use conversion.     

Analysis of volatile compounds and triglycerides of seed oils extracted from different poppy varieties (Papaver somniferum L.)

Poppy seed oil (Oleum Papaveris Seminis) is used for culinary and pharmaceutical purposes, as well as for making soaps, paints, and varnishes. Astonishingly, hardly anything was yet known about the volatile compounds of this promising comestible. Likewise, there are no current published data about the triglyceride (TAG) composition of poppy seed oils available. In this investigation solid-phase microextraction (SPME) with DVB/Carboxen/PDMS Stable-Flex fiber was applied to the study of volatile compounds of several seed oil samples from Papaver somniferum L. (Papaveraceae). 1-Pentanol (3.3-4.9%), 1-hexanal (10.9-30.9%), 1-hexanol (5.3-33.7%), 2-pentylfuran (7.2-10.0%), and caproic acid (2.9-11.5%) could be identified as the main volatile compounds in all examined poppy seed oil samples. Furthermore, the TAG composition of these oils was analyzed by MALDI-ReTOF- and ESI-IT-MS/MS. The predominant TAG components were found to be composed of linoleic, oleic, and palmitic acid, comprising approximately 70% of the oils. TAG patterns of the different poppy varieties were found to be very homogeneous, showing also no significant differences in terms of the applied pressing method of the plant seeds.     

Soil‐carbon turnover under different crop management: Evaluation of RothC‐model predictions under Pannonian climate conditions

Despite the importance of soil organic matter (SOM), very few long‐term data concerning soil organic‐C dynamics are available for calibrating and evaluating C models. The long‐term ¹⁴C‐turnover field experiment, established in 1967 in Fuchsenbigl, Lower Austria, offers the unique opportunity to follow the fate of labeled C under different crop‐management systems (bare fallow, spring wheat, crop rotation) over a period of more than 35 y. Compared with the crop‐rotation and spring‐wheat treatments, the decline of total organic C was largest in the bare‐fallow treatments, because no significant C input has occurred since 1967. Nonetheless, the decline was not as fast as predicted with the original RothC‐26.3‐model decomposition rate constants. In this work, we therefore calibrated the Roth‐C‐26.3 model for the Pannonian climatic region based on the field‐experiment results. The main adjustment was in the decomposition rate constant for the humified soil C pool (HUM), which was set to 0.009 instead of 0.02 y^–1 as determined in the original Rothamsted field trial. This resulted in a higher HUM pool in the calibrated model because of a longer turnover period (111 vs. 50 y). The modeled output based on the calibrated model fitted better to measured values than output obtained with the original Roth‐C‐26.3‐model parameters. Additionally, the original decomposition rate constant for resistant plant material (RPM) was changed from 0.3 to 0.6 y^–1 to describe the decomposition of ¹⁴C‐labeled straw more accurately. Application of the calibrated model (modified HUM decomposition rate) to simulate removal of crop residues showed that this can entail a long‐term decline of SOM. However, these impacts are strongly dependent on the crop types and on environmental conditions at a given location.     

Phytoextraction of Cadmium and Phytostabilisation with Mugwort (Artemisia vulgaris)

Artemisia vulgaris (mugwort) is a tall (1.0?C2.0 m) high biomass perennial herb which accumulates considerable amounts of metals on contaminated sites. An outdoor pot experiment was conducted on a sandy, slightly alkaline soil of moderate fertility to study the uptake of cadmium and the distribution of Cd in plant tissues of A. vulgaris. Cadmium was applied as CdCl₂ (a total of 1 l solution of 0, 10, 50 and 100 mg Cd l^?1) to 12-l pots with a height of 25 cm. HNO₃- and water-extractable concentrations of Cd were correlated with the applied Cd at 2-cm soil depth, but were not correlated at 20-cm soil depth, suggesting that Cd was either not mobile in the soil or completely taken up by mugwort roots. The Cd concentrations in different organs of A. vulgaris and litter increased with increasing soil contamination. Leaf/soil concentration ratios (BCFs) up to 65.93?±?32.26 were observed. Translocation of Cd to the aboveground organs was very high. The leaf/root Cd concentration ratio (translocation factor) ranged from 2.07?±?0.56 to 2.37 ± 1.31; however, there was no correlation of translocation factors to Cd enrichment, indicating similar translocation upon different soil contamination levels. In summary, A. vulgaris is tolerant to the metal concentrations accumulated, has a high metal accumulating biomass and accumulates Cd up to about 70% in the aboveground parts. Both a high phytoextraction potential and a high value for phytostabilisation would recommend mugwort for phytoremediation.