有机肥活化土壤中磷的微生物学机理

在好气条件下，猪粪和纤维素对两种水稻土中的磷均能起活化作用，嫌气条件下，尽管猪粪和纤维素均能克服因嫌气而使土壤微生物数量的减少，但促进土壤固磷成为主要矛盾，因而显著降低土壤有效磷。通过微生物对难溶性Ｃａ＿３（ＰＯ４）＿２的溶磷量及培养基总酸度的测定，发现这些微生物具有转化难溶性磷为可溶性磷的能力，属溶磷微生物并有致酸作用。经相关分析，土壤中活化的磷量、微生物数量、培养基中的溶磷量和总酸度之间均存在看显著或极显著的相关关系，其中以总酸度与其它变量间的关系最好。因此，在好气条件下有机肥活化土壤中磷的机理可描述为：有机肥促进土壤微生物增长→微生物对其生长的局部位置的土壤起酸化作用→酸溶解难溶性磷为可溶性磷。     

Influence of inoculation with arbuscular mycorrhizal fungi on stable isotopes of nitrogen in Phaseolus vulgaris

The interactions between Phaseolus vulgaris, Rhizobium spp. strains nodulating P. vulgaris, and arbuscular mycorrhizal (AM) fungi were assessed under greenhouse conditions in a nonsterilized Typic Haplustalf soil from Cauca, Colombia. Our results indicate a specific involvement of AM fungal species in nitrogen acquisition by the legume plants from symbiotic nitrogen fixation and from soil. A significant specific influence of inoculation with Glomus spp. on the ¹⁵N/¹⁴N ratio in plant shoots was dependent on the inoculated rhizobial strain, but AM fungal inoculation had no significant effect on shoot dry weight or nodule occupancy in the two different rhizobial strain treatments. The results imply that in low P soils the effects of an improved mycorrhizal symbiosis may include improved symbiotic N₂ fixation efficiency and/or improved soil N uptake. Received: 11 May 1996     

Das Potential von Apfel-Birne-Hybriden für die Kernobstzüchtung

Hybrids of apple and pear have been bred and described before, however no vital and fertile ones were found which could have been used for pome fruit breeding. Lately, the authors studied the putative hybrid bred by M. Zwintzscher in the eighties at genetic, physiological, and phenotypical levels and found it to be a true hybrid. Unlike other reports on such hybrids, this one allowed breeder H. Schimmelpfeng in the nineties to yield an offspring of five F2 plants from it as maternal plant. The F2 plants are meanwhile flowering and regularly set fruits. Three of the sister F2 lines seem to possess potential as cultivars. These vital and fertile hybrids offer the opportunity to combine various parts of the pear genome with the apple genome by classical breeding, introducing new genetic factors into the latter and enabling breeding with these. With such partial genomes of pear non-host-resistances of pear against specific apple pathogens like apple scab (Venturia inaequalis) or new genes for biosynthesis of aroma compounds could be introduced by crosses. A new project to establish such a F3 generation is presented here.     

Towards Enhancement of Early‐Stage Chilling Tolerance and Root Development in Sorghum F1 Hybrids

Sorghum (Sorghum bicolor L. Moench) is regarded a drought‐tolerant alternative to maize as a bioenergy and fodder crop, but its early‐stage chilling sensitivity is obstructing a successful implementation in temperate areas. While several studies have identified quantitative trait loci (QTL) underlying chilling tolerance‐related traits in sorghum lines, little is known about the inheritance of these traits in F₁ hybrids. We have conducted a comprehensive approach to analyse heterosis, combining ability and the relation between line per se and hybrid performance for emergence and early shoot and root development comprising both field trials and controlled environment experiments including chilling tests. To our best knowledge, this is the first study analysing heterosis for sorghum root parameters under chilling. Our results show that most traits are heterotic and that the mid‐parent values are rather poor predictors of hybrid performance. Hybrid breeding programmes should focus on efficient GCA tests and the establishment of genetically diverse pools to maximise heterosis rather than on a too strict selection among lines based on their per se performance. The medium‐to‐high heritabilities estimated for seedling emergence and juvenile biomass suggest that a robust breeding progress for these complex traits is feasible.     

Canopy leaching of cations in Central European forest ecosystems – a regional assessment

The leaching of Ca, Mg, and K from canopies is a major pathway of these cations into forest soils. Our aim was to quantify rates of canopy leaching and to identify driving factors at the regional scale using annual fluxes of bulk precipitation and throughfall from 37 coniferous and deciduous forests of North and Central Europe. Total deposition of Ca, Mg, K, and H⁺ was estimated with Na as an index cation. The median canopy leaching increased in the order: Mg (0.11 kmol_c ha^–1 a^–1) < Ca (0.31 kmol_c ha^–1 a^–1) < K (0.39 kmol_c ha^–1 a^–1). Canopy leaching of Ca and K was positively correlated with the calculated total H⁺ deposition and H⁺ buffered in the canopy, whereas canopy leaching of Mg was not. With contrasting effects, fluxes of SO₄‐S and NH₄‐N in throughfall explained to 64 % (P<0.001) of the Ca canopy leaching. Fluxes of NH₄‐N and Ca were negatively correlated, suggesting that buffering of H⁺ by NH₃ deposition reduced canopy leaching of Ca. Amount of bulk precipitation and SO₄‐S in throughfall were identified as much weaker driving factors for canopy leaching of K (r²=0.28, P<0.01). Our results show that Ca is the dominant cation in buffering the H⁺ input in the canopy. At the regional and annual scale, canopy leaching of Mg appears to be unaffected by H⁺ deposition and H⁺ buffering in the canopy.     

Repeated freeze–thaw events affect leaching losses of nitrogen and dissolved organic matter in a forest soil

Freezing and thawing may substantially influence the rates of C and N cycling in soils, and soil frost was proposed to induce NO losses with seepage from forest ecosystems. Here, we test the hypothesis that freezing and thawing triggers N and dissolved organic matter (DOM) release from a forest soil after thawing and that low freezing temperatures enhance the effect. Undisturbed soil columns were taken from a soil at a Norway spruce site either comprising only O horizons or O horizons + mineral soil horizons. The columns were subjected to three cycles of freezing and thawing at temperatures of –3°C, –8°C, and –13°C. The control columns were kept at constant +5°C. Following the frost events, the columns were irrigated for 20 d at a rate of 4 mm d^–1. Percolates were analyzed for total N, mineral N, and dissolved organic carbon (DOC). The total amount of mineral N extracted from the O horizons in the control amounted to 8.6 g N m^–2 during the experimental period of 170 d. Frost reduced the amount of mineral N leached from the soil columns with –8°C and –13°C being most effective. In these treatments, only 3.1 and 4.0 g N m^–2 were extracted from the O horizons. Net nitrification was more negatively affected than net ammonification. Severe soil frost increased the release of DOC from the O horizons, but the effect was only observed in the first freeze–thaw cycle. We found no evidence for lysis of microorganisms after soil frost. Our experiment did not confirm the hypothesis that soil frost increases N mineralization after thawing. The total amount of additionally released DOC was rather low in relation to the expected annual fluxes.     

Flavor of Cereal Products—A Review

The review is focused on studies presenting quantitative data and odor activity values (ratio of concentration to odor threshold) of key odorants in bread (wheat and rye), toasted bread, puff pastries made with different fats, fragrant and nonfragrant rices, sweet corn, popcorn, and tortillas. The influence of raw materials, processing parameters, and storage conditions on the concentrations of key odorants and some data on flavor precursors and formation pathways of these compounds are discussed.