University of Hohenheim

About: University of Hohenheim is a education organization based out in Stuttgart, Germany. It is known for research contribution in the topics: Population & Soil water. The organization has 8585 authors who have published 16406 publications receiving 567377 citations.

Methane mitigation from ruminants using tannins and saponins

Abstract: MethanereductionontrulydegradedsubstratebasisOMD Organic matter digestibilityPSM Plant secondary metabolitesQSE Quillaja saponaria extractSCFAs Short-chain fatty acidsTP Total phenolsTT Total tanninsIntroductionThe ruminal methane production is a by-product of themicrobial digestive process and represents a loss of 2–12%of the feed energy. Furthermore, emission of methane isconsidered as one of the most important global environ-mental issues (IPCC 2001). Therefore, decreasing methaneproduction is desirable for reducing the greenhouse gasemission with improved efficiency of the digested energyutilization (Johnson and Johnson 1995). A previous reportby Kurihara et al. (1999) indicated that methane energy lossin cattle fed on tropical forage diets was higher than inthose fed on temperate forage diets, due to relative highlevels of fibre and lignin and a low level of non-fibrecarbohydrate in tropical forages. Also, the livestock indeveloping countries are predominantly maintained on ahigh-roughage diet with little or no concentrate resulting inincreased ruminal methanogenesis. Therefore, the use ofbrowse species containing secondary compounds as feedsupplement rich in plant secondary metabolites (PSM) forruminants in many parts of the tropics is increasing in orderto improve animal performance and reduce methane(Abdulrazak et al. 2000). Tannins and saponins constitutethe major classes of PSM that are currently under researchin a number of laboratories. The antimicrobial action andeffects on rumen fermentation of these compounds dependon their nature, activity and concentration in a plant or plant

Root-derived cytokinins as long-distance signals for NO3−-induced stimulation of leaf growth

Abstract: Leaf growth of many plant species shows rapid changes in response to alterations of the form and the level of N supply. In hydroponically-grown tomato (Lycopersicon esculentum L.), leaf growth was rapidly stimulated by NO(3)(-) application to NH(4)(+) precultured plants, while NH(4)(+) supply or complete N deprivation to NO(3)(-) precultured plants resulted in a rapid inhibition of leaf growth. Just 10 microM NO(3)(-) supply was sufficient to stimulate leaf growth to the same extent as 2 mM. Furthermore, continuous NO(3)(-) supply induced an oscillation of leaf growth rate with a 48 h interval. Since changes in NO(3)(-) levels in the xylem exudate and leaves did not correlate with NO(3)(-)-induced alterations of leaf growth rate, additional signals such as phytohormones may be involved. Levels of a known inhibitor of leaf growth, abscisic acid (ABA), did not consistently correspond to leaf growth rates in wild-type plants. Moreover, leaf growth of the ABA-deficient tomato mutant flacca was inhibited by NH(4)(+) without an increase in ABA concentration and was stimulated by NO(3)(-) despite its excessive ethylene production. These findings suggest that neither ABA nor ethylene are directly involved in the effects of N form on leaf growth. However, under all experimental conditions, stimulation of leaf growth by NO(3)(-) was consistently associated with increased concentration of the physiologically active forms of cytokinins, zeatin and zeatin riboside, in the xylem exudate. This indicates a major role for cytokinins as long-distance signals mediating the shoot response to NO(3)(-) perception in roots.

Phosphorus depletion and pH decrease at the root–soil and hyphae–soil interfaces of VA mycorrhizal white clover fertilized with ammonium

Abstract: summary To study phosphorus (P) depletion and soil pH changes at the root–soil interface (rhizosphere) and at the hyphaesoil interface, mycorrhizal and non-mycorrhizal white clover (Trifolium repens L.) plants were grown for 7 wk in two sterilized soils (Luvisol and Cambisol) in pots comprising five compartments: a central one for root growth, two adjacent compartments, separated from the central compartment by a nylon net of 30 μm mesh size, for growth of vesicular-arbuscular (VA) mycorrhizal [Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe] hyphae (hyphal compartments), and two outer compartments, separated from the hyphal compartments by a 0.45 μm membrane, which neither roots nor hyphae could penetrate (bulk soil compartments). Phosphorus was supplied as Ca(H2PO4)2 at a rate of 50 mg P kg−1 soil in the root compartment and 150 mg P kg−1 soil in the hyphal and bulk soil compartments. Nitrogen was supplied as (NH4)2SO4 at the rate of 300 mg N kg−1 soil uniformly to all compartments. In both soils, shoot dry weight and P uptake were much higher in mycorrhizal plants compared with non-mycorrhizal plants. Hyphae of VA mycorrhizal fungi contributed 70% (Cambisol) or 80% (Luvisol) to total P uptake of mycorrhizal plants. In the hyphal compartments, concentrations of both H2O-extractable soil P (Cambisol and Luvisol) and NaHCO3-extractable soil P (Luvisol) were decreased drastically. Soil P depletion profiles developed not only at the root-soil interface (rhizosphere), but also at the hyphae-soil interface and extended several millimetres from the hyphae surface into the soil. Likewise, the soil pH was decreased at the root-soil interface, in the hyphal compartment and also at the hyphae-soil interface. The results demonstrate that, similarly to roots, hyphae of VA mycorrhizal fungi have the ability to form a P depletion zone and a zone of altered pH in the adjacent soil. Thus, as well as at the root-soil interface, soil conditions at the hyphae–soil interface may also differ considerably from conditions in the bulk soil.