Phosphorus deficiency increases the argon-induced decline of nodule nitrogenase activity in soybean and alfalfa

2 tables 3 graph.International audienc

Mycorrhizas improve nitrogen nutrition of Trifolium repens after 8 yr of selection under elevated atmospheric CO2 partial pressure

• Altered environmental conditions may change populations of arbuscular mycorrhizal fungi and thereby affect mycorrhizal functioning. We investigated whether 8 yr of free-air CO2 enrichment has selected fungi that differently influence the nutrition and growth of host plants. • In a controlled pot experiment, two sets of seven randomly picked single spore isolates, originating from field plots of elevated (60 Pa) or ambient CO2 partial pressure (pCO2), were inoculated on nodulated Trifolium repens (white clover) plants. Fungal isolates belonged to the Glomus claroideum or Glomus intraradices species complex, and host plants were clonal micropropagates derived from nine genets. • Total nitrogen (N) concentration was increased in leaves of plants inoculated with fungal isolates from elevated-pCO2 plots. These isolates took up nearly twice as much N from the soil as isolates from ambient-pCO2 plots and showed much greater stimulation of biological N2 fixation. The morpho-species identity of isolates had a more pronounced effect on N2 fixation and on root length colonized than isolate identity. • We conclude that rising atmospheric pCO2 may select for fungal strains that will help their host plants to meet increased N demands

Structure and activity of the nitrate-reducing community in the rhizosphere of Lolium perenne and Trifolium repens under long-term elevated atmospheric pCO2

International audienc

The effect of phosphorus nutrition on the response of white clover (Trifolium repens L.) to elevated PCO2

The first results from the suiss FACE experiment showed a sink-limitation in the response of Lolium perene to elevated PCO2

Arbuscular mycorrhiza infection enhances the growth response of Lolium perenne to elevated atmospheric pCO2

Elevated atmospheric pCO2 increases the C‐availability for plants and thus leads to a comparable increase in plant biomass production and nutrient demand. Arbuscular mycorrhizal fungi (AMF) are considered to play an important role in the nutrient uptake of plants as well as to be a significant C‐sink. Therefore, an increased colonization of plant roots by AMF is expected under elevated atmospheric pCO2. To test these hypotheses, Lolium perenne L. plants were grown from seeds in a growth chamber in pots containing a silica sand/soil mixture for 9 weeks with and without inoculation with Glomus intraradices (Schenck and Smith). The growth response of plants at two different levels of N fertilization (1.5 or 4.5 mM) combined with ambient (35 Pa) and elevated atmospheric pCO2 (60 Pa) was compared. The inoculation with G. intraradices, the elevated atmospheric pCO2 and the high N fertilization treatment all led to an increased plant biomass production of 16%, 20% and 49%, respectively. AMF colonization and high N fertilization increased the plant growth response to elevated atmospheric pCO2; the plant growth response to high N fertilization was also increased by AMF colonization. The root/shoot ratio was reduced by high N fertilization or elevated atmospheric pCO2, but was not affected by AMF colonization. The unchanged specific leaf area indicated that if AMF colonization represented an increased C‐sink, this was fully covered by the plant. Elevated atmospheric pCO2 strongly increased AMF colonization (60%) while the high N fertilization had a slightly negative effect. AMF colonization neither improved the N nor P nutrition status, but led to an improved total P uptake. The results underline the importance of AMF for the response of grassland ecosystems to elevated atmospheric pCO

Arbuscular mycorrhiza infection enhances the growth response of Lolium perenne to elevated atmospheric pCO2

ISSN:1460-2431ISSN:0022-095

Response in the root and shoot zone of permanent grassland model ecosystem in a five years face experiment

Longterm response of L. perenne and T. repens and their competitive ability to elevated CO2 and N fertilisation

Rhizodeposition and the enhanced mineralization of 2,4-dichlorophenoxyacetic acid in soil from the Trifolium pratense rhizosphere

Enhanced biodegradation of organic xenobiotic compounds in the rhizosphere is frequently recorded although the specific mechanisms are poorly understood. We have shown that the mineralization of 2,4-dichlorophenoxyacetic acid (2,4-D) is enhanced in soil collected from the rhizosphere of Trifolium pratense[e.g. maximum mineralization rate=7.9 days-1 and time at maximum rate (t1)=16.7 days for 12-day-old T. pratense soil in comparison with 4.7 days-1 and 25.4 days, respectively, for non-planted controls). The purpose of this study was to gain a better understanding of the plant-microbe interactions involved in rhizosphere-enhanced biodegradation by narrowing down the identity of the T. pratense rhizodeposit responsible for stimulating the microbial mineralization of 2,4-D. Specifically, we investigated the distribution of the stimulatory component(s) among rhizodeposit fractions (exudates or root debris) and the influence of soil properties and plant species on its production. Production of the stimulatory rhizodeposit was dependent on soil pH (e.g. t1 for roots grown at pH 6.5 was significantly lower than for those grown at pH 4.4) but independent of soil inorganic N concentration. Most strikingly, the stimulatory rhizodeposit was only produced by T. pratense grown in non-sterile soil and was present in both exudates and root debris. Comparison of the effect of root debris from plant species (three each) from the classes monocotyledon, dicotyledon (non-legume) and dicotyledon (legume) revealed that legumes had by far the greatest positive impact on 2,4-D mineralization kinetics. We discuss the significance of these findings with respect to legume-rhizobia interactions in the rhizosphere