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

Abstract

Rhizosphere soil was sampled in monocultures of Lolium perenne and Trifolium repens in June and October 2002, at two different nitrogen fertilisation levels (14 and 56 g N m(-2) year(-1)) and under two pCO(2) atmospheres (360 and 600 ppmv) at the Swiss FACE (Free Air Carbon dioxide Enrichment) site. Directly extracted soil DNA was analysed with restriction fragment length polymorphism (PCR-RFLP) by use of degenerated primers for the narG gene encoding the active site of the membrane-bound nitrate reductase. The corresponding enzyme activity of the nitrate reductase was determined colorimetrically after 24 h of anaerobic incubation. The narG PCR-RFLP fingerprints showed that the structure of the nitrate-reducing community was primarily affected by season and pH of the sampling site, whereas CO(2) enrichment, plant species or fertiliser treatment had no apparent effect. In contrast, the nitrate reductase activity responded to N fertilisation, CO(2) enrichment and plant species in October, whereas in June drought stress most likely kept the enzyme activity at a low level in all treatments. Apparently, the respiratory nitrate-reducing community adapted to different treatments primarily by altered enzyme activity.

Activity and Composition of the Denitrifying Bacterial Community Respond Differently to Long-Term Fertilization

“…We hypothesize that the long-term fertilization effect was, at least partially, attributable to an indirect effect by soil acidification, which has resulted in a selection of bacteria adapted to low pH after 20 years of fertilization with acid generating ammonium salts also suggest this. Recently, it has been shown that pH can affect the composition of the denitrifying communities in soil (9). However, no strong relationship between soil pH and the measurements of microbial activity was observed in our study.…”

“…All sequences from the specific RFLP pattern types (9,14,16,19) in the clone library from soil fertilized with (NH 4 ) 2 SO 4 (D) clustered together in the phylogram (Fig. 4).…”

“…The NosZ tree was constructed with sequences from 18 pure cultures and 18 soil clones (18,27,28,30,35) and the 47 sequences from this study. The NarG tree contains sequences from 18 pure cultures, 16 soil clones (7,9,18,25), and 46 sequences from this study.…”

Nitrogen fertiliser rate affects the frequency of nitrate-dissimilating Pseudomonas spp. in the rhizosphere of Lolium perenne grown under elevated pCO2 (Swiss FACE)

“…Various studies have shown that potential denitrifying enzyme activity may be stable or decrease (Hungate et al, 1997;Barnard et al, 2004), whereas N 2 O emissions may increase (Arnone and Bohlen, 1998;Baggs et al, 2003a,b) for herbaceous systems under elevated pCO 2 . Little is known about the response of microorganisms involved in denitrification (Roussel-Delif et al, in press;Deiglmayr et al, 2004), partly because of the widespread ability to denitrify, and functional differences among denitrifying microorganisms make it difficult to relate denitrification activity to soil microbial communities (Cavigelli and Robertson, 2001). Roussel-Delif et al (in press) recently showed that the frequency of root-associated nitrate-dissimilating Pseudomonas (NDP) in low fertilised (14 g N m K2 y K1 ) L. perenne swards was increased under elevated pCO 2 , suggesting that increased pCO 2 provided favourable conditions for the dissimilation of nitrate and related organisms.…”

Doğal Meralanrdan Toplanan Ak Üçgül (Trifolium repens L.) Genotiplerinin Performanslarının Belirlenmesi

“…This method also better predictor of similarities or dissimilarities (Marilley 1999;Hebeisen 1997;Deiglmayr 2006;Caradus 1986;Caradus 1992). Table 3 show that describing more than 70%, cumulative percent plant characteristics should be examined in five groups (Eigen value: 1,1254, proportion:0,080,cumulative percent: 76,1%).…”