Suppression of nitrification and nitrous oxide emission by the tropical grass Brachiaria humidicola

Ishikawa, Takayuki; Subbarao, G. V.; Ito, Osamu; Okada, Kensuke

doi:10.1007/978-94-017-2923-9_40

Cited by 32 publications

(40 citation statements)

References 23 publications

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“…Based on empirical studies that involved monitoring of soil nitrification following B. humidicola cultivation, we had earlier proposed the possible existence of BNI in B. humidicola (Ishikawa et al 2003). Field surveys in the past have reported low levels of NO 3 -in B. humidicola fields (Sylvester-Bradley et al 1988).…”

Section: Discussionmentioning

confidence: 97%

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A bioluminescence assay to detect nitrification inhibitors released from plant roots: a case study with Brachiaria humidicola

et al. 2006

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A bioluminescence assay using recombinant Nitrosomonas europaea was adopted to detect and quantify natural nitrification inhibitors in plant-soil systems. The recombinant strain of N. europaea produces a distinct two-peak luminescence due to the expression of luxAB genes, introduced from Vibrio harveyi, during nitrification. The bioluminescence produced in this assay is highly correlated with NO 2 -production (r 2 = 0.94). Using the assay, we were able to detect significant amounts of a nitrification inhibitor produced by the roots of Brachiaria humidicola (Rendle) Schweick. We propose that the inhibitory activity produced/released from plants be termed 'biological nitrification inhibition' (BNI) to distinguish it from industrially produced inhibitors. The amount of BNI activity produced by roots was expressed in units defined in terms of the action of a standard inhibitor allylthiourea (AT). The inhibitory effect from 0.22 lM AT in an assay containing 18.9 mM of NH 4 + is defined as one AT unit of activity. A substantial amount of BNI activity was released from the roots of B. humidicola (15-25 AT unit g -1 root dry wt day -1 ). The BNI activity released was a function of the growth stage and N content of the plant. Shoot N levels were positively correlated with the release of BNI activity from roots (r 2 = 0.76). The inhibitor/s released from B. humidicola roots suppressed soil nitrification. Additions of 20 units of BNI per gram of soil completely inhibited NO 3 -formation in a 55-day study and remained functionally stable in the soil for 50 days. Both the ammonia monooxygenase and the hydroxylaminooxidoreductase enzymatic pathways in Nitrosomonas were effectively blocked by the BNI activity released from B. humidicola roots. The proposed bioluminescence assay can be used to characterize and determine the BNI activity of plant roots, thus it could become a powerful tool in genetically exploiting the BNI trait in crops and pastures.

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Section: Discussionmentioning

confidence: 97%

“…b. To verify the nitrification inhibitory potential of root exudate of Brachiaria humidicola, a tropical grass grown extensively in South America and Africa (Sylvester-Bradley et al 1988;Ishikawa et al 2003). c. To evaluate the affects of physiological factors, such as plant N and growth stage on the release of BNI activity from the roots of B. humidicola.…”

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A bioluminescence assay to detect nitrification inhibitors released from plant roots: a case study with Brachiaria humidicola

et al. 2006

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“…Such activity has been reported for the tropical pasture grass, Brachiaria humidicola (Ishikawa et al 2003;Subbarao et al 2006bSubbarao et al , 2007a. Synthesis and release of BNIs from plant roots is a highly regulated plant attribute.…”

Section: Introductionmentioning

confidence: 95%

Free fatty acids from the pasture grass Brachiaria humidicola and one of their methyl esters as inhibitors of nitrification

et al. 2008

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The tropical pasture grass, Brachiaria humidicola (Rendle) Schweick, produces nitrification inhibitory compounds (termed biological nitrification inhibitors or BNIs) in its shoot and root tissues and releases BNIs from its roots. In the present study, two BNI compounds were isolated and identified from the shoot tissue of B. humidicola using activity-guided fractionation. The recombinant Nitrosomonas europaea containing luxAB genes derived from the bioluminescent marine gram-negative bacterium Vibrio harveyi, were used to determine BNI activity. The BNI compounds in the shoot tissue were identified as linoleic acid (LA) and linolenic acid (LN) using authenticchemicals obtained from ©Sigma (ED 80 16.0 μg ml −1 for both LA and LN) for verification. None of the other tested free fatty acids namely stearic acid, oleic acid, arachidonic acid, and cis-vaccenic acid showed any inhibitory effect on nitrification. Among the fatty acid methyl esters (FAME) evaluated [methyl oleate, methyl linoleate (LA-ME) and methyl linoleneate (LN-ME)], only LA-ME showed an inhibitory effect (ED 80 8.0 μg ml −1 ). The inhibitory effect of LA, LN and LA-ME in the soil was stable for 120 days at 20°C. Soil treated with LA, LN and LA-ME showed a very low accumulation of NO 3 − and the maintenance of soil inorganic N in the NH 4 + form. The inhibitory effect of LA-ME on soil nitrification was greater than that of LA or LN. In addition to BNI activity, both LA and LA-ME showed a suppressive effect on urea hydrolysis in soil. Both LA and LN blocked the AMO (ammonia monooxygenase) and HAO (hydroxylamino oxidoreductase) enzymatic pathways in Nitrosomonas. Since LA and LN can be produced from vegetable oils such as soybean, flax or sunflower, they have the potential for use as nitrification inhibitors in production agriculture.

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“…For example, certain grassland species have been proposed to have an inhibitory effect on soil nitrification (Ishikawa et al 2003;Lata et al 2004; see review Subbarao et al 2006a). Recent research has shown that certain tropical pasture grasses such as Brachiaria humidicola possess the ability to release chemical compounds from roots that suppress soil nitrification, and this attribute is termed biological nitrification inhibition (BNI) (Subbarao et al 2006b).…”

Section: Introductionmentioning

confidence: 98%

NH 4 + triggers the synthesis and release of biological nitrification inhibition compounds in Brachiaria humidicola roots

et al. 2006

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The release of chemical compounds from plant roots that suppress soil nitrification is termed biological nitrification inhibition (BNI). Determining the environmental factors that control the synthesis and release of BNI-compounds from Brachiaria humidicola (Rendle) Schweick, a tropical pasture grass that thrives on acid soils, is the focus of this investigation. Because the BNI trait is related to the N status of the plant, we investigated the possibility that the expression of this trait would be related to the forms of N found in the root environment. Plants were grown with two sources of N, NH 4 + or NO 3 -for 60 days and the release of BNI-compounds monitored. Only plants grown with NH 4 + released BNI-compounds from roots. The presence of NH 4 + and possibly the secondary effect of its uptake (i.e., acidic pH) in the root environment significantly enhanced the release of BNI-compounds. Both the NH 4 + and NO 3 -grown plants responded to the stimulus from NH 4 + in the root environment. BNI-compounds found in root tissue and their release were nearly three times greater in NH 4 + grown than from NO 3 -grown plants. The BNI-compounds released from roots composed of at least three active components-Type-I (stable to pH changes from 3.0 to 10), Type-II (temporarily loses its inhibitory effect at a pH higher than a threshold pH of 4.5 and the inhibitory effect is reestablished when the root exudate pH is adjusted to <4.5) and Type-III (inhibitory effect is irreversibly lost if the pH of the root exudate reaches 10.0 or above). A major portion of BNI-compounds released in the presence of NH 4 + is of Type-I. In the absence of NH 4 + , mostly Type-II and Type-III BNI-compounds were released. The BNI-compounds inhibited the function of Nitrosomonas europaea through the blocking of both ammonia monooxygenase and hydroxylamino oxidoreductase pathways. These results indicate that the release of BNIcompounds from B. humidicola roots is a regulated function and that presence of NH 4 + in the root environment is necessary for the sustained synthesis and release of BNI.

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Suppression of nitrification and nitrous oxide emission by the tropical grass Brachiaria humidicola

Cited by 32 publications

References 23 publications

A bioluminescence assay to detect nitrification inhibitors released from plant roots: a case study with Brachiaria humidicola

A bioluminescence assay to detect nitrification inhibitors released from plant roots: a case study with Brachiaria humidicola

Free fatty acids from the pasture grass Brachiaria humidicola and one of their methyl esters as inhibitors of nitrification

NH 4 + triggers the synthesis and release of biological nitrification inhibition compounds in Brachiaria humidicola roots

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