ABSTRACT

Rice root exudates can control nitrification by releasing biological nitrification inhibitors (BNIs), reducing nitrogen losses in agricultural soils. However, the inhibitory effect on nitrification and the abundance of ammonia oxidisers in different soil types remain unclear. Two temperate paddy soils with different organic matter contents were collected to investigate the impact on nitrification rates of two rice cultivar root exudates, El Paso 144 (O. sativa ssp. indica) and Tacuarí (O. sativa spp. japonica). Root exudates were extracted before the tillering growth stage, and their BNI potential was evaluated in a bioassay with luminescent Nitrosomonas europaea and in a 12-day soil microcosm incubation. While exudates from Tacuarí showed stronger BNI activity in the bioassay, its nitrification inhibition in both soils was similar to that of DCD. El Paso did not show BNI activity in Salto whose organic matter content was higher. The abundance of ammonia oxidisers was not affected by root exudates or DCD, but only ammonia-oxidising bacteria had a significant positive relationship with soil nitrate. Our results demonstrated that although the bioassay showed high BNI activity, its expression in soils varied depending on the rice cultivar and the type of soil, particularly with its organic matter content.

摘要

水稻根系分泌物可以通过释放生物硝化抑制剂 (BNI) 来控制硝化作用，减少农业土壤中的氮损失。然而，不同土壤类型对硝化作用的抑制作用和氨氧化剂的丰度尚不清楚。收集了两种具有不同有机质含量的温带水稻土，以研究两种水稻品种根系分泌物 El Paso 144 ( O. sativa ssp. indica ) 和 Tacuarí ( O. sativa spp. japonica )对硝化速率的影响。在分蘖生长阶段之前提取根系分泌物，并在发光的Nitrosomonas europaea生物测定中评估其 BNI 潜力并在为期 12 天的土壤微观孵化中。虽然 Tacuarí 的渗出液在生物测定中显示出更强的 BNI 活性，但其在两种土壤中的硝化抑制作用与 DCD 相似。埃尔帕索在有机质含量较高的萨尔托中没有表现出 BNI 活性。氨氧化菌的丰度不受根系分泌物或 DCD 的影响，但只有氨氧化菌与土壤硝酸盐呈显着正相关。我们的结果表明，虽然生物测定显示出高 BNI 活性，但其在土壤中的表达因水稻品种和土壤类型而异，尤其是其有机质含量。