Ariosa Yoanna, Quesada Antonio, Aburto Juan, Carrasco David, Carreres Ramón, Leganés Francisco, Fernández Valiente Eduardo
Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain.
Appl Environ Microbiol. 2004 Sep;70(9):5391-7. doi: 10.1128/AEM.70.9.5391-5397.2004.
The distribution of nitrogenase activity in the rice-soil system and the possible contribution of epiphytic cyanobacteria on rice plants and other macrophytes to this activity were studied in two locations in the rice fields of Valencia, Spain, in two consecutive crop seasons. The largest proportion of photodependent N(2) fixation was associated with the macrophyte Chara vulgaris in both years and at both locations. The nitrogen fixation rate associated with Chara always represented more than 45% of the global nitrogenase activity measured in the rice field. The estimated average N(2) fixation rate associated with Chara was 27.53 kg of N ha(-1) crop(-1). The mean estimated N(2) fixation rates for the other parts of the system for all sampling periods were as follows: soil, 4.07 kg of N ha(-1) crop(-1); submerged parts of rice plants, 3.93 kg of N ha(-1) crop(-1); and roots, 0.28 kg of N ha(-1) crop(-1). Micrographic studies revealed the presence of epiphytic cyanobacteria on the surface of Chara. Three-dimensional reconstructions by confocal scanning laser microscopy revealed no cyanobacterial cells inside the Chara structures. Quantification of epiphytic cyanobacteria by image analysis revealed that cyanobacteria were more abundant in nodes than in internodes (on average, cyanobacteria covered 8.4% +/- 4.4% and 6.2% +/- 5.0% of the surface area in the nodes and internodes, respectively). Epiphytic cyanobacteria were also quantified by using a fluorometer. This made it possible to discriminate which algal groups were the source of chlorophyll a. Chlorophyll a measurements confirmed that cyanobacteria were more abundant in nodes than in internodes (on average, the chlorophyll a concentrations were 17.2 +/- 28.0 and 4.0 +/- 3.8 microg mg [dry weight] of Chara(-1) in the nodes and internodes, respectively). These results indicate that this macrophyte, which is usually considered a weed in the context of rice cultivation, may help maintain soil N fertility in the rice field ecosystem.
在西班牙巴伦西亚稻田的两个地点，连续两个作物季研究了水稻-土壤系统中固氮酶活性的分布，以及水稻植株和其他大型植物上附生蓝细菌对该活性的可能贡献。在这两年以及两个地点，最大比例的光依赖性N₂固定与大型植物普通轮藻有关。与轮藻相关的固氮率始终占稻田中测得的全球固氮酶活性的45%以上。估计与轮藻相关的平均N₂固定率为27.53 kg N ha⁻¹作物⁻¹。所有采样期系统其他部分的平均估计N₂固定率如下：土壤，4.07 kg N ha⁻¹作物⁻¹；水稻植株的淹没部分，3.93 kg N ha⁻¹作物⁻¹；根部，0.28 kg N ha⁻¹作物⁻¹。显微研究揭示了轮藻表面存在附生蓝细菌。共聚焦扫描激光显微镜的三维重建显示轮藻结构内部没有蓝细菌细胞。通过图像分析对附生蓝细菌进行定量，结果表明节部的蓝细菌比节间更丰富（平均而言，节部和节间蓝细菌覆盖的表面积分别为8.4%±4.4%和6.2%±5.0%）。还使用荧光计对附生蓝细菌进行了定量。这使得能够区分哪些藻类群体是叶绿素a的来源。叶绿素a测量结果证实节部的蓝细菌比节间更丰富（平均而言，节部和节间的叶绿素a浓度分别为17.2±28.0和4.0±3.8 μg mg [干重]轮藻⁻¹）。这些结果表明，这种在水稻种植背景下通常被视为杂草的大型植物可能有助于维持稻田生态系统中的土壤氮肥力。
