Freiberg Elke
Abteilung Spezielle Botanik, Universität Ulm, D-89069 Ulm, Germany e-mail:
Oecologia. 1998 Nov;117(1-2):9-18. doi: 10.1007/s004420050625.
The acetylene reduction method was used to measure nitrogen fixation in the phyllosphere of attached leaves of different phorophytes under natural conditions in a premontane rain forest in Costa Rica. Maximum rates of nitrogen fixation (26 ng N · cm leaf area · h) - mainly due to the activity of two species of Scytonema (Cyanobacteria) - were measured in the rainy season in bright sunlight. Rates of nitrogen fixation were correlated with the leaf area covered by Scytonema. In periods without precipitation the fixation activity decreased to zero within 2-3 days. As long as the epiphylls were sufficiently supplied with water, other microclimatic factors like temperature and light intensity also influenced nitrogen fixation rates, but to a lesser extent. Relative humidity and species of phorophyte showed no direct influence. It was concluded that the most important factor for nitrogen fixation in the phyllosphere was the availability of liquid water. Linking these results to meteorological data, the input of nitrogen by biological nitrogen fixation in the phyllosphere in the investigation area was estimated to be as much as 1.6 ± 0.8 kg N · ha · year per unit of leaf area index (LAI). For an LAI of 2 for the understory the nitrogen input would vary between 2 and 5 kg N · ha · year. This work also demonstrates the importance of detailed knowledge of variation in microclimate throughout the year as a basis for extrapolation of the annual nitrogen input.
在哥斯达黎加山地雨林的自然条件下，采用乙炔还原法测定了不同附生植物附着叶片叶际的固氮情况。在雨季的强光下，测定到最大固氮速率（26 ng N·cm叶面积·h），这主要归因于两种伪枝藻属（蓝细菌）的活性。固氮速率与伪枝藻属覆盖的叶面积相关。在无降水期间，固氮活性在2 - 3天内降至零。只要叶表有充足的水分供应，温度和光照强度等其他微气候因素也会影响固氮速率，但影响程度较小。相对湿度和附生植物种类未显示出直接影响。得出的结论是，叶际固氮的最重要因素是液态水的可利用性。将这些结果与气象数据相关联，估计研究区域内叶际通过生物固氮的氮输入量，以单位叶面积指数（LAI）计高达1.6±0.8 kg N·ha·年。对于林下层LAI为2的情况，氮输入量每年在2至5 kg N·ha之间变化。这项工作还表明，详细了解全年微气候的变化对于推断年度氮输入量至关重要。
