Insausti Pedro, Soriano Alberto, Sanchez Rodolfo A
IFEVA, Departmento de Ecología, Facultad de Agronomía, Universidad de Buenos Aires, Avenida San Martín 4453, 1417, Buenos Aires, Argentina.
Oecologia. 1995 Jul;103(1):127-132. doi: 10.1007/BF00328433.
Strong fluctuations are exhibited by populations of the perennial herb Ambrosia tenuifolia in the grasslands of the Salado basin (Province of Buenos Aires, Argentina), an area frequently enduring prolonged floods. Flooding causes the death of most dicotyledon plants of the community, A. tenuifolia among them, opening numerous gaps of various sizes. After the recession of the flood the density of A. tenuifolia seedlings was higher in flooded than in non-flooded plots and it was larger in wider gaps. Canopy removal in non-flooded plots increased field seedling emergence of A. tenuifolia up to the levels found in flooded plots. Responses of the seeds in the soil to gap-associated environmental factors such as light quality and temperature regime were studied both in the field and under controlled were studied both in the field and under controlled conditions. Seedling emergence was significantly enhanced when the red:far-red ratio of natural light reaching the soil surface under the canopy of nonflooded plots was increased by means of copper sulfate filters. The influence of light quality and temperature on germination of the soil seed population was also tested using grassland soil monoliths or mesocosms, transported from the field to the laboratory, in which the canopy was clipped and the soil exposed to either red or far-red light and kept at constant or fluctuating temperatures. Significant seedling emergence was observed only when the soil samples were exposed to red light and incubated at alternating temperatures. No emergence was recorded in samples exposed to far-red light or incubated at a constant 25°C. Seeds stored dry in the laboratory were also stimulated to germinate by red light and alternating temperatures but only after dormancy was sufficiently decreased by low temperature stratification or by low temperature under immersion. The results are consistent with the hypothesis that primary dormancy of A. tenuifolia seeds is decreased by low temperatures in winter even if the seeds are submerged as happens when floods occur. The decrease in dormancy makes the seeds prone to be stimulated to germinate by the Pfr form of phytochrome in combination with alternating temperatures. These conditions are likely to be met in the gaps opened by the flood-caused death of dicotyledon plants.
在萨拉多盆地（阿根廷布宜诺斯艾利斯省）的草原上，多年生草本植物细叶豚草的种群呈现出强烈的波动，该地区经常遭受长期洪水。洪水导致群落中大多数双子叶植物死亡，细叶豚草也在其中，形成了许多大小不一的缺口。洪水退去后，被洪水淹没的地块中细叶豚草幼苗的密度高于未被洪水淹没的地块，且在较宽的缺口中密度更大。在未被洪水淹没的地块中去除植被冠层，可使细叶豚草的田间幼苗出土率提高到被洪水淹没地块的水平。在田间和控制条件下，研究了土壤中的种子对与缺口相关的环境因素（如光质和温度 regime）的反应。通过硫酸铜滤光片提高未被洪水淹没地块冠层下到达土壤表面的自然光的红：远红比例时，幼苗出土率显著提高。还使用从田间运到实验室的草原土壤整块或中宇宙，测试了光质和温度对土壤种子种群萌发的影响，在这些土壤中，植被冠层被修剪，土壤暴露于红光或远红光下，并保持在恒定或波动温度下。只有当土壤样品暴露于红光并在交替温度下培养时，才观察到显著的幼苗出土。在暴露于远红光或在恒定 25°C 下培养的样品中未记录到出土情况。实验室中干燥储存的种子也受到红光和交替温度的刺激而萌发，但前提是通过低温分层或浸没在低温下使休眠充分降低。结果与以下假设一致：即使种子在洪水发生时被淹没，冬季的低温也会降低细叶豚草种子的初级休眠。休眠的降低使种子易于被光敏色素的 Pfr 形式与交替温度共同刺激而萌发。这些条件很可能在双子叶植物因洪水死亡而形成的缺口中得到满足。
