Oecologia (Berlin) (1984) 62:418423 Oecologia 9 Springer-Verlag 1984 Rewetting of drought-resistant blue-green algae: Time course of water uptake and reappearance of respiration, photosynthesis, and nitrogen fixation Siegfried Scherer 1, Anneliese Ernst 1, Ting-Wei Chen 2, and Peter BiJger1 1 Lehrstuhl fiir Physiologic und Bioehemie der Pflanzen, Universit~it Konstanz, D-7750 Konstanz, Federal Republic of Germany 2 Soils and Fertilizer Institute, Chinese Academy of Agricultural Sciences, 30 Baishiqiao Lu, Beijing 100081, Peoples Republic of China Summary. The response of the terrestrial blue-green algae Nostoc flagelliforme, Nostoc commune, and Nostoc spec. to water uptake has been investigated after a drought period of approximately 2 years. Rapid half-times of rewetting (0.6, 3.3, and 15.5 min, respectively) are found. The surface- to-mass ratio of the three species is inversely Correlated to the speed of water uptake and loss. The ecological rele- vance of these different time courses is discussed. Respiration starts immediately after a 30-min rewetting period, whereas photosynthetic oxygen evolution reaches its maximum activity after 6 and 8 h with N. commune and N. flagelliforme, respectively. In the dark, recovery of oxy- gen uptake by N. commune is somewhat impaired, while slightly stimulated with N. flagelliforme. With both species, recovery of photosynthesis is inhibited by darkness. Using colonies kept dry for two years, nitrogenase activ- ity of N. commune attains its maximum 120 to 150 h after rewetting, while only 50 h were needed with algal mats kept dry for two days. Thus, after a 2-year drought period, the physiological sequence of reactivation is respiration - photosynthesis - nitrogen fixation. Respiration and photosynthesis precede growth and are exhibited by existing vegetative cells, where- as recovery of nitrogen fixation is dependent on newly dif- ferentiated heterocysts. Introduction Resistance towards extreme water stress, i.e. desiccation, is widely observed in the plant kingdom, preferably in li- chens and algae. Davis (1972) reported on more than 400 species of drought-tolerant green and blue-green algae (for general aspects of desiccation see reviews by Bewley 1979; Bewley and Krochko 1982). Terrestrial blue-green algae participate in soil erosion and production of organic matter, especially in extreme en- vironments (Cameron 1960; Fogg and Stewart 1968; Lund 1967). Furthermore, Nostoc species are used as food and medicine in China. Little is known about physiological responses following rewetting of blue-green algae (comp. Fogg et al. 1973). One of the earliest reports was published by Correns (1889) on water uptake by dried Gloeocapsa and Nostoc colonies. Ap- Offprint requests to: P. B6ger parently, blue-green algae have a long surviving time. Lip- man (1941) showed that at least desiccated Nostoc commune can survive for 87 years, and Cameron (1962), using the same herbarium collection, reported a longevity record of 107 years for this specimen. No data are available as yet on time courses of respira- tion and photosynthesis of blue-green algae together with water loss during and after rewetting. Few reports have been published on the resistance of nitrogen fixation against drought (Jones 1977; Paul et al. 1971; Wang et al. 1981; Whitton et al. 1979), which has been claimed as the essential factor to limit nitrogen fixation by blue-green algae in natu- ral habitats (Stewart 1974). Interestingly, the nitrogenase enzyme system of N. commune is highly frost-tolerant, if no desiccation occurs (Coxson and Kershaw 1983). This paper contributes some data on recovery of physio- logical activities of some blue-green algal species after re- wetting. Material and methods 1. Species The three Nostoc species used in this study were all collected at their natural habitats in China. Rarely, endospores were observed in the samples. Heterocysts were present either as single cells in the mats or at the ends of the filaments. Nostoc commune Vauch. (Gollerbach et al. 1953) is a terrestrial species widespread in China where it is called "earthy ear". It occurs mainly on the surface of soil of hilly limestone regions in South China, south of the Yangtze River. It is dominant at pH 7.5 to 7.8, but rare in acid soil and absent in paddy fields. In the rainy season, N. commune forms macroscopic gelatinous colonies often oc- cupying small depressions of limestone. The fresh samples of N. commune were collected during the rainy season in 1981 in Hunan province (Henyong district) and Guanshi Province (Guiling district) of Central China and stored in plastic bags after desiccation for 5 days at 50% relative humidity at 18-20 ~ C. NostocJIagelliforme (Berk. et Curt.) [= N. commune vat. flagelliforme (Berk. et Curt., Born et Flah.)] (comp. Hu Hong-Jaun 1980; Geitler and Pascher 1925)was collected during 1980 in the Gansu and Lingshia Province (Zongling and Haiyuang County) in North-west China. It grows on soil surfaces of arid regions at pH 7.5 to 8.0.