Biomass and Pigment Production in Three Isolates of Azolla II. Response to Light and Temperature Stress

Two isolates of Azolla caroliniana Willd. (RAR, M-3) and oneof Azolla filiculoides LAM. (LA) were compared and characterizedin defined growth environments. A moderate environment (200–230µ mol m^–2 S^–1, 18/6 h photoperiod and 26/22C thermoperiods) was selected to record growth in near-optimumconditions. All isolates doubled their fresh and dry weightsin approximately 2–3 d during the first week of trials.Acetylene reduction rates were low for all isolates, but RAR(from Amazonian Colombia) generally grew the fastest. RAR alsoaccumulated more chlorophyll, its chlorophyll doubling times(2.14 0.1 d) were 1–2 d faster than those of M-3 orLA, and it retained the most stable chlorophyll a/b ratios andtotal chlorophyll densities. Growth data for all isolates convergedduring the second week. Dry-weight doubling times were longerthan 3 d. None of the isolates excreted measureable amountsof nitrogen in month-long trials. Stress trials were conducted using high light (450–510µ mol m^–2 s^–1) and/or high temperature (35/31C conditions Biomass yields were usually least inhibited, ifat all, with elevation of only photon flux densities. High temperaturealone stimulated the dry-weight growth only of M-3 comparedwith its growth under moderate conditions. Biomass, chlorophyll,and acetylene reduction data suggested that M-3 may have a higheroptimum growth temperature than RAR or LA. The combined effectof light and temperature stress depressed acetylene reductionrates in RAR and M-3 to a greater extent than did either parameteralone. High light levels had more effect than high temperatures ininhibiting chlorophyll doubling times and inducing anthocyaninproduction in RAR and M-3. These two isolates did not form anyanthocyanin in elevated temperatures. Pre-incubation in darknessbefore exposure to elevated light/temperature conditions facilitatedanthocyanin production in all isolates. LA, however, provedto be the isolate most sensitive to stress by heat, alone oraugmented by light stress, according to all criteria used. Azolla caroliniana Willd., Azolla filiculoides Lam., biomass and chlorophyll accumulation, anthocyanin production, acetylene reduction, light/temperature stress