Studies of the reproductive biology of three species of Luehae (Tiliaceae) conducted in Costa Rican deciduous forest demonstrated that all species produce hermaphroditic flowers exhibiting nocturnal anthesis, anther dehiscence, nectar secretion, and fragrances consistent with adaptation for nocturnal moth pollination. Luehea candida, flowering during the wet season, has self—incompatible flowers pollinated primarily by sphingid moths. Generalist diurnal visitors, including stingless bees, flies, and butterflies, were also common flower visitors, but experiments showed that they were ineffective pollinators. Luehea candida apparently rejects pollen from nearby conspecifics as a means of limiting inbreeding resulting from pollination by poor outcrossers such as stingless bees. The principal pollinators of L. seemannii, which flowers during the dry season, were determined to be the same types of diurnal visitors that contributed nothing to pollination success of L. candida. Nocturnal moths were low in abundance during the dry season and pollinated few flowers. Individuals of the deciduous forest population of L. seemannii ranged from partially to fully self—compatible, though an evergreen forest population was self—incompatible. The partial breakdown of incompatibility, diurnal pollinators, and nectar analysis of L. seemannii suggest an ongoing evolutionary shift to diurnal pollination resulting from the scarcity of nocturnal pollinators and selection by diurnal insects, especially stingless bees, in the deciduous forest. Luehea speciosa, with floral morphology and behavior nearly identical to L. candida, rarely attracted sphingids during its blooming period in the early dry season even though these moths were present in the habitat. Chemical analysis showed that nectar of L. speciosa is of a type preferred by bats rather than sphingids, but no evidence for bat pollination could be found. This species may also be pollinated largely by opportinistic diurnal visitors.
The dynamics of microbial degradation of exogenous contaminants, n-hexadecane and its primary microbial oxidized metabolite, n-hexadecanoic (palmitic) acid, was studied for topsoils, under agricultural management and beech forest on the basis the changes in O 2 uptake, CO 2 evolution and its associated microbial and non-microbial carbon isotopic signature, the respiratory quotient (RQ) and the priming effect (PE) of substrates. Soil microbial communities in agricultural soil responded to the n-hexadecane addition more rapidly compared to those of forest soil, with lagperiods of about 23 ± 10 and 68 ± 13 hours, respectively. Insignificant difference in the lag-period duration was detected for agricultural (t lag = 30 ± 13 h) and forest (t lag = 30 ± 14 h) soils treated with n-hexadecanoic (palmitic) acid. These results demonstrate that the soil microbiota differed in metabolic activities for using n-hexadecane as a reductive hydrocarbon and n-hexadecanoic acid as a partly oxidized hydrocarbon. The corresponding δ 13 C of respired CO 2 after the addition of the hydrocarbon contaminants to soils indicates a shift in microbial activity towards the consumption of exogenous substrates with a more complete degradation of n-hexadecane in the agricultural soil, for which some initial contents of hydrocarbons are inherent. It was reflected in the carbon isotope signature of microbial biomass. It is supposed that the observed deviation of RQ from theoretically calculated value under microbial substrate mineralization is determined by difference in the time ( t i ) of registration of CO 2 production and O 2 consumption. Positive priming effect (PE) of n-hexadecane and negative PE of n-hexadecanoic (palmitic) acid were detected in agricultural and forest soils. It is suggested that positive PE of n-hexadecane is conditioned by the induction of microbial enzymes that perform hydroxylation/oxygenation of stable SOM compounds mineralized by soil microbiota to CO 2 . The microbial metabolism coupled with oxidative decarboxylation of n-hexadecanoic acid is considered as one of the most probable causes of the revealed negative PE value.
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