Nectar production in three melliferous species of Lamiaceae in natural and experimental conditions

The nectar production of Lamium maculatum, Lamiastrum galeobdolon and Ajuga reptans was evaluated by determining the Index of nectar production (INP) total nectar quantity per flower during 24h, nectar sugar concentration flowering period, flower longevity, and flower number per plant and per square unit. The diurnal dynamics of nectar secretion in these three melliferous species, grown under different microclimatic habitat conditions (natural and experimental field) was also analyzed, by measuring the amount of nectar per flower at two hour intervals. Nectar amount and sugar concentration varied among the studied species as a function of microclimatic habitat conditions (air temperature, air humidity and evaporation) and corolla morphology. Higher nectar production and lower sugar concentration were recorded in L. maculatum and L. galeobdolon grown in the forest, while for A. reptans in the same habitat, lower intensity of nectar secretion and higher sugar concentration were obtained. With regard to the average number of open flowers per plant during the nectar collecting day, total daily nectar volume per plant was the highest in L. maculatum (average volume 30.1 ml/plant). Considering the average size or density of the natural population of the species, the highest nectar yield per square unit was found in L. maculatum (1564.99 ml/m2) and the lowest in A. reptans (111.34 ml/m2). Diurnal variation in nectar production was also found and the secretion patterns were rather different in these three melliferous species. Regarding nectar secretion rate, A. reptans is a slow producer, secreting less than 0.02 ml/h. With respect to secretion intensity (on average 0.22 ml/h), total daily nectar production per flower (on average 5.368 ml) and the density of species population, the most melliferous species was L. maculatum