Temperate climates are the main climate type in Europe (Fig. 1–2). Middle, Eastern as well as Western Europe are generally characterized by a temperate climate, for instance, Austria, Czech Republic, France, Germany, the Netherlands, and the UK.
Duckstein et al. (2012) compared phenolic components from Alchemilla vulgaris L. and Alchemilla mollis (Buser) Rothm. (Rosaceae) growing in Germany. Leaves and stalks of Alchemilla were harvested in May (start of the flowering period) and August 2010 (end of the flowering period). In both species, agrimoniin (a dimeric hydrolysable tannin), one of the main components, was present by more than 100% higher in May than in August. The same trend was also observed for other ellagitannins and also the major flavonoid, a quercetin glucuronide, increased nearly by 30%.
Drøhse Høgedal and Mølgaard (2000) studied seasonal and diurnal variations in the contents of iridoids in cultivars of Antirrhinum majus L. (Plantaginaceae) grown in Denmark. Plants were harvested weekly between June 17 and September 30, and twice a week during the flowering period. Total iridoid contents revealed an accumulation, with high contents (around 100 mg/g dry matter), early and late in the season. All iridoids showed very low contents in August when plants were at the onset of flowering. The relative percentage of antirrhinoside was substantially higher before flowering than after bud break. The relative decrease in antirrhinoside was occurring in parallel with an increase of antirrhide, which occurred in significantly higher concentrations after the onset of flowering. The diurnal variation ranged from 20 to 60 mg/g. In contrast, no correlations related to light/darkness conditions, temperature patterns or water content were observed.
Wallaart et al. (2000) studied the levels of artemisinin, its biosynthetic precursors, and biosynthetically related sesquiterpenes during phenological stages in Artemisia annua L. (Asteraceae) of different origins. Seeds of A. annua originating from China, Germany, the USA, Vietnam, and Yugoslavia were obtained and then cultivated in an experimental field in the Netherlands. Leaves of each plant were sampled weekly at the middle of the day from July to November. A chemotype exhibiting high contents of artemisinin and dihydroartemisinic acid and low contents of artemisinic acid was represented by the Vietnamese A. annua accession. Other chemotypes presenting relatively low contents of artemisinin and dihydroartemisinic acid, but high artemisinic acid were represented by the Chinese, European, and American A. annua accessions. Specimens from Vietnam seemed to be the most suitable chemotype for the commercial production of artemisinin. In November, the artemisinin content of the Vietnamese A. annua had considerably increased by almost 58%, after a period of moderate decline. In parallel, the content of dihydroartemisinic acid had decreased by 39% and thus to a content lower than that of artemisinin. The authors found these radical changes in the natural products levels were coinciding with the onset of night frost.
Agerbirk et al. (2001) studied two different types of Barbarea vulgaris R.Br. (Brassicaceae) for seasonal changes in the contents of glucosinolates and the resistance of the plants of both types to the crucifer specialist flea beetle Phyllotreta nemorum Linnaeus. Leaves of B. vulgaris subsp. arcuata (Opiz) Hayek were harvested at seven natural growing locations in Denmark from August to November, once per month. The contents of all dominant glucosinolates in the plants showed an increase from August to November at five localities. In the remaining two localities, glucosinolates accumulated from September to November. Additionally, no correlation between glucosinolate contents and insect resistance was detected. Glucosinolate levels also did not correlate with the variation in resistance between the P-type (always susceptible) and the G-type (resistant in the summer season).
The variability of essential oil compositions of Clinopodium pulegium (Rochel) Bräuchler from its natural habitat and from cultivated plants was investigated by Slavkovska et al. (2013). Plants were harvested from the Svrljiški Timok gorge, Serbia (wild) and Niš, Serbia (cultivated) during different vegetative phases. The plants growing in the natural habitat yielded the lowest content of oil with 1.0% (v/w) in the vegetative stage, the content increased during the flowering period, 1.4%, while it decreased to 1.2% during the fruiting stage. The oil yield of the cultivated plants was 1.2% in the vegetative stage. It increased to a peak of 1.3% in the flowering stage, and was lowest [0.8% (v/w)] during the full fruiting stage. The dominance of the abundant components changed depending on the vegetative phases. Pulegone was prominent in the vegetative (76.1% wild population, 62.7% cultivated population) and the flowering (49.5%, 64.6%) stages, while menthone (48.5%, 65.3%) contents were higher than pulegone (34.7%, 18.4%) contents at the fruiting stage.
The roots of Echinacea purpurea (L.) Moench and Echinacea pallida (Nutt.) Nutt. (Asteraceae) grown in Denmark were analyzed by Thomsen et al. (2012) for their contents in lipophilic compounds and phenolic acids, depending on the season. Roots were sampled in early winter (December 15, 2009), early spring (March 23), late spring (May 25), summer (August 13), and mid-autumn (October 29) of 2010. A total of 16 alkamides, two ketoalkenes, two ketoalkynes, and four phenolic acids (caftaric acid, chlorogenic acid, cichoric acid and echinacoside) were detected in alcoholic extracts by LC–MS and quantified by RP-HPLC–DAD. Since the lipophilic compounds, alkamides in E. purpurea roots were dominant, while E. pallida was characterized by a dominance of ketoalkynes and ketoalkenes, the analysis of lipophilic compounds could be employed to distinguish the two species. The lowest levels of the main lipophilic compounds in roots of E. purpurea occurred in mid-autumn and early winter. The total contents of lipophilic compounds in E. pallida displayed a similar trend. Moreover, the contents of the main phenolic acids in E. purpurea peaked in spring. In E. pallida roots, echinacoside showed a significantly higher level in spring. Caftaric acid displayed a higher level in late spring, while cichoric acid reached a higher level from late spring to mid-autumn.
Menković et al. (2000) quantified xanthones and secoiridoids in aerial parts of Gentiana lutea L. (Gentianaceae) growing in Serbia. Wild plants were harvested every month from March until October at various stages of their development. The highest amounts of mangiferin and isoorientin occurred between June and July, and thus during the period of flowering. Lower amounts of mangiferin were detected in May and August, while there were only marginal changes in the isoorientin levels. In contrast, the highest amounts of isogentisin 3-O-primeveroside and isogentisin were observed in April and May respectively. In contrast, their amounts decreased significantly during the period of flowering. In October, the content of isogentisin 3-O-primeveroside again increased. It was concluded that during the period of flowering, leaves were rich in C-glycosides, while O-glycosides were mainly accumulated before flowering. In the case of secoiridoids, the content increased steadily during the vegetation period and reached maxima in October.
Seasonal variations in the contents of phenolics and antioxidant activities of Glechoma hederacea L. (Lamiaceae) were analyzed by Varga et al. (2016). The aerial parts were collected from six Hungarian locations in April, July, and October 2012. Specimens harvested in July in a population originating from an open-site park in Budapest showed the highest total phenol content (115 mg gallic acid equivalent/g dry material) and the strongest antioxidant activity (53.3 mg ascorbic acid equivalent/g dry material). Chlorogenic acid (357 mg/100 g) and rutin (950 mg/100 g) also reached the highest contents in July of samples from the Soroksár botanical garden population. In general, contents of the July collections were significantly higher than the ones from April and October. According to the results above, mid-summer was recommended as the best harvest time for ground ivy shoots.
Cheel et al. (2013) investigated the interactions of chemical profiles with biological activities of licorice, Glycyrrhiza glabra L. (Fabaceae) grown in the Czech Republic. Three thickened roots of four-year-old cultivated plants were sampled in every season of 2008. Total contents of phenols, flavonoids, and tannins showed peak amounts in November, August, and May, respectively. Liquiritin and glycyrrhizin, the main constituents, varied in the ranges between 28.7—62.8 and 41.8—114 mg/g dry weight, respectively. The relative proportions of glycyrrhizin glycoside, glabridin, glabrene, and liquiritigenin glycoside, varied in the ranges between 0.88—11.4%, 1.86—10.0%, 1.80—18.4%, and 5.53—16.3%, respectively. These fluctuations were related to the antioxidant and free radical scavenging activities of licorice. It was found that the sample from May showed the strongest free radical scavenging effect and the highest gastroprotective effect, whereas the sample from November showed the best antioxidant effects. Liquiritin and glycyrrhizin, the main components with the highest proportion in February and May, were related to the superoxide radical scavenging and gastroprotective effects. Glabridin and glabrene, the main components in November, contributed to the antioxidant and DPPH scavenging activities of licorice.
Mártonfi et al. (2006) studied changes of natural products during three developmental stages of reproductive structures in Hypericum maculatum Crantz (Hypericaceae) growing in Slovakia. Generative parts of the taxon were harvested from three populations with different growing conditions. Remarkable differences in the concentration of natural products, in the various flower parts were noticed. During the whole period of flowering, the concentration of all the studied metabolites kept constantly in green flower parts (sepals). The most apparent variations were present in the flowering phase with the decrease of hyperoside and isoquercitrin concentration in petals, the decrease of the I3, II8-biapigenin concentration in stamens, and the increase of hypericin and pseudohypericin concentration in both petals and stamens. The flavonoids hyperoside and isoquercitrin, whose concentration decreased during flowering, presented the highest contents in the pistil.
Tekel'ová et al. (2000) studied seasonal changes in natural product content during the flower ontogenesis of Hypericum perforatum subsp. veronense (Schrank) H.Lindb. (Hypericaceae) grown in Slovakia. Samples were collected eight times in different plant development stages. The amount of dianthrones, derivatives of quercetin, and hyperforin increased from the first budding phase (0.29%, 0.80%, and 2.47%, respectively) to the phase of freshly opened flowers (1.04%, 4.23% and 6.60%, respectively). The amounts of dianthrones and quercetin glycosides then showed a decrease (in unripe fruits to 0.11% and 0.08%, respectively), whereas the content of hyperforin increased to 8.07% in fruits. The amount of I3, II8-biapigenin displayed an increasing trend from 0.21 in small buds to 1.04% in buds just before opening and subsequently decreased steadily to the lowest of 0.02% in fruits.
Pěnčíková et al. (2011) determined the seasonal and plant age related variation of isoquinoline alkaloids contents of Macleaya microcarpa (Maxim.) Fedde (Papaveraceae) grown in the Czech Republic. The aerial parts and underground parts and of thirteen-year-old plants were collected during the vegetative period from April to October. The major alkaloids in spring samples were sanguinarine and chelerythrine, their concentrations were two times higher compared to autumn samples. During the following vegetation period, the content of both benzophenanthridines slowly decreased. In contrast, the concentrations of protopine and allocryptopine showed a rather low level in spring and reached a maximum in July. Then protopine and allocryptopine in leaves dropped significantly to a very low level, but in October, at the beginning of vegetative quiescence, their contents increased again slightly. For most alkaloids in roots, the contents changed considerably during the vegetative cycle and reached the highest levels during June and July. Protopine showed the highest content in May, while macarpine culminated during July and August. The highest contents of alkaloids described above were two- to threefold higher than the contents of autumn samples. The contents of chelirubine and chelilutine reached the highest levels during June and July. In addition, one-, two-, twelve- and thirteen-year-old plants were collected in October, at the end of the vegetative period to assess how plant age affects the content of alkaloids. Allocryptopine was the major component in both aerial and underground parts, but no obvious relation to the age of the plants was observed. Moreover, the authors found that minor chelilutine, chelirubine, macarpine, and sanguirubine were preferably accumulating in older roots.
Stochmal and Oleszek (2007) quantified variations in the contents of flavones identified in alfalfa Medicago sativa L. (Fabaceae), grown in Poland for three years (1999—2001). Aerial parts of ten plants were cut three times per year. Tricin and apigenin glycosides were the main flavonoids of alfalfa. Total content of flavonoids decreased gradually during seasons; the first spring cut displayed the highest concentration and this declined for the other two cuts. Simultaneously, the ratio of flavones acylated with hydroxycinnamic acids to non-acylated rose from 1.5 in the first to 1.8 for the other two cuts. This finding may indicate the relevance of acylated forms for the protection of plants against UV-B radiation during the summertime.
Skrzypczak-Pietraszek and Pietraszek (2012) studied seasonal variation of phenolic acid content in Melittis melissophyllum L. (Lamiaceae) growing in Poland. M. melissophyllum was sampled in two different habitats in May and September. Phenolic acid profiles of methanolic extracts were analyzed by HPLC–DAD. p-Hydroxybenzoic acid and p-coumaric acid were the main components, both of them showed higher levels of September samples than May samples in the same localities.
Skrzypczak-Pietraszek and Pietraszek (2014) also studied seasonal variations of flavonoid concentration in Melittis melissophyllum L. (Lamiaceae) growing in Poland. Plants were collected and separated into leaves and flowers in May and September. The highest total content of flavonoids was revealed in flowers (258—271 mg/100 g dry weight) and leaves (143—155 mg/100 g) collected in May, the lower ones were recorded in leaves obtained from September (83—92 mg/100 g). Geographical location had no obvious effect.
Grulova et al. (2015) recorded seasonal changes of the major constituents in essential oils of Mentha × piperita L. (Lamiaceae) cultivated in Slovakia. Plant material was collected monthly from April to September throughout three years. 97.1—98.7% of the total essential oil was based on menthol, menthone, limonene, menthyl acetate, menthofurane, and β-caryophyllene. The quantities of limonene in the same month of different years showed a decreasing tendency, the quantity decreased from 10.8 (April 2010) to 8.0% (April 2012) and from 3.2% (September 2010) to 2.3% (September 2012). In 2010, the menthone amount increased from April (15.3 ± 1.8%) to August (20.4 ± 0.4%) and decreased to 14.1 ± 1.1% in September. The tendency was different from 2011 and 2012. Menthone displayed the maximum accumulation at the beginning of the developmental stages (April 2011 and May 2012), while the lowest content was present in September of 2011 and 2012. The percentage of the major component, menthol, increased in 2010 and 2012 from April until July and decreased in September. This compound also showed an increasing tendency from April to August in 2011. The lowest levels of menthyl acetate were recorded in July 2011 and in August 2010 and 2012. The content of β-caryophyllene increased in May and June of the first two years followed by a sustained decline until the end of the year. During the three-year experiment, the seasons 2011 and 2012, had a higher mean temperature than in 2010; moreover, intense rainfalls in July 2011 and 2012 were recorded. The presented data imply that M. × piperita experienced different rain and temperature regimes, resulting in significant quantitative changes in essential oil composition.
Lubbe et al. (2013) studied the seasonal pattern of alkaloids in the bulbs, leaves, and roots of Narcissus pseudonarcissus L. cv. “Carlton” (Amaryllidaceae) grown in the Netherlands. Twenty-four plants were collected as followed points: (1) when shoots had emerged and were about 10 cm above ground, (2) before flowering, (3) during full flowering, (4) after flowering, and (5) after shoot senescence. Alkaloid contents of plants were monitored by quantitative 1H NMR during the growing season. The average galanthamine and haemanthamine concentrations in bulbs reached a maximum before flowering. The concentration showed a decreasing tendency during and after flowering, but increased slightly again at the end of growing cycle. Narciclasine was present in the bulbs with highest amount in the second and third time points, and thereafter gradually decreased. In the leaves, the concentration of haemanthamine fluctuated with highest level before flowering. Extracts of leaves contained similar levels of galanthamine and narciclasine, which showed consistent concentrations until the third time point, followed by a decrease afterwards. In the root, galanthamine and haemanthamine showed different variety patterns, galanthamine accumulated higher concentrations until before flowering, whereas haemanthamine showed significantly higher concentrations after senescence.
Krzyżanowska-Kowalczyk et al. (2018) compared the metabolite profiles of Pulmonaria officinalis L. (Boraginaceae) collected in Poland in spring and autumn. Spring samples were characterized by the dominance of rutin, nicotiflorin, and 3-O-caffeoyl-threonic acid. Salvianolic acid H, actinidioionoside, three isomers of coumaroylquinic acid, and pulmonarioside B were the major components in autumn samples. Quantitation data obtained by HPLC–MS were analyzed by univariate volcano plot analysis, combining t-tests and fold change examination and unsupervised principal component analysis (PCA) to determine several features linked with spring and autumn samples of Pulmonaria officinalis. A clear separation of samples was achieved with both approaches.
Lakušić et al. (2011) studied the chemical composition of Satureja horvatii Šilić (Lamiaceae), cultivated in Serbia (the taxon is naturally occurring in Montenegro) at different phenological stages. Essential oil yields varied from 0.5—1.3%. The lowest oil yield (0.5%) occurred before flowering in April, and the highest (1.3%) was recorded during late flowering and at the beginning of fruiting in September. The essential oil from samples obtained before flowering was dominated by linalool (37.4%), thymol (27.3%), and carvacrol (12.2%). In the flowering period (June), the proportion of linalool increased up to 56.6—57.5%, while that of thymol decrease to 15.5 -15.8%, carvacrol significantly dropped to 1.4—1.5%. The essential oil sampled from fruiting stage (September and October) was dominated by linalool (58.4 and 65.8%), followed by lower levels of thymol (7.6 and 1.3%), and carvacrol (0.7 and 0.1%). The authors also focused on differences between plant growing conditions. In Mediterranean natural habitats, the main oil components were the phenols thymol (63.7% for the Mt. Orjen in Montenegro) or carvacrol (68.1% for the Mt. Lovćen in Montenegro), while the oils from plants cultivated in temperate Belgrade were represented by linalool (up to 65.8% and 55.9% on average).
Šebrlová et al. (2015) studied Stylophorum lasiocarpum (Oliv.) Fedde (Papaveraceae) grown in the Czech Republic and its seasonal variation in alkaloid composition. Three individual plants of one- and two-year-old cultures were randomly harvested during the vegetation period from May to October. The extracts of the aerial part were characterized by a dominance of protoberberine alkaloids: coptisine, and stylopine, which were irrespective of the plants’ age and time of harvest. Higher levels of all alkaloids were present in roots than in the aerial parts. The levels of most alkaloids peaked in the middle of the vegetation period.
Raudone et al. (2017) studied phenological changes in triterpenic and phenolic composition of Thymus L. species (Lamiaceae) grown in Lithuania. The aerial parts of plants were harvested at different ontogenetic stages from May to September of 2016. The phenolic compounds accumulated the highest amounts during budding and full flowering. Amounts decreased during fruiting and displayed the lowest levels at the end of the vegetation period. Rosmarinic acid was the dominant component in all Thymus species tested, ranging from 6.3 mg/g to 28.8 mg/g. During full flowering, T. longicaulis C.Presl (28.8 mg/g) and T. × oblongifolius Opiz (28.3 mg/g) had the highest concentrations of rosmarinic acid, followed by T. × citriodorus Schweig. et Korte and T. pulegioides L. In contrast, T. sibthorpii Benth. and T. serpyllum L. possessed the lowest amounts, 9.32 mg/g and 11.7 mg/g, respectively. After full flowering, the level of rosmarinic acid declined slowly during the fruiting stage. At the end of vegetation, the concentration of rosmarinic acid decreased significantly, and the final concentrations were in the following order in the investigated Thymus species (T. longicaulis > T. pulegioides > T × oblongifolius > T × citriodorus > T. austriacus > T. praecox subsp. arcticus > T. sibthorpii > T. serpyllum). The concentration of ursolic acid was higher than that of betulinic, corosolic, and oleanolic acid. The accumulation pattern of these triterpenic acids varied significantly and depended on the particular Thymus species investigated.