Effects of photoperiod on the growth and physiological responses in Ulva prolifera under constant and diurnal temperature difference conditions

Photoperiod and temperature are two main factors in the growth of macroalgae, and changes in photoperiod and diurnal temperature difference exist in natural condition. In order to study the effects of photoperiod and diurnal temperature difference on the growth of green algae Ulva prolifera, we cultured this species under three light/dark cycles (light: dark = 10:14, 12:12 and 16:08) with constant (22 °C for light and dark period, noted as 22-22 °C) and diurnal temperature difference (22 °C and 16 °C for light and dark period, respectively, noted as 22-16 °C) conditions. The results showed that: 1) Compared with 10:14 light/dark cycle, the growth of U. prolifera under 12:12 light/dark cycle was significantly enhanced by 39% and 16% for 22-22 °C and 22-16 °C treatments, respectively, while the increase proportion decreased when the daylength increase from 12 h to 16 h. 2) The enhancement in growth induced by diurnal temperature difference was observed under 10:14 light/dark cycle, but not for 12:12 and 16:08 light/dark cycle treatments. 3) The Chl a content and photosynthetic rate increased under short light period and 22-22 °C conditions, while under 22-16 °C conditions, higher photosynthetic rate was observed under 12:12 light/dark cycle and no significant difference in Chl a content was observed. 4) Under 22-22 °C conditions, compared with 10:14 (L:D) treatment, the expression levels of proteins in light-harvesting complexes, PSII and carbon fixation were down regulated, while the photorespiration and pentose phosphate pathway (PPP) were up regulated by 16:08 light dark cycle. Then we speculate that the higher photosynthetic rate may be one compensation mechanism in short photoperiod, and under long light period condition the up regulations of photorespiration and PPP can be in charge of the decrease in enhancement growth induced by longer daylength.

Enhancement of growth in Ulva prolifera by diurnal temperature difference combined with nitrogen enrichment

Many studies have documented the responses of Ulva prolifera to environmental factors. However, the diurnal temperature differences and interactive effects of eutrophication are usually ignored. In this study, we selected U. prolifera as material to examine the effects of diurnal temperature on growth, photosynthesis and primary metabolites under two nitrogen levels. We cultured U. prolifera seedlings under two temperature conditions (22-22 °C: 22 °C during day and night; 22-18 °C: 22 °C during day and 18 °C at night) and two nitrogen levels (LN: 0.1235 mg L^-1; HN: and 0.6 mg L^-1). The results showed that 1) HN-grown thalli had higher growth rates, the chlorophyll a (Chl a) content, photosynthesis, superoxide dismutase (SOD) activity, soluble sugar, and protein contents under the two temperature conditions; 2) The growth of thalli was enhanced by 22-18 °C condition compared with 22-22 °C, but the increase was only significant under HN condition; 3) 22-18°C-grown thalli had a lower net photosynthetic rate, maximal quantum yield (F_v/F_m), and dark respiration rate (R_d) than those grown at 22-22 °C; 4) No significant effects of diurnal temperature difference were detected on the SOD activity and soluble sugar content under LN and HN conditions, while the soluble protein content was enhanced by 22-18 °C under LN condition; 5) The nitrogen affected metabolite variations in U. prolifera more significantly than the diurnal temperature difference. The metabolite levels in the tricarboxylic acid cycle, amino acid, phospholipids, pyrimidine, and purine metabolism pathways increased under HN condition. The levels of glutamine, γ-aminobutyrate (GABA), 1-aminocyclopropane-1-carboxylate (ACC), glutamic acid, citrulline, glucose, sucrose, stachyose, and maltotriose were enhanced by 22-18 °C, especially under HN condition. These results identify the potential role of the diurnal temperature difference and offer new insight into the molecular mechanisms for U. prolifera responses to eutrophication and temperature.

Differences in volatile profiles of Cabernet Sauvignon grapes grown in two distinct regions of China and their responses to weather conditions

Volatile compounds are considered important for plants to communicate with each other and interact with their environments. Most wine-producing regions in China feature a continental monsoon climate with hot-wet summers and dry-cold winters, giving grapes markedly different growing environments compared to the Mediterranean or oceanic climates described in previous reports. This study focused on comparing the volatile profiles of Vitis vinifera L. cv. Cabernet Sauvignon berries from two regions with distinct climate characteristics: Changli has a warm and semi-humid summer, and Gaotai has a cool-arid summer and a cold winter. The relationship between meteorological metrics and the concentrations of grape volatiles were also examined. In harvested grapes, benzyl alcohol, phenylethyl alcohol, 1-hexanol and 1-octen-3-ol were more abundant in the Changli berries, while hexanal, heptanal, 2-methoxy-3-isobutylpyrazine, and (E)-β-damascenone presented higher levels in the Gaotai berries. The fluctuation in the accumulation of volatile compounds observed during berry development was closely correlated with variations in short-term weather (weather in a week), especially rainfall. The concentration of some volatiles, notably aliphatic aldehydes, was significantly related to diurnal temperature differences. The variability during berry development of concentrations for compounds such as C6 volatile compounds, 2-methoxy-3-isobutylpyrazine and (E)-β-damascenone strongly depended upon weather conditions. This work expands our knowledge about the influence of continental monsoon climates on volatile compounds in developing grape berries. It will also improve the comprehension of the plant response to their surrounding environments through the accumulation of volatiles. The results will help growers to alter viticultural practices according to local conditions to improve the aromatic quality of grapes.