Distinct responses in sexual reproduction onset and growth of Chara braunii Gmelin to light level and temperature: evidence from a greenhouse experiment

Abstract

AbstractThe importance of oospores in the ecology and life cycle of annual charophyte species is now widely recognized. To elucidate the primary factor that determines the timing (onset) of sexual reproduction, a controlled 3 × 2 factorial experiment with various light levels (100%, 50% and 10% of natural irradiance) and temperatures (25 °C and 20 °C) was conducted to assess their interactive effects on Chara braunii Gmelin under greenhouse conditions. Results revealed that when the light level decreased from 100% to 10% of natural irradiance, the occurrence of gametangia was postponed for 8 days and the proportions of branch whorls with gametangia (PG) and oospores (PO) significantly decreased under high-temperature conditions. Decreased temperature significantly delayed the emergence of gametangia (100% of light levels for 10 days, 50% of light level for 6 days) and decreased PG and PO. Under low-temperature conditions, no gametangia were found at the lowest light level (10/20). This indicated that the combination of low light and low temperature could result in the absence of sexual reproduction in C. braunii. Furthermore, the internode length, dry weight length ratio and pigment pattern of cultured C. braunii were also significantly altered in response to different light levels and temperature treatments. Two-way ANOVA analysis revealed that temperature contributed more to PG and PO than light levels, while light levels contributed more to morphology and pigment ratio than temperature. This might suggest distinct responses of sexual reproduction onset and growth of C. braunii to varied light level and temperature.

Keywords

• Chara
• sexual reproduction
• light
• temperature
• gametangia