Proximate cues of flowering in a subtropical rain forest

Plants have evolved mechanisms to track seasonal variation in environmental resources, enabling them to time key life-history events to appropriate seasons. While the proximate cues for flowering initiation are well documented in the temperate region, it is still unclear what the flowering cues are in the tropics, especially in the subtropics. Our study compared first flowering dates (FFDs) predicted by eight hypothesized proximate cues concerning photoperiod, mean and directional changes in solar irradiance and warm/cool temperature, and rainfall with flowering dates observed over 19 years of weekly monitoring for 16 species in a subtropical rain forest. We observed considerable interannual variation in the median FFDs for the study species, ranging from 21 to 101 days. The early-spring flowering species tended to have greater interannual variation in FFDs than the summer flowering species. For 13 study species, temperature cues best explained interannual variation in FFDs. Cool temperatures in the previous fall/winter and warm temperatures in the current spring (or previous summer) might trigger the onset of flowering in these 13 species. Cues associated with photoperiod and irradiance also predicted interannual variation in FFDs with small root mean square error (<1.5 census intervals) for 12 species but generally had higher prediction errors than temperature-related cues. Cues associated with seasonal variation in rainfall failed to predict flowering times in any species. Our results suggest that future changes in temperature may alter flowering times for most species in subtropical forests, leading to changes in ecosystem processes and biosphere feedback to the climate system.

Abstract in Chinese is available with online material.

植物演化出許多不同的機制來追蹤環境資源的季節變化，讓關鍵的生活史事件發生在適當的季節。誘發植物開花的氣候因子在溫帶地區已有許多研究，但在熱帶，特別是亞熱帶地區，這類研究仍然相當缺乏。我們的研究使用了在亞熱帶雨林中進行19年的長期物候監測資料，分析16種植物的首次開花日期(first flowering date, FFD)的年間變化，以及光週期、太陽輻射、積溫、低溫以及雨量對於開花時間的影響。我們發現各植物的FFDs年間變化相當大，範圍從21到101天不等，早春開花的物種傾向於比夏季開花的物種具有更大的FFDs年間變異。溫度的年間變化可以準確預測13種植物的FFDs，前一年秋季/冬季的低溫和當年春季(或去年夏季)的高溫可能會誘發這13種植物的花芽發育。光周期和日照輻射也能夠預測12種植物的FFDs的年際變化，但通常比與溫度相關的物候模式具有較高的預測誤差。降雨量的年間變化並無法預測本研究16種植物的開花時間。由我們的研究結果推論，未來的氣溫變化可能會改變亞熱帶森林中大多數植物的開花時間，從而改變生態系與生物圈對氣候系統的反饋.