氣象專家介紹，在自然界的大多數(shù)綠色植物體內(nèi)都含有葉綠素、胡蘿卜素和葉黃素，但由于各種色素的含量和比例不同，其葉片就表現(xiàn)出不同的顏色。在氣溫較高的季節(jié)，特別是３０℃左右時(shí)，植物生長旺盛，葉綠素的比例較多，因此葉片多呈現(xiàn)出綠色。秋天到來之后，氣溫降低、空氣濕度減少、光照減弱，葉綠素的合成受到抑制。當(dāng)氣溫降低到１０℃以下，尤其是最低氣溫降至４℃以下時(shí)，會出現(xiàn)霜凍，植物體內(nèi)葉綠素的比例隨之明顯降低，葉片就會顯現(xiàn)出葉黃素、胡蘿卜素所特有的黃色。

According to meteorologists, most green plants in nature contain chlorophyll, carotene and lutein, but their leaves show different colors due to different contents and proportions of various pigments. In the season with high temperature, especially around 30 ℃, the plants grow vigorously, and the proportion of chlorophyll is more, so the leaves are mostly green. After autumn, the synthesis of chlorophyll was inhibited by the decrease of temperature, humidity and light. When the temperature is below 10 ℃, especially the lowest temperature is below 4 ℃, there will be frost, and the proportion of chlorophyll in plants will be significantly reduced, and the leaves will show the Yellow characteristic of lutein and carotene.

在同樣的自然條件下，楓樹、黃櫨、火炬樹、山楂樹、五葉爬山虎等少數(shù)樹種“紅臉”的秘密在于它們的葉子中除了含有葉綠素、葉黃素、胡蘿卜素外，還含有一種其他植物少有的特殊物質(zhì)——花青素。說它特殊，一是因?yàn)榛ㄇ嗨鼐哂小胺闯绷骶瘛薄ｋS著氣溫降低、晝夜溫差增大，花青素的含量不但不會減少，還會迅速增多；二是花青素具有遇酸變紅，遇堿“面不改色”的特點(diǎn)。據(jù)測定，只有楓樹等少數(shù)幾種植物葉子中的細(xì)胞液是酸性的，故而隨著秋天的降臨、花青素的增多，葉片會逐漸由綠變紅。而對于大多數(shù)植物而言，由于所含的花青素很少，或者花青素含量雖多，但細(xì)胞液是堿性的，所以無論氣候怎樣變化，葉片都不會變紅。

Under the same natural conditions, the secret of "red face" of a few tree species, such as maple, yellow croaker, torch tree, hawthorn tree and five leaf creeper, lies in that their leaves contain not only chlorophyll, lutein and carotene, but also anthocyanin, a special substance rarely found in other plants. The first reason is that anthocyanins have "anti trend spirit". With the decrease of temperature and the increase of temperature difference between day and night, the content of anthocyanin will not decrease, but will increase rapidly. Secondly, anthocyanin has the characteristics of turning red when encountering acid and "not changing color when encountering alkali". According to the test, only a few plant leaves, such as maple, have acidic cell fluid. Therefore, with the fall of autumn and the increase of anthocyanins, the leaves will gradually turn from green to red. But for most plants, because of the low content of anthocyanin or the high content of anthocyanin, but the cell fluid is alkaline, no matter how the climate changes, the leaves will not turn red.

由此看來，楓葉等少數(shù)植物的葉子秋天變紅的內(nèi)因是花青素與酸性細(xì)胞液發(fā)生化學(xué)反應(yīng)，外因則是入秋后天氣轉(zhuǎn)寒，促進(jìn)了花青素大量增多，即氣象條件發(fā)生變化造成的。

It seems that the reason for the leaves of a few plants such as maple leaves turning red in autumn is the chemical reaction between anthocyanin and acid cell fluid, and the external reason is that the weather turns cold after autumn, which promotes a large number of anthocyanins, that is, the change of meteorological conditions.