台灣南仁山亞熱帶雨林三種樹種的樹液流通量與風速及其他環境因子之關係

Abstract

植物藉由調控葉片氣孔的大小來控制蒸散作用和光合作用的速率，而這些生理功能亦受到外在環境因子，例如溼度、光度、溫度、土壤含水量、以及風力的影響。過往少有研究探討風力因子與蒸散作用之間的關係，因此本研究利用Granier-type Sensor測量不同風力影響下樹木的樹液流通量 (sap flux)的表現與差異。研究地區位於台灣南部的墾丁國家公園南仁山生態保護區內，前人研究指出保護區內的植被可區分為迎風、背風、緩風以及溪谷共四類型，本研究在迎風與緩風兩處生育地區選擇三種冠層優勢樹種，分別為迎風及緩風坡分布的港口木荷 (Schima superba var. kankaoensis)、廣泛分布的長尾栲 (Castanopsis cuspidate var. carlesii)，以及迎風坡分布的小葉赤楠 (Syzygium buxifolium)，每一種各選三株。在一年多的時間內連續監測樹液流通量，以探討三種樹種在不同時段內其樹液流通量的變化，並比較在相同生育地的三種樹種樹液流通量表現是否有所不同，以及在同種樹種不同生育地其樹液流通量表現是否有所不同。此外還同時測量光合作用有效光輻射光量 (photosynthetically active radiation；PAR)、溫度、相對溼度、風速與風向，來檢視環境因子與三種不同分佈類型樹種樹液流通量之間的關係，探討風力是否會影響三種樹種的樹液流通量的表現有所影響。 結果顯示，三種樹種在晴天時候的日樹液流通量分布圖大致成倒V字型，在中午期間樹液流通量為最高。但是在雨天的時候，日樹液流通量則大幅降低，呈現趨近0的平滑曲線。就季節變化而言，植株在冬季有較低的樹液流通量、夏季有較高的樹液流通量。三種樹種全部的樹液流通量值的出現頻率分布圖為反J型分布，表示樹液流通量值位於前半部較小的值出現的次數大於後半部的值，表示較小的樹液流通量佔有的地位相對重要。在颱風吹襲的狀態下，其樹液流通量的表現則類似於雨天的表現，但在強烈風速下，長尾栲的樹液流通量有異常上升的趨勢。 三種樹種的日總累積樹液流通量，以港口木荷的流通量最高，小葉赤楠的最低。在迎風與緩風生育地的比較上，三種樹種的樹液流通量皆有差異，其中港口木荷在迎風區有較高的樹液流通量，而長尾栲與小葉赤楠在緩風區有較高的樹液流通量，顯示不同物種間的日累積樹液流通量在兩生育地間有不同的表現。 根據環境因子與樹液流通量之關係和逐步迴歸分析的結果顯示，對港口木荷與小葉赤楠而言，光合作用有效光輻射光量值、日均溫與風速皆為影響樹液流通量的因子；但對長尾栲而言，風速並非明顯的影響因子。總結來看，光合作用有效光輻射光量與溫度為最主要影響日累積樹液流通量的因子，而風速只有微幅的調控，並且因樹種而異。但本實驗因水蒸氣壓差 (VPD)的數據資料有所缺失，使得水蒸氣壓差對於樹液流通量的影響程度難以清楚釐清。 在分級過後的環境因子中，風速對於港口木荷的影響較為明顯。在低溫時，較強的風速才會抑制港口木荷的樹液流通量；而當溫度升高的時候，低風速即會對樹液流通量產生抑制的作用。對長尾栲而言，並未發現風速對樹液流通量有明顯的影響。小葉赤楠大部分的樣木顯示出類似於長尾栲的表現，即風速對樹液流通量並無特殊的影響，但是有一棵樣木顯示類似港口木荷的反應，其風速對於樹液流通量有抑制的作用，導致樹液流通量在高光合作用有效光輻射光量之下也沒有快速升高的現象。 綜合以上結果推測，小葉赤楠及長尾栲則屬迎風型樹種和廣泛分布型樹種，對迎風環境上的長期適應，造成內部生理上 (氣孔調控)與外部形態上的特化，而產生抗風的機制，以減少水分的散失。緩風型樹種的港口木荷則在迎風區有較高的樹液流通量，顯示在水份充足的狀態下，港口木荷蒸散量的增加，有助於生長量的提升，幫助港口木荷在強風的狀態下能夠生長存活，為另一種適應的機制。 本研究顯示，在光合作用有效光輻射光量值高的期間 (如：中午、晴天與夏季)，植株有較高的樹液流通量， 顯示光合作用有效光輻射光量對樹液流通量有重要的影響，與其他地區的研究相符合。三種樹種在不同生育地的樹液流通量值有所不同，可能與樹種的葉片結構有關。相同樹種在風力影響程度不同的生育地，其樹液流通量的表現也有所差異，顯示與風力因子有關。在探討的環境因子中，光合作用有效光輻射光量與溫度對於樹液流通量的表現影響較大，風速則僅呈現微幅調控的效能。

Plants use stomata to control the rate of transpiration and photosynthesis. These physiological processes may be also regulated by environmental factors such as humidity, light, temperature, soil moisture, and wind stress.Only a few studies have attempted to investigat the relationship between wind speed and transpiration. Therefore, this study seeks to understand the performances of sap flux under different degrees of wind stress, using the Granier-type sensors to measure sap flux. The study site is located in the Nanjenshan Reserve, Ken-Ting National Park, southern Taiwan. Vegetation in the study area was classified into four habitat types, including windward, leeward, intermediate and valley. Three dominant canopy-tree species slected for this study were Schima superba var. kankaoensis (windward and intermediate type), Castanopsis cuspidate var. carlesii (widely distributed type) and Syzygium buxifolium (windward type). Three individuals (replicates) of each one of the three species were used for the following measurements. Sap flux values were continually measured for each individual over a period of 1.5 years. Sap flux patterns of three tree species were then compared with their circulation changes at different time scales. This study examined the performance of sap flux of three species in the same habitats and compared the performance of sap flux of the same species between windward and intermediate habitats. Photosynthetically active radiation (PAR), temperature, humility, wind speed and wind direction were recorded in the meantime. The relationships between sap flux and environmental factors were analyzed and the importance of wind effects was discussed. The results showed that in sunny days, the daily sap flux of all three species in different habitats had an inverted V-shaped pattern, with the highest flux occurring at noon. However, the daily sap flux decreased dramatically in rainy days, with a relatively smooth curves approximated to y = 0 line. As for yearly sap flux distribution patterns, sum of daily sap flux was higher in the summer than in the winter. Sap flux data of the three species were anti-J distributions. It means that the frequencies of low sap flux values are far higher than the frequencies of high sap flux values. The performance of sap flux during typhoon days was similar to that during rainy day, but sap flux of Castanopsis cuspidate var. carlesii showed an unusual increase in strong wind. In term of the sum of daily sap flux of the three species, Schima superba var. kankaoensis had highest values and Syzygium buxifolium the lowest values. Individuals of same species growing in windward and intermediate habitats had significant differences in sap flux, such that Schima superba var. kankaoensis in the windward habitat had higher sap flux than those in the intermediate habitat, but Castanopsis cuspidate var. carlesii and Syzygium buxifolium had opposite patterns. According to results from plotting the linear relationships between sap flux and environmental factors and the results of stepwise analysis, PAR, temperature and wind speed were the major factors determining the sap flux of Schima superba var. kankaoensis and Syzygium buxifolium. But for Castanopsis cuspidate var. carlesii, there was no obvious relationship between sap flux and wind speed. Due to missing data of vapor pressure difference (VPD), the relationship between sap flux and VPD is still not clarified. The distribution patterns of grading environmental factors and sap flux of three species are different. Sap flux of Schima superba var. kankaoensis was inhibited by the strong winds under low temperature. When the temperature increased, inhibition occurred at a lower wind speed. There was no special pattern between sap flux and wind for Castanopsis cuspidate var. carlesii and Syzygium buxifolium. Only one tree sample of Syzygium buxifolium showed a similar performance to Schima superba var. kankaoensis. It showed that wind speed could inhibit the rising of sap flux at high PAR. Castanopsis cuspidate var. carlesii and Syzygium buxifolium which are widely distributed and windward species are more plastic and able to adapt to their environment due to long-term morphological and physiological modifications. However, Schima superba var. kankaoensis, an intermediate species, had higher sap flux in the windward habitat. The increases of the transpiration of Schima superba var. kankaoensis result the increases of growth increment in the habitat which had sufficient water. This kind of adaptation mechanism could help Schima superba var. kankaoensis to survive in strong wind stress. This study shows that PAR has an important impact on sap flux because there is higher sap flux under PAR conditions (such as noon, sunny day, summer). The differences in sap flux values among three species in the same habitat might be related to differences in leaf structure. Sap flux values of individuals the same species in windward and intermediate habitats were different, suggesting that wind is related to transpiration activities. Among the examined environmental factors, PAR and temperature have greater effects on sap flux, while wind speed only affects the performance of sap flux slightly.