柳杉人工林林下三種闊葉稚樹生長及光合作用對小區塊疏伐的反應

Growth and Photosynthetic Responses of Understory Saplings of Three Hardwood Species to Small Patch Thinning in a Cryptomeria japonica Plantation

曾繁絢(Fan-Hsuan Tseng)

指導教授 ： 郭耀綸

國立屏東科技大學/農學院/森林系所/碩士(2013年)

https://doi.org/10.6346/NPUST.2013.00286

摘要

森林疏伐後，林內入射光資源增加，應對林下樹苗的生理活動及生長有所助益，然而甚少有研究驗證此假說。本研究於2007年12月至2009年2月間，調查南投縣人倫地區的柳杉林其林下三種闊葉樹苗，在疏伐孔隙區、孔隙邊區及對照區三種生育地，植株生理活動及形態生長的差異。試驗樹種為琉球雞屎樹、細枝柃木及山龍眼。結果發現，在孔隙區的植株可接受到約27%的相對光量，而孔隙邊區及對照區植株分別只接受到15及4%的光量。藉由一年12次的光合作用日變化測定，得知琉球雞屎樹的日平均淨光合作用率在三處樣區中並無顯著差異，細枝柃木則以對照區顯著較低，而山龍眼則三處樣區均具顯著差異，以孔隙區顯著最大。這三種樹種所有植株的光合作用日變化年平均值，與各植株接受到的光量間，都有極顯著直線正相關，但山龍眼該迴歸式的斜率最高，斜率為琉球雞屎樹的3倍。琉球雞屎樹在三處樣區的光飽和光合作用率(Asat)僅在 3.5~4.4 µmol CO2 m-2 s-1之間，細枝柃木及山龍眼生長於孔隙區植株的Asat分別為7.3及8.4 µmol CO2 m-2 s-1，顯著較生長於對照區植株的4.6及3.7 µmol CO2 m-2 s-1高。此外，琉球雞屎樹在孔隙區植株的葉片有黃化現象，且Fv/Fm值與葉綠素濃度指標僅為0.69與47.1，顯示該樹種遭受強光逆境。疏伐後一年，在孔隙區樹高相對生長率最大的是山龍眼，而葉面積相對生長率最大的是細枝柃木。山龍眼與細枝柃木所有植株的樹高及葉面積相對生長率，與各植株接受到的光量間，均具有極顯著直線正相關，而琉球雞屎樹則否。本研究發現此三種植物雖然都是耐陰的樹種，但山龍眼及細枝柃木在生理上有馴化高光的能力，在疏伐形成的孔隙環境不易遭光抑制，且較能有效利用疏伐後提高的光資源，提高光合作用率，因而有較高的相對生長率。琉球雞屎樹在生理不具馴化高光能力，在孔隙環境不能顯著增加生長。

關鍵字

光合作用日變化 ； 光資源 ； 光抑制 ； 生理馴化 ； 相對生長率

並列摘要

Three hardwood species, namely Lasianthus fordii Hance, Eurya loquaiana Dunn., and Helicia formosana Hemmsl., were investigated for their growth and photosynthetic responses to different light environments created after a small patch thinning in a Cryptomeria japonica D. Don. plantation in central Taiwan. Three different environments, including a gap site in the thinned stand, a non-gap site next to the gap site, and an unthinned control site, were investigated. In average, understory saplings of the 3 studied species received 27, 15, and 4% of relative light intensity in the gap, non-gap, and control site, respectively. For H. formosana and E. loquaiana, the light-saturated photosynthetic rates (Asat) of their saplings in the gap and non-gap site were all significantly higher than that in the control site, showing an obvious phenomenon of physiological acclimation. This acclimation phenomenon was not detected in the saplings of L. fordii. In addition, through monitoring 12 diurnal courses of photosynthesis in a year, the annual mean diurnal photosynthetic rates (Amean) of saplings of H. formosana and E. loquaiana in the gap and non-gap site were also significantly higher than that in the control site; however, no significant differences in Amean among the 3 sites were found with saplings of L. fordii. Regression analysis further revealed significant linear relationship between Amean and amount of light received by saplings in all 3 species, with H. formosana having the highest slope (a 3-fold higher value than that of L. fordii). The mean chlorophyll fluorescence value (Fv/Fm) of saplings of H. formosana in the gap site was ≧ 0.75, signifying no photoinhibition occurred; yet the Fv/Fm value of saplings of L. fordii in the gap and non-gap site indicated that their saplings might have suffered mild photoinhibition under higher light environment. One year after the thinning operation, saplings of H. formosana had the highest relative growth rate of height (RGR-H), while saplings of E. loquaiana had the highest relative growth rate of leaf area (RGR-A), in the gap site. With RGR-H and RGR-A data obtained from all the sampled saplings of H. formosana and E. loquaiana, we found significantly positive relationships between the growth data and the amount of available light received by the saplings. However, no such significant relationship was found for saplings of L. fordii. In conclusion, although the 3 studied species are essentially all shade-tolerant species, saplings of H. formosana and E. loquaiana possess the ability of acclimation to elevated light resources without suffering photoinhibition which could be induced by higher incident light in the gap environment formed after thinning. They are more capable of utilizing the elevated light resources and raising their photosynthesis accordingly, so that their growth is promoted. On the other hand, saplings of L. fordii do not have the ability of physiological acclimation to elevated light resources, and so their growth is not significantly promoted in the gap site.

並列關鍵字

acclimation ； diurnal ； photosynthesis ； light availability ； photoinhibition ； relative growth rate

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