台灣重要原生樹種綠葉及落葉氮、磷濃度

Abstract

氮與磷被普遍認為是對陸地植物生長兩個最重要的限制因子，植物族群的生物量產量通常由氮及磷所控制，葉子的氮與磷濃度也常被視為養分狀態的指標，所以植物葉部的氮、磷濃度的分析是植物生理生態學上重要的議題。自2006年7月至2008年8月，本研究在台灣中部山區天然林採集17種原生的闊葉樹種與5種針葉樹種的成熟綠葉與枯落葉進行氮、磷含量分析，以探討台灣森林樹木生長氮及磷的相對限制程度。 針葉樹種綠葉氮濃度低於闊葉樹，磷濃度則較高，且針葉樹綠葉的氮磷重量比顯著低於闊葉樹種，根據Koerselman and Meuleman (1996)所訂定的氮磷重量比門檻，針葉樹種的生長比較受到氮的限制(氮磷重量比＜14)，而闊葉樹種的生長比較受到磷的限制(氮磷重量比 > 16)。而根據Killingbeck (1996) 所訂定的氮、磷再吸收度標準，17種闊葉樹種有16種氮再吸收不完全(枯落葉氮濃度>1.0%)，而有10種磷再吸收不完全(枯落葉磷濃度>0.05%)，5種針葉樹種只有1種氮再吸收不完全，但有4種磷再吸收不完全，因此，針葉樹仍以氮的限制為主，闊葉樹以磷的限制為主。 生育地間綠葉氮濃度、磷濃度與氮磷比間有顯著差異(p＜0.0001)，原因可能是來自於生育地溫度或是土壤年齡的差異，根據Koerselman and Meuleman (1996)所訂定的氮磷重量比門檻，溪頭、神木村的植物生長比較受到氮的限制(氮磷重量比＜14)，塔塔加、合歡山植物生長比較受到磷的限制(氮磷重量比 >16)。根據Killingbeck (1996) 所訂定的氮、磷再吸收度標準，塔塔加與合歡山植物氮再吸收較完全，神木村植物P再吸收較完全，生育地間的氮再吸收率有顯著差異(p <0.05)，但磷再吸收率沒有顯著差異。 由於台灣針葉樹種分佈的海拔明顯高於大多數的闊葉樹種，因此針葉樹及闊葉樹的差異可能是反映生育地的差異。本研究的綠葉磷濃度與氮磷比與溫度的關係與「土壤母層年齡假說」(the Soil Substrate Age hypothesis)相符，但綠葉氮濃度與溫度的關係卻符合「溫度-生物環境化學假說」(°T-Biogeochemistry hypothesis)

Abstract Nitrogen (N) and phosphorous (P) are generally considered as the most important factors limiting plant growth and ecosystem productivity. Foliar concentrations of nitrogen and phosphorous are good indicators of nutrient status in plants, and thus have been one of the major topics in plant physiological ecology. In this study, from July 2006 to August 2008, I collected fresh leaf and leaf fall samples from 17 native broadleaf tree species and 5 native coniferous species in the montane forests of central Taiwan to analyze their nitrogen and phosphorous concentrations and to determine the relative limitation of N or P on the growths of forest trees in Taiwan. Compared with hardwood species, conifer species had higher foliar N concentrations and lower foliar P concentrations. According to the thresholds of foliar N: P weight ratio proposed in Koerselman and Meuleman (1996), N was the major limiting factor for conifers species (N: P weight ratio <14), and P for hardwood species (N: P weight ratio >16). According to the thresholds of resorption proficiency proposed in Killingbeck (1996), 16 out of 17 hardwood species had incomplete N resorption (N concentrations in leaf fall >1.0) and 10 out of 17 had incomplete P resorption (P concentrations in leaf fall >0.05). By contrast, only 1 out of 5 conifer species had incomplete N resorption and 4 out of 5 conifer species had incomplete P resorption. Therefore, these comparisons still suggest that N was the major limiting factor for conifers species and P for hardwood species. Nitrogen and P concentrations and N: P weight ratio differed significantly between sampling sites (p <0.0001), and may result from the variations in temperature and the soil age. According to the thresholds of foliar N: P weight ratio proposed in Koerselman and Meuleman (1996), N was the major limiting factor for trees in Chitou and Shen-Mu Village (N: P weight ratio < 14) but P for trees in Tatachia and Mt. Ho-Huan (N: P weight ratio >16). According to the thresholds of resorption proficiency proposed in Killingbeck (1996), trees in Tatachia and Mt. Ho-Huan had more completed N resorption than the other sites but trees in Shen-Mu Village had more completed P resorption than the other sites. Nitrogen resorption efficiency differed significantly between the sampling sites (p <0.05), but P resorption efficiency did not differ significantly. Since conifers species are distributed in higher elevations than hardwood species in Taiwan. The differences between conifer and hardwood species could simply reflect the differences between the sites. In my study, the relationships between foliar P/N:P ratio and temperature were correspond to the Soil Substrate Age hypothesis, but between foliar N and temperature were correspond to the °T-Biogeochemistry hypothesis.