近熱帶山區濕潤森林細根生長量時間動態的間接估測

Indirect Quantification Methods of Fine Root Temporal Dynamics in a Near Tropical Humid Mountainous Region

盧顯程(Xian-Cheng Lu)

指導教授 ： 黃倬英

國立臺灣大學/理學院/地理環境資源學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201803498

摘要

CO2是重要的溫室氣體，而森林是陸地生態系統中最大的碳庫，對於降低大氣中溫室氣體濃度起到十分關鍵的作用；隨著暖化，熱帶、近熱帶森林的生長在全球森林中所受到的衝擊較小，因此它們將作為碳吸存更重要的角色。
細根為直徑不大於2 mm的根，是植物吸收水分和養分的器官；作为森林碳库的组成部分，雖然其本身很微小，僅占森林生物量的5%，卻貢獻了凈初級生產量（Net Primary Production, NPP）的30% - 70%。因此，量化细根的生长，对研究森林生态系的碳循环是必要的。
森林地上部的信息（冠層密度、氣候條件等）可見而易得，甚至可以由遙測影像得到大範圍的資料；相反地，地下部根的觀測困難性造成對其研究相對較少，且傳統的細根量測方法具破壞性且耗費時間、人力。而藉由植物地上部與地下部的生態學關係，我們欲以地上部因子（生物性、非生物性）間接估測細根的生長。
研究樣區位於北台灣的棲蘭山，為以檜木為優勢物種的濕潤高山森林。野外調查於2016年2月開始，在三條樣線的共15個樣點，每三週採集枯落物、葉面積指數（Leaf Area Index, LAI）及拍攝細根影像，另收集樣區的氣象（溫度、濕度、雨量、光照、風速）、土壤（土壤溫度、土壤濕度）資料。本研究採用非破壞性而可進行時序觀測的微根管技術，將玻璃管永久埋入土壤，利用反射於管壁呈現細根影像並拍照。後續進行一系列圖像處理，包括遮罩、校正、切割、拼接、銳化、萃取、編號，最終計算得到細根於每一時期的體積，並轉換為生物量，進而建立細根生長量的經驗模型。
多元線性回歸的結果顯示，葉面積指數及其增量、光照、雨量、風速、土壤溫度，均對細根生長有顯著影響（R2 = 0.42, n = 36, p-value < 0.005)。生物因子上，葉（枯落物、冠層）與根的生長較為同步；而環境因子上，土壤與空氣（溫度、水分）特性對細根生長分別具有正、負向的影響效果。模型於時間尺度上可獲得細根生長動態，於空間尺度上亦可由遙測推估細根生長分佈。

關鍵字

細根生長量 ； 枯落物生產量 ； 葉面積指數（LAI） ； 氣象因子 ； 微根管技術 ； 圖像處理

並列摘要

Fine root, with diameter ≤ 2 mm, takes responsibility for water and nutrient transport. Besides being a carbon pool, it also provides a carbon flux pathway through plant canopy and soil, to contribute 30% to 70% of total net primary production (NPP) in the forest ecosystem, thus serving a dynamic role in its carbon cycling. Therefore, quantifying fine root productivity is necessary to study terrestrial carbon budget. However, compared to abundant studies on aboveground leaf and canopy, less is known about belowground root system due to its difficulty on observation and quantification. Based on the phenological correlation, we aimed to model fine root production by aboveground parameters.
The study was conducted in Chilan Mountain in northeast Taiwan, a near tropical moist forest. A study plot was set, with 15 minirhizotron tubes installed and root densities measured. We took fine root photographs by an interval of three weeks; presence and absence of fine roots were delineated by image processing algorithms to derive fine-root production (g C ha-1 d-1) through time.
As to the aboveground, we took biological and environmental factors into account, including litterfall production (branches and leaves), canopy density (leaf area index, LAI), meteorological (air temperature, air humidity, precipitation, solar radiation, wind speed), and soil physical conditions (soil temperature, soil moisture). As a result, the variables Leaf Area Index (LAI), △LAI, solar radiation, precipitation, wind speed, and soil temperature were particularly significant to root production, with adjusted R2 of 0.42 (n = 36, p-value < 0.005) by multiple linear regression. Synchrony existed in leaf flush and fine root emergence; in addition, environmental restrictions were more evident in soil than air conditions, where air temperature and precipitation were not limiting factors, which added the uniqueness to near tropical wet forests under global warming.
This study demonstrated the feasibility of utilized aboveground variables to indirectly assess fine root growth. The models could reveal fine root dynamics through time, or be further applied on the regional scale mapping with aid of remote sensing, where more validation need to be done to fill the intra- and inter-annual, plot- and region-scale gaps.

並列關鍵字

fine root productivity ； litterfall production ； LAI ； environmental factors ； minirhizotron ； image processing

參考文獻

References

Aragão, L., Malhi, Y., Metcalfe, D., Silva-Espejo, J., Jiménez, E., Navarrete, D., Almeida, S., Costa, A., Salinas, N., Phillips, O. (2009) Above-and below-ground net primary productivity across ten Amazonian forests on contrasting soils. Biogeosciences 6, 2759-2778.

Black, K., Harbron, C., Franklin, M., Atkinson, D., Hooker, J. (1998) Differences in root longevity of some tree species. Tree Physiology 18, 259-264.

Bonan, G.B., Chapin III, F.S., Thompson, S.L. (1995) Boreal forest and tundra ecosystems as components of the climate system. Climatic Change 29, 145-167.

Chen, J.M., Black, T. (1992) Defining leaf area index for non‐flat leaves. Plant, Cell & Environment 15, 421-429.