中亚热带13种树种幼苗叶片和细根可溶性有机碳的数量特征和结构特征

Quantitative and structural characteristics of dissolved organic carbon in 13 tree seedling leaves and fine roots in the mid-subtropics

植物叶片和细根输入的可溶性有机碳(Dissolved organic carbon, DOC)是森林生态系统最活跃的组成部分,对生态系统的碳循环有重要作用。以中亚热带13种典型树种为研究对象,测定其幼苗叶片和细根(0—1 mm和1—2 mm)的碳氮含量,淋溶产生的DOC浓度以及傅里叶红外光谱特征,分析不同树种和不同器官之间DOC的数量特征和结构特征。结果表明:(1)浙江桂在叶片和细根(0—1 mm和1—2 mm)的总碳含量上最高,竹柏在叶片和0—1 mm细根的总碳含量上最低,观光木在1—2 mm细根的总碳含量上最低。花榈木和罗汉松在叶片的总氮含量上分别为最高和最低,木荚红豆和观光木分别在0—1 mm和1—2 mm细根的总氮含量上最高,冬青在细根(0—1 mm和1—2 mm)的总氮含量上最低。(2)刨花楠、闽楠和浙江桂等樟科树种在叶片淋溶产生的DOC浓度上最高,而罗汉松和和竹柏等罗汉松科树种在叶片淋溶产生的DOC浓度上最低;花榈木和木荚红豆等红豆属树种在细根(0—1 mm和1—2 mm)淋溶产生的DOC浓度上最高;刨花楠、闽楠和浙江桂等樟科树种在细根(0—1 mm和1—2 mm)淋溶产生的DOC浓度上最低。(3)红外光谱显示,13种树种叶片和细根淋溶产生DOC的红外光谱特征具有一定的相似性,都有6个吸收峰和1个透射峰。浙江桂叶片淋溶产生的DOC在各个波段的吸收率上最高,冬青叶片最低;红豆杉细根(0—1 mm和1—2 mm)淋溶产生的DOC在各个波段的吸收率上最高,木荚红豆0—1 mm细根淋溶产生的DOC在各个波段吸收率上最低,丝栗栲1—2 mm细根淋溶产生的DOC在各个波段吸收率上最低。研究表明在植物生物多样性较高的亚热带常绿阔叶林,树种和器官类型在调节DOC的数量特征和结构特征上起重要作用,相关研究应充分考虑到不同材料之间的差异性。气候变化下树种分布、降雨强度与频率的改变,将强烈影响森林中可溶性有机碳的数量与组成,从而影响到亚热带森林土壤微生物活动与养分循环。因此,通过比较不同树种的叶片与细根产生的DOC数量与组成结构上的差异,为完善和补充气候变化下亚热带常绿天然林碳循环研究提供科学依据。

Dissolved organic carbon(DOC) from plant leaves and fine roots is one of the most active compounds in forest ecosystem. In this study, we chose 13 tree seedlings in mid-subtropical evergreen broadleaves forest and measured leaves and fine roots extraction by water to study DOC production and composition. We measured carbon and nitrogen concentration of leaves and fine roots(0—1 mm and 1—2 mm), DOC concentration and composition by using Fourier transform infrared spectroscopy(FTIR) in this study. Our results show that(1) Cinnamomum chekiangense has the highest carbon concentration in leaves and fine roots(0—1 mm and 1—2 mm), Podocarpus nagi has the lowest carbon concentration in leaves and 0—1 mm fine roots, and Tsoongiodendron odorum has the lowest carbon concentration in 1—2 mm fine roots. Ormosia henryi has the highest nitrogen concentration in leaves, while Podocarpus macrophyllus has the lowest nitrogen concentration in leaves. Ormosia xylocarpa has the highest nitrogen concentration in 0—1 mm fine roots, and Tsoongiodendron odorum has the highest nitrogen concentration in 1—2 mm fine roots, while LIlex chinensis has the lowest nitrogen concentration in fine roots(0—1 mm and 1—2 mm).(2) Lauraceae species such as Machilus pauhoi, Phoebe bournei and Cinnamomum chekiangense have the highest DOC concentration from leaves leaching, while Podocarpus macrophyllus and Podocarpus nagi have the lowest DOC concentration from leaves leaching. Ormosia henryi and Ormosia xylocarpa have the highest DOC concentration from fine roots(0—1 mm and 1—2 mm) leaching, while Machilus pauhoi, Phoebe bournei and Cinnamomum chekiangense have the lowest DOC concentration from fine root(0—1 and 1—2 mm) leaching.(3) The infrared spectra showed that all 13 species in leaves and fine roots(0—1 mm and 1—2 mm) have similar infrared spectra by 6 absorption peaks and 1 transmission peak. The DOC produced by the leaching of Cinnamomum chekiangense leaves has the highest absorption rate in each band, and the LIlex chinensis leaves have the lowest one. The DOC produced by the leaching of Taxus chinensis fine roots(0—1 mm and 1—2 mm) has the highest absorption rate in each band. The DOC produced by the leaching of 0—1 mm fine roots of Ormosia xylocarpa has the lowest absorption rate in each band. The DOC produced by the leaching of 1—2 mm fine roots of Castanopsis fargesii has the lowest absorption rate in each band. Our study indicated that tree species and organ types played the important roles in regulating the quantitative and structural characteristics of DOC, and these differences should be fully taken into account in relevant studies, especially in subtropical evergreen broad—leaved forests with high plant biodiversity. It has been showed climate change would result transfer of tree species, rainfall intensity and frequency, strongly affecting the amount and composition of DOC, soil microbial activities and nutrient cycling in subtropical forests. Therefore, this study will improve our understanding on carbon cycle of subtropical evergreen natural forests in the future climate changes.