摘要： 叶片中非结构性碳水化合物(NSC)不仅是植物维持代谢活动的重要物质基础, 也随凋落物归还土壤并为土壤微生物提供碳源, 对凋落物分解和土壤有机质形成具有重要意义。该研究比较了同质园中11个亚热带代表性树种新鲜叶与凋落叶NSC (可溶性糖、淀粉)含量。结果表明, 所有树种新鲜叶NSC含量均显著高于凋落叶, 新鲜叶中NSC含量为68.7-126.3 mg∙g-1, 而凋落叶中NSC含量为31.4-79.5 mg∙g-1。同时, 可溶性糖含量在新鲜叶和凋落叶中的变化幅度均远大于淀粉: 可溶性糖在新鲜叶中的平均含量是凋落叶的3.3倍; 而淀粉在新鲜叶中的平均含量仅为凋落叶的1.2倍。另外, 对不同功能类群的比较发现, 常绿阔叶树种与落叶阔叶树种NSC含量差异并不显著, 而针叶树种NSC含量明显低于阔叶树种。具体表现为: 在新鲜叶中, 常绿阔叶、落叶阔叶树种NSC含量平均为99.7和96.8 mg∙g-1, 而常绿针叶树种平均为75.4 mg∙g-1; 在凋落叶中, 常绿阔叶、落叶阔叶树种NSC含量平均为47.2和50.7 mg∙g-1, 而常绿针叶树种平均为33.3 mg∙g-1。这些结果表明, NSC作为林木碳代谢组分, 在叶片衰老前可能向新鲜叶转移, 反映了林木叶片碳存储策略。然而, 不管是新鲜叶还是凋落叶, 杉木(Cunninghamia lanceolata)、马尾松(Pinus massoniana)等针叶树种叶片NSC含量显著低于阔叶树种, 这可能降低这些针叶树种凋落叶初始基质质量。
叶片中非结构性碳水化合物(NSC)不仅是植物维持代谢活动的重要物质基础, 也随凋落物归还土壤并为土壤微生物提供碳源, 对凋落物分解和土壤有机质形成具有重要意义。该研究比较了同质园中11个亚热带代表性树种新鲜叶与凋落叶NSC (可溶性糖、淀粉)含量。结果表明, 所有树种新鲜叶NSC含量均显著高于凋落叶, 新鲜叶中NSC含量为68.7-126.3 mg∙g-1, 而凋落叶中NSC含量为31.4-79.5 mg∙g-1。同时, 可溶性糖含量在新鲜叶和凋落叶中的变化幅度均远大于淀粉: 可溶性糖在新鲜叶中的平均含量是凋落叶的3.3倍; 而淀粉在新鲜叶中的平均含量仅为凋落叶的1.2倍。另外, 对不同功能类群的比较发现, 常绿阔叶树种与落叶阔叶树种NSC含量差异并不显著, 而针叶树种NSC含量明显低于阔叶树种。具体表现为: 在新鲜叶中, 常绿阔叶、落叶阔叶树种NSC含量平均为99.7和96.8 mg∙g-1, 而常绿针叶树种平均为75.4 mg∙g-1; 在凋落叶中, 常绿阔叶、落叶阔叶树种NSC含量平均为47.2和50.7 mg∙g-1, 而常绿针叶树种平均为33.3 mg∙g-1。这些结果表明, NSC作为林木碳代谢组分, 在叶片衰老前可能向新鲜叶转移, 反映了林木叶片碳存储策略。然而, 不管是新鲜叶还是凋落叶, 杉木(Cunninghamia lanceolata)、马尾松(Pinus massoniana)等针叶树种叶片NSC含量显著低于阔叶树种, 这可能降低这些针叶树种凋落叶初始基质质量。
Abstract: Aims Non-structural carbohydrates (NSC) are available carbon in plants and can be utilized as an energy source during plant metabolism, so NSC are important components for plant growth and metabolic activities, particularly under environmental stress. Moreover, NSC in senescent leaves as litter-fall provide available carbon for soil microorganisms involving in soil organic matter formation and biogeochemical cycles in forests. Therefore, study on the variation in NSC between fresh and senescent leaves is of great significance for understanding the carbon metabolism during plant growth and carbon biogeochemical cycles during early decomposition of plant litter. The objective of this study was to determine the difference in NSC content between fresh and senescent leaves of 11 subtropical tree species and the variation between leaves with different plant functional types. Methods A common garden was established in the stands with similar soil development, aspect, slope, and management history at the Sanming Research Station of Forest Ecosystem and Global Change in February 2012. A total of 13 representative subtropical tree species (2-year-old) were planted in the common garden, which were designed according to random blocks with 4 replicates for each tree species (a total of 52 plots with approximately 0.1 hm2 for each plot). In this study, the fresh and senescent leaves of 11 tree species, including evergreen broadleaved species Schima superba, Lindera communis, Elaeocarpus decipiens, Michelia macclurei, Castanopsis carlesii and Cinnamomum camphora, deciduous broadleaved tree species Liriodendron chinense, Liquidambar formosana and Sapindus mukorossi, and coniferous tree species Cunninghamia lanceolata and Pinus massoniana were collected in August 2019. The contents of NSCs, including soluble sugars and starch, in fresh and senescent leaves of the 11 tree species were determined. Important findings The NSC content was significantly higher in fresh leaves than that in senescent leaves for all of the studied tree species. The NSC contents in fresh leaves were 68.7-126.3 mg∙g-1, while those in senescent leaves were 31.4-79.5 mg∙g-1. Notably, the variation in soluble sugar between fresh leaves and senescent leaves was much greater than that of starch. Specifically, the average content of soluble sugar in fresh leaves was 3.3 times greater than that of senescent leaves, and the average starch content in fresh leaves was 1.2 times greater than that of senescent leaves. Moreover, the NSC contents in both fresh and senescent leaves varied significantly among trees with different plant functional types. For example, the NSC contents in both fresh and senescent leaves of evergreen and deciduous broad-leaved trees showed similar levels, while the NSC contents in evergreen coniferous trees were significantly lower than those in broad-leaved trees. In fresh leaves, the average NSC contents in evergreen and deciduous broad-leaved trees were 99.7 and 96.8 mg∙g-1, respectively, while the average NSC content in evergreen coniferous trees was 75.4 mg∙g-1; In senescent leaves, the average NSC contents in evergreen and deciduous broad-leaved trees were 47.2 and 50.7 mg∙g-1, respectively, while the average NSC content in evergreen coniferous trees was 33.3 mg∙g-1. These results suggest that NSC, an important carbon metabolic component for trees, could be transferred from senescent leaves to fresh leaves before senescence; this is a significant strategy for carbon storage during plant growth. However, the NSC content was significantly lower in subtropical coniferous trees (such as Cunninghamia lanceolata and Pinus massoniana) than in broad-leaved trees, regardless of fresh and senescent leaves, suggesting that the initial substrate quality is lower in these coniferous litters with less labile components following forest plantation in subtropical China. This difference in NSC content in foliar litter has significant influence for litter decomposition and soil organic matter formation mediated by microbial metabolism and turnover. These results are of great significance for improving the theory of carbon metabolism during plant growth and for understanding the dynamic changes of carbon components during the early decomposition of leaves litter in subtropical forests.
Aims Non-structural carbohydrates (NSC) are available carbon in plants and can be utilized as an energy source during plant metabolism, so NSC are important components for plant growth and metabolic activities, particularly under environmental stress. Moreover, NSC in senescent leaves as litter-fall provide available carbon for soil microorganisms involving in soil organic matter formation and biogeochemical cycles in forests. Therefore, study on the variation in NSC between fresh and senescent leaves is of great significance for understanding the carbon metabolism during plant growth and carbon biogeochemical cycles during early decomposition of plant litter. The objective of this study was to determine the difference in NSC content between fresh and senescent leaves of 11 subtropical tree species and the variation between leaves with different plant functional types.
Methods A common garden was established in the stands with similar soil development, aspect, slope, and management history at the Sanming Research Station of Forest Ecosystem and Global Change in February 2012. A total of 13 representative subtropical tree species (2-year-old) were planted in the common garden, which were designed according to random blocks with 4 replicates for each tree species (a total of 52 plots with approximately 0.1 hm2 for each plot). In this study, the fresh and senescent leaves of 11 tree species, including evergreen broadleaved species Schima superba, Lindera communis, Elaeocarpus decipiens, Michelia macclurei, Castanopsis carlesii and Cinnamomum camphora, deciduous broadleaved tree species Liriodendron chinense, Liquidambar formosana and Sapindus mukorossi, and coniferous tree species Cunninghamia lanceolata and Pinus massoniana were collected in August 2019. The contents of NSCs, including soluble sugars and starch, in fresh and senescent leaves of the 11 tree species were determined.
Important findings The NSC content was significantly higher in fresh leaves than that in senescent leaves for all of the studied tree species. The NSC contents in fresh leaves were 68.7-126.3 mg∙g-1, while those in senescent leaves were 31.4-79.5 mg∙g-1. Notably, the variation in soluble sugar between fresh leaves and senescent leaves was much greater than that of starch. Specifically, the average content of soluble sugar in fresh leaves was 3.3 times greater than that of senescent leaves, and the average starch content in fresh leaves was 1.2 times greater than that of senescent leaves. Moreover, the NSC contents in both fresh and senescent leaves varied significantly among trees with different plant functional types. For example, the NSC contents in both fresh and senescent leaves of evergreen and deciduous broad-leaved trees showed similar levels, while the NSC contents in evergreen coniferous trees were significantly lower than those in broad-leaved trees. In fresh leaves, the average NSC contents in evergreen and deciduous broad-leaved trees were 99.7 and 96.8 mg∙g-1, respectively, while the average NSC content in evergreen coniferous trees was 75.4 mg∙g-1; In senescent leaves, the average NSC contents in evergreen and deciduous broad-leaved trees were 47.2 and 50.7 mg∙g-1, respectively, while the average NSC content in evergreen coniferous trees was 33.3 mg∙g-1. These results suggest that NSC, an important carbon metabolic component for trees, could be transferred from senescent leaves to fresh leaves before senescence; this is a significant strategy for carbon storage during plant growth. However, the NSC content was significantly lower in subtropical coniferous trees (such as Cunninghamia lanceolata and Pinus massoniana) than in broad-leaved trees, regardless of fresh and senescent leaves, suggesting that the initial substrate quality is lower in these coniferous litters with less labile components following forest plantation in subtropical China. This difference in NSC content in foliar litter has significant influence for litter decomposition and soil organic matter formation mediated by microbial metabolism and turnover. These results are of great significance for improving the theory of carbon metabolism during plant growth and for understanding the dynamic changes of carbon components during the early decomposition of leaves litter in subtropical forests.
表1 同质园11个树种种植7年后0-10 cm土壤物理性质(平均值±标准误, n = 3)
Table 1 Soil physical properties in 0-10 cm soil layer after 7 years of plantations of the 11 tree species in the subtropical common garden (mean ± SE, n = 3)
表2 同质园中11个代表性树种生长情况(平均值±标准误, n = 4)
Table 2 Plant growth status of the 11 tree species in the subtropical common-garden (mean ± SE, n = 4)
表3 树种和叶片类型对非结构性碳水化合物含量的双因素方差分析
Table 3 Two-way ANOVA analysis for the effects of tree species and leaf type on the content of non-structural carbohydrates
图1 亚热带同质园11个代表性树种新鲜叶和凋落叶的非结构性碳水化合物、可溶性糖、淀粉含量(A, C, E)及其在不同功能类型叶片之间的差异(B, D, F)(平均值±标准误, n = 3)。星号表示新鲜叶与凋落叶之间差异显著(*, p < 0.05; **, p < 0.01; ***, p < 0.001)。不同大写字母表示新鲜叶非结构性碳水化合物(可溶性糖、淀粉)含量在不同树种/不同功能类型叶片间差异显著(p < 0.05), 不同小写字母表示凋落叶非结构性碳水化合物(可溶性糖、淀粉)含量在不同树种/不同功能类型叶片间差异显著(p < 0.05)。CC, 米槠; CC1, 香樟; CL, 杉木; ED, 杜英; LC, 鹅掌楸; LC1, 香叶; LF, 枫香; MM, 火力楠; PM, 马尾松; SM, 无患子; SS, 木荷。Db, 落叶阔叶树种(n = 9); Eb, 常绿阔叶树种(n = 18); Ec, 常绿针叶树种(n = 6)。
Fig. 1 Contents of non-structural carbohydrates, soluble sugars and starch in fresh and senescent leaves of 11 trees in the subtropical common-garden (A, C, E), and difference in them among different plant functional types (B, D, F)(mean ± SE, n = 3). Asterisks denote significant differences between fresh and senescent leaves for the same tree species (*, p < 0.05; **, p < 0.01; ***, p < 0.001). Different uppercase letters denote significant differences in non-structural carbohydrates (soluble sugars, starch) content in fresh leaves among tree species/plant functional traits (p < 0.05), and different lowercase letters denote significant differences in non-structural carbohydrates (soluble sugars, starch) content in senescent leaves among tree species/plant functional traits (p < 0.05). CC, Castanopsis carlesii; CC1, Cinnamomum camphora; CL, Cunninghamia lanceolata; ED, Elaeocarpus decipiens; LC, Liriodendron chinense; LC1, Lindera communis; LF, Liquidambar formosana; MM, Michelia macclurei; PM, Pinus massoniana; SM, Sapindus mukorossi; SS, Schima superba. Db, deciduous broadleaved species (n = 9); Eb, evergreen broadleaved species (n = 18); Ec, evergreen coniferous species (n = 6).
图2 新鲜叶的非结构性碳水化合物(NSC)含量与碳(C)、氮(N)、磷(P)含量的相关关系。SS, 可溶性糖; St, 淀粉。数值为相关系数, 星号表示显著相关(**, p < 0.01)。
Fig. 2 Correlation between non-structural carbohydrates (NSC) and carbon (C), nitrogen (N), phosphorus (P) contents in fresh leaves. SS, soluble sugars; St, starch. The value is correlation coefficient, asterisks denote significant correlations (**, p < 0.01).