中国科学院水利部水土保持研究所机构知识库

      碳水化合物是植物光合作用的主要产物。非结构性碳水化合物(non-structural carbohydrate, NSC)是植物生长代谢过程中重要的能量供应物质，在植物的呼吸、生长和其它生理需求与光合作用不同步时提供碳的缓冲区。NSC 的变化不仅反映同化物储蓄和生长投资分配之间的动态平衡，而且进一步影响植物的生长和对环境变化的响应。全球氮（N）沉降对植物 NSC 含量的影响已成为该领域的研究热点，目的是揭示生态系统的碳平衡和物质循环对土壤有效 N 变化的响应机制，以此提出有参考价值的人工林培育和经营策略。本研究以一年生油松幼苗盆栽 N 添加实验为基础，设置 4 种氮添加水平(0、3、6、12 g N⋅m^-2⋅a^-1)，将植物器官分为叶片、枝干、不同径级(0-1mm、1-2mm、>2mm)根系 5 个器官，通过定期取样和脉冲标记等方法研究了氮添加对油松幼苗不同器官 NSC 及其组分（可溶性糖和淀粉）的含量、光合碳分配和碳水化合物中 δ¹³C 的影响过程和机制，主要结论如下：
     （1）高浓度的氮素添加(12 g N⋅m^-2⋅a^-1)处理显著提高了苗高和生物量，在 N₁₂ 水平下幼苗苗高和生物量分别比未施氮处理增加 26.62%和 28.57%。随氮添加水平增加，根冠比降低，叶重比、地上生物量增加，说明土壤有效 N 含量增加后，油松对根部生物量的投资相对减少，氮添加有利于植物地上生物量的增加。幼苗苗高、生物量及分配格局的改变表明油松幼苗可以通过调节生物量在地上与根系、叶与茎之间的分配适应外界环境条件的变化。
     （2）由于不同组织在植物生长中的主要作用和功能不同，1-2mm 根中可溶性糖、淀粉和 NSC 含量均显著高于叶片、枝干、0-1mm 根、>2mm 根，且在各组织中浓度大小均表现出 1-2mm 根>叶片>枝干、以及>2mm 根>枝干的大小关系；油松幼苗各器官中可溶性糖、淀粉和 NSC 含量存在明显的取样时间差异，后两次取样 NSC 及其组分含量明显降低，说明以上指标具有时间动态性；随着氮添加水平增加，油松幼苗中可溶性糖、淀粉、NSC 含量在不同器官间变化趋势存在差异，这说明油松幼苗不同器官对氮添加有不同的适应性，油松幼苗能通过改变 NSC 及其组分在各器官中的积累与分配来适应氮的增加，而改变的程度随氮素供应水平而不同。各器官中可溶性糖/淀粉的比值基本都小于 1，说明 NSC 主要以淀粉为主。随氮添加水平增加，土壤 pH 值呈现降低的趋势；并且随取样时间增加，油松幼苗中可溶性糖、淀粉、NSC 含量主要受土壤 pH 影响。总之，不同氮添加水平、取样时间对油松幼苗不同器官中 NSC 及其组分（可溶性糖和淀粉）含量的影响不同。
      （3）¹³C 稳定同位素标记表明，随氮添加水平增加，各器官中¹³C 含量和碳水化合物中 δ¹³C 值均呈增加的趋势，说明短期 N 添加有利于植物同化¹³C，并提高油松各器官碳水化合物中¹³C 的分配。可溶性糖、淀粉、纤维素中 δ¹³C 值在不同施氮处理以及不同器官间均表现一定的差异，说明植物对碳的同化及在不同器官中的分配受植物自身生理特征和土壤有效 N 变化的影响。
      总之，氮添加水平对油松幼苗中 NSC 及其组分的含量、碳在不同器官间的分配存在明显差异，说明全球 N 沉降可能对树木不同器官异速生长的影响不同，并因此对针叶林生态系统产生影响。

     Carbohydrate is the main product of plant photosynthesis. Non-structural carbohydrate (NSC) is an important energy supplying substance in plant growth and metabolism. It provides a carbon buffer when plant respiration, growth and other physiological needs are not synchronized with photosynthesis. The change of NSC not only reflects the dynamics between assimilation savings and growth investment allocation, but also further affects plant growth and response to environmental changes. The effect of global nitrogen (N) deposition on plant NSC content has become a research hotspot in this field. The aim is to reveal the response mechanism of carbon balance and material cycle of ecosystem to the change of soil available N, and to propose valuable strategies for plantation cultivation and management. Based on the pot experiment of N addition for one-year-old Pinus tabulaeformis seedlings, four levels of N addition (0, 3, 6, 12 g N⋅m^-2⋅a^-1) were set up. The plant organs were divided into five organs: leaves, branches, roots with different diameters (0-1mm, 1-2mm, > 2mm). The contents of NSC and its components (soluble sugar and starch) in different organs of Pinus tabulaeformis seedlings were studied by periodic sampling and pulse labeling. The process and mechanism of photosynthetic carbon distribution and the influence of δ¹³C in carbohydrates. The main conclusions are as follows:
     (1)The seedling height and biomass were significantly increased by high concentration of nitrogen (12 g N⋅m^-2⋅a^-1). At N₁₂ level, the seedling height and biomass were 26.62% and 28.57% higher than those without nitrogen application, respectively. With the increase of nitrogen addition level, root-shoot ratio decreased, leaf weight ratio and aboveground biomass increased, which indicated that the investment of Pinus tabulaeformis on root biomass decreased relatively with the increase of available N content in soil, and nitrogen addition was beneficial to the increase of aboveground biomass of plants. The changes of seedling height, biomass and distribution pattern indicated that Pinus tabulaeformis seedlings could adapt to the changes of external environmental conditions by adjusting the distribution of biomass between ground and root, leaf and stem.
     (2)The contents of soluble sugar, starch and NSC in 1-2mm roots were significantly higher than those in leaves, branches, 0-1mm roots and > 2mm roots because of the different functions and functions of different tissues in plant growth, and showed the size relationship between 1-2mm roots > leaves > branches and > 2mm roots > branches and trunks in all tissues. The contents of soluble sugar, starch and NSC in various organs of Pinus tabulaeformis seedlings had significant differences in sampling time. The content of NSC and its components in the latter two samples decreased significantly, it showed that the above indicators were time-dynamic. With the increase of nitrogen addition level, the change trend of soluble sugar, starch and NSC contents in different organs of Pinus tabulaeformis seedlings was different, which indicated that different
organs of Pinus tabulaeformis seedlings had different adaptability to nitrogen addition. Pinus tabulaeformis seedlings could adapt to the increase of nitrogen by changing the accumulation and distribution of NSC and its components in each organ. The degree of change varies with the level of nitrogen supply. The ratio of soluble sugar to starch in all organs was less than 1, and starch was the main component of NSC. With the increase of nitrogen level, soil pH value decreased, and with the increase of sampling time, the contents of soluble sugar, starch and NSC in Pinus tabulaeformis seedlings were mainly affected by pH. In conclusion, the effects of different nitrogen levels and sampling time on NSC content and its components (soluble sugar and starch) content in different organs of Pinus tabulaeformis seedlings were different.
     (3)¹³C stable isotope labeling showed that ¹³C content and δ¹³C in carbohydrates increased with the increase of nitrogen addition level, which indicated that short-term N addition was beneficial to plant assimilation of ¹³C and increased the distribution of ¹³C in carbohydrates in different organs of Pinus tabulaeformis. The value of δ¹³C in soluble sugar, starch and cellulose showed some differences among different nitrogen treatments and organs, indicating that the assimilation of carbon and its distribution in different organs were affected by the physiological characteristics of plants and the changes of soil available N.
     In conclusion, there are significant differences in NSC and its components content and carbon distribution among different organs in Pinus tabulaeformis seedlings at different nitrogen levels, indicating that global N deposition may have different effects on allometric growth of different organs of trees, and thus affect coniferous forest ecosystems.