不同光照条件下外源钙对“烟株-土壤”系统中光合碳分配的影响

  目的  探讨不同光照条件下外源钙对烟株光合碳分配及烟田土壤碳固持的调控作用。  方法  通过盆栽试验，采用13C-CO₂脉冲标记技术，定量研究3种光照条件下外源钙对光合碳在“烟株-土壤”系统中分配比例与周转状况的影响。  结果  （1）光强与外源钙的互作效应对烟草叶片和根系中13C浓度有显著影响, 在整个测定期内，叶片13C浓度降低72.4%~75.1%，而根系13C浓度增加30.3%~105.3%；外源CaCl₂对各组分13C浓度的增加具有显著促进效果，且在低光或高光胁迫条件下增加比例较高。（2）标记初期，“烟株-土壤”系统中的13C分配以叶片中最高，但随种植时间延长，源器官又重新将光合固定的碳分配给地下部根系和土体，至标记后30 d，根系和土体的13C分配率分别比标记第1 d时增加了1.7~2.6倍和1.0~2.1倍。（3）13C-SOC根际沉积效率在整个测定期内增加了1.3~1.9倍，喷钙处理的根际沉积效率分别比对照增加了5.4%~20.1%（低光）、3.5%~34.5%（中光）、5.6%~29.0%（高光）。随光强增加烟株根际沉积对土壤SOC更新率的贡献增强。（4）光强、外源钙及二者的互作效应显著增加了烟株地上部与根系的生物量积累，总体上表现为:叶 > 茎 > 根，与13C在各组分中的分配比例相对应。  结论  光强增加能够促进光合碳在烟株地上部与地下部间的周转及生物量的积累，喷施外源钙能够提高烟株光合碳同化能力并加速土壤中新碳的转化，提高根际沉积效率，促进土壤有机碳积累。 

Effects of exogenous calcium on distribution of photosynthesized carbon in tobacco-soil system under different levels of light intensity

Photosynthesized carbon is an important source of soil organic carbon in tobacco fields.In order to better understand the regulatory effect of exogenous calcium on photosynthesized carbon distribution m and the soil carbon sequestration in tobacco fields under different light intensity, the 13C plus-labeling method was used to quantify the dynamics and distribution of input photosynthesized carbon and its response to exogenous calcium application.The results showed that: (1) The interaction between light intensity and exogenous calcium had a significant influence on 13C concentration in leaves and roots were.The 13C concentration in leaves decreased by 72.4%-75.1% during the whole growth period, while the 13C concentration in roots increased by 30.3%-105.3%.Furthermore, the application of exogenous calcium significantly promoted the 13C concentration of tobacco, the 13C concentration in soil increased by 0.5%-49.3%, and the largest increase was observed at low light intensity.(2) The distribution proportion of photosynthesized 13C in the tobacco-soil system showed a decreasing trend in above-ground with the extending of planting time, and the highest distribution rate of photosynthesized 13C was observed in leaves.However, the distribution rate of photosynthesized 13C in below-ground roots and soil gradually increased by 1.7-2.6 times and 1.0-2.1 times, respectively at the 30th day after labeling compared with the 1st day after labeling.(3) The rhizodeposition efficiency increased with the extending of the growth period, with the increase amplitude reaching 1.3-1.9 times.In comparison to the unfertilized treatment, the application of exogenous calcium led to significant increase in the rhizodeposition efficiency during different light intensity by 5.4%-20.1% (at low light intensity), 3.5-34.5% (at moderate light intensity) and 5.6-29.0% (at high light intensity), respectively.The renewal rate of 13C-SOC was enhanced with the increase of light intensity.(4) Light intensity, exogenous calcium and their interaction effects significantly increased the biomass accumulation of shoots and roots, the dry biomass content of different components was ranked as follows: leaf > stem > root, which responded to the distribution pattern of photosynthesized 13C.Thus, increasing light intensity is conducive to the turnover of photosynthesized carbon between above-ground and below-ground in tobacco-soil system and also is extremely beneficial to the accumulation of biomass.With the application of exogenous calcium, the photosynthetic carbon assimilation ability was improved, meanwhile, the transformation of new carbon in soil was accelerated.Consequently, the rhizodeposition efficiency was improved and the photosynthesized carbon incorporated into the soil organic carbon in the form of rhizosphere sediments ultimately.