Kitao Mitsutoshi, Yazaki Kenichi, Kitaoka Satoshi, Fukatsu Eitaro, Tobita Hiroyuki, Komatsu Masabumi, Maruyama Yutaka, Koike Takayoshi
Department of Plant Ecology, Forestry and Forest Products Research Institute, Tsukuba 305-8687, Japan.
Hokkaido Research Center, Forestry and Forest Products Research Institute, Sapporo 062-8516, Japan.
Physiol Plant. 2015 Dec;155(4):435-45. doi: 10.1111/ppl.12335. Epub 2015 Mar 16.
To test the hypothesis that mesophyll conductance (gm ) would be reduced by leaf starch accumulation in plants grown under elevated CO2 concentration [CO2 ], we investigated gm in seedlings of Japanese white birch grown under ambient and elevated [CO2 ] with an adequate and limited nitrogen supply using simultaneous gas exchange and chlorophyll fluorescence measurements. Both elevated [CO2 ] and limited nitrogen supply decreased area-based leaf N accompanied with a decrease in the maximum rate of Rubisco carboxylation (Vc,max ) on a CO2 concentration at chloroplast stroma (Cc ) basis. Conversely, only seedlings grown at elevated [CO2 ] under limited nitrogen supply had significantly higher leaf starch content with significantly lower gm among the treatment combinations. Based on a leaf anatomical analysis using microscopic photographs, however, there were no significant difference in the area of chloroplast surfaces facing intercellular space per unit leaf area among treatment combinations. Thicker cell walls were suggested in plants grown under limited N by increases in leaf mass per area subtracting non-structural carbohydrates. These results suggest that starch accumulation and/or thicker cell walls in the leaves grown at elevated [CO2 ] under limited N supply might hinder CO2 diffusion in chloroplasts and cell walls, which would be an additional cause of photosynthetic downregulation as well as a reduction in Rubisco activity related to the reduced leaf N under elevated [CO2 ].
为了验证在高二氧化碳浓度（[CO₂]）下生长的植物中，叶肉导度（gm）会因叶片淀粉积累而降低这一假设，我们通过同步气体交换和叶绿素荧光测量，研究了在正常和高[CO₂]条件下，氮供应充足和有限时日本白桦幼苗的gm。高[CO₂]和有限的氮供应均降低了基于面积的叶片氮含量，同时以叶绿体基质中的二氧化碳浓度（Cc）为基础，Rubisco羧化最大速率（Vc,max）也随之降低。相反，在处理组合中，仅在有限氮供应下于高[CO₂]环境中生长的幼苗叶片淀粉含量显著更高，而gm显著更低。然而，基于使用显微照片进行的叶片解剖分析，各处理组合之间单位叶面积上面向细胞间隙的叶绿体表面积并无显著差异。通过减去非结构性碳水化合物后的单位面积叶质量增加表明，在氮有限条件下生长的植物细胞壁更厚。这些结果表明，在有限氮供应下于高[CO₂]环境中生长的叶片中，淀粉积累和/或更厚的细胞壁可能会阻碍二氧化碳在叶绿体和细胞壁中的扩散，这将是光合下调的另一个原因，也是与高[CO₂]下叶片氮减少相关的Rubisco活性降低的原因。
