Differences in net primary production allocation and nitrogen use efficiency between Moso bamboo and Japanese cedar forests along a slope

The responses of forest production and nitrogen (N) utilization to belowground resource availability may be stronger in Moso bamboo forests than in woody forests because the former have higher N and water demands than the latter. The aim of this study was to clarify the different effects of mountain slope-induced belowground resource limitation on forest production between a Moso bamboo forest and a Japanese cedar forest. We compared the changes in biomass, net primary production, net primary production allocation, N utilization, N content per organ, and N use efficiency in response to soil resource availability at five different slope positions in each forest type. In the bamboo forest, the aboveground net primary production decreased upslope and the belowground net primary production allocation increased with decreasing upslope soil water availability. In contrast, leaf N content of the bamboo forest increased upslope, and N use efficiency decreased upslope with an increasing upslope soil N mineralization rate. Although a greater N use efficiency has often been reported at higher slope positions due to lower N availability, this phenomenon was observed at lower slope position in the bamboo forest. The soil N supply might exceed the soil N demand at higher slope positions, resulting in lower N use efficiency. The responses observed in the bamboo forest were absent in the Japanese cedar forest. The higher demand for belowground resources and environmental plasticity explained the higher productivity of the bamboo forest.