Effects of the experimental alteration of fine roots on stomatal conductance and photosynthesis: Case study of devil maple (Acer diabolicum) in a cool temperate region

•Effects of decreasing roots on stomatal conductance and photosynthesis were studied.•Saplings of devil maple growing in the cool temperate regions of Japan were used.•The model predictions were consistent with the results from laboratory experiments.•The saplings produced roots more than sufficient for water demand of photosynthesis.

Water is absorbed by fine roots and transported with essential substances to conduct photosynthesis in leaves. To determine how many fine roots are required to absorb adequate water and maximise photosynthesis, the effects of decreasing fine root biomass on stomatal conductance (GS) and photosynthetic rate (A) were evaluated using theoretical simulations and laboratory experiments. We used saplings of devil maple (Acer diabolicum), a typical woody species in the cool temperate regions of Japan, grown in high- and low-light environments. A–GS relationships and whole-plant hydraulic conductance (KW) were determined and used for the simulations. Gradual changes in KW, A, and GS were also evaluated with a stepwise decrease in fine roots in the laboratory experiments. The model predicted that KW, GS, and A decreased moderately with a decrease in fine roots. For example, A decreased by only 12% when fine roots were decreased by 50%. The model predictions were nearly consistent with the results from laboratory experiments. In conclusion, saplings of devil maple produced fine roots that were more than sufficient in meeting the water demands of photosynthesis. These characteristics may be beneficial in surviving severe drought and in maintaining adequate hydraulic conductance under conditions of moderate water stress.