Growth rate and carbon biomass
The growth rate (F = 59.65, p < 0.001) and C
biomass (F = 286.9, p < 0.001) ofScenedesmus were significantly different among the culture media
prepared from 11 types of leaf litter leachates in the control treatment
(Fig. 1a). The addition of micronutrients to the culture medium had a
significant positive effect on the algal growth rate of in the leaf
litter leachates of oak, Japanese elm, and Japanese hemlock. However,
the micronutrient amendment had a negative effect on growth in the
culture medium prepared from the leaf litter leachate of hinoki cypress.
For the algal C biomass, a significant positive effect of micronutrient
amendment was detected only in the culture medium prepared from the leaf
litter leachate of Japanese hemlock (Fig. 1b). However, algal C biomass
was not affected by the micronutrient amendment in culture media
prepared from other leaf litter leachates.
Because TDN and TDP concentrations varied among the different types of
leaf litter leachates, we examined whether variations in the algal
growth rate and C biomass of Scenedesmus were related to these
nutrient concentrations in the culture media prepared from the leaf
litter leachate. Due to the large variation of growth rate at TDN
concentrations < 5 μM, the growth rate was not related to TDN
concentration regardless of the micronutrient amendment (Fig. 2a and b).
However, the algal growth rate tended to increase with TDP concentration
in the amended treatment but not in the control, although the growth
rate also varied widely and decreased when TDP concentration was
< 2 μM (Fig. 2c and d).
Unlike the growth rate, the algal C biomass increased significantly with
TDN in the control treatment, although the increasing trend was
attenuated when TDN exceeded 5 μM, as shown by the segmented regressions
with breakpoints at 5.31 μM (Fig. 2e and f). In the amended treatment,
the relationship between the algal C biomass and TDN was not improved.
It was almost the same as in the control treatment, as indicated by
similar values in the segmented regressions (Fig. 2e and f). Similarly,
algal C biomass tended to increase with TDP regardless of the
micronutrient amendment, although the increasing trend was not
significant due to low C biomass values relative to TDP in some culture
media, such as those prepared from leaf litter leachates of Siebold’s
beech, Japanese elm and Japanese red pine (species ID 5, 6, 9 in Fig. 2g
and h).