Community biomass and biodiversity effects in Phase II
Community biomass significantly increased with plant species richness in
Phase II (Table 1, Fig. 3b). However, plant richness effects on
community biomass significantly varied with soil moisture treatments,
resulting in a significant plant species richness × soil moisture in
Phase I × soil moisture in Phase II interaction (Table 1).
Over all treatments, the BE increased with plant species richness (Table
2, Fig. 4d). However, the CE and SE showed different directions of
responses to plant species richness. Positive CE values were greater in
higher plant species richness levels, while negative SE increased with
higher plant species richness (Table 2, Fig. 4e and f). Soil moisture
treatments in Phase I significantly influenced the BE, CE and SE in
Phase II (Table 2). Both the BE and CE were greater in mesocosms with
drought treatments than those with ambient treatments from Phase I (Fig.
4d and e). However, drought treatments from Phase I caused more negative
SE in Phase II (Fig. 4f). Drought in Phase II generally decreased the
magnitude of positive BE and CE values, and it had no general influence
on SE (Table 2, Fig. 4).
Plant species richness and soil moisture treatments of Phase I and II
interacted to influence both the CE and SE (Table 2). In mesocosms with
two species, the CE did not vary among soil moisture treatment
combinations, while at higher richness levels, the CE was greater in the
Drought-Ambient treatment and lower in the Ambient-Ambient treatment
compared to the other treatment combinations (Fig. 4e). There were no
significant differences in SE among soil moisture treatment combinations
for mesocosms with two or four species. However, in treatments with six
or twelve species, the SE was positive in the Ambient-Ambient treatment,
and the values were negative for the other treatment combinations. The
negative SE was greatest in the Drought-Ambient treatment and with
twelve plant species (Fig. 4f). Relationships between species richness
and the BE did not vary among treatment combinations of soil moisture in
Phase I and II (Fig. 4d), and thus there was no plant species richness ×
soil moisture in Phase I × soil moisture in Phase II interaction (Table
2).