Fig. 3. Plant species richness (above) and plant functional
group richness (below) effects on the phenological synchrony above and
belowground dynamics. The first column (A, D) refers to the spring
(pre-mowing) period, the middle column (B, E) refers to the summer
(post-mowing) period, and the third column (C, F) refers to the winter
period. Only significant (p <0.05) relationships are
shown (solid lines). Each point refers to one plot. For the full
results, please see Table S2.
Seasonal effects of plant diversity and abiotic factors on
aboveground and belowground
responses
We tested the direct and indirect effects (via soil microclimate)
of plant diversity (i.e. species richness and functional group richness)
on plants and soils. Across the seasonal cycle, the timing of events
above and below the ground was markedly influenced by the interplay of
plant diversity and abiotic dynamics. However, across the seasons, these
influences shifted in strength and direction.
During spring (Fig. 5a), richer communities showed higher plants, with
increased root growth and enhanced activity of detritivores, but with
less plant greenness. Instead, plant greenness increased with soil
temperature, increasing root production and detritivore feeding
activity. Plant functional group richness and soil moisture did not
explain significant variation in response variables during spring. Plant
community height was associated with all other activities - positively
with greenness and root production, and negatively with detritivore
feeding activity. Moving into summer (Fig. 5b), higher plant species
richness corresponded to enhanced root production and detritivore
activity. However, increased plant functional group richness was
observed to decrease detritivore activity. Notably, the impacts of
abiotic factors on all studied ecosystem processes were predominantly
negative. Root growth declined with rising soil temperature and
moisture, while detritivore activity decreased with increasing soil
moisture. Communities with taller plants showed cooler soil temperatures
and higher soil moisture content. Interestingly, in contrast to spring
observations, taller plant communities favored detritivore activity
during summer while reducing plant greenness. Moreover, greenness was
found to affect detritivore activity positively. As winter approached
(Fig. 5c), richer plant communities showed enhanced root growth and soil
moisture retention. Conversely, increased root growth and detritivore
activity were observed in colder soils. Surprisingly, root production
decreased detritivore activity during this season.
All models fitted the data well (Fisher’s C and p -values in Fig.
5). Plant height was only explained by a fixed term in the spring model
(marginal R2 = 0.42), but its variation was also
explained by the random terms (conditional R2 = 0.45).
Greenness was explained only by the fixed terms (marginal and
conditional R2 = 0.39 in the spring and
R2 = 0.05 in the summer model). The variation of root
production was greatly explained by fixed terms in all models (marginal
R2 = 0.24, 0.32, and 0.20 for spring, summer, and
winter, respectively). Still, the random terms increased explanatory
power greatly (conditional R2 = 0.90, 0.75, and 0.64
for spring, summer, and winter, respectively). The variation in
detritivore feeding activity explained by random terms decreased along
the year (marginal R2 = 0.06 and 0.30 for spring and
summer; conditional R2 = 0.23 and 0.37 for spring and
summer, respectively), to the point that random terms increased
explanatory power only slightly in winter (marginal and conditional
R2 = 0.14 and 0.15, respectively).