3 Result
N addition and drought significantly
changed the relationship between herbivore and plant communities. For
instance, the relationship between plant community and plant suckers was
found to be significant, and it was driven primarily by plant biomass
under natural condition (βbal/βgra =
168%) (Fig.1a) but by plant species turnover under experimental drought
(βsim/βsne = 188%) (Fig.1b&4).
Moreover, omnivores were subject to both species turnover and plant N
content under drought condition but not to them under any other
experimental treatment. Drought engendered significant effects of plant
species turnover on herbivores regardless of N addition, and N addition
stimulated the significant effects of plant N content on herbivores
(plant suckers and detritivores) whether with or without drought.
There were three remarkable points in the interaction of arthropod
functional groups in networks (Fig.1): (a) the interacting functional
group pairs (i.e., plant suckers vs. vegetation hunters, plant suckers
vs. parasitoids, detritivores vs. parasitoids) were observed in all the
treatments including ambient condition. Both web spiders and ground
hunters were strongly correlated with herbivore/detritivores (including
both plant suckers and detritivores) under ambient condition and N
addition, yet part of links of web spiders and ground hunters has been
lost under experimental drought; (b) Under N addition, further
application of experimental drought did not impact the relative
abundance of vegetation hunters, but exerted a negative effect on the
interaction between plant chewers and vegetation hunters, and a positive
effect on the interaction between vegetation hunters and parasitoids.
(c) omnivores appeared a key functional group as both its relative
abundance and number of interactions with other arthropod functional
groups increased by experimental drought regardless of N addition.
Finally, by quantifying ecological network properties, we found that
both experimental drought and N addition decreased CFG,
ID and IS of the interactions between arthropod functional groups and
their sum except for increased ID and IS of
carnivores-carnivores and ID of
herbivores-carnivores (Fig.2). The IS of environmental factors on
arthropod functional groups has been significantly increased by
experimental drought, and the change of micro-habitat exerted
significant effects on much more arthropod functional groups under
experimental drought than ambient condition (Fig.1&3).Our manipulation
of snowmelt effectively maintained snow cover for 1.7 days (in 2019) and
10.8 days (in 2020) longer. Compared with drought and N addition,
delaying snowmelt only exerted a modest impact on plant and arthropod
communities in the peak of growing season (Table.1&2&3; but see
Fig.S1). Thus, we ignored the influence of delaying snowmelt when
analyzing the ecological network at the peak of the growing season.