J. Mikola et al., Response of soil food-web structure to defoliation of different plant species combinations in an experimental grassland community, SOIL BIOL B, 33(2), 2001, pp. 205-214
We established a greenhouse experiment based on replicated mini-ecosystems
to evaluate the effects of defoliation of different plant species combinati
ons on soil food-web structure in grasslands. Plant communities, composed o
f white clover (Trifolium repens), perennial ryegrass (Lolium perenne) and
plantain (Plantago lanceolata), were subjected to the following defoliation
treatments: no defoliation of any species (control) and selective trimming
of all possible one-. two- and three-way combinations of the species tithe
r to 27 cm height tweak defoliation) or to 15 cm height (strong defoliation
) above the soil surface three times over a 10-week period. Successive defo
liations removed the largest amounts of shoot mass from systems in which T.
repens was included among the defoliated species because T. repens dominat
ed aboveground plant biomass. At the final harvest shoot mass was lowest in
treatments that included defoliation of T. repens, while total root mass w
as on average lower in strongly than in weakly defoliated systems and did n
ot differ between the control and defoliation treatments. Total shoot produ
ction was not affected by defoliation. Microbial basal respiration and soil
NO3-N concentration differed between the combinations of defoliated specie
s; e.g. microbial respiration was on average 32% lower in systems in which
only L. perenne was defoliated than in systems in which only T. repens was
defoliated. Microbial biomass and soil NH4-N concentration were not signifi
cantly affected by defoliation treatments. Enchytraeid abundance differed s
ignificantly between the combinations of defoliated species: in systems in
which only L. perenne was defoliated enchytraeid abundance was on average 8
8% lower than in systems in which all species or only T. repens were defoli
ated. Enchytraeid abundance was also positively associated with total defol
iated shoot mass. Abundances of both bacterial-feeding and fungal-feeding n
ematodes were affected by the combination of defoliated species; e.g. the a
bundance of bacterial feeders was on average 52% lower in systems in which
only T. repens was defoliated than in systems in which both P. lanceolata a
nd T. repens were defoliated. Fungal-feeding nematodes were also more numer
ous in strongly than in weakly defoliated systems and positively associated
with total defoliated shoot mass. Herbivorous nematode abundance was not s
ignificantly affected by defoliation treatments. The results show that the
response of soil food webs to defoliation can be affected by which combinat
ion of species in a plant community is defoliated. Further, it seems that t
he role of the combination of species that are defoliated may for some comp
onents of the soil biota (e.g. fungal-feeding nematodes) be explicable simp
ly in terms of the total mass of foliage removed. However, for other compon
ents of the soil biota (e.g, bacterial-feeding nematodes and enchytraeids)
species-specific properties of different plant species in the combination o
f defoliated species are also clearly important, over and above simple mass
removal effects of defoliation. (C) 2001 Elsevier Science Ltd. All rights
reserved.