No abstract

The consequences of permanent loss of species or species groups from plant communities are poorly understood, although there is increasing evidence that individual species effects are important in modifying ecosystem properties. We conducted a field experiment in a New Zealand perennial grassland ecosystem, creating artificial vegetation gaps and imposing manipulation treatments on the reestablishing vegetation. Treatments consisted of continual removal of different subsets or ''functional groups'' of the flora. We monitored vegetation and soil biotic and chemical properties over a 3-yr period. Plant competitive effects were clear: removal of the C 3 grass Lolium perenne L. enhanced vegetative cover, biomass, and species richness of both the C 4 grass and dicotyledonous weed functional groups and had either positive or negative effects on the legume Trifolium repens L., depending on season. Treatments significantly affected total plant cover and biomass; in particular, C 4 grass removal reduced total plant biomass in summer, because no other species had appropriate phenology. Removal of C 3 grasses reduced total root biomass and drastically enhanced overall shoot-to-root biomass ratios. Aboveground net primary productivity (NPP) was not strongly affected by any treatment, indicating strong compensatory effects between different functional components of the flora.Removing all plants often negatively affected three further trophic levels of the decomposer functional food web: microflora, microbe-feeding nematodes, and predaceous nematodes. However, as long as plants were present, we did not find strong effects of removal treatments, NPP, or plant biomass on these trophic groupings, which instead were most closely related to spatial variation in soil chemical properties across all trophic levels, soil N in particular. Larger decomposer organisms, i.e., Collembola and earthworms, were unresponsive to any factor other than removal of all plants, which reduced their populations. We also considered five functional components of the soil biota at finer taxonomic levels: three decomposer components (microflora, microbe-feeding nematodes, predaceous nematodes) and two herbivore groups (nematodes and arthropods). Taxa within these five groups responded to removal treatments, indicating that plant community composition has multitrophic effects at higher levels of taxonomic resolution. The principal ordination axes summarizing community-level data for different trophic groups in the soil food web were related to each other in several instances, but the plant ordination axes were only significantly related to those of the soil microfloral community. There were time lag effects, with ordination axes of soil-associated herbivorous arthropods and microbial-feeding nematodes being related to ordination axes representing plant community structure at earlier measurement dates. Taxonomic diversity of some soil organism groups was linked to plant removals or to plant diversity. For herbivorous arthropods, removal of C 4 grasses enhanc...

Summary 0The development of general principles regarding biotic interactions involving plants\ or plant species e}ects in ecosystems\ is best achieved through simultaneous evaluation of several species[ We utilized a comparative approach involving 19 dicotyledonous herbaceous species\ to explore possible relationships between several plant eco! physiological traits and plant litter decomposition\ interactions involving competition and herbivory\ and plant species e}ects on soil properties[ 1 Decomposition rates of plant stem and leaf litter were negatively related to plant mass\ time until~owering and vegetative growth rate\ and positively related to stem nitrogen content[ Root decomposition was also related to several traits[ Multiple regression relationships showed that 63) and 73) of the variation across species for stem and root litter decomposition\ respectively\ could be predicted by plant traitst his suggests that plant traits may be powerful predictors of decomposition and have potential as alternative predictors to the litter quality characteristics that previous studies have concentrated on[ 2 Palatability of both seedlings and leaf discs by the invertebrate herbivores Deroceras reticulatum and Listronotus bonariensis were frequently related to plant traits[ Those traits that showed the strongest relationships with the palatability data included various vegetative growth characteristics and "for the leaf disc data# nitrogen con! centrations of~owering plant stems[ 3 Competitive e}ects of the dicotyledonous species against a phytometer species\ the grass Lolium perenne\ were negatively related to leaf nitrogen concentration\ and multiple regression relationships involving this trait in combination with others explai! ned over 49) of the variation across species[ The competitive response of both plant mass and total seed production to L[ perenne was poorly related to plant traits[ 4 The e}ects of plant species on soil properties including microbial biomass and activity\ pH\ nitrate concentration and total nitrogen were often closely related to various plant traits[ Multiple regression relationships revealed that combinations of several traits were often important in determining these e}ects^the strongest relationships found were for e}ects of senescent plants on soil respiration and for the e}ects of~owering plants on soil nitrate[ Plant traits were therefore clearly important in determining plant species e}ects on soils[ 5 Our study emphasizes the importance of plant traits in understanding "and pre! dicting# species interactions and e}ects in communities and ecosystems\ and shows that properties considered at the whole plant level have the potential to manifest

The consequences of permanent loss of species or species groups from plant communities are poorly understood, although there is increasing evidence that individual species effects are important in modifying ecosystem properties. We conducted a field experiment in a New Zealand perennial grassland ecosystem, creating artificial vegetation gaps and imposing manipulation treatments on the reestablishing vegetation. Treatments consisted of continual removal of different subsets or “functional groups” of the flora. We monitored vegetation and soil biotic and chemical properties over a 3‐yr period. Plant competitive effects were clear: removal of the C3 grass Lolium perenne L. enhanced vegetative cover, biomass, and species richness of both the C4 grass and dicotyledonous weed functional groups and had either positive or negative effects on the legume Trifolium repens L., depending on season. Treatments significantly affected total plant cover and biomass; in particular, C4 grass removal reduced total plant biomass in summer, because no other species had appropriate phenology. Removal of C3 grasses reduced total root biomass and drastically enhanced overall shoot‐to‐root biomass ratios. Aboveground net primary productivity (NPP) was not strongly affected by any treatment, indicating strong compensatory effects between different functional components of the flora. Removing all plants often negatively affected three further trophic levels of the decomposer functional food web: microflora, microbe‐feeding nematodes, and predaceous nematodes. However, as long as plants were present, we did not find strong effects of removal treatments, NPP, or plant biomass on these trophic groupings, which instead were most closely related to spatial variation in soil chemical properties across all trophic levels, soil N in particular. Larger decomposer organisms, i.e., Collembola and earthworms, were unresponsive to any factor other than removal of all plants, which reduced their populations. We also considered five functional components of the soil biota at finer taxonomic levels: three decomposer components (microflora, microbe‐feeding nematodes, predaceous nematodes) and two herbivore groups (nematodes and arthropods). Taxa within these five groups responded to removal treatments, indicating that plant community composition has multitrophic effects at higher levels of taxonomic resolution. The principal ordination axes summarizing community‐level data for different trophic groups in the soil food web were related to each other in several instances, but the plant ordination axes were only significantly related to those of the soil microfloral community. There were time lag effects, with ordination axes of soil‐associated herbivorous arthropods and microbial‐feeding nematodes being related to ordination axes representing plant community structure at earlier measurement dates. Taxonomic diversity of some soil organism groups was linked to plant removals or to plant diversity. For herbivorous arthropods, removal of C4 grasses enhanced dive...

No abstract