SummaryFumigants, such as 1,3-dichloropropene and chloropicrin, have become key to pre-plant pest management in almond production. Whilst the use of these fumigants has become increasingly restricted due to human health concerns, less is known about their below-ground non-target effects in orchards and how nematode communities recover from fumigation over time. In this study, replicated trials compared 1,3-dichloropropene + chloropicrin to non-treated controls in two almond orchards in California, USA. Nematode communities, nematode indices and nematode metabolic footprints were quantified soon after fumigation and for 2 years afterwards. Fumigation reduced the Herbivore Metabolic Footprint in year 1, and populations of Pratylenchus vulnus in year 3. Fumigation also reduced populations of larger omnivores and predators, resulting in lower levels of the Structure Index at one site. Populations of fungal-feeding nematodes were more adversely affected by fumigation than bacterial-feeding nematode populations. At both sites, fumigation still influenced nematode community composition 2 years after treatment application.

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1. The extent to which plants can reduce nutrient concentrations in soil and thereby compete with others may increase with nutrient mobility. Hyphae of arbuscular mycorrhizal fungi (AMF) can extend the soil volume from which plants acquire phosphorus (P), thus increasing competition for these resources with neighbours.In this study, we tested whether the suppression of hyphal interconnections between neighbour plants mitigates their competitive interactions and consequently affects plant community structure.2. We used custom-built microcosms that used a wire system to suppress the development of a common mycorrhizal network (CMN) between plant neighbours. We applied this CMN treatment to plants without neighbours (competition-free controls), with conspecific neighbours (monocultures) or with heterospecific neighbours (two and four species communities), all assembled from two pools of four separate temperate grassland species each. We analysed changes in species and community-level productivity and P acquisition. 3. The CMN treatment affected species differently. Most species had reduced shoot biomass while root biomass increased with CMN disconnection. Productivity and nutrient acquisition of Plantago lanceolata in four-species mixtures was negatively affected, leading to a less even distribution of P among species, but communitylevel P acquisition was not affected. On average, two-species and four-species mixtures produced similar community biomass and had the same P content as monocultures. 4. Synthesis. Common mycorrhizal network disconnection affected competitive interactions among species only little. One explanation may be that the absence of pronounced competitive hierarchy among the species investigated led to relatively symmetric interactions among species that were stable with respects to additional common mycorrhizal network effects. Another explanation is that common mycorrhizal network effects are less important in natural soils with natural arbuscular mycorrhizal fungi communities than experiments with few arbuscular mycorrhizal fungi strains and often sterilized soils suggest. Additional supporting information may be found online in the Supporting Information section at the end of the article. How to cite this article: Milkereit J, Frossard E, Stoll P, Wagg C, Niklaus PA. Experimental disconnection from common mycorrhizal networks has little effect on competitive interactions among common temperate grassland species.

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Drought affects many agriculturally important areas, hampering the cultivation of water intensive crops such as tomatoes. Unlike processing tomatoes, deficit irrigation of fresh market tomatoes is not currently practiced. Deficit irrigation could have negative trade‐offs for yield and pest populations by changing plant nutritional values and the microenvironment. The present study compared crop response and insect populations at two field locations: an on‐farm trial with 0%, 15% and 30% water deficit treatments, and a research station trial with 0%, 10%, 20% and 30% water deficit treatments. At the on‐farm trial, water deficits of 30% affected fruit yield, leaf relative water content (RWC) and leaf δ13C, whereas, in the research station trial, water deficits only affected leaf RWC. Treatments did not change the abundance of any insect groups. Sap‐feeding insects such as silverleaf whitefly (Bemisia tabaci) increased with plant traits indicating hydration such as canopy temperature depression (CTD) and RWC. Furthermore, CTD influenced the composition of insect communities. Sap‐feeding insect abundance may vary with traits indicating hydration because of turgor pressure required for feeding, as well as a more suitable microenvironment.