Biodiversity increases the resistance of ecosystem productivity to climate extremes

It remains unclear whether biodiversity buffers ecosystems against climate extremes, which are becoming increasingly frequent worldwide1. Early results suggested that the ecosystem productivity of diverse grassland plant communities was more resistant, changing less during drought, and more resilient, recovering more quickly after drought, than that of depauperate communities2. However, subsequent experimental tests produced mixed results3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13. Here we use data from 46 experiments that manipulated grassland plant diversity to test whether biodiversity provides resistance during and resilience after climate events. We show that biodiversity increased ecosystem resistance for a broad range of climate events, including wet or dry, moderate or extreme, and brief or prolonged events. Across all studies and climate events, the productivity of low-diversity communities with one or two species changed by approximately 50% during climate events, whereas that of high-diversity communities with 16–32 species was more resistant, changing by only approximately 25%. By a year after each climate event, ecosystem productivity had often fully recovered, or overshot, normal levels of productivity in both high- and low-diversity communities, leading to no detectable dependence of ecosystem resilience on biodiversity. Our results suggest that biodiversity mainly stabilizes ecosystem productivity, and productivity-dependent ecosystem services, by increasing resistance to climate events. Anthropogenic environmental changes that drive biodiversity loss thus seem likely to decrease ecosystem stability14, and restoration of biodiversity to increase it, mainly by changing the resistance of ecosystem productivity to climate events

Foraging and life history strategies in multi-trophic communities

SIGLEAvailable from British Library Document Supply Centre- DSC:D183918 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Microbial-mediated plant growth promotion and pest suppression varies under climate change.

Climate change is altering the dynamics of crop pests and diseases resulting in reduced crop yields. Using beneficial soil bacterial to increase crop health is a quickly developing area in sustainable agriculture, but it is unknown if climate change or interactions with other species could alter their effect. The plant growth-promoting rhizobacteriumAcidovorax radicisN35 is known to increase barley (Hordeum vulgare) plant growth under laboratory conditions, and we tested the stability of the plant-bacterial interactions when exposed to elevated carbon dioxide (CO2) and ozone (O-3) levels while infesting the aboveground leaves with cereal aphids (Sitobion avenae) and the soil with beneficial earthworms.Acidovorax radicisN35 increased plant growth and reduced insect growth - with greatest effect in a high-stress elevated O(3)environment, but reduced effects under elevated CO2. Earthworms promoted both plant and insect growth, but inoculation withA. radicisN35 alleviated some of the earthworm-mediated increase in pest abundance, particularly in the ambient environment. The consistency of these beneficial effects highlights the potential of exploiting local species interactions for predicting and mitigating climate change effects in managed systems. We conclude that microbial bioprotectants have high potential for benefiting agricultureviaplant-growth promotion and pest suppression

Ant attendance of the cotton aphid is beneficial for okra plants: deciphering multitrophic interactions

First published: 9 April 2016Aphids are pest species of many crops and biocontrol methods are often ineffective. Ant–aphid associations can be mutualistic or antagonistic, with ants increasing or reducing aphid numbers. Within-species plant variation or other herbivores may further influence these ant–aphid interactions. Okra is an economically important crop in Cameroon. Several okra varieties are grown here and attacked by the facultatively ant-tended cotton aphid Aphis gossypii. We conducted field and screenhouse experiments where plant variety, ant presence and predator access were manipulated to investigate the multitrophic interactions on okra and their effects on okra yield. In the field, ants did not protect aphids from their natural enemies and syrphid larvae reduced aphids by 42%. Additionally, aphid recruitment of ants reduced chewing herbivore damage by 11% and indirectly increased okra fruit set. We also found aphid numbers, aphid predation by syrphids and chewing herbivory to vary across okra varieties. Finally, in the screenhouse, we recorded a 24% reduction in aphid numbers on plants with ant presence. The present study highlights the importance of direct and indirect biotic interactions for pest biocontrol. Tropical agricultural systems are complex and understanding such interactions can help in designing pest control measures in sustainable agriculture

Additive effects of plant chemotype, mutualistic ants and predators on aphid performance and survival.

1.Cascading effects in ecological systems acting across three or more trophic levels can be either of a resource‐based (bottom‐up) or natural enemy‐based (top‐down) nature. But, due to their complexity these effects are often considered separately and their relative strength, acting simultaneously, remains unknown. 2.In a semi‐natural field experiment using tansy (Tanacetum vulgare L.) and the specialised tansy aphid Metopeurum fuscoviride Stroyan as a model system, we compared the effects of four distinct plant chemotypes (i.e. bottom‐up), defined by the bouquet of their volatile terpenoids, on aphid population dynamics by manipulating the presence/absence of mutualistic ants and presence/absence of naturally‐occurring predators (i.e. top‐down). 3.Predators reduced aphid abundance and colony survival but did not reduce initial growth rate due to a time lag until predators arrived on the plants. Ants directly benefited initial aphid growth rates and abundance, even in the absence of predators, but not the number of days an aphid colony persisted on the plant. 4.Plant chemotype directly affected aphid growth rate and final abundances across the different plants and indirectly affected the abundances of tending ants and predators through effects on aphids. We found that tending ants were more abundant on one plant chemotype. Although ant abundance did not affect aphid population development, it became clear that ants had a preference towards aphids on certain chemotypes. However, a higher number of predators led to a lower number of aphids. 5.The results confirm the importance of plant chemical variation, acting through multiple effects on many species in arthropod communities, and support results from field studies. In a natural population, with a diverse selection of host‐plant variants, aphid populations and their interacting species can therefore be structured at the level of an individual plant. Specialist aphids on patchily‐distributed host plants can exhibit metacommunity dynamics at very local scales. Plant within‐species variation within a local population is often ignored in metacommunity ecology, yet our work shows that this can have strong effects on insect‐ant‐natural enemy dynamics and therefore future research should incorporate this into current theory and experimental studies

Chemotypic variation in terpenes emitted from storage pools influences early aphid colonisation on tansy.

Tansy plants (Tanacetum vulgare L.) exhibit high chemical variation, particularly in mono- and sesquiterpenes that are stored in specialised glands on the plant surface. In the present work we investigated the effects of terpene chemotypes on Metopeurum fuscoviride, an aphid species specialised on tansy, and their tending ants, at the field scale. Previous studies have chemotyped tansy by assessing dominant compounds; here we propose a method of chemotyping using all volatile compounds that are likely emitted from the storage glands. The analysis is based on two extraction methods: GC-MS analysis of leaf hexane extracts and SBSE analysis of headspace emissions. In an initial screening we identified the subset of compounds present in both chemical patterns, labelled as 'compounds likely emitted from storage'. In a large field survey we could show that the putative chemotypic emission pattern from storage pools significantly affected the early aphid colonisation of tansy. Moreover, the statistical analyses revealed that minor compounds exerted a stronger influence on aphid and tending-ant presence than dominant compounds. Overall we demonstrated that within the enormous chemotypic variation of terpenes in tansy plants, chemical signatures of volatile terpenes can be related to the occurrence of insects on individual plants in the field

Does plant diversity influence phosphorus cycling in experimental grasslands?

Plant diversity was shown to influence the N cycle, but plant diversity effects on other nutrients remain unclear. We tested whether plant species richness or the presence/absence of particular functional plant groups influences P partitioning among differently extractable pools in soil, P concentrations in soil solution, and exploitation of P resources (i.e. the proportion of total bioavailable Pin plants and soil that was stored in aboveground biomass) by the plant community in a 5-year biodiversity experiment in grassland.The experimental grassland site established in 2002 had 82 plots with different combinations of numbers of species (1, 2, 4, 8, 16, 60) and functional groups (grasses, small non-leguminous herbs, tall non-leguminous herbs, legumes). In 2007, we determined P partitioning (Hedley) in soil of all experimental plots. We sampled plant community biomass and continuously extracted soil solution with suction plates from March 2003 to February 2007 and determined PO4-P concentrations in all samples.The presence of legumes increased aboveground P storage in plants and decreased labile P-i concentrations in soil because of their higher demands for P associated with N-2 fixation. During cold periods, readily plant-available PO4-P concentrations in soil solution increased in legume-containing mixtures likely caused by leaching from P-rich residues. We found a consistently positive effect of plant species richness on P exploitation by the plant community which was independent of the presence of particular plant functional groups. With proceeding time after establishment, plant species richness increasingly contributed to the explanation of the variance in P exploitation. Therefore, plant strategies to efficiently acquire P seem to become increasingly important in these grasslands. We conclude that diverse plant communities are better prepared than less diverse mixtures to respond to P limitation induced by continuously high atmospheric N deposition. (C) 2011 Elsevier B.V. All rights reserved