221. Deciphering the mechanisms that drive variation in biomass production across plant 23 communities of contrasting species composition and diversity is a main challenge of 24 biodiversity-ecosystem functioning research. Niche complementarity and selection effect have 25 been widely investigated to address biodiversity-productivity relationships. However, the 26 overlooking of the specific role played by key species have limited so far our capacity to 27 comprehensively assess the relative importance of other potential drivers of biodiversity effects. 28 2. Here, we conducted a grassland diversity-productivity experiment to test how four potential 29 facets of biodiversity effects, namely species richness, functional diversity, species identity and 30 the relaxation of intraspecific competition, account for variations in above and root biomass 31 production. 32 3. We grew six plant species in monoculture, as well as in every combinations of two, three and 33 six species. Plant density was kept constant across the richness gradient but we additionally 34 grew each species in half-density monoculture to estimate the strength of intraspecific 35 competition for each studied species. We characterized eight functional traits, including root 36 traits, related to nutrient and light acquisition and computed both the functional dissimilarity 37 and the community weighted mean (CWM) of each trait. We further partitioned aboveground 38 biodiversity effect into complementarity and selection effects. 39 4. We observed strong positive biodiversity effects on both aboveground and root biomass as 40 well as strong positive complementarity effect. These arose largely from the presence of a 41 particular species (Plantago lanceolata) and from CWM trait values more than from a higher 42 functional dissimilarity in plant mixtures. P. lanceolata displayed the highest intraspecific 43 competition, which was strongly relaxed in species mixtures. By contrast, the presence of 44 Sanguisorba minor negatively affected the productivity of plant mixtures, this species suffering 45 more from interspecific than intraspecific competition. 46 5. This study provides strong evidences that the search for key species is critical to understand 47 the role of species diversity on ecosystem functioning and demonstrates the major role that the 48 balance between intraspecific and interspecific competition plays in biodiversity-ecosystem 49 functioning relationships. Developing more integrative approaches in community and 50 ecosystem ecology can offer opportunities to better understand the role that species diversity 51 plays on ecosystem functioning. 52 53 Key words: biodiversity-ecosystem functioning, complementarity effect, functional trait, 54 functional distinctiveness, niche difference, roots, selection effect, species coexistence 55 56 57 58 59 60 61 62 63 64 65 Because ecological niches are theoretically linked to a suite of functional traits (Violle 91 & Jiang 2009), functional traits appear to be a promising tool for understanding diversity...
Premise of the Study Despite long‐term research efforts, a comprehensive perspective on the ecological and functional properties determining plant weediness is still lacking. We investigated here key functional attributes of arable weeds compared to non‐weed plants, at large spatial scale. Methods We used an intensive survey of plant communities in cultivated and non‐cultivated habitats to define a pool of plants occurring in arable fields (weeds) and one of plants occurring only in open non‐arable habitats (non‐weeds) in France. We compared the two pools based on nine functional traits and three functional spaces (LHS, reproductive and resource requirement hypervolumes). Within the weed pool, we quantified the trait variation of weeds along a continuum of specialization to arable fields. Key Results Weeds were mostly therophytes and had higher specific leaf area, earlier and longer flowering, and higher affinity for nutrient‐rich, sunny and dry environments compared to non‐weeds, although functional spaces of weeds and non‐weeds largely overlapped. When fidelity to arable fields increased, the spectrum of weed ecological strategies decreased as did the overlap with non‐weeds, especially for the resource requirement hypervolume. Conclusions Arable weeds constitute a delimited pool defined by a trait syndrome providing tolerance to the ecological filters of arable fields (notably, regular soil disturbances and fertilization). The identification of such a syndrome is of great interest to predict the weedy potential of newly established alien plants. An important reservoir of plants may also become weeds after changes in agricultural practices, considering the large overlap between weeds and non‐weeds.
It is well known that alien plant invasion modifies the composition and diversity of resident plant communities, yet our ability to predict patterns of vegetation responses to invasion is hampered by a poor understanding of which functional traits make some resident plants more or less vulnerable to invader impacts. For example, resident species may be more likely to persist and coexist with the invader if they display different strategies of resource use (i.e. high niche differences) or if they share similar highly competitive traits (i.e. competitive hierarchy).Here, we used a trait-based approach to 1) specifically test whether species changes in abundance following plant invasion is random or depends on specific functional trait values, 2) identify which functional strategies allow resident species to coexist with the invader and 3) assess to what extent communities where the invader has been removed return to a reference state. To do so, we applied a semi-experimental approach with the annual vine Humulus japonicus, an invasive species in riparian habitats of Southern France. We monitored plant communities seven times over two years in non-invaded reference plots, invaded plots and removal plots in which the invader had been removed at the seedling stage. We quantified species richness and functional richness as well as mean community trait values of seven traits.The comparison of invaded and removal plots highlighted a strong impact of Humulus japonicus on both species and functional richness of riparian communities. Resident species that had a distinct flowering onset from the invader faced less pronounced declines. Specifically, species that flowered before the invader reached high cover, and species that had a short flowering duration had lower risk of declining. In addition, species coexisting with the invader when it reached its maximum cover displayed high stature and high seed mass. These results suggest that both niche differentiation (in terms of flowering strategy) and competitive hierarchies (in terms of height and regeneration strategy) play a role in explaining plant community responses to plant invasion. Finally, while species richness recovered rapidly in removal plots, functional richness remained lower than in non-invaded plots, pointing to a stateshift that would otherwise go undetected. Overall, our study highlights that the analysis of the functional traits of both invaders and resident species, combined with regular monitoring over time of non-invaded reference plots, invaded and removal plots can greatly improve our understanding of the impact of plant invasion on resident communities.
Most organisms in ephemeral habitat patches have resting stages which form a local species pool in response to temporal variations in the patch's availability and suitability. Temporal dispersal from the local species pool may, therefore, be an important process shaping the community assembly, particularly soon after patch creation, and possibly interacting with environmental filtering. As the temporal variation of the environmental conditions has a major effect on the composition of the local species pool, we investigated how well contemporary conditions (both patch availability and patch suitability) and temporal dispersal (approximated by environmental temporal variation and temporal distance) explain the changes in community composition in a given locality through successive ephemeral habitat cycles. We used arable weeds in annual crops as models. We calculated temporal weed community dissimilarity indices between weed communities surveyed in cropping seasons at intervals of two to eight years within a given field. The weeds were surveyed twice each cropping season to account for any changes in the relative contributions of temporal dispersal and contemporary conditions during the season. Patch availability explained most of the temporal weed dissimilarity, suggesting that patch dynamics have the greatest effect on weed community assembly. Temporal distance and temporal variation of the environmental conditions had more effect at the start of the cropping season than later, while patch suitability had more effect in the middle of the season. These results suggest that temporal dispersal drives the weed community assembly when ephemeral habitat patches are created. These assemblies are further shaped by environmental filtering. This is consistent with a temporal source sink dynamic mechanism where the seed bank acts as the main weed source. However, a large part of temporal weed dissimilarity remains unexplained, suggesting that other ecological processes such as spatial dispersal and founder effect may also shape the weed community.
1.Combining several crop species and associated agricultural practices in a crop sequence has the potential to control weed abundance while promoting weed diversity in arable fields. However, how the variability in environmental conditions that arise from crop sequences affects weed diversity and abundance remains poorly understood, with most studies to-date simply opposing weed communities in monoculture and in crop rotation. Here, we describe crop sequences along gradients of disturbance and resource variability using a crop functional trait and associated agricultural practices. We tested the hypothesis that in disturbances reduces weed abundance, whereas variability in resources promotes weed diversity. 2.We used functional Hill's numbers to compute crop sequence functional diversity based on sowing date, herbicide spectrum and crop height-these are the respective proxies of disturbance timings, disturbance types and light availability. Using a large-scale weed monitoring database, we assessed crop sequence diversity for 1,045 crop sequences of five consecutive cropping seasons. We computed weed richness and abundance at pluri-annual (pool of weeds observed across five cropping seasons) and annual (pool of weeds observed during a winter cereal cropping season preceded by five cropping seasons) scales. We also accounted for herbicide and tillage intensities to test whether management intensity affects the response of weed diversity and abundance to crop sequence diversity. 3.At the pluri-annual scale, weed richness increased with the diversity of crop height and sowing date, whereas weed abundance decreased with sowing date diversity.Annual weed richness decreased with sowing date diversity, whereas annual weed abundance poorly relied on crop sequence diversity. Synthesis and applications.This study establishes a scientific basis for designing crop sequences according to specific weed management goals. We show that farmers may enhance arable weed diversity on a pluri-annual scale by sequentially sowing crop species that differ in their competitive ability and sowing date. They may also achieve a better control of weed abundance by increasing the diversity of crop sowing dates across the crop sequence. Additional supporting information may be found online in the Supporting Information section at the end of the article. How to cite this article: Mahaut L, Gaba S, Fried G. A functional diversity approach of crop sequences reveals that weed diversity and abundance show different responses to environmental variability.
Ensuring the temporal stability of national food production is crucial for avoiding sharp drops in domestic food availability. The average stability of individual crop yields and asynchrony among crop yield fluctuations are two candidate mechanisms to stabilize national food production. However, the quantification of their respective influence on the stability of national food production is lacking, as is the identification of the factors regulating both mechanisms. Using yield data for 138 crops and 115 countries over a 50-year period, we first show that the stability of total national yield mostly relies on the fluctuations of the yield of crops covering the largest share of cropland. The average yield stability of these crops exert a stabilizing effect on national food production that is twice as important as the one of the asynchronous yield fluctuations among them. Climate variability reduces the stability of national food production by synchronizing yield fluctuations among crops and destabilizing the yield of individual crops. However, our results suggest that increasing crop diversity can counteract the synchronizing effects of climate variability by enhancing asynchronous dynamics among crops. Irrigation can promote the average stability of individual crop yields but cannot compensate for the destabilizing effect of climate variability. Considering both the response of each crop to climatic variations and the dynamics emerging from crop baskets will help agricultural policies to ensure stable food supply at the national level.
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