How Past and Present Influence the Foraging of Clonal Plants?

Clonal plants spreading horizontally and forming a network structure of ramets exhibit complex growth patterns to maximize resource uptake from the environment. They respond to spatial heterogeneity by changing their internode length or branching frequency. Ramets definitively root in the soil but stay interconnected for a varying period of time thus allowing an exchange of spatial and temporal information. We quantified the foraging response of clonal plants depending on the local soil quality sampled by the rooting ramet (i.e. the present information) and the resource variability sampled by the older ramets (i.e. the past information). We demonstrated that two related species, Potentilla reptans and P. anserina, responded similarly to the local quality of their environment by decreasing their internode length in response to nutrient-rich soil. Only P. reptans responded to resource variability by decreasing its internode length. In both species, the experience acquired by older ramets influenced the plastic response of new rooted ramets: the internode length between ramets depended not only on the soil quality locally sampled but also on the soil quality previously sampled by older ramets. We quantified the effect of the information perceived at different time and space on the foraging behavior of clonal plants by showing a non-linear response of the ramet rooting in the soil of a given quality. These data suggest that the decision to grow a stolon or to root a ramet at a given distance from the older ramet results from the integration of the past and present information about the richness and the variability of the environment

Physiological integration of the clonal plant Carex arenaria and its response to soil-borne pathogens

We test the hypothesis that the expansive horizontal clonal growth of Carex arenaria may provide a method of escape from soil-borne pathogens (fungi and nematodes) by growing away from the site of infection. Plants were grown in non-sterilized or sterilized dune sand, i.e., with or without soil-borne pathogens. The effects of soil-borne pathogens were studied on the whole genet, on the mother alone, and on the first primary rhizome. Genets with the mother plant infected produced less total biomass and had less biomass allocated to roots than genets with uninfected mothers. Infected genets had fewer primary rhizomes and lower total rhizome length, but rhizome specific weight or the distance between shoots did not decrease in infected plants. In C. arenaria, uninfected mothers with an infected first primary rhizome produced shorter and fewer rhizomes than uninfected genets. The infected first rhizome continued to grow at the same speed as uninfected rhizomes, probably by support from the uninfected mother plant. However, secondary rhizome branching was affected only by direct exposure to soil pathogens and not by the status of the mother plant. The results provide evidence that clonal growth may facilitate escape from soil-borne pathogens. The rhizome explores a patchy environment by supporting the growth of young tillers when passing pathogenic patches. [KEYWORDS: Ammophila-arenaria; population biology; growth; consequences; nematodes; tillers; fungi; herb]

Long-term persistence of GM oilseed rape in the seedbank

Coexistence between genetically modified (GM) and non-GM plants is a field of rapid development and considerable controversy. In crops, it is increasingly important to understand and predict the GM volunteer emergence in subsequent non-GM crops. Theoretical models suggest recruitment from the seedbank over extended periods, but empirical evidence matching these predictions has been scarce. Here, we provide evidence of long-term GM seed persistence in conventional agriculture. Ten years after a trial of GM herbicide-tolerant oilseed rape, emergent seedlings were collected and tested for herbicide tolerance. Seedlings that survived the glufosinate herbicide (15 out of 38 volunteers) tested positive for at least one GM insert. The resulting density was equivalent to 0.01 plants m−2, despite complying with volunteer reduction recommendations. These results are important in relation to debating and regulating coexistence of GM and non-GM crops, particularly for planting non-GM crops after GM crops in the same field

The variability of processes involved in transgene dispersal—case studies from Brassica and related genera

Background, aim, and scope We strive to predict consequences of genetically modified plants (GMPs) being cultivated openly in the environment, as human and animal health, biodiversity, agricultural practise and farmers' economy could be affected. Therefore, it is unfortunate that the risk assessment of GMPs is burdened by uncertainty. One of the reasons for the uncertainty is that the GMPs are interacting with the ecosystems at the release site thereby creating variability. This variability, e. g. in gene flow, makes consequence analysis difficult. The review illustrates the great uncertainty of results from gene-flow analysis. Main features Many independent experiments were performed on the individual processes in gene flow. The results comprise information both from laboratory, growth chambers and field trials, and they were generated using molecular or phenotypic markers and analysis of fitness parameters. Monitoring of the extent of spontaneous introgression in natural populations was also performed. Modelling was used as an additional tool to identify key parameters in gene flow. Results The GM plant may affect the environment directly or indirectly by dispersal of the transgene. Magnitude of the transgene dispersal will depend on the GM crop, the agricultural practise and the environment of the release site. From case-to-case these three factors provide a variability that is reflected in widely different likelihoods of transgene dispersal and fitness of introgressed plants. In the present review, this is illustrated through a bunch of examples mostly from our own research on oilseed rape, Brassica napus. In the Brassica cases, the variability affected all five main steps in the process of gene dispersal. The modelling performed suggests that in Brassica, differences in fitness among plant genome classes could be a dominant factor in the establishment and survival of introgressed populations. Discussion Up to now, experimental analyses have mainly focused on studying the many individual processes of gene flow. This can be criticised, as these experiments are normally carried out in widely different environments and with different genotypes, and thus providing bits and pieces difficult to assemble. Only few gene-flow studies have been performed in natural populations and over several plant generations, though this could give a more coherent and holistic view. Conclusion The variability inherent in the processes of gene flow in Brassica is apparent and remedies are wished for. One possibility is to expose the study species to additional experiments and monitoring, but this is costly and will likely not cover all possible scenarios. Another remedy is modelling gene flow. Modelling is a valuable tool in identifying key factors in the gene-flow process for which more knowledge is needed, and identifying parameters and processes which are relatively insensitive to change and therefore require less attention in future collections of data. But the interdependence between models and experimental data is extensive, as models depend on experimental data for their development or testing. Recommendations More and more transgenic varieties are being grown worldwide harbouring genes that might potentially affect the environment ( e. g. drought tolerance, salt tolerance, disease tolerance, pharmaceutical genes). This calls for a thorough risk assessment. However, in Brassica, the limited and uncertain knowledge on gene flow is an obstacle to this. Modelling of gene flow should be optimised, and modelling outputs verified in targeted field studies and at the landscape level. Last but not least, it is important to remember that transgene flow in itself is not necessarily a thread, but it is the consequences of gene flow that may jeopardise the ecosystems and the agricultural production. This emphasises the importance of consequence analysis of genetically modified plants

Processes affecting genetic structure and conservation: a case study of wild and cultivated Brassica rapa

When planning optimal conservation strategies for wild and cultivated types of a plant species, a number of influencing biological and environmental factors should be considered from the outset. In the present study Brassica rapa was used to illustrate this: to develop Scandinavian conservation strategies for wild and cultivated B. rapa, DNA-marker analysis was performed on 15 cultivated and 17 wild accessions of B. rapa plus 8 accessions of the cross compatible B. napus. The B. rapa cultivars were bred in Sweden and Finland in 1944-1997 and the wild B. rapa material was collected from Denmark, Sweden and United Kingdom. The B. napus accessions were bred within the last 20 years in the Scandinavian countries. Results were based on scoring of 131 polymorphic ISSR markers in the total plant material. A Bayesian Markov chain Monte Carlo (MCMC) approach implemented in NewHybrids demonstrated a clear distinction of B. rapa and B. napus individuals except for three individuals that seemed to be backcrosses. The backcrossed hybrids descended from two Swedish populations, one wild and one escaped. The overall pattern of genetic variation and structure in B. rapa showed that cultivated and wild B. rapa accessions formed two almost separated clusters. Geographical origin and breeding history of cultivars were reflected in these genetic relationships. In addition, wild populations from Denmark and Sweden seemed to be closely related, except for a Swedish population, which seemingly was an escaped cultivar. The study point to that many processes, e.g. spontaneous introgression, naturalisation, breeding and agricultural practise affected the genetic structure of wild and cultivated B. rapa populations

Extensive physiological integration in Carex arenaria and Carex disticha in relation to potassium and water availability

Physiological integration between ramets is beneficial when acquiring heterogeneously distributed resources, and is hypothesized to occur when the benefits of resource sharing outweigh the costs. Our aim was to investigate if resource availability affected physiological integration in Carex arenaria and Carex disticha. Ramet systems were grown in high potassium and high water (K+ W+), high K and low water (K+ W-), or low K and high water (K- W+) for 1 month. Thereafter, water and K transport were traced with erythrosin and rubidium, respectively. Carex arenaria and C. disticha transported erythrosin over seven ramet generations and rubidium throughout the whole ramet system, but C. arenaria exported 20% more rubidium from the labelled shoot than C. disticha. A detailed analysis of subset of plants suggested that C. disticha in low K abundance shared more rubidium than in high K abundance, and that C. arenaria ramets in both K+ W- and K- W+ shared more resources than K+ W+ ramets. We demonstrated long-distance resource transport for K and water in C. arenaria and C. disticha. The distance of integration was not affected by resource availability in C. arenaria or C. disticha, but local concentrations of K showed marked and contrasting responses to nutrient and water treatment in both species

Soil food web properties explain ecosystem services across European land use systems

Intensive land use reduces the diversity and abundance of many soil biota, with consequences for the processes that they govern and the ecosystem services that these processes underpin. Relationships between soil biota and ecosystem processes have mostly been found in laboratory experiments and rarely are found in the field. Here, we quantified, across four countries of contrasting climatic and soil conditions in Europe, how differences in soil food web composition resulting from land use systems (intensive wheat rotation, extensive rotation, and permanent grassland) influence the functioning of soils and the ecosystem services that they deliver. Intensive wheat rotation consistently reduced the biomass of all components of the soil food web across all countries. Soil food web properties strongly and consistently predicted processes of C and N cycling across land use systems and geographic locations, and they were a better predictor of these processes than land use. Processes of carbon loss increased with soil food web properties that correlated with soil C content, such as earthworm biomass and fungal/bacterial energy channel ratio, and were greatest in permanent grassland. In contrast, processes of N cycling were explained by soil food web properties independent of land use, such as arbuscular mycorrhizal fungi and bacterial channel biomass. Our quantification of the contribution of soil organisms to processes of C and N cycling across land use systems and geographic locations shows that soil biota need to be included in C and N cycling models and highlights the need to map and conserve soil biodiversity across the world