Within-trophic group interactions of bacterivorous nematode species and their effects on the bacterial community and nitrogen mineralization.

Knowledge of the interactions between organisms within trophic groups is important for an understanding of the role of biodiversity in ecosystem functioning. We hypothesised that interactions between bacterivorous nematodes of different life history strategies would affect nematode population development, bacterial community composition and activity, resulting in increased N mineralization. A microcosm experiment was conducted using three nematode species (Bursilla monhystera, Acrobeloides nanus and Plectus parvus). All the nematode species interacted with each other, but the nature and effects of these interactions depended on the specific species combination. The interaction between B. monhystera and A. nanus was asymmetrically competitive (0,–), whereas that between B. monhystera and P. parvus, and also A. nanus and P. parvus was contramensal (+, –). The interaction that affected microcosm properties the most was the interaction between B. monhystera and P. parvus. This interaction affected the bacterial community composition, increased the bacterial biomass and increased soil N mineralization. B. monhystera and P. parvus have the most different life history strategies, whereas A. nanus has a life history strategy intermediate to those of B. monhystera and P. parvus. We suggest that the difference in life history strategies between species of the same trophic group is of importance for their communal effect on soil ecosystem processes. Our results support the idiosyncrasy hypothesis on the role of biodiversity in ecosystem functioning

Nematodes

Plant-parasitic nematodes (PPNs) represent an important constraint for plant production worldwide. They are widely distributed around the world and are able to parasitize every plant species. Furthermore, the current restrictions on the use of chemical nematicides have increased the problems caused by PPNs, irrespec-tive of the production system. Intensive vegetable production under protected culti-vation is the system most vulnerable to PPN, especially to root-knot nematodes.Postprint (published version

Maximum rooting depth of vegetation types at the global scale

The depth at which plants are able to grow roots has important implications for the whole ecosystem hydrological balance, as well as for carbon and nutrient cycling. Here we summarize maximum rooting depth of species belonging to the major terrestrial biomes. We found 290 observations of maximum rooting depth in the literature which covered 255 woody and herbaceous species. Maximum rooting depth ranged from 0.3 m for some tundra species to 68 m for Boscia albitrunca in the central Kalahari; 196 species had roots at least 2 m deep, 50 species had roots at a depth of 5 m or more, and 22 species had roots as deep as 10 m or more. The average for the globe was 4.6 +0.5 m. Maximum root depth by biome was 2.0 m for boreal forest, 2.1 m for cropland, 9.5 m for desert, 5.2 m for sclerophyllous shrubland and forest, 3.9 m for temperate coniferous forest, 2.9 m for temperate deciduous forest, 2.6 m for temperate grassland, 3.7 m for tropical deciduous forest, 7.3 m for tropical evergreen forest, 15.0 m for tropical grassland/savanna, and 0.5 m for tundra. Grouping all species across biomes (except croplands) by three basic functional groups (trees, shrubs, and herbaceous plants), the average maximum rooting depth was 7.0 m for trees, 5.1 m for shrubs, and 2.6 m for herbaceous plants

Exploring the transport of plant metabolites using positron emitting radiotracers

Short-lived positron-emitting radiotracer techniques provide time-dependent data that are critical for developing models of metabolite transport and resource distribution in plants and their microenvironments. Until recently these techniques were applied to measure radiotracer accumulation in coarse regions along transport pathways. The recent application of positron emission tomography (PET) techniques to plant research allows for detailed quantification of real-time metabolite dynamics on previously unexplored spatial scales. PET provides dynamic information with millimeter-scale resolution on labeled carbon, nitrogen, and water transport over a small plant-size field of view. Because details at the millimeter scale may not be required for all regions of interest, hybrid detection systems that combine high-resolution imaging with other radiotracer counting technologies offer the versatility needed to pursue wide-ranging plant physiological and ecological research. In this perspective we describe a recently developed hybrid detection system at Duke University that provides researchers with the flexibility required to carry out measurements of the dynamic responses of whole plants to environmental change using short-lived radiotracers. Following a brief historical development of radiotracer applications to plant research, the role of radiotracers is presented in the context of various applications at the leaf to the whole-plant level that integrates cellular and subcellular signals and∕or controls