Nematode exclusion and recovery in experimental soil microcosms

Abstract

Experimental manipulations of soil fauna are a powerful tool for assessing causal relationships between belowground biodiversity and key ecosystem properties. However, preparing soil microcosm treatments without soil fauna for ecological experiments can be problematic. Methods to exclude nematodes, a ubiquitous and functionally important component of terrestrial ecosystems, have been developed for a few specific ecosystems, some of them involving the application of nematicides that may have interactive effects throughout the soil food web. Our goal was to develop a method to remove nematodes from soils of three Long Term Ecological Research (LTER) grassland sites, ranging from desert to moist, without use of chemicals and with moderate disturbance. Moreover, we aimed at testing whether the nematode removal would remain effective up to several weeks later. The following treatments were applied to ~3-kg soil microcosms in the laboratory: (1) a 72-hours heating (65°C) -freezing (-20°C) -heating (65°C) cycle using soil maintained at its original water content, and pre-wetting soil 24 hours before heating (65°C) for either (2A) 48 hours or (2B) 24 hours. We measured treatment effects on total abundance and trophic structure of the nematode community. To investigate whether nematodes would recolonize eight weeks after treatments, we conducted a greenhouse experiment where individual seedlings of the dominant grass species for each ecosystem were transplanted to treated and non-treated (control) soils. A heat-freeze-heat cycle of 72h using soil in its original field water content killed 60, 95, and 99% of the nematodes for the desert, semi-arid, and moist tallgrass prairie soils, respectively. Pre-wetting soil before heating increased mortality to 99% for all ecosystems after only 24h at 65°C.Root-feeders were the most resistant nematode trophic group. Eight weeks after treatments, there was no significant nematode recolonization for the pre-wetted 48h heated soils from the three sites, while for the semi-arid and moist sites there was a slight recovery in abundance in soil from the 24h heating treatment. Therefore, a treatment at 65°C for 48h using pre-wetted soil is recommended for eight-week long manipulative experiments in order to assure the effectiveness of the nematode removal throughout the experiment.

Dynamic biospeckle analysis, a new tool for the fast screening of plant nematicide selectivity

“…This is in broad agreement with our finding that for bacterial feeders at around double that concentration only negligible biospeckle activity was observed after 24 h. Overall, bacterial feeder populations are reported to be more tolerant of pollution-induced stress than plant feeders [9]. This, however, appears to be largely due to plant feeders having lower reproductive capacity, while bacterial feeders tend to have high metabolic rates and the ability to re-populate contaminated soil quickly [61, 62]. In general, in the presence of stressors such as toxins, relative abundance is thought to shift in favour of colonising bacterial feeders [9].…”

Drought suppresses soil predators and promotes root herbivores in mesic, but not in xeric grasslands

“…These results suggest that increases in precipitation through time in more mesic grassland ecosystems, where predators are naturally more numerous, constrain root feeders and microbivores by promoting their nematode consumers. Predaceous nematodes are known to be highly responsive to environmental changes (24,30). In contrast to mesic environments, these findings indicate a less influential role of predation on the mechanism through which water availability controls nematode communities in xeric environments, suggesting that in drier ecosystems populations of nematodes are predominantly controlled by resource availability rather than predation.…”

Differential Metabolic Profiles during the Developmental Stages of Plant-Parasitic Nematode Meloidogyne incognita

“…It is spread all over the world and has been reported in Asia, Africa, North, Central and South America, the Caribbean, Europe, and Oceania [ 3 ]. Different approaches to control such plant-parasitic nematodes (PPNs) are arising as hitherto employed methods are either detrimental to the environment or becoming obsolete [ 4 , 5 , 6 ]. The life cycle of this plant-parasitic nematode consists of five stages including egg, juvenile J2, J3, J4, and female/male.…”