Seasonal dynamics and vertical distribution of plant-feeding nematode communities in grasslands

Summary

The vertical distribution and seasonal dynamics of plant- and fungal-feeding nematode taxa in permanent grasslands were investigated. Dolichodoridae, Paratylenchus, Pratylenchus, Tylenchidae and Aphelenchoides dominated the upper 10 cm soil and their numbers strongly decreased with depth. The vertical distribution of these nematodes was correlated with the distribution of roots in the soil profile. Longidorus elongatus, Helicotylenchus pseudorobustus and Aphelenchus avenae were, however, also prevalent in the deeper soil layers. Trichodoridae and Hemicycliophora thornei seemed to prefer a depth of 30-40 cm. Most of the plant-feeding nematode taxa had an annual cycle in their abundance and population structures, which could largely be related to seasonal changes in the temperature and moisture contents of the soil. Although adult stages of sedentary endoparasitic genera were not counted, the peak number of juvenile Heterodera and Subanguina nematodes in spring indicated a distinct annual population cycle for these genera. The lowest densities of the semi-endoparasite Helicotylenchus pseudorobustus and the ectoparasites Geocenamus nanus, Tylenchorhynchus dubius, Paratylenchus nanus, Paratylenchus veruculatus and, to a lesser extent, Tylenchorhynchus maximus were found in winter/early spring, but their densities increased in summer/autumn. Generally, the population growth of these species in summer was preceded by a large proportion of adults followed by an increased number of juveniles. Taxa with short life cycles that could produce more generations per year, such as Tylenchidae and Aphelenchidae, and taxa with generation times of more than a year, such as Longidorus elongatus, generally did not show a distinct annual cycle.