g., [17, 35, 36]). Based on a large collection of field measures, Hui and Jackson [8] concluded that the proportion of the below-ground net biomass production in the total net primary production was negatively correlated with the average annual temperature and precipitation Sunitinib buy across sites. Our results indicate higher root increments in cool and wet highland and mountain sites, while lower values in dry and warmer environments of lowland sites were found. Perez and Frangi [37] reported that below-ground net productivity in grassland sites increased with altitude. On the other hand, a greater root production at lower than at higher elevated sites was found in several temperate grasslands [38]. Nevertheless, root production may not be a simple function of altitude [38, 39].

In our case, both altitude and amount of rainfall can explain obtained results of individual sites.The repeated measures analysis also exhibited the effect of year on YRI in all studied grasslands. The results show the lowest YRI in the dry treatment of the lowland dry grassland and a decreased root production in the dry treatments of the highland and mountain grasslands, particularly during the first three years. This fact can be associated with the lower regular rainfall recorded during this period. The YRI significantly increased in the Festuca lowland grassland in 2009 and 2010. In these years, the amount of precipitation was above the long-term averages. In the mountain grassland, the YRI varied over a wide range of values. This could also be associated with fluctuating amounts of the current precipitation.

Production of new roots was observed during periods of favourable soil water conditions [40, 41] and the decline in the below-ground net biomass production was found in dry years [15, 16, 18]. In addition, the below-ground net primary production was not related to the early but to the late rainfall in the rainy season [17]. However, Fitter et al. [39] concluded that a yearly increase in root biomass can be rather a function of changes in length of the growing season, not soil temperature. In the present study, in the drier vegetation seasons (2007 and 2008) decreased YRIs were recorded in nearly all grasslands and treatments, but particularly in the mountain grassland. Thus these interannual variations in root production reflected not only the experimentally manipulated amount of precipitation but also the current rainfall, that is, dry and wet conditions of individual growing seasons.4.2. Below-Ground Plant Parts and Their Interannual VariationsWe expected to find a lower accumulation Cilengitide of below-ground plant parts in dry conditions.