Mechanisms shaping plant biomass and species richness: plant strategies and litter effect in alkali and loess grasslands

Abstract

Question Explaining the biomass–species richness relationship is key to understanding vegetation dynamics. Several possible mechanisms have been suggested, but complex analysis of plant strategies, major biomass and species richness components along a long productivity gradient is still lacking. We provide a detailed analysis of the relationship between major biomass components (total above‐ground biomass, green biomass and litter), plant strategies and species richness along a long gradient of alkali and loess grasslands in a steppe landscape in Central Europe. Location Hortobágy, Great Hungarian Plain, East Hungary. Methods Above‐ground biomass of characteristic alkali and loess grassland stands was sampled along a gradient of increasing productivity. In each grassland stand, a 25‐m2 sample site was randomly selected. Within each site, ten above‐ground biomass samples (20 × 20 cm) were collected randomly in June 2009, at the peak of biomass production. We classified all species into mixed C‐S‐R strategy types. To obtain correlations between various biomass and species richness data, Spearman rank correlation was used. The relationship between plant strategies and species composition were displayed with a DCA ordination. Results The frequently detected humped‐back relationship was valid for the relation of total biomass and species richness. With increasing amount of total biomass, we detected an increasing proportion of competitors, and a decreasing proportion of stress tolerators in green biomass. A low proportion of ruderals was detected at both low and high biomass levels. Species richness was affected positively by litter at low litter scores, but there was a negative litter effect from much lower scores than detected previously (from 400 g·m−2). There was a positive relationship between green biomass production and species richness. Conclusions The study revealed that at the initial part of a productivity gradient, stress is likely responsible for low species richness. Our results show that litter can shape changes in species richness along the whole biomass gradient, thus the litter effect is one of the major mechanisms structuring grassland diversity.

Fine-scale vertical position as an indicator of vegetation in alkali grasslands – Case study based on remotely sensed data

“…Achilleo-Festucetum had the widest range of vertical position in our study site, likely because this association is characterised by moderate soil fertility and/or moderate salinity, which conditions are likely provided in different elevation zones (Kelemen et al, 2013). Accordingly its species pool includes some generalist species, shared with neighbouring associations, such as Achillea spp.…”

“…Loess grasslands are exposed to drought stress, but not affected by salt-stress and nutrientdeficiency. In contrast alkali steppes are exposed to moderate levels of drought and salt-stress; open alkali swards are exposed to high levels of drought and salinity; while alkali meadows are characterised by no drought and only moderate salt stress Kelemen et al, 2013). Thus, these marked differences in abiotic stress factors -especially topographically controlled soil moisture and salinity (Moeslund et al, 2013a,b) -likely resulted in the clear separation of main vegetation groups.…”

“…They were typically situated on the highly elevated plateaux, which probably provided optimal conditions (nutrientrich chernozem soil, low salt content and dry conditions) for loess grassland species, such as Euphorbia cyparissias, Festuca rupicola and Galium verum (Kelemen et al, 2013).…”

“…Due to the high salt content of the soil open alkali swards have a low vegetation cover (5-30%) and a species-poor vegetation mainly built by halophyte species (Török et al, 2012). They comprise three associations: Camphorosmetum annuae; Puccinellietum Table 1 Environmental characteristics of the studied associations (after Kelemen et al, 2013;Deák et al, 2014 limosae; Pholiuro pannonici-Plantaginetum tenuiflorae (hereafter Camphorosmetum, Puccinellietum and Pholiuro-Plantaginetum).…”

Cultural heritage and biodiversity conservation – plant introduction and practical restoration on ancient burial mounds

“…It was also found in former studies that species with large seeds can better tolerate the shading effect of litter and can also germinate below thick litter layers . Litter accumulation is typical in the loess grasslands of the region; Kelemen et al (2013) reported amounts of litter ranging between 161-516 g/m 2 . This suggests that large-seeded species can have an establishment advantage compared to small-seeded ones under such conditions (see also Ambika et al 2014).…”