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We determined how the vegetation and spatial heterogeneity (spatial variation) in species richness and species composition in salinized grasslands are affected by soil salinity level, and whether the Grime's hypothesis regarding species richness is accepted, to understand vegetation on salinized soil. To address these questions, we surveyed three grassland sites in Inner Mongolia. All sites had been degraded heavily by livestock grazing, and had different salinity levels: heavy (electrical conductivity 1.18–8.15 dS m−1), intermediate (0.38–0.70 dS m−1) and non-salinized (0.07–0.20 dS m−1). We set 50 square quadrats (0.25 m2 per quadrat), divided into four sub-quadrats (0.0625 m2 each), along two 25 m transects in each site, and recorded all plant species in each sub-quadrat. The species richness of the sites per 0.25 m2 was in the order: intermediate salinity > non-salinized > heavy salinity. At the heavy and intermediate sites, the spatial heterogeneity of vegetation per sub-quadrat was higher than expected from a random pattern, but not at the non-salinized site. At the heavily salinized site, the spatial patterns of two halophytes with the highest occurrences drove the high spatial heterogeneity in species richness. In contrast, at the non-salinized site, two low-level halophytes with the highest occurrences determined the random pattern. The intermediate salinity site, where high- and low-level halophytes could coexist in accordance with small-scale spatial changes in salinity, had the highest species richness with relatively high spatial heterogeneity (which accepted the Grime's hypothesis). Our working hypothesis for remediating vegetation and soil in salinized grasslands is to inhibit grazing, and to grow species that accumulate organic matter in soil. For this, halophyte species with large spatial heterogeneity/body size would be effective. |
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