3.1 Plant traits
ANOVA results (Table 2) showed that average plant height, cover, shoot biomass and total biomass were most affected by plant species (F=277~611, p<0.01), followed by gravel content (F=90~195, p<0.01) and their interaction (F=5~51, p<0.05); root biomass was most affected by gravel content (F=130, p<0.01). Plant total biomass, shoot biomass, root biomass and their biomass ratio(shoot/root) among different soils overall decreased in the order of low˃high˃medium gravel content(Fig 1). In addition, different types of plants shoot biomass, root biomass and total biomass overall decreased in the order ofFe+Ed+Ms ˃Fe ˃Fe+Ms ˃Fe+Ed ˃Ms ˃Ms+Ed ˃Ed . Among them, Ms (2.15kg m-2) andFe+Ed+Ms (2.08kg m-2) on low gravel content soil had the highest total biomass, while Ed(l0.69~0.74kgm-2) had the lowest total biomass and showed no significant difference among three gravel soils (p>0.05).
Table 2 ANOVA results of the effects of gravel content, plant species and their interaction on plant traits.
Fig 1 . The changes of total, shoot, root biomass and their ratio with gravel content for different plant species. Error bars refer to standard deviation. Different lowercase letters indicate significant differences among different gravel soils; different capital letters indicate significant differences among all treatments (p<0.05). Fe, Festuca elata ; Ed,Elymus dahuricus ; Ms, Medicago sativa ; Fe+Ed,Festuca elata plus Elymus dahuricus ; Fe+Ms, Festuca elata plus Medicago sativa ; Ms+Ed, Medicago sativa plus Elymus dahuricus ;Fe+Ms+Ed, Festuca elata plus Medicago sativa plus Elymus dahuricus .
Fig. 2 The changes of plant height and coverage with gravel content for different plant species. (a), Total coverage; (b), Plant height; (c), Coverage of different plant species; (d), Height of different plant species. Error bars refer to standard deviation. Different lowercase letters indicate significant differences among different gravel soils (p<0.05). Fe, Festuca elata ; Ed,Elymus dahuricus ; Ms, Medicago sativa ; Fe+Ed,Festuca elata plus Elymus dahuricus ; Fe+Ms, Festuca elata plus Medicago sativa ; Ms+Ed, Medicago sativa plus Elymus dahuricus ;Fe+Ms+Ed, Festuca elata plus Medicago sativa plus Elymus dahuricus .
Fig. 2 shows that plant average height, and coverage among different gravel contents overall decreased in the order of low˃ high˃ medium gravel content. Among different soils, the average height of Msand Fe+Ed+Ms decreased in the order of low˃medium˃high; the average coverage of Ed decrease in the order of low˃medium˃high, while that of Fe+Ed , Fe+Ed+Ms followed an opposite trend.