The mechanism of community assembly is the core of ecological research. Using phylogenetic-based and functional trait-based methods jointly to explore the processes is a useful way to explain the change in assembly mechanisms. The present study combined these methods to explore the mechanism of plant community assembly in alpine meadows at different altitudes on the northeast Qinghai-Tibet Plateau. We established a permanent study plot of 1.85 Â 10 5 m 2 and investigated 162 quadrats of 50 Â 50 cm. We calculated the species richness, phylogenetic diversity (PD), standardized effect sizes PD (SESÁPD), mean pairwise distance (SESÁMPD), mean nearest taxon distance (SESÁMNTD), and analyzed plant functional traits and phylogenetic signals. We found that the species richness and PD of plant community showed a "hump-shaped" pattern, SESÁPD showed a decreasing trend, and the phylogenetic structure changed from overdispersion (SESÁMPD > 0, SESÁMNTD > 0) to clustering (SESÁMPD < 0, SESÁMNTD < 0) with increasing altitude. The functional structure changed from overdispersion (nearest function index [NFI] < 0) to clustering (NFI > 0) with increasing altitude. Specific leaf area, leaf carbon content, and leaf phosphorus content had weak phylogenetic signals (K < 1, p < 0.05), and the other functional traits (plant height, leaf nitrogen content, leaf dry matter content, and relative chlorophyll content) did not show phylogenetic signals (K < 1, p > 0.05). The above results showed that competitive exclusion was the main driving force of community assembly at low altitudes (3000 and 3250 m), and habitat filtration was the main driving force of community assembly at high altitudes (4000 and 4500 m). For medium altitudes (3500 and 3750 m), the habitat was more complex because it was in the transition area between high and low altitudes, so the process of community construction may be random, habitat filtering, or competitive exclusion. On the whole, the niche process (deterministic process) was more important in

No abstract

In this study, the effects of slope aspects and depths on soil organic carbon (SOC), soil total nitrogen (STN), and soil total phosphorus (STP) were quantified in disturbed restoration regions of Gaolan County, located in the Gansu Province of semi-arid loess Plateau of China. Soil samples were collected at 0–10, 10–20, 20–40, 40–60, 60–80, and 80–100 cm on southern, southwestern, western, northwestern, and northern slope aspects of three hills. A total of 75 soil profiles and 450 soil samples were analyzed. Results showed that the SOC, STN, and STP content varied from 1.65 to 12.87 g/kg, 0.45 to 1.53 g/kg, and 0.07 to 0.78 g/kg, and the SOCD, STND, and STPD at 0–100 cm varied from 3.9 to 9.5 kg/m2, 0.58 to 1.35 kg/m2, and 0.33 to 0.56 kg/m2, which increased from the southern to northern slope aspects. The SOC, STN, and STP contents and SOCD, STND, and STPD were mainly in the 0–60 and 60–100 cm soil layers. The vertical descent rate was γSOC &gt; γSTN &gt; γSTP for both content and density. For a single soil nutrient, the decline rate of its content and density on the northern slope aspect was greater than that on the southern slope aspect, that is γN &gt; γ All &gt; γS. The correlation degree between soil properties and SOC and STN content were above 0.6, the overall correlation with STP content was &lt;0.6. These results confirmed that topography (slope aspects) was the most significant factor controlling the distribution patterns of SOC, STN, and STP in hill ecosystems. Overall, the northern slope aspect (vs. southern slope aspect) was more favorable to the preservation of SOC, STN, and STP. Accordingly, in the Loess Plateau and similar fragile environments, soil nutrient protection and vegetation restoration are selective to some extent.