Search

The mid-domain effect (MDE) is a vital hypothesis to explain altitudinal patterns of species diversity of mountainous plants with different gradients, but it is bounded in terms of its application at the plant level. To verify the MDE hypothesis, we chose a typical mountain with obvious elevation gradients and considerable plant coverage as a study area in the east of the Loess Plateau and partitioned various elevation belts across this mountain. Through measuring the species diversity of arbor, shrub and herb communities in forest ecosystems, we explored altitudinal patterns of species diversity of mountainous plants with different gradients. We determined that the family numbers of the herb and shrub communities, as well as the species diversity of the arbor community, reached their maximums at intermediate elevations. The family numbers of the herb and shrub communities presented unimodal patterns across altitudinal gradients, and the highest values occurred at intermediate elevations. The family number of the arbor community showed a monotonic decreasing pattern, and the importance values of dominant families in the shrub and arbor communities presented unimodal patterns, but the lowest values occurred at intermediate elevations. The species diversity of the herb, shrub and arbor communities conformed to unimodal change patterns following altitudinal gradients, but the greatest diversity occurred at high, low and intermediate elevations, respectively. At higher elevations, weeds and grasses grew well, whereas sedges grew well at lower elevations. With respect to the importance values of different arbor life forms, their responses to altitudinal gradients indicated a certain variation pattern, which was greater for evergreen coniferous arbor species than for deciduous coniferous arbor species and deciduous broad-leaved arbor species. It is concluded that the MDE hypothesis of species diversity for mountainous plants is influenced greatly by the community life form and family flora at the plant level in a temperate semi-arid region of the Loess Plateau, China. This conclusion tests and modifies the MDE hypothesis and can be valuable for fueling prediction of biodiversity models and for the comparison with similar studies in different regions.

Background. Researchers frequently discuss spatial distribution patterns of species diversity and biomass together with their correlations along geographical gradients. Typical subalpine meadows occur widely on the east of the Loess Plateau, China. In recent years, with a rapid development of tourism and pasture husbandry, subalpine meadows have experienced extensive and severe degradation caused by humans in the mountain systems of the Plateau, where their environments are sensitive and fragile, meadows degradation had been increasing, and biodiversity has been threatened seriously. Methods. In our study, we selected nine mountains belonging to four mountain systems from north to south on the east of the plateau. We analyzed five latitudinal and longitudinal gradients together with six elevational gradients to study the spatial distribution patterns of species diversity (including α, β, and γ diversity) and biomass plus with their relationships at various scales. Results. For diversity, α-Diversity manifested unimodal variation patterns in horizontal spaces, peaking at high latitude and low longitude. However, α-diversity was not sensitive to elevation in vertical spaces and tended to decrease with increasing elevation. With increased latitude, longitude, and elevation, β-Diversity diminished; meanwhile, the rate of species turnover decreased and the similarity of community composition enlarged. γ-Diversity demonstrated quadratic function changes that were initially incremental and then decreased with increasing longitude, elevation, and latitude from 37.5° to 40°. For biomass, changes of aboveground biomass (AB) were more obvious along latitudinal gradients, whereas variations of belowground biomass (BB) had smaller differences along longitudinal and latitudinal gradients. More biomass was allocated to BB toward the north and east, whereas total biomass (TB) allocation was more evident at greater latitude than greater longitude. With increased elevation, more TB was also allocated to BB, and the relationship of biomass to elevation was closer in AB. In addition, species diversity had the strongest positive influence on AB. The Patrick and Shannon indices had correlations of power functions with AB and root-to-shoot ratio, respectively, indicating that an allometric model could be used to model relationships between species diversity and biomass. Discussion. The unique geomorphological structures with a series of basins between mountain systems on the east of the Loess Plateau, meant that subalpine meadows were mostly distributed along latitudinal directions, so the spatial distribution of species diversity and biomass was more evident along latitudinal gradients, and thus the response of aboveground biomass was more sensitive to variations of spatial gradients and species diversity.

Soil water content (SWC) regulation on the responses of soil respiration (Rs), autotrophic respiration (Ra), and heterotrophic respiration (Rh) to warming are rarely investigated in alpine meadow ecosystem in the Qinghai-Tibet Plateau (QTP). We conducted a warming experiment to investigate how SWC regulates the responses of Rs and its components (Ra and Rh) to warming. Infrared heaters were used to simulate climatic warming. Soil respiration was measured inside surface collars (2–3 cm deep) and Rh was measured inside deep collars (50 cm deep), which excludes root respiration. Autotrophic respiration was calculated by subtracting Rh from Rs. Warming increased the average Rs and Rh by 9.9% and 12.7% but had no significant effect on Ra. Interaction between warming and SWC had significant effect on Rs and its components. Soil respiration and Ra decreased by 5.8% and 36.3% in dry conditions, but they increased by 23.5% and 47.7% in wet conditions. Growing season above-ground biomass was enhanced by 0....