Aims: Identifying factors that determine plant diversity remains an important issue in community ecology and biogeography. Many studies have demonstrated that plant diversity is tightly associated with a suite of environmental factors, such as elevation, contemporary climate, paleoclimate, soil nutrient availability, and aboveground biomass (AGB). However, their effects and relative importance on plant diversity is still unknown due to lack of comprehensive study.
Methods: To assess relative importance of elevation, contemporary climate, paleoclimate, soil nutrient availability and AGB on early spring annual ephemeral plant(s) (ESAE), we surveyed species richness of ESAE across 32 sites in 2017 and 2018 in northern Xinjiang. We used general linear models to explore relationships of mean species richness (SR) of ESAE with elevation, climate (including annual mean temperature, precipitation in winter, precipitation from February to May, and anomaly of precipitation from February to May since the Last Glacial Maximum), soil nutrient availability (pH, soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), the ratio of SOC to TN (C : N); the ratio of SOC to TP (C : P), the ratio of TN to TP (N : P), and AGB. We then adapted partial least squares path modeling (PLS-PM) to measure the relative importance of each of these variables in regulating SR of ESAE.
Results: We found that SR of ESAE exhibited a significant unimodal pattern with increasing elevation, annual mean temperature, precipitation from February to May, anomaly of precipitation from February to May since the Last Glacial Maximum, soil pH, C : N, and AGB, but a U-shaped pattern with increasing precipitation in winter. Elevation, climate, and soil nutrients availability could influence SR of ESAE by altering AGB either directly or indirectly. Among these factors, climate was the most important factor in regulating SR of ESAE, followed by AGB, elevation, and soil nutrient availability, respectively.
Conclusion: Elevation, soil nutrients availability, climate and aboveground biomass had significant effects on species richness of EASA via their direct and indirect effects, but climate was the most important factor in regulating diversity of EASA.