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Aims The aim of this paper is to assess morphological and leaf stoichiometric responses of Dendrosenecio keniensis and Lobelia gregoriana to extreme environmental conditions along an elevation gradient in tropical mountains. Methods In this study, we assessed the variation of the morphological traits, including plant height, leaf area, leaf thickness, leaf dry weight, specific leaf area and the leaf stoichiometry traits nitrogen, carbon and phosphorous of the two endemic species D. keniensis and L. gregoriana. We further explored the relations of these morphological traits to soil organic carbon, soil total nitrogen, soil phosphorous, annual mean temperature, annual mean precipitation, annual total solar radiation, water vapor pressure and the topographic variables aspect, slope and hill shade along the elevation gradient. Ninety 10 m × 10 m sampling plots were set up along the elevation gradient ranging from 3500 to 4300 m. We used 1 km × 1 km grid cells to rasterize our study area in ArcGIS 10.5 for easy access to data pertaining to the climate of each elevation band. We performed linear regression of the morphological and leaf stoichiometric traits with elevation as explanatory variable. We conducted correlation analysis on the morphological and leaf stoichiometric traits with climatic, soil and topographic variables along the elevation gradient. Important Findings Dendrosenecio keniensis had wool-like pubescent leaves while L. gregoriana had mucilage packed succulent and waxy cuticle leaves to avoid freezing. Both species exhibited reduced metabolic rates as shown by the low leaf phosphorous content. Our results also showed that changes in morphology and leaf stoichiometry were determined by a combination of climate, soil and topographic variables that change along elevation on Mount Kenya. The observed variations in the morphological and leaf stoichiometric traits of D. keniensis and L. gregoriana, which grow side by side along the elevation gradient, were interpreted as adaptation to the harsh environmental conditions.

Background Numerous studies have been conducted on species richness patterns along elevation gradients in temperate, tropical and sub-tropical mountains. However, few studies have been done to evaluate the combined effect of area and environmental heterogeneity (abiotic and biotic) on species richness. Numerous ecological studies have also failed to quantify environmental heterogeneity which we have done in this research. In this research, we studied the impact of area on environmental heterogeneity on species richness by considering the climate factors, annual mean temperature (AMT), annual mean precipitation (AMP), annual total solar radiation (ATSR), and Soil factors, soil organic carbon (SOC), Soil total nitrogen (STN), Soil extractable phosphorous (SEP), and Soil extractable potassium (SEK).Results Our analysis showed that species richness had a skewed hump-shaped pattern, with the highest species richness being at mid-elevation. The results also showed that climate factors had a strong positive correlation with species richness in relation to area as compared to soil factors. We also found that soil factors could be used to explain the species richness when combined rather than being interpreted individually. This study has showed that area could have profound effect on environmental heterogeneity therefore shaping species richness pattern along the elevation gradient in Mount Kenya.Conclusion The hump shaped species richness pattern can be due to the Ecophysiological constraints for example, low temperatures as elevation increases. The high species richness at the mid-elevation is because this zone has a large land area and also acts as transition zone between the extremes of the upper elevation range and lower elevation and species from either side can coexist since the environmental conditions are on the lower and higher limits for the existence of these plant species.