Do slope orientation and sampling location determine soil biota composition?

“Evolution Canyon”is a typical Mediterranean-basin canyon with a summer dry stream at the bottom and large differences in vegetation cover and solar radiation between the north-facing slope(NFS)and the south-facing slope(SFS).It is known to act as an abiotic mediator influencing the community structure of soil fauna.The aim of this study was to determine the spatial dispersion of soil microbial and free-living nematode communities in the open sites(between shrubs)in the upper(0-10 cm)soil layer at four altitudes on both slopes.The combination of relative soil moisture availability and temperature,known to be one of the main triggers for soil biota activity,was explained by slope orientation.The above-mentioned differences were found to significantly affect microbial biomass and CO_(2)evolution resulting in temporary stress,corresponding to higher values in metabolic quotient(qCO_(2))values.These differences may represent microbial investment in energy in order to overcome stress resulting from the microclimatic differences between the two slopes.Moreover,the degree of substrate limitation(primary production due to the differences in plant cover)of microbial activity was explained by the difference in microbial functional groups.The total abundance of soil free-living nematodes was found to be 2-fold higher on the SFS than on the NFS.Thirty-nine genera,including 12 bacteria-feeders,5 fungifeeders,12 plant-parasites,and 10 omnivore-predators,were found at the study site,with 34 genera on the NFS and 29 on the SFS.The generic diversity of the bacteriafeeding nematodes was higher on the SFS than on the NFS.This study elucidates the importance of slope orientation and its effect on the structural levels of soil microbial and nematode communities.

The Effects of Terrain Slope and Orientation on Different Weather Processes in China under Different Model Resolutions

Currently, short horizontal surface wave radiation at the ground surface （GSW） is calculated under the assumption of a This method of estimating the GSW may lead to considerable errors when the model resolution becomes higher and the model terrain becomes steeper. In this paper, to improve the short wave solar radiation simulations, a terrain slope and orientation parameterization has been implemented into the non-hydrostatic mesoscale model GRAPES （Global/Regional Assimilation and Prediction System）. The effects of the terrain slope and orientation on different short range weather processes in China under different model resolutions are simulated and discussed. In the simulations, topography height is taken from NCEP （National Centers for Environmental Prediction） with a resolution of 1 km, and the slope and orientation of terrain are calculated using different staggering schemes and under different weather conditions. The results show that when the model resolution is low （30 and 60 km） and the slope of terrain is not large, the influence of the slope and orientation of terrain on the GSW is not evident; otherwise, however, it is not negligible. Under high model resolutions （3 and 6 km）, the increase （decrease） of simulated precipitation corresponds to the decrease （increase） of the GSW induced by the slope effect, and the variations of precipitation are usually ranged between -5 and 5 ram. Under the high resolution, the surface temperature and heat fluxes are strongly correlated to each other and the high correlation exists mostly in the complex terrain regions. The changes of the GSW, precipitation, surface temperature, and heat fluxes induced by the effects of the terrain slope and orientation are more obvious in mountainous regions, due to the alternations in the atmospheric circulation. It is found as well that under the weather condition of less cloud and less precipitation, the effects of the terrain slope and orientation can be more realistically seen. Therefore, the terrain slope and orientation can usually be neglected in numerical models when the horizontal model resolution is low and the slopes are moderate, but should be taken into account when the model resolution becomes high and the terrain is steep and undulating.