Microtopographic variation in soil respiration and its controlling factors vary with plant phenophases in a desert–shrub ecosystem

Abstract

Abstract. Soil respiration (R s ) and its biophysical controls were measured over a fixed sand dune in a desertshrub ecosystem in northwest China in 2012 to explore the mechanisms controlling the spatial heterogeneity in R s and to understand the plant effects on the spatial variation in R s in different phenophases. The measurements were carried out on four slope orientations (i.e., windward, leeward, north-and south-facing) and three height positions on each slope (i.e., lower, upper, and top) across the phenophases of the dominant shrub species (Artemisia ordosica). Coefficient of variation (i.e., standard deviation/mean) of R s across the 11 microsites over our measurement period was 23.5 %. Soil respiration was highest on the leeward slope, and lowest on the windward slope. Over the measurement period, plant-related factors, rather than microhydrometeorological factors, affected the microtopographic variation in R s . During the flower-bearing phase, root biomass affected R s most, explaining 72 % of the total variation. During the leaf coloration-defoliation phase, soil nitrogen content affected R s the most, explaining 56 % of the total variation. Our findings highlight that spatial pattern in R s was dependent on plant distribution over a desert sand dune, and plantrelated factors largely regulated topographic variation in R s , and such regulations varied with plant phenology.

Modelling the diurnal and seasonal dynamics of soil CO<sub>2</sub> exchange in a semiarid ecosystem with high plant–interspace heterogeneity

“…1a), Ningxia, China (see Wang et al, 2014Wang et al, , 2015. The long-term (1954The long-term ( -2004 mean temperature is 8.1 • C, and the mean annual precipitation is 287 mm, most of which falls from July to September (Jia et al, 2014).…”

“…In the horizontal direction, root biomass was set to decrease linearly with the distance from the centre of a shrub crown (Zhang et al, 2008). The N content was parameterized following the measurement of Wang et al (2015).…”

“…The specific respiration rate of roots (k R ), however, could be much greater during vegetative growing stage than other periods, e.g. at the defoliation stage (Fu et al, 2002;Wang et al, 2015). Here, we linked k R to the development of foliage in modelling using the approach of Curiel Yuste et al (2004):…”

“…These parameters included pH, nitrogen content, water-thermal conditions, root biomass, production rates and decomposition rates of litter, which are often key factors for regulating the soil C processes but likely to vary within and among ecosystems (see, e.g. Ma et al, 2011;Gong et al, 2016;Wang et al, 2015). Furthermore, we tested the model sensitivities to several newly defined parameters (i.e.…”

“…soil water content, abundance of substrates and microbial activities (Curiel Yuste et al, 2007; W. Wang et al, 2014;B. Wang et al, 2014B. Wang et al, , 2015.…”