Abstract.The current understanding of the responses of soil respiration (Rs) to soil temperature (Ts) and soil moisture is limited for desert ecosystems. Soil CO 2 efflux from a desert shrub ecosystem was measured continuously with automated chambers in Ningxia, northwest China, from June to October 2012. The diurnal responses of Rs to Ts were affected by soil moisture. The diel variation in Rs was strongly related to Ts at 10 cm depth under moderate and high volumetric soil water content (VWC), unlike under low VWC. Ts typically lagged Rs by 3-4 h. However, the lag time varied in relation to VWC, showing increased lag times under low VWC. Over the seasonal cycle, daily mean Rs was correlated positively with Ts, if VWC was higher than 0.08 m 3 m −3 . Under lower VWC, it became decoupled from Ts. The annual temperature sensitivity of Rs (Q 10 ) was 1.5. The short-term sensitivity of Rs to Ts varied significantly over the seasonal cycle, and correlated negatively with Ts and positively with VWC. Our results highlight the biological causes of diel hysteresis between Rs and Ts, and that the response of Rs to soil moisture may result in negative feedback to climate warming in desert ecosystems. Thus, global carbon cycle models should account the interactive effects of Ts and VWC on Rs in desert ecosystems.

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.

The contribution of fine roots to forest ecosystem health (FEH) is still poorly understood, although fine roots are recognized to provide benefits to ecosystems. To address the relationship between fine roots and forest health, minirhizotrons was used to observe fine root (, 2 mm) dynamics during a 1-year period in nine Moso bamboo [Phyllostachys pubescens Mazel ex J. Houz.] plots having three levels of forest health (health, general health, and sub-health) 6 months after minirhizotron installation in the Dagang mountains (China). Forest health status was assessed by an improved Costanza model in 2011, 3 years after the great 2008 Chinese ice storm. Fine root number, length, and turnover in health plots were significantly higher than those in general health and sub-health plots, indicating that fine root number, length, and turnover rate were positively correlated with forest health condition. On the contrary, fine root diameter increased from 0.39^0.03 to 0.52^0.04 mm as forest health decreased, suggesting a strong negative correlation between fine root diameter and forest health condition. Fine root turnover rate ranged from 0.68^0.19 to 1.37^0.32 year 21 as forest health condition increased. All trees in the nine plots showed a unimodal peak of fine root production with distinct seasonality. The fine root number growth rate peaked in mid-summer and declined over the remainder of the growing season. Thus, fine root of Moso bamboo appear highly sensitive to forest health status, and this study concluded that fine root turnover rate of the minirhizotron tube surface can be used as an indicator to assess FEH in Dagang mountain.