Partitioning of evapotranspiration and the influencing factors of evapotranspiration components in a shrub ecosystem dominated by Artemisia ordosica and Hedysarum fruticosum var. mongolicum in the Mu Us Desert, Northwest China.

Evapotranspiration (ET) is an important part of water cycle and energy flow in ecosystem. Accurate estimation of ET and its components is critical for understanding the impacts of ecophysiological processes on ecosystem water balance and plant water use strategy. Using the eddy-covariance technique and the micro-lysimeter, we measured ET, evaporation (E), transpiration (T) of the Artemisia ordosica-Hedysarum fruticosum var. mongolicum shrubland in the Mu Us Desert during May 20 to September 15, 2019, quantified the ET components, and analyzed the seasonal characteristics and influencing factors of ET and its components. The results showed that T was the main component of ET in the growing season, with a T/ET of 53.1%. T/ET increased and E/ET decreased as precipitation decreased. The partitioning of evapotranspiration was regulated by precipi-tation. At the seasonal scale, the value of E was positively correlated with soil water content at 10 cm depth (SWC10) and net radiation (Rn), while SWC10 was the main factor influencing E. The value of T increased with the increases of Rn and leaf area index (LAI), and increased first and then decreased with the increases of soil water content at 30 cm layer (SWC30). T was affected by SWC30, Rn and LAI. Moisture was the main influencing factor of ET. The ET/P in the growing season was 109.2% and was 250.5% in May, indicating that the water consumption of ET in early growing season was partly from the precipitation in non-growing season.

[Net ecosystem carbon exchange and its affecting factors in a deciduous broad-leaved forest in Songshan, Beijing, China]. / åŒ—äº¬æ¾å±±å¤©ç„¶è½å¶é˜”å¶æž—ç”Ÿæ€ç³»ç»Ÿå‡€ç¢³äº¤æ¢ç‰¹å¾åŠå ¶å½±å“å› å­.

Forests play an important role in terrestrial carbon cycles. The mechanism underlying carbon balance in temperate deciduous broad-leaved forests is not clear. In this study, net ecosystem exchange (NEE) and environmental factors, including air temperature (Ta), soil temperature (Ts), photosynthetically active radiation (PAR), vapor pressure deficit (VPD), soil water content (SWC) and precipitation (P) were continually measured using eddy covariance techniques in 2019 in a deciduous broad-leaved forest in Songshan, Beijing. We analyzed the characteristics of NEE and its response to environmental factors. The results showed that, at diurnal scale, the monthly averaged NEE exhibited a "U" shape curve (i.e., being a carbon sink over daytime while being a carbon source during nighttime) over the growing season. During the non-growing season, NEE was positive (i.e., carbon source) at diurnal scale. At the seasonal scale, NEE exhibited a unimodal curve. The annual cumulative NEE was -111 g C·m-2·a-1. Annual ecosystem respiration was 555 g C·m-2·a-1, while gross ecosystem productivity was 666 g C·m-2·a-1. Carbon sequestration peaked in June, while emission peaked in November. PAR was the dominant factor affecting daytime NEE (NEEd). VPD was the main factor that indirectly affected daytime NEEd, with an optimal VPD value that maximizes daytime NEE around 1-1.5 kPa. Soil temperature was the main factor affecting nighttime NEE (NEEn). SWC was a limiting factor for NEEn. Too high or too low SWC would inhibit NEEn, with an optimal SWC value of 0.28 m3·m-3.

[Net carbon exchange and its environmental affecting factors in a forest plantation in Badaling, Beijing of China].

By using eddy covariance technique, a year-round (November, 2011-October, 2012) continuous measurement of net ecosystem carbon dioxide exchange (NEE) was conducted in a 4-year old mixed forest plantation in Badaling of Beijing. The forest plantation ecosystem was a net carbon sink in July and August, but a carbon source in the rest months. The monthly net carbon loss and uptake were the largest in April and July, respectively. The annual net ecosystem productivity was (-256 +/- 21) g C x m(-2) x a(-1), in which, the ecosystem respiration was (950 +/- 36) g C x m(-2) x a(-1), and the gross ecosystem productivity was (694 +/- 17) g C x m(-2) x a(-1). The nighttime NEE increased exponentially with the soil temperature at 10 cm depth, with the estimated temperature sensitivity of ecosystem respiration (Q10 ) being 2.2. During the growth season (May-September), the daytime NEE increased with photosynthetically active radiation (PAR) as described by the Michaelis-Menten rectangular hyperbola. The ecosystem quantum yield varied seasonally, ranging from 0.0219 micromol CO2 x micromol(-1) in May to 0.0506 micromol CO2 x micromol(-1) in July. The maximum carbon assimilation rate and the average daytime respiration followed the seasonal trends of PAR and air temperature. In July and August, vapor pressure deficit and soil moisture played a significant role in determining daytime NEE.

Influence of disturbance on soil respiration in biologically crusted soil during the dry season.

Soil respiration (Rs) is a major pathway for carbon cycling and is a complex process involving abiotic and biotic factors. Biological soil crusts (BSCs) are a key biotic component of desert ecosystems worldwide. In desert ecosystems, soils are protected from surface disturbance by BSCs, but it is unknown whether Rs is affected by disturbance of this crust layer. We measured Rs in three types of disturbed and undisturbed crusted soils (algae, lichen, and moss), as well as bare land from April to August, 2010, in Mu Us desert, northwest China. Rs was similar among undisturbed soils but increased significantly in disturbed moss and algae crusted soils. The variation of Rs in undisturbed and disturbed soil was related to soil bulk density. Disturbance also led to changes in soil organic carbon and fine particles contents, including declines of 60-70% in surface soil C and N, relative to predisturbance values. Once BSCs were disturbed, Q 10 increased. Our findings indicate that a loss of BSCs cover will lead to greater soil C loss through respiration. Given these results, understanding the disturbance sensitivity impact on Rs could be helpful to modify soil management practices which promote carbon sequestration.

Respiratory responses of Scots pine stems to 5 years of exposure to elevated CO2 concentration and temperature.

Stem respiration in 20-year-old Scots pine (Pinus sylvestris L.) trees was examined following 5 years of exposure to ambient conditions (CON), elevated atmospheric carbon dioxide concentration ([CO2]) (ambient + 350 micromol mol(-1), (EC)), elevated temperature (ambient + 2-6 degrees C, (ET)) or a combination of elevated [CO2] and elevated temperature (ECT). Stem respiration varied seasonally regardless of the treatment and displayed a similar trend to temperature, with maximum rates occurring around Day 190 in summer and minimum rates in winter. Respiration normalized to 15 degrees C (R15) was higher in the growing season than in the non-growing season, whereas the temperature coefficient (Q10) was lower in the growing season. Annually averaged R15 was 0.36, 0.43, 0.40 and 0.44 micromol m(-2) s(-1) under CON, EC, ET and ECT conditions, respectively, whereas the corresponding values for total stem respiration were 6.55, 7.69, 7.50 and 7.90 mol m(-2) year(-1). The EC, ET and ECT treatments increased R15 by 18, 11 and 22%, respectively, relative to CON, and increased the modeled annual total stem respiration by 18, 15 and 21%. The increase in modeled annual stem respiration under EC and ECT conditions was caused mainly by higher maintenance respiration (22 and 25%, respectively, whereas the increase in growth respiration was 9 and 12%). Growth respiration was unaltered by ET. The treatments did not significantly affect the respiratory response to stem temperature; the mean Q10 value was 2.04, 2.10, 1.99 and 2.12 in the CON, EC, ET and ECT treatments, respectively. It is suggested that the increase in stem respiration was partly a result of the increased growth rate. We conclude that elevated [CO2] increased the maintenance component of respiration more than the growth component.