Temperature dependence of nitrogen mineralization and microbial status in O_H horizon of a temperate forest ecosystem

It was hypothesized that increasing air and/or soil temperature would increase rates of microbial processes including litter decomposition and net N mineralization, resulting in greater sequestration of carbon and nitrogen in humus, and consequently development in OH horizon （humus horizon）. To quantify the effect of temperature on biochemical processes controlling the rate of OH layer development three adjacent forest floors under beech, Norway spruce and mixed species stands were investigated at Soiling forest, Germany by an incubation experiment of OH layer for three months. Comparing the fitted curves for temperature sensitivity of OH layers in relation to net N mineralization revealed positive correlation across all sites. For the whole data set of all stands, a Q10 （temperature sensitivity index） value of 2.35-2.44 dependent on the measured units was found to be adequate for describing the temperature dependency of net N mineralization at experimental site. Species-specific differences of substrate quality did not result in changes in biochemical properties of OH horizon of the forest floors. Temperature elevation increased net N mineralization without significant changes in microbial status in the range of I to 15℃. A low Cmic /Corg （microbial carbon/organic carbon） ratio at 20℃ indicated that the resource availability for decomposers has been restricted as reflected in significant decrease of microbial biomass.

Temperature dependence of carbon mineralization and nitrous oxide emission in a temperate forest ecosystem

The measurement of CO2 and N2O effiux from forest soils is of great importance in evaluating the role of forests as sequestering agents of atmospheric CO2 and nitrogen. To quantify the effect of site on temperature dependence of net C-mineralization and N2O-N emissions, three adjacent forest floors under beech, Norway spruce and mixed species stands were investigated at Soiling forest, Germany, by an incubation experiment for three months. The investigated net C-mineralization and N2O-N emissions from all forest floors exhibited an exponential increase with respect to temperature elevation. The temperature coefficient function （Q10 value）, was fitted to flux rates to describe the temperature sensitivity of forest floors on temperature in the range of 1-20℃. Comparing the fitted curves for temperature sensitivity of the forest floors in relation to net carbon mineralization and nitrous oxide emission rates revealed a strong positive correlation across all sites. For the whole data set of all stands, a Q10 value of 1.73-2.10 for net C-mineralization and 2.81-3.58 for N2O-N emissions per measured unit was found to describe the temperature dependency of net C-mineralization and N20-N efflux at experimental site. The absence of clear differences between beech and spruce in mono and mixed species cultures on temperature dependencies of net C-mineralization and N2O-N emission rates indicated that the flux rates were not affected by species-specific differences of litter quality.

Does a General Temperature-Dependent Q10 Model of Soil Respiration Exist at Biome and Global Scale？

Soil respiration （SR） is commonly modeled by a Q10 （an indicator of temperature sensitivity） function in ecosystem models. Q10 is usually treated as a constant of 2 in these models, although Q10 value of SR often decreases with increasing temperatures. It remains unclear whether a general temperature- dependent Q10 model of SR exists at biome and global scale. In this paper, we have compiled the long-term Q10 data of 38 SR studies ranging from the Boreal, Temperate, to Tropical/Sublropical biome on four continents. Our analysis indicated that the general temperature-dependent biome Q10 models of SR existed, especially in the Boreal and Temperate biomes. A single-exponential model was better than a simple linear model in fitting the average Q10 values at the biome scale. Average soil temperature is a better predictor of Q10 value than average air temperature in these models, especially in the Boreal biome. Soil temperature alone could explain about 50% of the Q10 variations in both the Boreal and Temperate biome single-exponential Q10 model. Q10 value of SR decreased with increasing soil temperature but at quite different rates among the three biome Q10 models. The k values （Q10 decay rate constants） were 0.09, 0.07, and 0.02/℃ in the Boreal, Temperate, and Tropical/Subtropical biome, respectively, suggesting that Q10 value is the most sensitive to soil temperature change in the Boreal biome, the second in the Temperate biome, and the least sensitive in the Tropical/ Subtropical biome. This also indirectly confirms that acclimation of SR in many soil warming experiments probably occurs. The k value in the ＂global＂ single-exponential Q10 model which combined both the Boreal and Temperate biome data set was 0.08/℃. However, the global general temperature-dependent Q10 model developed using the data sets of the three biomes is not adequate for predicting Q10 values of SR globally. The existence of the general temperature-dependent Q10 models of SR in the Boreal and Temperate biome has important implications for modeling SR, especially in the Boreal biome. More detail model runs are needed to exactly evaluate the impact of using a fixed Q10 vs a temperature-dependent Q10 on SR estimate in ecosystem models （e.g., TEM, Biome-BGC, and PnET）.

Spatial patterns in temperature sensitivity of soil respiration in China: Estimation with inverse modeling

Temperature sensitivity of soil respiration (Q10) is an important parameter in modeling the effects of global warming on ecosystem carbon release. Experimental studies of soil respiration have ubiquitously indicated that Q10 has high spatial heterogeneity. However, most biogeochemical models still use a constant Q10 in projecting future climate change and no spatial pattern of Q10 values at large scales has been derived. In this study, we conducted an inverse modeling analysis to retrieve the spatial pattern of Q10 in China at 8 km spatial resolution by assimilating data of soil organic carbon into a proc-ess-based terrestrial carbon model (CASA model). The results indicate that the optimized Q10 values are spatially heterogeneous and consistent to the values derived from soil respiration observations. The mean Q10 values of different soil types range from 1.09 to 2.38, with the highest value in volcanic soil, and the lowest value in cold brown calcic soil. The spatial pattern of Q10 is related to environmental factors, especially precipitation and top soil organic carbon content. This study demonstrates that inverse modeling is a useful tool in deriving the spatial pattern of Q10 at large scales, with which being incorporated into biogeochemical models, uncertainty in the projection of future carbon dynamics could be potentially reduced.

Eff ects of environmental factors on the temporal and spatial variations in branch and leaf CO_(2)effl ux of Larix gmelinii var.principis-rupprechtii Mayr

The CO_(2)effl ux of branches and leaves plays an important role in ecosystem carbon balance.Using a carbon fl ux system,the effl ux of Larix gmelinii var.principisrupprechtii(Dahurian larch)was investigated in 27 years(immature),31 years(near-mature),and 47 years(mature)stands at diurnal,seasonal,and spatial scales(direction and height)as well as its connection with environmental factors from May to October 2020.Diurnal variation in effl ux was a single peak,and the maximum occurring between 14:00 and 16:00.Seasonal variation also exhibited a single peak,with the maximum in late July and the minimum in early October.From May to September,effl ux on the south side was the largest among the three stands,and mean values on the south side of 27 year-old,31 year-old,and 47 year-old trees were 0.50,0.97 and 1.05μmol·m^(–2)·s^(–1),respectively.The minimum occurred on the north side.Except for the maximum in July and September in the 27 year-old stand in the middle of the canopy,the maximum effl ux in the upper canopy,and the means in the 27 year-old,31 year-old,and 47 year-old stands were 0.49,0.96 and 1.04μmol·m^(-2)·s^(-1),respectively;the minimum occurred in the lower canopy.Temperatures and relative humidity infl uenced seasonal variations in effl ux.Seasonal variation in temperature sensitivity coeffi cient(Q 10)was opposite that of temperature,increasing with decreasing temperature.At the spatial scale,maximum Q 10 occurred in the mid canopy.With the effl ux and temperature data in diff erent locations,it is possible to better estimate effl ux variations in each stand.

干旱区盐湖沿岸土壤呼吸特征及其影响因素

明确不同生态系统土壤碳排放规律及其影响因素对准确评估全球碳循环具有重要意义。为揭示干旱区典型盐湖沿岸土壤呼吸(Rs)、土壤呼吸温度敏感系数(Q10)变化特征及其影响因素,以新疆干旱区达坂城盐湖和巴里坤湖沿岸土壤为研究对象,在2015-2016年5~10月利用LI-8100土壤碳通量自动测量系统对盐湖沿岸土壤呼吸速率进行测定,分析了土壤呼吸季节性变化特征及其影响因子。结果表明,干旱区盐湖土壤呼吸变幅较大(0.07~11.59μmol·m-2·s-1),平均值为2.45μmol·m-2·s-1,7月土壤呼吸速率最高为4.69μmol·m-2·s-1,10月最低(1.01μmol·m-2·s-1);土壤CO2累积排放量为9.30 g·m-2·d-1,7月累积排放量最大为17.82 g·m-2·d-1。Q10呈"降低-增加-降低"趋势,6月最低(2.25)9月最高(3.52),平均值为2.79。干旱区盐湖沿岸土壤呼吸受土壤有机碳(SOC)、5 cm土壤温度(ST5)、土壤含水量(SM)和土壤盐分(Salt)的共同影响,单因素模型模拟可解释土壤呼吸速率变化的41.7%~75.7%(R2=0.417~0.757,P<0.05),多因子综合模型拟合结果最佳Rs=0.001×SOC+0.039×SM-0.534×Salt-0.116×ST5+5.06(R2=0.804,P=0.05),且均表明盐分是影响干旱区盐湖沿岸土壤呼吸速率的主要因子。因此,在考虑陆地生态系统碳收支和碳循环时不能忽略干旱区盐湖沿岸土壤碳过程,以及盐分对盐湖生态系统碳排放的影响。

微量添加元素对MonelK 500合金的高温塑性的作用

发现微量Ｍｇ、Ｃｒ 和Ｃｏ 元素对ＭｏｎｅｌＫ５００型的高温塑性具有明显的改善作用， 实验合金在高温下表现出一定的超塑性。测定了超塑性的应变速率敏感指数ｍ 值和形变激活能， 发现合金在超塑性变形时激活能较低。超塑性变形可能是一个扩散所控制的过程。通过微量杂质在晶界偏聚的断裂功计算表明， Ｍｇ、Ｃｒ 和Ｃｏ 具有改善ＮｉＣｕ 基合金晶界结合力的作用， 与试验结果符合。

中度火干扰对兴安落叶松林土壤呼吸的影响

通过测定中度火干扰后塔河地区兴安落叶松(Larix gmelinii)林生长季土壤呼吸(R_s),并进一步探究火干扰后影响土壤呼吸变化的主要环境因子。选择在塔河林业局火烧4年后兴安落叶松林中度火烧迹地设置样地,选择临近未过火区域设置对照样地。土壤呼吸通量用LI-8100进行测量,土壤异养呼吸(R_h)采用壕沟法进行测量。火烧迹地与未火烧对照样地生长季土壤呼吸速率平均值分别为(3.67±1.03)μmol CO_2m^(-2)s^(-1),(4.21±1.25)μmol CO_2m^(-2)s^(-1)。火烧迹地土壤呼吸速率显著降低(P<0.05)。生长季土壤呼吸组分的动态变化表明,土壤呼吸速率的降低是因为土壤自养呼吸(R_a)显著降低导致的(P<0.05)。温度是控制这一地区生长季土壤呼吸变化的主要环境因子。与对照样地相比,火烧迹地土壤呼吸的变化与土壤温度具有更强的相关性。塔河地区兴安落叶松林火烧迹地和未火烧对照样地Q_(10)分别为5.85±1.06,4.25±1.19,火干扰后Q_(10)显著增加(P<0.05)。研究结果表明:在全球气候变化的背景下火干扰后中国塔河地区兴安落叶松林生态系统对温度的变化更为敏感。本研究结果将为研究中国塔河地区火干扰后碳循环变化提供数据支持。

Dependence of Soil Respiration on Soil Temperature and Soil Moisture in Successional Forests in Southern China

The spatial and temporal variations in soil respiration and its relationship with biophysical factors In forests near the Tropic of Cancer remain highly uncertain. To contribute towards an Improvement of actual estimates, soil respiration rates, soil temperature, and soil moisture were measured In three successional subtropical forests at the Dlnghuahan Nature Reserve （DNR） In southern China from March 2003 to February 2005. The overall objective of the present study was to analyze the temporal variations of soil respiration and Its biophysical dependence in these forests. The relationships between biophysical factors and soil respiration rates were compared In successional forests to test the hypothesis that these forests responded similarly to biophysical factors. The seasonality of soil respiration coincided with the seasonal climate pattern, with high respiration rates in the hot humid season （April-September） and with low rates In the cool dry season （October-March）. Soil respiration measured at these forests showed a clear Increasing trend with the progressive succession. Annual mean （± SD） soil respiration rate In the DNR forests was （9.0 ± 4.6） Mg CO2-C/hm^2 per year, ranging from （6.1 ± 3.2） Mg CO2-C/hm^2 per year in early successional forests to （10.7 ± 4.9） Mg CO2-C/hm^2 per year in advanced successional forests. Soil respiration was correlated with both soil temperature and moisture. The T/M model, where the two biophysical variables are driving factors, accounted for 74%-82% of soil respiration variation In DNR forests. Temperature sensitivity decreased along progressive succession stages, suggesting that advanced-successional forests have a good ability to adjust to temperature. In contrast, moisture Increased with progressive succession processes. This increase is caused, in part, by abundant respirators In advanced-successional forest, where more soil moisture is needed to maintain their activities.

Diurnal and Seasonal Dynamics of Soil Respiration at Temperate Leymus Chinensis Meadow Steppes in Western Songnen Plain, China

To evaluate the diurnal and seasonal variations in soil respiration （Rs） and understand the controlling factors, we measured carbon dioxide （CO2） fluxes and their environmental variables using a LI-6400 soil CO2 flux system at a temperate Leymus chinensis meadow steppe in the western Songnen Plain of China in the growing season （May-October） in 2011 and 2012. The diurnal patterns of soil respiration could be expressed as single peak curves, reaching to the maximum at 11：00-15：00 and falling to the minimum at 21：00-23：00 （or before dawn）. The time-window between 7：00 and 9：00 could be used as the optimal measuring time to represent the daily mean soil CO2 efflux. In the growing season, the daily value of soil CO2 efflux was moderate in late spring （1.06-2.51μnol/（m2.s） in May）, increased sharply and presented a peak in summer （2.95-3.94 μmol/（m2.s） in July）, and then decreased in autumn （0.74-0.97 μmol/（m2.s） in October）. Soil temperature （Ts） exerted dominant control on the diurnal and seasonal variations of soil respiration. The temperature sensitivity of soil respiration （Q10） exhibited a large seasonal variation, ranging from 1.35 to 3.32, and decreased with an increasing soil temperature. Rs gradually increased with increasing soil water content （Ws） and tended to decrease when Ws exceeded the optimum water content （27%） of Rs. The Ts and Ws had a confounding effect on Rs, and the two-variable equations could account for 72% of the variation in soil respiration （p 〈 0.01）.

Response of Ecosystem Respiration to Experimental Warming and Clipping at Daily Time Scale in an Alpine Meadow of Tibet

The alpine meadow, as one of the typical vegetation types on the Tibetan Plateau, is one of the most sensitive terrestrial ecosystems to climate warming. However, how climate warming affects the carbon cycling of the alpine meadow on the Tibetan Plateau is not very dear. A field experiment under controlled experimental warming and clipping conditions was conducted in an alpine meadow on the Northern Tibetan Plateau since July 2008. Open top chambers （0TCs） were used to simulate climate warming. The main objective of this study was to examine the responses of ecosystem respiration （Reco） and its temperature sensitivity to experimental warming and clipping at daily time scale. Therefore, we measured Reco once or twice a month from July to September in 2010, from June to September in 2011 and from August to September in 2012. Air temperature dominated daily variation of Reco whether or not experimental warming and clipping were present. Air temperature was exponentially correlated with Reco and it could significantly explain 58-96% variation of Redo at daily time scale. Experimental warming and clipping decreased daily mean Reco by 5.8-37.7% and -11.9-23.0%, respectively, although not all these changes were significant. Experimental warming tended to decrease the temperature sensitivity of Reco, whereas clipping tended to increase the temperature sensitivity of Reco at daily time scale. Our findings suggest that Reco wasmainly controlled by air temperature and may acclimate to climate warming due to its lower temperature sensitivity under experimental warming at daily time scale.

Modeling the contribution of abiotic exchange to CO_2 flux in alkaline soils of arid areas

Recent studies on alkaline soils of arid areas suggest a possible contribution of abiotic exchange to soil CO2 flux(Fc).However,both the overall contribution of abiotic CO2 exchange and its drivers remain unknown.Here we analyzed the environmental variables suggested as possible drivers by previous studies and constructed a function of these variables to model the contribution of abiotic exchange to Fc in alkaline soils of arid areas.An automated flux system was employed to measure Fc in the Manas River Basin of Xinjiang Uygur autonomous region,China.Soil pH,soil temperature at 0–5 cm(Ts),soil volumetric water content at 0–5 cm(θs)and air temperature at10 cm above the soil surface(Tas)were simultaneously analyzed.Results highlight reduced sensitivity of Fc to Ts and good prediction of Fc by the model Fc=R10Q10(Tas–10)/10+r7q7(pH–7)+λTas+μθs+e which represents Fc as a sum of biotic and abiotic components.This presents an approximate method to quantify the contribution of soil abiotic CO2 exchange to Fc in alkaline soils of arid areas.

Non-cropping period accounting for over a half of annual nitric oxide releases from cultivated calcareous-soil alpine ecosystems with marginally low emission factors

Nitric oxide(NO)emissions from alpine ecosystems conventionally being long-term cultivated with feed crops are not well quantified.The authors attempted to address this knowledge gap by performing a year-round experimental campaign in the northeastern Tibetan Plateau.Fertilized(F)and unfertilized(UF)treatments were established within a flat calcareous-soil site for the long-term cultivation of feed oats.NO fluxes and five soil variables were simultaneously measured.A single plow tillage accounted for approximately 54%–73%of the NO releases during the cropping period(CP);and the non-cropping period(NCP)contributed to 51%–58%of the annual emissions.The direct NO emissions factor(EFd)was 0.021%±0.021%.Significantly lower Q10 values(p<0.01)occurred in the F treatment during the CP(approximately 3.6)compared to those during the other period or in the other treatment(approximately 4.9?5.1),indicating a fertilizer-induced reduction in the temperature sensitivity.The selected soil variables jointly accounted for up to 72%(p<0.01)of the variance for all the fluxes across both treatments.This finding suggests that temporally and/or spatially distributed fluxes from alpine calcareous-soil ecosystems for feed crop production may be easily predicted if data on these soil variables are available.Further studies are needed to test the hypothesis that the EFd is larger in alpine feed-oat fields than those in this study if the soil moisture content is higher during the period following the basal application of ammoniumor urea-based fertilizer.

Soil CO2 Efflux Dynamics and Its Relationship with the Environmental Variables in a Sub-Tropical Mixed Forest

Soil CO2 efflux is an ongoing process of respiration from soil;plant parts/ microbes below the ground to the atmosphere which is known for faster cycling of carbon sources. A large portion of carbon sequestered and fixed by forests is returned to the atmosphere through soil CO2 efflux and multiple controlling parameters mainly temperature, precipitation, and growth factors interact with the soil CO2 efflux variation. This study assessed the soil CO2 efflux every month for consecutive 2-years (August 2015 to July 2017) by using the closed chamber method to determine the role of ecological parameters that govern the soil CO2 efflux and its temporal modification in a sub-tropical mixed forest of central region in Nepal. The results of this study manifested that soil CO2 efflux accounted 63.2% (y = 31.96e0.128x), 71.3% (y = 44.77e0.123x) and 64.5% (y = 44.11e0.117x) variations in soil temperature with significantly (p < 0.05) exponential positive relation in the year 2015/2016, 2016/2017 and the two years when merged. And the temperature sensitivity value (Q10) of the soil CO2 efflux was 3.6, 3.4, and 3.2, respectively. Soil water content also expressed significantly (p < 0.05) positive exponential effect on soil CO2 efflux and accounted 62.0% (y = 138.3e0.057x), 46.1% (y = 88.42e0.052x) and 40.5% (y = 133.1e0.0447x) in its variability in different years and the merged years. Evident variations of soil CO2 efflux, soil temperature, soil water content, and litter were observed in the forest seasonally and inter-annually. Two years mean total annual soil CO2 efflux of the forest was estimated at 904.76 g C·m-2·y-1. The study revealed that sub-tropical forests could be more influenced by precipitation regimes in progressing warm climates i.e. vulnerable to climate change, illustrating the comprehensive dynamics of the representative forest carbon cycle in the tropical region.