重复添加植物残体后土壤微生物活性和生物量对盐度的响应特征

Microbial adaptation to salinity can be achieved through synthesis of organic osmolytes,which requires high amounts of energy;however,a single addition of plant residues can only temporarily improve energy supply to soil microbes.Therefore,a laboratory incubation experiment was conducted to evaluate the responses of soil microbes to increasing salinity with repeated additions of plant residues using a loamy sand soil with an electrical conductivity in saturated paste extract（EC_e） of 0.6 dS m^-1.The soil was kept non-saline or salinized by adding different amounts of NaCl to achieve EC_e of 12.5,25.0 and 50.0 dS m^-1.The non-saline soil and the saline soils were amended with finely ground pea residues at two rates equivalent to 3.9 and 7.8 g C kg^-1 soil on days 0,15 and29.The soils receiving no residues were included as a control.Cumulative respiration per g C added over 2 weeks after each residue addition was always greater at 3.9 than 7.8 g C kg^-1 soil and higher in the non-saline soil than in the saline soils.In the saline soils,the cumulative respiration per g C added was higher after the second and third additions than after the first addition except with3.9 g C kg^-1 at EC_e of 50 dS m^₁.Though with the same amount of C added(7.8 g C kg^-1),salinity reduced soil respiration to a lesser extent when 3.9 g C kg^-1 was added twice compared to a single addition of 7.8 g C kg^-1.After the third residue addition,the microbial biomass C concentration was significantly lower in the soils with EC_e of 25 and 50 dS m^₁ than in the non-saline soil at3.9 g C kg^-1,but only in the soil with EC_e of 50 dS m^-1 at 7.8 g C kg^-1.We concluded that repeated residue additions increased the adaptation of soil microbial community to salinity,which was likely due to high C availability providing microbes with the energy needed for synthesis of organic osmolytes.     

Uncoupling of microbial CO2 production and release in frozen soil and its implications for field studies of arctic C cycling

Knowledge of seasonal trends and controls of soil CO₂ emissions to the atmosphere is important for simulating atmospheric CO₂ concentrations and for understanding and predicting the global carbon cycle. This is particularly the case for high arctic soils subject to extreme fluctuating environmental conditions. Based on field measurements of soil CO₂ efflux, temperature, water content, pore gas composition in soil and frozen cores as well as detailed temperature experiments performed in the laboratory, we evaluated seasonal controls of CO₂ effluxes from a well-drained tundra heath site in NE-Greenland. During the growing season, near-surface temperatures correlated well with observed CO₂ effluxes (r²>0.9). However, during intensive thawing of near-surface layers we observed up to 1.5-fold higher effluxes than expected due to temperature alone. These high rates were consistent with high CO₂ concentrations in frozen soil (>10% CO₂) and suggested a spring burst event during soil thawing and a corresponding trapping of produced CO₂ during winter. Laboratory experiments revealed that microbial soil respiration continued down to a least −18 °C and that up to 80% of the produced CO₂ was trapped in soil at temperatures between 0 and −9 °C. The trapping of CO₂ in frozen soil was positively correlated with soil moisture (r²=0.85) and led to an abrupt change of the temperature sensitivity (Q₁₀) observed for soil CO₂ release at 0 °C with Q₁₀ values below 0 °C being up to 100-fold higher than above 0 °C. The results of sub-zero CO₂ production allowed us to predict the microbial soil respiration throughout the year and to evaluate to what extent burst events during thawing can be explained by the release of CO₂ being produced and trapped during winter. Taking only the upper 20 cm of the soil into account, winter soil respiration accounted for about 40% of the annual soil respiration. At least 14% of the winter CO₂ production was trapped during the winter 2000-2001 and observed to be released upon thawing. Thus, the site-specific winter soil respiration is an important part of the annual C cycle and CO₂ trapping should be accounted for in future field and modelling studies of soil respiration dynamics in arctic ecosystems. In conclusion, we have discovered a soil moisture dependent uncoupling of CO₂ production and release in frozen soils with important implications for future field studies of Arctic C cycling.     

澳大利亚盐渍土中自然草的盐分积累状况及其生理学特性

Salinity is a major soil contamination problem in Australia. To explore salinity remediation, we evaluated the concentrations of sodium (Na), potassium (K), magnesium (Mg), and calcium (Ca) in roots and shoots and in the supporting soil of the naturally occurring grasses, Cynodon dactylon and Thinopyrum ponticum, at two salt-affected sites, Gumble and Cundumbul in central-western New South Wales, Australia. The physiological parameters of the two grass species, including net photosynthetic rate (Pn), stomatal conductance (gs), and intercellular CO2 concentration (Ci), were investigated using one mature leaf from C. dactylon and T. ponticum populations. Increasing salinity levels in the topsoil had a significant influence on Ci and gs, whereas no significant effect occurred on Pn in C. dactylon and T. ponticum. The Pn values in C. dactylon and T. ponticum were greater at Cundumbul than at Gumble. The greater Mg concentration facilitated greater Pn in C. dactylon and T. ponticum populations at Cundumbul than Gumble. With increasing salinity levels in the soil, Na accumulation increased in C. dactylon and T. ponticum. The ratio between K and Na was > 1 in roots and shoots of both populations irrespective of the sites. Bioaccumulation factor (BF) and translocation factor (TF) results revealed that K and Na translocations were significantly higher in T. ponticum than in C. dactylon, whereas Ca and Mg translocations were significantly higher in C. dactylon than in T. ponticum. Accumulation of Na, K, Mg, and Ca ions was higher in T. ponticum than in C. dactylon; therefore, we suggest that T. ponticum as a greater salt accumulator than C. dactylon could be used for revegetation and phytoremediation of the salt-affected soils.     

大气CO2浓度升高对黄花蒿生长和氮磷钾养分吸收的影响

Annual wormwood (Artemisia annua L.) is the only viable source of artemisinin, an antimalarial drug. There is a pressing need to optimize production per cultivated area of this important medicinal plant; however, the effect of increasing atmospheric carbon dioxide (CO₂) concentration on its growth is still unclear. Therefore, a pot experiment was conducted in a free-air CO₂ enrichment (FACE) facility in Yangzhou City, China. Two A. annua varieties, one wild and one cultivated, were grown under ambient (374 μmol mol^-1) and elevated (577 μmol mol^-1) CO₂ levels to determine the dry matter accumulation and macronutrient uptake of aerial parts. The results showed that stem and leaf yields of both A. annua varieties increased significantly under elevated CO₂ due to the enhanced photosynthesis rate. Although nitrogen (N), phosphorus (P), and potassium (K) concentrations in leaves and stems of both varieties decreased under elevated CO₂, total shoot N, P, and K uptake of the two varieties were enhanced and the ratios among the concentrations of these nutrients (N:P, N:K, and P:K) were not affected by elevated CO₂. Overall, our results provided the evidence that elevated CO₂ increased biomass and shoot macronutrient uptake of two A. annua varieties.     

Two-dimensional simulation of airflow and carbon dioxide transport over a forested mountain: Part II. Carbon dioxide budget analysis and advection effects

We apply a high-resolution atmospheric model to assess the influence of mesoscale advection of CO₂ on the estimation of net ecosystem exchange (NEE) using eddy-covariance CO₂ flux measurements at a Fluxnet-Canada forest site located on sloping terrain on Vancouver Island, Canada. The numerical simulation is performed for fair-weather conditions over an idealized two-dimensional mountain bounded by water. The model is enhanced to include a CO₂ budget with a treatment of canopy photosynthesis and soil respiration.The simulation captures the transport of CO₂ by nocturnal drainage flows and weak land breezes. The resulting vertical profiles and time evolution of CO₂ concentration show a significant variation near the ground, associated with stability changes in the atmospheric boundary layer. The simulated vertical CO₂ gradients are found to be large around sunset and sunrise. The decrease of CO₂ concentration over land after midnight and the CO₂ accumulation over the neighboring water surface indicate CO₂ advection.A CO₂ budget analysis of the numerical-model output shows that the mean horizontal and vertical advection have significant fluctuations and opposite signs during daytime, with the net result that they largely counteract each other. At night, mean advection results in the underestimation by 20% of the nocturnal respiration. The estimated NEE at night is dominated by sub-grid-scale vertical flux in this simulation. Further evaluation using 3D simulations with higher resolution is needed to see if our results hold where vertical fluxes are much better resolved.     

水分和CO2对玉米光合性能及水分利用率的影响

利用环境生长室探讨不同CO₂浓度和土壤水分亏缺处理下玉米植株生物量、气孔形态与分布特征、叶片气体交换参数、叶绿素荧光参数等生长及生理指标的变化规律。以‘郑单958’ 玉米品种为试材,利用环境生长室设置2个CO₂浓度和4个土壤水分梯度对玉米进行CO₂浓度和水分处理。结果表明：1）不同程度土壤水分亏缺均显著降低玉米地上生物量（P<0.05）,但CO₂浓度升高增加了轻度水分亏缺条件下玉米地上生物量（P<0.01）和总生物量（P<0.01）。2）大气CO₂浓度升高导致轻度和中度水分亏缺条件下玉米的净光合速率（P_n）分别提高15.8%（P<0.05）和25.7%（P=0.001）,而CO₂浓度升高却降低了玉米叶片蒸腾速率（P<0.001）和气孔导度（P<0.001）,最终导致玉米瞬时水分利用效率均显著提高（P<0.001）。3）不同水分处理对玉米叶片气孔密度和单个气孔形态特征均造成显著影响（P<0.01）。因此,大气CO₂浓度升高可以增加轻度水分亏缺条件下玉米叶片氮含量、叶片非结构性碳水化合物含量和光合电子传递速率,从而提高玉米植株的生物量累积以及叶片碳同化能力和水分利用效率。研究结果将为深入理解气候变化背景下玉米对大气CO₂浓度升高和土壤水分亏缺的生理生态响应机制提供科学依据。     

黄土区刺槐林土壤含水量变化对土壤呼吸强度的影响

通过室内培养实验来评估土壤含水量的变化对土壤枯落物层、不同深度土壤层及DOC淋失后的土壤呼吸的影响.采集安塞纸坊沟31a刺槐林土样及林下混合枯落物,通过碱液吸收法测定100％,20％和2％含水量条件下3个深度土样(20,40和60 cm);去除DOC土样(仅100％含水量条件下);3种处理枯落物混合土样(林下混合枯落物、刺槐枯落物和草本类枯落物)培养过程中CO2的累计释放量.结果表明,100％和20％含水量条件下各深度土壤CO2释放量为20 cm土样＞60 cm土样＞40 cm土样;20 cm土样去除DOC后CO2释放量明显减少,40 cm明显增加,60 cm没有明显变化;混合枯落物土样在l00％含水量条件下CO2释放量最高;20％和2％含水量条件下刺槐枯落物CO2释放量明显大于草类,而100％含水量条件下草类枯落物略大于刺槐枯落物.研究证明土壤含水量对SOC组分含量和枯落物种类不同的土壤层呼吸强度存在差异性影响,强降水对DOC的淋失可造成表层土壤呼吸的减弱.     

Field measurement of carbon dioxide evolution from soil by a flow-through chamber method using a portable photosynthesis meter

Extract

Since a rise in atmospheric carbon dioxide (CO₂) concentration is expected to lead to global warming, it is important to quantify the global carbon circulation. The CO₂ evolution rate from soil has usually been measured by one of three methods: 1) CO₂ absorption (Anderson 1982), where the evolved CO₂ is absorbed in an alkali solution and the content subsequently determined, 2) closed chamber (Rolston 1986) in which the CO₂ evolution rate is calculated from the increase of the CO₂ concentration in a closed chamber covering the soil surface, and 3) flow-through chamber (Rolston 1986) in which a fixed rate of ambient air is pumped through an open chamber and the difference in the. CO₂ concentration between the inlet and the outlet is measured. Although the CO₂ absorption method is very simple in terms of apparatus and procedure, the determined CO₂ evolution rate tends to be underestimated in cases where the evolved CO₂ is not fully absorbed in the alkali solution (Ewel et al. 1987; Sakamoto and Yoshida 1988), or overestimated in cases where the CO₂ concentration in the chamber is too low to stimulate microbial activity (Koizumi et al. 1991; Nakadai et al. 1993), In the closed chamber method, when the gas concentration in the chamber is higher than that of the ambient air, gas diffusion from the soil to the atmosphere is restricted (Denmead 1978). At this point, the flow-through chamber method seems to be most suitable for measuring the CO₂ evolution rate, because the rate is determined under nearly natural conditions. However, this method has a disadvantage in that the apparatus is composed of an infra-red CO₂ analyzer, air pumps, mass flow meters, a recorder, and other items, which are too large, heavy, and complex to use in the field (Freijer and Bouten 1991). Hence, in spite of the above limitations, most of the studies on CO₂ evolution in situ have been carried out using the CO₂ absorption method (Kowalenko et al. 1978; Seto et al. 1978a, b; Ewel et al 1981, 1987; Gupta and Singh 1981; Reinke et al. 1981; Edwards and Ros-Todd 1983; Grahammer et al. 1991) or the closed chamber method (Naganawa et al. 1989; Mariko et al. 1994). The flow-through chamber method has been used only at sites where electric power supply and other types of equipment were available (Mathes and Schriefer 1985; Ewel et al. 1987; Nakadai et al. 1993). In the present report a flow-through chamber method using a portable CO₂ analyzer system was examined, for the determination of CO₂ evolution from soil without an electric power supply or other special equipment.