Birch Effect Research Articles

Drying and rewetting conditions differentially affect the mineralization of fresh plant litter and extant soil organic matter

Drought is becoming more common globally and has the potential to alter patterns of soil carbon (C) storage in terrestrial ecosystems. After an extended dry period, a pulse of soil CO2 release is commonly observed upon rewetting (the so-called ‘Birch effect’), the magnitude of which depends on soil rewetting frequency. But the source and implications of this CO2 efflux are unclear. We used a mesocosm field experiment to subject agricultural topsoil to two distinct drying and rewetting frequencies, measuring Birch effects (as 3-day cumulative CO2 efflux upon rewetting) and the overall CO2 efflux over the entire drying-rewetting cycle. We used 14C-labelled wheat straw to determine the contribution of fresh (recently incorporated) plant litter or extant soil organic matter (SOM) to these fluxes, and assessed the extent to which the amount of soil microbial biomass + K2SO4-extractable organic C (fumigated-extracted C, FEC) before rewetting determined the magnitude of Birch effect CO2 pulses. Our results showed a gradual increase in SOM-derived organic solutes within the FEC fraction, and a decrease in soil microbial biomass, under more extreme drying and rewetting conditions. But, contrary to our hypothesis, pre-wetting levels of FEC were not related to the magnitude of the Birch effects. In the longer term, rewetting frequency and temperature influenced the overall (31-day cumulative) amount of CO2–C released from SOM upon rewetting, but the overall 14CO2–C respired from fresh straw was only influenced by the rewetting frequency, with no effect of seasonal temperature differences of ∼15 °C. We conclude that the mineralization of fresh plant litter in soils is more sensitive to water limitations than extant SOM in soils under drying-rewetting conditions. Moreover, we found little evidence to support the hypothesis that the availability of microbial and soluble organic C before rewetting determined the magnitude of the Birch effects, and suggest that future work should investigate whether these short-term CO2 pulses are predominantly derived from substrate-supply mechanisms resulting from the disruption of the soil organo-mineral matrix.

Volatile Organic Compound Emissions From Soil Following Wetting Events

AbstractDynamics of carbon dioxide (CO2) emissions following the wetting of dry soil have been widely studied in field and laboratory settings. Nonmethane volatile organic compounds (VOCs) are also emitted from soil following a rain event and are evident from the characteristic smell of wet soil. Few studies have documented VOC emissions before and after soil rewetting. Soil emissions were studied using a dynamic flux chamber system purged with VOC‐free air, with identification and quantification of emissions performed by gas chromatography/mass spectrometry. All soils exhibited a rewetting‐induced pulse of VOC emissions, with VOC emissions 14 times higher (on average) in the few hours after rewetting compared to moist soils 2 days after rewetting. This VOC rewetting pulse mirrored the CO2 rewetting pulse (the so‐called “Birch Effect”) but was shorter in duration. Average VOC emissions were 5.0 ± 2.0% of CO2 emissions (molar C equivalent) and increased with increasing soil organic matter content (ρ = 0.40, ρ = 0.99 with one soil excluded). The amounts and types of VOCs varied with time since rewetting and across the five studied soil types, though acetone and small hydrocarbons were the dominant compounds emitted from all soils. Some of the VOCs emitted are likely important mediators of microbial activities and relevant to atmospheric chemical dynamics. Soil VOC emissions, similar to CO2 emissions, are strongly affected by rewetting events, and it is important to consider these rewetting dynamics when modeling soil and ecosystem VOC emissions and understand their relevance to terrestrial ecosystem functioning and atmospheric processes.

The effect of cisplatin administration on certain trace elements homeostasis in rats and the protective effect of silver birch (Betula pendula) sap

BackgroundA clinically active structure with known antitumor activities is cisplatin (CDDP), but this it comes with toxicity characteristics which can be faded by the beneficial effects of Silver birch (Betula pendula) sap. ObjectiveWe aimed to assess the cisplatin activity on: Mn, Mg, Cu, Fe and Zn homeostasis in rats and to observe the effect of birch sap. MethodsHealthy Wistar rats (n = 10/group) were divided in four groups: Control: receiving 1 mL saline I.P. way + water; E1: cisplatin 20 mg kgbw−1, I.P.; E2: cisplatin 20 mg kgbw−1, I.P. + birch sap and Control sap group: 1 mL saline I.P. + birch sap. Blood was collected: at the trial’s start and after 48 h, and blood and organs (liver, kidney and spleen) for the cytoarchitecture investigation and readings were sampled after seven days. Samples were processed in nitric acid by microwave digestion and readings were completed by flame atomic absorption spectroscopy, the outcomes being statistically analyzed by ANOVA. ResultsCisplatin produced a significant imbalance in the trace elements homeostasis, the birch sap administration recovering them usual homeostasis status. Comparatively with the Control, rats exposed to cisplatin presented a not significant (p > 0.05) decrease of Zn (−26.74%) and Mg (−10.25%), a significant (p < 0.05) decrease of Cu (−27.73%) at 48 h, a highly significant (p < 0.01) decrease of Cu (−56.08%) and Fe (−85.35%) at seven days after administration and a not significant (p > 0.05) increase of Mn (+28.16%). Birch sap administration after Cisplatin was followed by restoration or nevertheless significant increase (p < 0.05) of the investigated trace elements Zn (+56.88% to 48 h/+89.94% after seven days), Mg (+26.86%/+95.74%), Cu (+23.13%/+74.56%), Fe (+39.64%/+440.11%) and Mn (+4.30%/+15.87%), suggesting them defence against cisplatin. Histology revealed the order of main altered organs after the CDDP exposure: kidney, spleen and liver. ConclusionsThe study recommended the important protective role of Betula pendula sap against diverse cisplatin deleterious side-effects.

Unconsidered sporadic sources of carbon dioxide emission from soils in taiga forests.

Long-term monitoring in the Russian taiga zone has shown that all known extreme destructive effects resulting in the weakening and death of tree stands (windfalls, pest attacks, drought events, etc.) can be sporadic, but significant sources of CO2 soil emission. Among them are (i) a recently found effect of the multiyear CO2 emission from soil at the bottom of deadwood of spruce trees that died due to climate warming and subsequent pest outbreaks, (ii) increased soil CO2 emissions due to to the fall of tree trunks during massive windfalls, and (iii) pulse CO2 emission as a result of the so-called Birch effect after drought events in the taiga zone. According to the modeling, while depending on the spatial and temporal scales of their manifestation, the impact of these sporadic effects on the regional and global soil respiration fluxes could be significant and should be taken into consideration. This is due to continuing Climate Change, and further increase of local, regional and Global human impacts on the atmospheric greenhouse gases balance, and land use, as well.

Changes in carbon pool and CO2 emission in the course of postagrogenic succession on gray soils (Luvic Phaeozems) in European Russia

An analogous time series of fallow ecosystems (gray soils (Luvic Phaeozems) plowed and fallowed for 2, 7, 20, 60, and more than 120 years) in the broad-leaved forest zone of Orel oblast has been analyzed. Changes in carbon pool and CO2 emission in the course of postagrogenic succession during the vegetation and winter seasons have been estimated. The restoration of ecosystems on Luvic Phaeozems follows regularities revealed in analogous studies of southern taiga Podzols and forest-steppe Chernozems. Analogously to the other studied zonal chronosequences, total annual soil respiration on Luvic Phaeozems reaches the initial level of undisturbed ecosystems simultaneously with the restoration of phytomass reserve, although significantly earlier than the organic carbon reserve in soils is restored. According to regression models, among the zonal fallows in European Russia, including the southern taiga (Podzols), mixed forests (Luvisols), broadleaved forests (Luvic Phaeozems ), forest-steppe (Chernozems) and dry steppe (Calcisol–Solonetz soil complexes), the mean annual soil respiration is maximum in the zone of gray soils and Chernozems. The increase in soil respiration under artificial wetting (Birch effect) on fallows in the broad-leaved forest zone is minimum among the studied zonal chronosequences: 1.1 ± 0.6 (no effect), which corresponds to the optimal hydrothermal conditions in this zone.

Effects of long-term application of mineral and organic fertilizers on dynamics of nitrogen pools in the sandy soil of the Sahel region, Niger

Our study on soil N dynamics was conducted in the rainy season of 2005 and 2006. It focused on the effects of soil managements with sole and combined applications of mineral and organic fertilizers in the long-term experiment conducted since 1993 in the Niamey Center of the International Crop Research Institute for the Semi-Arid Tropics, Niger. Treatments were established with each three input levels of chemical fertilizer as urea and SSP, pearl millet residue, and cattle manure. The lowest and highest levels were focused in our study. Treatments with 2700kgha−1 of applied crop residue showed high total N in the soil surface (< 30cm), but did not show any change in the deeper layer (> 30cm) or seasonal changes. Phosphate-buffer extractable organic nitrogen (PEON) as an indicator to estimate available N in the soil was not affected by the different treatments; however, similar seasonal changes were identified in all treatments. PEON in soil surface was high right before the rainy season began, then gradually decreased with increasing rainfall and remained at approx. 10mgkg−1 until the end of the season. In deeper layer, leaching was identified after heavy rainfall but at least 5mgkg−1 of PEON remained during the season. Inorganic N (NO3N plus NH4N) increased in the soil surface right after fertilizer application but its effect disappeared in a few weeks. The ‘Birch effect’ affected the fluctuations of PEON and inorganic N at the start of rains in the Sahel region of Niger.

MP48-11 THE EFFECT OF MORPHINE AND ITS INHIBITORS ON RT112 BLADDER CANCER CELL GROWTH

You have accessJournal of UrologyBladder Cancer: Basic Research & Pathophysiology II1 Apr 2017MP48-11 THE EFFECT OF MORPHINE AND ITS INHIBITORS ON RT112 BLADDER CANCER CELL GROWTH Brian Birch, Bashir Lwaleed, Alan Cooper, Phil Harper, and Iliana Giatsidou Brian BirchBrian Birch More articles by this author , Bashir LwaleedBashir Lwaleed More articles by this author , Alan CooperAlan Cooper More articles by this author , Phil HarperPhil Harper More articles by this author , and Iliana GiatsidouIliana Giatsidou More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2017.02.1492AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Clinical studies suggest opioid use affects rates of metastasis in breast and prostate cancer. Results are variable and conflicting. This investigation tested the effects of morphine on bladder cancer cell growth in vitro and examined whether those effects can be reversed with receptor blockers. METHODS Cell lines: Adherent epithelial cell lines were used:RT-112 - Human urinary bladder transitional carcinoma cell lines, histological grade G2 (moderately differentiated). PNT2 - Normal (virally transformed) Human prostate epithelial cell line. These cells were grown using routine cell culture techniques supplemented with 10% foetal calf serum and antibiotics. Proliferation assay: The assay recorded residual viable biomass (RVB) 72 hours into exposure with the agent being studied RESULTS Doubling dilution of morphine produced a bell-shaped curve, with high (non-clinical)concentrations inhibiting growth, followed by stimulation between 100 and 1 microgram per ml (clinically relevant concentrations shown in Figure 1 green circle), reverting to control levels thereafter. The near-normal PNT-2 cell line showed minimal responsiveness to morphine Incubation with naloxone alone has little effect on residual biomass compared to controls Conversely, pre-incubating with a fixed concentration of Naloxone, then titrating morphine across the plate showed stimulation to decrease as the relative proportion of blocker rises (Figure 2) CONCLUSIONS Morphine in clinically relevant concentrations stimulated growth in the RT-112 transitional carcinoma cell line, as assessed by the MTT assay. This effect was minimal under the same conditions using the virally transformed normal prostate cell line (PNT2). Treating cells with the antagonists Naloxone or Naltrexone inhibited the action of morphine. The tentative implication is that using opioids in cancer patients despite their important role in pain relief may also tend to promote tumour growth. © 2017FiguresReferencesRelatedDetails Volume 197Issue 4SApril 2017Page: e640-e641 Advertisement Copyright & Permissions© 2017MetricsAuthor Information Brian Birch More articles by this author Bashir Lwaleed More articles by this author Alan Cooper More articles by this author Phil Harper More articles by this author Iliana Giatsidou More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Respiration Rates of Organic Soil Depending on Changes of Moisture and Aeration

This paper aims at analyzing changes in soil respiration depending on the levels of soil moisture and aeration. Organic forest soil was used in the experiments. Watering of the soil was applied starting from two initial moisture contents: 1) GWC > 0.1, desiccated soil, respiration equals to zero; 2) GWC between 0.46 - 0.78, moisture of the soil approximately the same as at the time of sample collection. Watering of the soil was applied once or continuously during the experiment. The experiments were conducted under both: unrestricted air-supply and anoxic conditions. Measurements of: oxygen consumption, carbon dioxide emission, and RQ were determined with a volumetric respirometer. Soil desiccation, which occurs under good access of the air, and leads to the increase of respiration rate (the “Birch effect”), is predominantly related to aerobic respiration following the change in soil aeration. If respiration of non-desiccated soil is assumed as 100%, the oxygen consumption of desiccated soil equaled to 209.90% of such value in the non-desiccated soil at the lowest moisture level, and only to 51% at the highest. Carbon dioxide emission equaled to 191.92% and 111% at the lowest and the highest moisture levels, respectively. Desiccation did not increase the respiration rate under anoxic conditions. It either decreased or remained statistically unchanged. However, obtained values of RQ index suggest that under anoxic conditions desiccation affects fermentation processes in the soil. The value of RQ index at the moisture level lower than GWC 1 was very low attaining merely 0.3 - 0.4, which suggests active fermentation processes. At higher moisture content yet, RQ value exceeded 2.

Unraveling the mechanisms underlying pulse dynamics of soil respiration in tropical dry forests

Tropical dry forests are already undergoing changes in the quantity and timing of rainfall, but there is great uncertainty over how these shifts will affect belowground carbon (C) cycling. While it has long been known that dry soils quickly release carbon dioxide (CO2) upon rewetting, the mechanisms underlying the so-called ‘Birch effect’ are still debated. Here, we quantified soil respiration pulses and their biotic predictors in response to simulated precipitation events in a regenerating tropical dry forest in Costa Rica. We also simulated the observed rewetting CO2 pulses with two soil carbon models: a conventional model assuming first-order decay rates of soil organic matter, and an enzyme-catalyzed model with Michaelis–Menten kinetics. We found that rewetting of dry soils produced an immediate and dramatic pulse of CO2, accompanied by rapid immobilization of nitrogen into the microbial biomass. However, the magnitude of the rewetting CO2 pulse was highly variable at fine spatial scales, and was well correlated with the size of the dissolved organic C pool prior to rewetting. Both the enzyme-catalyzed and conventional models were able to reproduce the Birch effect when respiration was coupled directly to microbial C uptake, although models differed in their ability to yield realistic estimates of SOC and microbial biomass pool sizes and dynamics. Our results suggest that changes in the timing and intensity of rainfall events in tropical dry forests will exert strong influence on ecosystem C balance by affecting the dynamics of microbial biomass growth.

The effects of birch (Betula spp.) biochar and pyrolysis temperature on soil properties and plant growth

The addition of biochar to agricultural soils is recommended to improve soil functions and plant growth. However, due to high variability in the quality of biochar, its effects on soils and plants are likely to differ. We explored the impacts of pyrolysis temperature on the quality and usability of birch wood biochar as a soil amendment. The impact of three biochar types – pyrolysed at 300, 375 or 475°C – on soil characteristics and the growth of lettuce (Lactuca sativa), radish (Raphanus sativus), barley (Hordeum vulgare) and ryegrass (Lolium perenne) was investigated in a greenhouse experiment. In addition, the potential adverse effects of biochar on soil organisms (nematodes, earthworms, microbial biomass and activity) were studied.Biochar produced at the lowest temperature had initial transient negative effect on the germination and biomass of lettuce, while biochar produced at higher temperatures had no such effect. After five weeks, pyrolysis temperature had only a marginal influence on biochar-induced effects on soil pH, WHC, soil organisms and plant growth. Our results suggest that birch biochar, irrespective of pyrolysis temperature, has a parallel effect on plant biomass production and soil characteristics but the effect depends on plant type and biochar application rate.

Litter dominates surface fluxes of carbonyl sulfide in a Californian oak woodland

AbstractCarbonyl sulfide (COS) is a promising tracer for partitioning terrestrial photosynthesis and respiration from net carbon fluxes, based on its daytime co‐uptake alongside CO2 through leaf stomata. Because ecosystem COS fluxes are the sum of plant and soil fluxes, using COS as a photosynthesis tracer requires accurate knowledge of soil COS fluxes. At an oak woodland in Southern California, we monitored below‐canopy surface (soil + litter) COS and CO2 fluxes for 40 days using chambers and laser spectroscopy. We also measured litter fluxes separately and used a depth‐resolved diffusion‐reaction model to quantify the role of litter uptake in surface COS fluxes. Soil and litter were primarily COS sinks, and mean surface COS uptake was small (∼1 pmol m−2 s−1). After rainfall, uptake rates were higher (6–8 pmol m−2 s−1), and litter contributed a significant fraction (up to 90%) to surface fluxes. We observed rapid concurrent increases in COS uptake and CO2 efflux following the onset of rain. The patterns were similar to the Birch effect widely documented for soils; however, both COS and CO2 flux increases originated mainly in the litter. The synchronous COS‐CO2 litter Birch effect indicates that it results from a rapid increase in litter microbial activity after rainfall. We expect that the drying‐rewetting cycles typical for mediterranean and other semiarid ecosystems create a pronounced seasonality in surface COS fluxes. Our results highlight that litter uptake is an important component of surface COS exchange that needs to be taken into account in ecosystem COS budgets and model simulations.

人工模拟降水条件下旱作农田土壤“Birch效应”及其响应机制

PDF HTML阅读 XML下载 导出引用 引用提醒 人工模拟降水条件下旱作农田土壤“Birch效应”及其响应机制 DOI: 10.5846/stxb201403120428 作者: 作者单位: 西北大学,西北大学,西北大学,中国科学院水利部水土保持研究所,ARS Northern Plains Agricultural Research Laboratory 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目(31270484,41171033);教育部科技重点项目(209123);西北大学研究生自主创新项目(YZZ13006) Response of soil "Birch Effect" to simulated rainfalls in dry croplands Author: Affiliation: Northwest university,Northwest university,Northwest university,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:降水事件引起干土复湿刺激土壤CO2脉冲释放的现象被称为"Birch效应",其作用机制可能是降水刺激土壤"底物供给"增加或引起土壤"微生物胁迫"所致。为深入了解土壤"Birch效应"对降水格局改变的响应过程及内在机制,在冬小麦拔节期和夏闲期分别进行了不同降水量(1-32 mm)人工模拟降水实验,系统观测了降水后0-72 h土壤呼吸及土壤碳组分变化特征,结果表明:土壤呼吸随降水量的增大而增强,1-16 mm降水土壤呼吸峰值出现在降水后4 h,而32 mm降水土壤呼吸峰值出现时间滞后了4 h。与较小降水量相比,较大的降水量能增加土壤呼吸但会推迟土壤呼吸峰值出现时间。土壤呼吸速率峰值(SR-P)与降水量(P)呈幂相关(拔节期:SR-P=0.97P0.09, R2=0.5, P < 0.05;夏闲期:SR-P=1.07P0.09, R2=0.98, P < 0.01)。降水后72 h累积CO2释放量(CO2-P)与降水量呈线性相关(拔节期:CO2-P=0.03P+5.99, R2=0.58, P < 0.05;夏闲期:CO2-P=0.11P+6.04, R2=0.86, P < 0.01)。土壤呼吸温度敏感性系数和降水量之间存在二次曲线关系(拔节期:Q10=-0.007P2+0.2P+0.7, R2=0.32P < 0.05;夏闲期:Q10=-0.01P2+0.3P+0.2, R2=0.86, P < 0.01)。逐步回归分析表明,冬小麦拔节期所有降水量处理土壤呼吸与土壤微生物量碳相关性均达到显著水平(P < 0.05),指示土壤"Birch效应"是由"微生物胁迫"所致。而在夏闲期,当降水量小于8 mm时土壤呼吸与微生物量碳相关性显著,即以微生物胁迫机制占主导;8 mm降水处理下土壤呼吸与氯仿熏蒸-K2SO4提取态有机碳相关性达到极显著水平,指示则为两种机制共同起作用,而当降水量大于16 mm时,土壤呼吸主要与可提取态有机碳显著相关,"Birch"效应转为以底物供给机制占主导。与夏闲期相比,冬小麦拔节期作物生长会削弱"Birch效应",并改变其响应机制。 Abstract:In the dry cropping lands, soil rewetting due to precipitation can stimulate soil CO2 efflux pulses, which is called the "Birch Effect". Two types of responding mechanisms:"Substrate supply" and "Microbial stress", were proposed to explain the soil "Birch effect". To elucidate how precipitation change affects the "Birch effect "and its responding mechanism, we conducted precipitation simulation experiments in a winter wheat field to measure the short-term response of precipitation levels(1-32 mm) on soil respiration from 0 to 72 h at the jointing stage and during the summer fallow period on the Loess Plateau. The results showed that soil respiration peaked at 4 h with 1 to 16 mm of precipitation, but the peak was delayed by another 4 h at 32 mm precipitation. Higher precipitation delayed, but increased soil respiration compared to lower precipitation. The peak value for the soil respiration rate(SR-P) increased exponentially with increased precipitation(P)(jointing:SR-P=0.97P0.09, R2=0.5, P < 0.05, fallow:SR-P=1.07P0.09, R2=0.98, P < 0.01). Cumulative soil respiration after 72 h(CO2-P) increased linearly with the precipitation level(jointing:CO2-P=0.03P+5.99, R2=0.58, P < 0.05; fallow:CO2-P=0.11P+6.04, R2=0.86, P < 0.01). The temperature sensitivity of soil respiration(Q10) was correlated binomially with the precipitation level(jointing:Q10=-0.007P2+0.2P+0.7, R2=0.32, P < 0.05; fallow:Q10=-0.01P2+0.3P+0.2, R2=0.86, P < 0.01). Stepwise correlation analysis between soil carbon fractions and soil respiration rate showed that soil respiration rate was significantly correlated with soil microbial biomass C at the jointing stage for all precipitation levels, indicating that a "microbial stress" mechanism dominated the "Birch effect" during growing season. However, during summer fallow period, soil respiration rate was significantly correlated with microbial biomass C, which suggested "microbial stress", when the precipitation amount was lower than 8 mm, but correlated with chloroform-fumigated extracted C, which suggested that both mechanisms were operating when precipitation amount was equal to 8 mm. However, soil respiration was significantly correlated with K2SO4-extracted soil C when precipitation amount was equal to or higher than 16 mm, indicating a shift to the "Substrate supply" mechanism. Compared with that during the summer fallow period, the soil "Birch effect" was weaker and its responding mechanism had changed at the wheat jointing stage due to root respiration and shading effects. 参考文献 相似文献 引证文献

Soil respiration simulation based on soil temperature and water content in artificial smooth brome grassland

Correctly quantifying the relationships between soil respiration and environmental factors and their sources of variability is essential to predict future carbon fluxes and climate feedback. Soil water conditions and soil temperature strongly affect soil respiration and the dynamics of soil organic matter. Despite this, simulation of soil respiration (Rs) based on soil temperature (Ts) and soil volumetric water content (θ) must still be improved, as demonstrated by its discrepant model performance among different seasons. With the objective of gaining a further understanding of the relationships of Rs with Ts and θ and providing an improved model to simulate Rs variations, we measured hourly Rs, Ts and θ using the chamber technique in artificial smooth brome grassland for analysis. We began by dividing the four seasons of a year according to the daily mean air temperature, followed by representing the seasonal variation of Rs, Ts and θ. We found that Rs correlated significantly with Ts in an exponential relationship and with θ in a parabolic relationship seasonally, where the determination coefficient of the Rs-θ relationship was significantly larger than that of the Rs-Ts relationship. We also discovered that the shape of the Rs-θ relationship was seasonally dependent because the optimal θ and the width of the peak Rs around the optimal θ were seasonally specific. Finally, by considering seasonality, the combinational simulation model explained more variation of soil respiration. Thus, seasonality should be considered for more reliable model simulations of soil respiration. These findings are relevant for more accurate predictions and modelling of soil respiration, particularly in temperate artificial grasslands with a continental monsoon climate, where the ‘Birch effect’ strengthens seasonality, and these findings further our understanding of changes in the rates of soil carbon losses as artificial grassland is established.

The severity of sediment desiccation affects the adsorption characteristics and speciation of phosphorus.

Phosphorus is an important nutrient for plants and algae, and can be the limiting nutrient in aquatic ecosystems. However, oversupply can lead to significant water quality issues. The largest source and sink of P in most aquatic systems is the sediment. As a consequence of drought, in many places sediments that normally would have remained inundated are now being desiccated. Based on previous studies, it is often difficult to predict what impact drying will have on the cycling of P. This is because most of these studies have looked at drying across a chronosequence in the field, where there may be differences in sediment composition or microbial community structure. In this paper we present the results of a study where sediment was exposed to progressively more severe drying in the laboratory - starting with wet sediment, followed by air drying and then sequential oven drying at 30, 50 and 85 °C. Drying resulted in a shift in P speciation, notably with an increase in NaHCO3-extractable reactive P and a decline in NaHCO3-extractable unreactive P, likely indicating an increase in bioavailable, easily exchangeable P. Drying also resulted in a decline in the microbial-P fraction. Drying significantly affected the P adsorption characteristics of the sediment. The total amount of P adsorbed by the sediment and the linear adsorption co-efficient both declined, while the amount of native P adsorbed to the sediment and the equilibrium P concentration both increased. Drying also affected iron speciation with a shift from more reactive oxalate-extractable Fe to more recalcitrant citrate-dithionate-bicarbonate-extractable Fe, suggesting an increase in iron crystallinity and hence decrease in P adsorption capacity. The increase in crystallinity is consistent with Fe EXAFS results, which showed that drying resulted in an increase in edge-sharing neighbours. We hypothesise that the shifts in P speciation, the decline in P adsorption capacity, the increase in the equilibrium P concentration, as well as the death of micro-organisms (as evidenced by a decline in microbial P) on drying all contribute to the Birch effect - the initial pulse of P and/or N upon inundation of dried soils or sediments.

Synergistic effects of diffusion and microbial physiology reproduce the Birch effect in a micro-scale model

Large rainfall events following drought cause pulses of CO2 flux that are higher than models predict. This phenomenon, named the “Birch effect” after its discoverer, has been observed for decades, and will influence carbon-climate feedbacks as drying–rewetting (DRW) cycles become more common under intensified climates. Yet, the many interacting factors that determine how soil DRW cycles affect C balance have been difficult to separate empirically. Here we use a spatially explicit biogeochemical–microbial model to examine the mechanisms underlying CO2 dynamics under DRW. We independently model physiological activity and diffusion based on how they vary with (constant) moisture levels in nature, and subject the model to DRW to test the importance of different mechanisms in models with one or two microbial functional groups (cheaters and producers). Our model reproduces respiration patterns similar to empirical observations of the Birch effect when we include mechanisms that link water content to microbial growth and to diffusion rate, whereas inclusion of either mechanism alone produces significantly lower pulses upon rewetting. Diffusion limitation under drought increases substrate availability under rewetting, a process mediated by biogeochemical hotspots and continued enzyme activity under drought. At the same time, high microbial growth under rewetting is needed to replenish enzyme pools and to sustain the biomass required to generate respiration pulses under repeated DRW. Inclusion of cheaters in the model dampens the size of the rewetting pulse and the cumulative amount of CO2 release, as cheaters outcompete producers and reduce overall biomass. Our results provide several novel hypotheses regarding the microbial, biogeochemical, and spatial processes that mediate the Birch effect, which will contribute to a better mechanistic understanding of this important deviation from model predictions.

Soil carbon dioxide emissions in response to precipitation frequency in the Loess Plateau, China

Precipitation events can induce episodic CO2 emissions, so called the “Birch Effect”, which could be affected by soil microbial activity in dryland cropping systems. Our objective was to evaluate the effect of precipitation frequencies on soil CO2 fluxes and the mechanism responsible for the Birch Effect during fallow after winter wheat harvest in the Loess Plateau of China. A simulated precipitation of 240mm was applied at 5, 10, and 20 days intervals (I5, I10, and I20, respectively) for 60 days and soil CO2 flux, K2SO4-extractable C (EOC) and microbial biomass C (MBC) were measured. The CO2 flux increased immediately following precipitation events, with peak fluxes of 7.9, 8.2, and 7.7μmol CO2m−2s−1 for I5, I10, and I20, respectively. Cumulative CO2 flux from days 55–60 was greater for I5 and I10 than I20. The EOC and MBC were not affected by precipitation simulation at the first event, but MBC increased from the first to the last precipitation event, especially for I5 and I10. The CO2 flux was strongly correlated with EOC at the first event (r=0.73, 0.85 and 0.90 for I5, I10 and I20, P<0.01, respectively), but not correlated with EOC at the last event for I5 and I10 and the correlation decreased from the first to the last event (r=0.47, P<0.01) for I20. In contrast, the correlation coefficient of CO2 flux with MBC was not significant at first event and increased to 0.81 (P<0.01), 0.44 and 0.47 (P<0.05) at the last event for I5, I10 and I20, respectively. Higher precipitation frequency at shorter intervals increased CO2 emissions compared to lower frequency at longer intervals due to enhanced microbial activity as a result of increased substrate availability from accelerated soil aggregate destruction. The dominant mechanism for the “Birch Effect” shifted from “substrate supply” at the first precipitation event to “microbial stress” at the last event, especially for shorter precipitation intervals.

Dynamic interactions of ecohydrological and biogeochemical processes in water‐limited systems

Water is the essential reactant, catalyst, or medium for many biogeochemical reactions, thus playing an important role in the activation and deactivation of biogeochemical processes. The coupling between hydrological and biogeochemical processes is particularly evident in water‐limited arid and semi‐arid environments, but also in areas with strong seasonal precipitation patterns (e.g., Mediterranean) or in mesic systems during droughts. Moreover, this coupling is apparent at all levels in the ecosystems—from soil microbial cells to whole plants to landscapes. Identifying and quantifying the biogeochemical “hot spots” and “hot moments”, the underlying hydrological drivers, and how disturbance‐induced vegetation transitions affect the hydrological‐biogeochemical interactions are challenging because of the inherent complexity of these interactions, thus requiring interdisciplinary approaches. At the same time, a holistic approach is essential to fully understand function and processes in water‐limited ecosystems and to predict their responses to environmental change. This article examines some of the mechanisms responsible for microbial and vegetation responses to moisture inputs in water‐limited ecosystems through a synthesis of existing literature. We begin with the initial observation of Birch effect in 1950s and examine our current understanding of the interactions among vegetation dynamics, hydrology, and biochemistry over the past 60 years. We also summarize the modeling advances in addressing these interactions. This paper focuses on three opportunities to advance coupled hydrological and biogeochemical research: (1) improved quantitative understanding of mechanisms linking hydrological and biogeochemical variations in drylands, (2) experimental and theoretical approaches that describe linkages between hydrology and biogeochemistry (particularly across scales), and (3) the use of these tools and insights to address critical dryland issues of societal relevance.

Effects of thinning paper birch on conifer productivity and understory plant diversity

Naturally regenerated paper birch (Betula papyrifera Marsh.) is commonly removed from juvenile interior Douglas-fir (Pseudotsuga menziesii var. glauca [Beissn.] Franco) plantations in southern interior British Columbia, Canada, to increase conifer productivity and create a free-growing stand; however, this practice is expensive and contentious because of possible negative ecological impacts. One solution is to retain an optimal density of birch where growth gains of understory Douglas-fir are balanced against losses to Armillaria ostoyae (Romagn.) Herink and understory plant species diversity. We sought to find this optimal density by comparing four evenly applied birch density reduction treatments (0, 400, 1111, and 4444 retained birch stems ha−1) and an unthinned control (>7300 retained birch stems ha−1). The mortality rate of Douglas-fir due to Armillaria root disease increased non-significantly with thinning intensity. Mean diameter increment of surviving Douglas-fir improved the most where birch was completely removed, with little variation among intermediate thinning treatments. Height growth was unaffected by the thinning treatments. Diversity of cryptogams was significantly greater in the control than where all birch was removed. We suggest that the treatment with 4444 retained birch stems ha−1 provides the best balance for improving Douglas-fir growth while minimizing risk of increased Armillaria root disease and reduced understory plant diversity in young mixed stands.

How do biodegradable organic residues affect soil CO2 emissions? Case study of a Mediterranean agro-ecosystem

Soil respiration is the main carbon flux in the second largest terrestrial carbon pool, soil environment. Emissions of CO2 from soils are five times higher than from anthropogenic emissions (USDOE, 2008). Despite increasing atmospheric CO2 concentrations, the dynamics and driving forces for soil CO2 emissions are not well understood. This work investigates the evolution of soil respiration (Rs) in a semiarid Mediterranean agro-ecosystem after the application of three different biodegradable organic residues (BOR): municipal solid waste compost (MSWC), anaerobically (ANSS) and aerobically (AESS) digested sewage sludge. We also studied how these amendments affect the relationship between Rs and soil climate variables. The results showed a clear increase in Rs at very short time after the application, especially in AESS-treated soils. Annual evolution of Rs was highly correlated with the carbon fractions of the BORs applied, with the highest effect seen in AESS-treated soils after the application, and a moderate but more persistent effect in MSWC. ANSS showed an intermediate behaviour. The type of amendment explained 54.7% of Rs variability. The application of BOR also changed the relationship between Rs and soil climate conditions. The results showed that BOR application produced an increase in Rs positive dependence on soil temperature (Ts) and the Birch effect, and a decrease in the negative dependence on soil moisture (Ms). In untreated soils (CONT) Ts-Ms interaction was the main factor which drove Rs evolution. The results suggest using highly composted wastes (MSWC) as the best option of those analysed for medium-term carbon management in agricultural practices.

Modeling pulsed soil respiration in an African savanna ecosystem

Savannas cover 60% of the African continent and play an important role in the global carbon (C) emissions from fire and land use. To better characterize the biophysical controls over soil respiration in these settings, half-hourly observations of volumetric soil–water content, temperature, and the concentration of carbon dioxide (CO2) at different soil depths were continually measured from 2005 to 2007 under trees (“sub-canopy”) and between trees (“inter-canopy”) in a savanna vegetation near Skukuza, Kruger National Park, South Africa. The measured soil climate and CO2 concentration data were assimilated into a process-based model that estimates the CO2 production and flux with coupled dynamics of dissolved organic C (DOC) and microbial biomass C. Our results show that temporal and spatial variations in CO2 flux were strongly influenced by precipitation and vegetation cover, with two times greater CO2 flux in the sub-canopy plots (∼2421gCO2m−2yr−1) than in the inter-canopy plots (∼1290gCO2m−2yr−1). Precipitation influenced soil respiration by changing soil temperature and moisture; however, our modeling analysis suggests that the pulsed response of soil respiration to precipitation events (known as “Birch effect”) is a key control on soil fluxes at this site. At this site, “Birch effect” contributed to approximately 50% and 65% of heterotrophic respiration or 20% and 39% of soil respiration in the sub-canopy and inter-canopy plots, respectively. These results suggest that pulsed response of respiration to precipitation events is an important component of the C cycle of savannas and should be considered in both measurement and modeling studies of carbon exchange in similar ecosystems.