Cytosolic monoterpene biosynthesis is supported by plastid‐generated geranyl diphosphate substrate in transgenic tomato fruits

Geranyl diphosphate (GPP), the precursor of most monoterpenes, is synthesized in plastids from dimethylallyl diphosphate and isopentenyl diphosphate by GPP synthases (GPPSs). In heterodimeric GPPSs, a non‐catalytic small subunit (GPPS‐SSU) interacts with a catalytic large subunit, such as geranylgeranyl diphosphate synthase, and determines its product specificity. Here, snapdragon (Antirrhinum majus) GPPS‐SSU was over‐expressed in tomato fruits under the control of the fruit ripening‐specific polygalacturonase promoter to divert the metabolic flux from carotenoid formation towards GPP and monoterpene biosynthesis. Transgenic tomato fruits produced monoterpenes, including geraniol, geranial, neral, citronellol and citronellal, while exhibiting reduced carotenoid content. Co‐expression of the Ocimum basilicum geraniol synthase (GES) gene with snapdragon GPPS‐SSU led to a more than threefold increase in monoterpene formation in tomato fruits relative to the parental GES line, indicating that the produced GPP can be used by plastidic monoterpene synthases. Co‐expression of snapdragon GPPS‐SSU with the O. basilicum α–zingiberene synthase (ZIS) gene encoding a cytosolic terpene synthase that has been shown to possess both sesqui‐ and monoterpene synthase activities resulted in increased levels of ZIS‐derived monoterpene products compared to fruits expressing ZIS alone. These results suggest that re‐direction of the metabolic flux towards GPP in plastids also increases the cytosolic pool of GPP available for monoterpene synthesis in this compartment via GPP export from plastids.     

Seasonal emission of monoterpenes by the Mediterranean tree Quercus ilex in field conditions: Relations with photosynthetic rates, temperature and volatility

The relationships of monoterpene emission with temperature, light, photosynthesis and stomatal conductance (g_s) were studied in Quercus ilex L. trees throughout the four annual seasons under field conditions. The highest monoterpene emission was measured in spring and summer (midday average of 11 μg [g DW]^?1 h^?1), whereas the lowest rates were found in autumn and winter (midday averages of 0.51 and 0.23 μg [g DW]^?1 h^?1, respectively). In spring and summer, limonene was the monoterpene emitted at highest rate (midday averages of 5.27–6.69 μg [g DW]^?1 h^?1), whereas α-pinene was emitted the most in autumn and winter (midday averages of 0.31 μg [g DW]^?1 h^?1). The monoterpenes limonene, α-pinene and β-pinene represented about 75–95% of total detected monoterpenes. The total monoterpene emission rates represented about 0.04% of carbon fixed in autumn, 0.17% in winter, 0.84–2.51% in spring and 1.22–5.13% in summer. Significant correlations of total monoterpene emission with temperature were found when considering either summer emission or the emission over the entire year, whereas significant correlations with net photosynthetic rates were only found when considering summer season. Among individual terpenes, the most volatile, α-pinene and β-pinene, were more correlated with temperature than with net photosynthetic rates whereas the less volatile limonene was more correlated with net photosynthetic rate. Thus, under field conditions it seems that dependency of monoterpene emission on photosynthetic rate or temperature is partly related with volatility of the compounds. Influences of seasonality, temperature, photosynthetic rates and volatility should be considered in inventories and models of emission rates in Mediterranean ecosystems.     

Biosynthesis of the Monoterpenes Limonene and Carvone in the Fruit of Caraway : I. Demonstration of Enzyme Activities and Their Changes with Development

The biosynthesis of the monoterpenes limonene and carvone in the fruit of caraway (Carum carvi L.) proceeds from geranyl diphosphate via a three-step pathway. First, geranyl diphosphate is cyclized to (+)-limonene by a monoterpene synthase. Second, this intermediate is stored in the essential oil ducts without further metabolism or is converted by limonene-6-hydroxylase to (+)-trans-carveol. Third, (+)-trans-carveol is oxidized by a dehydrogenase to (+)-carvone. To investigate the regulation of monoterpene formation in caraway, we measured the time course of limonene and carvone accumulation during fruit development and compared it with monoterpene biosynthesis from [U-¹⁴C]Suc and the changes in the activities of the three enzymes. The activities of the enzymes explain the profiles of monoterpene accumulation quite well, with limonene-6-hydroxylase playing a pivotal role in controlling the nature of the end product. In the youngest stages, when limonene-6-hydroxylase is undetectable, only limonene was accumulating in appreciable levels. The appearance of limonene-6-hydroxylase correlates closely with the onset of carvone accumulation. At later stages of fruit development, the activities of all three enzymes declined to low levels. Although this correlates closely with a decrease in monoterpene accumulation, the latter may also be the result of competition with other pathways for substrate.     

Respiratory carbon use and carbon storage in mid‐rotation loblolly pine (Pinus taeda L.) plantations: the effect of site resources on the stand carbon balance

We used estimates of autotrophic respiration (R_A), net primary productivity (NPP) and soil CO₂ evolution (S_ff), to develop component carbon budgets for 12‐year‐old loblolly pine plantations during the fifth year of a fertilization and irrigation experiment. Annual carbon use in R_A was 7.5, 9.0, 15.0, and 15.1 Mg C ha^?1 in control (C), irrigated (I), fertilized (F) and irrigated and fertilized (IF) treatments, respectively. Foliage, fine root and perennial woody tissue (stem, branch, coarse and taproot) respiration accounted for, respectively, 37%, 24%, and 39% of R_A in C and I treatments and 38%, 12% and 50% of R_A in F and IF treatments. Annual gross primary production (GPP=NPP+R_A) ranged from 13.1 to 26.6 Mg C ha^?1. The I, F, and IF treatments resulted in a 21, 94, and 103% increase in GPP, respectively, compared to the C treatment. Despite large treatment differences in NPP, R_A, and carbon allocation, carbon use efficiency (CUE=NPP/GPP) averaged 0.42 and was unaffected by manipulating site resources. Ecosystem respiration (R_E), the sum of S_ff, and above ground R_A, ranged from 12.8 to 20.2 Mg C ha^?1 yr^?1. S_ff contributed the largest proportion of R_E, but the relative importance of S_ff decreased from 0.63 in C treatments to 0.47 in IF treatments because of increased aboveground R_A. Aboveground woody tissue R_A was 15% of R_E in C and I treatments compared to 25% of R_E in F and IF treatments. Net ecosystem productivity (NEP=GPP‐R_E) was roughly 0 in the C and I treatments and 6.4 Mg C ha^?1 yr^?1 in F and IF treatments, indicating that non‐fertilized treatments were neither a source nor a sink for atmospheric carbon while fertilized treatments were carbon sinks. In these young stands, NEP is tightly linked to NPP; increased ecosystem carbon storage results mainly from an increase in foliage and perennial woody biomass.     

Inhibition of monoterpene cyclases by inert analogues of geranyl diphosphate and linalyl diphosphate

The tightly coupled nature of the reaction sequence catalyzed by monoterpene synthases has prevented direct observation of the topologically required isomerization step leading from geranyl diphosphate to the enzyme-bound, tertiary allylic intermediate linalyl diphosphate, which then cyclizes to the various monoterpene skeletons. X-ray crystal structures of these enzymes complexed with suitable analogues of the substrate and intermediate could provide a clearer view of this universal, but cryptic, step of monoterpenoid cyclase catalysis. Toward this end, the functionally inert analogues 2-fluorogeranyl diphosphate, (±)-2-fluorolinalyl diphosphate, and (3R)- and (3S)-homolinalyl diphosphates (2,6-dimethyl-2-vinyl-5-heptenyl diphosphates) were prepared, and compared to the previously described substrate analogue 3-azageranyl diphosphate (3-aza-2,3-dihydrogeranyl diphosphate) as inhibitors and potential crystallization aids with two representative monoterpenoid cyclases, (-)-limonene synthase and (+)-bornyl diphosphate synthase. Although these enantioselective synthases readily distinguished between (3R)- and (3S)-homolinalyl diphosphates, both of which were more effective inhibitors than was 3-azageranyl diphosphate, the fluorinated analogues proved to be the most potent competitive inhibitors and have recently yielded informative liganded structures with limonene synthase.     

Phenyl Disulfide Additive for Solution‐Mediated Carbon Dioxide Utilization in Li–CO2 Batteries

Phenyl disulfide (PDS) is employed as an electrolyte additive in lithium–carbon dioxide (Li–CO₂) batteries to allow for a solution‐mediated carbon dioxide reduction pathway. Thiophenolate anions, generated via electrochemical reduction of PDS, act as CO₂ capture agents by forming the adduct S‐phenyl carbonothioate (SPC^?) in solution. A mechanism of SPC^?‐mediated CO₂ capture and utilization is proposed and supported via carbon‐13 nuclear magnetic resonance spectroscopy and Fourier‐transform infrared spectroscopy. Reversible formation and decomposition of lithium carbonate and amorphous carbon during cycling, facilitated by the solution‐mediated pathway, are demonstrated with an array of characterization techniques. Li–CO₂ batteries employing the PDS additive show vastly improved capacity, energy efficiency, and cycle life. The enhanced Li–CO₂ battery performance offered by the proposed solution‐mediated reaction pathway offers a compelling step forward in the pursuit of reversible CO₂ utilization.     

Monoterpene ‘thermometer’ of tropical forest‐atmosphere response to climate warming

Tropical forests absorb large amounts of atmospheric CO₂ through photosynthesis but elevated temperatures suppress this absorption and promote monoterpene emissions. Using ¹³CO₂ labeling, here we show that monoterpene emissions from tropical leaves derive from recent photosynthesis and demonstrate distinct temperature optima for five groups (Groups 1–5), potentially corresponding to different enzymatic temperature‐dependent reaction mechanisms within β‐ocimene synthases. As diurnal and seasonal leaf temperatures increased during the Amazonian 2015 El Niño event, leaf and landscape monoterpene emissions showed strong linear enrichments of β‐ocimenes (+4.4% °C^?1) at the expense of other monoterpene isomers. The observed inverse temperature response of α‐pinene (?0.8% °C^?1), typically assumed to be the dominant monoterpene with moderate reactivity, was not accurately simulated by current global emission models. Given that β‐ocimenes are highly reactive with respect to both atmospheric and biological oxidants, the results suggest that highly reactive β‐ocimenes may play important roles in the thermotolerance of photosynthesis by functioning as effective antioxidants within plants and as efficient atmospheric precursors of secondary organic aerosols. Thus, monoterpene composition may represent a new sensitive ‘thermometer’ of leaf oxidative stress and atmospheric reactivity, and therefore a new tool in future studies of warming impacts on tropical biosphere‐atmosphere carbon‐cycle feedbacks.     

Monoterpene emission and monoterpene synthase activities in the Mediterranean evergreen oak Quercus ilex L. grown at elevated CO2 concentrations

Monoterpene emissions, monoterpene synthase activities, photosynthesis, fluorescence yield in the dark and drought stress indicators (stomatal conductance and mid‐day water potential) were concurrently measured under similar temperature and illumination in current‐year leaves of Quercus ilex L. of plants grown in open‐top chambers at ambient (350 ppm) and elevated (700 ppm) CO₂. The study was undertaken to understand the effect of CO₂ on monoterpene biosynthesis, and to predict and parameterize the biogenic emissions at growing CO₂ concentrations. The results of the 1998 and 1999 studies show that at elevated CO₂, and in the absence of persistent environmental stresses, photosynthesis was stimulated with respect to ambient CO₂, but that the emission of the three most abundantly emitted monoterpenes (α‐pinene, sabinene and β‐pinene) was inhibited by approximately 68%. The enzyme activities of the monoterpene synthases catalysing the formation of the three monoterpenes were also inhibited at elevated CO₂ and an excellent relationship was found between monoterpene emission and activity of the corresponding enzyme both at ambient and elevated CO₂. Interestingly, however, limonene emission was enhanced in conditions of elevated CO₂ as it was also the corresponding synthase. The ratio between enzyme activity and emission of the three main monoterpenes was high (above 20) at ambient CO₂ but it was below 10 at elevated CO₂ and, for limonene, on both treatments. Our results indicate that the overall emission of monoterpenes at elevated CO₂ will be inhibited because of a concurrent, strong down‐regulation of monoterpene synthase activities. When the enzyme activity does not change, as for limonene, the high photosynthetic carbon availability at elevated CO₂ conditions may even stimulate emission. The results of the 1997 study show that severe and persistent drought, as commonly occurs in the Mediterranean, may inhibit both photosynthesis and monoterpene (α‐pinene) emission, particularly at ambient CO₂. Thus, emission is probably limited by photosynthetic carbon availability; the effect of elevated CO₂per se is not apparent if drought, and perhaps other environmental stresses, are also present.     

Gross primary production responses to warming,elevated CO2, and irrigation: quantifying the drivers of ecosystem physiology in a semiarid grassland

Determining whether the terrestrial biosphere will be a source or sink of carbon (C) under a future climate of elevated CO₂ (eCO₂) and warming requires accurate quantification of gross primary production (GPP), the largest flux of C in the global C cycle. We evaluated 6 years (2007–2012) of flux‐derived GPP data from the Prairie Heating and CO₂ Enrichment (PHACE) experiment, situated in a grassland in Wyoming, USA. The GPP data were used to calibrate a light response model whose basic formulation has been successfully used in a variety of ecosystems. The model was extended by modeling maximum photosynthetic rate (A_max) and light‐use efficiency (Q) as functions of soil water, air temperature, vapor pressure deficit, vegetation greenness, and nitrogen at current and antecedent (past) timescales. The model fits the observed GPP well (R² = 0.79), which was confirmed by other model performance checks that compared different variants of the model (e.g. with and without antecedent effects). Stimulation of cumulative 6‐year GPP by warming (29%, P = 0.02) and eCO₂ (26%, P = 0.07) was primarily driven by enhanced C uptake during spring (129%, P = 0.001) and fall (124%, P = 0.001), respectively, which was consistent across years. Antecedent air temperature (Tair_ant) and vapor pressure deficit (VPD_ant) effects on A_max (over the past 3–4 days and 1–3 days, respectively) were the most significant predictors of temporal variability in GPP among most treatments. The importance of VPD_ant suggests that atmospheric drought is important for predicting GPP under current and future climate; we highlight the need for experimental studies to identify the mechanisms underlying such antecedent effects. Finally, posterior estimates of cumulative GPP under control and eCO₂ treatments were tested as a benchmark against 12 terrestrial biosphere models (TBMs). The narrow uncertainties of these data‐driven GPP estimates suggest that they could be useful semi‐independent data streams for validating TBMs.     

Seasonal controls on interannual variability in carbon dioxide exchange of a near-end-of rotation Douglas-fir stand in the Pacific Northwest, 1997–2006

This study analyzes 9 years of eddy‐covariance (EC) data carried out in a Pacific Northwest Douglas‐fir (Pseudotsuga menzesii) forest (58‐year old in 2007) on the east coast of Vancouver Island, Canada, and characterizes the seasonal and interannual variability in net ecosystem productivity (NEP), gross primary productivity (GPP), and ecosystem respiration (R_e) and primary climatic controls on these fluxes. The annual values (± SD) of NEP, GPP and R_e were 357 ± 51, 2124 ± 125, and 1767 ± 146 g C m^?2 yr^?1, respectively, with ranges of 267–410, 1592–2338, and 1642–2071 g C m^?2 yr^?1, respectively. Spring to early summer (March–June) accounted for more than 80% of annual NEP while late spring to early autumn (May–August) was mainly responsible for its interannual variability (～80%). The major drivers of interannual variability in annual carbon (C) fluxes were annual and spring mean air temperatures (T_a) and water deficiency during late summer and autumn (July–October) when this Douglas‐fir forest growth was often water‐limited. Photosynthetically active radiation (Q), and the combination of Q and soil water content (θ) explained 85% and 91% of the variance of monthly GPP, respectively; and 91% and 96% of the variance of monthly R_e was explained by T_a and the combination of T_a and θ, respectively. Annual net C sequestration was high during optimally warm and normal precipitation years, but low in unusually warm or severely dry years. Excluding 1998 and 1999, the 2 years strongly affected by an El Niño/La Niña cycle, annual NEP significantly decreased with increasing annual mean T_a. Annual NEP will likely decrease whereas both annual GPP and R_e will likely increase if the future climate at the site follows a trend similar to that of the past 40 years.     

Chemical Variability of the Needle Oil of Juniperus communis ssp. alpina from Corsica

The composition of 109 samples of essential oil isolated from the needles of Juniperus communis ssp. alpina growing wild in Corsica was investigated by GC (in combination with retention indices), GC/MS, and ¹³C‐NMR. Forty‐four compounds accounting for 86.7–96.7% of the oil were identified. The oils consisted mainly of monoterpene hydrocarbons, in particular, limonene (9.2–53.9%), β‐phellandrene (3.7–25.2%), α‐pinene (1.4–33.7%), and sabinene (0.1–33.6%). The 109 oil compositions were submitted to k‐means partitioning and principal component analysis, which allowed the distinction of two groups within the oil samples. The composition of the major group (92% of the samples) was dominated by limonene and β‐phellandrene, while the second group contained mainly sabinene beside limonene and β‐phellandrene.     

The rice terpene synthase gene OsTPS19 functions as an (S)‐limonene synthase in planta,and its overexpression leads to enhanced resistance to the blast fungus Magnaporthe oryzae

Rice blast disease, caused by the fungus Magnaporthe oryzae, is the most devastating disease of rice. In our ongoing characterization of the defence mechanisms of rice plants against M. oryzae, a terpene synthase gene OsTPS19 was identified as a candidate defence gene. Here, we report the functional characterization of OsTPS19, which is up‐regulated by M. oryzae infection. Overexpression of OsTPS19 in rice plants enhanced resistance against M. oryzae, while OsTPS19 RNAi lines were more susceptible to the pathogen. Metabolic analysis revealed that the production of a monoterpene (S)‐limonene was increased and decreased in OsTPS19 overexpression and RNAi lines, respectively, suggesting that OsTPS19 functions as a limonene synthase in planta. This notion was further supported by in vitro enzyme assays with recombinant OsTPS19, in which OsTPS19 had both sesquiterpene activity and monoterpene synthase activity, with limonene as a major product. Furthermore, in a subcellular localization experiment, OsTPS19 was localized in plastids. OsTPS19 has a highly homologous paralog, OsTPS20, which likely resulted from a recent gene duplication event. We found that the variation in OsTPS19 and OsTPS20 enzyme activities was determined by a single amino acid in the active site cavity. The expression of OsTPS20 was not affected by M. oryzae infection. This indicates functional divergence of OsTPS19 and OsTPS20. Lastly, (S)‐limonene inhibited the germination of M. oryzae spores in vitro. OsTPS19 was determined to function as an (S)‐limonene synthase in rice and plays a role in defence against M. oryzae, at least partly, by inhibiting spore germination.     

Purification and Characterisation of the Enantiospecific Dioxygenases from Delftia acidovorans MC1 Initiating the Degradation of Phenoxypropionate and Phenoxyacetate Herbicides

After cultivation on (R,S)‐2‐(2,4‐dichlorophenoxy)propionate, two α‐ketoglutarate‐dependent dioxygenases were isolated and purified from Delftia acidovorans MC1, catalysing the cleavage of the ether bond of various phenoxyalkanoate herbicides. One of these enzymes showed high specificity for the cleavage of the R‐enantiomer of substituted phenoxypropionate derivatives: the K_m values were 55 μM and 30 μM, the k_cat values 55 min^–1 and 34 min^–1 with (R)‐2‐(2,4‐dichlorophenoxy)propionate [(R)‐2,4‐DP] and (R)‐2‐(4‐chloro‐2‐methylphenoxy)propionate, respectively. The other enzyme predominantly utilised the S‐enantiomers with K_m values of 49 μM and 22 μM, and k_cat values of 50 min^–1 and 46 min^–1 with (S)‐2‐(2,4‐dichlorophenoxy)propionate [(S)‐2,4‐DP] and (S)‐2‐(4‐chloro‐2‐methylphenoxy)propionate, respectively. In addition, it cleaved phenoxyacetate herbicides (i.e. 2,4‐dichlorophenoxyacetate: K_m = 123 μM, k_cat = 36 min^–1) with significant activity. As the second substrate, only α‐ketoglutarate served as an oxygen acceptor for both enzymes. The enzymes were characterised by excess substrate inhibition kinetics with apparent K_i values of 3 mM with (R)‐2,4‐DP and 1.5 mM with (S)‐2,4‐DP. The reaction was strictly dependent on the presence of Fe²⁺ and ascorbate; other divalent cations showed inhibitory effects to different extents. Activity was completely extinguished within 2 min in the presence of 100 μM diethylpyrocarbonate (DEPC).     

Is productivity of mesic savannas light limited or water limited? Results of a simulation study

A soil–plant–atmosphere model was used to estimate gross primary productivity (GPP) and evapotranspiration (ET) of a tropical savanna in Australia. This paper describes model modifications required to simulate the substantial C4 grass understory together with C3 trees. The model was further improved to include a seasonal distribution of leaf area and foliar nitrogen through 10 canopy layers. Model outputs were compared with a 5‐year eddy covariance dataset. Adding the C4 photosynthesis component improved the model efficiency and root‐mean‐squared error (RMSE) for total ecosystem GPP by better emulating annual peaks and troughs in GPP across wet and dry seasons. The C4 photosynthesis component had minimal impact on modelled values of ET. Outputs of GPP from the modified model agreed well with measured values, explaining between 79% and 90% of the variance and having a low RMSE (0.003–0.281 g C m^?2 day^?1). Approximately, 40% of total annual GPP was contributed by C4 grasses. Total (trees and grasses) wet season GPP was approximately 75–80% of total annual GPP. Light‐use efficiency (LUE) was largest for the wet season and smallest in the dry season and C4 LUE was larger than that of the trees. A sensitivity analysis of GPP revealed that daily GPP was most sensitive to changes in leaf area index (LAI) and foliar nitrogen (N_f) and relatively insensitive to changes in maximum carboxylation rate (V_cmax), maximum electron transport rate (J_max) and minimum leaf water potential (ψ_min). The modified model was also able to represent daily and seasonal patterns in ET, (explaining 68–81% of variance) with a low RMSE (0.038–0.19 mm day^?1). Current values of N_f, LAI and other parameters appear to be colimiting for maximizing GPP. By manipulating LAI and soil moisture content inputs, we show that modelled GPP is limited by light interception rather than water availability at this site.     

CHARACTERIZATION OF A MYRCENE SYNTHASE FROM SUSPENSION CULTURES OF THE MARINE RED ALGA OCHTODES SECUNDIRAMEA

Wise, M. L.¹, Rorrer, G. L.², Polzin, J. J.², Croteau, R. B.^{1 1}Institute of Biological Chemistry, Washington State University, Pullman, WA. 99164 USA; ² Department of Chemical Engineering, Oregon State University, Corvallis, OR. 96331USA A monoterpene synthase from suspension cultures of the marine red alga Ochtodes secundiramea is shown to biosynthesize myrcene from geranyl diphosphate (GPP) using cell free extracts. This is the first in vitro characterization of a monoterpene synthase from a marine organism. Myrcene is the likely progenitor of the unusual halogenated monoterpenes characteristic of this marine alga and, as such, represents a key step in the biosynthetic pathway. Based on mechanistic considerations from reaction with the biologically relevant substrate GPP, as well as neryl diphosphate (the cis isomer of GPP) and linalyl diphosphate (LPP), the enzyme appears incapable of catalyzing the isomerization of GPP to LPP, a mechanistic feature of most terrestrial monoterpene synthases, perhaps reflecting its evolutionarily ancient origin. The ability to assay and quantitatively monitor the expression of this enzyme in suspension cultures, under strictly defined growth conditions, presents an unparalleled opportunity to delineate, at the molecular level, factors eliciting the biosynthesis of this class of secondary metabolites, to evaluate the metabolic pathway leading to halogenated monoterpenes and to investigate their role in the chemical ecology of marine algae.     

Seasonal and interannual variations in carbon dioxide exchange over a cropland in the North China Plain

In China, croplands account for a relatively large form of vegetation cover. Quantifying carbon dioxide exchange and understanding the environmental controls on carbon fluxes over croplands are critical in understanding regional carbon budgets and ecosystem behaviors. In this study, the net ecosystem exchange (NEE) at a winter wheat/summer maize rotation cropping site, representative of the main cropping system in the North China Plain, was continuously measured using the eddy covariance technique from 2005 to 2009. In order to interpret the abiotic factors regulating NEE, NEE was partitioned into gross primary production (GPP) and ecosystem respiration (R_eco). Daytime R_eco was extrapolated from the relationship between nighttime NEE and soil temperature under high turbulent conditions. GPP was then estimated by subtracting daytime NEE from the daytime estimates of R_eco. Results show that the seasonal patterns of the temperature responses of R_eco and light‐response parameters are closely related to the crop phenology. Daily R_eco was highly dependent on both daily GPP and air temperature. Interannual variability showed that GPP and R_eco were mainly controlled by temperature. Water availability also exerted a limit on R_eco. The annual NEE was ?585 and ?533 g C m^?2 for two seasons of 2006–2007 and 2007–2008, respectively, and the wheat field absorbed more carbon than the maize field. Thus, we concluded that this cropland was a strong carbon sink. However, when the grain harvest was taken into account, the wheat field was diminished into a weak carbon sink, whereas the maize field was converted into a weak carbon source. The observations showed that severe drought occurring during winter did not reduce wheat yield (or integrated NEE) when sufficient irrigation was carried out during spring.     

Electrochemical Energy Storage with a Reversible Nonaqueous Room‐Temperature Aluminum–Sulfur Chemistry

A reversible room‐temperature aluminum–sulfur (Al‐S) battery is demonstrated with a strategically designed cathode structure and an ionic liquid electrolyte. Discharge–charge mechanism of the Al‐S battery is proposed based on a sequence of electrochemical, microscopic, and spectroscopic analyses. The electrochemical process of the Al‐S battery involves the formation of a series of polysulfides and sulfide. The high‐order polysulfides (S_x^2?, x ≥ 6) are soluble in the ionic liquid electrolyte. Electrochemical transitions between S₆^2? and the insoluble low‐order polysulfides or sulfide (S_x ^2?, 1 ≤ x < 6) are reversible. A single‐wall carbon nanotube coating applied to the battery separator helps alleviate the diffusion of the polysulfide species and reduces the polarization behavior of the Al‐S batteries.     

Chemical composition and mosquito repellency of essential oil of Conyza newii propagated in different geographical locations of Kenya

Previously, essential oil of Conyza newii (Asterale: Asteracea, Oliv. & Hiern) growing in the northern part of West Pokot (35°E, 1°N) of Kenya was shown to be highly repellent [RD₅₀ = 8.9 × 10^?5 mg/cm², 95% confidence interval (CL)] to Anopheles gambiae s.s. Fumigant toxicity of the oil to the mosquito was also demonstrated. The major constituents of the oil were found to be monoterpenoids, including (S)‐(‐)‐perillyl alcohol, (S)‐(‐)‐perillaldehyde, geraniol, (R)‐(+)‐limonene, trans‐β‐ocimene and 1,8‐cineol. In this study, the chemical composition and repellency of essential oils of the plant seedlings collected from West Pokot (35°E, 1°N) and propagated in seven different geographical regions of Kenya [West Pokot (35°E, 1°N), Kilome (37°E, 1°S), Naivasha (36°E, 0°), Webuye (34°E, 1°N), Nyakach (34°E, 0°), Kericho (35°E, 0°) and Nairobi (36°E, 1°S)] were compared. There were significant variations (P < 0.01, 95% CL) in the relative proportions of the six constituents and this was reflected in the repellency of the essential oils (P < 0.01, 95% CL). Higher repellency of the oil was associated with greater proportions of (S)‐(‐) perillyl alcohol, (S)‐(‐)‐perillaldehyde and geraniol, and lower repellency was associated with an increased proportion of (R)‐(+)‐limonene. The results suggest significant epigenetic (chemotypic) variations in the repellency and composition of C. newii essential oils growing in different regions of Kenya.     

Solar‐induced chlorophyll fluorescence is strongly correlated with terrestrial photosynthesis for a wide variety of biomes: First global analysis based on OCO‐2 and flux tower observations

Solar‐induced chlorophyll fluorescence (SIF) has been increasingly used as a proxy for terrestrial gross primary productivity (GPP). Previous work mainly evaluated the relationship between satellite‐observed SIF and gridded GPP products both based on coarse spatial resolutions. Finer resolution SIF (1.3 km × 2.25 km) measured from the Orbiting Carbon Observatory‐2 (OCO‐2) provides the first opportunity to examine the SIF–GPP relationship at the ecosystem scale using flux tower GPP data. However, it remains unclear how strong the relationship is for each biome and whether a robust, universal relationship exists across a variety of biomes. Here we conducted the first global analysis of the relationship between OCO‐2 SIF and tower GPP for a total of 64 flux sites across the globe encompassing eight major biomes. OCO‐2 SIF showed strong correlations with tower GPP at both midday and daily timescales, with the strongest relationship observed for daily SIF at the 757 nm (R² = 0.72, p < 0.0001). Strong linear relationships between SIF and GPP were consistently found for all biomes (R² = 0.57–0.79, p < 0.0001) except evergreen broadleaf forests (R² = 0.16, p < 0.05) at the daily timescale. A higher slope was found for C₄ grasslands and croplands than for C₃ ecosystems. The generally consistent slope of the relationship among biomes suggests a nearly universal rather than biome‐specific SIF–GPP relationship, and this finding is an important distinction and simplification compared to previous results. SIF was mainly driven by absorbed photosynthetically active radiation and was also influenced by environmental stresses (temperature and water stresses) that determine photosynthetic light use efficiency. OCO‐2 SIF generally had a better performance for predicting GPP than satellite‐derived vegetation indices and a light use efficiency model. The universal SIF–GPP relationship can potentially lead to more accurate GPP estimates regionally or globally. Our findings revealed the remarkable ability of finer resolution SIF observations from OCO‐2 and other new or future missions (e.g., TROPOMI, FLEX) for estimating terrestrial photosynthesis across a wide variety of biomes and identified their potential and limitations for ecosystem functioning and carbon cycle studies.