Impacts of Drought and Rehydration Cycles on Isoprene Emissions in Populus nigra Seedlings.

The volatile organic compounds emitted by plants significantly impact the atmospheric environment. The impacts of drought stress on the biogenic volatile organic compound (BVOC) emissions of plants are still under debate. In this study, the effects of two drought-rehydration cycle groups with different durations on isoprene emissions from Populus nigra (black poplar) seedlings were studied. The P. nigra seedlings were placed in a chamber that controlled the soil water content, radiation, and temperature. The daily emissions of isoprene and physiological parameters were measured. The emission rates of isoprene (Fiso) reached the maximum on the third day (D3), increasing by 58.0% and 64.2% compared with the controlled groups, respectively, and then Fiso significantly decreased. Photosynthesis decreased by 34.2% and 21.6% in D3 in the first and second groups, respectively. After rehydration, Fiso and photosynthesis recovered fully in two groups. However, Fiso showed distinct inconsistencies in two groups, and the recovery rates of Fiso in the second drought group were slower than the recovery rates of Fiso in the first groups. The response of BVOC emissions during the drought-rehydration cycle was classified into three phases, including stimulated, inhibited, and restored after rehydration. The emission pattern of isoprene indicated that isoprene played an important role in the response of plants to drought stress. A drought-rehydration model was constructed, which indicated the regularity of BVOC emissions in the drought-rehydration cycle. BVOC emissions were extremely sensitive to drought, especially during droughts of short duration. Parameters in computational models related to BVOC emissions of plants under drought stress should be continuously improved.

On the molecular mechanisms implicated in the bipolar cancellation of membrane electroporation.

Bipolar cancellation is the phenomenon in which the permeability of cell membranes subjected to high intensity short pulsed electric field (ns-µs range) is reduced or eliminated when the system is subjected to bipolar instead of monopolar pulses. Although several studies have tried to explain bipolar cancellation, the underlying mechanisms remain unclear. Very few articles study bipolar cancellation by means of molecular dynamics (MD) simulation. In this paper, we investigated the molecular mechanisms underlying the difference in electroporation induced by bipolar and monopolar picosecond electric pulses (EPs) using MD simulation. The electric field gradients and electric forces on water molecules of the two pulses were analyzed in detail for the first time. For a certain pulse width, when the field intensity is relatively small, the direction of bipolar electric force on the interfacial water molecule reverses as the bipolar EPs reverse, while the electric force on interfacial water molecules of the cathode side remains in the same direction as that of applied monopolar EPs. The bipolar electric force reversal delays the water protrusion and increases the pore formation time. Therefore, this phenomenon could correspond to bipolar cancellation. When the field intensity is relatively large, although the bipolar electric force direction still reverses, half of the total time of the monopolar EPs has no electric fields. The electric forces of monopolar no-field half-cycles are much smaller than those of the bipolar EPs. Therefore, the pore formation time of bipolar EPs reduces, and this phenomenon is called bipolar enhancement. The occurrence of bipolar cancellation or bipolar enhancement depends on conditions such as the width and intensity of the pulse.

The Effect of Low Irradiance on Leaf Nitrogen Allocation and Mesophyll Conductance to CO2 in Seedlings of Four Tree Species in Subtropical China.

Low light intensity can lead to a decrease in photosynthetic capacity. However, could N-fixing species with higher leaf N contents mitigate the effects of low light? Here, we exposed seedlings of Dalbergia odorifera and Erythrophleum fordii (N-fixing trees), and Castanopsis hystrix and Betula alnoides (non-N-fixing trees) to three irradiance treatments (100%, 40%, and 10% sunlight) to investigate the effects of low irradiance on leaf structure, leaf N allocation strategy, and photosynthetic physiological parameters in the seedlings. Low irradiance decreased the leaf mass per unit area, leaf N content per unit area (Narea), maximum carboxylation rate (Vcmax), maximum electron transport rate (Jmax), light compensation point, and light saturation point, and increased the N allocation proportion of light-harvesting components in all species. The studied tree seedlings changed their leaf structures, leaf N allocation strategy, and photosynthetic physiological parameters to adapt to low-light environments. N-fixing plants had a higher photosynthesis rate, Narea, Vcmax, and Jmax than non-N-fixing species under low irradiance and had a greater advantage in maintaining their photosynthetic rate under low-radiation conditions, such as under an understory canopy, in a forest gap, or when mixed with other species.

Coupling coordination relationship between ecosystem services and water-land resources for the Daguhe River Basin, China.

Water and land resource utilization is an important driving force of changes in ecosystem services; therefore, research on multi-parameter coupling systems that consider "ecosystem services, water resources, and land resources" together has key significance for river basins. This study aims to reveal the interaction and mutual influence of ecosystem services and water and land resources in the Daguhe River Basin, China, based on the coupling coordination degree model. The results showed that during the period from 2000 to 2010, the coupling coordination degree values for the years 2000, 2005, and 2010 were 0.6005, 0.7292, and 0.8037. The corresponding coupling coordination classifications were categorized as "primary coordinated development", "intermediate coordinated development," and "well-coordinated development", respectively. These results reflected the fact that the relationship between water and land resource utilization and the environment tends to evolve in the direction of coordinated development (an improvement in one part corresponds to an improvement in another part) with variation in water and land utilization types, and eventually pushes the whole resource, as well as ecological and environmental systems, from low to high levels of coupling coordination degrees as observed in case of the Daguhe River Basin, China. Our research provides an overview of the interaction between ecosystem services and water and land resources in the Daguhe Basin and even in the Shandong Province. With our results, we offer new perspectives on river basin management and for planning future eco-environmental policies (the policy is specifically designed for the ecological environment) by combining water and land resource utilization.

Complex Permittivity Characterization of Liquid Samples Based on a Split Ring Resonator (SRR).

A complex permittivity characterization method for liquid samples has been proposed. The measurement is carried out based on a self-designed microwave sensor with a split ring resonator (SRR), the unload resonant frequency of which is 5.05 GHz. The liquid samples in capillary are placed in the resonant zone of the fabricated senor for high sensitivity measurement. The frequency shift of 58.7 MHz is achieved when the capillary is filled with ethanol, corresponding a sensitivity of 97.46 MHz/µL. The complex permittivity of methanol, ethanol, isopropanol (IPA) and deionized water at the resonant frequency are measured and calibrated by the first order Debye model. Then, the complex permittivity of different concentrations of aqueous solutions of these materials are measured by using the calibrated sensor system. The results show that the proposed sensor has high sensitivity and accuracy in measuring the complex permittivity of liquid samples with volumes as small as 0.13 µL. It provides a useful reference for the complex permittivity characterization of small amount of liquid chemical samples. In addition, the characterization of an important biological sample (inositol) is carried out by using the proposed sensor.

The Effect of KcsA Channel on Lipid Bilayer Electroporation Induced by Picosecond Pulse Trains.

Membrane proteins are the major component of plasma membranes, and they play crucial roles in all organisms. To understand the influence of the presence of KcsA channel on cell membrane electroporation induced by picosecond pulse trains (psPT), in this paper, the electroporation of KcsA membrane protein system and bare lipid bilayer system (POPC) with the applied psPT are simulated using molecular dynamics (MD) method. First, we find that the average pore formation time of the KcsA system is longer than the bare system with the applied psPT. In the KcsA system, water protrusions appear more slowly. Then, the system size effects of psPT in the MD simulations are investigated. When the system size decreases, the average pore formation time of small KcsA membrane protein system is shorter than the bare system with the applied psPT. It is found that the psPT makes the protein fluctuation of small system increase greatly; meanwhile the instability of protein disturbs the water and then affects the water protrusion appearance time. Furthermore, it shows that the protein fluctuation of constant electric field is smaller than that of psPT and no field, and protein fluctuation increases with the psPT repetition frequency increasing.

Transient proton transfer of base pair hydrogen bonds induced by intense terahertz radiation.

Local oriented intense electric fields play a vital role in biochemical reactions such as enzyme catalysis. Many researchers have gradually applied external oriented electric fields to control specific chemical reactions. The rapidly developing intense field of terahertz technology can provide a strong enough oriented electric field with specific polarization direction on a sub-picosecond timescale, which matches the timescale and intensity requirements for affecting specific ultrafast chemical reactions. Inspired by this, this paper theoretically studied the full quantum model of the proton transfer process in DNA base pair hydrogen bonds induced by intense terahertz radiation (ITR) with a sub-picosecond-oriented electric field through simulation based on density functional theory (DFT) and the Schrodinger equation. The result shows that the ITR with an electric field intensity up to 10 GV m-1 in a specific polarization direction can precisely control the proton transfer process in the base pair hydrogen bonds. Based on flexible optical methods, the ITR is expected to go beyond the traditional techniques for applying strong electric fields to chemical systems through solid electrodes and become a catalyst for controlling chemical reactions or a scalpel to manipulate molecular structures.

Interpretation of the molecular mechanism of the electroporation induced by symmetrical bipolar picosecond pulse trains.

Picosecond pulse trains (psPTs) are emerging as a new characteristic diagnostic and therapeutic tool in biomedical fields. To specifically determine the stimulus provided to cells, in this article, we use a molecular dynamics (MD) model to show the molecular mechanisms of electroporation induced by symmetrical bipolar psPTs and predict a bipolar cancellation for the studied picosecond pulses. Electric field conditions that do not cause electroporation reveal that the interfacial water molecules continuously flip and redirect as the applied bipolar psPT reverses, and the molecules cannot keep moving in one direction or leave the lipid-water interface. Based on our simulation results, we determine the threshold for electroporation with symmetrical bipolar psPTs. For a fixed electric field intensity, a lower repetition frequency leads to more rapid electroporation. For a fixed repetition frequency, a higher electric field intensity leads to more rapid electroporation. We found that the water dipole relaxation time decreases as the electric field magnitude increases. Additionally, the influences of the symmetrical bipolar psPT intensity and frequency on the pore formation time are presented. Discrete nanoscale pores can form with the applied psPT at terahertz (THz) repetition frequency. When the psPT amplitude increases or the frequency decreases, the number of water bridges will increase. Moreover, for the first time, the molecular mechanism of bipolar cancellation for the studied picosecond pulse is discussed preliminarily. Our results indicate that the influence of the unipolar picosecond pulse on the interfacial water dipoles will accumulate in one direction, but the bipolar picosecond pulse does not cause this effect.

Effects of soil nitrogen (N) deficiency on photosynthetic N-use efficiency in N-fixing and non-N-fixing tree seedlings in subtropical China.

Soil nitrogen (N) deficiencies can affect the photosynthetic N-use efficiency (PNUE), mesophyll conductance (gm), and leaf N allocation. However, lack of information about how these physiological characteristics in N-fixing trees could be affected by soil N deficiency and the difference between N-fixing and non-N-fixing trees. In this study, we chose seedlings of two N-fixing (Dalbergia odorifera and Erythrophleum fordii) and two non-N-fixing trees (Castanopsis hystrix and Betula alnoides) as study objects, and we conducted a pot experiment with three levels of soil N treatments (high nitrogen, set as Control; medium nitrogen, MN; and low nitrogen, LN). Our results showed that soil N deficiency significantly decreased the leaf N concentration and photosynthesis ability of the two non-N-fixing trees, but it had less influence on two N-fixing trees. The LN treatment had lower gm in D. odorifera and lower leaf N allocated to Rubisco (PR), leaf N allocated to bioenergetics (PB), and gm in B. alnoides, eventually resulting in low PNUE values. Our findings suggested that the D. odorifera and E. fordii seedlings could grow well in N-deficient soil, and adding N may increase the growth rates of B. alnoides and C. hystrix seedlings and promote the growth of artificial forests.

Seedling leaves allocate lower fractions of nitrogen to photosynthetic apparatus in nitrogen fixing trees than in non-nitrogen fixing trees in subtropical China.

Photosynthetic-nitrogen use efficiency (PNUE) is a useful trait to characterize leaf physiology and survival strategy. PNUE can also be considered as part of 'leaf economics spectrum' interrelated with leaf nutrient concentrations, photosynthesis and respiration, leaf life-span and dry-mass investment. However, few studies have paid attention to PNUE of N-fixing tree seedlings in subtropical China. In this study, we investigated the differences in PNUE, leaf nitrogen (N) allocation, and mesophyll conductance (gm) in Dalbergia odorifera and Erythrophleum fordii (N-fixing trees), and Betula alnoides and Castanopsis hystrix (non-N-fixing trees). PNUE of D. odorifera and E. fordii were significantly lower than those of B. alnoides and C. hystrix mainly because of their allocation of a lower fraction of leaf N to Rubisco (PR) and bioenergetics (PB). Mesophyll conductance had a significant positive correlation with PNUE in D. odorifera, E. fordii, and B. alnoides, but the effect of gm on PNUE was different between species. The fraction of leaf N to cell wall (PCW) had a significant negative correlation with PR in B. alnoides and C. hystrix seedling leaves, but no correlation in D. odorifera and E. fordii seedling leaves, which may indicate that B. alnoides and C. hystrix seedling leaves did not have enough N to satisfy the demand from both the cell wall and Rubisco. Our results indicate that B. alnoides and C. hystrix may have a higher competitive ability in natural ecosystems with fertile soil, and D. odorifera and E. fordii may grow well in N-poor soil. Mixing these non-N-fixing and N-fixing trees for afforestation is useful for improving soil N utilization efficiency in the tropical forests.

Terahertz Electric Field-Induced Membrane Electroporation by Molecular Dynamics Simulations.

In this paper, the membrane electroporation induced by the terahertz electric field is simulated by means of the molecular dynamics method. The influences of the waveform and frequency of the applied terahertz electric field on the electroporation and the unique features of the process of the electroporation with the applied terahertz electric field are given. It shows that whether the electroporation can happen depends on the waveform of the applied terahertz electric field when the magnitude is not large enough. No pore appears if the terahertz electric field direction periodically reverses, and dipole moments of the interfacial water and the bulk water keep reversing. The nm-scale single pore forms with the applied terahertz trapezoidal electric field. It is found that the average pore formation time is strongly influenced by the terahertz electric field frequency. An abnormal variation region that shows decline exists on the correlation curve of the average pore formation time and the trapezoidal electric field frequency, whereas the overall trend of the curve is increasing. The decrease of the water oriented polarization degree results in the increase of the electroporation time, and the abnormal variation region appearance may be related to the drastic change of average water hydrogen bond number that is resulted from the resonance of water hydrogen bond network and the applied electric field. Compared to the nanosecond electric pulse and constant electric field, the numbers of the water protrusions and the water bridges are smaller and the pore formation time is relatively longer with the applied terahertz electric field.

Fagaceae tree species allocate higher fraction of nitrogen to photosynthetic apparatus than Leguminosae in Jianfengling tropical montane rain forest, China.

Variation in photosynthetic-nitrogen use efficiency (PNUE) is generally affected by several factors such as leaf nitrogen allocation and leaf diffusional conductances to CO2, although it is still unclear which factors significantly affect PNUE in tropical montane rain forest trees. In this study, comparison of PNUE, photosynthetic capacity, leaf nitrogen allocation, and diffusional conductances to CO2 between five Fagaceae tree species and five Leguminosae tree species were analyzed in Jianfengling tropical montane rain forest, Hainan Island, China. The result showed that PNUE of Fagaceae was significantly higher than that of Leguminosae (+35.5%), attributed to lower leaf nitrogen content per area (Narea, -29.4%). The difference in nitrogen allocation was the main biochemical factor that influenced interspecific variation in PNUE of these tree species. Fagaceae species allocated a higher fraction of leaf nitrogen to the photosynthetic apparatus (PP, +43.8%), especially to Rubisco (PR, +50.0%) and bioenergetics (PB +33.3%) in comparison with Leguminosae species. Leaf mass per area (LMA) of Leguminosae species was lower than that of Fagaceae species (-15.4%). While there was no significant difference shown for mesophyll conductance (gm), Fagaceae tree species may have greater chloroplast to total leaf surface area ratios and that offset the action of thicker cell walls on gm. Furthermore, weak negative relationship between nitrogen allocation in cell walls and in Rubisco was found for Castanopsis hystrix, Cyclobalanopsis phanera and Cy. patelliformis, which might imply that nitrogen in the leaves was insufficient for both Rubisco and cell walls. In summary, our study concluded that higher PNUE might contribute to the dominance of most Fagaceae tree species in Jianfengling tropical montane rain forest.

[Soil microbial community structure of monoculture and mixed plantation stands of native tree species in south subtropical China].

The effects of three plantation stands, Erythrophleumf ordii (EF), Pinus massoniana (PM), and their mixed plantation (MP), on soil microbial biomass and microbial community structure in south subtropical China were studied by the method of phospholipid fatty acids (PLFAs) analysis. The results showed that the amounts of microbial total PLFAs and PLFAs of each microbial group in these three plantation stand soils were significantly higher in dry season than in rainy season. In dry season, the amounts of microbial total PLFAs, bacteria PLFAs, fungi PLFAs, and actinomycetes PLFAs were the highest in the PM soil, moderate in the MP soil, and the lowest in the EF soil. But in rainy season, the amounts of microbial total PLFAs, bacteria PLFAs, fungi PLFAs, and arbuscular mycorrhizal fungi (AMF) PLFAs in the EF soil were higher than in the MP soil, and were significantly higher than in the PM soil. Principal component analysis (PCA) indicated that the variations in soil microbial community structure composition were affected by both plantation types and seasons. Redundancy analysis (RDA) of soil microbial community structure and environmental factors showed that soil temperature and moisture, pH, total nitrogen content, and ammonium nitrogen content had significant correlations with PLFA signatures. In addition, the ratio of fungi PLFAs to bacteria PLFAs in the MP soil was the highest among the three stand soils within the whole year, indicating that mixed plantation stands could facilitate the stability of the soil ecosystem.