The Protective Role of Non-Photochemical Quenching in PSII Photo-Susceptibility: A Case Study in the Field.

Non-photochemical quenching (NPQ) has been regarded as a safety valve to dissipate excess absorbed light energy not used for photochemistry. However, there exists no general consensus on the photoprotective role of NPQ. In the present study, we quantified the Photosystem II (PSII) photo-susceptibilities (mpi) in the presence of lincomycin, under red light given to five shade-acclimated tree species grown in the field. Photosynthetic energy partitioning theory was applied to investigate the relationships between mpi and each of the regulatory light-induced NPQ [Y(NPQ)], the quantum yield of the constitutive nonregulatory NPQ [Y(NO)] and the PSII photochemical yield in the light-adapted state [Y(PSII)] under different red irradiances. It was found that in the low to moderate irradiance range (50-800 µmol m-2 s-1) when the fraction of open reaction centers (qP) exceeded 0.4, mpi exhibited no association with Y(NPQ), Y(NO) and Y(PSII) across species. However, when qP < 0.4 (1,500 µmol m-2 s-1), there existed positive relationships between mpi and Y(NPQ) or Y(NO) but a negative relationship between mpi and Y(PSII). It is postulated that both Y(NPQ) and Y(NO) contain protective and damage components and that using only Y(NPQ) or Y(NO) metrics to identify the photo-susceptibility of a species is a risk. It seems that qP regulates the balance of the two components for each of Y(NPQ) and Y(NO). Under strong irradiance, when both protective Y(NPQ) and Y(NO) are saturated/depressed, the forward electron flow [i.e. Y(PSII)] acts as the last defense to resist photoinhibition.

Insight into the reversible conversion-(de)incorporation of redox-active dopants within a polymer-based electrode.

We combined a microporous polymer backbone with an organic redox-active dopant to construct a reversible electrode system based on the conversion-(de)incorporation behaviour of the dopant. The correspondence between the reversible conversion-(de)incorporation mechanism of the dopant and the electrochemical performance of the designed electrode system was established by electrochemical quartz crystal microbalance and in situ Fourier transform infrared spectroscopy.

Stomatal Sensitivity to Vapor Pressure Deficit and the Loss of Hydraulic Conductivity Are Coordinated in Populus euphratica, a Desert Phreatophyte Species.

There are considerable variations in the percentage loss of hydraulic conductivity (PLC) at mid-day minimum water potential among and within species, but the underpinning mechanism(s) are poorly understood. This study tested the hypothesis that plants can regulate leaf specific hydraulic conductance (K l) via precise control over PLC under variable ΔΨ (water potential differential between soil and leaf) conditions to maintain the -m/b constant (-m: the sensitivity of stomatal conductance to VPD; b: reference stomatal conductance at 1.0 kPa VPD), where VPD is vapor pressure deficit. We used Populus euphratica, a phreatophyte species distributed in the desert of Northwestern China, to test the hypothesis. Field measurements of VPD, stomatal conductance (g s), g s responses to VPD, mid-day minimum leaf water potential (Ψ lmin), and branch hydraulic architecture were taken in late June at four sites along the downstream of Tarim River at the north edge of the Taklamakan desert. We have found that: 1) the -m/b ratio was almost constant (=0.6) across all the sites; 2) the average Ψ 50 (the xylem water potential with 50% loss of hydraulic conductivity) was -1.63 MPa, and mid-day PLC ranged from 62 to 83%; 3) there were tight correlations between Ψ 50 and wood density/leaf specific hydraulic conductivity (k l) and between specific hydraulic conductance sensitivity to water potential [d(k s)/dln(-Ψ)] and specific hydraulic conductivity (k s). A modified hydraulic model was applied to investigate the relationship between g s and VPD under variable ΔΨ and K l conditions. It was concluded that P. euphratica was able to control PLC in order to maintain a relatively constant -m/b under different site conditions. This study demonstrated that branchlet hydraulic architecture and stomatal response to VPD were well coordinated in order to maintain relatively water homeostasis of P. euphratica in the desert. Model simulations could explain the wide variations of PLC across and within woody species that are often observed in the field.

[Effects of controlled-release fertilizer and organic amendment on the construction of nutrients reserves in Larix olgensis container seedlings].

A 2 x 2 factorial experiment was conducted to study the effect of fertilization on Larix olgensis container seedlings. 36.36 or 18.18 mg controlled-release fertilizer (CRF) N and 0 or 1.82 g FM organic amendment (OA) per seedling were applied. There were no significant responses to fertilization in the seedling height, collar diameter, biomass, and potassium (K) uptake. Applying FM OA increased the number of first-order lateral roots with a length > 1 cm (P = 0.040), the tap root length (TRL) (P = 0.012), and the ratio of TRL to seedling height (P = 0.008). Comparing with low application rate CRF N, high application rate CRF N increased the N concentration in root (P = 0.035) as well as the N reserves in stem (P = 0.005), root (P = 0.037), and stem plus root (P = 0.030), and the P reserves in stem (P = 0.047). Applying 36.36 mg CRF N plus 1.82 g FM OA increased the N concentrations in leaf and in stem plus root by 137% (P = 0.040) and 21% (P = 0.013), respectively, and the N reserves in stem (P = 0.020), root (P = 0.017), and stem plus root (P = 0.013). Vector analysis revealed that high application rate of CRF N led to the excess of seedlings N and P, while applying FM OA alleviated the N and P deficiency but led to the K depletion. For nursing L. olgensis container seedlings, a solution of CRF 18 mg N combined with 1.82 g FM OA per seedling was recommended.