Stoichiometry Patterns Research Articles

Leaf nitrogen and phosphorus stoichiometry across forty-two woody species in Southeast China

Abstract Ecological stoichiometry is an indicator of function and nutrient limitation from individual to ecosystem levels, yet it is still unclear whether leaf stoichiometry patterns are homologous at different scales. We determined the leaf nitrogen (N) and phosphorous (P) concentrations, N:P ratio and leaf traits across 42 woody species planted at Hangzhou Bay Coastal Shelter Forest Experimental Site in Southeast China. We analyzed variation patterns in leaf stoichiometry, correlated leaf stoichiometry with leaf traits, and determined nutrient limitations based on leaf stoichiometry. Leaf N and P concentrations and N:P ratio averaged 18.58 mg g −1 , 2.24 mg g −1 and 9.56, respectively. Leaf N and P concentrations were positively correlated while leaf P and leaf N:P ratio were negatively correlated across all species. Leaf dry matter content (LDMC) had a significant relationship with leaf P concentration and N:P ratio for all species, while specific leaf area (SLA) was significantly related to leaf N concentration for broadleaf species. Leaf N concentration and N:P ratio varied greatly within a site. Among the 42 species, 27 were found to be limited by N, one by P, one co-limited by N and P, and the rest not limited by either N or P. Our results provide a theoretical guideline for the construction and management of coastal shelter forests in Southeast China.

Solid Crystal Network of Self-Assembled Cyclodextrin and Nonionic Surfactant Pseudorotaxanes

The title system allows the straightforward formation of three-dimensional crystals of self-assembled pseudorotaxanes formed by the nonionic surfactant Igepal CO-520 and beta-cyclodextrin (beta-CD) in aqueous solution. The work involves a combination of X-ray powder diffraction, high resolution electron transmission microscopy, and (13)C CP/MAS NMR studies of the solid crystal, supported by single crystal structural analysis. The results indicate a lamellar self-assembly of pseudorotaxanes with preferential orientation and disorder in the structure. For the single crystal, the unit cell was found to be triclinic (P1) and contains a beta-CD dimer. The surfactant molecules are located in the channel formed by these dimers along the c axis of the crystal network. The individual pseudorotaxane structure is formed by a dimer of beta-CDs threaded by the oxyethylene hydrophilic segment of Igepal CO-520, and a beta-CD dimer that binds the hydrophobic region of the surfactant. Thus, as in a CD polyrotaxane structure, this system results in an ordered self-assembly of pseudorotaxanes through the formation of a network of hydrogen bonds between head-to-head beta-CD dimers. Moreover, the analysis of the (1)H NMR spectra in solutions of pseudorotaxanes formed by beta-CD and Igepals with different lengths of the hydrophilic tails indicates equal stoichiometry patterns of both oxyethyelene and hydrophobic regions for the different supramolecules. Whereas the common hydrophobic moiety threads two macrocycles, the ratio between complexed oxyehtlyene segments and beta-CD is 2.5 for the hydrophilic tails. All these results show that nonionic surfactants can be used as alternative and effective linear threads to polymers and copolymers in the synthesis of supramolecular polyrotaxane solid crystals with CDs.

Biomass cofiring impacts on flame structure and emissions

The impacts of cofiring biomass and coal on flame structure and NO emissions are investigated in the context of a swirl-stabilized, pilot-scale burner with straw and coal fired independently. The comparatively low energy density of biomass generally leads to higher transport air requirements per unit energy, increasing the momentum of biomass streams relative to an energy equivalent coal stream in burner feeds. Increasing the primary momentum in this manner alters the flow field and stoichiometry patterns of the burner. Detailed species concentration measurements as well as particle sampling were employed to investigate the flame structures of both high and low straw primary air flowrates. Large straw particles penetrate the internal recirculation zone at the high primary air flowrate, elongating the flame structure by forming fuel-rich eddies. The knees (relatively dense sections of straw) of the straw penetrated much further into the reactor, forming a secondary combustion zone. The NO emission was seen to decrease as the straw primary air flowrate increased because of increased numbers of fuel-rich eddies providing more reducing zone, where the fuel nitrogen from the large particles was released. It is also shown that the fuel-rich eddies served as reburning and/or advanced reburning centers, reducing the effluent NO emission further.

Improved Fluorescent Proteins for Single-Molecule Research in Molecular Tracking and Co-Localization

Three promising variants of autofluorescent proteins have been analyzed photophysically for their proposed use in single-molecule microscopy studies in living cells to compare their superiority to other fluorescent proteins previously reported regarding the number of photons emitted. The first variant under investigation the F46L mutant of eYFP has a 10% greater photon emission rate and >50% slower photobleaching rate on average than the standard eYFP fluorophore. The monomeric red fluorescent protein (mRFP) has a fivefold lower photon emission rate, likely due to the monomeric content, and also a tenfold faster photobleaching rate than the DsRed fluorescent protein. In contrast, the previously reported eqfp611 has a 50% lower emission rate yet photobleaches more than a factor 2 slowly. We conclude that the F46L YFP and the eqfp611 are superior new options for single molecule imaging and tracking studies in living cells. Studies were also performed on the effects of forced quenching of multiple fluorescent proteins in sub-micrometer regions that would show the effects of dimerization at low concentration levels of fluorescent proteins and also indicate corrections to stoichiometry patterns with fluorescent proteins previously in print. We also introduce properties at the single molecule level of new FRET pairs with combinations of fluorescent proteins and artificial fluorophores.