Variation in plant functional traits explains the substitution distribution and allocation strategy of Stipa species across natural grasslands of Ningxia, Northern China.

Functional traits reflect plants' adaptability to their environment, and environmental gradients influence their distribution. But few studies have investigated the link between these traits and species substitution patterns or the relevant ecological factors. We measured the aboveground (leaf) and belowground (root) functional traits of Stipa species in 17 plots across natural grasslands in Ningxia in Northern China. Redundancy analysis was used to explore the relationships between Stipa's functional traits and its species substitution distribution. Then, on the species substitution gradient, principal component analysis (PCA) was used to verify and quantify the leaf economic spectrum (LES), root economic spectrum (RES), and whole-plant economic spectrum (WPES), with the relation between these spectra investigated by fitting standardized major axis regressions. The effects of aboveground, belowground, and whole-plant ecological factors were quantified and ranked by variance decomposition and hierarchical partitioning. Our results showed that functional traits drive the substitution distribution of Stipa species, in being variously coupled with its desert, typical, and meadow steppe habitat types. The leaf, root, and whole-plant economic spectra of Stipa species in desert steppe exhibit a "quick investment-acquisition" strategy. In typical steppe, the leaf and whole-plant economic spectra of Stipa species correspond to a "fast investment-acquisition" strategy, whereas the root economic spectrum adopts a "slow investment-acquisition" strategy. On meadow steppe, the leaf, root, and whole-plant economic spectra of Stipa species similarly adopt a "slow investment-acquisition" strategy. Finally, when considering the environmental factors involved, we find that the substitution distribution of Stipa spp. is chiefly a response to shifting soil patterns, these mainly driven by soil total nitrogen and nitrogen/phosphorus ratio. Collectively, these findings provide an important reference for the ecological restoration and reconstruction of grassland ecosystems, to better understand the relationship between plant functional traits and ecological niche attributes, and thus guide the reasonable restoration of grassland vegetation.

Comparison of species composition and community characteristics of Quercus forests on south and north slopes of Taibai Mountain, China.

We examined species composition, community characteristics, diversity, and community similarity of five Quercus communities composed of three Quercus species (Q. variabilis, Q. aliena var. acutiserrata, Q. wutaishanica) on the altitudinal gradient on the south and north slopes of Taibai Mountain. The results showed that there was an altitudinal transition pattern from Q. variabilis pure forest to Q. variabilis-Q. aliena var. acutiserrata mixed forest, Q. aliena var. acutiserrata pure forest, Q. aliena var. acutiserrata-Q. wutaishanica mixed forest and Q. wutaishanica pure forest on the south and north slopes of Taibai Mountain. The main companion species of Quercus community on the north slope were Pinus armandii, Castanea seguinii, and Sorbus alnifolia, and were Pinus tabuliformis, C. seguinii, Carpinus cordata, and Q. spinosa on the south slope. Species richness, woody plant density, and Quercus species dominance on the north slope of Taibai Mountain were higher than those on the south slope. α diversity of tree layer in Quercus community on the south and north slopes of Taibai Mountain increased first, then decreased and then increased with altitude. α diversity of tree layer was higher in mixed forests than pure forests. α diversity of shrub layer was higher than that of tree layer and herb layer in Quercus community on south and north slopes. ß diversity fluctuated greatly along the altitudinal gradient on the south and north slopes, indicating that species composition changed greatly with altitude. Results of redundancy analysis showed that mean warmest month temperature, altitude and tree height accounted for 79.0% of the community diversity on the north slope, and that soil water content, tree height, canopy density and mean annual temperature accounted for 79.6% of the community diversity on the south slope. Overall, Quercus dominance was higher on the north slope of Taibai Mountain, and the substitution distribution pattern of Quercus species was clearer than that on the south slope. Environmental factors related to temperature and precipitation jointly affected α diversity of Quercus communities.

Elucidation of substituted ester group position in octenylsuccinic anhydride modified sugary maize soluble starch.

The octenylsuccinic groups in esterification-modified sugary maize soluble starches with a low (0.0191) or high (0.0504) degree of substitution (DS) were investigated by amyloglucosidase hydrolysis followed by a combination of chemical and physical analysis. The results showed the zeta-potential remained at approximately the same value regardless of excessive hydrolysis. The weight-average molecular weight decreased rapidly and reached 1.22 × 10(7) and 1.60 × 10(7) g/mol after 120 min for low-DS and high-DS octenylsuccinic anhydride (OSA) modified starch, respectively. The pattern of z-average radius of gyration as well as particle size change was similar to that of Mw, and z-average radius of gyration decreased much more slowly, especially for high-DS OSA starch. Compared to native starch, two characteristic absorption peaks at 1726.76 and 1571.83 cm(-1) were observed in FT-IR spectra, and the intensity of absorption peaks increased with increasing DS. The NMR results showed that OSA starch had several additional peaks at 0.8-3.0 ppm and a shoulder at 5.56 ppm for OSA substituents, which were grafted at O-2 and O-3 positions in soluble starch. The even distribution of OSA groups in the center area of soluble starch particle has been directly shown under CLSM. Most substitutions were located near branching points of soluble starch particles for a low-DS modified starch, whereas the substituted ester groups were located near branching points as well as at the nonreducing ends in OSA starch with a high DS.

Position of modifying groups on starch chains of octenylsuccinic anhydride-modified waxy maize starch.

Octenylsuccinic anhydride (OSA)-modified starches with a low (0.018) and high (0.092) degree of substitution (DS) were prepared from granular native waxy maize starch in aqueous slurry. The position of OS substituents along the starch chains was investigated by enzyme hydrolysis followed by chromatographic analysis. Native starch and two OS starches with a low and high DS had ß-limit values of 55.9%, 52.8%, and 34.4%, respectively. The weight-average molecular weight of the ß-limit dextrin from the OS starch with a low DS was close to that of the ß-limit dextrin from native starch but lower than that of the ß-limit dextrin from the OS starch with a high DS. Debranching of OS starches was incomplete compared with native starch. OS groups in the OS starch with a low DS were located on the repeat units near the branching points, whereas the OS substituents in the OS starch with a high DS occurred both near the branching points and the non-reducing ends.

¹H and ¹³C chemical shift assignment of the monomers that comprise carboxymethyl cellulose.

(1)H and (13)C chemical shift assignment of the anhydroglucose units (AGUs) that comprise sodium carboxymethyl cellulose (CMC) with a degree of substitution (DS) of 0.70 was performed using 2D NMR spectra obtained from COSY, TOCSY, HSQC, and HSQC-TOCSY experiments. In the 2D COSY and TOCSY spectra, there are eight correlation networks for the H1 to H6' atoms of AGU; each (1)H resonance of the eight AGUs was assigned from the changes in the intensities of the resonances with mixing times during the TOCSY experiments. The ring (13)C resonances were assigned via analysis of HSQC-TOCSY spectra and confirmed via the HSQC spectra. Comparison of the shift data enabled the assignment of the eight AGUs as two types of both 2,3,6-tri-O- and 3,6-di-O-carboxymethylated, one type each of 2,6-di-O-, 2-mono-O-, and 6-mono-O-carboxymethylated AGU, and unsubstituted AGU. The obtained shift data will also be useful for characterization of the substitution distribution of other cellulose derivatives.