Stoichiometry of leaf carbon, nitrogen, and phosphorus along a geographic, climatic, and soil gradients in temperate desert of Hexi Corridor, northwest China

Aims Understanding the regional pattern of leaf stoichiometry and its contributing variables are of importance for predicting plant responses to global change and modelling the productivity and nutrient fluxes of ecosystems. In this study, we investigated leaf stoichiometry of plants that sampled from Hexi Corridor, a typical arid region in China, and tried to explore the contribution variables on leaf stoichiometry along the geographic, climatic, and soil gradients. Methods In August 2012, 70 sites in Hexi Corridor were investigated. Plant leaves and soils from five equivalent plots within each site were sampled. C, N, and P contents of leaf and soil were measured. Important findings Compared with leaf N and P contents in regional and global scales, leaf N content in Hexi Corridor was close to them with the value of 20.19 mg g-1, while leaf P content was lower than them with the value of 1.34 mg g-1. Overall, leaf N:P value in Hexi Corridor was 15.70. Individually, leaf N:P values of shrubs and herbs were 16.81 and 14.80, respectively. Scaling exponents for leaf N vs. P of overall and shrubs in Hexi Corridor were 1.29, higher than the scaling exponent of herbs (1.08). Leaf stoichiometry of shrubs and herbs did not show significant latitudinal and longitudinal patterns, meanwhile, it has no significant correlation with mean annual precipitation (MAP), mean annual temperature (MAT), and soil elements. However, only leaf stoichiometry of herbs has significant correlation with altitude and aridity degree. These results indicate that plants in Hexi Corridor are possibly co-limited by N and P, while shrubs are mainly limited by soil P and herbs are limited by soil N. Scaling relationship reveals that leaf N vs. P of herbs is isometric. With increasing altitude, the quadratic regression for leaf C and N contents and the linear regression for leaf P content of herbs reflect the difference responses of the three elements on the variation of MAT along the altitude and it could be explained by plant physiology hypothesis and biogeochemical hypotheses. With decreasing aridity, leaf N and N:P of herbs increased significantly, inferring that herbs growth would be limited by P increasingly and strengthening the increasing nitrogen availability with increasing precipitation. In conclusion, different altitude and aridity patterns for leaf stoichiometry of herbs and shrubs reveal the plastic survive strategies of different xerophytes in Hexi Corridor. Moreover, leaf stoichiometry of herbs in Hexi Corridor could be as indicator of the changing environment that caused by aridity.

Observations of Tripsacum dactyloides and T. floridanum (Poaceae): measuring climate and soil gradient effects on Tripsacum in Texas, U.S.A.

Reports of Tripsacum floridanum Porter ex Vasey in Texas have been countered with two arguments. First is that narrow-leafed Texas plants, when grown under favorable conditions, are more typical of wider-leafed T. dactyloides (L.) L. Second is that the offspring from crosses of T. dactyloides with T. floridanum are sterile or partially so. The support for these two claims is examined. The conclusion is narrow-leafed Texas plants typical of T. floridanum are in Texas, and crosses between the two produce fully fertile offspring. This raises the question of what factors are at play to segregate the wider-leafed from the narrower-leafed Texas populations. To investigate, two statistical models were constructed using separate data. First, a simultaneous system of seven equations was used to predict phenological and morphological plant characteristics given environmental factors. Second, a single logit equation predicted the probability of narrow-leafed diploid versus widerleafed diploid and tetraploid plants given environmental factors. Predictions allow for the measurement of plant characteristics from climate and soil gradients. Results suggest that narrow-leafed diploid plants occupy distinct habitats with the larger tetraploid plants coping by adapting mechanisms to overcome interspecies competition while the smaller diploid plants adapt with mechanisms to overcome stress. In conclusion, findings support consideration of T. floridanum as a variety of T. dactyloides and conservation implications are reviewed.