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Mount Gongga spans 6500 m in elevation and has intact and continuous vertical vegetation belts, ranging from subtropical evergreen broad-leaved vegetation to an alpine frigid sparse grass and desert zone. Investigating the altitudinal trends in leaf nitrogen (N) on Mount Gongga can increase our understanding of the global biogeography of foliar N. In this study, 460 leaf samples from mosses, ferns, and seed plants were collected along an altitudinal gradient on the eastern slope of Mount Gongga, and the variation in leaf N concentration (mass basis) with elevation was analyzed. There are considerable differences in leaf N between mosses and ferns, mosses and seed plants, C(4) and C(3) plants, and evergreen and deciduous woody plants. The general altitudial pattern of leaf N in Mount Gongga plants was that leaf N kept increasing until an elevation of about 2200 m above sea level, with a corresponding mean annual temperature (MAT) of 8.5°C, and then decreased with increasing elevation. However, the evergreen woody plants displayed a decline trend in leaf N across the altitude gradient. Our findings provide an insight into the altitudinal variation in leaf N.

The natural abundances of stable nitrogen isotopes in plants and soils have been viewed as recorders that can be used to reconstruct paleoclimate and ecological processes or to indicate the biogeochemical cycle of nitrogen in nature. This study systematically measured the nitrogen isotope composition (δ(15)N) in plants and surface soils along an altitudinal transect of elevation range of 1200 to 4500 m on the eastern slope of Mount Gongga in southwest China. The influences of photosynthetic pathways on plant δ(15)N as well as the effects of temperature and precipitation on δ(15)N altitudinal trends in plants and surface soils are discussed. Across this altitude transect, the δ(15)N values of C(3) and C(4) plants on Mount Gongga range between -9.87‰ and 7.58‰ with a mean value of -1.33‰, and between -3.98‰ and 4.38‰ with a mean value of -0.25‰, respectively. There is an evident δ(15)N difference between C(3) plants and C(4) plants. If, however, you only compare C(4) plants with those C(3) plants growing at the same altitudinal range, no significant difference in δ(15)N exists between them, suggesting that photosynthetic pathway does not have an influence on the plant δ(15)N values. In addition, we found that C(3), C(4) plants and surface soil (0-5 cm depth) all trend significantly towards more negative δ(15)N with increasing elevation. Furthermore, this study shows that the mean annual temperature and the mean annual precipitation positively and negatively correlate with δ(15)N in C(3) and C(4) plants, respectively. This indicates that precipitation and temperature are the main controlling factors of the δ(15)N variation in plants with altitude. We propose that lower δ(15)N values of plants and soils at higher altitude should be attributed to lower mineralization and lower net nitrification rates induced by low temperature and abundant rainfall., (Copyright © 2010 John Wiley & Sons, Ltd.)

Significant correlations between leaf carbon isotope discrimination (Delta) and altitude and between gas exchange and altitude have been reported in previous studies, raising the question of whether the altitudinal variations in discrimination and gas exchange can be attributed to genetic differences among populations from different altitudes. Studies that focus on in situ analysis cannot distinguish the effects of genetic variation from environmental variation. This article describes an experiment in which seeds of Plantago depressa (C3 species) and Setaria viridis (C4 species) collected from a wide altitudinal range were grown in the same environment. Carbon isotopic ratios (delta(13)C) and gas exchange of the seedlings were measured. The progenies of P. depressa and S. viridis no longer display any significant Delta decreases with the altitude of origin as seen in situ. Furthermore, photosynthetic rate, stomatal conductance, the ratio of intercellular to ambient CO(2) and intrinsic water use efficiency for P. depressa and S. viridis grown in the greenhouse are also not significantly related to the altitude of origin. The observations suggest that altitudinal variations in Delta and gas exchange are not because of genotypic differences, independent of photosynthetic type.

Carbon isotope ratios (δ13C) of plants, litter and soil organic matter (0-5 cm, 5-10 cm and 10-20 cm) on the eastern slope of Mount Gongga were measured. The results show that δ13C values of plants, litter and soil organic matter all decrease first and then increase with altitude, i.e. d 13C values gradually decrease from 1200 to 2100 m a.s.l., and increase from 2100 to 4500 m a.s.l. The δ13C altitudinal variations are related to the distribution of C3 and C4 plants on the eastern slope of Mount Gongga, because C4 plants are observed to grow only below 2100 m, while C3 plants occur at all altitudes. There are significantly positive correlations among d 13C of vegetation, δ13C of litter and δ13C of soil organic matter, and litter, 0-5 cm, 5-10 cm and 10-20 cm soil organic matter are 0.56‰, 2.87‰, 3.04‰ and 3.49‰ greater in δ13C than vegetation, respectively. Considering the influences of rising concentration of atmospheric CO2 and decreasing δ13C of atmospheric CO2 since the industry revolution on δ13C of plants, 1.57‰ is proposed to be the smallest correction value for reconstruction of paleovegetation using δ13C of soil organic matter. [ABSTRACT FROM AUTHOR]

Variations in carbon isotopic ratios ( δ13C) of C3 plants and distribution of C4 plants were investigated along an altitudinal transect on the eastern slope of Mount Gongga, and the environmental effects on them were discussed. It is shown that plants with C4 photosynthetic pathway mainly occur at altitudes below 2100 m a.s.l., suggesting that the low summer temperature is responsible for the distributional pattern. In addition, δ13C of C3 plants increases with elevation at the region above 2000 m a.s.l. with the characteristics of humid climate, and the increase rate in δ13C for C3 plants is about 1.3% per kilometer. Temperature determines the altitudinal trend of δ13C. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soil C and N stoichiometry increase with increasing altitude on the sunny slope. • Soil C and N stoichiometry are non-linear with altitude on the shady slope. • Altitudinal patterns of soil C and N dynamics vary across slope aspects. • Soil C significantly correlated with soil N on the sunny and shady slopes. • Soil C and N dynamics in drylands kept coupled under climate change. Climate change is predicted to be more dramatic in arid regions. Soil carbon (C) and nitrogen (N) dynamics maintain various functions in terrestrial ecosystems. It has been suggested that soil C and N dynamics are biologically coupled due to the strict proportions of C and N in organisms. However, whether dramatic climate change in drylands would break this coupling remained largely unknown. Given that climate change could occur over short distances in mountainous terrain, this study conducted a soil sampling across an altitude transect in Tianshan Mountains, China, which are the largest mountain system in drylands across the world. To avoid the disturbance of the influence of slope aspect, we therefore collected soil samples on the sunny and shady slopes of Tianshan Mountains. Our results showed that soil C and N concentrations and C:N ratio all increased with increasing altitude on the sunny slope and their changes were affected by temperature, soil sand content and precipitation. For the shady slope, soil C and N concentrations and C:N ratio all first increased then decreased along the altitude gradient. Soil pH, precipitation, temperature and soil sand content influenced soil C and N dynamics at altitude below 2650 m; soil pH and soil sand content affected soil C and N dynamics at altitude above 2650 m. These results indicated that soil C and N dynamics on the sunny and shady slopes both kept coupled under the condition of changing altitude. Furthermore, although the altitudinal patterns of soil C and N dynamics on the sunny and shady slopes were different, the correlations between soil C and N concentrations on these two slopes both were significant with a correlation coefficient of about 0.9. Hence, this study suggested that the coupling of soil C and N dynamics in drylands would still exist under climate change. [ABSTRACT FROM AUTHOR]