Lirong Zhang

Gene or environment? Species-specific control of stomatal density and length

Stomatal characteristics are used as proxies of paleo-environment. Only a few model species have been used to study the mechanisms of genetic and environmental effects on stomatal initiation. Variation among species has not been quantified. In this paper, results from an in situ reciprocal transplant experiment along an elevation gradient in the northeast Tibetan Plateau are reported, in which the relative effects of genetics (original altitude) and environment (transplant altitude) on stomatal density (SD) and length (SL) were quantified. In Thalictrum alpinum, only the environment significantly influenced SD, with the variance component () of the environment found to be much greater than that of genetics () (). In Kobresia humillis, only genetics significantly influenced SD and SL, with the genetics variance component found to be greater than that of the environment (, for SD). These results suggest that the extent to which genetics and the environment determine stomatal initiation and development is species-specific. This needs to be considered when studying genetic or environmental controls of stomatal initiation, as well as when SD and SL are used as proxies for ancient climate factors (e.g., CO2 concentration).

Warming decreased and grazing increased plant uptake of amino acids in an alpine meadow

Abstract Organic nitrogen (N) uptake by plants has been recognized as a significant component of terrestrial N cycle. Several studies indicated that plants have the ability to switch their preference between inorganic and organic forms of N in diverse environments; however, research on plant community response in organic nitrogen uptake to warming and grazing is scarce. Here, we demonstrated that organic N uptake by an alpine plant community decreased under warming with 13C–15N‐enriched glycine addition method. After 6 years of treatment, warming decreased plant organic N uptake by 37% as compared to control treatment. Under the condition of grazing, warming reduced plant organic N uptake by 44%. Grazing alone significantly increased organic N absorption by 15%, whereas under warming condition grazing did not affect organic N uptake by the Kobresia humilis community on Tibetan Plateau. Besides, soil NO 3–N content explained more than 70% of the variability observed in glycine uptake, and C:N ratio in soil dissolved organic matter remarkably increased under warming treatment. These results suggested warming promoted soil microbial activity and dissolved organic N mineralization. Grazing stimulated organic N uptake by plants, which counteracted the effect of warming.

Understanding the wide geographic range of a clonal perennial grass : plasticity versus local adaptation

Both phenotypic plasticity and local adaptation may allow widely distributed plant species to either acclimate or adapt to environmental heterogeneity. Given the typically low genetic variation of clonal plants across their habitats, phenotypic plasticity may be the primary adaptive strategy allowing them to thrive across a wide range of habitats. In this study, we used field investigation and controlled experiments to test this. We found that plasticity in water use efficiency (reflected by foliar δ13C) is more important than local adaptation in allowing the studied clonal plants to occupy a wide range of habitats.

Effects of sampling method on foliar δ (13)C of Leymus chinensis at different scales.

Stable carbon isotope composition (δ13C) usually shows a negative relationship with precipitation at a large scale. We hypothesized that sampling method affects foliar δ13C and its response pattern to precipitation. We selected 11 sites along a precipitation gradient in Inner Mongolia and collected leaves of Leymus chinensis with five or six replications repeatedly in each site from 2009 to 2011. Additionally, we collected leaves of L. chinensis separately from two types of grassland (grazed and fenced) in 2011. Foliar δ13C values of all samples were measured. We compared the patterns that foliar δ13C to precipitation among different years or different sample sizes, the differences of foliar δ13C between grazed and fenced grassland. Whether actual annual precipitation (AAP) or mean annual precipitation (MAP), it was strongly correlated with foliar δ13C every year. Significant difference was found between the slopes of foliar δ13C to AAP and MAP every year, among the slopes of foliar δ13C to AAP from 2009 to 2011. The more samples used at each site the lower and convergent P-values of the linear regression test between foliar δ13C and precipitation. Furthermore, there was significant lower foliar δ13C value in presence of grazed type than fenced type grassland. These findings provide evidence that there is significant effect of sampling method to foliar δ13C and its response pattern to precipitation of L. chinensis. Our results have valuable implications in methodology for future field sampling studies.

Responses of biotic interactions of dominant and subordinate species to decadal warming and simulated rotational grazing in Tibetan alpine meadow

Warming increases competition among plant species in alpine communities by ameliorating harsh environmental conditions, such as low temperatures. Grazing, as the main human activity, may mitigate the effect of warming, as previously reported. However, it is critical to refine the effects of warming on biotic interactions among species, for example, by taking the competitive ability of species into consideration. Based on a 10-year warming and grazing experiment in a Tibetan alpine meadow, we evaluated interspecific biotic interactions of dominant and subordinate species, using the approach of interspecific spatial associations. Warming significantly increased competition between subordinate and dominant species as well as among subordinate species, but not among dominant species. Moreover, facilitation of dominant-subordinate species also increased under warming. Simulated rotational grazing had similar effects to warming, with increasing interspecific competition. Our results show that, when studying the effects of warming on biotic interactions among species, it is necessary to characterize different species pairs relative to their competitive ability, and that simulated rotational grazing does not mitigate the effects of warming in the long term. Our results also provide evidence that the spatial pattern of species is a critical mechanism in species coexistence.

Plant organic N uptake maintains species dominance under long-term warming

Background and aimsThere is ample experimental evidence for shifts in plant community composition under climate warming. To date, however, the underlying mechanisms driving these compositional shifts remain poorly understood.MethodsThe amount and form of nitrogen (N) available to plants are among the primary factors limiting productivity and plant coexistence in terrestrial ecosystems. We conducted a short-term 15N tracer experiment in a ten-year warming and grazing experiment in an alpine grassland to investigate the effects of warming and grazing on plant uptake of NO3−-N, NH4+-N, and glycine-N. Four dominant plant species (Kobresia humilis, Potentilla anseria, Elymus nutans, Poa annua) were selected. Results We found that 10-years of warming decreased plant uptake of inorganic N by up to 80% in all species. In contrast, warming increased the uptake of organic N in K. humilis, P. anseria, and E. nutans but not in P. annua. Results showed that plant relative biomass increased hyperbolically with the ratio of the plant species total uptake of available N and plant community uptake of available N. And a significant positive correlation between plant species uptake of soil glycine-N and the uptake of total available N.ConclusionsThe stable relative biomass of plant species is largely dependent on organic N uptake by plants. We conclude that plant organic N uptake maintains species dominance under long-term warming.