R. Z. Wang

Photosynthetic Pathway and Morphological Functional Types in the Steppe Vegetation from Inner Mongolia, North China

Photosynthetic pathway (C3, C4, and CAM) and morphological functional types were identified for the forage species from steppe vegetation in Inner Mongolia, China, using the data from both field survey and references. Of the total 136 identified vascular species, in 29 families and 89 genera, 78 % were found with C3 photosynthesis, including dominant herbs, e.g. Stipa grandis P. Smirn., S. krylovii Roshev., and Leymus chinensis (Trin.) Tzvel. These C3 species covered about 90 % of the total herbage production in the steppe. 20 % were found with C4 photosynthesis and 2 % with CAM photosynthesis. Photosynthetic pathway functional types were coarse and may not fit for the studies and land management in small scales, because of the high C3 photosynthesis composition and the few families in which C4 species occur. Morphological functional types (e.g. shrubs, high perennial grasses, short perennial graminaceous plants, annual grasses, annual forbs, perennial forbs, and succulents) may be practical for spatial and temporal descriptions of steppe ecosystems in local and region scales. Classification for plant functional types, especially morphological types, may contribute to studying the links between plant species and communities, ecosystems, and global changes, and for steppe management decisions in the region.

Photosynthetic Pathways and Life Forms in Different Grassland Types from North China

Photosynthetic pathways (C4, C3, and CAM species) and plant life forms of three grassland types in North China were compared. Of the total 201 species, 144 species in 78 genera and 34 families had C3 photosynthetic pathway, 56 species in 35 genera and 11 families had C4 photosynthetic pathway, and 1 species had CAM photosynthetic pathway. The number of C4 species in Songnen meadow was 70–80 % greater than that in Xilinguole steppe and Hunshandak desert grassland, but that for C3 species did not differ significantly among the three grassland types. The number of therophytes in the Songnen meadow was relatively greater than that of the other two grassland types, but that of hemicryptophytes was lower. Thus the distribution of C4 species and plant life form is probably related to precipitation.

The Effects of Warming and Nitrogen Addition on Soil Nitrogen Cycling in a Temperate Grassland, Northeastern China

Background Both climate warming and atmospheric nitrogen (N) deposition are predicted to affect soil N cycling in terrestrial biomes over the next century. However, the interactive effects of warming and N deposition on soil N mineralization in temperate grasslands are poorly understood. Methodology/Principal Findings A field manipulation experiment was conducted to examine the effects of warming and N addition on soil N cycling in a temperate grassland of northeastern China from 2007 to 2009. Soil samples were incubated at a constant temperature and moisture, from samples collected in the field. The results showed that both warming and N addition significantly stimulated soil net N mineralization rate and net nitrification rate. Combined warming and N addition caused an interactive effect on N mineralization, which could be explained by the relative shift of soil microbial community structure because of fungal biomass increase and strong plant uptake of added N due to warming. Irrespective of strong intra- and inter-annual variations in soil N mineralization, the responses of N mineralization to warming and N addition did not change during the three growing seasons, suggesting independence of warming and N responses of N mineralization from precipitation variations in the temperate grassland. Conclusions/Significance Interactions between climate warming and N deposition on soil N cycling were significant. These findings will improve our understanding on the response of soil N cycling to the simultaneous climate change drivers in temperate grassland ecosystem.

Photosynthetic Pathways, Life Forms, and Reproductive Types for Forage Species Along the Desertification Gradient on Hunshandake Desert, North China

Floristic compositions, life forms, reproductive types for forage species, and their responses to desertification in Hunshandake desert were studied. 164 species, in 30 families and 94 genera, were identified with C3 (137 species), C4 (25 species), and CAM (2 species) photosynthesis. Of the 25 C4 species, 76 % were grasses and Chenopodiaceae species (hereafter chenopods). This suggests that the C4 species mainly occurred in a few families in the desert region. The reduction of C3 species and the increase of C4 species with desertification indicated that C4 species might have higher tolerance to environmental stresses (e.g. dry and poor soil). Relatively more hemicrytophyte and therophyte forms in the desert are related to the local temperate climate and vegetation dynamics. Relatively greater proportions of C4/C3 and clonal species/sexual species at mobile dune showed that the C4 species and clonal species could make greater contribution to sand land restoration in the Hunshandake desert.

The C4 Photosynthetic Pathway and Life Forms in Grassland Species from North China

C4 photosynthetic pathway and life form were determined for 159 species in 71 genera and 13 families in the grassland of North China. 45 % of the C4 species were found in Graminae, 19 % in each of Cyperaceae and Chenopodiaceae. More than 51 % of these C4 species were in therophyta and 36 % hemicryptophyta, while fewer species were in nanophanerophyta (9 %) or geophyta (5 %). The numbers of C4 species and their life forms were closely related with grassland deterioration and succession in North China. This indicated that the C4 species had greater capacity to tolerate environmental stress (e.g. drought and salinity) caused by animal grazing and cultivation.

Anatomical and Physiological Plasticity in Leymus chinensis (Poaceae) along Large-Scale Longitudinal Gradient in Northeast China

Background Although it has been widely accepted that global changes will pose the most important constrains to plant survival and distribution, our knowledge of the adaptive mechanism for plant with large-scale environmental changes (e.g. drought and high temperature) remains limited. Methodology/Principal findings An experiment was conducted to examine anatomical and physiological plasticity in Leymus chinensis along a large-scale geographical gradient from 115° to 124°E in northeast China. Ten sites selected for plant sampling at the gradient have approximately theoretical radiation, but differ in precipitation and elevation. The significantly increasing in leaf thickness, leaf mass per area, vessel and vascular diameters, and decreasing in stoma density and stoma index exhibited more obvious xerophil-liked traits for the species from the moist meadow grassland sites in contrast to that from the dry steppe and desert sites. Significant increase in proline and soluble sugar accumulation, K+/Na+ for the species with the increasing of stresses along the gradient showed that osmotic adjustment was enhanced. Conclusion/Significance Obvious xerophytic anatomical traits and stronger osmotic adjustment in stress conditions suggested that the plants have much more anatomical and physiological flexibilities than those in non-stress habitats along the large-scale gradient.

Plant functional types and their ecological responses to salinization in saline grasslands, Northeastern China

Photosynthetic pathways (C3, C4, and CAM) and morphological functional types (e.g. shrubs, high perennial grasses, short perennial graminaceous plants, annual grasses, annual forbs, perennial forbs, halophytes, and hydrophytes) were identified for the species from salinity grasslands in Northeastern China, using the data from both stable carbon isotope ratios (δ13C) and from the references published between 1993 and 2002. 150 species, in 99 genera and 37 families, were found with C3 photosynthesis, and most of these species are dominants [e.g.Leymus chinensis (Trin.) Tzvel., Calamagrostis epigeios (L.), Suaeda corniculata (C.A. Mey.) Bunge]. 40 species in 25 genera and 8 families were identified with C4 photosynthesis [e.g.Chloris virgata Sw., Aeluropus littoralis (Gouan) Parlat] and 1 species with CAM photosynthesis. Gramineae is the leading family with C4 photosynthesis (27 species), Chenopodiaceae ranks the second (5 species). The significant increase of C4 proportions with intense salinity suggested this type plant is remarkable response to the grassland salinization in the region. 191 species were classified into eight morphological functional types and the changes of most of these types (e.g. PEF, HAL, and HPG) were consistent with habitats and vegetation dynamics in the saline grassland. My findings suggest that the photosynthetic pathways, combined with morphological functional types, are efficient means for studying the linkage between species and ecosystems in this type of saline grassland in Northeastern China.

Photosynthetic Pathway Types of Forage Species Along Grazing Gradient from the Songnen Grassland, Northeastern China

Photosynthetic pathway types (C3 and C4 species) and their dynamics along grazing gradient were determined for 42 plant species in 30 genera and 13 families from the Songnen grassland, Northeastern China. Of the total, 10 species in 9 genera and 4 families had C4 photosynthesis; 32 species in 21 genera and 12 families had C3 photosynthesis. The proportion of C4 species in total plants and C4/C3 increased with grazing intensity, and peaked in overgrazed plot. Most of the increased C4 species (6 of 10) along the grazed gradient were annual grasses and halophytes. This indicated that the C4 species had greater capacity to tolerate environmental stresses (e.g. drought and saline) caused by animal grazing in the Songnen grassland, Northeastern China.

Soil Microbial Properties and Plant Growth Responses to Carbon and Water Addition in a Temperate Steppe: The Importance of Nutrient Availability

Background Global climatic change is generally expected to stimulate net primary production, and consequently increase soil carbon (C) input. The enhanced C input together with potentially increased precipitation may affect soil microbial processes and plant growth. Methodology/Principal Findings To examine the effects of C and water additions on soil microbial properties and plant growth, we conducted an experiment lasting two years in a temperate steppe of northeastern China. We found that soil C and water additions significantly affected microbial properties and stimulated plant growth. Carbon addition significantly increased soil microbial biomass and activity but had a limited effect on microbial community structure. Water addition significantly increased soil microbial activity in the first year but the response to water decreased in the second year. The water-induced changes of microbial activity could be ascribed to decreased soil nitrogen (N) availability and to the shift in soil microbial community structure. However, no water effect on soil microbial activity was visible under C addition during the two years, likely because C addition alleviated nutrient limitation of soil microbes. In addition, C and water additions interacted to affect plant functional group composition. Water addition significantly increased the ratio of grass to forb biomass in C addition plots but showed only minor effects under ambient C levels. Our results suggest that soil microbial activity and plant growth are limited by nutrient (C and N) and water availability, and highlight the importance of nutrient availability in modulating the responses of soil microbes and plants to potentially increased precipitation in the temperate steppe. Conclusions/Significance Increased soil C input and precipitation would show significant effects on soil microbial properties and plant growth in the temperate steppe. These findings will improve our understanding of the responses of soil microbes and plants to the indirect and direct climate change effects.

Seasonal Dynamics in Resource Partitioning to Growth and Storage in Response to Drought in a Perennial Rhizomatous Grass, Leymus chinensis

A natural grassland in northeastern China dominated by Leymus chinensis (Trin.) was subject to drought treatments to determine the seasonal dynamics in resource partitioning to shoot and storage organs in response to drought. The growing season was divided into six stages according to the phenology of L. chinensis. Plant samples of L. chinensis were collected at each stage to determine biomass, gross calorific value, relative water content, and key mineral contents of plant parts, including rhizomes, roots, leaves, and stems. Resource partitioning to shoot and storage organs as measured by biomass, gross calorific value, and N, K+, and Na+ contents varied significantly among phenologic stages. Drought treatment (natural precipitation, 50–60 % of field capacity) significantly reduced biomass, gross calorific value, relative water content of shoot, and N and K+ contents in both shoot and storage organs, but it enhanced rhizome : shoot ratio and Na+ content. A negative correlation in biomass, gross calorific value, and K+ and Na+ contents between shoot and storage organs was found throughout the growing season, which may have been accentuated by drought when soil moisture was limited. Our results indicate that resource partitioning to storage plays an important role in regulating plant growth of L. chinensis, especially under drought conditions.