Shuxia Zheng

Differential responses of plant functional trait to grazing between two contrasting dominant C3 and C4 species in a typical steppe of Inner Mongolia, China

Plant functional traits have been widely used to study the linkage between environmental drivers, trade-offs among different functions within a plant, and ecosystem structure and functioning. Here, the whole-plant traits, leaf morphological and physiological traits of two dominant species, Leymus chinensis (C3 perennial rhizome grass) and Cleistogenes squarrosa (C4 perennial bunchgrass), were studied in the Inner Mongolia grassland of China, with a grazing experiment including five stocking rates (0, 3.0, 4.5, 7.5, and 9.0 sheep/ha) in 2008 (wet year) and 2009 (dry year). Our results demonstrated that, for both species, the effects of stocking rate, year, and stocking rate × year on whole-plant traits and leaf morphological and physiological traits were highly significant in most cases. The differential responses of plant trait to variation in precipitation were caused by trait trade-offs between the wet and dry years. L. chinensis adopted the high N content and net photosynthetic rate (Pn) in the wet year but both the low N content and Pn in the dry year under grazed conditions. The trait trade-offs of C. squarrosa were characterized by high specific leaf area (SLA) and Pn in the dry year vs. low SLA and Pn in the wet year. Our findings also indicate that C. squarrosa is more resistant to grazing than L. chinensis in terms of avoidance and tolerance traits, particularly under heavy grazing pressure and in the dry year.

Vertebrate herbivore‐induced changes in plants and soils: linkages to ecosystem functioning in a semi‐arid steppe

Summary 1. Large grazing herbivores have been reported to determine the structure and function of grassland ecosystems. However, the ecological linkages between structure and functioning components have yet been thoroughly explored. 2. Here, we test the hypothesis of the impact of grazing on soil nematode community (e.g. structure and composition) and linkages to ecosystem functioning (e.g. soil N mineralization and ANPP) via changes in pathways of plant community, soil nutrients and soil environment using a field experiment maintained for 5 years with seven levels of grazing intensity in the Inner Mongolian grassland. 3. A structural equation model (SEM) with nematode abundances as response variables showed that plant-feeding and fungal-feeding nematodes were driven by changes in the plant community, and bacterial-feeding nematodes were affected by soil abiotic nutrients and environment, while omnivorous + carnivorous nematodes were altered by soil environment and bacterial-feeding nematodes. This indicates that the top-down control by grazing leads to bottom-up control in the soil food web. 4. We found that grazing affected the ecosystem functioning via different pathways. Grazing effects soil N mineralization by changing plant community, soil nutrients, soil environment and nematodes community structure, while it affects ANPP by altering soil N mineralization and soil environment. 5. Our findings could provide a better understanding of the responses of plants and soils to grazing and the linkages between structure and functioning of above-ground and belowground in the semi-arid steppe.

Ecological properties of soil water and effects on forest vegetation in the Loess Plateau

In the Loess Plateau of China, soil water has three ecological properties: high infiltration capacity, high storage capacity and availability to deep plant roots. Soil desiccation is the most serious problem for forest vegetation in the Loess Plateau. Arid soils are the result of intensified soil desiccation caused by disturbances in plant succession, which constitute the ecological foundation of soil water. The negative effects of the arid soil layer on surface water infiltration for recharging underground water are discussed in terms of ecological hydrology. The arid soil layer disrupts the link between surface water and underground water and prevents vertical precipitation infiltration from supplementing underground water. Forest vegetation has a significant runoff-retaining efficiency that reduces total runoff from forest areas leading to low surface and ground runoff which affect the water cycle on a watershed scale.

Scale-Dependent Effects of Grazing on Plant C: N: P Stoichiometry and Linkages to Ecosystem Functioning in the Inner Mongolia Grassland

Background Livestock grazing is the most prevalent land use of grasslands worldwide. The effects of grazing on plant C, N, P contents and stoichiometry across hierarchical levels, however, have rarely been studied; particularly whether the effects are mediated by resource availability and the underpinning mechanisms remain largely unclear. Methodology/Principal Findings Using a multi-organization-level approach, we examined the effects of grazing on the C, N, and P contents and stoichiometry in plant tissues (leaves and roots) and linkages to ecosystem functioning across three vegetation types (meadow, meadow steppe, and typical steppe) in the Inner Mongolia grassland, China. Our results showed that the effects of grazing on the C, N, and P contents and stoichiometry in leaves and roots differed substantially among vegetation types and across different hierarchical levels (species, functional group, and vegetation type levels). The magnitude of positive effects of grazing on leaf N and P contents increased progressively along the hierarchy of organizational levels in the meadow, whereas its negative effect on leaf N content decreased considerably along hierarchical levels in both the typical and meadow steppes. Grazing increased N and P allocation to aboveground in the meadow, while greater N and P allocation to belowground was found in the typical and meadow steppes. The differences in soil properties, plant trait-based resource use strategies, tolerance or defense strategies to grazing, and shifts in functional group composition are likely to be the key mechanisms for the observed patterns among vegetation types. Conclusions/Significance Our findings suggest that the enhanced vegetation-type-level N contents by grazing and species compensatory feedbacks may be insufficient to prevent widespread declines in primary productivity in the Inner Mongolia grassland. Hence, it is essential to reduce the currently high stocking rates and restore the vast degraded steppes for sustainable development of arid and semiarid grasslands.

Foliar δ13C values of nine dominant species in the Loess Plateau of China

The foliar stable carbon isotope compositions (δ13C) of nine dominant species in seven sites, Yangling, Yongshou, Tongchuan, Fuxian, Ansai, Mizhi, and Shenmu, standing from the south to the north in the Loess Plateau of China were studied. The results showed that foliar δ13C values ranged from −22.61 to −30.73 ‰ with an average of −27.23 ‰ in 141 C3 plant samples collected from the Loess Plateau. Foliar δ13C values varied significantly (p<0.001) among the nine C3 species, which were Pinus tabulaeformis Carr., Robinia pseudoacacia L., Zizyphus jujuba Mill. var. spinosus Hu., Rubus parvifolius L., Hippophae rhamnoides L., Caragana korshinskii Kom., Lespedeza davurica (Laxm.) Schindl., Artemisia sacrorum Ledeb. var. incana Mattf., and Agropyron cristatum Gaertn. Comparatively, R. pseudoacacia, H. rhamnoides, and C. korshinskii had much higher δ13C values than the other six species, while A. sacrorum had the lowest δ13C value. There was no significant difference in foliar δ13C value among five species, P. tabulaeformis, Z. jujuba, R. parvifolius, L. davurica, and A. cristatum. Considering the life forms categorized from nine C3 species, trees and shrubs had significantly higher δ13C values than herbs (p<0.001). The deciduous tree R. pseudoacacia had much higher δ13C value than the evergreen tree P. tabulaeformis (p<0.01). Among the four shrubs, foliar δ13C values in H. rhamnoides and C. korshinskii were markedly higher (p<0.01) than those in Z. jujuba and R. parvifolius. Among the three herbs, L. davurica and A. cristatum had significantly higher δ13C values than A. sacrorum (p<0.01). Leguminous species such as R. pseudoacacia, C. korshinskii, and L. davurica as well as a non-leguminous species with nitrogen-fixation capacity, H. rhamnoides, had higher δ13C values than other non-leguminous species with same life-form. The mean δ13C value increased by about 7 % from Yangling in the south to Shenmu in the north as climatic drought increased, and foliar δ13C values differed much (p<0.001) among the seven sites. For nine species in the Loess Plateau, foliar δ13C values were significantly and negatively (p<0.001) correlated with the mean annual precipitation, moreover, an increase of 100 mm in annual precipitation would result in a decrease of 1.2 ‰ in δ13C value.

Functional trait responses to grazing are mediated by soil moisture and plant functional group identity

Abundant evidence has shown that grazing alters plant functional traits, community structure and ecosystem functioning of grasslands. Few studies, however, have tested how plant responses to grazing are mediated by resource availability and plant functional group identity. We examined the effects of grazing on functional traits across a broad range of species along a soil moisture gradient in Inner Mongolia grassland. Our results showed that trait syndromes of plant size (individual biomass) and shoot growth (leaf N content and leaf density) distinguished plant species responses to grazing. The effects of grazing on functional traits were mediated by soil moisture and dependent on functional group identity. For most species, grazing decreased plant height but increased leaf N and specific leaf area (SLA) along the moisture gradient. Grazing enhanced the community-weighted attributes (leaf NCWM and SLACWM), which were triggered mainly by the positive trait responses of annuals and biennials and perennial grasses, and increased relative abundance of perennial forbs. Our results suggest that grazing-induced species turnover and increased intraspecific trait variability are two drivers for the observed changes in community weighted attributes. The dominant perennial bunchgrasses exhibited mixed tolerance–resistance strategies to grazing and mixed acquisitive–conservative strategies in resource utilization.

Testing the scaling effects and mechanisms of N‐induced biodiversity loss: evidence from a decade‐long grassland experiment

Summary 1. Although extensive studies demonstrate that nitrogen (N) enrichment frequently reduces plant diversity within small quadrats (0.5– 4m 2 ), only a few studies have evaluated N effects on biodiversity across different spatial scales. 2. We conducted the first experimental test of the scale dependence of N effects on species richness from a 10-year N treatment (1.75–28 g N m � 2 year � 1 ) in a typical steppe. We used species–area relationship (SAR) to analyse the scale dependence of species loss with power model S = cA z (S is species number, A is area, c is intercept, and z is slope). 3. Absolute species loss decreased at sampling area > 8 m 2 . Proportional species loss (compared to control) decreased and critical threshold (Ncrit) for biodiversity losses increased with sampling areas. 4. These scale dependences were quantified as increasing slope (z-value) of SAR with N addition. Through SAR decomposition, we found that this overall positive effect was in response to positive effects of changes to the species abundance distribution over negative effects of overall species richness losses. 5. Synthesis. As nitrogen (N) enrichment typically occurs at scales much larger than individual plots, understanding how N enrichment affects the scaling patterns of biodiversity is necessary for biodiversity conservation and ecosystem management in response to anthropogenic N deposition.

Relationship between delta C-13 and photosynthetic parameters and their responses to leaf nitrogen content in six broadleaf tree species

Stable carbon isotope composition (δ13C), net photosynthetic rate (PN), actual quantum yield of photosystem 2 (PS2) electron transport (ΦPS2), nitrogen content (Nc), and photosynthetic nitrogen use efficiency (PNUE) in the leaves of six broadleaf tree species were determined under field environmental conditions. The six tree species were Magnolia liliflora Desr., M. grandiflora Linn., M. denudata Desr., Prunus mume (Sieb.) Sieb. et Zucc. cv. Meiren Men, P. mume (Sieb.) Sieb. et Zucc. f. alphandii (Carr.) Rehd., and P. persica (L.) Batsch. var. rubro-plena. The relationships among δ13C, ΦPS2, PN, and PNUE, as well as their responses to Nc in the six species were also studied. Both PN and δ13C negatively correlated with Nc, but ΦPS2 positively correlated with Nc. This indicated that with Nc increase, PN and δ13C decreased, while ΦPS2 increased. There were weak negative correlations between δ13C and PNUE, and strong negative correlations (p<0.01) between ΦPS2 and PNUE. According to the variance analysis of parameters, there existed significant interspecific differences (p<0.001) of δ13C, PN, ΦPS2, PNUE, and Nc among the tree seedlings of the six tree species, which suggests that the potential photosynthetic capacities depend on plant species, irradiance, and water use capacity under field conditions.

Changes of stomatal parameters of four typical species in the Loess Plateau of China over the last century

Abstract The variation and correlations of the stomatal densities, lengths, widths, areas in four C3 species of the Loess Plateau from 1930s to 2002 were studied. The response of stomatal density to climatic change differed among the four species. Over the years from 1930s to 2002, the stomatal density did not change in Quercus liaotungensis, rising only by 1.32%, and slightly decreased by 9.79% in Ostryopsis davidiana. However, the stomatal density decreased significantly by 27.86% and 46.85% in Zizyphus jujuba var. spinosa and Sophora viciifolia, respectively. The influences of climatic change on other stomatal parameters were also species-specific. The stomatal length, width, and area varied more significantly in Zizyphus jujuba var. spinosa than in Quercus liaotungensis and Ostryopsis davidiana over the last century. The correlation analysis among the stomatal parameters of the three species showed that there were positive correlations among the stomatal length, width and area, but there were negative correlations between the stomatal length, width, area and density.