Effects of grazing on photosynthetic characteristics of major steppe species in the Xilin River Basin, Inner Mongolia, China

Abstract

Species composition and photosynthetic characteristics of dominant species of ungrazed plot (UG), overgrazed plot (OG), and restored grazed plot (RG) were determined in the Xilin River Basin, Inner Mongolia, China. Both heavily grazing and restoration significantly affected the composition of different species and life forms. Leymus chinensis, Stipa grandis, and Cleistogenes polyphylla, three dominant perennial grasses in UG plot, contributed 58.9 % aboveground biomass to that of whole community, and showed higher net photosynthetic rate (P N ), transpiration rate (E), and intrinsic water-use efficiency (WUE). In OG plot, relative biomass of L. chinensis and S. grandis significantly decreased, while relative biomass of three shrubs/sub-shrubs, Caragana microphylla, Artemisia frigida, and Kochia prostrata, obviously increased. Heavy grazing significantly decreased P N , E, and WUE of L. chinensis and S. grandis, while shrubs/subshrubs showed significantly higher photosynthetic activity and WUE than the grasses. After 18-year restoration, photosynthetic activities of L. chinensis and S. grandis were significantly higher than those in the OG plot. The proportion of L. chinensis, S. grandis, and C. microphylla significantly increased, and relative biomass of C. polyphylla, A. frigida, and K. prostrata markedly declined in RG plot. We found close relationships between physiological properties of species and their competitive advantage in different land use types. Higher photosynthetic capability means more contribution to total biomass. The variations in physiological characteristics of plants could partly explain the changes in species composition during degrading and restoring processes of Inner Mongolia typical steppes.

Dependence of Co2 Flux on the Key Abiotic and Biotic Parameters in Semi-Natural Grasslands Either Traditionally Grazed or Excluded From Grazing

“…Stronger and positive correlation is measured in grassland excluded from grazing while in case of the grazed area the correlation is low and negative from the aspect of carbon fixation. The extent of regression is stronger in the not grazed grassland (R 2 = 0.204), however in contrast to the results of Chen et al (2005) based on leaf-level measurements the stand level ET values fluctuated in similar range as data measured in the grazed grassland. The somewhat surprising negative correlation of the grazed stand is the result of a few outliers.…”

“…In case of CO 2 flux examinations typically leaf-level measurements have been made. These latter studies showed the higher net photosynthesis and transpiration of species excluded from grazing (Chen et al, 2005).…”

Effects of exclosure on aboveground biomass, vegetation constitution, and midday gross primary productivity in semi-arid Mongolian steppe

“…It is well known that S. collina and K. scoparia prefer disturbed areas (Commissione Redactorum Florae Intramongolicae, 1990). An exclosure study in Inner Mongolia demonstrated that the AGB of C. squarrosa was larger in a grazed plot than in a nongrazed plot (Chen et al, 2005). These studies may explain the increased ratio of C4 AGB to total AGB in the GA in the KBU steppe.…”

“…However, although the aboveground biomass (AGB) inside an exclosure is enhanced, the protected vegetation has lower species diversity than the grazed vegetation because of selective feeding and trampling of grasses outside the exclosure (Tessier et al, 2003;Chen et al, 2005;Pei et al, 2008).…”

Promoting seedling physiological performance and early establishment in degraded Mediterranean-type ecosystems

“…Physiological measurements can be used to monitor direct responses to restoration treatments and hence provide a powerful tool for the evaluation of restoration efforts (Cooke and Suski 2008). Leaf gas-exchange and leaf water potentials provide sensitive indicators of changes in plant water and carbon relations associated with restoration treatments (Chen et al 2005 ).…”