Micro-scale spatial heterogeneity and the loss of carbon, nitrogen and phosphorus in degraded grassland in Ordos Plateau, northwestern China

The micro-scale spatial distribution and loss of carbon, nitrogen and phosphorus were examined in degraded grassland near Ordos, in the Mu Us Sand-land, northwestern China. Five communities that represented a series of successionally degraded stages in desertification were chosen for the work. The dominant plant of Community 1 was the steppe grass Stipa bungeana; Community 2 was dominated by a mix of S. bungeana and the shrub Artemisia ordosia; Community 3 was A. ordosia; Community 4 was a mix of A. ordosia and the desert grass Cynanchum komorovii; and Community 5 was C. komorovii. The soils in root-spheres and in the bare openings between plants in five successionally degraded plant communities were analyzed for total organic carbon (TOC), total nitrogen (TN), inorganic nitrogen (IN), total phosphorus (TP), and available phosphorus (AP). The results showed that the heterogeneity process of the soil chemistry was characterized first by TOC heterogeneity and later by TN heterogeneity. The heterogeneity process of TP was only characterized in the community 3. No significant heterogeneity was present for AP in the five community stages. At the beginning of degradation, invasion by the shrub A. ordosia of S. bungeana grassland was found to lead to competition for soil elements between S. bungeana and A. ordosia and made the Community 2 soil environment temporarily homogeneous. In Community 3, however, the soil elements became spatially heterogeneous, and this led to the development of `islands of fertility'. The concentrations of soil elements (TOC, TN and IN) were greatest in the shrub root-spheres. With further desertification (from Community 4 to Community 5), the islands of fertility began to collapse, and the concentrations of the main soil elements declined rapidly. The dynamics of soil phosphorus under progressive desertification were different from those of the other soil elements. TP decreased from form Community 1 to Community 5, while the AP concentration did not change in mid-level desertification (Community 3), but increased with serious desertification (Community 5).

[1]  D. Schimel,et al.  Organic matter turnover in a sagebrush steppe landscape , 1989 .

[2]  D. W. Nelson,et al.  Total Nitrogen Analysis of Soil and Plant Tissues , 1980 .

[3]  D. Tongway,et al.  Small-scale resource heterogeneity in semi-arid landscapes , 1994 .

[4]  F. J. Barnes,et al.  Interrelationships between plant functional types and soil moisture heterogeneity for semiarid landscapes within the grassland/forest continuum: a unified conceptual model , 2004, Landscape Ecology.

[5]  Thomas L. Kieft,et al.  TEMPORAL DYNAMICS IN SOIL CARBON AND NITROGEN RESOURCES AT A GRASSLAND–SHRUBLAND ECOTONE , 1998 .

[6]  Moshe Shachak,et al.  Ecosystem Management of Desertified Shrublands in Israel , 1998, Ecosystems.

[7]  Nutrient losses in runoff from grassland and shrubland habitats in Southern New Mexico: I. rainfall simulation experiments , 1999 .

[8]  W. Schlesinger,et al.  Nutrient losses in runoff from grassland and shrubland habitats in Southern New Mexico: I. rainfall simulation experiments , 1999 .

[9]  N. West,et al.  Plant-Induced Soil Chemical Patterns in Some Shrub-Dominated Semi-Desert Ecosystems of Utah , 1975 .

[10]  Li Xinrong.  Study on shrub community diversity of Ordos Plateau, Inner Mongolia, Northern China , 2001 .

[11]  William H. Schlesinger,et al.  Desertification alters patterns of aboveground net primary production in Chihuahuan ecosystems , 2002 .

[12]  P. Greig-Smith,et al.  QUANTITATIVE PLANT ECOLOGY , 1959 .

[13]  Shirong Liu,et al.  The correlation between the desertification of grassland and the change of vegetation biomass in Erduosi , 2001 .

[14]  K. Gross,et al.  Spatial variation in nitrogen availability in three successional plant communities , 1995 .

[15]  Katherine L. Gross,et al.  8 – Assessing the Heterogeneity of Belowground Resources: Quantifying Pattern and Scale , 1994 .

[16]  J. Zak,et al.  Water and nitrogen effects on growth and allocation patterns of creosotebush in the northern Chihuahuan Desert. , 1988 .

[17]  W. Schlesinger,et al.  Nutrient losses in runoff from grasslandand shrubland habitats in southern New Mexico: II. Field plots , 2000 .

[18]  I. Burke,et al.  Heterogeneity of soil and plant N and C associated with individual plants and openings in North American shortgrass steppe , 1991, Plant and Soil.

[19]  J. A. Trofymow,et al.  A rapid accurate wet oxidation diffusion procedure for determining organic and inorganic carbon in plant and soil samples , 1984 .

[20]  W. Schlesinger,et al.  Plant regulation of soil nutrient distribution in the northern Chihuahuan Desert , 1999, Plant Ecology.

[21]  Júlia Seixas,et al.  Assessing heterogeneity from remote sensing images: The case of desertification in southern Portugal , 2000 .

[22]  Robert B. Jackson,et al.  Geostatistical Patterns of Soil Heterogeneity Around Individual Perennial Plants , 1993 .

[23]  N. West,et al.  Micro-patterns of nitrogen mineralization activity in soils of some shrub-dominated semi-desert ecosystems of Utah , 1977 .

[24]  Yosef Steinberger,et al.  A proposed mechanism for the formation of ‘Fertile Islands’ in the desert ecosystem , 1989 .

[25]  James D. Wickham,et al.  Desertification Evaluated Using an Integrated Environmental Assessment Model , 1997 .

[26]  William H. Schlesinger,et al.  ON THE SPATIAL PATTERN OF SOIL NUTRIENTS IN DESERT ECOSYSTEMS , 1995 .

[27]  J F Reynolds,et al.  Biological Feedbacks in Global Desertification , 1990, Science.

[28]  I. Burke.  Control of Nitrogen Mineralization a Sagebrush Steppe Landscape , 1989 .

[29]  R. B. Jackson,et al.  The Scale of Nutrient Heterogeneity Around Individual Plants and Its Quantification with Geostatistics , 1993 .

[30]  I. Burke,et al.  Plant-soil Interactions in Temperate Grasslands , 1998 .

[31]  G. Robertson,et al.  The spatial variability of soil resources following long-term disturbance , 1993, Oecologia.

[32]  G. Robertson,et al.  Spatial Variability in a Successional Plant Community: Patterns of Nitrogen Availability , 1988 .

[33]  J. H. Manwaring,et al.  Rapid physiological adjustment of roots to localized soil enrichment , 1990, Nature.