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Resumen. La demanda de una mayor produccion bovina en la region del Caldenal en la zona centro de Argentina ha resultado en un sobrepastoreo continuo determinante de una estructura de la vegetacion en parches. Estos parches son claramente identificados en base a las especies dominantes resultantes de la historia de pastoreo. El objetivo principal del presente trabajo fue examinar la influencia de las plantas individuales sobre el patron multivariado de nutrientes del suelo en cada parche, evaluando asimismo la magnitud de la asociacion entre la concentracion de nutrientes en planta y suelo. El analisis discriminante canonico senalo a los contenidos de materia organica, fosforo disponible y zinc en el suelo como las variables de mayor impacto en la segregacion de los parches de vegetacion. El analisis de correlacion canonica entre las variables de suelo y planta indico una asociacion significativa entre ambos grupos (R2 0,97). Los parches con diferente historia de pastoreo pueden ser identificados no solo por las especies vegetales dominantes, sino tambien a traves del patron de atributos del suelo. Esta informacion puede contribuir al desarrollo de practicas de manejo orientadas a la recuperacion de los parches degradados por sobrepastoreo.

The effect of single-tree influence areas on the physicochemical properties of the soil surface mineral horizon (0–18 cm) was studied in three stands of Pinus radiata D. Don introduced into Sierra de la Ventana, Argentina, grasslands 50 yr ago. Soil samples were taken at distances of 0, 1, and 2 m in transects from the tree to the periphery of the crown. Adjacent grassland soils with mollic epipedons were used as controls. Soil alteration was found to be highest near the trunk, with clear evidence of acid hydrolysis of primary silicates; the epipedon close to the trunk was classified as umbric rather than mollic. Decreasing values of pH, Ca, and exchangeable Mg, and increasing values of exchangeable H and Al, and also of fulvic acid-complexed Al, were registered from the grassland toward the axes of the trees. The soil properties analyzed fall into a distinctive spatial pattern of radial symmetry around each individual tree, with systematic and predictable variations, thus confirming the validity of the concept of “single-tree influence circles” for the study area. Each stand of P. radiata generates a patch of soil alteration within the undisturbed habitat matrix; the internal structure of these patches shows a radial pattern of different polypedons spatially and genetically associated with the inner ring of bark litter and the outer ring of leaf and twig litter. The present work shows that the introduction of P. radiata triggered changes in the evolutionary trend of the soils of such magnitude as to be reflected at the highest taxonomic level in soil taxonomy.

[1] Black carbon (BC) is the product of incomplete burning processes and a significant component of the passive soil organic carbon (SOC) pool. The role of BC in the global carbon cycle is still unclear. This study aimed to quantify and characterize BC in major grassland ecosystems of the world. Twenty-eight representative soil profiles (mainly Mollisols) were sampled in the Russian Steppe, the U.S. Great Plains, the Argentinian Pampa, the Manchurian Plains in China, and the Chernozem region in central Germany. Black carbon contents were estimated using benzene polycarboxylic acids (BPCA) as a molecular marker, and indications about the origin of the BC were derived from bulk and compound-specific δ 13 C analyses and radiocarbon dating of bulk soil organic matter (SOM). Our findings suggest that between 5% and 30% of SOC stocks consist of BC. Maximum BC contributions to SOC frequently were found at deeper parts of the A horizon with 14 C ages younger than 7000 years BP; that is, incorporation of C as charred particles accompanied ecosystem development since the mid-Holocene. Most of this BC formed from local vegetation, as indicated by a 13 C isotope signature similar to that of bulk SOM. At some sites, also nonlocal sources contributed to soil BC, e.g., fossil fuel BC inputs at the German sites. Black carbon stocks were highest in Chernozems and lowest in Kastanozems. The Russian Steppe and Chinese Manchurian sites stored about 3-4 times more BC (around 3 kg m -2 ) than did the other sites because of thicker A horizons that were rich in BC. On a global scale, we estimate that steppe ecosystems contain between 4 and 17 Pg BC.

Zur Charakterisierung der Anteile von Lössen und Verwitterungsprodukten der liegenden Keuper- und Liasgesteine innerhalb kolluvialer Mischsedimente und holozäner Terrassenkörper erweisen sich in Oberfranken neben Korngrößenverteilungen insbesondere Quarz-Feldspat- und Albit-Mikroklin-Quotienten als geeignete Indizes. Danach sind an den untersuchten bodenerosiv überprägten Flachhängen bevorzugte Abtragung von Löß und Liegendmaterial an den Oberhängen, vorherrschender Durchtransport an den Mittelhängen und Ablagerung von Mischsedimenten an den Unterhängen zu erkennen. In den holozänen Sedimenten der Vorfluter sind Lößderivate demgegenüber nur gering vertreten, woraus auf vorherrschenden Durchtransport dieses Materials in den untersuchten Talstrecken und — im Vergleich mit niedersächsischen Beispielen entsprechender Größenordnung — auf eine regionale Differenzierung der holozänen fluvialen Dynamik geschlossen wird, die möglicherweise auf Unterschiede des Regionalklimas zurückzuführen ist., research