Dormición y tipo de suelo como determinantes de la germinación y establecimiento de Chloris berroi en la Pampa Deprimida

75-80En los pastizales halófitos de la Pampa Deprimida la historia pastoril habría inducido deterioros en la diversidad florísticos y propiedades edáficas. La recuperación de las especies nativas de alto valor forrajero constituye una valiosa estrategia para la regeneración forrajera del sistema. Ello requiere un profundo conocimiento de los aspectos ecológicos de estas especies que, en el caso de Chloris berroi, nativa y potencial regeneradora de ambientes degradados, es desconocida. En este trabajo evaluamos dos hipótesis: (1) la dormición de C. berroi se debe a las estructuras que recubren la cariópside e inhiben su germinación durante un cierto período después de la cosecha y (2) el establecimiento de plántulas de C. berroi es afectado por el tipo de suelo. Realizamos dos ensayos: uno evaluó el efecto de la remoción de glumas y glumelas sobre la germinación en semillas de C. berroi con dos tiempos de almacenamiento (2 y 8 meses) y sembradas sobre tres suelos distintos (dos Natracualf típicos de estepa de halófitas contiguas pero con diferentes historias en el manejo del pastoreo (continuo-rotativo) y un Argiudol Vértico de una pradera húmeda de mesófitas con pastoreo rotativo). El segundo evaluó la capacidad de establecimiento de la especie sobre cada suelo. La remoción de la cubierta seminal promovió significativamente la germinación solo en las semillas de menor tiempo de almacenamiento. El tipo de suelo no afectó la germinación, en tanto, el establecimiento de plántulas se redujo significativamente sobre el Natracualf bajo pastoreo continuo. Los resultados sugieren que efectivamente las cubiertas seminales inducirían dormición por algunos meses (menor 8). El pastoreo rotativo favorecería la preservación de C berroi en las comunidades halófitas y su ausencia en las comunidades vegetales correspondiente a suelos Argiudol vértico no respondería a cuestiones edáficas

Arbustos de la estepa patagónica : ¿adaptados a tolerar la sequía o el pastoreo?

61-70Features that confer plants tolerance to drought also provide tolerance to herbivory. Therefore, even the plants of arid zones with a short grazing history would be tolerant to herbivory. Evolutionary history of grazing in central and northwest Patagonian steppes has been considered brief and dominant spiny shrubs have been considered adapted to tolerate drought. Here, we present experimental evidences that question that conceptual model. (1) The three most conspicuous shrubs in the dominant community at south-western Chubut (Mulinum spinosum, Adesmia volckmanni and Senecio filaginoides) are not subjected to severe water stress conditions because their roots explore deep soil layers with relatively high water potentials almost all year. That is reflected in high leaf water potential, high isotopic discrimination against heavy carbon isotope and low response to rainfall. (2) Instead, the three shrubs show evasion herbivory strategies. M. spinosum and A. volckmanni have very aggressive thorns, while S. filaginoides has a high content of carbon-based secondary metabolites. These chemical compounds are believed to have an anti-herbivory role. Besides that, in two of these three species, levels of physical or chemical defences were increased under grazing conditions. (3) Finally, as defensive strategies do not preclude herbivore consumption in absolute terms, shrubs are important components of sheep diet. Sheeps eat leaves of non-chemically defended species and flowers of all of them. These evidences suggest that grazing pressure of native herbivores would have been high and persistent enough to promote natural selection processes that conducted to dominance of grazing resistant shrub genotypes

Nitrogen and Carbon Isotopic Dynamics of Subarctic Soils and Plants in Southern Yukon Territory and its Implications for Paleoecological and Paleodietary Studies

We examine here the carbon and nitrogen isotopic compositions of bulk soils (8 topsoil and 7 subsoils, including two soil profiles) and five different plant parts of 79 C3 plants from two main functional groups: herbs and shrubs/subshrubs, from 18 different locations in grasslands of southern Yukon Territory, Canada (eastern shoreline of Kluane Lake and Whitehorse area). The Kluane Lake region in particular has been identified previously as an analogue for Late Pleistocene eastern Beringia. All topsoils have higher average total nitrogen δ15N and organic carbon δ13C than plants from the same sites with a positive shift occurring with depth in two soil profiles analyzed. All plants analyzed have an average whole plant δ13C of −27.5 ± 1.2 ‰ and foliar δ13C of ±28.0 ± 1.3 ‰, and average whole plant δ15N of −0.3 ± 2.2 ‰ and foliar δ15N of ±0.6 ± 2.7 ‰. Plants analyzed here showed relatively smaller variability in δ13C than δ15N. Their average δ13C after suitable corrections for the Suess effect should be suitable as baseline for interpreting diets of Late Pleistocene herbivores that lived in eastern Beringia. Water availability, nitrogen availability, spacial differences and intra-plant variability are important controls on δ15N of herbaceous plants in the study area. The wider range of δ15N, the more numerous factors that affect nitrogen isotopic composition and their likely differences in the past, however, limit use of the modern N isotopic baseline for vegetation in paleodietary models for such ecosystems. That said, the positive correlation between foliar δ15N and N content shown for the modern plants could support use of plant δ15N as an index for plant N content and therefore forage quality. The modern N isotopic baseline cannot be applied directly to the past, but it is prerequisite to future efforts to detect shifts in N cycling and forage quality since the Late Pleistocene through comparison with fossil plants from the same region

Range assessment using remote sensing in Northwest Patagonia (Argentina)

A methodology based on remotely sensed data (LANDSAT MSS) was used for rapid assessment of rangelands in the grass and shrub steppes of NW Patagonia (Argentina). We calibrated Normalized Difference Vegetation Index (NDVI) data using total plant cover, grass cover, shrub cover, and floristic data. Total vegetation cover and grass cover was predicted with high accuracy from Normalized Difference Vegetation Index data. The correlation between observed and estimated cover was 0.87 and 0.82 (P < 0.01) for total cover and grass cover respectively. The correlation was lower for shrub cover than for grass (r = 0.45, p < 0 .01). Normalized Difference Vegetation Index data was used to accurately predict cover of Festuca pallescens (St. Yves) Parodi (coiron blanco) and Nassau via glomerulosa (Lag.) Don (colapiche), 2 species with contrasting response to grazing in the Occidental district of Patagonia, and typical of vegetation with very different grazing values. The correlation between observed and estimated from the Normalized Difference Vegetation Index cover was 0.67 and 0.53 (P < 0.01) for Festuca pallescens (coiron blanco) and Nassauvia glomerulosa (colapiche) respectively.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202