Premise of research. The soil seed bank (SSB) plays a critical role in vegetation regeneration after stress and/or disturbance events. Here, we analyzed how drought and grazing influence the SSB of ...shrub patches and interpatches in a rangeland from northern Patagonia.
Methodology. Soil samples were collected from shrub patches and interpatches on heavily grazed, moderately grazed, and ungrazed sites at the end of a multiyear drought and 2 yr after the end of the drought. Sampling was done immediately before seed dispersion of the dominant species in order to study the persistent seed bank. Seeds were separated from the mineral soil by elutriation and grouped into four life-forms: annual grasses, perennial grasses, forbs, and shrubs.
Pivotal results. In all sampling conditions, the SSB was markedly dominated by forbs. Total seed density and seed density of every life-form were higher in shrub patches than in interpatches. Seed density of grasses and shrubs was not influenced by drought and grazing in both shrub patches and interpatches. In contrast, seed density of forbs was negatively influenced by drought in interpatches and positively influenced by grazing in shrub patches.
Conclusions. The results suggest that in patchy rangelands of northern Patagonia the SSB of shrub patches is less severely depleted than that of interpatches during multiyear droughts, particularly for forbs under high grazing intensity. However, the growth of the SSB after drought is a slow process in both shrub patches and interpatches. Our results highlight the importance of grazing pressure alleviation during drought conditions to safeguard the SSB, which is the only source of seedling recruitment for most species in northern Patagonia rangelands.
Abstract
Adequate drinking water is essential to maintain acceptable production levels in beef cattle operations. In the context of global climate change, the water scarcity forecasted for the future ...is a growing concern and it would determine an increase in the use of poorer quality water by the agricultural sector in many parts of the world. However, consumption of high-salt water by cattle has consequences often overlooked. A meta-analysis was carried out to assess the impact of utilizing high-salt water on dry matter (DMI) and water intake (WI), and performance in beef cattle. The dataset was collected from 25 studies, which were conducted between 1960 and 2020. Within the dataset, the water quality was divided into three categories according to the ratio of sulfates (SO4) or sodium chloride (NaCl) to total dissolved solids (TDS): 1) TDS = all studies included (average SO4:TDS = 0.4); 2) NaCl = considered studies in which water salinity was dominated by NaCl (average SO4:TDS = 0.1); and 3) SO4 = considered studies in which water salinity was dominated by SO4 (average SO4:TDS = 0.8). Results showed that DMI and WI were negatively affected by high-salt water consumption, although the magnitude of the effect is dependent on the type of salt dissolved in the water. There was a quadratic effect (P < 0.01) for the WI vs. TDS, WI vs. NaCl, DMI vs. TDS, and DMI vs. NaCl, and a linear effect (P < 0.01) for WI vs. SO4 and WI vs. SO4. Average daily gain (ADG) and feed efficiency (FE) were quadratically (P < 0.01) affected by high-salt water, respectively. This study revealed significant negative effects of high-salt water drinking on beef cattle WI, DMI, and performance. However, the negative effects are exacerbated when cattle drink high-sulfate water when compared with high-chloride water. To the best of our knowledge, this is the first approach to evaluate animal response to high-salt water consumption and could be included in the development of future beef cattle models to account for the impact of water quality on intake and performance. In addition, this meta-analysis highlights the need for research on management strategies to mitigate the negative effects of high-salt water in cattle.
Unpalatable forage resources (low nutrient density, potentially toxic metabolites) are widespread and represent a challenge for ruminant nutrition, health, and welfare. Our objective was to ...synthesize the role of biophysical and social experience on the use of unpalatable forages by ruminants, and highlight derived behavioural solutions for the well-being of soils, plants, and animals. Environmental experiences early in life modulate gene expression and promote learning, which alters morpho-physiological and psychological mechanisms that modify behavioural responses and change food and habitat selection. In this process, ruminants can become better adapted to the habitat where they are reared. Moreover, experiential learning provides flexibility in diet selection, which is critical for changing foraging environments. Learned associations between unpalatable and palatable foods, if ingested in appropriate amounts, sequence, and close temporal association, induce the development of preference for the former type of food. In this way, a more uniform use of resources can be achieved from the landscape level down to the individual plant, with the associated benefits to ecosystem integrity and stability. Ruminants can also learn the medicinal benefits of ingesting foods with toxins (e.g., condensed tannins and saponins with antiparasitic properties). This knowledge on behavioural processes can be translated into behavioural applications that provide low-cost solutions to many challenges that producers face in managing sustainable livestock production systems.
Pasture-based production systems represent a significant sustainable supplier of animal source foods worldwide. For such systems, mounting evidence highlights the importance of plant diversity on the ...proper functioning of soils, plants and animals. A diversity of forages and biochemicals –primary and secondary compounds- at appropriate doses and sequences of ingestion, may lead to benefits to the animal and their environment that are greater than grazing monocultures and the isolated effects of single chemicals. Here we review the importance of plant and phytochemical diversity on animal nutrition, welfare, health, and environmental impact while exploring some novel ideas about pasture design and management based on the biochemical complexity of traditional and non-traditional forage sources. Such effort will require an integration and synthesis on the morphology, ecophysiology, and biochemistry of traditional and non-traditional forage species, as well as on the foraging behavior of livestock grazing diverse pasturelands. Thus, the challenge ahead entails selecting the “right” species combination, spatial aggregation, distribution and management of the forage resource such that productivity and stability of plant communities and ecological services provided by grazing are enhanced. We conclude that there is strong experimental support for replacing simple traditional agricultural pastures of reduced phytochemical diversity with multiple arrays of complementary forage species that enable ruminants to select a diet in benefit of their nutrition, health and welfare, whilst reducing the negative environmental impacts caused by livestock production systems.
Land use has changed the original composition of the natural grasslands in the dry pampas of central Argentina, to the detriment of palatable perennial grasses (PPG). Long-term elimination of ...anthropogenic disturbances has not been enough to effectively recover the PPG, which suggests that availability of seeds and/or habitats may be limiting their recruitment. Therefore, our objectives in a degraded grassland site were to assess: (1) the germinable soil seed bank and (2) changes in botanical composition after addition of PPG seed following canopy disturbance. In autumn 2015, we randomly selected 10-paired plots, measured the aboveground biomass and took soil samples to assess the germinable soil seed bank. Afterwards, we disturbed the resident vegetation in each paired plot and either added PPG seeds or left the plot without any seed addition as a control. We quantified the seedling density of seeded and spontaneous species in the spring of 2015 and 2016, and the aboveground biomass at the end of 2017. Annual grasses and forbs (AGFS) dominated the soil seed bank, while PPG and unpalatable perennial grasses (UPG) occurred at low seed density and richness. Addition of PPG seeds resulted in the successful establishment of one key seeded PPG (Poa ligularis). In the spring 2017, the aerial biomass of PPG was highest in the seeded plots, where P. ligularis accounted for 94%. Our results showed that PPG were poorly represented in the soil seed bank of the degraded grassland and that disturbance of the resident vegetation combined with PPG seed addition enabled successful recruitment of a key PPG. So, enhancement of the pastoral value of degraded dry pampas grasslands would be possible through disturbance of the resident vegetation and addition of PPG seed.
La producción ganadera extensiva en la Patagonia Sur se realiza sobre cuadros de pastoreo de gran superficie, escasa receptividad animal y fragilidad ambiental elevada. El manejo histórico del ...pastoreo, desde fines del siglo XIX, causó la desertificación del paisaje en gran parte del territorio. Diferentes esfuerzos institucionales buscaron mejorar el manejo de los pastizales a través de adecuar la carga animal en los cuadros. No obstante, la heterogeneidad del paisaje dentro de éstos permite que los animales se concentren en los lugares que más prefieren. En este contexto, el desarrollo de recomendaciones técnicas para controlar el pastoreo heterogéneo requiere un conocimiento actualizado de la percepción de los productores frente a esta problemática. Por ello, se llevó adelante una encuesta a 82 productores ganaderos extensivos de Santa Cruz con el objetivo de caracterizar el manejo que realizan en los cuadros de pastoreo, los criterios para su diseño y su visión sobre el problema del pastoreo heterogéneo. Un porcentaje alto de productores (~75%) detecta la problemática, pero sólo 8.3% de ellos aplica más de 2 tecnologías para enfrentarla. En su conjunto, los productores muestran conocer una gran variedad de tecnologías. Sin embargo, los entrevistados señalaron diversas limitantes que determinan que las tecnologías no se consoliden como prácticas de uso común. El sistema extensivo de producción en la Patagonia Sur se sigue llevando adelante mayormente bajo un esquema de mínima intervención del paisaje, tal como en sus inicios. Es posible que sea necesario revisar el sistema de transferencia tecnológica desde las instituciones de investigación y extensión, pero también es imprescindible que el Estado participe diseñando e implementando políticas orientadas a proveer instrumentos idóneos para incentivar, promover, apoyar y monitorear la adopción de tecnología.
Background and Aims Phytolith reference collections are a prerequisite for accurate interpretation of soil phytolith assemblages aimed at reconstructing past vegetation. In this study a phytolith ...reference collection has been developed for several grasses native to central Argentina: Poa ligularis, Piptochaetium napostaense, Stipa clarazii, Stipa tenuis, Stipa tenuissima, Stipa eriostachya, Stipa ambigua, Stipa brachychaeta, Pappophorum subbulbosum, Digitaria californica. Bothriochloa edwardsiana and Aristida subulata. Methods For each species, phytoliths present in the leaf blades were classified into 47 morphotypes, and their relative frequency determined by observing 300-400 phytoliths per sample (n = 5). Data were analyzed by complete linkage cluster analysis, using the Morisita Index as measure of association. Key Results The results showed differentiation among phytolith assemblages at species level or at plant functional type level. Cluster analysis separated C3 from C4 species and palatable from non-palatable species. Conclusions This study highlights the possibility of reconstructing past vegetation in central Argentina grasslands through the analysis of soil phytolith assemblages.
Abstract This study determined whether early experiences by sheep to monotonous or diverse diets influence: (1) plasmatic profiles of cortisol, a hormone involved in stress responses by mammals, ...before and after an ACTH challenge, (2) the readiness to eat new foods in a new environment, (3) general fearfulness and response to separation – as measured by the open field test (OFT) and stress induced hyperthermia (SIH) – and (4) the link between (2) and (3). Thirty, 2-mo-old lambs were randomly assigned to 3 treatments (10 lambs/treatment). Lambs in one treatment (Diversity — DV) received in successive periods of exposure all possible 4-way choice combinations of 2 foods high in energy and 2 foods high in protein from an array of 6 foods: 3 high in energy (beet pulp, oat grain, and a mix of grape pomace:milo 40:60) and 3 high in protein (soybean meal, alfalfa, corn gluten meal). Lambs in another treatment (DV+T) received the same exposure described for DV but two phytochemicals, oxalic acid (1.5%) and quebracho tannins (10%) were randomly added within any period of exposure to foods high in energy or to foods high in protein. Lambs in the third treatment (Monotony — MO) received a monotonous balanced ration containing all 6 foods fed to the other groups. After exposure, lambs were offered a choice of the aforementioned 6 foods (DV; DV+T) or the monotonous diet (MO). Lambs were intravenously injected with ACTH 1 h after food presentation, and sampled at 1, 2, and 3 h post feeding for determinations of plasma cortisol concentrations. Reluctance to eat novel flavored foods (onion-, coconut- and cinnamon-flavored wheat bran), open field behavior, and SIH was assessed in all treatments. Lambs in MO showed greater concentrations of plasma cortisol 1 h after food presentation than lambs in the DV or DV+T treatments (P = 0.04). However, the difference was small and no differences among treatments were detected after an ACTH challenge (P > 0.1). Lambs in DV consumed more onion-flavored wheat bran than lambs in MO (P = 0.05). Lambs in DV also showed a greater cumulative consumption of novel flavors on d 2 than lambs in MO (treatment × day; P = 0.01). Lambs in DV showed lower increase in rectal temperature (P = 0.07) than lambs in MO. Only lambs in DV exhibited a positive relationship between consumption of cinnamon-flavored wheat bran and attempts of escape (R2 = 0.58; P = 0.02). Our results suggest that exposure to diverse foods early in life may be less stressful than exposure to monotonous rations, as measured by plasma cortisol concentrations after food ingestion, and by changes in rectal temperature after exposure to the OFT. Lambs exposed to diverse diets early in life may also increase the initial acceptance of new flavors in novel environments relative to lambs exposed early in life to monotonous diets.
Background: The occurrence of shrub patches, alternating with either bare soil or low herbaceous cover, is a common feature in arid and semi-arid shrublands throughout the world. This patchy pattern ...of vegetation may result from water limitation, modulated by plant interactions; grazing (offtake and tramping) by livestock may cause further patchiness vegetation structure.
Aims: We hypothesised that vegetation patchiness in the semi-arid shrublands of north-eastern Patagonia would be increased by livestock grazing, but not by positive interactions between adult plants of shrubs and grasses.
Methods: We compared vegetation cover and pattern at three grazing intensities (exclosure, light and heavy grazing) and measured the growth of a representative shrub and grass in the presence and absence of the other to quantify the role of plant-to-plant interactions and its interaction with grazing for vegetation structure.
Results: In the grazing exclosure and in moderately grazed areas, vegetation cover among shrub patches was larger, whereas the top cover of shrubs was lower than in the heavily grazed areas. We did not find any evidence of positive interactions between shrub and grass life forms.
Conclusions: Our results were consistent with the hypothesis that livestock grazing increased the formation of patchy vegetation cover in arid and semi-arid shrublands.
One of the potential mechanisms for the impact of herbivores on nutrient cycling is the effect of selective grazing on litter quality through changes in species composition. However, the scarce ...evidence collected on this mechanism is controversial and seemingly influenced by site-specific variables. In this paper, we explored the consequences of grazing-induced changes in species composition on litter quality and nitrogen cycling with a regional perspective. Along a 900-mm of mean annual rainfall gradient, we selected species promoted and diminished by grazing from three natural rangelands of Argentina, analyzed their litter quality, and determined their decomposition and nutrient release kinetics under common greenhouse conditions. Litter quality and decomposition rates were strongly associated with plant response to grazing. However, the magnitude and direction of these differences depended on the ecosystem considered. In the wettest site, the species promoted by grazing (forbs) had higher nitrogen and phosphorus contents, faster decomposition rates, and higher release of nitrogen to the soil than species diminished by grazing ( C3 and C4 grasses). In the intermediate and dry sites, species promoted by grazing had lower nitrogen and phosphorus contents, and slower decomposition rates than those diminished by grazing ( C3 grasses in both cases). Decomposition of the entire group of species was not correlated with mean annual rainfall, but when litter of the species diminished by grazing was analyzed, it was negatively correlated with precipitation. Nitrogen was immobilized more often than mineralized, even after one year of incubation. Immobilization was negatively correlated with precipitation. All these results indicate that grazing may significantly alter nutrient cycling by affecting litter quality through changes in species composition. These effects seem to be larger when species replacements induced by grazing either involve functional groups, as it was the case in our wettest site, or change root to shoot ratios. Therefore, the functional groups involved in the replacement of species as well as shifts between belowground and aboveground allocation should play a key role in grazing-induced changes on nitrogen cycling.
PDF
