Heteropogon Contortus Research Articles

Elevated carbon dioxide and fire reduce biomass of native grass species when grown in competition with invasive exotic grasses in a savanna experimental system

Invasive exotic grasses are known to increase fire severity and frequency in a number of fire prone systems. If elevated atmospheric carbon dioxide (CO2) increases growth rates and biomass production of these grasses, or increases their competitive ability, fire regimes may be further affected with detrimental consequences for native vegetation composition and diversity. Mesocosms containing three invasive exotic C4 grasses (Andropogon gayanus, Cenchrus polystachios, Cenchrus ciliaris), and three native C4 grasses (Heteropogon triticeus, Heteropogon contortus, Eriachne triseta), all from savanna woodlands of northern Australia, were grown as mixtures in field soil in glasshouses under elevated (700 ppm) and ambient (385 ppm) CO2, burnt and assessed for resprouting response. We found no effect of elevated CO2 on community biomass, however biomass of the invasive exotic grasses was much greater than that of native grasses at both CO2 concentrations. Species’ responses to elevated CO2 were varied. Two native grasses (H. triticeus and H. contortus) had significantly less biomass under elevated compared with ambient CO2 after burning, indicating an effect of elevated CO2 on resprouting response of these species when grown in competition. These results suggest that although overall productivity of this community may not change with increases in CO2 and fire frequency, community composition and species interactions in this fire-prone community may alter, shifting to a more exotic-dominated community and potentially resulting in an intensified fire frequency due to positive feedbacks.

Urocystis skirgielloi, a new graminicolous smut fungus infecting Heteropogon contortus in India

<em>Urocystis skirgielloi</em> M. Piątek sp. nov. is described and illustrated on the basis of infected leaves of <em>Heteropogon contortus</em> (L.) Roem. & Schult. collected in India. This is the first <em>Urocystis</em> species on the grass genus <em>Heteropogon</em> as well as on any grass genera belonging to the subtribe <em>Anthistiriinae</em> of the tribe <em>Andropogoneae</em> (<em>Poaceae</em>).

Effects of vegetation restoration types on soil quality in Yuanmou dry-hot valley, China

Soil erosion has resulted in serious land degradation in Yuanmou dry-hot valley, Yunnan province, China. Vegetation restoration had been widely developed in this hot and arid area. In this work we investigate the quality of rhizosphere soils under four restoration species in the towns of Zuolin (gully bed) and Yuanma (slope area). The vegetation included two trees [Leucaena leucocephala (Lam.) de Wit. and Eucalyptus camaldulensis L.] for the slope area, one shrubland [Dodonaea viscosa (Linn.) Jacq. Enum.] and one native, natural grassland [Heteropogon contortus (L.) Beauv.] for gully bed. Soil physical (bulk density and soil moisture content), chemical [pH, soil organic matter, nitrogen (N), phosphorus (P) and potassium (K) contents], and microbial (microbial biomass and microbe quantity) properties and soil enzyme (catalase, protease and urease) activities were determined. Compared to the soils collected from other vegetation types, the soil under Leucaena leucocephala had the highest content of soil organic matter, total N, available N, total P, available P, available K, microbial biomass carbon (C), and the highest microbe quantity and enzyme activities. Five parameters (organic matter, pH, microbial biomass N, total K and protease activity), which had the greatest weight in the principal components analysis, were selected to calculate the soil quality index (SQI). The final SQI values implied that restoring Leucaena leucocephala greatly improved the soil quality, while restoration with Eucalyptus camaldulensis decreased the soil quality of the slope area. Plant recovery with Dodonaea viscosa and Heteropogon contortus on the gully bed affected the population of soil microbial communities but didn't improve the SQI values. It can therefore be seen that types of plants used for recovery in gully-developed regions in dry-hot valleys must be chosen cautiously: Leucaena leucocephala is a good choice for soil revegetation of the slope area, but the revegetation patterns on the gully bed still need further study.

Nutritive Value of Grasses in Semi-arid Rangelands of Ethiopia: Local Experience Based Herbage Preference Evaluation versus Laboratory Analysis.

We examined the nutritive value of common grass species in the semi-arid rangelands of Borana in southern Ethiopia using local experience based herbage preference (LEBHP) perception and laboratory techniques. Local pastoralists in the study area were asked to identify common grass species and rank them according to the species’ preferences and palatability to cattle. The pastoralists listed a total of 15 common grass species which were then sampled during the main rain and cold dry seasons and analyzed for crude protein (CP), Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF) and ash content to verify pastoralists’ claim regarding the quality of individual species. The relative feed value (RFV) and dry matter digestibility (DMD) were also calculated using NDF and ADF contents. Spearman’s rank correlation was used to examine possible relationships between laboratory results and pastoralists’ experience on grass quality. Cenchrus ciliaris, Chrysopogon aucheri, Digitaria milanjiana, Eragrostis papposa and Panicum maximum were the top five species based on LEBHP perception. There were indications of inconsistency in terms of LEBHP perception among the different pastoral communities. The chemical composition of all grass species showed significant (p<0.05) variation between sites, seasons and species. The results showed that the CP values for the Borana rangelands were in the range of 8.7% in the main rain season to 5.1% for the cold dry season. The fiber constituents were relatively low in the main rain season compared to the cold dry season. Overall, Digitaria milanjiana had the highest CP (16.5%) content, while the least was recorded with Heteropogon contortus (10.8) and Aristida adoensis (9.8%) during the main rain season. It seems that the spatial variability of landscapes within the wider geographical regions, soil properties and texture, and land-use patterns probably contributed to site differences in species quality. Generally, the RFV of individual grass species was significantly (p<0.05) varied between and within sites. The ranking of species by pastoralists according to their preferences by cattle was highly correlated with the chemical composition of laboratory results of individual grass species with ‘r’ values for CP (0.94), ash (0.95), NDF (−0.98), ADF (−0.93) and ADL (−0.93). We suggest the complimentary use of LEBHP and laboratory techniques in evaluating the nutritive quality of rangeland forage species for sustainable animal production.

Long‐distance dispersal of Black Spear Grass (Heteropogon contortus) seed on socks and trouser legs by walkers in Kakadu National Park

SummaryHumans can contribute to the long‐distance dispersal of many plants, including weeds. We assessed the distance for which seed remained attached to the socks and trouser legs of walkers. The experiment in Kakadu National Park, Australia used seed of the Australian native Black Spear Grass (Heteropogon contortus) as a surrogate for the potential dispersal of weed seed. Two models were fitted to the data, with a double exponential model fitting the data slightly better than a power exponential model. Although 19% of seed were dispersed within the first 5 m of walking, most (55%) seed remained attached to socks and trousers at 5 km. Humans may, therefore, unintentionally carry and eventually disperse this grass and other invasive grasses with similar long awns and pointed seeds over long distances. Implementing strategies to reduce the potential for seed to attach to walkers (gaiters) and reduce potential dispersal (removal and careful disposal of seed) would reduce the risks posed by this type of human‐mediated seed dispersal.

Diversity of Arbuscular Mycorrhizal Fungal Spores Present in the Rhizospheric Soil of Four Different Grasses in Gujarat, India

Arbuscular mycorrhizal fungi are the most important members of soil microbial community in ecosystem. These useful organisms form an indespensible component of any fertile soil. It is said that a good quality of 1 kg soil is almost equal to 1 kg of gold. Symbiotic relationships of AMF provide an alternative for survival of plants in highly stressed areas, this association helps in uptake of P as well as other minerals, maintain better water balance, increase plant biomass and produce growth promoting substances. Strategies to promote plantation in poor or degraded soil includes introduction of native AMF in soil. During present study a survey was undertaken in degraded forest areas with certain grasses in Godhra and Baria divisions, 115 kms from Vadodara city in India. Rhizospheric soil samples were collected from 22 different places. Soil samples of Heteropogon contortus showed more number of AM spores (220/100 g) as compared to that of Themeda triandra 165/100 g. Kalitalai soil samples Chloris barbata showed more number of spores (150/100 g) than that of Rampara (110/100 g). The percentage occurence of AM spores was more in Bandheli. Analysis of AM spores resulted in identification of different species belonging to three genera i.e. Glomus, Gigaspora, and Acaulospora.

Native plant diversity in tropical savannas decreases when exotic pasture grass cover increases

The invasion of exotic plants into savanna ecosystems can disrupt the natural pattern of vegetation. Indian couch Bothriochloa pertusa was introduced into Australia as a species for rehabilitation of degraded grazing land. In this study the effect of increasing B. pertusa cover on native plant diversity and possible mechanisms of its spread were examined. Forty sites were sampled in uncleared Queensland rangelands with a range of B. pertusa and Bothriochloa ewartiana (a native species) cover. The mean number of native species per quadrat declined with increasing B. pertusa cover but remained stable over sites with increasing B. ewartiana cover. Mean species richness accumulated at a significantly lower rate for sites with B. pertusa present. Canonical analysis of principle coordinates suggested that three groups of sites, ranging from low to high species richness and cover of native plants, were correlated along gradients of B. pertusa cover, grazing intensity and basal area of dead trees. Generalised linear modelling indicated significant negative relationships between B. pertusa cover and total ground cover, forbs and perennial grass richness and cover, and cover of nine native perennial tussock grasses (Aristida leptopoda, B. decipiens, B. ewartiana, Chrysopogon fallax, Dichanthium fecundum, D. sericeum, Heteropogon contortus, H. triticeus and Themeda triandra). This study suggests that an increase in B. pertusa is associated with a substantial change in the cover and species richness of native plant communities. This was considered to occur via competitive effects as well as a result of cattle grazing, rainfall deficit and tree death. Regardless of the mechanism, continued spread of exotic pasture species has the potential to cause significant changes to rangeland biodiversity.

Germination Responses of Several Poaceae Members towards Differential Storage Durations

Concerns over biodiversity loss and increasing biological invasion have forced interest on assessment of the effects on native plant species diversity in grassland community. To observe different patterns of grass emergence (dormancy/germination) in the warm tropical grasslands of India, time span of a seed from the seedling stage to a mature plant becomes very crucial for the community development. In the present study seed germination response of six dominant species of the selected study area were tested to record the various effects of dry storage conditions on seed germinability. The species selected were Apluda mutica L., Cenchrus ciliaris L., Chrysopogon fulvus (Spreng.) Chiov., Dichanthium annulatum (Forsk.) Stapf., Heteropogon contortus (L.) P. Beauv. ex Roem. and Schult. and Themeda triandra (R. Br.) Stapf. For this purpose, seed collection at mature seed stage, seed processing and dry seed storage were followed by the germination test system. Obtained results are exhibited in the form of different responses such as, species response patterns towards capacity for immediate germination, responses to dormancy, dry storage and temperature fluctuation. The extent of the requirement in breakage of primary dormancy was highly correlated with the timing of seed maturity, precursors of seed dormancy and seed viability. In present screening out of the six studied species Apluda mutica, Cenchrus ciliaris and Dichanthium annulatum showed dependable germination pattern to fluctuating temperature. The correlation between viability and germination suggests that the germination of Apluda mutica, Cenchrus ciliaris and Themeda triandra are linearly dependent on the viability that the seeds of these species have. As these species showed less influence with the relative fluctuating environment, they can be stored for longer period and frequently can be use for community regeneration in pasture development.

Managing for rainfall variability: impacts of grazing strategies on perennial grass dynamics in a dry tropical savanna

Rainfall variability remains a major challenge to sustainable grazing management in northern Australia with perennial grasses the key to the stability of the resources that maintain a sustainable grazing industry. This paper describes the dynamics of five perennial grasses – Bothriochloa ewartiana (Domin) C.E. Hubb., Chrysopogon fallax S.T. Blake, Aristida spp., Panicum effusum R. Br. and Heteropogon contortus (L.) P. Beauv. ex Roem. &amp; Schult. in relation to three grazing strategies – moderate stocking at long-term carrying capacity, heavy stocking and rotational wet season spelling. The research was conducted in permanent quadrats on the predominant land type in an extensive grazing study in an Aristida-Bothriochloa pasture in north Australia between 1998 and 2010. Summer rainfall was above average for two periods – 1998 – 2001 and 2008 – 2010 with drought and below-average rainfall from 2002 to 2007. Low rainfall affected the dynamics of all grasses by reducing survival and basal area through its effect on plant size; this impact was most noticeable for the shorter-lived Aristida spp., P. effusum and H. contortus. The impact of grazing was greatest on the long-lived B. ewartiana and C. fallax; this effect was accentuated by the 2002–07 drought. Heavy grazing during this period further reduced the survival and size of B. ewartiana in comparison with the moderate stocking and rotational spell treatments. In contrast, the survival of C. fallax was reduced in the moderate stocking and rotational spelling treatment during drought, relative to that under heavy grazing. The density of B. ewartiana declined even under moderate grazing and despite two sequences of above-average rainfall because seedling recruitment failed to offset mature plant death. Results from this study emphasised the importance of maintaining the existing populations of key long-lived species such as B. ewartiana through good management. These results also supported the overall findings from the grazing study indicating that stocking at the long-term carrying capacity is sustainable in managing for climate variability.

Herbaceous biomass, species composition and soil properties of keygrazing patches in coastal forest thornveld and two grassland types of theEastern Cape province, South Africa

In spite of predictions of communal rangeland collapse due to continuous grazing and increased livestock populations, this grazing system remains prevalent in communal areas, suggesting animals utilise heterogeneity found in these areas. A study was conducted to compare biomass and herbaceous species composition in patches frequently grazed by cattle to randomly selected control sites in three communal areas located in Lesotho Highland Basalt Grassland (Magwiji), Bhisho Thornveld (Mnyameni) and Tsomo Grassland (Cala). The relationship of vegetation parameters in frequently selected patches to the corresponding soil properties, topography and human impact was also examined. Biomass of frequently selected patches was significantly (p < 0.05) higher in the dry season (June) at Magwiji (528 kg ha−1) than in less frequently selected patches (130 kg ha−1). There was an association between sites selected in winter and soil organic carbon, and these sites were dominated by Cynodon dactylon and Pennisetum clandestinum. The floristic patterns observed in Magwiji were associated with soil organic carbon content. Low-lying swampy patches had high soil pH in Cala, while mountain top soils in Magwiji had low electrical conductivity and these areas selected in winter were associated with grass species such as Eragrostis superba and Heteropogon contortus.

Differences in drought sensitivities and photosynthetic limitations between co-occurring C3 and C4 (NADP-ME) Panicoid grasses.

The success of C4 plants lies in their ability to attain greater efficiencies of light, water and nitrogen use under high temperature, providing an advantage in arid, hot environments. However, C4 grasses are not necessarily less sensitive to drought than C3 grasses and are proposed to respond with greater metabolic limitations, while the C3 response is predominantly stomatal. The aims of this study were to compare the drought and recovery responses of co-occurring C3 and C4 NADP-ME grasses from the subfamily Panicoideae and to determine stomatal and metabolic contributions to the observed response. Six species of locally co-occurring grasses, C3) species Alloteropsis semialata subsp. eckloniana, Panicum aequinerve and Panicum ecklonii, and C4 (NADP-ME) species Heteropogon contortus, Themeda triandra and Tristachya leucothrix, were established in pots then subjected to a controlled drought followed by re-watering. Water potentials, leaf gas exchange and the response of photosynthetic rate to internal CO2 concentrations were determined on selected occasions during the drought and re-watering treatments and compared between species and photosynthetic types. Leaves of C4 species of grasses maintained their photosynthetic advantage until water deficits became severe, but lost their water-use advantage even under conditions of mild drought. Declining C4 photosynthesis with water deficit was mainly a consequence of metabolic limitations to CO2 assimilation, whereas, in the C3 species, stomatal limitations had a prevailing role in the drought-induced decrease in photosynthesis. The drought-sensitive metabolism of the C4 plants could explain the observed slower recovery of photosynthesis on re-watering, in comparison with C3 plants which recovered a greater proportion of photosynthesis through increased stomatal conductance. Within the Panicoid grasses, C4 (NADP-ME) species are metabolically more sensitive to drought than C3 species and recover more slowly from drought.

Impacts of grazing management options on pasture and animal productivity in a Heteropogon contortus (black speargrass) pasture in central Queensland. 1. Pasture yield and composition

An extensive grazing study was conducted between 1988 and 2001 in a Heteropogon contortus (black speargrass) pasture in central Queensland. The study was designed to measure the effects of stocking rate on native pasture, native pasture with legume oversown, and native pasture with animal diet supplement/spring burning on pasture and animal production. Summer rainfall throughout the study was below the long-term mean. Mean annual pasture utilisation ranged from 13% at 8 ha/steer up to 61% at 2 ha/steer. Increasing stocking rate treatments reduced total pasture yields while total yields in legume oversown treatments were similar to those in native pasture at the same stocking rate. When spring burning was possible, total yields were reduced in the subsequent autumn. Increasing stocking rate in native pasture tended to reduce H. contortus and Bothriochloa bladhii, increased the composition of intermediate species, such as B. decipiens and Chloris divaricata, and also changed the frequencies of a range of minor species. Oversowing legumes resulted in Stylosanthes scabra cv. Seca increasing from &lt;1% of pasture composition in 1988 to 50% in 2000 and was associated with a reduction in H. contortus and changes in the frequencies of some minor species. Stocking rates heavier than 4 ha/steer resulted in annual pasture utilisation greater than 30% and were unsustainable because they reduced total yield and resulted in undesirable changes in species composition. It was concluded that pasture production was sustainable when stocking rates were maintained at 4 ha/steer, which equates to 30% annual pasture utilisation, and through the judicious use of spring burning.

Impacts of grazing management options on pasture and animal productivity in a Heteropogon contortus (black speargrass) pasture in central Queensland. 4. Animal production

Steer liveweight gains were measured in an extensive grazing study conducted in a Heteropogon contortus (black speargrass) pasture in central Queensland between 1988 and 2001. Treatments included a range of stocking rates in native pastures, legume-oversown native pasture and animal diet supplement/spring‐burning pastures. Seasonal rainfall throughout this study was below the long-term mean. Mean annual pasture utilisation ranged from 13 to 61%. Annual liveweight gains per head in native pasture were highly variable among years and ranged from a low of 43 kg/steer at 2 ha/steer to a high of 182 kg/steer at 8 ha/steer. Annual liveweight gains were consistently highest at light stocking and decreased with increasing stocking rate. Annual liveweight gain per hectare increased linearly with stocking rate. These stocking rate trends were also evident in legume-oversown pastures although both the intercept and slope of the regressions for legume-oversown pastures were higher than that for native pasture. The highest annual liveweight gain for legume-oversown pasture was 221 kg/steer at 4 ha/steer. After 13 years, annual liveweight gain per unit area occurred at the heaviest stocking rate despite deleterious changes in the pasture. Across all years, the annual liveweight advantage for legume-oversown pastures was 37 kg/steer. Compared with native pasture, changes in annual liveweight gain with burning were variable. It was concluded that cattle productivity is sustainable when stocking rates are maintained at 4 ha/steer or lighter (equivalent to a utilisation rate around 30%). Although steer liveweight gain occurred at all stocking rates and economic returns were highest at heaviest stocking rates, stocking rates heavier than 4 ha/steer are unsustainable because of their long-term impact on pasture productivity.

Impacts of grazing management options on pasture and animal productivity in a Heteropogon contortus (black speargrass) pasture in central Queensland. 2. Population dynamics of Heteropogon contortus and Stylosanthes scabra cv. Seca

The dynamics of Heteropogon contortus and Stylosanthes scabra cv. Seca populations were studied in a subset of treatments in an extensive grazing study conducted in central Queensland between 1988 and 2001. These treatments were 4 stocking rates in native pasture and 2 of these stocking rates in legume oversown and supplement/spring burning treatments. For the 1999–2000 summer, population data for H. contortus in 5 of these native pasture and supplement/burning treatments were compared with those for an additional burnt treatment. Seasonal rainfall throughout this study was below the long-term mean and mean annual pasture utilisation ranged from 24 to 61%. Increasing stocking rate from 5 to 2 ha/steer in native pasture reduced H. contortus plant density. Increasing stocking rate reduced seedling recruitment as a result of its effect on soil seedbanks. Seedling recruitment was the major determinant of change in plant density, although some individual H. contortus plants did survive throughout the study. Burning in spring 1999, particularly at light stocking rate, promoted seedling recruitment above that in both unburnt native and legume oversown pasture and resulted in increased H. contortus plant density. In the legume oversown treatments, S. scabra cv. Seca density increased rapidly from 15 plants/m2 in 1988 to 140 plants/m2 in 2001 following a lag phase between 1988 and 1993. This increased S. scabra density was associated with an eventual decline in H. contortus plant density through reduced seedling recruitment. It was concluded that H. contortus population density is sustainable at stocking rates of 4 and 5 ha/steer (30% pasture utilisation) and that spring burning at light stocking rate can promote H. contortus populations. Increasing densities of S. scabra need to be managed to prevent its dominance.

Impacts of grazing management options on pasture and animal productivity in a Heteropogon contortus (black speargrass) pasture in central Queensland. 3. Diet composition in autumn

The diet selected in autumn by steers fistulated at the oesophageous was studied in a subset of treatments in an extensive grazing study conducted in a Heteropogon contortus pasture in central Queensland between 1988 and 2001. These treatments were a factorial array of three stocking rates (4, 3 and 2 ha/steer) and three pasture types (native pasture, legume-oversown native pasture and animal diet supplement/spring-burning native pasture). Seasonal rainfall throughout this study was below the long-term mean and mean annual pasture utilisation ranged from 30 to 61%. Steers consistently selected H. contortus with levels decreasing from 47 to 18% of the diet as stocking rate increased from 4 ha/steer to 2 ha/steer. Stylosanthes scabra cv. Seca was always selected in legume-oversown pastures with diet composition varying from 35 to 66% despite its plant density increasing from 7 to 65 plants/m2 and pasture composition from 20 to 50%. Steers also selected a diet containing Chrysopogon fallax, forbs and sedges in higher proportions than they were present in the pasture. Greater availability of the intermediate grasses Chloris divaricata and Eragrostis spp. was associated with increased stocking rates. Bothriochloa bladhii was seldom selected in the diet, especially when other palatable species were present in the pasture, despite B. bladhii often being the major contributor to total pasture yield. It was concluded that a stocking rate of 4 ha/steer will maintain the availability of H. contortus in the pasture.

Changes in soil characteristics and grass layer condition in relation to land management systems in the semi-arid savannas of Swaziland

The issue of sustainability and productivity of open communal rangelands compared to fenced rangelands is often subject to controversy. This study investigated differences in soil and grass layer variables between land management systems having high (communal land), low (government ranch) and medium (game reserve) stocking rates, and soil types (lithosol and vertisol or raw mineral). The results showed that differences in land management systems had caused considerable variations in most soil and vegetation variables. Soil from low or moderate stocking rate had highest K, Ca, P and N levels. Cenchrus ciliaris, Panicum maximum and Heteropogon contortus were most abundant in the low stocking rate, while annuals Tragus berteronianus and Aristida bipartita were most frequent on high stocking rate. There were differences in frequency of these species between soil types. Significant variations for most vegetation and soil variables between land management systems suggested grazing pressure differences might be the primary cause. This supports the equilibrium model, which stresses the importance of livestock density on the soil and vegetation dynamics.

Molecular diversity of arbuscular mycorrhizal fungi and their distribution patterns related to host-plants and habitats in a hot and arid ecosystem, southwest China

The communities of arbuscular mycorrhizal fungi (AMF) colonizing the roots of Bothriochloa pertusa, Cajanus cajan and Heteropogon contortus in a fallow land (FL) and an undisturbed land (UL) were characterized. The large subunit rDNA genes of AMF from roots were amplified and cloned. A total of 2353 clones were screened by restriction fragment length polymorphism, and 428 clones were subsequently sequenced. A total of 393 AMF sequences, which were grouped into 100 operational taxonomic units, were obtained. Phylogenetic analysis revealed that the AMF sequences belonged to Glomus, Acaulospora and Scutellospora, and that Glomus was the dominant genus. Of the 393 AMF sequences, 81% were novel. The diversity of AMF colonizing the same plant species was higher in the UL than in the FL, which confirmed strongly from the molecular evidence that soil disturbance reduced AMF population and species richness. The results revealed that AMF communities were significantly different among host-plant species and between the two habitats. The similarity of AMF communities colonizing different plant species within a habitat was higher than that of the same plant species from different habitats. The molecular evidence supported our previous hypothesis based on morphological analyses that AMF communities were more influenced by habitats compared with host preference.

Molecular diversity of arbuscular mycorrhizal fungi associated with two dominant xerophytes in a valley-type savanna, southwest China

The diversity of arbuscular mycorrhizal fungi (AMF) colonizing the roots and rhizosphere soils of Heteropogon contortus and Dodonaea viscose growing in a valley-type savanna, southwest China, were analyzed by the large subunit ribosomal RNA genes (LSU). A total of 547 AMF sequences were screened for establishment of four clone libraries. Phylogenetic analysis revealed that the sequences clustered in at least 8 discrete sequence groups, all belonging to the genus Glomus. Among the Glomus spp., Glo 1 (GlGr A) and Glo 7 (GlGr B) were the most common in all root and soil samples of the two xerophytes, accounting for 42% and 33% of all screened clones, respectively. The ∫-LIBSHUFF analysis revealed that the composition of AMF communities associated with the two xerophytic hosts varied greatly both in roots and their rhizosphere soils.

The horizontal barrier effect of stems on the foraging behaviour of cattle grazing five tropical grasses

The rate of nutrient intake (RNI) is a primary determinant of animal performance in grazing cattle and depends on both diet quality and instantaneous intake rate (IIR). In turn, diet quality and IIR are a function of the foraging behaviour of the animal (selectivity, bite mass and bite rate) and the characteristics of the sward. In this study we evaluated the effect of the stem density and the tensile resistance of stems on the foraging behaviour of cattle grazing tropical pasture species. The methodology involved the use of small sown microswards offered to tethered cattle. The experiment consisted of a factorial combination of five tropical grasses [ Bothriochloa pertusa (Bp), Chloris barbata (Cb), Chloris gayana (Cg), Cynodon dactylon (Cd) and Heteropogon contortus (Hc)] and three stem densities (0, 400 and 800 stems m − 2 ). Bp and Cd had stems of significantly lower tensile resistance (19 and 15 N respectively) (Group 1) than those of Cb, Cg and Hc (110, 211 and 167 N respectively) (Group 2). The steers avoided stems of Group 2 and thus, reduced bite area, bite mass, IIR and RNI as stem density increased. However, the animals did not avoid stems of Group 1 and there was no effect of stem density on any of the foraging behaviour variables when cattle grazed species in Group 1. These results confirm that RNI and plant part selection is closely associated with the tensile resistance of the stem.

Chemical composition and in vitro ruminal fermentation of selected grasses in the semiarid savannas of Swaziland

Little is known about the grass species type, composition and nutritive value in the semiarid savannas that sustain most of Swaziland's cattle population through the seven-month-long dry season. This study was conducted to investigate the nutritional characteristics of grasses collected from two grazing areas (Big Bend and Simunye), which differed mainly in soil types. Mature grass species were harvested and evaluated for chemical composition (organic matter, neutral detergent fibre [NDF], acid detergent fibre [ADF], crude protein [CP] and minerals) and in vitro ruminal fermentation (in vitro gas production, in vitro organic matter degradability and partitioning factors). The most common grass species in the Big Bend grazing area were Bothriochloa insculpta, Cenchrus ciliaris and Urochloa mosambicensis. In the Simunye grazing area the most common species were B. insculpta, U. mosambicensis, Heteropogon contortus, Panicum deustum and P. maximum. For grasses harvested from Simunye, the most (P < 0.05) degradable (532 mg g−1 dry matter) was B. insculpta, which also had the least fibre (597 g kg−1 NDF and 351 g kg−1 ADF) and the highest CP content (79.8 g kg−1). The most common grass species harvested from the Big Bend area did not differ (P > 0.05) in their Mg, P, Cu, Fe, Zn, CP and NDF content. However, U. mosambicensis had the highest (P < 0.05) ADF content. The least fermentation efficiency (partitioning factor = 2.2 mg degradable organic matter [DOM] ml−1 gas) was observed for U. mosambicensis as a result of low DOM coupled with high cumulative gas production. It was concluded that all the grasses investigated in this study show a deficit for Ca, P and protein. Therefore, supplementation is needed to ensure maximum forage utilisation and to satisfy nutrient requirements of ruminant livestock.