Haltbarkeit von Silagen und die sie beeinflussenden Faktoren

Content of p‐coumaric (PCA) and ferulic (FA) acid was determined by the HPLC method in fourteen forbs with a potential utilization as forages (range of nutrient content per kg DM: 100 to 244gCP, 339 to 528 g NDF and 180–369 g ADF. PCA and FA were determined after methanol extraction in four fractions: free phenolic acids extracted into ether, ester‐bound phenolic acids after alkaline hydrolysis, glycoside‐bound phenolic acids after acid hydrolysis, and cell wall‐bound phenolic acids after alkaline hydrolysis of the solid residue after the extraction with methanol.

Cell wall‐bound phenols were quantitatively the most important fraction (50% of total PCA and 47% of total FA, respectively). The differences among plant species in total PCA plus FA content were significant (F‐value 775, P < 0.01). The range of total phenol content was 31.3 to 416.3 mg/100g DM, the overall mean was 84 mg/100g DM.

Content of phenolic acids was correlated neither with ADF, NDF or ADL content (R ² = 1–3%, P > 0.05) nor with CP degradability (R ² = 3% and R ² = 1% for PCA and FA, respectively, P > 0.05).

95.4% and 30.9% of total PCA, and 98.3% and 72.5% of total FA disappeared in the rumen from the sample of Glechoma hederacea (species with the highest phenol content) and from the sample of Galium aparine (species with low phenol content), respectively, within the four hour incubation interval.

It is presumed that in comparison with grasses, PCA and FA concentration in tested forbs represents a much lower risk in potential ruminant nutrition.     

Response of aboveground grassland biomass and soil moisture to moderate long-term CO2 enrichment

Rising atmospheric CO₂ concentrations may alter C cycling and community composition, however, long-term studies in (semi-)natural ecosystems are still rare. In May 1998, the Giessen FACE (Free Air Carbon dioxide Enrichment) experiment started in a grassland ecosystem near Giessen, Germany, consisting of three enrichment (E plots) and three ambient control rings (A plots). Carbon dioxide concentrations were raised to +20% above ambient all-year-round during daylight hours. The wet grassland (Arrhenatheretum elatioris Br.-Bl.; not ploughed for >100 years) has been fertilized with 40 kg ha⁻¹ yr⁻¹ N, and mown two times each year for decades. Since 1993, the biomass has been monitored and since 1997 it was divided into grasses, legumes and non-leguminous forbs.During the 5 years prior to CO₂ enrichment, the annual biomass yield from the A plots was non-significantly higher (3%) than the later E plots yield. Under CO₂ enrichment, the biomass increased significantly from the third enrichment year on by 9.8%, 7.7% and 11.2% in the years 2000–2002, respectively. The increase was surprisingly high considering the moderate CO₂ enrichment regime of only +20% and sub-optimal N supply, possibly suggesting a non-linear response of temperate grassland ecosystems to rising atmospheric CO₂ levels.The leaf area index did not change significantly under elevated CO₂, nor did the soil moisture in the top 15 cm increase. No correlation existed between the magnitude of the yield stimulation under elevated CO₂ and the precipitation sums preceding the respective harvests. The grass biomass increased significantly under FACE, while the forb biomass declined strongly in the fourth and fifth year. The legume fraction was mostly below 1% of the total yield, and did not respond to CO₂ enrichment. These findings are in contrast to other grassland results and possible reasons are discussed.     

Effects of ambient UV-B radiation on the above-ground biomass of seven temperate-zone plant species

Variations in the amount of solar ultraviolet-B radiation (UV-B) reaching the biosphere may alter productivity in non-agricultural plants. We examined how ambient levels of UV-B modify the biomass of seven temperate-zone species including three grass species (Echinochloa crusgalli, Setaria faberi, Elymus virginicus), three forbs (Verbascum blattaria, Lactuca biennis, Oenothera parviflora), and one tree species (Quercus rubra). Plants were grown outside in enclosures near Morgantown, WV, USA (39° N, 79° W) for one season under near-ambient or no UV-B conditions. The different levels of UV-B were achieved using filters which differentially transmit UV-B irradiance. There was a trend towards reduced above-ground biomass in L. biennis (14%) and significantly increased above-ground biomass in O. parviflora (10.2%) under ambient UV-B. The partitioning of biomass between individual plant parts was altered by ambient UV-B in O. parviflora. Leaf biomass was significantly increased (18%), and there were trends toward increased stem (6.7%) and reproductive (9%) biomass. In addition to biomass stimulations, O. parviflora grew significantly taller (5.3%) under ambient UV-B. This study provides evidence that some non-agricultural plants exhibit species-specific growth responses to variable UV-B, with short-lived forbs appearing to be the most sensitive. If the biomass and morphological alterations observed for the forbs in this study were to persist over several years, they might modify population dynamics, competitive interactions, and productivity in ecosystems as UV-B levels fluctuate in the future.     

Determinants of C3 forb growth and production in a C4 dominated grassland

Forbs are the most abundant species within the vascular flora of tallgrass prairie and they make the greatest contribution to biodiversity of all growth forms. However, little is known about the factors that determine their productivity and growth rates. The objective of this study was to assess the controls of forb growth (absolute and relative) and production in tallgrass prairie from a long-term burning experiment at the Konza Prairie in NE Kansas. Over the 14-year study, forbs comprised 9% of the total biomass production on sites with a high fire frequency vs. 29% on the low fire frequency site, with gramminoids accounting for the remainder. Although interannual variations in peak biomass of the grasses was strongly correlated with environmental variables related to water availability, there were no similar relationships for forbs, suggesting that production of forbs and grasses responded to interannual variations in climate in different ways. Multivariate analysis of climatic controls on growth rates of grasses and forbs yielded similar results. Although forbs had low biomass and absolute growth per unit ground area in frequently burned prairie, their relative growth rates were highest in such sites. Thus, it appears that reduced growth rates of individual forbs per se do not limit forb success in annually burned prairie. Instead, direct negative effects of fire on forbs (increased mortality) may be responsible. Determinants of forb growth and productivity in unburned prairie remain unresolved.     

Granivory reduces biomass and lignin concentrations of plant tissue during grassland assembly

Small mammals can influence grassland assembly by selecting against palatable plants – the community can become dominated by the plants they avoid. This predation-based selection could have indirect effects on community biomass and tissue quality, especially given how untasty plants may have higher concentrations of recalcitrant carbon compounds including lignin. We tested small mammal effects on biomass and tissue quality of roots and shoots in a two-year-old 18 ha restored tallgrass prairie with established zones of high and low plant predation. We focused on the three dominant herbaceous functional groups of tallgrass prairie (perennial forbs, C₃ and C₄ grasses), and targeted the early stages of assembly given that plant predation by small animals can unfold quickly and is difficult to subsequently quantify. We predicted rodent predation to create communities with reduced biomass but an increased abundance of lignin-rich plants; we only observed the former. Rodents reduced aboveground biomass by 46% but preferentially targeted lignin-rich plants, with the latter result explained by the predominance of granivory over herbivory – there was no opportunity for selection based on tissue palatability. Based strictly on aboveground biomass, we estimated small mammals reduced standing stocks of recalcitrant carbon by 65 kg ha⁻¹, with reductions in belowground stocks almost certainly higher given that root:shoot ratios averaged 21:1. Given that the quantity and quality of plant production can affect ecosystem functions including decomposition and the regulation of soil carbon stocks, our work suggests that non-random plant predation may substantially affect rates of soil carbon accumulation in the early stages of grassland development.     

Root plasticity of native and invasive Great Basin species in response to soil nitrogen heterogeneity

Soil nutrients are heterogeneously distributed in natural systems. While many species respond to this heterogeneity through root system plasticity, little is known about how the magnitude of these responses may vary between native and invasive species. We quantified root morphological and physiological plasticity of co-occurring native and invasive Great Basin species in response to soil nitrogen heterogeneity and determined if trade-offs exist between these foraging responses and species relative growth rate or root system biomass. The nine study species included three perennial bunchgrasses, three perennial forbs, and three invasive perennial forbs. The plants were grown in large pots outdoors. Once a week for 4 weeks equal amounts of ¹⁵NH₄ ¹⁵NO₃ were distributed in the soil either evenly through the soil profile, in four patches, or in two patches. All species acquired more N in patches compared to when N was applied evenly through the soil profile. None of the species increased root length density in enriched patches compared to control patches but all species increased root N uptake rate in enriched patches. There was a positive relationship between N uptake rate, relative growth rate, and root system biomass. Path analysis indicated that these positive interrelationships among traits could provide one explanation of how invasive forbs were able to capture 2 and 15-fold more N from enriched patches compared to the native grasses and forbs, respectively. Results from this pot study suggest that plant traits related to nutrient capture in heterogeneous soil environments may be positively correlated which could potentially promote size-asymmetric competition belowground and facilitate the spread of invasive species. However, field experiments with plants in different neighbor environments ultimately are needed to determine if these positive relationships among traits influence competitive ability and invader success.     

Effects of aqueous smoke solutions and heat on seed germination of herbaceous species of the Sudanian savanna-woodland in Burkina Faso

Smoke generated by burning of plant materials has widely been recognized as a germination cue for some species from both fire prone and fire-free ecosystems. It is an important factor for the understanding of vegetation dynamics and could have potential use for ecological management and rehabilitation of disturbed areas. Individual species, however, seem to have a specific requirement for the type and dosage of smoke treatments. In the present study, six different concentrations of smoke solution were tested on 13 herbaceous species by soaking the seeds for 24 h. The germination of a forb species, Borreria scabra, was significantly stimulated (p<0.05) by the smoke treatment while that of the annual grass species, Euclasta condylotricha, was significantly inhibited (p<0.05) by 100% smoke solution treatment. Contrary to our expectation that another fire-related cue, heat shock, would break the physical dormancy of the species tested, it was not promotive. For non-dormant seeds of B. scabra and Borreria radiata, high temperatures were lethal while low temperature induced physiological dormancy that was overcome in the former species within 30 days of the germination trial. For some species, responses to smoke did not corroborate with the field-observed response to fire, making ecological interpretation challenging. For responsive species, the smoke treatment could be a simple approach for promoting their re-establishment in areas where it is needed. More investigations are needed to assess the spread of response to smoke.