Climate change and cattle nutritional stress

Owing to the complex interactions among climate, plants, cattle grazing, and land management practices, the impacts of climate change on cattle have been hard to predict. Predicting future grassland ecosystem functioning relies on understanding how changes in climate alter the quantity of forage produced, but also forage quality. Plant protein, which is a function of plant nitrogen concentrations, and digestible energy limit the performance of herbivores when in short supply; moreover, deficiencies can be expensive to mitigate. To better understand how changes in temperature and precipitation would affect forage protein and energy availability, we analyzed over 21 000 measurements of cattle fecal chemistry acquired over 14 years in the continental US. Our analysis of patterns in forage quality among ecologically defined regions revealed that increasing temperature and declining precipitation decreased dietary crude protein and digestible organic matter for regions with continental climates. Within regions, quality also declined with increased temperature; however, the effects of precipitation were mixed. Any future increases in precipitation would be unlikely to compensate for the declines in forage quality that accompany projected temperature increases. As a result, cattle are likely to experience greater nutritional stress in the future. If these geographic patterns hold as a proxy for future climates, agriculture will require increased supplemental feeds or the consequence will be a decrease in livestock growth.     

Long-term studies at a benthic station off the coast of Northumberland

Biannual sampling (March and September) has been carried out over the period 1972 to 1985 at a muddy sand station, 55 m depth, with fauna belonging to the deeper offshore edge of Petersen's Amphiura filiformis community.During the period 1974 to 1980 the community exhibited a high degree of persistence stability. This stability was lost between 1980 and 1983, with rising total numbers and biomass and changes in species ranking. There is some evidence of a downward reversal between 1984–85.Evidence suggests that the principal stabilising process is density dependent mortality mediated by competition in a food limited environment. The principal destabilising process appears to be periodic fluctuations in the organic flux to the bottom. A secondary destabilising process is clearly concerned with fluctuating winter temperature. In competitive terms, cold winters favour increased survival in the dominant species at the expense of the lesser ranked species. This process is, however, more ephemeral and subject to adjustment within the time scale of a year.     

Tannin,nitrogen, and cell wall composition of green vs. senescent Douglas-fir foliage

Summary Tannin, cell wall, and nitrogen composition of green foliage and needle litter of similar-aged Douglas-fir (Pseudotsuga menziesii Mirb. Franco) from two stands differing in density and crown closure were compared. Trees in the closed-canopy stand had a lower basal area growth rate than those in the open-canopy stand. Stands did not differ in wood basal area/ha or forest floor C/N ratios, but the closed-canopy stand had a significantly larger accumulation of forest floor biomass and significantly higher levels of field-extractable nitrogen and nitrogen mineralization rates. Green foliage from trees in the closed-canopy stand had significantly lower nitrogen, astringency, and lignin contents, but higher cellulose concentration than trees in the open-canopy stand. These trends, inconsistent with the inverse relationship often observed between nitrogen and polyphenol contents of foliage, may result from differences in relative resource availability in the two stands. In contrast to green foliage, needle litter from the two stands had comparable contents of nitrogen, cellulose, and lignin, but astringency was significantly higher in litter from the closed-canopy stand. It is suggested that, within the constraints imposed by site conditions, evergreens may alter the tannin composition of senescing foliage, potentially affecting herbivory and decomposition differently.     

Potentiality of the cox1 gene in the taxonomic resolution of soil fungi

We explored the potential of the cox1 gene in the species resolution of soil fungi and compared it with the nuclear internal transcribed spacer (ITS) and small subunit (SSU)-rDNA. Conserved primers allowing the amplification of the fungal cox1 gene were designed, and a total of 47 isolates of Zygomycota and Ascomycota were investigated. The analysis revealed a lack of introns in >90% of the isolates. Comparison of the species of each of the six studied genera showed high interspecific sequence polymorphisms. Indeed, the average of nucleotide variations (4.2–11%) according to the genus, due mainly to the nucleotide substitutions, led to the taxonomic resolution of all the species studied regarding both ITS and SSU-rDNA, in which <88% were discriminated. The phylogenetic analysis performed after alignment of the cox1 gene across distant fungal species was in accordance with the well-known taxonomic position of the species studied and no overlap was observed between intra- and interspecific variations. These results clearly demonstrated that the cox1 sequences could provide good molecular markers for the determination of the species composition of environmental samples and constitute an important advance to study soil fungal biodiversity.     

Resistance of Anhydrobiotic Aphelenchus avenae to Methyl Bromide Fumigation

The effect of methyl bromide (MB) was tested on active and anhydrobiotic Aphelenchus avenae. A. avenae was induced into anhydrobiosis by three different techniques. Both active and anhydrobiotic nematodes were subjected to 3,000 μ1 MB/liter air for 14 periods from 0 to 82 h. Anhydrobiotic nematodes were more resistant to fumigation than active nematodes, regardless of the technique used to induce anhydrobiosis. The percent survival decreased with increasing MB exposures (μ1 MB × h). For an LD₉₅ of 45,000-54,000 μ1/1 × h were required for active nematodes and >279,000 μ1/1 × h for anhydrobiotic nematodes.     

Frequent,low‐amplitude disturbances drive high tree turnover rates on a remote,cyclone‐prone Polynesian island

Aim How important are frequent, low‐intensity disturbances to tree community dynamics of a cyclone‐prone forest? We tested the following hypotheses concerning the ‘inter‐cataclysm’ period on a remote Polynesian island: (1) tree turnover would be high and recruitment rates would be significantly higher than mortality; (2) low‐intensity disturbance would result in a marginal increase in tree mortality in the short term; (3) turnover would vary among species and would be associated with plant traits linked to differences in life history; and (4) mortality and recruitment events would be spatially non‐random. Location Tutuila, a volcanic island in the Samoan Archipelago, Polynesia. Methods We censused the tree (stem diameter ≥ 10 cm) community in 3.9 ha of tropical forest three times over a 10‐year period, 1998–2008. We calculated annual mortality, recruitment and turnover rates for 36 tree species. We tested for non‐random spatial patterns and predictors of mortality, and non‐random spatial patterns of tree recruitment. A 2004 cyclone passing within 400 km allowed us to measure the effects of a non‐cataclysmic disturbance on vital rates. Results Annual turnover was 2.8% and annual recruitment was 3.6%; these are some of the highest rates in the tropics, and likely to be a response to a cyclone that passed < 50 km from Tutuila in 1991. Species turnover rates over 10 years were negatively correlated with wood specific gravity, and positively correlated with annual stem diameter increment. Mortality was spatially aggregated, and a function of site, species and an individual’s growth rate. Recruitment was highest on ground with low slope. The low‐magnitude cyclone disturbance in 2004 defoliated 29% of all trees, but killed only 1.8% of trees immediately and increased annual mortality over 5 years by 0.7%. Main conclusions The inter‐cataclysm period on Tutuila is characterized by frequent, low‐amplitude disturbances that promote high rates of tree recruitment and create a dynamic, non‐equilibrium or disturbed island disequilibrium tree community. Species with low wood density and fast growth rates have enhanced opportunities for recruitment between cataclysms, but also higher probabilities of dying. Our results suggest that increases in the frequency of cyclone activity could shift relative abundances towards disturbance‐specialist species and new forest turnover rates.     

Role of plant parasitic nematodes and abiotic soil factors in growth heterogeneity of sugarcane on a sandy soil in South Africa

A feature of many sugarcane fields is the patchy growth. This is often thought to be due to physical or chemical differences in the soil. In this paper we investigate the causes of growth heterogeneity of sugarcane on a sandy soil in KwaZulu-Natal, South Africa. To identify the factors that were associated with the good and poor areas, soil texture, pH, organic matter content and a number of soil chemical elements and nematode community data were subjected to principal component analysis (PCA). The numbers of each of the nematode species (Meloidogyne sp., Pratylenchus zeae, Helicotylenchus dihystera, Xiphinema elongatum and Paratrichodorus sp.) were first converted to relative proportions of ectoparasites and endoparasites. The data were collected from the 2nd ratoon crop of a nematicide trial, where half of the plots had been treated with aldicarb in the preceding two crops. Yields of control plots varied from 34.7 to 126.8 t cane ha^–1 and from 85.4 to 138.7 for the treated plots. The yield data were centred and normalised separately for the treated and control plots and the values projected on the trial map to study spatial distribution. Plots with above-average yields, whether treated or untreated, occurred in the lower part of the trial site. The PCA factorial values were also projected onto the map of the trial. According to the first factor of the analysis of the abiotic soil characteristics in the 0–20 cm surface layer, the trial site could be divided into two areas, one on the left and one on the right. PCA of the soil data from the 0–20 and 20–40 cm layers showed that there was little or no difference between the two that might explain the two growth areas. However, analysis of the nematode community distinguished two main areas that largely corresponded to the distribution of the plots of low and high yielding cane. Correlation analysis confirmed the relationship between nematodes and yield. H. dihystera was positively correlated with yield of cane whereas the reverse was true for the Meloidogyne species.