Relationship of macrophyte-mediated changes in the water column to periphyton composition and abundance

SUMMARY. 1. Dense growths of Myriophyllum heterophyllum influenced temperature, dissolved oxygen, pH and light levels in the littoral waters of Lake Winnipesaukee, a soft-water. New England lake. Periphyton species composition and abundance (algal units cm' stem) were related to the macrophyte-mediated changes in the physicochemical environment.
2. Duringearlysummer, M. heterophyllum occupied onlythe lower part of the water column. Limnetic and littoral waters exchanged readily and were chemically similar. Early summer periphyton species composition was dominated by diatoms from the phytoplankton, entangled in the finely dissected leaves of M. heterophyllum.
3. By mid-summer, M. heterophyllum occupied the entire watercolumn of the littoral zone. The metabolic and photosynthetic activity and dense foliage of M. heterophyllum created marked vertical gradients in physicochemical conditions. Mid-day temperature, dissolved oxygen, pH and light levels were maximal in the surface waters of the M. heterophyllum mat during the summer. Concurrently, periphyton species composition shifted to blue-green and then to a filamentous green alga on the apex and mid-stem. On the lower stem, diatoms consistently dominated the periphyton.
4. Periphyton abundance on the apex was inversely related to apical elongation. Temporal fluctuations of periphyton abundance on the lower and mid-stem were small throughout the study. Periphyton abundance was lowest on the lower stem, where the deteriorating leaves provided less surface area for colonization.     

Localisation of coconut foliar decay virus in coconut palm

Coconut foliar decay virus (CFDV) occurs at a very low concentration in coconut palm. A 1203 nucleotide segment of the sequenced encapsidated circular single-stranded 1291 nucleotide CFDV-DNA has been amplified and transcribed for use as a ³²P cDNA probe for the virus. A rapid method for the extraction of DNA from coconut palm has been devised for a dot-blot hybridisation assay using this probe. An alternative non-radioactive probe has also been developed for future use in CFDV diagnosis. CFDV-DNA was shown to be distributed unevenly in a range of infected palms, necessitating the use of multiple sampling to reliably detect infection in diagnostic tests. Viral DNA was detected in symptomatic and asymptomatic palms of both high and low susceptibility, in disease-free tolerant cultivars, and in palms in remission from disease. Within the same palm, detectability of viral DNA varied little within leaflets, but varied more within and between fronds. CFDV-DNA was detected 6–8 months after insect-mediated inoculation, and symptoms generally appeared after another 1–4 months. In situ hybridisation of rachis tissue showed localisation of DNA within the phloem, but its distribution in the phloem was uneven. CFDV-DNA was detected in tissue adjacent to and within necrotic zones which develop into the petiolar lesions associated with the disease-specific collapse of fronds. Virus was detected in the body of the insect vector, and, where its distribution could be resolved, in the abdomen rather than the head.     

A novel method for collection and preservation of faeces for genetic studies

Quantitative and qualitative measurements of DNA were used to compare faecal sample storage in ethanol and silica with a novel method (two‐step) in which samples are soaked in ethanol and then desiccated with silica. Silica‐preserved samples had the lowest DNA concentrations. The two‐step method yielded significantly more DNA in high quality samples (average DNA concentrations > 100 pg/µL with all storage methods). However, for lower quality samples, the ethanol and two‐step methods performed similarly. The amounts and rates of sample degradation were not strongly affected by storage method and neither was the percentage of target DNA (< 1%) obtained from the samples.     

Leaf phenology in 22 North American tree species during the 21st century

Recent shifts in phenology are the best documented biological response to current anthropogenic climate change, yet remain poorly understood from a functional point of view. Prevailing analyses are phenomenological and approximate, only correlating temperature records to imprecise records of phenological events. To advance our understanding of phenological responses to climate change, we developed, calibrated, and validated process-based models of leaf unfolding for 22 North American tree species. Using daily meteorological data predicted by two scenarios (A2: +3.2 °C and B2: +1 °C) from the HadCM3 GCM, we predicted and compared range-wide shifts of leaf unfolding in the 20th and 21st centuries for each species. Model predictions suggest that climate change will affect leaf phenology in almost all species studied, with an average advancement during the 21st century of 5.0 days in the A2 scenario and 9.2 days in the B2 scenario. Our model also suggests that lack of sufficient chilling temperatures to break bud dormancy will decrease the rate of advancement in leaf unfolding date during the 21st century for many species. Some temperate species may even have years with abnormal budburst due to insufficient chilling. Species fell into two groups based on their sensitivity to climate change: (1) species that consistently had a greater advance in their leaf unfolding date with increasing latitude and (2) species in which the advance in leaf unfolding differed from the center to the northern vs. southern margins of their range. At the interspecific level, we predicted that early-leafing species tended to show a greater advance in leaf unfolding date than late-leafing species; and that species with larger ranges tend to show stronger phenological changes. These predicted changes in phenology have significant implications for the frost susceptibility of species, their interspecific relationships, and their distributional shifts.