Increased soil stable nitrogen isotopic ratio following phosphorus enrichment: historical patterns and tests of two hypotheses in a phosphorus-limited wetland.

We used a P enrichment gradient in the Everglades to investigate patterns of the stable N isotopic ratio (delta(15)N) in peat profiles as an indicator of historic eutrophication of this wetland. We also tested two hypotheses to explain the effects of P on increased delta(15)N of organic matter including: (1) increased N mineralization/N loss, and (2) reduced isotopic discrimination during macrophyte N uptake. Spatial patterns of delta(15)N in surface litter and soil (0-10 cm) mimic those of the aboveground macrophytes (Typha domingensis Pers. and Cladium jamaicense Crantz). Peat profiles also show increased delta(15)N in the peat accumulated in areas near the historic P discharges since the early 1960s. The increased delta(15)N of bulk peat correlated well with both measured increases in soil total P and the historical beginning of nutrient discharges into this wetland. In 15-day bottle incubations of soil, added P had no effect on the delta(15)N of NH (4) (+) and significantly increased the delta(15)N of water-extractable organic N. Measurements of surface soils collected during a field mesocosm experiment also revealed no significant effect of P on delta(15)N even after 5 years of P addition. In contrast, delta(15)N of leaf and root tissues of hydroponically grown Typha and Cladium were shown to increase up to 12 per thousand when grown at elevated levels of P and fixed levels of N (as NH (4) (+) ). The magnitude of changes in delta(15)N resulting from altered discrimination during N uptake is significant compared with other mechanisms affecting plant delta(15)N, and suggests that this may be the dominant mechanism affecting delta(15)N of organic matter following P enrichment. The results of this study have implications for the interpretation of delta(15)N as an indicator of shifts in relative N limitation in wetland ecosystems, and also stress the importance of experimental validation in interpreting delta(15)N patterns.

Are sleep problems under-recognised in general practice?

AIMS: To evaluate the frequency of sleep problems in Australian children aged 4.5-16.5 years, and to determine whether the frequency of sleep problems on questionnaire predicts the reporting of sleep problems at consultation. METHODS: Parents of 361 children (aged 4.5-16.5 years) attending their general practitioner for "sick" visits were asked to assess their child's sleep over the previous six months using the Sleep Disturbance Scale for Children, from which six sleep "disorder" factors and a total sleep problem score were obtained. RESULTS: The percentage of children with a total sleep problem score indicative of clinical significance (T score >70 or >95th centile) was 24.6% (89/361). Despite this high frequency, parents only addressed sleep problems in 4.1% (13/317) of cases and reported that GPs discussed sleep problems in 7.9% (25/317) of cases. Of the 79 children who reported total sleep problem T scores in the clinical range, only 13.9% (11/79) discussed sleep with their general practitioner within the previous 12 months. Regression analyses revealed an age related decrease in problems with sleep-wake transition and sleep related obstructive breathing; sleep hyperhydrosis, initiating and maintaining sleep, and excessive daytime sleepiness did not significantly decrease with age. No significant gender differences were observed. CONCLUSIONS: Results suggest that chronic sleep problems in Australian children are significantly under-reported by parents during general practice consultations despite a relatively high frequency across all age groups. Given the impact on children and families, there is a need for increased awareness of children's sleep problems in the community and for these to be more actively addressed at consultation.

Design and performance of the Phyto-Nutri-Tron: a system for controlling the root and shoot environment for whole-plant ecophysiological studies.

A controlled environment system, termed the Phyto-Nutri-Tron (PNT), has been established to study whole plant ecophysiological responses to multiple environmental factors. The PNT is a computer-controlled highly flexible growth facility with independent control of the shoot and the root environment. The facility consists of two growth cabinets each containing four separate hydroponic growth systems. The growth cabinets can be used as assimilation chambers with individual control of temperature, humidity, light, CO2 and monitoring of O2. The hydroponic growth systems are connected to nutrient supply units with disinfection systems and individual control of temperature, pH and oxygen. The ionic composition of the solutions has automated feedback control through a PO4 autoanalyzer and a flow injection analyzer which also analyzes NH4+, NO2- and NO3-. Other ions are automatically monitored by ICP-AES. The system has automated calibration procedures of the analytical equipment and prolonged studies of plant growth can be performed under constant environmental conditions. This paper describes the design and construction of the PNT, the results of a number of tests showing the degree of control of environmental factors and the results of a comparative study on NH4+ and NO3- uptake kinetics by Juncus effusus conducted in the PNT demonstrate the use of the PNT in ecophysiological studies.