A functional-structural model of ephemeral seagrass growth influenced by environment.

Background and Aims: Ephemeral seagrasses that respond rapidly to environmental changes are important marine habitats. However, they are under threat due to human activity and are logistically difficult and expensive to study. This study aimed to develop a new functional-structural environmentally dependent model of ephemeral seagrass, able to integrate our understanding of ephemeral seagrass growth dynamics and assess options for potential management interventions, such as seagrass transplantation. Methods: A functional-structural plant model was developed in which growth and senescence rates are mechanistically linked to environmental variables. The model was parameterized and validated for a population of Halophila stipulacea in the Persian Gulf. Key Results: There was a good match between empirical and simulated results for the number of apices, net rhizome length or net number of internodes using a 330 d simulation. Simulated data were more variable than empirical data. Simulated structural patterns of seagrass rhizome growth qualitatively matched empirical observations. Conclusions: This new model successfully simulates the environmentally dependent growth and senescence rates of our case-study ephemeral seagrass species. It produces numerical and visual outputs that help synthesize our understanding of how the influence of environmental variables on plant functional processes affects overall growth patterns. The model can also be used to assess the potential outcomes of management interventions like seagrass transplantation, thus providing a useful management tool. It is freely available and easily adapted for new species and locations, although validation with more species and environments is required.

Effects of high salinity from desalination brine on growth, photosynthesis, water relations and osmolyte concentrations of seagrass Posidonia australis.

Highly saline brines from desalination plants expose seagrass communities to salt stress. We examined effects of raised salinity (46 and 54psu) compared with seawater controls (37psu) over 6weeks on the seagrass, Posidonia australis, growing in tanks with the aim of separating effects of salinity from other potentially deleterious components of brine and determining appropriate bioindicators. Plants survived exposures of 2-4weeks at 54psu, the maximum salinity of brine released from a nearby desalination plant. Salinity significantly reduced maximum quantum yield of PSII (chlorophyll a fluorescence emissions). Leaf water potential (Ψw) and osmotic potential (Ψπ) were more negative at increased salinity, while turgor pressure (Ψp) was unaffected. Leaf concentrations of K+ and Ca2+ decreased, whereas concentrations of sugars (mainly sucrose) and amino acids increased. We recommend leaf osmolarity, ion, sugar and amino acid concentrations as bioindicators for salinity effects, associated with brine released in desalination plant outfalls.

Seafood-associated disease outbreaks in New York, 1980-1994.

BACKGROUND: Seafood-associated disease outbreaks in New York were examined to describe their epidemiology and to identify areas for prevention and control efforts. METHODS: We reviewed reports submitted to the New York State Department of Health (NYSDOH) of seafood-associated outbreaks occurring from January 1, 1980, through December 31, 1994. RESULTS: During 1980-1994, 339 seafood-associated outbreaks were reported, resulting in 3959 illnesses, 76 hospitalizations, and 4 deaths. During this period, seafood-associated outbreaks accounted for 19% of all reported foodborne outbreaks and 10% of foodborne illnesses. Shellfish, the most frequently implicated seafood item, accounted for 64% of seafood outbreaks, followed by finfish (31% of outbreaks). Of the 148 seafood-associated outbreaks with a confirmed etiologic agent, Norwalk virus and scombrotoxin were the most frequently identified agents: Norwalk virus accounted for 42% of outbreaks and 42% of illnesses, and scombrotoxin accounted for 44% of outbreaks and 19% of illnesses. Three of the 4 seafood-associated deaths were caused by Clostridium botulinum; the remaining death was caused by Vibrio vulnificus. CONCLUSIONS: Reducing the number of seafood outbreaks will require continued and coordinated efforts by many different agencies, including those involved with water quality; disease surveillance; consumer education; and seafood harvesting, processing, and marketing. New York's foodborne disease surveillance data highlight potential areas on which to focus prevention efforts, including: (1) commodities and associated pathogens causing the largest number of seafood-associated outbreaks and illnesses, namely shellfish-associated viral gastroenteritis and finfish-associated scombroid fish poisoning, and (2) venues at which seafood were most frequently consumed in reported outbreaks, such as commercial food establishments and catered events.

Leaf Respiration in Light and Darkness (A Comparison of Slow- and Fast-Growing Poa Species).

We investigated whether leaf dark respiration (nonphotorespiratory mitochondrial CO2 release) is inhibited by light in several Poa species, and whether differences in light inhibition between the species are related to differences in the rate of leaf net photosynthesis. Four lowland (Poa annua L., Poa compressa L., Poa pratensis L., and Poa trivialis L.), one subalpine (Poa alpina L.), and two alpine (Poa costiniana Vick. and Poa fawcettiae Vick.) Poa species differing in whole plant relative growth rates were grown under identical controlled conditions. Nonphotorespiratory mitochondrial CO2 release in the light (Rd) was estimated according to the Laisk method. Photosynthesis was measured at ambient CO2 partial pressure (35 Pa) and 500 [mu]mol photons m-2 s-1. The rate of photosynthesis per unit leaf mass was positively correlated with the relative growth rate, with the slow-growing alpine Poa species exhibiting the lowest photosynthetic rates. Rates of both Rd and respiration in darkness were also substantially lower in the alpine species. Nonphotorespiratory CO2 release in darkness was higher than Rd in all species. However, despite some variation between the species in the level of light inhibition of respiration, no relationship was observed between the level of inhibition and the rate of photosynthesis. Similarly, the level of inhibition was not correlated with the relative growth rate. Our results support the suggestion that rates of leaf respiration in the light are closely associated with rates in darkness.

SO42- Deprivation Has an Early Effect on the Content of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase and Photosynthesis in Young Leaves of Wheat.

Wheat (Triticum aestivum cv Chinese Spring) supplied with 0.45 mM SO42- for 14 d with relative growth rates (RGR) of 0.22 to 0.24 d-1 was deprived of S for 7 to 8 d. There was no significant effect on RGR or leaf development (leaf 2 length was constant; leaf 3 expanded for 2-4 d; leaf 4 emerged and elongated throughout the experiment) during the S deprivation. In controls the net assimilation rate (A) closely reflected leaf ontogeny. S deprivation affected A in all leaves, particularly leaf 4, in which A remained at 8 to 10 [mu]mol CO2 m-2 s-1, whereas in controls A rose steadily to >20 [mu]mol CO2 m-2 s-1. In leaf 2, with a fully assembled photosynthetic system, A decreased in S-deprived plants relative to controls only at the end of the experiment. Effects on A were not due to altered stomatal conductance or leaf internal [CO2] ([C]i); decreases in the initial slope of A/[C]i curves indicated an effect of S deprivation on the carboxylase efficiency. Measurement of Rubisco activity and large subunit protein abundance paralleled effects on A and A/[C]i in S-deprived leaves. Negative effects on photosynthesis in S-deprived plants are discussed in relation to mobilization of S reserves, including Rubisco, emphasizing the need for continuous S supply during vegetative growth.