Drying half of the root-zone from mid fruit growth to maturity in ‘Hass’ avocado (Persea americana Mill.) trees for one season reduced fruit production in two years

We tested the effect of extended drying of half the root system on fruit yield and fruit Ca concentration, an indirect measure of fruit quality, in avocado (Persea americana Mill. cv Hass). In a field experiment on a sandy soil, withholding irrigation and plastic sheeting was used to dry the root-zone beneath the whole canopy (DD) or half the canopy (WD), compared with well-watered trees (WW). The irrigation water contained added nutrients and was slightly saline. Yield, shoot growth, leaf conductance, leaf and fruit water status and mineral concentrations of leaves and fruit were studied. The responses of treated trees were assessed in the following season during which normal irrigation practices were restored. With respect to yield, the WD treatment behaved the same as the DD treatment. It reduced yield by more than half and proportionately more than the reduction in water supply thus reducing irrigation efficiency. Re-watering did not restore yield of WD or DD-trees in the next season. The WD and DD treatments had no effect on the concentration of Ca in the fruit mesocarp and so are unlikely to affect fruit quality. The main impact of reduced water supply on the trees was fruit abscission and this was linked to dry soil around the roots rather than the water status of the leaves or fruits. We conclude that extended drying of half of the root-zone in one season reduced irrigation efficiency for two seasons by promoting the abscission of developing fruit to the same extent as occurred when the whole root system was exposed to extended drying.     

Relating tradable credits for biodiversity to sustainability criteria in a dynamic landscape

Tradable biodiversity credit systems provide flexible means to resolve conflicts between development and conservation land-use options for habitats occupied by threatened or endangered species. We describe an approach to incorporate the influence of habitat fragmentation into the conservation value of tradable credits. Habitat fragmentation decreases gene flow, increases rates of genetic drift and inbreeding, and increases probabilities of patch extinction. Importantly, tradable credit systems will change the level of fragmentation over time for small and/or declining populations. We apply landscape equivalency analysis (LEA), a generalizable, landscape-scale accounting system that assigns conservation value to habitat patches based on patch contributions to abundance and genetic variance at landscape scales. By evaluating habitat trades using two models that vary the relationship between dispersal behaviors and landscape patterns, we show that LEA provides a novel method for limiting access to habitat at the landscape-scale, recognizing that the appropriate amount of migration needed to supplement patch recruitment and to offset drift and inbreeding will vary as landscape pattern changes over time. We also found that decisions based on probabilities of persistence alone would ignore changes in migration, genetic drift, and patch extinction that result from habitat trades. The general principle of LEA is that habitat patches traded should make at least equivalent contributions to rates of recruitment and migration estimated at a landscape scale. Traditional approaches for assessing the “take” and “jeopardy” standards under the Endangered Species Act based on changes in abundance and probability of persistence may be inadequate to prevent trades that increase fragmentation.     

Historical influences dominate the composition of regenerating plant communities in abandoned citrus groves in north-central Florida

The question of what determines plant community composition is fundamental to the study of plant community ecology. We examined the relative roles of historical land use, landscape context, and the biophysical environment as determinants of plant community composition in regenerating citrus groves in north-central Florida. Results were interpreted in light of plant functional traits. Herbaceous and woody plants responded differently to broad-scale variables; herbs correlated most strongly with surrounding land cover at a scale of 8 km, while the only significant determinant of woody species distributions was local land use history. There were significant correlations between herbaceous species and spatial context, habitat isolation, environmental variables, and historical variables. Partial Mantel tests indicated that each variable provided a unique contribution in explaining some of the variation in the herbaceous dataset. The correlation between woody plants and local historical variables remained significant even with other effects corrected for. In the herbaceous community, species composition was linked to functional traits much as expected from classical theory. While spatial influences in our study system are important for both woody and herbaceous plants, the primary determinant of plant community composition in regenerating citrus groves is historical land use. Our results suggest that the fine-scale mechanisms of local competition, tolerance and facilitation invoked by many classical studies may ultimately be less important than land use history in understanding current plant community composition in regenerating agricultural areas.     

Effectiveness of l‐ascorbyl‐2‐monophosphate Na/Ca as a vitamin C source for yellowtail Seriola quinqueradiata juveniles

A feeding experiment was conducted to examine the efficacy of a vitamin C (L‐ascorbic acid, AsA) derivative, l ‐ascorbyl‐2‐monophosphate Na/Ca (AMP‐Na/Ca) by comparing to l ‐ascorbyl‐2‐monophosphate‐Mg (AMP‐Mg) in terms of growth, AsA content in tissues, and hematology in yellowtail Seriola quinqueradiata juvenile (1.10 ± 0.01 g). Furthermore, a stress resistance test for the species fed AMP‐Na/Ca was also conducted. In experiment 1, 11 test pellet diets with different levels of AMP‐Na/Ca (0, 12, 43, 88, 440 and 881 mg AsA kg^?1diet) and AMP‐Mg (0, 16, 52, 106, 595 and 1164 mg AsA kg^?1 diet) were formulated and fed to the yellowtail three times per day for 50 days. In both the vitamin C sources, the survival rates of the fish fed diets without supplemental AsA were lower than 50% at day 20, and more than 50% mortality occurred in fish that fed the diets containing 12 or 16 mg AsA kg^?1 after day 30. However, no significant differences were detected in survival and growth among fish that fed the diets containing more than 43 mg AsA kg^?1. Liver and brain AsA concentrations generally increased with increasing dietary AsA level in both sources. In experiment 2, test diets were formulated to contain 43, 88, 440 and 881 mg AsA kg^?1 using AMP‐Na/Ca, and after 60 days of feeding, yellowtail juveniles were subjected to low salinity and air exposure stress. The fish that received diets with 440 mg AsA kg^?1 showed significantly higher tolerance to low salinity stress and higher survival rate in air exposure stress than those of other groups. The present study demonstrated that yellowtail juveniles could utilize AMP‐Na/Ca as an AsA source like AMP‐Mg, and that supplementation of 43–52 mg AsA kg^?1 diet was optimum for normal growth. However, this study showed that dietary inclusion of 440 mg AsA kg^?1 would be necessary to improve stress resistance of this species.     

Comparative intestinal absorption of amino acids in rainbow trout (Oncorhynchus mykiss), totoaba (Totoaba macdonaldi) and Pacific bluefin tuna (Thunnus orientalis)

The kinetics of amino acid absorption in the proximal section of three fish species were studied using an everted intestine technique and a pancreatic digest of casein (Tryptone), as the model amino acid mixture. Fresh intestine of rainbow trout (Oncorhynchus mykiss) was used to set up the experimental system, and results were compared with those obtained using intestines from totoaba (Totoaba macdonaldi) and bluefin tuna fish (Thunnus orientalis). The kinetics of amino acid absorption was sigmoidal for all amino acids and for each species of fish tested. In general, specific absorptions of essential amino acids were higher than those of non‐essential ones. No correlation between the concentration of amino acids in the Tryptone solution and the corresponding absorptions was found. The maximum specific absorption rates of all amino acids for trout were 10 times higher than those determined for totoaba and bluefin tuna. The relative amounts of the different amino acids preferentially absorbed in all three species were different. Results obtained from the everted technique may be applicable to the design of formulated diets for large fish species with commercial value.     

Effects of different dietary protein and lipid levels on growth, feed utilization and body composition of red porgy (Pagrus pagrus) fingerlings

Two feeding trials were conducted to determine the minimum dietary protein level producing maximum growth, and the optimum protein to energy ratio in diets for red porgy (Pagrus pagrus) fingerlings, respectively. In the first trial, six isoenergetic diets were formulated with protein levels ranging from 400 to 650 g kg^?1 in increments of 50 g kg^?1, and fed for 11 weeks to 2.8 g average initial weight fish. Weight gain, specific growth rate and feed efficiency were significantly higher with diets containing higher protein levels, when compared with dietary levels below 500 g kg^?1. The highest protein efficiency ratios were obtained in fish fed 500 g kg^?1 dietary protein. The minimum dietary protein level producing maximum fish growth was found to be 500 g kg^?1. In the second trial, 15 g average initial weight fish were fed for 12 weeks, six diets containing three different lipid levels (100, 150 and 200 g kg^?1) combined with two protein levels (450 and 500 g kg^?1). Weight gain values increased when dietary lipids increased from 100 to 150 g kg^?1, with a further decrease for 200 g kg^?1 lipids in diets; the lowest fish growth being supported by 200 g kg^?1 dietary lipids. Fish growth was significantly higher when dietary protein increased from 450 to 500 g kg^?1. There was no evidence of a protein‐sparing effect of dietary lipids. Liver protein and lipid contents were low when compared with other fish species. All diet assayed produced high liver glycogen accumulation. The recommended protein and lipid levels in diets for red porgy fingerlings were 500 and 150 g kg^?1, respectively.     

Towards an integrated understanding of green space in the European built environment

In recent years social, economic and environmental considerations have led to a reevaluation of the factors that contribute to sustainable urban environments. Increasingly, urban green space is seen as an integral part of cities providing a range of services to both the people and the wildlife living in urban areas. With this recognition and resulting from the simultaneous provision of different services, there is a real need to identify a research framework in which to develop multidisciplinary and interdisciplinary research on urban green space. In order to address these needs, an iterative process based on the delphi technique was developed, which comprised email-mediated discussions and a two-day symposium involving experts from various disciplines. The two outputs of this iterative process were (i) an integrated framework for multidisciplinary and interdisciplinary research and (ii) a catalogue of key research questions in urban green space research. The integrated framework presented here includes relevant research areas (i.e. ecosystem services, drivers of change, pressures on urban green space, human processes and goals of provision of urban green space) and emergent research themes in urban green space studies (i.e. physicality, experience, valuation, management and governance). Collectively these two outputs have the potential to establish an international research agenda for urban green space, which can contribute to the better understanding of people's relationship with cities.     

Bahiagrass crop coefficients from eddy correlation measurements in central Florida

Bahiagrass (Paspalum notatum) is a warm-season grass used primarily in pastures and along highways and other low maintenance public areas in Florida. It is also used in landscapes to some extent because of its drought tolerance. Bahiagrass can survive under a range of moisture conditions from no irrigation to very wet conditions. Its well-watered consumptive use has not been reported previously. In this study, bahiagrass crop coefficients (K _c) for an irrigated pasture were determined for July 2003 through December 2006 in central Florida. The eddy correlation method was used to estimate crop evapotranspiration (ET_c) rates. The standardized reference evapotranspiration (ET_o) equation (ASCE-EWRI standardization of reference evapotranspiration task committee report, 2005) was applied to calculate ET_o values using on site weather data. Daily K _c values were estimated from the ratio of the measured ET_c and the calculated ET_o. The recommended K _c values for bahiagrass are 0.35 for January–February, 0.55 for March, 0.80 for April, 0.90 for May, 0.75 for June, 0.70 for July–August, 0.75 for September, 0.70 for October, 0.60 for November, and 0.45 for December in central Florida. The highest K _c value of 0.9 in May corresponded with maximum vapor pressure deficit conditions as well as cloud free conditions and the highest incoming solar radiation as compared to the rest of the year. During the summer (June to August), frequent precipitation events increased the cloud cover and reduced grass water use. The K _c annual trend was similar to estimated K _c values from another well-watered warm-season grass study in Florida.     

Evaluating eddy covariance cotton ET measurements in an advective environment with large weighing lysimeters

Eddy covariance (EC) systems are being used to assess the accuracy of remote sensing methods in mapping surface sensible and latent heat fluxes and evapotranspiration (ET) from local to regional scales, and in crop coefficient development. Therefore, the objective was to evaluate the accuracy of EC systems in measuring sensible heat (H) and latent heat (LE) fluxes. For this purpose, two EC systems were installed near large monolithic weighing lysimeters, on irrigated cotton fields in the Texas High Plains, during the months of June and July 2008. Sensible and latent heat fluxes were underestimated with an average error of about 30%. Most of the errors were from nocturnal measurements. Energy balance (EB) closure was 73.2–78.0% for daytime fluxes. Thus, daylight fluxes were adjusted for lack of EB closure using the Bowen ratio/preservation of energy principle, which improved the resulting EC heat flux agreement with lysimetric values. Further adjustments to EC-based ET included nighttime ET (composite) incorporation, and the use of ‘heat flux source area’ (footprint) functions to compensate ET when the footprint expanded beyond the crop field boundary. As a result, ET values remarkably matched lysimetric ET values, with a ‘mean bias error ± root mean square error’ of −0.03 ± 0.5 mm day⁻¹ (or −0.6 ± 10.2%).