Elevated temperature is more effective than elevated [CO2 ] in exposing genotypic variation in Telopea speciosissima growth plasticity: implications for woody plant populations under climate change.

Intraspecific variation in phenotypic plasticity is a critical determinant of plant species capacity to cope with climate change. A long-standing hypothesis states that greater levels of environmental variability will select for genotypes with greater phenotypic plasticity. However, few studies have examined how genotypes of woody species originating from contrasting environments respond to multiple climate change factors. Here, we investigated the main and interactive effects of elevated [CO2 ] (CE ) and elevated temperature (TE ) on growth and physiology of Coastal (warmer, less variable temperature environment) and Upland (cooler, more variable temperature environment) genotypes of an Australian woody species Telopea speciosissima. Both genotypes were positively responsive to CE (35% and 29% increase in whole-plant dry mass and leaf area, respectively), but only the Coastal genotype exhibited positive growth responses to TE . We found that the Coastal genotype exhibited greater growth response to TE (47% and 85% increase in whole-plant dry mass and leaf area, respectively) when compared with the Upland genotype (no change in dry mass or leaf area). No intraspecific variation in physiological plasticity was detected under CE or TE , and the interactive effects of CE and TE on intraspecific variation in phenotypic plasticity were also largely absent. Overall, TE was a more effective climate factor than CE in exposing genotypic variation in our woody species. Our results contradict the paradigm that genotypes from more variable climates will exhibit greater phenotypic plasticity in future climate regimes.

The capacity to cope with climate warming declines from temperate to tropical latitudes in two widely distributed Eucalyptus species.

As rapid climate warming creates a mismatch between forest trees and their home environment, the ability of trees to cope with warming depends on their capacity to physiologically adjust to higher temperatures. In widespread species, individual trees in cooler home climates are hypothesized to more successfully acclimate to warming than their counterparts in warmer climates that may approach thermal limits. We tested this prediction with a climate-shift experiment in widely distributed Eucalyptus tereticornis and E. grandis using provenances originating along a ~2500 km latitudinal transect (15.5-38.0°S) in eastern Australia. We grew 21 provenances in conditions approximating summer temperatures at seed origin and warmed temperatures (+3.5 °C) using a series of climate-controlled glasshouse bays. The effects of +3.5 °C warming strongly depended on home climate. Cool-origin provenances responded to warming through an increase in photosynthetic capacity and total leaf area, leading to enhanced growth of 20-60%. Warm-origin provenances, however, responded to warming through a reduction in photosynthetic capacity and total leaf area, leading to reduced growth of approximately 10%. These results suggest that there is predictable intraspecific variation in the capacity of trees to respond to warming; cool-origin taxa are likely to benefit from warming, while warm-origin taxa may be negatively affected.

Elevated [CO2] does not ameliorate the negative effects of elevated temperature on drought-induced mortality in Eucalyptus radiata seedlings.

It has been reported that elevated temperature accelerates the time-to-mortality in plants exposed to prolonged drought, while elevated [CO(2)] acts as a mitigating factor because it can reduce stomatal conductance and thereby reduce water loss. We examined the interactive effects of elevated [CO(2)] and temperature on the inter-dependent carbon and hydraulic characteristics associated with drought-induced mortality in Eucalyptus radiata seedlings grown in two [CO(2)] (400 and 640 µL L(-1)) and two temperature (ambient and ambient +4 °C) treatments. Seedlings were exposed to two controlled drying and rewatering cycles, and then water was withheld until plants died. The extent of xylem cavitation was assessed as loss of stem hydraulic conductivity. Elevated temperature triggered more rapid mortality than ambient temperature through hydraulic failure, and was associated with larger water use, increased drought sensitivities of gas exchange traits and earlier occurrence of xylem cavitation. Elevated [CO(2)] had a negligible effect on seedling response to drought, and did not ameliorate the negative effects of elevated temperature on drought. Our findings suggest that elevated temperature and consequent higher vapour pressure deficit, but not elevated [CO(2)], may be the primary contributors to drought-induced seedling mortality under future climates.

Nocturnal stomatal conductance responses to rising [CO2], temperature and drought.

The response of nocturnal stomatal conductance (g(s,n)) to rising atmospheric CO(2) concentration ([CO(2)]) is currently unknown, and may differ from responses of daytime stomatal conductance (g(s,d)). Because night-time water fluxes can have a significant impact on landscape water budgets, an understanding of the effects of [CO(2)] and temperature on g(s,n) is crucial for predicting water fluxes under future climates. Here, we examined the effects of [CO(2)] (280, 400 and 640 µmol mol(-1)), temperature (ambient and ambient + 4°C) and drought on g(s,n,) and g(s,d) in Eucalyptus sideroxylon saplings. g(s,n) was substantially higher than zero, averaging 34% of g(s,d). Before the onset of drought, g(s,n) increased by 85% when [CO(2)] increased from 280 to 640 µmol mol(-1), averaged across both temperature treatments. g(s,n) declined with drought, but an increase in [CO(2)] slowed this decline. Consequently, the soil water potential at which g(s,n) was zero (Ψ(0)) was significantly more negative in elevated [CO(2)] and temperature treatments. g(s,d) showed inconsistent responses to [CO(2)] and temperature. g (s,n) may be higher in future climates, potentially increasing nocturnal water loss and susceptibility to drought, but cannot be predicted easily from g(s,d). Therefore, predictive models using stomatal conductance must account for both g(s,n) and g(s,d) when estimating ecosystem water fluxes.

Impacts of drought on leaf respiration in darkness and light in Eucalyptus saligna exposed to industrial-age atmospheric CO2 and growth temperature.

Our study assessed the impact of a wide range of industrial-age climate scenarios on leaf respiration (R) in Eucalyptus saligna. Well-watered or sustained drought-treated plants were grown in glasshouses differing in atmospheric CO2 concentration ([CO2]) (280, 400 and 640 µl l⁻¹) and temperature (26 and 30°C). Rates of R in darkness (R(dark) ) and light (R(light) ), photosynthesis (A) and related leaf traits (mass : area relationships, and nitrogen, phosphorus, starch and sugar concentrations) were measured. Light inhibited R in all cases (R(light) < R(dark) ) (well-watered: 40%; drought-treated: 73%). Growth [CO2] and temperature had little impact on area-based rates of R(dark) or R(light) , with R(light) exhibiting minimal thermal acclimation. By contrast, sustained drought resulted in reduced R(dark), R(light) and A, with the inhibitory effect of drought on A and R(light) (c. 50-70%) greater than that on R(dark) (c. 15%). Drought effects were fully reversible after watering. Variability in R(light) appeared to be dependent on the underlying rate of R(dark) and associated Rubisco activity. Collectively, our data suggest that there is an asynchronous response of leaf carbon metabolism to drought, and a tighter coupling between R(light) and A than between R(dark) and A, under both past and future climate scenarios. These findings have important implications for ecosystem/global models seeking to predict carbon cycling.

Mental health functioning among children and adolescents with perinatal HIV infection and perinatal HIV exposure.

Mental health problems (MHPs) among children with perinatal HIV infection have been described prior to and during the highly active antiretroviral therapy (HAART) era. Yet child, caregiver and socio-demographic factors associated with MHPs are not fully understood. We examined the prevalence of MHPs among older children and adolescents with perinatal HIV exposure, including both perinatally HIV-infected (PHIV +) and perinatally HIV-exposed but uninfected (PHEU) youth. Our aims were to identify the impact of HIV infection by comparing PHIV + and PHEU youth and to delineate risk factors associated with MHPs, in order to inform development of appropriate prevention and intervention strategies. Youth and their caregivers were interviewed with the Behavior Assessment System for Children, 2nd edition (BASC-2) to estimate rates of at-risk and clinically significant MHPs, including caregiver-reported behavioral problems and youth-reported emotional problems. The prevalence of MHPs at the time of study entry was calculated for the group overall, as well as by HIV status and by demographic, child health, and caregiver characteristics. Logistic regression models were used to identify factors associated with youth MHPs. Among 416 youth enrolled between March 2007 and July 2009 (295 PHIV +, 121 PHEU), the overall prevalence of MHPs at entry was 29% and greater than expected based on recent national surveys of the general population. MHPs were more likely among PHEU than among PHIV + children (38% versus 25%, p < 0.01). Factors associated with higher odds of MHPs at p < 0.10 included caregiver characteristics (psychiatric disorder, limit-setting problems, health-related functional limitations) and child characteristics (younger age and lower IQ). These findings suggest that PHEU children are at high risk for MHPs, yet current models of care for these youth may not support early diagnosis and treatment. Family-based prevention and intervention programs for HIV affected youth and their caregivers may minimize long-term consequences of MHPs.

What you don't know can hurt you: health hazards in the work environment.

Perianesthesia nurses are aware of health hazards in the work environment including radiation, chemotherapeutic drugs, and blood-borne pathogens. Results of a 2005 survey reveal that there may be more hazards to consider. Substances used by nurses and patients every day such as hand disinfecting agents, personal care products, and housekeeping chemicals may also pose a threat to the health of patients, nurses, and the nurses' children. Perianesthesia nurses are exposed to these commonly occurring hazards and to other materials including second-hand anesthetic gases, latex, and sterilizing agents. A survey of more than 1,500 nurses from across the country conducted by a coalition of environmental and nursing organizations revealed exposures that can have serious health effects. These survey results illuminate health implications all nurses need to know to take the necessary steps to protect patients, themselves, and their children.

CO2 and temperature effects on morphological and physiological traits affecting risk of drought-induced mortality.

Despite a wealth of eco-physiological assessments of plant response to extreme drought, few studies have addressed the interactive effects of global change factors on traits driving mortality. To understand the interaction between hydraulic and carbon metabolic traits influencing tree mortality, which may be independently influenced by atmospheric [CO2] and temperature, we grew Eucalyptus sideroxylon A. Cunn. ex Woolls from seed in a full-factorial [CO2] (280, 400 and 640 µmol mol-1, Cp, Ca and Ce, respectively) and temperature (ambient and ambient +4 °C, Ta and Te, respectively) experiment. Prior to drought, growth across treatment combinations resulted in significant variation in physiological and morphological traits, including photosynthesis (Asat), respiration (Rd), stomatal conductance, carbohydrate storage, biomass and leaf area (LA). Ce increased Asat, LA and leaf carbohydrate concentration compared with Ca, while Cp generated the opposite response; Te reduced Rd. However, upon imposition of drought, Te hastened mortality (9 days sooner compared with Ta), while Ce significantly exacerbated drought stress when combined with Te. Across treatments, earlier time-to-mortality was mainly associated with lower (more negative) leaf water potential (Ψl) during the initial drought phase, along with higher water loss across the first 3 weeks of water limitation. Among many variables, Ψl was more important than carbon status in predicting time-to-mortality across treatments, yet leaf starch was associated with residual variation within treatments. These results highlight the need to carefully consider the integration, interaction and hierarchy of traits contributing to mortality, along with their responses to environmental drivers. Both morphological traits, which influence soil resource extraction, and physiological traits, which affect water-for-carbon exchange to the atmosphere, must be considered to adequately predict plant response to drought. Researchers have struggled with assessing the relative importance of hydraulic and carbon metabolic traits in determining mortality, yet an integrated trait, time-dependent framework provides considerable insight into the risk of death from drought for trees.

Photosynthesis and carbon allocation are both important predictors of genotype productivity responses to elevated CO2 in Eucalyptus camaldulensis.

Intraspecific variation in biomass production responses to elevated atmospheric carbon dioxide (eCO2) could influence tree species' ecological and evolutionary responses to climate change. However, the physiological mechanisms underlying genotypic variation in responsiveness to eCO2 remain poorly understood. In this study, we grew 17 Eucalyptus camaldulensis Dehnh. subsp. camaldulensis genotypes (representing provenances from four different climates) under ambient atmospheric CO2 and eCO2. We tested whether genotype leaf-scale photosynthetic and whole-tree carbon (C) allocation responses to eCO2 were predictive of genotype biomass production responses to eCO2. Averaged across genotypes, growth at eCO2 increased in situ leaf net photosynthesis (Anet) (29%) and leaf starch concentrations (37%). Growth at eCO2 reduced the maximum carboxylation capacity of Rubisco (-4%) and leaf nitrogen per unit area (Narea, -6%), but Narea calculated on a total non-structural carbohydrate-free basis was similar between treatments. Growth at eCO2 also increased biomass production and altered C allocation by reducing leaf area ratio (-11%) and stem mass fraction (SMF, -9%), and increasing leaf mass area (18%) and leaf mass fraction (5%). Overall, we found few significant CO2 × provenance or CO2 × genotype (within provenance) interactions. However, genotypes that showed the largest increases in total dry mass at eCO2 had larger increases in root mass fraction (with larger decreases in SMF) and photosynthetic nitrogen-use efficiency (PNUE) with CO2 enrichment. These results indicate that genetic differences in PNUE and carbon sink utilization (in roots) are both important predictors of tree productivity responsiveness to eCO2.

The temperature response of leaf dark respiration in 15 provenances of Eucalyptus grandis grown in ambient and elevated CO2.

The effects of elevated CO2 on the short-term temperature response of leaf dark respiration (R) remain uncertain for many forest tree species. Likewise, variation in leaf R among populations within tree species and potential interactive effects of elevated CO2 are poorly understood. We addressed these uncertainties by measuring the short-term temperature response of leaf R in 15 provenances of Eucalyptus grandis W. Hill ex Maiden from contrasting thermal environments grown under ambient [CO2] (aCO2; 400µmolmol-1) and elevated [CO2] (640µmolmol-1; eCO2). Leaf R per unit area (Rarea) measured across a range of temperatures was higher in trees grown in eCO2 and varied up to 104% among provenances. However, eCO2 increased leaf dry mass per unit area (LMA) by 21%, and when R was expressed on a mass basis (i.e. Rmass), it did not differ between CO2 treatments. Likewise, accounting for differences in LMA among provenances, Rmass did not differ among provenances. The temperature sensitivity of R (i.e. Q10) did not differ between CO2 treatments or among provenances. We conclude that eCO2 had no direct effect on the temperature response of R in E. grandis, and respiratory physiology was similar among provenances of E. grandis regardless of home-climate temperature conditions.

Warming alters the positive impact of elevated CO2 concentration on cotton growth and physiology during soil water deficit.

Alterations in climate factors such as rising CO2 concentration ([CO2]), warming and reduced precipitation may have significant impacts on plant physiology and growth. This research investigated the interactive effects of elevated [CO2], warming and soil water deficit on biomass production, leaf-level physiological responses and whole-plant water use efficiency (WUEP) in cotton (Gossypium hirsutum L.). Cotton was grown in the glasshouse under two [CO2] treatments (CA, 400µLL-1; CE, 640µLL-1) and two temperature treatments (TA, 28°C:17°C day:night; TE, 32°C:21°C day:night). Plants were subjected to two progressive water deficit cycles, with a 5-day recovery period between the water deficit periods. CE increased vegetative biomass and photosynthetic rates, and decreased stomatal conductance in TA; however, these responses to CE were not evident under TE. CE increased whole-plant water loss under TA, but increased WUEp, whereas increased whole-plant water loss in TE decreased WUEp regardless of atmospheric [CO2]. CE may provide some positive growth and physiological benefits to cotton at TA if sufficient water is available but CE will not mitigate the negative effects of rising temperature on cotton growth and physiology in future environments.

The effect of elevated atmospheric [CO2] and increased temperatures on an older and modern cotton cultivar.

Changes in atmospheric [CO2], temperature and precipitation under projected climate change scenarios may have significant impacts on the physiology and yield of cotton. Understanding the implications of integrated environmental impacts on cotton is critical for developing cotton systems that are resilient to stresses induced by climate change. The objective of this study was to quantify the physiological and growth capacity of two cotton cultivars under current and future climate regimes. This experiment compared the early-season growth and physiological response of an older (DP16, released in the 1970s) and a modern (Sicot 71BRF, released in 2008) cotton cultivar grown in ambient and elevated atmospheric [CO2] (CA, 400µLL-1 and CE, 640µLL-1 respectively) and two temperature (TA, 28/17°C and TE, 32/21°C, day/night, respectively) treatments under well-watered conditions. CE increased biomass and photosynthetic rates compared with CA, and TE increased plant biomass. Although limited by the comparison of one older and one modern cultivar, our results suggest that substantial potential may exist to increase breeding selection of cotton cultivars that are responsive to both TE and CE.

Drought responses of two gymnosperm species with contrasting stomatal regulation strategies under elevated [CO2] and temperature.

Future climate regimes characterized by rising [CO2], rising temperatures and associated droughts may differentially affect tree growth and physiology. However, the interactive effects of these three factors are complex because elevated [CO2] and elevated temperature may generate differential physiological responses during drought. To date, the interactive effects of elevated [CO2] and elevated temperature on drought-induced tree mortality remain poorly understood in gymnosperm species that differ in stomatal regulation strategies. Water relations and carbon dynamics were examined in two species with contrasting stomatal regulation strategies: Pinus radiata D. Don (relatively isohydric gymnosperm; regulating stomata to maintain leaf water potential above critical thresholds) and Callitris rhomboidea R. Br (relatively anisohydric gymnosperm; allowing leaf water potential to decline as the soil dries), to assess response to drought as a function of [CO2] and temperature. Both species were grown in two [CO2] (C(a) (ambient, 400 µl l(-1)) and C(e) (elevated, 640 µl l(-1))) and two temperature (T(a) (ambient) and T(e) (ambient +4 °C)) treatments in a sun-lit glasshouse under well-watered conditions. Drought plants were then exposed to a progressive drought until mortality. Prior to mortality, extensive xylem cavitation occurred in both species, but significant depletion of non-structural carbohydrates was not observed in either species. Te resulted in faster mortality in P. radiata, but it did not modify the time-to-mortality in C. rhomboidea. C(e) did not delay the time-to-mortality in either species under drought or T(e) treatments. In summary, elevated temperature (+4 °C) had greater influence than elevated [CO2] (+240 µl l(-1)) on drought responses of the two studied gymnosperm species, while stomatal regulation strategies did not generally affect the relative contributions of hydraulic failure and carbohydrate depletion to mortality under severe drought.

Executive Functioning in Children and Adolescents With Perinatal HIV Infection.

BACKGROUND: Perinatal HIV (PHIV) infection may place youth at risk for impairments in executive functioning (EF). We examined associations of EF with HIV infection, disease severity and other factors among youth with PHIV and perinatally HIV-exposed, uninfected youth (PHEU). METHODS: Within the US-based Pediatric HIV/AIDS Cohort Study, 354 PHIV and 200 PHEU youth completed a standardized EF measure (Children's Color Trails Test, CCTT) and youth and/or caregivers completed a questionnaire measuring everyday EF (Behavior Rating Inventory of Executive Function, BRIEF). Covariates included HIV status, current and historical disease severity, demographic and caregiver variables and other cognitive measures. Analyses used linear and logistic regression and proportional odds models. RESULTS: No significant HIV status group differences were found on CCTT scores. Caregiver BRIEF ratings indicated significantly fewer problems for PHIV than PHEU youth. However, PHIV youth with past encephalopathy self-endorsed significantly greater metacognitive (ie, cognitive regulation) problems on the BRIEF and performed more slowly on the CCTT than PHEU youth. CCTT and caregiver BRIEF scores had significant associations with indicators of past and present disease severity. Both PHIV and PHEU had significantly worse scores than population means on CCTT and BRIEF; scores had significant associations with demographic covariates. CONCLUSIONS: Youth with PHIV show EF problems likely associated with risk factors other than HIV. However, cognitive slowing and self-reported metacognitive problems were evident in PHIV youth with a history of encephalopathy. Assessment and treatment of EF impairment may be important to identifying PHIV youth at particular risk for poor health and behavioral outcomes.

Rising temperature may negate the stimulatory effect of rising CO2 on growth and physiology of Wollemi pine (Wollemia nobilis).

Rising atmospheric [CO2] is associated with increased air temperature, and this warming may drive many rare plant species to extinction. However, to date, studies on the interactive effects of rising [CO2] and warming have focussed on just a few widely distributed plant species. Wollemi pine (Wollemia nobilis W.G.Jones, K.D.Hill, & J.M.Allen), formerly widespread in Australia, was reduced to a remnant population of fewer than 100 genetically indistinguishable individuals. Here, we examined the interactive effects of three [CO2] (290, 400 and 650ppm) and two temperature (ambient, ambient+4°C) treatments on clonally-propagated Wollemi pine grown for 17 months in glasshouses under well-watered and fertilised conditions. In general, the effects of rising [CO2] and temperature on growth and physiology were not interactive. Rising [CO2] increased shoot growth, light-saturated net photosynthetic rates (Asat) and net carbon gain. Higher net carbon gain was due to increased maximum apparent quantum yield and reduced non-photorespiratory respiration in the light, which also reduced the light compensation point. In contrast, increasing temperature reduced stem growth and Asat. Compensatory changes in mesophyll conductance and stomatal regulation suggest a narrow functional range of optimal water and CO2 flux co-regulation. These results suggest Asat and growth of the surviving genotype of Wollemi pine may continue to increase with rising [CO2], but increasing temperatures may offset these effects, and challenges to physiological and morphological controls over water and carbon trade-offs may push the remnant wild population of Wollemi pine towards extinction.

Early viral suppression improves neurocognitive outcomes in HIV-infected children.

OBJECTIVE: To estimate the association of age of viral suppression and central nervous system penetration effectiveness (CPE) score with neurocognitive functioning among school-age children with perinatally acquired HIV infection (PHIV+). DESIGN: We analyzed data from two US-based multisite prospective cohort studies. METHODS: Multivariable general linear regression models were used to evaluate associations of age at viral suppression and CPE scores (of initial antiretroviral therapy regimen and weighted average) with the Wechsler Intelligence Scale for Children, Third or Fourth Edition neurocognitive assessments [Full-Scale Intelligence Quotient (FSIQ); Performance IQ/Perceptual Reasoning Index (PIQ/PRI); and Verbal IQ/Verbal Comprehension Index (VIQ/VCI)], adjusted for demographic and clinical covariates. Sensitivity analyses were stratified by birth cohort (before versus after 1996). RESULTS: A total of 396 PHIV+ children were included. Estimated differences in mean FSIQ (comparing virally suppressed versus unsuppressed children) by each age cutoff were 3.7, 2.2, 3.2, 4.4, and 3.9 points at ages 1, 2, 3, 4, and 5, respectively. For PIQ/PRI, estimated mean differences were 3.7, 2.4, 2.2, 4.6, and 4.5 at ages 1 through 5, respectively. In both cases, these differences were significant only at the age 4 and 5 thresholds. After stratifying by birth cohort, the association between age at suppression and cognitive function persisted only among those born after 1996. Age at viral suppression was not associated with VIQ/VCI; CPE score was not associated with FSIQ, verbal comprehension, or perceptual reasoning indices. CONCLUSION: Virologic suppression during infancy or early childhood is associated with improved neurocognitive outcomes in school-aged PHIV+ children. In contrast, CPE scores showed no association with neurocognitive outcomes.

Non-structural carbohydrates in woody plants compared among laboratories.

Non-structural carbohydrates (NSC) in plant tissue are frequently quantified to make inferences about plant responses to environmental conditions. Laboratories publishing estimates of NSC of woody plants use many different methods to evaluate NSC. We asked whether NSC estimates in the recent literature could be quantitatively compared among studies. We also asked whether any differences among laboratories were related to the extraction and quantification methods used to determine starch and sugar concentrations. These questions were addressed by sending sub-samples collected from five woody plant tissues, which varied in NSC content and chemical composition, to 29 laboratories. Each laboratory analyzed the samples with their laboratory-specific protocols, based on recent publications, to determine concentrations of soluble sugars, starch and their sum, total NSC. Laboratory estimates differed substantially for all samples. For example, estimates for Eucalyptus globulus leaves (EGL) varied from 23 to 116 (mean = 56) mg g(-1) for soluble sugars, 6-533 (mean = 94) mg g(-1) for starch and 53-649 (mean = 153) mg g(-1) for total NSC. Mixed model analysis of variance showed that much of the variability among laboratories was unrelated to the categories we used for extraction and quantification methods (method category R(2) = 0.05-0.12 for soluble sugars, 0.10-0.33 for starch and 0.01-0.09 for total NSC). For EGL, the difference between the highest and lowest least squares means for categories in the mixed model analysis was 33 mg g(-1) for total NSC, compared with the range of laboratory estimates of 596 mg g(-1). Laboratories were reasonably consistent in their ranks of estimates among tissues for starch (r = 0.41-0.91), but less so for total NSC (r = 0.45-0.84) and soluble sugars (r = 0.11-0.83). Our results show that NSC estimates for woody plant tissues cannot be compared among laboratories. The relative changes in NSC between treatments measured within a laboratory may be comparable within and between laboratories, especially for starch. To obtain comparable NSC estimates, we suggest that users can either adopt the reference method given in this publication, or report estimates for a portion of samples using the reference method, and report estimates for a standard reference material. Researchers interested in NSC estimates should work to identify and adopt standard methods.

Discordance of cognitive and academic achievement outcomes in youth with perinatal HIV exposure.

BACKGROUND: To evaluate achievement in youth with perinatally acquired HIV (PHIV) compared with HIV-exposed uninfected peers (HEU) and to examine differential effects of HIV on cognition-achievement concordance. METHODS: Cognition and achievement were assessed using standardized measures. Intelligence quotient-derived predicted achievement scores were subtracted from observed achievement scores to calculate discrepancy values. Linear regression models were used to compare achievement discrepancies between PHIV and HEU, adjusting for demographic covariates. PARTICIPANTS: 295 PHIV and 167 HEU youth; 71% black, 48% male, mean age 13.1 and 11.3 years, respectively. PHIV youth were relatively healthy (mean CD4%, 32%; viral load ≤400 copies/mL, 72%). PHIV and HEU youth had cognitive and achievement scores significantly below population norm means (P < 0.001), but did not differ in cognition (mean full scale IQ = 86.7 vs. 89.4, respectively). In unadjusted models, HEU outperformed PHIV youth on total achievement (mean = 89.2 vs. 86.0, P = 0.04) and numerical operations (mean = 88.8 vs. 82.9, P < 0.001); no differences remained after adjustment. Mean observed-predicted achievement discrepancies reflected "underachievement". History of encephalopathy predicted poorer achievement (P = 0.039) and greater underachievement, even after adjustment. PHIV showed greater underachievement than HEU for numerical operations (P < 0.001) and total achievement (P = 0.03), but these differences did not persist in adjusted models. CONCLUSIONS: Both PHIV and HEU youth demonstrated lower achievement than normative samples and underachieved relative to predicted achievement scores. Observed-predicted achievement discrepancies were associated with prior encephalopathy, older age and other non-HIV factors. PHIV youth with prior encephalopathy had significantly lower achievement and greater underachievement compared with PHIV without encephalopathy and HEU youth, even in adjusted models.

Industrial-age changes in atmospheric [CO2] and temperature differentially alter responses of faster- and slower-growing Eucalyptus seedlings to short-term drought.

Climate change may alter forest composition by differentially affecting the responses of faster- and slower-growing tree species to drought. However, the combined effects of rising atmospheric CO2 concentration ([CO2]) and temperature on drought responses of trees are poorly understood. Here, we examined interactive effects of temperature (ambient, ambient + °C) and [CO2] (290, 400 and 650mu;l l(-1)) on drought responses of Eucalyptus saligna Sm. (faster-growing) and E. sideroxylon A. Cunn. ex Woolls (slower-growing) seedlings. Drought was imposed via a controlled reduction in soil water over 1-2 weeks, re-watering seedlings when leaves visibly wilted. In ambient temperature, the effect of drought on the light-saturated net photosynthetic rate (Asat) in E. saligna decreased as [CO2] increased from pre-industrial to future concentrations, but rising [CO2] did not affect the response in Eucalyptus sideroxylon. In contrast, elevated temperature exacerbated the effect of drought in reducing Asat in both species. The drought response of Asat reflected changes in stomatal conductance (gs) associated with species and treatment differences in (i) utilization of soil moisture and (ii) leaf area ratio (leaf area per unit plant dry mass). Across [CO2] and temperature treatments, E. saligna wilted at higher soil water potentials compared with E. sideroxylon. Photosynthetic recovery from drought was 90% complete 2 days following re-watering across all species and treatments. Our results suggest that E. saligna (faster-growing) seedlings are more susceptible to drought than E. sideroxylon (slower-growing) seedlings. The greater susceptibility to drought of E. saligna reflected faster drawdown of soil moisture, associated with more leaf area and leaf area ratio, and the ability of E. sideroxylon to maintain higher gs at a given soil moisture. Inclusion of a pre-industrial [CO2] treatment allowed us to conclude that susceptibility of these species to short-term drought under past and future climates may be regulated by the same mechanisms. Further, the beneficial effects of rising [CO2] and deleterious effects of elevated temperature on seedling response to drought were generally offsetting, suggesting susceptibility of seedlings of these species to short-term drought in future climates that is similar to pre-industrial and current climate conditions.

Leaf structural responses to pre-industrial, current and elevated atmospheric [CO2] and temperature affect leaf function in Eucalyptus sideroxylon.

Leaf structure and chemistry both play critical roles in regulating photosynthesis. Yet, a key unresolved issue in climate change research is the role of changes in leaf structure in photosynthetic responses to temperature and atmospheric CO2 concentration ([CO2]), ranging from pre-industrial to future levels. We examined the interactive effects of [CO2] (290, 400 and 650µLL-1) and temperature (ambient, ambient +4°C) on leaf structural and chemical traits that regulate photosynthesis in Eucalyptus sideroxylon A.Cunn. ex Woolls. Rising [CO2] from pre-industrial to elevated levels increased light-saturated net photosynthetic rates (Asat), but reduced photosynthetic capacity (Amax). Changes in leaf N per unit area (Narea) and the number of palisade layers accounted for 56 and 14% of the variation in Amax, respectively, associated with changes in leaf mass per area. Elevated temperature increased stomatal frequency, but did not affect Amax. Further, rising [CO2] and temperature generally did not interactively affect leaf structure or function. These results suggest that leaf Narea and the number of palisade layers are the key chemical and structural factors regulating photosynthetic capacity of E. sideroxylon under rising [CO2], whereas the lack of photosynthetic responses to elevated temperature may reflect the limited effect of temperature on leaf structure and chemistry.