Nighttime Respiration Rates Research Articles

Alternative oxidase 1a and 1d enable metabolic flexibility during Ala catabolism in Arabidopsis.

Ala is a central metabolite in leaf cells whose abundance is related to pyruvate (Pyr) metabolism and nocturnal respiration rates. Exposure of Arabidopsis (Arabidopsis thaliana) leaf disks to certain exogenous amino acids including Ala led to substantial increases in nighttime respiration rates as well as increases in alternative oxidase (AOX) 1d transcript and protein levels. During Ala treatment, AOX1d accumulation, but not AOX1a accumulation, was dependent upon the catabolism of Ala. Complete loss of AOX expression in aox1a aox1d leaf disks did not significantly affect oxygen consumption rates (OCR) under Ala treatment, indicating that AOX capacity per se was not essential for respiratory stimulation by Ala. Rather, Ala treatments caused induction of select antioxidant mechanisms in leaf disks, including a large increase of the ascorbate pool, which was substantially more oxidized in aox1a aox1d leaf disks. Furthermore, we observed differences in the accumulation of a sequence of TCA cycle intermediates from Pyr to 2-oxoglutarate (2-OG) in wild type (WT) upon Ala treatment that did not occur in aox1a aox1d leaf disks. The results indicate that AOX induction during enhanced Ala catabolism in leaves mediates mitochondrial redox status, allowing greater metabolic flexibility in mitochondrial organic acid metabolism.

Effects of CO2 concentration and soil water content on short-term water-use efficiency at whole-plant level

Uncovering the variations of short-term water-use efficiency (WUEp) at whole-plant level in response to CO2 concentration (Ca) and soil water content (SWC) can improve the understanding of plant survival strategies under climate change. In this study, Platycladus orientalis saplings were cultured in simulated climate chambers.There were totally 15 treatments, including Ca of 400 (C400), 600 (C600) and 800 (C800) μmol·mol-1 and SWC of 35%-45% field water holding capacity (FC), 50%-60%FC, 60%-70%FC, 70%-80%FC and 95%-100%FC. The WUEp was measured by mini-lysimeters, weighting method, and static assimilation chamber. The results showed that both daytime (0.12-1.87 mol·h-1) and nighttime transpiration rates (0.01-0.16 mol·h-1) at whole-plant level reached the maximum at C400×70%-80%FC, while the whole-plant daytime net photosynthetic rate (2.12-22.10 mmol·h-1) reached the maximum at C800×70%-80%FC. In contrast, nighttime respiration rate (0.84-4.41 mmol·h-1) increased with increasing SWC, but decreased with increasing of Ca, reaching the maximum at C400×95%-100%FC. For WUEp (5.37-24.35 mmol·mol-1), it reached the maximum at C800×50%-60%FC, indicating that plants could use less water and fixed more carbon by adjusting adaptation strategies under high Ca and drought conditions. In addition, leaf instantaneous water-use efficiency was a good predictor of WUEP when the canopy structure was similar.

Open Field Simulating Nocturnal Warming on Summer Maize Performance in the North China Plain

Climate changes show asymmetrical warming, and warming is typically greater at night than during the day. To understand how nocturnal warming (NW) affects the performance of maize (Zea mays L.), an open-field experiment with a free air temperature increase (FATI) facility was conducted for three seasons during 2014 to 2016 at Luancheng eco-agro-experimental station on the North China Plain (NCP). Three nocturnal warming scenarios were set up: the entire growing period (T1, from V4 to maturity), only the vegetative stages (T2, from V4 to a week presilking) and the reproductive stages (T3, from a week presilking to R6). The treatment without NW was the control. Maize lodged seriously in 2015 due to heavy rainfall combined with strong winds, and the experiment failed. The results from 2014 and 2016 were analyzed in this study. During the experimental duration, the average nocturnal temperature was increased by approximately 3.6 and 3.3 °C at 150 cm height and 2.0 and 1.7 °C at the soil surface during the vegetative stages. The corresponding increases were 2.1 and 2.5 °C and 0.7 and 1.2 °C at the soil surface during the reproductive stages in 2014 and 2016, respectively, as compared with that of the CK treatment. NW during the whole growth period significantly decreased maize yield for the two seasons. Treatment T2 had a smaller impact on maize yield than T1 and T3. The silking stage was delayed by 2 days in 2014 and 2016 under T1. As a result, presilking duration and VT-R1 interval were prolonged by 1–2 days; and the postsilking duration were shortened by 1–3 days under T1. The soil moisture in the warmed plots was slightly lower than that in the control plots in the 2014 and during the stages before the earlier grain-filling stages in 2016, but NW decreased soil water content greatly at the later grain-filling stages in 2016, which caused the fast green leaf senescence and exacerbated the negative effects of NW on maize yield. NW for the whole growth duration (T1) significantly decreased seed weight and harvest index. NW increased leaf nighttime respiration rate in both seasons. No significant effects of NW on ear leaf net photosynthesis, leaf area, and specific leaf weight at early grain-filling stage were observed, irrespective of the warming stage and season. The results suggested that reproductive stages were more sensitive to NW compared to vegetative stages under the growing conditions of NCP. The negative effects of NW were worsened in dry seasons. The reduction in maize yield with nocturnal warming was driven by the reduction in the aboveground carbon allocation from shoot to grain during postanthesis stage.

Annual ecosystem respiration of maize was primarily driven by crop growth and soil water conditions

In the context of global warming, carbon dioxide emissions have become a global concern. Cropland respiration is an important component of carbon dioxide emissions from terrestrial ecosystem. A large number of studies have investigated cropland respiration, although many controversies remain about its interannual variations and mechanisms.In this study, an eddy covariance instrument was used to observe carbon fluxes in a maize field for four consecutive years (2014–2017) in the arid region of Northwest China. The night-time respiration rates measured by eddy covariance were used to validate the accuracy of the Van’t Hoff, Arrhenius, and Taylor models in estimating the respiration rate of a maize field.All three models performed well, although the Van’t Hoff model had the highest accuracy. The three models were used to simultaneously estimate the respiration rate of the maize field throughout the growth season. The results showed that in the years 2014, 2015, 2016, and 2017, the annual respiration rates were 485, 1063, 711, and 651 g m−2y-1, respectively. Surprisingly, the respiration rate in 2015 was markedly higher than that in the other three years, and the values were 119%, 49%, and 63% higher than the rates in 2014, 2016, and 2017, respectively. To interpret this observation, this article analyzed the relationships between the respiration rate in the maize field ecosystem and the maximum leaf area index, air temperature, soil surface temperature, and soil water content. The results show that at the interannual scale, the ecosystem respiration showed significant linear positive correlations with the maximum leaf area index and soil water content. The highest values for canopy area, net radiation, irrigation rate, and soil water content were observed in 2015; the crop biomass in 2015 was also greater than that in the other three years, which significantly increased the crop respiration and caused 2015 to have the highest respiration rate.The results showed that at the interannual scale, crop growth and soil surface water conditions were the critical determinants of respiration. This study provided a new perspective and a basis for an in-depth understanding of the mechanism of carbon dioxide emission in croplands.

Hypersalinity as a trigger of seagrass (Thalassia testudinum) die-off events in Florida Bay: Evidence based on shoot meristem O2 and H2S dynamics

The mechanisms initiating rapid, large-scale (>50 km2) seagrass die-off events globally remain elusive. Thalassia testudinum, a dominant habitat-forming tropical seagrass of the Caribbean and tropical Atlantic region, experiences recurrent die-off events in Florida Bay. Thus, T. testudinum provides an excellent case study to identify triggers of large-scale seagrass mortality. Presently, seagrass die-off events in Florida Bay are correlated to high total sulfide (H2S, HS−, S2−) concentrations in the sediment porewater (≥2000 μM), water column hypoxia, high temperature and hypersalinity (salinity > 45). Because the mortality appears to be initiated at the shoot base within the meristem, we examined the response of shoot meristematic O2 and H2S dynamics using microsensors over a 5-hour nighttime simulation. Shoots were held at salinity 35 (ambient) or 65 (hypersaline) using microsensors in intact cores with plants from the field. The rate of H2S intrusion in the dark and oxidation in the light were similar at 35 and 65 salinity. However, the tissue O2 consumption rate was significantly higher under hypersaline conditions (−11.07 ± 4.32 kPa pO2 h−1) compared to ambient (−3.93 ± 0.88 kPa pO2 h−1) in the dark. Consequently, the meristematic pO2 threshold (~1.5 kPa O2) where H2S intrusion occurred in the meristem was reached more rapidly, increasing the time H2S accumulated (1.5 to 2.8 h). Longer H2S accumulation time significantly increased maximum meristem H2S levels at 65 (536 ± 330 μM H2S) compared to 35 salinity (121 ± 62 μM H2S). These results in T. testudinum provide evidence for a triggering mechanism that links an enhanced respiratory rate under hypersaline conditions to sulfide toxicity. We propose that hypersalinity in Florida Bay, or any stressor that significantly increases nighttime respiration rates, can subject seagrasses to longer and higher concentrations of sulfide, a known phytotoxin, within the shoot meristem. This mechanism likely explains large-scale mass mortality of T. testudinum in Florida Bay during periods of high salinity and elevated porewater sulfide levels, although field experiments are required to further validate this supposition.

Night Light-Adaptation Strategies for Photosynthetic Apparatus in Yellow-Poplar (Liriodendron tulipifera L.) Exposed to Artificial Night Lighting

Plants can undergo external fluctuations in the natural light and dark cycle. The photosynthetic apparatus needs to operate in an appropriate manner to fluctuating environmental factors, especially in light. Yellow-poplar seedlings were exposed to nighttime artificial high-pressure sodium (HPS) lighting to evaluate night light-adaptation strategies for photosynthetic apparatus fitness relative to pigment contents, photosystem II photochemistry, photosynthetic parameters, histochemical analysis of reactive oxygen species, and plant biomass. As a result, seedlings exhibited dynamic changes including the enhancement of accessory pigments, the reduction of photosystem II photochemistry, increased stomatal limitation, downregulation of photosynthesis, and the decreased aboveground and belowground biomass under artificial night lighting. Histochemical analysis with 3,3′-diaminobenzidine (DAB) and nitroblue tetrazolium (NBT) staining indicates the accumulation of in situ superoxide radicals (O2−) and hydrogen peroxide (H2O2) in leaves exposed to the lowest level of artificial night lighting compared to control. Moreover, these leaves exposed to artificial night lighting had a lower nighttime respiration rate. These results indicated that HPS lighting during the night may act as a major factor as repressors of the fitness of photosynthesis and growth patterns, via a modification of the photosynthetic light harvesting apparatus.

Biogeochemical processes in infiltration basins and their impact on the recharging effluent, the soil aquifer treatment (SAT) system of the Shafdan plant, Israel

Soil aquifer treatment (SAT) systems utilize infiltration basins for recharging pre-treated effluent into the aquifer for water quality improvement. The present research focuses on the diurnal and seasonal variations of oxygen, carbon and nitrogen species in the infiltration basins and in the uppermost vadose zone for determining the impact of different environmental conditions on the composition of the infiltrating effluent. The study was conducted in one of the infiltration basins of the Dan Region Sewage Reclamation Project (Shafdan), Israel. Solar radiation and aeration were recognized to be the two main factors controlling the chemical composition of the effluent within the basin and the uppermost vadose zone. The effluent entering the basin show initial enrichment with dissolved oxygen (DO) due to gas exchange caused by “injection” through the inlet fountain and turbulence during basin filling. The DO, pH and dissolved inorganic carbon (DIC) fluctuate diurnally as a result of intense in-basin daylight photosynthesis and nighttime respiration. DO and pH increase during day and decrease during night and the DIC shows an opposite behavior. The daylight net primary production was ∼240μmolL−1d−1 and the diurnal respiration rate was ∼430μmolL−1d−1 (assuming that the nighttime respiration rate is constant over a whole diurnal cycle). The gross primary production during daylight was ∼450μmolL−1d−1. Dissolved organic carbon (DOC) and inorganic nitrogen species (NH4++NO3−) varied significantly in the uppermost vadose zone, however, neither the vadose zone nor the basin showed diurnal fluctuations. It appears that chemical variations between three sampling campaigns conducted in different seasons stemmed mainly from the efficiency of basin aeration that resulted from changes in basin’s operation regime and local environmental conditions. The results of this study lead to the following basin management recommendations: (1) keeping short flooding and drying cycles and allowing complete basin desiccation before the next flooding; and (2) flooding the basin during daytime, starting at dawn to maximize oxygen production and minimize infiltration during nighttime. Following these routines would result in higher redox potential of the infiltrating effluent.

Impacts of nighttime post-anthesis warming on rice productivity and grain quality in East China

The impacts of nighttime post-anthesis warming on rice productivity and grain quality in East China were evaluated for two cultivars, II You 128, an indica rice, and Wuyunjing 7, a japonica rice. Warming by 3.0°C stimulated the nighttime respiration rate and decreased the photosynthesis rate, resulting in significant decreases of 21.2% and 24.9% in aboveground biomass accumulation for II You 128 and Wuyunjing 7, respectively. Warming significantly reduced the rates of seed setting and grain filling, especially of inferior kernels (those lower in panicles), while the filling rate of superior kernels remained almost unchanged. As a result, 1000-grain weight and grain yield were respectively 3.7% and 30.0% lower for II You 128 and 12.8% and 34.3% for Wuyunjing 7 in warmed plots than in the unwarmed control. Nighttime warming also significantly reduced the grain milling and appearance quality of both varieties. More negative effects of warming on inferior than on superior kernels were found. The above results have important implications for rice variety cultivation in East China.

Combining the Information of Unconstrained Electrocardiography and Ballistography in the Detection of Night-Time Heart Rate and Respiration Rate

An unobtrusive bed integrated system for monitoring physiological parameters during sleep is presented and evaluated. The system uses textile electrodes attached to a bed sheet for measuring multiple channels of electrocardiogram. The channels are also combined in order to form several additional ECG leads. One lead at a time is selected for beat-to-beat-interval detection. The system also includes force sensors located under a bed post for detecting respiration and movements. The movement information is also used to assist in heart rate detection and combining the ECG derived respiration information with respiration information derived from force sensors, is investigated. The authors tested the system with ten subjects in one hour recordings and achieved an average of 95.9% detection coverage and 99 percentile absolute error of 3.47 ms for the BB-interval signal. The relative mean absolute error of the detected respiration cycle lengths was 2.1%.

In Situ Coral Reef Oxygen Metabolism: An Eddy Correlation Study

Quantitative studies of coral reefs are challenged by the three-dimensional hard structure of reefs and the high spatial variability and temporal dynamics of their metabolism. We used the non-invasive eddy correlation technique to examine respiration and photosynthesis rates, through O2 fluxes, from reef crests and reef slopes in the Florida Keys, USA. We assessed how the photosynthesis and respiration of different reef habitats is controlled by light and hydrodynamics. Numerous fluxes (over a 0.25 h period) were as high as 4500 mmol O2 m−2 d−1, which can only be explained by efficient light utilization by the phototrophic community and the complex canopy structure of the reef, having a many-fold larger surface area than its horizontal projection. Over diel cycles, the reef crest was net autotrophic, whereas on the reef slope oxygen production and respiration were balanced. The autotrophic nature of the shallow reef crests implies that the export of organics is an important source of primary production for the larger area. Net oxygen production on the reef crest was proportional to the light intensity, up to 1750 µmol photons m−2 s−1 and decreased thereafter as respiration was stimulated by high current velocities coincident with peak light levels. Nighttime respiration rates were also stimulated by the current velocity, through enhanced ventilation of the porous framework of the reef. Respiration rates were the highest directly after sunset, and then decreased during the night suggesting that highly labile photosynthates produced during the day fueled early-night respiration. The reef framework was also important to the acquisition of nutrients as the ambient nitrogen stock in the water had sufficient capacity to support these high production rates across the entire reef width. These direct measurements of complex reefs systems yielded high metabolic rates and dynamics that can only be determined through in situ, high temporal resolution measurements.

Seasonal variation of carbon exchange from a revegetation area in a Chinese desert

Revegetation is a common method to combat desertification and to reduce soil carbon loss in arid and semi-arid areas worldwide. Revegetated areas in the temperate arid Shapotou area of Northern China were established to stabilize sand dunes in an area subject to wind erosion. The objective of this study was to characterize the carbon flux of a 20-year old revegetated area. During the measurement period from May 2008 to December 2010 carbon flux was measured by the eddy covariance technique, and rainfall, temperature, and soil water content were monitored simultaneously with the aim of understanding the relationship between carbon flux and meteorological factors. We found that the revegetated ecosystem is a carbon sink during the growing season when most of the annual precipitation falls. The revegetated area changed from being a carbon source to a sink in the 1 or 2 days following an effective rainfall event. In the non-growing season the ecosystem was a carbon source. The soil water content (SWC) affected the relationship between ecosystem respiration and temperature. The nighttime respiration rate increased with soil temperature. When the SWC was ≥3% the correlation between respiration rate and soil temperature was stronger (R2=0.23) than when SWC was <3% (R2=0.08). Although the net ecosystem carbon flux (NEE) in temperate arid desert areas is relatively small compared to that of humid areas, it represents huge carbon fixation potential because of the very large area of desert in northern China. Further research is required to clarify the effects of climatic factors on the various components of temperate arid ecosystems, especially the roles of cryptogam and biological soil crusts in the carbon exchange processes.

Responses of biomass growth and grain yield of midseason rice to the anticipated warming with FATI facility in East China

Crop model projections and historical data analyses have shown that global warming may cause serious decrease in crop productivity, however, many uncertainities remain on the impact quantification due to the unclear understanding of actual crop response. Therefore, we performed a three-year field warming experiment with free air temperature increase (FATI) facility to investigate the actual response of midseason rice growth in East China. There were four treatments (AW: all-day warming; DW: daytime warming; NW: nighttime warming; CK: ambient control) with three replicates. This FATI facility presented a good simulation of the local air temperature pattern with an increase in the daily mean temperature of about 1.1–2.0 °C during rice whole growth duration compared to the ambient control. Warming shortened the pre-heading phase respectively by 3.3 d, 1.7 d and 2.0 d in the AW, DW and NW plots, while the post-heading phase stayed almost unchanged. During the three years, warming slightly decreased the aboveground biomass by an average of 9.1%, 10.3% and 3.3%, and the grain yield by an average of 0.9%, 6.4% and 6.1% in the AW, DW and NW plots, respectively. Warming tended to decrease rice photosynthesis rate and stimulate the nighttime respiration rate. It also enlarged the flag leaf area and increased its chlorophyll content. No significant difference and interaction in the actual response of rice growth were found between the warming regimes. The above evidences suggest that the expected warming less than 2.0 °C may not cause significant decrease in rice productivity in East China.

METHANE AND CARBON DIOXIDE DYNAMICS IN WETLAND MESOCOSMS: EFFECTS OF HYDROLOGY AND SOILS

Methane and carbon dioxide fluxes in created and restored wetlands, and the influence of hydrology and soils on these fluxes, have not been extensively documented. Minimizing methane fluxes while maximizing productivity is a relevant goal for wetland restoration and creation projects. In this study we used replicated wetland mesocosms to investigate relationships between contrasting hydrologic and soil conditions, and methane and carbon dioxide fluxes in emergent marsh systems. Hydrologic treatments consisted of an intermittent flooding regime vs. continuously inundated conditions, and soil treatments utilized hydric vs. non-hydric soils. Diurnal patterns of methane flux were examined to shed light on the relationship between emergent macrophytes and methane emissions for comparison with vegetation-methane relationships reported from natural wetlands. Microbially available organic carbon content was significantly greater in hydric soils than nonhydric soils, despite similar organic matter contents in the contrasting soil types. Mesocosms with hydric soils exhibited the greatest rates of methane flux regardless of hydrology, but intermittent inundation of hydric soils produced significantly lower methane fluxes than continuous inundatation of hydric soils. Methane fluxes were not affected significantly by hydrologic regime in mesocosms containing non-hydric soils. There were no diurnal differences in methane flux, and carbon dioxide and methane fluxes were not significantly correlated. The highest rates of CO2 uptake occurred in the continuously inundated treatment with non-hydric soils, and there were no significant differences in nighttime respiration rates between the treatments. Implications for hydrologic design of created and restored wetlands are discussed.

Leaf area index is the principal scaling parameter for both gross photosynthesis and ecosystem respiration of Northern deciduous and coniferous forests

Data on net CO 2 exchange from eight forests in Denmark, Sweden, Finland and Iceland were used to analyse which factors were controlling photosynthesis and respiration. The forests consisted of different species ranging in climatic condition from temperate to subarctic. Only well mixed conditions were analysed ( u * > 0.3 m s -1 ). The parameters of a light response function showed strong seasonal variations with similar behaviour for all stands except for a beech forest where the development of a vigorous ground vegetation in spring affected the photosynthesis parameters differently as compared to the other forests. The beech forest also showed the highest respiration rates in the earlier part of the growing season in contrast to the other forests that showed maximum values in late part of July. The mean half-monthly nighttime respiration rates were well explained by an equation with one fitting parameter, the respiration rate at 10 °C, with an r 2 = 0.864 for all stands together. The difference between the stands concerning both photosynthesis and respiration parameters were largely explained by the differences in LAI. After normalizing for LAI, the only remaining correlation was between respiration and stand age. These results are promising for application of remote sensing for estimation of respiration as well as gross primary productivity from forests. DOI: 10.1111/j.1600-0889.2007.00330.x

Leaf area index is the principal scaling parameter for both gross photosynthesis and ecosystem respiration of Northern deciduous and coniferous forests

Data on net CO2 exchange from eight forests in Denmark, Sweden, Finland and Iceland were used to analyse which factors were controlling photosynthesis and respiration. The forests consisted of different species ranging in climatic condition from temperate to subarctic. Only well mixed conditions were analysed (u∗ > 0.3 ms-1). The parameters of a light response function showed strong seasonal variations with similar behaviour for all stands except for a beech forest where the development of a vigorous ground vegetation in spring affected the photosynthesis parameters differently as compared to the other forests. The beech forest also showed the highest respiration rates in the earlier part of the growing season in contrast to the other forests that showed maximum values in late part of July. The mean halfmonthly nighttime respiration rates were well explained by an equation with one fitting parameter, the respiration rate at 10 ◦C, with an r2 = 0.864 for all stands together. The difference between the stands concerning both photosynthesis and respiration parameters were largely explained by the differences in LAI. After normalizing for LAI, the only remaining correlation was between respiration and stand age. These results are promising for application of remote sensing for estimation of respiration as well as gross primary productivity from forests.

Environmental controls on the CO2 exchange in north European mires

Net CO2 exchange measured under well-mixed atmospheric conditions in four different mires in Sweden and Finland were used to analyse which factors were controlling photosynthesis and respiration. The parameters of a light response function showed strong seasonal variations with similar behaviour for all mires. The half-monthly nighttime respiration rates in the central part of the growing season were about two times higher in the southernmost, warmest site, Fåje, as compared to the northernmost, coldest site, Kaamanen. However, Kaamanen had high photosynthesis rates, and this in combination with the long daylight periods in the middle of the summer caused Kaamanen to have the largest net ecosystem exchange (NEE) during the summer period. Fåje that showed the highest productivity had also the highest respiration and therefore, the lowest NEE during summer. Correlation between half-monthly components and different environmental variables showed the highest correlation between the components themselves. Thereafter came temperature except for Fåje where water table depth (WTD) explained most of the variance both for detrended and temperature-normalized components. All sites showed dependencies between WTD and the respective components during drying up periods. Temperature sensitivity was higher for productivity than for respiration indicating that CO2 uptake would increase during global warming.

Increasing CO2 from subambient to elevated concentrations increases grassland respiration per unit of net carbon fixation

AbstractRespiration (carbon efflux) by terrestrial ecosystems is a major component of the global carbon (C) cycle, but the response of C efflux to atmospheric CO2 enrichment remains uncertain. Respiration may respond directly to an increase in the availability of C substrates at high CO2, but also may be affected indirectly by a CO2‐mediated alteration in the amount by which respiration changes per unit of change in temperature or C uptake (sensitivity of respiration to temperature or C uptake). We measured CO2 fluxes continuously during the final 2 years of a 4‐year experiment on C3/C4 grassland that was exposed to a 200–560 μmol mol−1 CO2 gradient. Flux measurements were used to determine whether CO2 treatment affected nighttime respiration rates and the response of ecosystem respiration to seasonal changes in net C uptake and air temperature. Increasing CO2 from subambient to elevated concentrations stimulated grassland respiration at night by increasing the net amount of C fixed during daylight and by increasing either the sensitivity of C efflux to daily changes in C fixation or the respiration rate in the absence of C uptake (basal ecosystem respiration rate). These latter two changes contributed to a 30–47% increase in the ratio of nighttime respiration to daytime net C influx as CO2 increased from subamient to elevated concentrations. Daily changes in net C uptake were highly correlated with variation in temperature, meaning that the shared contribution of C uptake and temperature in explaining variance in respiration rates was large. Statistically controlling for collinearity between temperature and C uptake reduced the effect of a given change in C influx on respiration. Conversely, CO2 treatment did not affect the response of grassland respiration to seasonal variation in temperature. Elevating CO2 concentration increased grassland respiration rates by increasing both net C input and respiration per unit of C input. A better understanding of how C efflux varies with substrate supply thus may be required to accurately assess the C balance of terrestrial ecosystems.

A Whole-Genome Scan for 24-Hour Respiration Rate: A Major Locus at 10q26 Influences Respiration During Sleep

Identification of genes causing variation in daytime and nighttime respiration rates could advance our understanding of the basic molecular processes of human respiratory rhythmogenesis. This could also serve an important clinical purpose, because dysfunction of such processes has been identified as critically important in sleep disorders. We performed a sib-pair-based linkage analysis on ambulatory respiration rate, using the data from 270 sibling pairs who were genotyped at 374 markers on the autosomes, with an average distance of 9.65 cM. Uni- and multivariate variance-components-based multipoint linkage analyses were performed for respiration rate during three daytime periods (morning, afternoon, and evening) and during nighttime sleep. Evidence of linkage was found at chromosomal locations 3q27, 7p22, 10q26, and 22q12. The strongest evidence of linkage was found for respiration rate during sleep, with LOD scores of 2.36 at 3q27, 3.86 at 10q26, and 1.59 at 22q12. In a simultaneous analysis of these three loci, >50% of the variance in sleep respiration rate could be attributed to a quantitative-trait loci near marker D10S1248 at 10q. Genes in this area (GFRA1, ADORA2L, FGR2, EMX2, and HMX2) can be considered promising positional candidates for genetic association studies of respiratory control during sleep.

Influence of decreasing soil moisture on stem water potential, transpiration rate and carbon exchange rate of the lowbush blueberry (Vaccinium angustifolium Ait.) in a controlled environment

SummaryA controlled environment study was performed to examine the direct short-term effects of decreasing soil moisture in the lowbush blueberry. Four computer controlled growth chambers were used and stem water potential (SWP), transpiration rate and net carbon exchange rate (NCER) were measured. The experiment was arranged as a randomized complete block design including a control and drought stressed treatment replicated six times using individual growth chambers as the blocking factor. At the conclusion of the experiment, the control treatment displayed a soil moisture value of 75% while the drought treatment had decreased to 50%. After 116 h of nonreplenished moisture loss, the drought stressed plants showed greater variability and a decrease of at least 60% in stem water potential. Decreasing water availability resulted in lowered transpiration and photosynthetic rates (Pn), with a slight decrease in nighttime respiration rates in the drought stressed plants compared with the control plants. Like most drought tolerant plants, the adaptive mechanism of the lowbush blueberry appears to regulate water loss via stomatal and mesophyll conductance.

Night-time respiration rate and leaf carbohydrate concentrations are not coupled in two alpine perennial species.

• The relationship between night-time respiration rate and carbohydrate supply are measured in two alpine perennials, Bistorta bistortoides and Campanula rotundifolia. • Natural populations of B. bistortoides and C. rotundifolia were subjected to high and low light treatments. During the following night, respiration rate and carbohydrate content of leaves were measured. • At the beginning of the dark period, leaf carbohydrate concentrations were significantly lower in plants exposed to lower irradiance on the previous day. The night-time respiration rate in leaves of both species was rarely affected by the previous days' irradiance; over the course of the night, respiration rate remained unchanged in C. rotundifolia and decreased, but not consistently, in B. bistortoides. No significant interaction was found between irradiance and the night-time pattern of carbohydrate concentration or respiration rate. Nocturnal carbohydrate export was positively correlated with the previous days' irradiance in leaves of C. rotundifolia only. • Leaf respiration rate is uncoupled from carbohydrate supply in leaves of B. bistortoides and C. rotundifolia, possibly allowing more carbohydrate to be exported to underground storage organs.