Nighttime Respiration Rates Research Articles

Effects of Elevated CO2 Concentration on the Respiratory Behavior of the Branches of Field-Grown Hinoki Cypress (Chamaecyparis obtusa)

The effects of elevated atmospheric CO2 concentrations on the nighttime respiration were examined for two sample branches of a hinoki cypress tree (Chamaecyparis obtusa) growing in the field with an open gas exchange system for a one-year period from July 1994 to June 1995. The branches were of a similar size and located at a similar position within the crown. One branch was subjected to an elevated CO2 concentration of 800 μmol mol−1 and the other was subjected to ambient air which had a CO2 concentration of about 370 μmol mol−1. Nighttime respiration rate was higher in elevated CO2 level than in ambient CO2 level. The relationship between nighttime respiration and the corresponding nighttime air temperature was fitted by the exponential function in every month of the year. The segregation of regression lines between the two CO2 treatments increased gradually as the seasons progressed during the treatment period. TheQ10 values for nighttime respiration were lower in elevated CO2 (1.9 ≤Q10 ≤ 3.7) than in ambient CO2 (2.4 ≤Q10 ≤ 4.5) in every month of the year. TheQ10 was inversely related to the monthly mean nighttime air temperature in both elevated and ambient CO2. The estimated daily nighttime respiration rate under both CO2 treatments had a similar seasonal pattern, which almost synchronized with the temperature change. The respiration ratio of elevated CO2 to ambient CO2 increased gradually from 1.1 to 1.6 until the end of the experiment. Our results indicate that the CO2 level and the temperature have a strong interactive effect on respiration and suggest that a potential increase in respiration of branches will occur when ambient CO2 increases.

ASSESSMENT OF GRASSLAND ECOSYSTEM RESPONSES TO ATMOSPHERIC CHANGE USING LINKED PLANT–SOIL PROCESS MODELS

Models of photosynthesis, plant growth, and biophysical processes were linked with models that simulate water, nutrient, and carbon flows through plant–soil ecosystems. The linked ecosystem model was applied to examine ecosystem-level responses to CO2, temperature, precipitation, and global-warming scenarios in grasslands of Colorado and Kansas, USA, and Kenya. The model predicted that increased temperatures would decrease primary production at current CO2 levels, but decreases were reversed by doubling atmospheric CO2 concentration. Greater increases in daily minimum temperatures than daily maximum temperatures mitigated reductions in photosynthesis and water-use efficiency (WUE) later in the day, more than offseting increases in nighttime respiration rates under warmer temperatures. A temperature increase of 5°C reduced organic carbon in grassland soils by 20–30%, through effects on plant growth and decomposition, but the doubled CO2 negated soil carbon losses by increasing plant growth. Under higher pr...

Respiratory Behaviour of Young Hinoki Cypress (Chamaecyparis obtusa) Trees under Field Conditions

Abstract Night-time respiration rates of aerial parts of six sample trees in a 9-year-old hinoki cypress [Chamaecyparis obtusa(Sieb. et Zucc.) Endl.] stand were measured at monthly intervals over a 1-year period, by an enclosed whole-tree method. When the relationships between annual respiration rate and mean phytomass, and between annual respiration rate and annual phytomass increment were examined, one sample tree, which was under stress, did not follow the trend of the rest, indicating that its lower respiration rate did not correspond to its size because of its negligible phytomass increment. Respiration was partitioned into maintenance and growth respiration to explain this phenomenon. The maintenance coefficients were 0.0345, 0.0373, 0.0352, 0.0211, 0.0316 and 0.0200g CO2g-1month-1, in decreasing order of tree size. The maintenance coefficients of the stressed (i.e. 0.0211g CO2g-1month-1) and suppressed (i.e. 0.0200g CO2g-1month-1) trees were similar and smaller than those of the rest which were larger and alike, indicating that stress and suppression reduced the coefficient. The growth coefficients were 1.45, 1.51, 1.28, 1.80, 1.45 and 1.64g CO2g-1, in decreasing order of tree size. The growth coefficient of the stressed tree (i.e. 1.80g CO2g-1) was the largest followed by that of the smallest and suppressed tree (i.e. 1.64g CO2g-1), suggesting that stress and suppression reduced the efficiency of conversion of substrate into new structural phytomass. The stressed tree respired mainly to maintain itself. The respiratory behaviour of the sample trees, including the stressed tree, was compatible with the concept of growth and maintenance respiration.

Respiratory Behaviour of Young Hinoki Cypress ( Chamaecyparis obtusa) Trees under Field Conditions

Night-time respiration rates of aerial parts of six sample trees in a 9-year-old hinoki cypress [ Chamaecyparis obtusa(Sieb. et Zucc.) Endl.] stand were measured at monthly intervals over a 1-year period, by an enclosed whole-tree method. When the relationships between annual respiration rate and mean phytomass, and between annual respiration rate and annual phytomass increment were examined, one sample tree, which was under stress, did not follow the trend of the rest, indicating that its lower respiration rate did not correspond to its size because of its negligible phytomass increment. Respiration was partitioned into maintenance and growth respiration to explain this phenomenon. The maintenance coefficients were 0.0345, 0.0373, 0.0352, 0.0211, 0.0316 and 0.0200g CO 2g -1month -1, in decreasing order of tree size. The maintenance coefficients of the stressed (i.e. 0.0211g CO 2g -1month -1) and suppressed (i.e. 0.0200g CO 2g -1month -1) trees were similar and smaller than those of the rest which were larger and alike, indicating that stress and suppression reduced the coefficient. The growth coefficients were 1.45, 1.51, 1.28, 1.80, 1.45 and 1.64g CO 2g -1, in decreasing order of tree size. The growth coefficient of the stressed tree (i.e. 1.80g CO 2g -1) was the largest followed by that of the smallest and suppressed tree (i.e. 1.64g CO 2g -1), suggesting that stress and suppression reduced the efficiency of conversion of substrate into new structural phytomass. The stressed tree respired mainly to maintain itself. The respiratory behaviour of the sample trees, including the stressed tree, was compatible with the concept of growth and maintenance respiration.

Carbon Dioxide Exchange between an Undisturbed Old‐Growth Temperate Forest and the Atmosphere

We used the eddy—correlation technique to investigate the exchange of CO2 between an undisturbed old—growth forest and the atmosphere at a remote Southern Hemisphere site on 15 d between 1989 and 1990. Our goal was to determine how environmental factors regulate ecosystem CO2 exchange, and to test whether present knowledge of leaf—level processes was sufficient to understand ecosystem—level exchange. On clear summer days the maximum rate of net ecosystem CO2 uptake exceeded 15 μmol°m—2°s—1, about an order of magnitude greater than the maximum values observed on sunny days in the winter. Mean nighttime respiration rates varied between °—2 and —7 μmol°m—2°s—1. Nighttime CO2 efflux rate roughly doubled with a 10°C increase in temperature. Daytime variation in net ecosystem CO2 exchange rate was primarily associated with changes in total photosynthetically active photon flux density (PPFD). Air temperature, saturation deficit, and the diffuse PPFD were of lesser, but still significant, influence. These results are in broad agreement with expectations based on the biochemistry of leaf gas exchange and penetration of radiation through a canopy. However, at night, the short—term exchange of CO2 between the forest and the atmosphere appeared to be regulated principally by atmospheric transport processes. There was a positive linear relationship between nocturnal CO2 exchange rate and downward sensible heat flux density. This new result has implications for the development of models for diurnal ecosystem CO2 exchange. The daytime light—use efficiency of the ecosystem (CO2 uptake/incident PPFD) was between 1.6 and 7.1 mmol/mol on clear days in the summer but decreased to 0.8 mmol/mol after frosts on clear winter days. Ecosystem CO2 uptake was enhanced by diffuse PPFD, a result of potentially global significance given recent increases in Northern Hemisphere haze.

Diel cycles of planktonic respiration rates in briefly incubated water samples from a fertile earthen pond

Planktonic community respiration rates were assessed every 30 min through two 48-h periods in near-surface water taken automatically from a fertilized carthen pond and incubated in a plastic chamber for 2 1 min of each sampling cycle. Parallel records of water temperature, air temperature, windspccd, and solar irradiance permitted calculation of gross and net primary production and photosynthesis-irradiance relationships. Nighttime respiration rates generally matched oxygen depletion rates in pond water, indicating that incubation-based rates were representative of a quickly darkened pond community throughout the day. Daytime rates averaged nearly 2 times the mean night rate and 58% higher than the mean day rate determined by a typical interpolation used in free-water production calculations. Daily gross production ranged from 0.7 to 1.2 mmol 0, liter-l d I; respiration constituted 65-75% of gross rates. Gross oxygen production per unit Chl a during sampling intervals was light saturated at irradiance values >600 PEinst m-2 s-l, with an asymptotic value of 1.58 pmol 0, (kg Chl a) -I h I. This system and method were capable ofresolving respiration and gross and net production when chlorophyll concentrations were near 40 pg liter-l.

Structure, Productivity, and Transpiration of a Subtropical Dry Forest in Puerto Rico

Structure, Productivity, and Transpiration of a Subtropical Dry Forest in Puerto Rico

Mass, heat and momentum exchange between a mature eucalyptus forest and the atmosphere

The exchanges of momentum, sensible heat and CO 2 between a mature Eucalyptus forest and the atmosphere were measured between April 17 and 27, 1975, using aerodynamic flux-profile relationships. The accuracy of these estimates of the flux are heavily dependent on the reliability of the measurements of the very small gradients of mean windspeed, temperature and carbon dioxide concentrations above the forest, and on the proper determination of the aerodynamic parameters of the forest; viz., the zero plane displacement d, the roughness length z 0 or a friction coefficient C f. d, z 0 and C f were determined from wind profiles under neutral conditions on the assumption that the logarithmic law is valid for measurements made “close” to the roughness elements. It was further assumed that these parameters are independent of atmospheric stability, and that d may be identified with the height of the mean sink for momentum within the canopy. A common value of d was used in the calculation of the fluxes of momentum, sensible heat and CO 2 from profiles of windspeed, temperature and CO 2. The fluxes of momentum calculated using wind profiles agreed well in all stability classes with the estimates of τ computed using a low-level windspeed and the friction coefficient C f. These latter values of τ also provided estimates of the fluxes of sensible heat and CO 2 which were equally as good as those obtained from aerodynamic flux-profile formulae. In view of the great difficulty in establishing the correct values of d and C f, it is desirable that other studies involving the flux-gradient approach should use an independently measured flux (such as sensible heat) as a tracer for estimating the CO 2 flux. The results of the present study show that the eucalypt forest has rates of CO 2 exchange which are comparable with other natural vegetation types. Typical midday rates of photosynthesis were 1 – 7 · 10 −7 kg CO 2 m −2 s −1 and night-time respiration rates of 0 – 3 · 10 −7 kg CO 2 m −2 s −1.