Seasonal Patterns Of Photosynthesis Research Articles

Model-data fusion to assess year-round CO2 fluxes for an arctic heath ecosystem in West Greenland (69°N)

Quantifying net CO2 exchange (NEE) of arctic terrestrial ecosystems in response to changes in climatic and environmental conditions is central to understanding ecosystem functioning and assessing potential feedbacks of the carbon cycle to future climate changes. However, annual CO2 budgets for arctic tundra are rare due to the difficulties of performing measurements during non-growing seasons. It is still unclear to what extent arctic tundra ecosystems currently act as a CO2 source, sink or are in balance. This study presents year-round eddy-covariance (EC) measurements of CO2 fluxes for an arctic heath ecosystem on Disko Island, West Greenland (69 °N) over five years. Based on a fusion of year-round EC-derived CO2 fluxes, soil temperature and moisture, the process-oriented model (CoupModel) has been constrained to quantify an annual budget and characterize seasonal patterns of CO2 fluxes. The results show that total photosynthesis corresponds to -202 ± 20 g C m−2 yr-1 with ecosystem respiration of 167 ± 28 g C m-2 yr-1, resulting in NEE of -35 ± 15 g C m-2 yr-1. The respiration loss is mainly described as decomposition of near-surface litter. A year with an anomalously deep snowpack shows a threefold increase in the rate of ecosystem respiration compared to other years. Due to the high CO2 emissions during that winter, the annual budget results in a marked reduction in the CO2 sink. The seasonal patterns of photosynthesis and soil respiration were described using response functions of the forcing atmosphere and soil conditions. Snow depth, topography-related soil moisture, and growing season warmth are identified as important environmental characteristics which most influence seasonal rates of gas exchange.

Spatial and Seasonal Variations of Standardized Photosynthetic Parameters under Different Environmental Conditions for Young Planted Larix olgensis Henry Trees

Understanding the spatial and seasonal variations in leaf physiology is critical for accurately modeling the carbon uptake, physiological processes and growth of entire canopies and stands. For a 17-year-old Larix olgensis Henry plantation, vertical whorl-by-whorl sampling and analyses of seasonally repeated measurements of major photosynthetic parameters were conducted, and the correlations between photosynthetic parameters and environmental conditions, leaf morphological traits and spatial position within the crown were analyzed. According to the correlations, the photosynthetic parameters were standardized based on the environmental conditions to avoid the influence of the changing environment on the patterns of spatial and seasonal variations of photosynthetic parameters. The results showed that the standardized light-saturated net photosynthetic rate (SPmax), standardized dark respiration (SRd) and standardized stomatal conductance under saturated light (Sgs-sat) were all negatively related to the relative depth into the crown (RDINC) throughout the growing season. However, their vertical patterns were different during the development of the phenological phase. In addition, different gradients of environmental conditions also influenced the values and the range of the vertical variation in photosynthesis. High temperature and low humidity usually resulted in smaller values and weaker vertical variations of SPmax and Sgs-sat, but larger values and more obvious vertical variations in SRd. SPmax and Sgs-sat usually exhibited a parabolic seasonal pattern in different vertical positions within the crown; however, SRd generally followed a concave pattern. These seasonal patterns were all weaker with increasing RDINC. Different environments also exhibited a significant influence on the seasonal patterns of photosynthesis. We suggested that standardization is necessary before analyzing spatial and seasonal variations. A single environmental condition could not represent the spatial and seasonal patterns under all gradients of the environment. Spatial and seasonal variations should be simultaneously analyzed because they are related to each other.

The metabolic regimes of flowing waters

AbstractThe processes and biomass that characterize any ecosystem are fundamentally constrained by the total amount of energy that is either fixed within or delivered across its boundaries. Ultimately, ecosystems may be understood and classified by their rates of total and net productivity and by the seasonal patterns of photosynthesis and respiration. Such understanding is well developed for terrestrial and lentic ecosystems but our understanding of ecosystem phenology has lagged well behind for rivers. The proliferation of reliable and inexpensive sensors for monitoring dissolved oxygen and carbon dioxide is underpinning a revolution in our understanding of the ecosystem energetics of rivers. Here, we synthesize our current understanding of the drivers and constraints on river metabolism, and set out a research agenda aimed at characterizing, classifying and modeling the current and future metabolic regimes of flowing waters.

Photosynthesis and growth of Thujopsis dolabrata var. hondai seedlings in the understory of trees with various phenologies

We have studied the photosynthetic production and growth of Thujopsis dolabrata var. hondai (hiba) seedlings under typical light conditions found in mixed forests, including constant shade, phenological gaps under broad-leaved trees with different lengths of foliation period, and in an open plot. Leaves sampled from the open plot had significantly higher rates of light-saturated gross photosynthesis and dark respiration, and a significantly lower specific leaf area than leaves from the other plots. The relative growth rate of whole plant biomass was significantly higher in plots that received larger amounts of light. The variations in these properties under the various light conditions are considered to reflect the ability of hiba seedlings to adapt to available light. In the late autumn, leaves sampled from the open and from the gap under deciduous trees indicated photoinhibition. However, the estimated value of monthly net photosynthesis of hiba seedlings was greater in these plots, indicating that the benefit of a greater light intensity for photosynthesis seems to be larger than the detriment of photoinhibition. The seasonal pattern of photosynthesis by understory hiba seedlings was affected by the phenology of canopy trees. Light availability under the canopy of deciduous trees associated with phenological gaps helped hiba seedlings to tolerate the relatively dark conditions during the subsequent foliation period. These results for reaction to the light regime and for the phenology of hiba seedlings are practicable for hiba forest management.

Novel Patterns of Seasonal Photosynthetic Acclimation, Including Interspecific Differences, in Conifers over an Altitudinal Gradient

Photosynthesis, as the basis of most food chains and a crucial global carbon sink, makes chief contributions to overall ecosystem carbon budgets, but specific responses of the plant component cannot be obtained from such budgets. To gain much-needed further information on possible interspecies differences in seasonal patterns of photosynthesis, capacities for light- and CO2-saturated rates of oxygen evolution at 25°C (photosynthetic capacity) were determined during the summer-fall-winter transition for five conifer species over their natural distribution along a steep altitudinal gradient. Findings include (i) a transient upregulation of photosynthetic capacity during the summer-to-fall transition in all five conifer species that preceded the previously reported winter downregulation in conifers. However, there were (ii) interspecific differences in this response at the highest altitudes, with higher maximal photosynthetic capacities displayed by pine and spruce species compared to fir species. Lastly, the winter downregulation of photosynthetic capacity was not as complete in the present study (winter of 2006) as that which has been reported for previous winter seasons, which has implications for the winter survival strategy of conifers in response to global warming.

Spatial and temporal variation of photosynthesis in intertidal Mazzaella laminarioides (Bory)Fredericq (Rhodophyta, Gigartinales)

The red alga Mazzaella laminarioides is an economically important species with an extended latitudinal distribution along the Chilean coast. Its populations form mid-intertidal stands, several meters wide, and therefore are differentially exposed to environmental variables that result in temporal and spatial variability in productivity. We evaluated the effect of latitude and intertidal height on productivity by in situ measurement of photosynthetic performance. Daily and seasonal variations of O2-evolution rate and maximal quantum yield (Fv/Fm) were determined in plants from the upper and lower intertidal zone at two localities 1500,km apart. Results suggest that plant responses were mainly affected by irradiation, temperature and desiccation. At local level, upper intertidal plants showed a reduced photosynthetic rate and quantum efficiency as compared to those displayed by plants from the lower intertidal, indicating their higher level of excitation energy acclimation. Stronger acclimation differences between upper and lower intertidal plants were observed in spring and summer. Differences in photosynthetic parameters between reproductive phases were recorded in autumn and winter, regardless of the position of the individuals in the intertidal zone. The effects of tidal elevation on seasonal patterns of photosynthesis were also influenced by latitude. Seasonal variation in photosynthetic efficiency was observed in plants from the northern population at both intertidal elevations, but only at the upper intertidal level in the southern population. This study shows that production variability in M. laminarioides results from differences in the intensity of environmental factors observed seasonally at local (intertidal) and latitudinal scales.

Automated foliage chamber method for long-term measurement of CO2 flux in the uppermost canopy

Direct monitoring of CO2 exchange in forest ecosystems is necessary for evaluation of the annual net CO2 flux. We developed an automated foliage chamber system for long-term in situ measurement of the CO2 flux in foliage. The chamber closes automatically for 5 min in every 30. We found a high correlation between the photosynthesis rates measured by this system and by a portable H2O/CO2 analyzer (LCA-3, ADC). We used the new system to continuously monitor the CO2 flux in foliage of Quercus serrata. There was a positive correlation between CO2 flux and short-wave radiation. The daily photosynthesis rate varied widely depending on the environmental conditions. It increased from May to July and decreased temporarily in August. The seasonal pattern of photosynthesis was almost the same as that measured by the eddy covariance method. These results suggest that the new system is effective for tracking long-term seasonal change of the CO2 flux in foliage.

Seasonal patterns of photosynthesis in Douglas fir seedlings during the third and fourth year of exposure to elevated CO2 and temperature

ABSTRACTThe interactive effects of elevated atmospheric CO2 and temperature on seasonal patterns of photosynthesis in Douglas fir (Psuedotsuga menziesii (Mirb.) Franco) seedlings were examined. Seedlings were grown in sunlit chambers controlled to track either ambient (~400 p.p.m.) CO2 or ambient +200 p.p.m. CO2, and either ambient temperature or ambient +4 °C. Light‐saturated net photosynthetic rates were measured approximately monthly over a 21 month period. Elevated CO2 increased net photosynthetic rates by an average of 21% across temperature treatments during both the 1996 hydrologic year, the third year of exposure, and the 1997 hydrologic year. Elevated mean annual temperature increased net photosynthetic rates by an average of 33% across CO2 treatments during both years. Seasonal temperature changes also affected net photosynthetic rates. Across treatments, net photosynthetic rates were highest in the spring and autumn, and lowest in July, August and December–January. Seasonal increases in temperature were not correlated with increases in the relative photosynthetic response to elevated CO2. Seasonal shifts in the photosynthetic temperature optimum reduced temperature effects on the relative response to elevated CO2. These results suggest that the effects of elevated CO2 on net photosynthetic rates in Douglas fir are largely independent of temperature.

Seasonal Patterns of Photosynthesis and Stomatal Conductance in Lowbush Blueberry Plants Managed in a Two-year Production Cycle

Seasonal patterns of CO2 assimilation (ACO2), leaf water potential (ψ1) and stomatal conductance (g1) were studied in three clones (`Augusta', `Brunswick', and `Chignecto') of lowbush blueberry (Vaccinium angustifolium Ait.) over two growing seasons. Plants were managed in a 2-year cycle of fruiting (year 1) and burn-prune (year 2). In the fruiting year, ACO2 was lowest in mid-June and early September. Rates peaked between 10 and 31 July and declined after fruit removal in late August. Compared with the fruiting year, ACO2 in the prune year was between 50% and 130% higher in the early season, and between 80% and 300% higher in mid-September. In both years, however, mid-season maximum ACO2 for each clone was between 9 and 10 μmol·m–2·s–1CO2. Assimilation of CO2 increased with increasing photosynthetic photon flux (PPF) to between 500 and 600 μmol·s–1·m–2 in `Augusta' and `Brunswick', and to between 700 and 800 μmol·s–1·m–2 in `Chignecto'. Midday ψ1 was generally lower in the prune year than in the fruiting year, reflecting year-to-year differences in soil water content. Stomatal conductance (g1), however, was generally higher in the prune year than in the fruiting year over similar vapor pressure deficit (VPD) ranges, especially in June and September when prune year g1 was often twice that observed in the fruiting year. In the fruiting year, g1 declined through the day in response to increasing VPD in June, but was quite constant in mid-season. It tended to be higher in `Augusta' than in the other two clones. Stomatal closure imposes limitations on ACO2 in lowbush blueberries, but not all seasonal change in C-assimilative capacity can be explained by changes in g1.

Seasonal Patterns of Photosynthesis in Alpine and Subalpine Populations of the Lichen Nephroma arcticum

Photosynthetic characteristics of an alpine and a subalpine population of Nephroma arcticum, assumed to represent different ecotypes, were measured to investigate possible adaptations to their respective environments. The light compensation levels in the alpine population were consistently higher than those in the subalpine ones, and the chlorophyll contents of the former were, on average, about half those of the latter, reflecting the differences in light regimes between sites. In both populations, altitude accounted for a significant part of the variation in photosynthesis at suboptimal thallus water contents assumed to correspond to levels resulting from normal in-situ hydration (...)

Seasonal Patterns of Photosynthesis and Physiological Parameters and the Effects of Emersion in Littoral Seaweeds

Seasonal Patterns of Photosynthesis and Physiological Parameters and the Effects of Emersion in Littoral Seaweeds

Photosynthesis, Photorespiration, and Organic Carbon Release inNymphaea tuberosaPaine andNuphar variegatumEngelm

ABSTRACT Within two sympatric populations of Nymphaea tuberosa and Nuphar variegatum in a productive hardwater lake, both species exhibited similar seasonal patterns of photosynthesis, but the rates were much higher in Nymphaea than in Nuphar. Rates of photorespiration and organic carbon release were very low in both species during most of the growth season and were not a factor in the difference in photosynthetic rates. Both species were growing under optimal conditions, and the superior photosynthetic capacity of Nymphaea appeared to be associated with phenological differences permitting this species to compete successfully (i.e. coexist) with the earlier emerging, broader leaved Nuphar species.

Seasonal patterns of photosynthesis and respiration of red spruce saplings from two elevations in declining southern Appalachian stands

Exploratory studies were initiated at two high-elevation red spruce (Picearubens Sarg.) stands in the Great Smoky Mountains of western North Carolina to document the magnitude and physiological basis of differences in tree growth at the two sites. Increment core data indicate that conditions have become relatively less favorable for mature trees at the upper site during the past 20 years and that annual height growth of sapling trees has been 40% less at that site compared with a similar site at an elevation 215 m lower. Seasonal measurements of net photosynthesis and dark respiration rates of saplings indicated that differences in sapling growth rates at the upper site were associated with increases in dark respiration and less favorable net photosynthesis:dark respiration ratios. Basal diameter increment was most closely associated with differences in current net photosynthesis rates among trees at the upper site, whereas height and diameter growth of the upper canopy related most closely to the net photosynthesis rate among lower-elevation trees. Reduced foliar calcium and magnesium, reduced foliar chlorophyll, increased foliar aluminum, and low ratios of calcium:aluminum were found at the upper site. Tissue and soil aluminum levels that are in the range of those associated with aluminum toxicity to red spruce provide a preliminary indication that current high atmospheric inputs of the strong anions SO4 and NO3 to acidic soils may be adversely affecting growth and physiology of trees at the high-elevation site.

Seasonal changes in photosynthesis of four understory herbs in deciduous forests

Seasonal patterns of photosynthesis and respiration of single leaves of four understory perennial herbs in deciduous forests were investigated in relation to their leaf growth and light conditions on the forest floor.Anemone flaccida shows rapid growth of leaf area and high rates of gross photosynthesis at light saturation (Psat) in its early stage of development. Its photosynthetic activity is restricted to a brief period of high light intensity before the closure of overstory canopies.Disporum smilacinum possesses light-photosynthesis curves of the shade-leaf type throughout its whole growing period. A shading experiment has shown that this plant is low-light adapted and can utilize weak light efficiently. The light-photosynthesis curve ofSyneilesis palmata shifts from the sun-leaf type to the shade-leaf type in response to the seasonal change of light regime on the forest floor. Evergreen leaves ofPyrola japonica have three year longevity, and light-photosynthesis curves of the shade-leaf type. They maintain some photosynthetic activity even in late autumn and winter.

In SituPhotosynthesis and Respiration in the Littoral Sedge,Scirpus acutusMuhl

ABSTRACT Seasonal patterns of photosynthesis and respiration in Scirpus acutus Muhl. were assayed in situ during the 1978 growth season, using a closed system infrared gas analysis (IRGA) technique. The seasonal maximum rate of photosynthesis occurred early in the season (June) at 0.59 mg C g−1 h−1 and decreased through the remainder of the growth season, correlating negatively with plant age; correlations with light and temperature over the season were low. S. acutus had a CO2 compensation point of 45 ppm in June and 95 ppm in August. Photorespiratory loss was minimal in June and highest in October when 46 percent of gross photosynthesis was lost by respiration in the light. Experimentally elevated oxygen enhanced the rates of CO2 loss both in the light and in the dark.

Gas exchange in a 20‐year‐old stand of Scots pine

Net photosynthesis of current and one‐year‐old shoots in Scots pine (Pinus sylvestris L.) was measured during a two‐year period (1977–1978). The measurements were carried out in Central Sweden using a system that allowed in situ measurements throughout the year. The photosynthetically active period, defined as months with a positive carbon dioxide balance, was nine months per year for one‐year‐old shoots and six months for current shoots. The daily rates of net photosynthesis were low in spring and late autumn and 95% of the annual photosynthetic production occurred from May to October. In spring net photosynthesis was limited by a low photosynthetic capacity and a restricted access to water caused by the frozen ground. It took more than three months in spring and early summer to restore full photosynthetic capacity in the one‐year‐old shoots, but the rate of recovery varied considerably between the two years. In late autumn the rates of photosynthesis were mainly limited by low photon flux densities.The seasonal patterns of photosynthesis were similar between the two years, and even though there were pronounced differences for individual months, the total annual photosynthetic production of the two years only differed by 1.4% for the one‐year‐old shoots. The differences in photosynthetic production for current shoots were much higher as an effect of different rates of needle development and differences in photosynthetic capacity during the two years. An estimate of the carbon balance of the current shoots showed that the shoots had not photosynthesized their own weight in terms of carbon until late August (1978) or early September (1977), which means that their photosynthetic production was of minor importance for the formation of stem wood.

Diurnal and Seasonal Patterns of Photosynthesis and Respiration by Stems of Populus tremuloides Michx.

The photosynthetic and respiratory rates of 5- to 7-year-old aspen stems (Populus tremuloides Michx.) were monitored in the field for 1 year to determine the seasonal patterns. The stem was not capable of net photosynthesis, but the respiratory CO(2) loss from the stem was reduced by 0 to 100% depending on the time of year and the level of illumination as a result of bark photosynthesis. The monthly dark respiratory rate ranged from 0.24 mg CO(2)/dm(2). hr in January to a maximum 7.4 mg CO(2)/dm(2). hr in June. Individual measurements ranged from 0.02 mg CO(2)/dm(2). hr in February to 12.3 mg CO(2)/dm(2). hr in June. Gross photosynthesis followed a pattern similar to the dark respiratory rate. The mean monthly rate was highest in June (1.65 mg CO(2)/dm(2). hr) and lowest in December (0.02 mg CO(2)/dm(2). hr). Individual measurements ranged from 0.0 mg CO(2)/dm(2). hr in winter to 5.5 mg CO(2)/dm(2). hr in July.Winter studies showed that stem respiration continued down to -11 C, the coldest temperature during this study. Upon warning to -3 C, the dark respiratory rate showed a sudden sharp increase (7- to 12-fold) which required many hours to return to normal levels. No measurable photosynthesis occurred below -3 C. Between -3 and 0 C, the maximal photosynthetic rate was reduced to less than 50% of the respiratory rate, but increased to 89% between 5 to 10 C.On a yearly basis, bark photosynthesis in P. tremuloides reduced the stem respiratory CO(2) loss by 28.7% on a daytime basis and an estimated 16 to 18% on a 24-hour basis.

Seasonal Pattern of Photosynthesis in Individual Grass Leaves and Other Plant Parts in Arctic Alaska with a Portable14CO2System

A portable system for photosynthesis determinations has been used under field conditions in the Arctic at Barrow, Alaska. Maximum photosynthetic rates were greater than 18 mg CO2·dm-2·h$^{-1}$ in a number of species and were comparable with those of other C3 plants in arctic and temperate areas. Rates were closely coupled to irradiance Plant components other than expanded blades were active in CO2 uptake. In Dupontia fischeri, leaf sheaths and culms possessed rates greater than 50% those of mature leaves. The leaves of D. fischeri and Alopecurus alpinus are produced sequentially and possess distinct seasonal patterns which appear related to leaf growth, maturation, and senescence stages. Thus, even in the short growing season of the Arctic, these grasses possess sequential patterns of leaf development and photosynthesis rather than a synchronized early season burst of leaf production.