Daily Photosynthetic Photon Flux Density Research Articles

Optimization of Photoautotrophic Growth Regimens of Scenedesmaceae alga: The Influence of Light Conditions and Carbon Dioxide Concentrations

Improving methods for landless production of bioproducts is considered an important stage in the development of the modern bioeconomy. In this context, microalgal biomass is one of the most promising sources of valuable substances due to its rich biochemical composition. Despite the high adaptability of microalgae to various environmental factors, the effectiveness of cultivation systems depends on precisely selected parameters. Both the light conditions and the supply of inorganic carbon sources are key in determining the efficiency of photoautotrophic cultivation. In this work, the effect of a high daily photosynthetic photon flux density (PPFD) ranging from 37.44 to 112.32 mol m−2 day−1 on the growth and productivity of a novel Scenedesmaceae alga, strain EZ-B1, was assessed. The next stage of cultivation consisted of selecting the optimal CO2 concentration. Improved performance of microalga during cultivation in a photobioreactor was achieved at 112.32 mol m−2 day−1 (24 h photoperiod) and by supplying 2% CO2, as evidenced by the high biomass productivity (0.69 g L−1 day−1), total biomass yield (5.23 g L−1), and ammonium nitrogen consumption rate. The data obtained suggest that a higher level of PPFD led to the highest growth rate of the novel strain and the highest biomass productivity, which, in practice, will increase production capacity.

Predicting sunlight availability for vertical shelves using simulation

Vertical farming (VF) allows for a higher number of plants to be grown in a limited land area, maximizing agricultural land use. VF employs multiple vertical shelves. Each shelf consists of several levels. This paper aims to develop a computer simulation model. The computer model could predict the sunlight availability received at each level of the shelves. The model was developed using RHINO (RHINOCEROS) software with Grasshopper plug-in. The VF shelf was constructed for the experiment in Chiang Mai, Thailand. The experiment data is used to validate the computer model. The validated computer simulation model is then used to predict the daily averaged Photosynthetic Photon Flux Density (PPFD) received by each level of vertical shelves. Year-round daily averaged PPFD provides insights into the seasonal variations of sunlight availability. For the VF shelf constructed for experiment in Chiang Mai, it was found that the top level of the shelf would receive a yearly average of 1275.17 PPFD. The middle and bottom would receive 781.29 and 617.67 PPFD, respectively. The month with the lowest amount of sunlight is in January. This computer simulation model will help predict solar radiation received by each vertical farming shelf. The farmers could identify suitable shelf designs to provide enough PPFD for specific crops to be grown.

Estimating Light Acclimation Parameters of Cucumber Leaves Using Time-Weighted Averages of Daily Photosynthetic Photon Flux Density.

Leaves acclimate to day-to-day fluctuating levels of photosynthetic photon flux density (PPFD) by adjusting their morphological and physiological parameters. Accurate estimation of these parameters under day-to-day fluctuating PPFD conditions benefits crop growth modeling and light environment management in greenhouses, although it remains challenging. We quantified the relationships between day-to-day PPFD changes over 6 days and light acclimation parameters for cucumber seedling leaves, including leaf mass per area (LMA), chlorophyll (Chl) a/b ratio, maximum net photosynthetic rate (Pnmax), maximum rate of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Vcmax), and maximum rate of electron transport (Jmax). The last two parameters reflect the capacity of the photosynthetic partial reactions. We built linear regression models of these parameters based on average or time-weighted averages of daily PPFDs. For time-weighted averages of daily PPFDs, the influence of daily PPFD was given a specific weight. We employed three types of functions to calculate this weight, including linear, quadratic, and sigmoid derivative types. We then determined the trend of weights that estimated each parameter most accurately. Moreover, we introduced saturating functions to calibrate the average or time-weighted averages of daily PPFDs, considering that light acclimation parameters are usually saturated under high PPFDs. We found that time-weighted average PPFDs, in which recent PPFD levels had larger weights than earlier levels, better estimated LMA than average PPFDs. This suggests that recent PPFDs contribute more to LMA than earlier PPFDs. Except for the Chl a/b ratio, the average PPFDs estimated Pnmax, Vcmax, and Jmax with acceptable accuracy. In contrast, time-weighted averages of daily PPFDs did not improve the estimation accuracy of these four parameters, possibly due to their low response rates and plasticity. Calibrating functions generally improved estimation of Chl a/b ratio, Vcmax, and Jmax because of their saturating tendencies under high PPFDs. Our findings provide a reasonable approach to quantifying the extent to which the leaves acclimate to day-to-day fluctuating PPFDs, especially the extent of LMA.

Recent levels of daily photosynthetic photon flux density have a larger influence on light acclimation responses of cucumber leaves than earlier levels

Recent levels of daily photosynthetic photon flux density have a larger influence on light acclimation responses of cucumber leaves than earlier levels

Relationships between light environment and subsurface accumulation during the daytime in the red-tide dinoflagellate Karenia mikimotoi

Diurnal vertical migration of the red-tide dinoflagellate Karenia mikimotoi and environmental conditions were measured in Hiroshima Bay and the Yatsushiro Sea in July of 2012 and 2015, respectively. The uppermost daytime depths for K. mikimotoi were 1.3–6.0 m and did not correspond to the pycnocline; most cells reached the bottom each night. Although the incident photosynthetic photon flux density (PPFD) varied among days, average PPFDs at the mean cell distribution depths were similar (59–65 µmol m−2 s−1) between compensation and saturation PPFDs for photosynthesis. Total daily PPFD at the mean depth was between the growth threshold and that for maximum growth rates. Among visible wavelengths, the photon flux density of green and yellow light (500–600 nm) at the mean depth was major (about 61% of the total), and the PFD of blue (400–500 nm) was always relatively minor (about 20%). Laboratory results identified green light as sufficient for K. mikimotoi growth, yielding growth rates equivalent to those under blue light. This study suggests that the vertical cell distribution depth during the daytime is regulated by underwater light transmission and that green light is valuable for growth and photosynthesis of K. mikimotoi.

Covariation between understorey light environments and soil resources in Bornean mixed dipterocarp rain forest

Abstract:Variation in understorey irradiance is both a cause and consequence of the structure and dynamics of closed-canopy forests, which are also influenced by soil nutrients and water availability. We tested the hypothesis that understorey light regimes differ among four mixed dipterocarp forest types that share the same rainfall, but grow on different soils along an edaphic gradient at one site in Borneo. Based on data from photosynthetically active radiation sensors deployed at 1-m height at 36 locations for 351 sensor-days, we found significant soil-related variation in irradiance. The more productive forest types on clay and fine loam had lower daily photosynthetic photon flux density (PPFD) than those on the more nutrient-depleted and better-drained sandy loam and loam. They also had fewer moderate to high-intensity sunflecks, and a greater proportion of their daily PPFD came from low-intensity light. Understorey irradiance did not, however, monotonically decline with increasing soil resources. Forests on intermediate soils had greater irradiance than those with more and less soil resources, due to steeper slopes. Plant communities arrayed on resource gradients are commonly used to test hypotheses of environmental factors driving their assembly. Our results indicate that consideration of multiple resource dimensions in such tests is critical.

Day‐length effects on carbon stores for respiration of perennial ryegrass

• The mechanism controlling the use of stored carbon in respiration is poorly understood. Here, we explore if the reliance on stores as respiratory substrate depends on day length. • Lolium perenne (perennial ryegrass) was grown in continuous light (275 μmol photons m(-2) s(-1) ) or in a 16 : 8 h day : night regime (425 μmol m(-2) s(-1) during the photoperiod), with the same daily photosynthetic photon flux density (PPFD). Plants in stands were labelled with (13)CO(2) : (12)CO(2) for various time intervals. The rates and isotopic signatures of shoot- and root-respired CO(2) were measured after labelling, and water-soluble carbohydrates were determined in biomass. The tracer kinetics in respired CO(2) was analysed with compartmental models to infer the sizes, half-lives and contributions of respiratory substrate pools. • Stores were the main source for respiration in both treatments (c. 60% of all respired carbon). But, continuous light slowed the turnover (+270%) and increased the size (+160%) of the store relative to the 16 : 8 h day : night regime. This effect corresponded with a greatly elevated fructan content. Yet, day length had no effect on sizes and half-lives of other pools serving respiration. • We suggest that the residence time of respiratory carbon was strongly influenced by partitioning of carbon to fructan stores.

Comparing indices of understory light availability between hemlock and hardwood forest patches

We evaluated whether two indices of light availability resolved differences among microsites within deeply shaded understories (<12% of above-canopy photosynthetic photon flux density (PPFD)) and also whether marked differences in forest canopy structure affected how the two indices related to direct measures of incident photosynthetically active radiation (PAR). Incident PAR was measured with gallium–arsenide–phosphide photodiodes at numerous points in two adjacent forest patches in Michigan, USA: one dominated by the evergreen conifer eastern hemlock ( Tsuga canadensis (L.) Carrière), and the other by the deciduous hardwood sugar maple ( Acer saccharum Marsh.). The two indices tested were canopy openness, measured with the LI-COR LAI-2000 plant canopy analyzer, and the percentage of above-canopy PPFD measured in the understory during overcast conditions (%PPFD). Canopy openness and %PPFD did not effectively predict the long-term mean of daily PPFD. However, both indices reliably predicted the long-term mean of daily median PPFD, an alternative standard of directly measured incident PAR that reduces the relative contribution of sunflecks. The relationships of both indices with mean daily median PPFD differed between hemlock and hardwood patches. Hence, the effect of canopy structure should be considered when using these indices to draw conclusions about differences in light availability between forest patches, particularly when narrow ranges of light availability in deep shade are important.

Temperature controls ecosystem CO2 exchange of an alpine meadow on the northeastern Tibetan Plateau

AbstractAlpine ecosystems are extremely vulnerable to climate change. To address the potential variability of the responses of alpine ecosystems to climate change, we examined daily CO2 exchange in relation to major environmental variables. A dataset was obtained from an alpine meadow on the Qinghai‐Tibetan Plateau from eddy covariance measurements taken over 3 years (2002–2004). Path analysis showed that soil temperature at 5 cm depth (Ts5) had the greatest effect on daily variation in ecosystem CO2 exchange all year around, whereas photosynthetic photon flux density (PPFD) had a high direct effect on daily variation in CO2 flux during the growing season. The combined effects of temperature and light regimes on net ecosystem CO2 exchange (NEE) could be clearly categorized into three areas depending on the change in Ts5: (1) almost no NEE change irrespective of variations in light and temperature when Ts5 was below 0 °C; (2) an NEE increase (i.e. CO2 released from the ecosystem) with increasing Ts5, but little response to variation in light regime when 0 °C≤Ts5≤8 °C; and (3) an NEE decrease with increase in Ts5 and PPFD when Ts5 was approximately >8 °C. The highest daily net ecosystem CO2 uptake was observed under the conditions of daily mean Ts5 of about 15 °C and daily mean PPFD of about 50 mol m−2 day−1. The results suggested that temperature is the most critical determinant of CO2 exchange in this alpine meadow ecosystem and may play an important role in the ecosystem carbon budget under future global warming conditions.

The carbon cycle in a bioregenerative life support system with a soil-like substrate

A mass-flow model of carbon cycle in a bioregenerative life support system (BLSS) including Resource, Plant Growth, Food Processing, Human, Waste Processing, and Waste Storage Modules was developed. A human received food from Plant Growth and Resource Modules. Plants were assumed to be growing on the soil-like substrate (SLS). Another function of SLS was balancing the carbon cycle. The input of BLSS was set to 81 g of carbon per day along with food from the Resource Module. To balance the carbon cycle an equal amount of carbon was removed from BLSS along with urine, feces, plant wastes, and SLS. A mass flow of carbon cycle was used to simulate the effect of light intensity on the basic parameters of the Plant Growth Module. It was calculated that the stationary dry mass of SLS increases from 10 to 35 kg m - 2 with increase canopy-level daily photosynthetic photon flux (PPF) from 34 to 178 mol m - 2 d - 1 . On the contrary dry mass of SLS needed to provide one person with plant food is not dependent on light intensity.

Photosynthesis and Optimal Light Microhabitats for a Rare Cactus, Mammillaria gaumeri, in Two Tropical Ecosystems

ABSTRACT Mammillaria gaumeri, an endemic cactus from Yucatan, is threatened due to human‐mediated habitat fragmentation but knowledge regarding factors that would inform management plans is limited, including information on optimal microhabitats and growth. We studied seasonal patterns of microclimate, net CO2 uptake and growth of adult individuals during the dry, rainy and northwind (late fall to winter) seasons in separate populations located in a coastal dune and in a dry forest. To provide an assay of primary productivity, we measured the production of new axillary buds (areoles) from the apex. We found that patterns of net CO2 uptake in the three seasons were consistent with obligate crassulacean acid metabolism. The reduction in soil water potential and the increase in water vapor pressure deficit led to a reduction in 24‐h net CO2 uptake from 18.0 to 1.3 mmol CO2/m2, after 30 d of drought. Dry‐weight gain was maximal during the rainy season and there was no growth during the dry season, thus seasonal patterns of net CO2 uptake and growth for M. gaumeri reflected soil and atmospheric water contents. Annual dry‐weight gain increased linearly with plant size and with total daily photosynthetic photon flux density (PPFD) up to 80 percent of ambient. Maximal growth was in exposed microhabitats receiving 60–80 percent of total ambient PPFD. We hypothesize that low‐magnitude disturbances, resulting in more exposed microhabitats, might be beneficial for growth and conservation of adult individuals of this rare species.

Photosynthetic capacity and nitrogen partitioning in foliage of the evergreen shrub Daphniphyllum humile along a natural light gradient

We examined the effects of leaf age and mutual shading on the morphology, photosynthetic properties and nitrogen (N) allocation of foliage of an evergreen understory shrub, Daphniphyllum humile Maxim, growing along a natural light gradient in a deciduous Fagus crenata-dominated forest in Japan. Seedlings in high-light environments were subject to greater mutual shading and 1-year-old foliage survival was lower than in seedlings in low-light environments, indicating that the survival rates of foliage were related to the degree of mutual shading. Although specific leaf area (SLA) in current- and 1-year-old foliage was curvilinearly related to daily photosynthetic photon flux (PPF), SLA was unaffected by leaf age, indicating that foliage in D. humile may not acclimate morphologically to annual changes in light caused by mutual shading. Light-saturated net photosynthetic rates (Pmax) were correlated with daily PPF in current-year foliage. In addition, a strong, positive relationship was found between nitrogen concentration per unit leaf area and Pmax. In contrast, the relationship among PPF, N and photosynthetic parameters in 1-year old foliage was weak because of the strong remobilization of N from older leaves to current-year foliage in plants growing in high light. However, the relationship between daily PPF and both photosynthetic N-use efficiency and the ratio of maximum electron transport rate to maximum carboxylation rate did not differ between current-year and 1-year-old foliage, suggesting that these responses help maintain a high photosynthetic efficiency even in older foliage. We conclude that D. humile maximizes whole-plant carbon gain by maintaining a balance among photosynthetic functions across wide ranges of leaf ages and light environments.

(50) Evaluating Low Light Level Effects on Chlorophyll Content and Commercial Quality in Several Species of Bambuseae

Bamboo has increasingly become a popular exterior ornamental plant because of its durability, versatility, and evergreen qualities in conditions of extreme temperature and moisture variations. Use as an interior foliage plant has been limited due to the difficulty of finding species adaptable to lower light levels. Nineteen species from seven genera (Bambusa, Cephalostachyum, Dendrocalamus, Gigantochloa, Schizostachyum, Thyrsostachys, and Vietnamosasa) were evaluated. Fifteen plants from each species were potted in like conditions (50% leaf mold; 50% topsoil; 5 g of 14–14–14 controlled-release fertilizer) and grown under a maximum daily photosynthetic photon flux density (PPFD) range between 1200 to 2000 μmol·m-2·s-1 for 6 weeks. Chlorophyll content of leaves was measured. The commercial quality of leaves, culms, and general appearance was also recorded. Light was then limited to a maximum PPFD of 150 to 300 μmol m-2s-1 for 6 weeks and all measurements were again recorded. Five species had significant increases in chlorophyll content after the 6-week period of reduced light levels. Species with a larger maturity size had a greater mortality percentage as well as lower quality leaf and overall appearance when grown under reduced light levels. Culm quality remained constant in 18 of the 19 species after the 6-week period. Vietnamosasa ciliata showed the greatest increase in chlorophyll levels as well as highest commercial quality of leaf and overall appearance.

Acclimation of Plant Populations to Shade: Photosynthesis, Respiration, and Carbon Use Efficiency

Cloudy days cause an abrupt reduction in daily photosynthetic photon flux (PPF), but we have a poor understanding of how plants acclimate to this change. We used a unique 10-chamber, steady-state, gas-exchange system to continuously measure daily photosynthesis and night respiration of populations of a starch accumulator [tomato (Lycopersicon esculentum Mill. cv. Micro-Tina)] and a sucrose accumulator [lettuce (Lactuca sativa L. cv. Grand Rapids)] over 42 days. All measurements were done at elevated CO2 (1200 μmol·mol-1) to avoid any CO2 limitations and included both shoots and roots. We integrated photosynthesis and respiration measurements separately to determine daily net carbon gain and carbon use efficiency (CUE) as the ratio of daily net C gain to total day-time C fixed over the 42-day period. After 16 to 20 days of growth in constant PPF, plants in some chambers were subjected to an abrupt PPF reduction to simulate shade or a series of cloudy days. The immediate effect and the long term acclimation rate were assessed from canopy quantum yield and carbon use efficiency. The effect of shade on carbon use efficiency and acclimation was much slower than predicted by widely used growth models. It took 12 days for tomato populations to recover their original CUE and lettuce CUE never completely acclimated. Tomatoes, the starch accumulator, acclimated to low light more rapidly than lettuce, the sucrose accumulator. Plant growth models should be modified to include the photosynthesis/respiration imbalance and resulting inefficiency of carbon gain associated with changing PPF conditions on cloudy days.

Photosynthetic Irradiance and Nutrition Effects on Growth of English Ivy in Subirrigation Systems

The growth of three english ivy cultivars in ebb-and-flow subirrigation systems was examined under three photosynthetic photon flux (PPF) treatments (low, medium, or high, corresponding to an average daily PPF of 3.2, 5.4, or 8.5 mol·m–2·d–1, respectively) and four fertilizer concentrations (0, 100, 200, or 300 mg·L–1 N) geared toward production of acclimatized foliage plants. Marketable quality english ivy can be subirrigated with 100 mg·L–1 N. Although 8.5 mol.m–2.d–1 produced the maximum shoot dry weight (SDW), good quality plants also were produced under 5.4 mol·m–2·d–1. `Gold Child', `Gold Dust', and `Gold Heart' english ivy produced with low fertility and low light may be better acclimatized and show superior performance in interior environments. Under light levels lower than 8.5 mol·m–2·d–1, `Gold Heart' had less variegation (12% or 21% for ivy grown under 3.2 or 5.4 mol·m–2·d–1, respectively). `Gold Dust' and `Gold Child' had 65% and 22% variegated leaf area, respectively, when grown under 5.4 mol·m–2·d–1 PPF. Under 5.4 mol·m–2·d–1 PPF, `Gold Dust' retains attractive foliage with overall perception of increased lighter-green coloration.

Carbon Dioxide Exchange Between the Atmosphere and an Alpine Shrubland Meadow During the Growing Season on the Qinghai‐Tibetan Plateau

Abstract: In the present study, we used the eddy covariance method to measure CO2 exchange between the atmosphere and an alpine shrubland meadow ecosystem (37°36’N, 101°18’E; 3 250 m a.s.l.) on the Qinghai‐Tibetan Plateau, China, during the growing season in 2003, from 20 April to 30 September. This meadow is dominated by formations of Potentilla fruticosa L. The soil is Mol‐Cryic Cambisols. During the study period, the meadow was not grazed. The maximum rates of CO2 uptake and release derived from the diurnal course of CO2 flux were ‐9.38 and 5.02 μmol·m‐2·s‐1, respectively. The largest daily CO2 uptake was 1.7 g C·m‐2·d‐1 on 14 July, which is less than half that of an alpine Kobresia meadow ecosystem at similar latitudes. Daily CO2 uptake during the measurement period indicated that the alpine shrubland meadow ecosystem may behave as a sink of atmospheric CO2 during the growing season. The daytime CO2 uptake was correlated exponentially or linearly with the daily photo synthetic photon flux density each month. The daytime average water use efficiency of the ecosystem was 6.47 mg CO2/g H2O. The efficiency of the ecosystem increased with a decrease in vapor pressure deficit.(Managing editor: Ya‐Qin HAN)

Physiological and ecological significance of sunflecks for dipterocarp seedlings

Irradiance is highly dynamic in many plant canopies. Photosynthesis during sunflecks provides 10-90% of daily carbon gain. The survivorship of tree seedlings in the deeply shaded understorey of tropical rain forests is limited by their ability to maintain a positive carbon balance. Dipterocarp seedlings from the SE Asian rain forest were used as a model system to test novel aspects of the physiological and ecological significance of sunflecks. First, understorey seedlings experienced leaf temperatures up to 38 degrees C in association with sunflecks. Under controlled environment conditions, the inhibition of carbon gain at 38 degrees C, compared with 28 degrees C, was significantly greater during a sequence of sunflecks (-59%), than under uniform irradiance (-40%), providing the same total photosynthetic photon flux density (PPFD). Second, the relative enhancement effects of elevated [CO2] were greater under sunflecks (growth +60%, carbon gain +89%), compared with uniform irradiance (growth +25%, carbon gain +59%), supplying the same daily PPFD. Third, seedling growth rates in the forest understorey were 4-fold greater under a dynamic irradiance treatment characterized by long flecks, compared with a regime of short flecks. Therefore, stresses associated with dynamic irradiance may constrain photosynthetic carbon gain. Additionally, seedling photosynthesis and growth may be more responsive to interactions with abiotic factors, including future changes in climate, than previously estimated. The sensitivity of seedling growth to varying patterns of dynamic irradiance, and the increased likelihood of species-specific responses through interactions with environmental factors, indicates the potential for sunflecks to influence regeneration processes, and hence forest structure and composition.

Light Intensity and Fertilizer Concentration: II. Optimal Fertilizer Solution Concentration for Species Differing in Light Requirement and Growth Rate

To evaluate the effects of increasing photosynthetic photon flux (PPF) on optimal fertilizer concentrations, we grew wax begonia (Begonia semperflorens-cultorum Hort.) and petunia (Petunia ×hybrida Hort. Vilm-Andr.) seedlings in a soilless growing medium without starter fertilizer under three PPF treatments (high, medium, and low corresponding to an average daily PPF of 23.2, 15.6, and 9.8 mol·m-2.d-1, respectively) and subirrigated with six fertilizer concentrations [electrical conductivity (EC) of 0.12, 0.65, 1.18, 1.71, 2.24, and 2.77 dS·m-1]. Compared to low PPF, shoot dry mass of wax begonia and petunia seedlings increased 2- and 3-fold, respectively, at high PPF. Fertilizer EC resulting in maximum shoot dry mass was the same (1.28 and 1.87 dS·m-1 for wax begonia and petunia, respectively) in the three PPF treatments. Shoot dry mass and leaf area of petunias decreased little at higher than optimal fertilizer EC in the three PPF treatments, while growth of begonia was inhibited at high fertilizer EC. The optimal fertilizer range, calculated as the lower and upper limits of fertilizer EC within which plant growth was not reduced by >10% as compared to the optimum EC was 0.65 to 1.71 dS·m-1 in wax begonia and 1.18 to >2.77 dS·m-1 for petunia. Compared to those grown at 1.18 dS·m-1, wax begonias grown at 1.71 dS·m-1 had similar dry mass, but were shorter in all three PPF treatments (average height reduction of 6.5%). In general, EC of the top layer of the growing medium was higher than that of the bottom layer of the growing medium, and this difference increased with increasing EC.

Microenvironment of a corn–soybean–oat strip intercrop system

The microenvironment of a corn ( Zea mays L.)–soybean ( Glycine max [L.] Merr.)–oat ( Avena sativa L.) narrow strip intercrop system was studied on four farms in Iowa, USA during 1991–1993 (one or two farms studied each year) with the objective of explaining previously observed patterns of strip-crop yields. Air and soil temperatures, humidity, wind, and photosynthetic photon flux density (PPFD) for each row in a strip were recorded continuously during 4–13-day periods several times during each growing season; short-term measurements of light extinction through the corn and soybean canopies were made late in the 1993 growing season. Soybean biomass in September 1993 was also determined. Early in the growing season, there typically were no significant differences among rows within a strip in any environmental or growth variable. Later in the growing season, daily PPFD received varied more across each strip than any other environmental variable measured; the outer side of edge rows of corn in north–south rows typically received significantly higher daily PPFD (2–38% more) than inner rows in the strip, while the outside of the soybean row furthest from corn received 36–140% greater PPFD than the corn-side of the row next to the corn strip. Soybean height; leaf mass per leaf area; and leaf mass, stem mass, and pod mass per unit land area in September were strongly related to daily PPFD, with all except height increasing with greater PPFD. Total biomass increased by 32% from the row closest to corn to the row furthest from corn, although there was no change in the ratio of leaf:stem:pod with row position. Thus, PPFD varied the most across the strips of any environmental variable, and crop growth was closely related to PPFD received.

Carbon dioxide exchange between the atmosphere and an alpine meadow ecosystem on the Qinghai–Tibetan Plateau, China

We used the eddy covariance method to measure the CO 2 exchange between the atmosphere and an alpine meadow ecosystem (37°29–45′N, 101°12–23′E, 3250 m a.s.l.) on the Qinghai–Tibetan Plateau, China in the 2001 and 2002 growing seasons. The maximum rates of CO 2 uptake and release derived from the diurnal course of CO 2 flux ( F CO 2 ) were −10.8 and 4.4 μmol m −2 s −1, respectively, indicating a relatively high net carbon sequestration potential as compared to subalpine coniferous forest at similar elevation and latitude. The largest daily CO 2 uptake was 3.9 g C m −2 per day on 7 July 2002, which is less than half of those reported for lowland grassland and forest at similar latitudes. The daily CO 2 uptake during the measurement period indicated that the alpine ecosystem might behave as a sink of atmospheric CO 2 during the growing season if the carbon lost due to grazing is not significant. The daytime CO 2 uptake was linearly correlated with the daily photosynthetic photon flux density each month. The nighttime averaged F CO 2 showed a positive exponential correlation with the soil temperature, but apparently negative correlation with the soil water content.