Measurements Of Net Photosynthesis Research Articles

Combo chloro-photosynthetic device and applications for greenhouse gas reduction campaign and smart agriculture

The increasing carbon dioxide (CO2) levels in the air pose a direct threat to all living organisms and the environment. Leveraging the ability of plants to absorb CO2 is one of the most effective methods for countering these rising CO2 levels. The present study aimes to develop a combo photosynthetic and chlorophyll-a sensor based on Non-Dispersive Infrared (NDIR) spectroscopy and an optical method. This sensor enables simultaneous, intensive measurement of net photosynthesis and chlorophyll-a content and yields accurate information. Comparative analysis of the efficacy of the sensors to that of a commercial instrument demonstrated that the measurement values obtained from the developed photosynthetic and chlorophyll-a sensors were not significantly different from those acquired with the commercial instrument (portable photosynthesis system LI-6400) and chlorophyll metre (SPAD-502), with a 95 % confidence level. Furthermore, the developed photosynthetic sensor could be used as a new correlation unit for chlorophyll-a content and net photosynthesis. Therefore, the sensor can be used to propose effective plantation processes to reduce atmospheric CO2 levels and in smart farming systems to control the quality of yields.

Anti-Transpirant Effects on Vine Physiology, Berry and Wine Composition of cv. Aglianico (Vitis vinifera L.) Grown in South Italy

In viticulture, global warming requires reconsideration of current production models. At the base of this need there are some emerging phenomena: modification of phenological phases; acceleration of the maturation process of grapes, with significant increases in the concentration of sugar musts; decoupling between technological grape maturity and phenolic maturity. The aim of our study was to evaluate the effect of a natural anti-transpirant on grapevine physiology, berry, and wine composition of Aglianico cultivar. For two years, Aglianico vines were treated at veraison with the anti-transpirant Vapor Gard and compared with a control sprayed with only water. A bunch thinning was also applied to both treatments. The effectiveness of Vapor Gard were assessed through measurements of net photosynthesis and transpiration and analyzing the vegetative, productive and qualitative parameters. The results demonstrate that the application of anti-transpirant reduced assimilation and transpiration rate, stomatal conductance, berry sugar accumulation, and wine alcohol content. No significant differences between treatments were observed for other berry and wine compositional parameters. This method may be a useful tool to reduce berry sugar content and to produce wines with a lower alcohol content.

Photosynthetic activity of two life history stages of Costaria costata (Laminariales, Phaeophyceae) in response to PAR and temperature gradient

:Photosynthetic responses to photosynthetically active radiation (PAR) and temperature were investigated in the macroscopic sporophyte (SPO) and microscopic gametophyte (GAM) stages of the brown alga Costaria costata from Hokkaido, Japan. Measurements of net photosynthesis, respiration rates and photochemical efficiency were carried out using dissolved oxygen sensors and a pulse amplitude–modulated fluorometer. Net photosynthesis–irradiance curves of the two life history stages revealed a similarity in their light-saturated photosynthesis rates but a difference in initial slopes, with lower efficiency in oxygenic evolution for SPO than for GAM. Consequently, compensation PAR (Ec = 9 μmol photons m−2 s−1) and saturation PAR (Ek = 243 μmol photons m−2 s−1) of the sporophyte were higher than for the gametophyte (Ec = 1 μmol photons m−2 s−1; Ek = 44 μmol photons m−2 s−1). This reflects the low-PAR adaptation of the microscope stage that is commonly found on the underside of rocks or in crevices where light exposure is limited. Continuous exposures to low (6 h, 100 μmol photons m−2 s−1) and high PAR (1000 μmol photons m−2 s−1) induced photoinhibition of photosynthesis, with larger declines in gametophyte effective quantum yields (ΦPSII). Gametophyte maximum quantum yields (Fv/Fm) also did not fully recover even after 12 h of dark acclimation, indicating photodamage. As for the temperature response in C. costata, gross photosynthesis and Fv/Fm characteristics were similar for both developmental stages, with temperature optima ranging from 14°C to 22°C. Their Fv/Fm and oxygenic net photosynthesis were relatively insensitive to low temperatures but declined above 24°C. This may explain the disappearance of C. costata sporophytes from their habitat during summer as well as their southern distributional limit in the western Pacific.

N2 fixation and primary productivity in a red sea Halophila stipulacea meadow exposed to seasonality

AbstractThe tropical seagrass Halophila stipulacea exhibits a limited capacity to use nitrate, but has a high uptake capacity and efficiency for ammonium. Consequently, N2 fixation by associated diazotrophic epiphytes may be important in providing ammonium needed for seagrass photosynthesis and growth. When exposed to seasonality, this association could provide a competitive advantage for H. stipulacea in relation to other seagrass species, but related knowledge is scarce. Here, we thus report measurements of net photosynthesis (O2 fluxes) and N2 fixation (acetylene reduction) associated with H. stipulacea from the Northern Red Sea over all four seasons of 2013. In parallel, we characterized the seagrass meadow areal extent, shoot and leaves density, and the leaf area index. Using this data, we quantified meadow net primary production and N2 fixation and estimated the photo‐metabolic N demand met by N2 fixation at the community level. Results revealed a marked seasonality of meadow N2 fixation, with rates ranging from 0.06 in winter to 4.60 mmol N m−2 d−1 in summer, i.e., an increase by two orders of magnitude. In summer, when nutrient concentrations in the water column were lowest and light intensity and temperature highest, there was a significant positive linear relationship between meadow net primary production and N2 fixation, with the latter accounting for ca. 20% of the photo‐metabolic N demand. These findings suggest that N2 fixation by associated diazotrophic epiphytes can mitigate N limitation of H. stipulacea meadows under N scarcity. This trait may also favor the ongoing geographical expansion of H. stipulacea.

Photosynthetic performance of the red alga Solieria pacifica (Solieriaceae) from two different depths in the sublittoral waters of Kagoshima, Japan

Photosynthetic responses to photosynthetically active radiation (PAR) and temperature were examined in the red alga Solieria pacifica from deep (35 m) and shallow (5 m) portions of the sublittoral zone in Kagoshima, Japan. Dissolved oxygen sensors and pulse-amplitude modulated (PAM) fluorometry were used for the measurements of net photosynthesis, dark respiration rates, and photochemical efficiency. The photosynthetic performances of the deep- and shallow-water ecotypes provided substantial evidence of their adaptation to the ambient PAR and temperature conditions of their respective habitats. Both algal samples showed different temperature optima for photosynthesis: 19.5–19.9 °C for S. pacifica from Mageshima (MAG) and 18.6–27.0 °C for species from Yatsushiro Bay (YAT), that reflect the temperature ranges in the 35- and 5-m depths of the sublittoral zone, respectively. Maximum net photosynthetic rate (P max = 3.73 μg O2 gfw −1 min−1), compensation PAR (E c = 21 μmol photons m−2 s−1), and saturation PAR (E k = 131 μmol photons m−2 s−1) were higher in YAT S. pacifica than in MAG samples (P max = 1.55 μg O2 gfw −1 min−1, E c = 3 μmol photons m−2 s−1, E k = 15 μmol photons m−2 s−1), which can be attributed to the higher PAR levels experienced by the seaweeds occurring at depths of 5 m. The large depressions in effective quantum yields (Φ PSII) after chronic PAR exposures and failed recovery in maximum quantum yields (F v /F m) after dark acclimation of MAG S. pacifica suggest a greater tendency for photodamage in the deep-water ecotype. As for the shallow-water S. pacifica (YAT), complete recovery occurred only at 20 °C. Low temperature limitation may account for the decreased gross photosynthetic rates and delayed recovery of post-dark acclimation F v /F m of YAT S. pacifica at temperatures below their optimum, which can occur during winter.

CO2 sequestration in two mediterranean dune areas subjected to a different level of anthropogenic disturbance

Coastal sand dunes are among the most threatened habitats, especially in the Mediterranean Basin, where the high levels of human pressure impair the presence of plant species, putting at risk the maintenance of the ecosystem services, such as CO2 sequestration provided by these habitats. The aim of this study was to analyze how disturbance-induced changes in plant species abundance patterns account for variations in annual CO2 sequestration flow (CS) of Mediterranean sand dune areas. Two sites characterized by a high (site HAD) and a lower (site LAD) anthropogenic disturbance level were selected. At both sites, plant species number, cover, height and CS based on net photosynthesis measurements were sampled. At the plant species level, our results highlighted that Ammophila arenaria and Pancratium maritimum, had a key role in CS. Moreover, the results revealed a patchy species assemblage in both sites. In particular, HAD was characterized by a higher extension of the anthropogenic aphytoic zone (64% of the total transect length) than LAD. In spite of the observed differences in plant species composition, there were not significant differences between HAD and LAD in structural and functional traits, such as plant height and net photosynthesis. As a consequence, HAD and LAD had a similar CS (443 and 421 Mg CO2 ha−1 y−1, respectively). From a monetary point of view, our estimates based on the social costs of carbon revealed that the flow of sequestered CO2 valued on an average $ 3181 ± 114 ha−1 year−1 (mean value for the two sites). However, considering also the value of the CO2 negative flow related to loss of vegetated area, the annual net benefit arising from CO2 sequestration amounted to $ 1641 and $ 1772 for HAD and LAD, respectively. Overall, the results highlighted the importance to maximize the efforts to preserve dune habitats by applying an effective management policy, which could allow maintaining also a regulatory ecosystem service such as CO2 sequestration.

Measuring whole plant CO2 exchange with the environment reveals opposing effects of the gin2–1 mutation in shoots and roots of Arabidopsis thaliana

Using a cuvette for simultaneous measurement of net photosynthesis in above ground plant organs and root respiration we investigated the effect of reduced leaf glucokinase activity on plant carbon balance. The gin2–1 mutant of Arabidopsis thaliana is characterized by a 50% reduction of glucokinase activity in the shoot, while activity in roots is about fivefold higher and similar to wild type plants. High levels of sucrose accumulating in leaves during the light period correlated with elevated root respiration in gin2–1. Despite substantial respiratory losses in roots, growth retardation was moderate, probably because photosynthetic carbon fixation was simultaneously elevated in gin2–1. Our data indicate that futile cycling of sucrose in shoots exerts a reduction on net CO2 gain, but this is over-compensated by the prevention of exaggerated root respiration resulting from high sucrose concentration in leaf tissue.

Simulated climate change reduced the capacity of lichen-dominated biocrusts to act as carbon sinks in two semi-arid Mediterranean ecosystems

The importance of biological soil crusts (biocrusts) for the biogeochemistry of drylands is widely recognized. However, there are significant gaps in our knowledge about how climate change will affect these organisms and the processes depending on them. We conducted a manipulative full factorial experiment in two representative dryland ecosystems from central (Aranjuez) and southeastern (Sorbas) Spain to evaluate how precipitation, temperature and biocrust cover affected the assimilation and net C balance of biocrusts. Chlorophyll fluorescence, net photosynthesis and dark respiration were measured in situ bimonthly during a year. We also conducted daily cycle measurements of net photosynthesis in winter and at the end of spring. In Sorbas, warming reduced the fixation of atmospheric C in biocrust-dominated microsites throughout the year. In Aranjuez, there was an interaction between the three factors evaluated; during winter, net photosynthesis was significantly greater in high biocrust cover plots under natural conditions and in the rainfall exclusion treatment. During the daily surveys, rainfall exclusion and warming reduced C fixation in Sorbas and in Aranjuez respectively. The effects of the treatments evaluated varied with the rainfall and non-rainfall water inputs (NRWIs) registered before the measurements. Our results suggest that changes in NRWI regimes as consequence of warming could have a greater impact on the C balance of biocrusts than changes in rainfall amounts. They also indicate that climate change may reduce the photosynthetic ability of lichens, with a consequent reduction of their dominance in biocrust communities at the mid to long term. This could reduce the ability of dryland ecosystems to fix atmospheric C.

Thermal acclimation of photosynthesis: on the importance of adjusting our definitions and accounting for thermal acclimation of respiration

While interest in photosynthetic thermal acclimation has been stimulated by climate warming, comparing results across studies requires consistent terminology. We identify five types of photosynthetic adjustments in warming experiments: photosynthesis as measured at the high growth temperature, the growth temperature, and the thermal optimum; the photosynthetic thermal optimum; and leaf-level photosynthetic capacity. Adjustments of any one of these variables need not mean a concurrent adjustment in others, which may resolve apparently contradictory results in papers using different indicators of photosynthetic acclimation. We argue that photosynthetic thermal acclimation (i.e., that benefits a plant in its new growth environment) should include adjustments of both the photosynthetic thermal optimum (T opt) and photosynthetic rates at the growth temperature (A growth), a combination termed constructive adjustment. However, many species show reduced photosynthesis when grown at elevated temperatures, despite adjustment of some photosynthetic variables, a phenomenon we term detractive adjustment. An analysis of 70 studies on 103 species shows that adjustment of T opt and A growth are more common than adjustment of other photosynthetic variables, but only half of the data demonstrate constructive adjustment. No systematic differences in these patterns were found between different plant functional groups. We also discuss the importance of thermal acclimation of respiration for net photosynthesis measurements, as respiratory temperature acclimation can generate apparent acclimation of photosynthetic processes, even if photosynthesis is unaltered. We show that while dark respiration is often used to estimate light respiration, the ratio of light to dark respiration shifts in a non-predictable manner with a change in leaf temperature.

Diurnal courses of net photosynthesis and photosystem II quantum efficiency of submerged Lagarosiphon major under natural light conditions

An optode device for net-photosynthesis measurements, based on oxygen-depending quenching of fluorescence from O2-specific sensors, and PAM fluorometry have been used to study diurnal courses of net-photosynthesis and the Fv/Fm ratio of the submerged plant Lagarosiphon major. Plants were pre-cultivated and studied in large mesocosm flow-through outdoor tanks under 50% and 80% shade cloth, respectively. Growth under the different shade cloths resulted in similar light compensation points (∼20μmol photonsm−2s−1), but strongly different light saturation levels, with about 150μmolm−2s−1 for plants grown under 80% shade cloth and about 350μmolm−2s−1 for plants grown under 50% shade cloth. Plants under both growth conditions showed a transient reduction of the maximum Fv/Fm value in the afternoon (down to 70% of the morning control values under 80% shade cloth and down to 85% under 50% shade cloth), which was not accompanied by a reduction of the net photosynthetic rate. This indicated that the fluorescence parameter Fv/Fm must not be a reliable indicator of the rate of photosynthesis under all conditions. The new photo-optical device became evidenced as a valuable tool not only for laboratory experiments, but also for field studies of gas exchange of submerged plants.

The influence of elevated temperature, elevated atmospheric CO2 concentration and water stress on net photosynthesis of loblolly pine (Pinus taeda L.) at northern, central and southern sites in its native range

AbstractWe investigated the effect of elevated [CO2] (700 μmol mol−1), elevated temperature (+2 °C above ambient) and decreased soil water availability on net photosynthesis (Anet) and water relations of one‐year old potted loblolly pine (Pinus taeda L.) seedlings grown in treatment chambers with high fertility at three sites along a north‐south transect covering a large portion of the species native range. At each location (Blairsville, Athens and Tifton, GA) we constructed four treatment chambers and randomly assigned each chamber one of four treatments: ambient [CO2] and ambient temperature, elevated [CO2] and ambient temperature, ambient [CO2] and elevated temperature, or elevated [CO2] and elevated temperature. Within each chamber half of the seedlings were well watered and half received much less water (1/4 that of the well watered).Measurements of net photosynthesis (Anet), stomatal conductance (gs), leaf water potential and leaf fluorescence were made in June and September, 2008. We observed a significant increase in Anet in response to elevated [CO2] regardless of site or temperature treatment in June and September. An increase in air temperature of over 2 °C had no significant effect on Anet at any of the sites in June or September despite over a 6 °C difference in mean annual temperature between the sites. Decreased water availability significantly reduced Anet in all treatments at each site in June. The effects of elevated [CO2] and temperature on gs followed a similar trend. The temperature, [CO2] and water treatments did not significantly affect leaf water potential or chlorophyll fluorescence. Our findings suggest that predicted increases in [CO2] will significantly increase Anet, while predicted increases in air temperature will have little effect on Anet across the native range of loblolly pine. Potential decreases in precipitation will likely cause a significant reduction in Anet, though this may be mitigated by increased [CO2].

Inhibition and acclimation of C3 photosynthesis to moderate heat: a perspective from thermally contrasting genotypes of Acer rubrum (red maple)

Effects of moderate heat on growth and photosynthesis were investigated in two clonal genotypes of Acer rubrum L., originally collected from the thermally contrasting habitats of Florida and Minnesota, USA, and known in the horticultural trade for sensitivity and insensitivity to heat, respectively. Under both common garden and warm greenhouse conditions (day/night temperature of 33/25 degrees C), the Florida genotype exhibited more growth than the Minnesota genotype. To determine the physiological parameters associated with this response, plants were acclimated to ambient (27/25 degrees C) or moderately elevated (33/25 degrees C) temperatures for 21 days before measurement of net photosynthesis at temperatures ranging from 25 to 48 degrees C. In vivo measurements of gas exchange and chlorophyll a fluorescence of ambient-acclimated plants revealed that, compared with the Minnesota genotype, the Florida genotype maintained a higher photosynthetic rate, higher stomatal conductance, more open PSII reaction centers, a greater PSII quantum yield and a lower quantum requirement for photosystem II (phi(PSII)) per mole of CO(2) fixed (phi(CO(2) )) throughout the measurement temperature range. When both genotypes were acclimated at 33/25 degrees C and measured at 33 degrees C, analysis of the response of net photosynthesis to calculated intercellular CO(2) concentration indicated that the maximal rate of Rubisco carboxylation (V(cmax)) decreased more in the Minnesota genotype than in the Florida genotype in response to elevated temperature. Additionally, phi(PSII)/phi(CO(2) ) at 33 degrees C was markedly higher for Minnesota plants under photorespiratory conditions, but similar to Florida plants under non-photorespiratory conditions. The results indicate that the higher net photosynthetic rate at 33/25 degrees C of the Florida genotype compared with the Minnesota genotype could be a result of several mechanisms, including the maintenance of a higher V(cmax )and a more efficient quantum requirement of PSII per mole of CO(2) fixed, which is likely the result of lower photorespiration.

Morpho-physiological responses of cowpea leaves to salt stress

The effect of salt stress of known intensity and duration on morpho-physiological changes in leaves of different ages from cowpea [Vigna unguiculata (L.) Walp.] plants was studied, aiming for a better understanding of the acclimation process of the whole-plant. Seeds were sown in vermiculite and seedlings were transferred to plastic trays containing aerated nutrient solution, and kept in a greenhouse. When the first trifoliate leaf emerged the seedlings were transplanted into 3 L plastic pots containing aerated nutrient solution. Salt additions started 5 d later, and the salt-treated plants received 25 mmol L-1 per day until reaching a final concentration of 75 mmol L-1. During the experimental period primary leaves and the 1st, 2nd, and 3rd trifoliate leaves were used for measurements of net photosynthesis, leaf area, leaf succulence, specific leaf mass, ions and chlorophyll concentrations. Growth analysis of the whole-plant was performed at the end of the experimental period. Salinity did not affect net photosynthesis, but reduced dry mass production and the number of lateral branches. Leaf concentrations of Na+, Cl-, K+ and P increased in salt-stressed plants, but these responses were dependent upon stress duration and leaf age. The higher concentration of potentially toxic ions (Na+ and Cl-) in older leaves could contribute to the reduced ion accumulation in growing tissues, but the tendency of K and P accumulation in leaves appeared to be the result of reduced re-translocation, i.e., not related to plant acclimation. Salinity also increased the source/sink ratio, leaf succulence, specific leaf mass, and chlorophyll accumulation per unit of leaf area, suggesting that the observed changes could be part of an integrated mechanism of whole-plant acclimation to salt stress.

Response of potato (Solanum tuberosum L.) to elevated atmospheric CO2 in the North American Subarctic

The response of potato ( Solanum tuberosum L., cv. Shepody) to elevated CO 2 was studied in 1994 at Fairbanks, Alaska using open-top chambers (OTC). Three CO 2 exposure levels were used in OTC: ambient (A); A + 175 μmol mol −1 CO 2 (A + 175); A + 350 μmol mol −1 CO 2 (A + 350). Plots were also established outside chambers (ANC) to test chamber affects. Potato leaf appearance rate and canopy development did not differ between CO 2 treatments. Six plants in each plot were harvested in late July and August. At the first harvest, the number of stems, total stem weight, number of flowers, and total flower dry weight decreased with increasing CO 2 . Biomass allocated to stems and leaves declined while allocation to tubers increased with elevated CO 2 . Root:shoot ratio was larger and percent leaf nitrogen declined 12.6% with increased CO 2 . At the final harvest, total tuber dry weight in A + 350 chambers was 36% higher than in the A treatment, but yields in open-top chamber plots were lower than the no-chamber plots possibly due to 7–14% less photosynthetic active radiation in chambers. Net photosynthesis measurements made on July 13 showed no differences due to CO 2 treatment; however, on August 5, net photosynthesis of leaves grown at A + 350 was 53% greater than at ambient CO 2 . Tuber initiation and growth began between the two photosynthesis measurements. Before tuber initiation, photosynthetic rates may have been down-regulated by insufficient carbon sink capacity.

TEMPERATURE EFFECTS ON PHOTOSYNTHESIS, GROWTH RESPIRATION, AND MAINTENANCE RESPIRATION OF MARIGOLD

TEMPERATURE EFFECTS ON PHOTOSYNTHESIS, GROWTH RESPIRATION, AND MAINTENANCE RESPIRATION OF MARIGOLD

Niche partitioning and photosynthetic response of alectorioid lichens from subalpine spruce–fir forest in north-central British Columbia, Canada: the role of canopy microclimate gradients

The distribution of alectorioid lichens in subalpine spruce–fir forests of north-central British Columbia is strongly influenced by vertical position within the canopy; Bryoria dominates upper canopy exposures, while Alectoria dominates lower canopy positions. The hypothesis that this height-related niche partitioning reflects differential growth responses to gradients in canopy microclimate is examined. Field measurements of canopy microclimate, taken over a 2-year period, were used in conjunction with laboratory-based measurements of net photosynthesis (NP) and dark respiration to model net assimilation (NA) response of Alectoria sarmentosa and Bryoria spp. (mixed collections of Bryoria fremontii and B. pseudofuscescens) at two different heights (15 and 4 m) within the canopy. Microclimate measurements indicate that lichen thalli are regularly hydrated from snowmelt events during the winter period (October–April), totalling 26 and 29% of the time, respectively, for Alectoria and Bryoria, though most winter hydration exposure ( c. 75%) occurred in the dark. In the summer (May–September), rainfall was the major hydration source, with Alectoria and Bryoria each hydrated c. 16% of the time (45% of this in the dark). The NP temperature optimum ( T opt) in light saturated thalli of Alectoria was 18·1 and 22·9°C, for winter and summer measurements, respectively. In Bryoria the corresponding seasonal rise in T optwas smaller, from 15·9 to 16·3°C. Both species showed an increase in maximum rates of NP during the summer period, from 1·52 to 1·92 mg CO 2 g −1 h −1for Alectoria, and from 1·79 to 2·33 mg CO 2 g −1 h −1for Bryoria. Although lichen hydration events peaked in early winter (October and November), NA modelling predicts that maximum growth should occur during the summer period. In Alectoria, higher rates of NA were predicted for thalli in lower canopy positions, especially during the summer months. In Bryoria, no clear trends of NA uptake with canopy position were observed. Thus, while NP response to gradients of canopy microclimate may provide a basis for niche partitioning in Alectoria, other factors (perhaps exclusionary) may be more important for Bryoria. One such factor is documented, namely the greater sensitivity of Bryoria to extended hydration exposure and we speculate that greater rates of fragmentation in upper canopy exposures may limit upper canopy biomass accumulation in Alectoria. Niche partitioning in these alectorioid lichens may therefore reflect both positive (growth responses) and negative (physical and physiological limitations) responses to gradients in canopy microclimate.

Overestimation of respiration rates in commercially available clamp‐on leaf chambers. Complications with measurement of net photosynthesis

AbstractThe possible interference when measuring gas exchange with respiratory CO2 produced under the gasket of commercially available clamp‐on leaf chambers was investigated. Two of these chambers were compared with a leaf chamber that accommodated an entire leaf without clamping it under a gasket. An overestimation of dark respiration rate (RD) by 55% was found with Plantago major leaves, a species with homobaric leaves that have high resistance for lateral gaseous transport. The percentage was similar in the heterobaric Ficus benjamina, but was 32% in the highly porous homobaric Nicotiana tabacum. Net photosynthetic rate at low photon flux density was underestimated by 35% in the clamp‐on chamber. However, the gasket effect was not detectable at light saturation because the error was small in comparison with the high photosynthetic rates. Estimation of respiration in the light (RL) in Nicotiana as derived from CO2 exchange at low CO2 concentrations was complicated by three factors. The inward diffusion of respiratory CO2 from under the gasket was added to a diffusion of CO2 from outside through the gasket material and through the leaf, which produced an even larger error in RL in comparison with RD at ambient CO2. These errors are significant for estimations of carbon gain at whole plant and canopy level and also at the leaf level when photosynthetic rates are low. Possible improvements in gasket design and corrections of CO2 exchange measurements for the gasket effect are discussed.

Clonal variability in biomass production and conversion efficiency of poplar during the establishment year of a short rotation coppice plantation

A high density, intensively managed field trial with 17 different poplar ( Populus) clones was established in April 1996 in Boom (province of Antwerpen, Belgium) on a former waste disposal site. All plants were cut back at the end of the establishment year and the above ground biomass production, as well as carbon concentration were measured. Significant clonal variation was observed in overall mortality rates and length of the growing season. Mortality rates ranged from 2 to 55% due to difficult soil conditions. Based on incoming available photosynthetically active radiation, length of growing season and above ground biomass production, conversion efficiency ratios were calculated. These were rather low, ranging from 0.002 to 0.041 g MJ −1, with the highest values calculated for the poplar clone Hoogvorst. The carbon concentration of the wood ranged from 46 to 47%, with 3.2 to 5.5% remaining in the ash. Net photosynthesis measurements were made in the field during mid-summer and revealed significant clonal differences in maximum photosynthetic rate and carboxylation efficiency. Clonal differences in net photosynthetic rate, length of growing season, mortality and biomass production rate are relevant to overall carbon uptake rates of short rotation biomass plantations.

Increasing Sennoside Yields in Tinnevelly Senna (Cassia angustifolia) I: Effects of Drought, Foliar Nitrogen Spray and Crop Type

Experiments were conducted to evaluate the promise of Tinnevelly senna, Cassia angustifolia Vahl, as an alternative crop for stressful agroecosystems. Effects of drought, foliar nitrogen application and crop type on sennoside yields were studied with simultaneous measurements of net photosynthesis. Short term drought increased sennoside A + B concentration (% dw). After drought-induced morphological changes had occurred, long term drought did not influence sennoside A + B concentration but severe loss of leaf biomass caused 78% reduction of the sennoside yield per plant. Foliar nitrogen application increased the total sennoside A + B content per plant by 140% when the plants were not water stressed, but in severely droughted plants, no effect of foliar nitrogen application was detected. Although foliar nitrogen application increased sennoside A + B per plant, the sennoside concentration (% dw) decreased. The latter effect was still persistent three months after the nitrogen treatments were discontinued. In a comparison among three crop types of Tinnevelly senna, ratoon plants had the highest sennoside A + B concentration in leaves followed by seedlings and cuttings. However, seedlings produced the highest sennoside A + B yield per plant due to the higher leaf biomass. Except in long term drought, sennoside levels were higher in leaves with lower net photosynthesis, and were increased by treatments that induced physiological stress. Lower net photosynthesis occurred in short term and long term drought, and with deprivation of foliar nitrogen supplement. In contrast, sennoside yields per plant are readily increased by treatments that increase the total leaf biomass. Short term drought, nitrogen stress and ratooning are promising component technologies for field and on-farm investigations with the goal of increasing sennoside yields.

Photosynthesis and Transpiration in Damaged and Undamaged Spruce Trees

Abstract The investigations presented here focus on the CO2/H2O gas exchange in damaged and undamaged spruce trees while using open-air measurements as well as measurements under defined conditions in the laboratory. The studies were performed at two different sites in the Hunsrück and the Westerwald mountains. In the laboratory the CO2/H2O gas exchange was measured on detached branches under controlled conditions in the course of two years. CO2 saturation curves were also generated. In addition CO2 compensation points were deter­ mined employing a closed system. In the natural habitat diurnal course measurements of photosynthesis and transpiration as well as light-saturation curves for photosynthesis were performed. In parallel with the photosynthesis and transpiration measurements, measurements of the water potential were taken at both locations. The photosynthetic capacity and transpiration rate show a typical annual course with pronounced maxima in spring and late summer and minima in summer and winter. The needles of the damaged trees exhibit higher transpiration rates and a distinct reduction in photosyn­ thesis than the needles of the undamaged trees during two seasons. The diurnal course measurements of net photosynthesis and transpiration show a maximum in photosynthesis and transpiration in the afternoon in May and September, but a characteristic midday depression in July. Photosynthesis was markedly lower and transpiration higher in the needles of the damaged trees. The damaged trees show a lower increase in the light and CO2 saturation curves and higher CO2 compensation points as compared to the undamaged trees. The water potential reaches much lower values during the course of the day in needles of the dam­ aged trees. The reduction of the photosynthetic rate on one hand and the increase in transpiration on the other hand result in an extreme lowering of the water use efficiency in photosynthesis. The damage to the thylakoid membranes and to the guard cells obviously results in a pro­ found disturbance of the physiological homeostasis of the needles and could thus lead to premature needle loss.