Photosynthetic Response of Carrots to Varying Irradiances

Response to irradiance of leaf net photosynthetic rates (P _N) of four carrot cultivars: Cascade, Caro Choice (CC), Oranza, and Red Core Chantenay (RCC) were examined in a controlled environment. Gas exchange measurements were conducted at photosynthetic active radiation (PAR) from 100 to 1 000 μmol m⁻² s⁻¹ at 20 °C and 350 μmol (CO₂) mol⁻¹(air). The values of P _N were fitted to a rectangular hyperbolic nonlinear regression model. P _N for all cultivars increased similarly with increasing PAR but Cascade and Oranza generally had higher P _N than CC. None of the cultivars reached saturation at 1 000 μmol m⁻² s⁻¹. The predicted P _N at saturation (P _Nmax) for Cascade, CC, Oranza, and RCC were 19.78, 16.40, 19.79, and 18.11 μmol (CO₂) m⁻² s⁻¹, respectively. The compensation irradiance (I _c) occurred at 54 μmol m⁻² s⁻¹ for Cascade, 36 μmol m⁻² s⁻¹ for CC, 45 μmol m⁻² s⁻¹ for Oranza, and 25 μmol m⁻² s⁻¹ for RCC. The quantum yield among the cultivars ranged between 0.057–0.033 mol(CO₂) mol⁻¹(PAR) and did not differ. Dark respiration varied from 2.66 μmol m⁻² s⁻¹ for Cascade to 0.85 μmol m⁻² s⁻¹ for RCC. As P _N increased with PAR, intercellular CO₂ decreased in a non-linear manner. Increasing PAR increased stomatal conductance and transpiration rate to a peak between 600 and 800 μmol m⁻² s⁻¹ followed by a steep decline resulting in sharp increases in water use efficiency. This revised version was published online in August 2006 with corrections to the Cover Date.     

Variation in Photosynthetic Characteristics and Leaf Area Contributes to Spathiphyllum Cultivar Differences in Biomass Production

Three genetically related Spathiphyllum cultivars, Claudia, Double Take, and Petite with similar initial sizes and biomass, were grown in a shaded greenhouse and fertilized with a constant supply of nitrogen at 200 g m^–3 using an ebb-and-flow fertigation system. Seven months later, Claudia and Double Take had plant sizes and biomasses significantly greater than Petite. Stomatal conductances of Claudia and Double Take were 30 % greater, thus net photosynthetic rates (P _N) were significantly higher than in Petite. In addition, the leaf areas (LA) of Claudia and Double Take were 60 % larger than of Petite. Since P _N was expressed per leaf surface area, the greater the LA was, the more CO₂ was fixed. Thus, the differences in plant size and biomass production of Claudia and Double Take compared to Petite are attributed to high P _N and increased LA.     

Effects of Elevated Temperature on Growth and Gas Exchange in Dominant Plant Species from Maowusu Sandland,China

We compared the effect of elevated temperature on morphological development, biomass accumulation and allocation, and gas exchange of three dominant plants (Caragana intermedia Kuanget H.C. Fu, Hedysarum mongolicum Turcz., and Artemisia ordosica Krasch.) growing in Chinese Maowusu sandland. Plants were grown in two temperature chambers (25/20, 28/23 °C, day/night) during 60 d. Tree height, number of leaves, and leaf area were increased in C. intermedia and H. mongolicum seedlings, while in A. ordosica temperature only affected tree height. Elevated temperature increased biomass and reduced the root : shoot ratio in C. intermedia and H. mongolicum seedlings, but not in A. ordosica seedlings. The net photosynthetic rate (P _N) and transpiration rate (E) were increased at days 40 and 60 in C. intermedia and H. mongolicum seedlings, while in A. ordosica seedlings no significant effects on E were observed, and P _N was increased only at day 60. Water use efficiency (WUE) was reduced at days 40 and 60 in H. mongolicum seedlings, and at day 60 in C. intermedia seedlings. No temperature effect on WUE was observed in A. ordosica seedlings. These different responses indicate that climate change could alter plant communities in Maowusu sandland.     

The effects of food consumption rate, body size and temperature on net food conversion efficiency in saithe and whiting

Net food conversion efficiency κ was estimated from growth experiments on saithe Pollachius virens and whiting Merlangius merlangus that were fed natural prey at a range of ration levels including satiation rations. The conversion efficiency, which specifies the net energy fraction of ingested energy C , was described appropriately by a simple power function of food consumption rate as κ  = 0·272 C ^0·18 and κ  = 0·426 C ^0·11 for saithe and whiting. This functional relationship was supported by the patterns of accretion of lipids and proteins in saithe. No significant effects of temperature and body size on κ was, however, demonstrated in this study except for the indirect influence using feeding levels (rations expressed relatively to satiation rations) in bioenergetics models.     

Comparison of soil nitrogen mineralization and nitrification in a mixed grassland and forested ecosystem in central Taiwan

We used the buried bag incubation method to study temporal patterns of net N mineralization and net nitrification in soils at Ta-Ta-Chia forest in central Taiwan. The site included a grassland zone, (dominant vegetation consists of Yushania niitakayamensis and Miscanthus transmorrisonensis Hayata) and a forest zone (Tsuga chinensis var. formosana and Yushania niitakamensis). In the grassland, soil concentration NH₄ ⁺ in the organic horizon (0.1–0.2 m) ranged from 1.0 to 12.4 mg N kg^–1 soil and that of NO₃ ^– varied from 0.2 to 2.1 mg N kg^–1 soil. In the forest zone, NH₄ ⁺ concentration was between 2.8 and 25.0 mg N kg^–1 soil and NO₃ ^–varied from 0.2 to 1.3 mg N kg^–1 soil. There were lower soil NH₄ ⁺ concentrations during the summer than other seasons. Net N mineralization was higher during the summer while net nitrification rates did not show a distinct seasonal pattern. In the grassland, net N mineralization and net nitrification rates were between –0.1 and 0.24 and from –0.04 to 0.04 mg N kg^–1 soil day^–1, respectively. In the forest zone, net N mineralization rates were between –0.03 and 0.45 mg N kg^–1 soil day^–1 and net nitrification rates were between –0.01 and 0.03 mg N kg^–1 soil day^–1. These differences likely result from differing vegetation communities (C₃ versus C₄ plant type) and soil characteristics.     

Macrophytic, epipelic and epilithic primary production in a semiarid Mediterranean stream

Summary 1. Primary production by Chara vulgaris and by epipelic and epilithic algal assemblages was measured in a semiarid, Mediterranean stream (Chicamo stream, Murcia, Spain) during one annual cycle. 2. The rates of gross primary production (GPP) and community respiration (CR) were determined for each algal assemblage using oxygen change in chambers. The net daily metabolism (NDM) and the GPPd^?1 : CR₂₄ ratio were estimated by patch‐weighting the assemblage‐level metabolism values. 3. Gross primary production and CR showed significant differences between assemblages and dates. The highest rates were measured in summer and spring, while December was the only month when there were no significant differences in either parameters between assemblages. GPP was strongly correlated with respiration, but not with algal biomass. 4. Chara vulgaris showed the highest mean annual metabolic rates (GPP = 2.80 ± 0.83 gC m^?2 h^?1, CR = 0.76 ± 0.29 gC m^?2 h^?1), followed by the epilithic assemblage (GPP = 1.97 ± 0.73 gC m^?2 h^?1, CR = 0.41 ± 0.12 gC m^?2 h^?1) and epipelic algae (GPP = 1.36 ± 0.22 gC m^?2 h^?1, CR = 0.39 ± 0.06 gC m^?2 h^?1). 5. The epipelic assemblage dominated in terms of biomass (82%) and areal cover (88%), compared with the other primary producers. Epipelic algae contributed 84% of gross primary production and 86% of community respiration in the stream. 6. Mean monthly air temperature was the best single predictor of macrophyte respiration and of epipelic GPP and CR. However, ammonium concentration was the best single predictor of C. vulgaris GPP, and suspended solid concentration of epilithon GPP and CR. 7. Around 70% of the variation in both mean GPP and mean CR was explained by the mean monthly air temperature alone. A multiple regression model that included conductivity, PAR and nitrates in addition to mean monthly air temperature, explained 99.99% of the variation in mean CR. 8. Throughout the year, NDM was positive (mean value 7.03 gC m^?2 day^?1), while the GPP : CR₂₄ ratio was higher than 1, confirming the net autotrophy of the system.     

Do species evenness and plant density influence the magnitude of selection and complementarity effects in annual plant species mixtures?

Abstract Plant species richness influences primary productivity via mechanisms that (1) favour species with particular traits (selection effect) and (2) promote niche differentiation between species (complementarity). Influences of species evenness, plant density and other properties of plant communities on productivity are poorly defined, but may depend on whether selection or complementarity prevails in species mixtures. We predicted that selection effects are insensitive to species evenness but increase with plant density, and that the converse is true for complementarity. To test predictions, we grew three species of annuals in monocultures and in three‐species mixtures in which evenness of established plants was varied at each of three plant densities in a cultivated field in Texas, USA. Above‐ground biomass was smaller in mixtures than expected from monocultures because of negative ‘complementarity’ and a negative selection effect. Neither selection nor complementarity varied with species evenness, but selection effects increased at the greatest plant density as predicted.     

The Temperature Gradient Air–Soil as a Factor in the Optimization of Net Photosynthesis in Whole Plants

The effect of soil temperature on the net photosynthetic rate was studied by the method of multifactor analysis at early growth stages of narrow-leaved lupine (Lupinus angustifolius L.), white cabbage (Brassica capitata Lisg.), spring wheat (Triticum aestivum L.), cucumber (Cucumis sativus L.), tomato (Lycopersicon esculentum Mill.), and cotton (Gossypium hirsutum L.) plant species and cultivars contrasting in their heat demand. The optimum level of the net photosynthetic rate was observed in a wide range of soil and air temperatures, from cold- to heat-hardening temperatures, irrespective of the sign of the temperature gradient, whereas the magnitude and sign of the temperature gradient favorable for the highest potential net photosynthetic rate were species- and cultivar-specific and were not related to the cold tolerance of a species or cultivar.     

Carbon emissions from fires in tropical and subtropical ecosystems

Global carbon emissions from fires are difficult to quantify and have the potential to influence interannual variability and long‐term trends in atmospheric CO₂ concentrations. We used 4 years of Tropical Rainfall Measuring Mission (TRMM) Visible and Infrared Scanner (VIRS) satellite data and a biogeochemical model to assess spatial and temporal variability of carbon emissions from tropical fires. The TRMM satellite data extended between 38°N and 38°S and covered the period from 1998 to 2001. A relationship between TRMM fire counts and burned area was derived using estimates of burned area from other satellite fire products in Africa and Australia and reported burned areas from the United States. We modified the Carnegie‐Ames‐Stanford‐Approach (CASA) biogeochemical model to account for both direct combustion losses and the decomposition from fire‐induced mortality, using both TRMM and Sea‐viewing Wide Field of view Sensor (SeaWiFS) satellite data as model drivers. Over the 1998–2001 period, we estimated that the sum of carbon emissions from tropical fires and fuel wood use was 2.6 Pg C yr^?1. An additional flux of 1.2 Pg C yr^?1 was released indirectly, as a result of decomposition of vegetation killed by fire but not combusted. The sum of direct and indirect carbon losses from fires represented 9% of tropical and subtropical net primary production (NPP). We found that including fire processes in the tropics substantially alters the seasonal cycle of net biome production by shifting carbon losses to months with low soil moisture and low rates of soil microbial respiration. Consequently, accounting for fires increases growing season net flux by ～12% between 38°N and 38°S, with the greatest effect occurring in highly productive savanna regions.