Effects of sink removal on leaf photosynthetic attributes of rose flower shoots (Rosa hybrida L., cv. Dallas)

Two experiments were conducted under greenhouse conditions to evaluate the effects of sink removal (flower shoot harvest and debudding) on the gas-exchange capacity (i) of leaves left on the parent shoot after flower shoot harvest and (ii) of flower shoot leaves after flower-bud removal. In the first experiment, gas-exchange measurements were performed on three 5-foliate leaves (leaf 1: uppermost parent shoot leaf, and two leaves inserted just below: leaves 2–3). It was found that, after bud sprouting, the leaf nearest to the young growing shoot (leaf 1) experienced a significant reduction in leaf maximum net CO₂ assimilation rate, A_lm, stomatal conductance, g_s, and transpiration rate, E_l, over time in comparison to the corresponding values observed for leaves 2–3. Leaf water use efficiency, WUE, significantly changed over time, while the ratio of leaf internal to ambient CO₂ concentration, C_i/C_a, was rather conservative throughout the entire shoot growing period. In the second experiment, leaf gas-exchange measurements were performed for adult flower shoots that were either debudded or left intact. Both types of shoots exhibited a similar along-shoot distribution pattern of physiological fluxes, g_s, and WUE. Bud removal did not significantly affect the magnitude of gas-exchange, with the exception of E_l. One week after bud removal, only slight differences were observed for A_lm, g_s and E_l between the two types of shoots. These results suggest (i) that the contribution of the uppermost parent shoot leaf to the assimilates demand of newly growing shoot significantly affects its photosynthetic capacity; and (ii) that flower-bud removal does not change the overall photosynthetic capacity of the flower shoot leaves, which divert the surplus of produced assimilates towards alternative sink organs and plant reserve pools.     

Does root-sourced ABA play a role for regulation of stomata under drought in quinoa (Chenopodium quinoa Willd.)

The Andean seed crop quinoa (Chenopodium quinoa Willd.) is traditionally grown under drought and other adverse conditions that constrain crop production in the Andes, and it is regarded as having considerable tolerance to soil drying. The objective of this research was to study how chemical and hydraulic signalling from the root system controlled gas exchange in a drying soil in quinoa. It was observed that during soil drying, relative g_s and photosynthesis A_max (drought stressed/fully watered plants) equalled 1, until the fraction of transpirable soil water (FTSW) decreased to 0.82 ± 0.152 and 0.33 ± 0.061, respectively, at bud formation, indicating that photosynthesis was maintained after stomata closure. The relationship between relative g_s and relative A_max at bud formation was represented by a logarithmic function (r² = 0.79), which resulted in a photosynthetic water use efficiency WUE_Amax_/gs$\text{WU}{\text{E}}_{A_{\text{max}}/g_{\text{s}}}$ of 1 when FTSW > 0.8, and increased by 50% with soil drying to FTSW 0.7–0.4. Mild soil drying slightly increased ABA in the xylem. It is concluded that during soil drying, quinoa plants have a sensitive stomatal closure, by which the plants are able to maintain leaf water potential (ψ_l) and A_max, resulting in an increase of WUE. Root originated ABA plays a role in stomata performance during soil drying. ABA regulation seems to be one of the mechanisms utilised by quinoa when facing drought inducing decrease of turgor of stomata guard cells.     

Additional nitrogen fertilization affects salt tolerance of lemon trees on different rootstocks

Irrigation with saline water is one of the major problems in citrus crop in arid and semi-arid regions. Because rootstock and fertilization play an important role in citrus salt tolerance, we investigated the influence of the nitrogen fertilization and rootstock on salt tolerance of 2-year-old potted Fino 49 lemon trees. For that, trees grafted on Citrus macrophylla (M) or Sour orange (SO) rootstocks were watered for 12 weeks with complete nutrient solution containing either 0 mM NaCl (control, C), 50 mM NaCl (S), 50 mM NaCl with an additional 10 mM potassium nitrate (S + N), or 50 mM NaCl with a 1% KNO₃ (S + Nf) foliar spray application. Trees on M were more vigorous than trees on SO and saline treatments reduced leaf growth similarly in trees on both rootstocks. Trees on SO had a lower leaf Cl⁻ and Na⁺ concentration than those on M. Additional soil nitrogen (S + N) decreased leaf Cl⁻ concentration and increased leaf K⁺ concentration in salinized trees on both rootstocks. However, the salinity-induced reduction leaf growth was similar in S + N and S trees. This was due to osmotic effect, beside leaf Cl⁻ and Na⁺ toxicity, played an important role in the growth response of Fino 49 lemon to the salt stress. Additional foliar nitrogen in the S + Nf treatment also reduced leaf Cl⁻ concentration relative to the S treatment but trees from S + Nf treatment had the lowest leaf growth. Net assimilation of CO₂ (ACO₂$A_{\text{C}{\text{O}}_2}$), stomatal conductance (g_s) and plant transpiration were reduced similarly in all three salt treatments, regardless rootstock. Salinity reduced leaf water and osmotic potential such that leaf turgor was increased. Thus, the salinity-induced ACO₂$A_{\text{C}{\text{O}}_2}$ reductions were not due to loss of turgor but rather due to high salt ion accumulation in leaves.     

Effects of shoot size,number of continuous-light cycles and solar radiation on flower initiation in the carnation

Carnation plants (Dianthus cary ophyllus L.) cultivar ‘White Sim’, were grown in containers in a glasshouse under short (8 h) days. When the primary shoots had 4, 8 or 12 pairs of visible leaves, the plants were moved to a continuous-light area, lit by tungsten lamps for 5, 10, 15 or 30 days, and then returned to short days. This was repeated with several sets of plants at different times of year to obtain a range of radiation flux densities.The number of continuous-light cycles required to initiate a given proportion of shoots was dependent upon the radiation integral, a generalised linear model gave quantitative relationships between the proportion of responding shoots, the number of cycles of continuous light (CL) and the radiation integral. For shoots with 4 visible leaf pairs the model

$\text{keta;=μ+∝X}{}_1\text{+βX}{}_2$

accounted for 83% of the deviance, where η is the linear predictor, μ, α and β are parameters, X₁ = log_e (number of CLs + 1) and X₂ = log_e mean radiation (calories cm^?2 day^?1). For shoots with 8 visible leaf-pairs, 76% of the deviance was removed.Under low radiation integrals, intra-plant competition resulted in only a small proportion of shoots on a plant initiating flowers; increasing the number of CL cycles only partially mitigated this effect. At low radiation integrals, shoots that failed to initiate flowers in CL were often delayed by this treatment and initiated flowers later than shoots in short days. Both the CL-requirement and the limiting effect of the radiation integral on the proportion of shoots that initiated flowers decreased as shoot size increased.It is concluded that competition for photosynthetic assimilates under low radiation conditions can severely limit flower initiation in the carnation.     

Photosynthetic characteristics and protective mechanisms against photooxidation during high temperature stress in two citrus species

Exposure of Satsuma mandarin (Citrus unshiu Marc.) and Navel orange (Citrus sinensis Osbeck) plants to high temperature (38 °C) led to reductions of the net photosynthetic rate (Pn), the photorespiration rate (Pr), the quantum efficiency CO₂ assimilation (ΦCO₂${\Phi }_{\text{C}{\text{O}}_2}$), the maximal photochemical efficiency of PS2 (Fv/Fm), the photochemical quenching (qP) and the quantum efficiency of PS2 photochemistry (Φ_PS2), whereas the minimal fluorescence yield (Fo) and the non-photochemical quenching (qN) increased. Increase in the value of Pr/Pn and ΦPS₂/ΦCO₂${\Phi }_{\text{PS}2}/{\Phi }_{\text{C}{\text{O}}_2}$ was attributed to the greater decrease in Pn and ΦCO₂${\Phi }_{\text{C}{\text{O}}_2}$ than Pr and Φ_PS2. In addition, the superoxide radical (O₂⁻) production, the H₂O₂ concentration and the activities of antioxidant enzymes such as the superoxide dismutase (SOD, EC 1.15.1.1), the ascorbate peroxidase (APX, EC 1.11.1.11), the dehydroascorbate reductase (DHAR, EC 1.8.5.1) and the catalase (CAT, EC 1.11.1.6) were raised. On the other hand, the chlorophyll concentration in leaves decreased during high temperature stress. These results suggest that decline in Pn related to inactivation of PS2 reaction centers may be due to the enhanced number of active oxygen species in the citrus leaves. The water–water cycle may play a role in limiting the degree of photodamage caused by high temperature. Lower O₂⁻ production rate, the H₂O₂ concentration and the antioxidant enzymes activity were observed in high temperature tolerant species of citrus. The exogenous active oxygen scavenger ascorbic acid (Asc) enhanced the ability to clear the O₂⁻ in citrus plants, and quicken the recovery of photosynthetic apparatus.     

Water relations between leaf water potential,photosynthesis and agronomic vine response as a tool for establishing thresholds in irrigation scheduling

During the last few years, leaf water potential has been a useful tool in controlling vine water status. However, the time of measurement that could best explain short- and long-term vine responses remains a matter of discussion. The objectives of this work were to study the relationship between vine water status and vine performance and to determine what time of day leaf water potential is best correlated to physiological performance and agronomic vine response. The assay was conducted in Madrid, Spain. Plant material was Cabernet-Sauvignon (Vitis vinifera L.) grafted onto SO₄. Three irrigation treatments were established: T1 was non-irrigated, and T2 and T3 were irrigated with a constant fraction of the ETo, k = 0.45 and 0.2, respectively. Vine water status was monitored through predawn, midmorning and noon leaf water potential. Their relationships with net CO₂ assimilation rate, vegetative growth rate, yield components and must composition at harvest were studied for 3 consecutive years. Shoot growth rate and net CO₂ assimilation rate were better correlated with midmorning and noon leaf water potentials – Ψ_m and Ψ_n – than predawn leaf water potential – Ψ_pd – but all of them were significant. Shoot growth rate was zero for Ψ_pd = −0.48, Ψ_m = −1.12 and Ψ_n = −1.18 MPa. Berry size was better correlated with the water stress integral for predawn (S_Ψpd$S_{{\Psi }_{\text{pd}}}$) although the water stress integral for midmorning (S_Ψm$S_{{\Psi }_{\text{m}}}$) and noon (S_Ψn$S_{{\Psi }_{\text{n}}}$) performed quite well. No relationship was found between the water stress integral and TSS, total acidity or pH. Leaf water potential performed as a good parameter for determining both vine water status and agronomic response, but not for evaluating must composition.     

Flower production in Gerbera: I. Correlations between shoot,leaf and flower formation in seedlings

Flower production of seedling plants of Gerbera was shown to be positively correlated with the number of lateral shoots and with the number of leaves per flower. The most productive plants were those which formed 2–5 lateral shoots during the first year and had a $\text{leaf}\text{flower}$ ratio of 2–4. The number of lateral shoots at the moment the first flower bud became visible was strongly correlated with the number of lateral shoots after 1 year.There was a positive correlation between the number of lateral shoots and total number of leaves, but hardly at all between total leaf number and flower production, as the $\text{leaf}\text{flower}$ ratio increased with the number of lateral shoots.     

Leaf development,net assimilation and leaf nitrogen concentrations of five Prunus rootstocks in response to root temperature

Rootstocks differentially influence tree physiology and these differences may be due to varying responses to root zone temperature (RZT). To determine if this is the case, the physiology, leaf development and nitrogen relationships of five different Prunus rootstocks with chill requirements between 100 and 1100 h were examined during and after growth at RZTs of 5, 12 and 19 °C for 6 weeks. RZT correlated positively with leaf numbers, expansion rates and final leaf area, and significant differences existed among the rootstocks in the magnitude of these parameters at different RZTs. In particular, leaf expansion and area were less affected at low RZT in the low chill varieties. Net assimilation (A_n), leaf nitrogen (N%) and photosynthetic nitrogen use efficiency (A_n/N) also correlated positively with RZT: again, there were differences in the magnitude of these parameters among the rootstocks. No associations amongst A_n, N% or A_n/N could be found for the rootstocks; hence, they all differed in their physiological responses to RZT. Low RZT alone was sufficient to reduce A_n and decreased both leaf area and photosynthetic activity. Leaf expansion was related to N%, as the varieties with the lowest N% also had the lowest expansion rates. Infrared thermography of the cv. Golden Queen showed a negative correlation between RZT and leaf temperature with leaves of plants at the lowest RZT being 2 °C warmer than ambient whilst those at the highest RZT were 2 °C cooler than ambient. These differences were due to transpiration, as transpiration for the variety used decreased with reducing RZT. Transpiration from the other rootstock varieties was lowest at the 5 °C RZT but, depending on variety, at 12 °C was either higher, lower or the same as that from plants whose roots were at 19 °C. Together, the results of this study explain some of the rootstock-induced changes in tree growth and suggest the need to incorporate seasonal changes in RZT into development models for peaches.     

Partitioning of photosynthates originating from bent shoots in the arching and high-rack culture systems of cut rose production

The arching and high-rack culture systems were developed and patented by Japanese rose growers. Both culture systems have bent canopies (lower bent shoots). In the arching culture system, shoots sprouting from the crown are harvested as cut flowers. However, the high-rack culture system also has a bent canopy originating from the mother stem (upper bent shoots) and flower stems sprout and is harvested at the top of each mother stem. Partitioning of photosynthates originating from bent shoots in arching and high-rack culture systems of rose production was investigated to elucidate how carbohydrates are re-allocated from the bent shoots in different culture systems of roses. At the flowering stage in both culture systems, 50–70% of ¹³C-photosynthates originated from bent shoots were exported to other parts within 72 h after ¹³CO₂ feeding to the bent shoot. In the arching culture system, photosynthates from lower bent shoots were partitioned mainly to the roots and crown. Similarly, in the high-rack culture system, between 71 and 86% of the exported carbon from the bent shoots were allocated to below the point of bending (roots + crown + mother stems) and only 9–28% was allocated to flowering shoots above the point of bending. In both culture systems, photosynthate translocation from the lower bent shoot directly to flowers was low. Accordingly, bent shoots in rose plants acted as a source of photosynthates, independent of culture system. The height of the bent shoots determined for a great deal in the re-allocation of the photosynthates, and provides a partial explanation for difference in production of cut roses.     

The effect of defoliation on bulb production of tulip cultivar ‘Apeldoorn’

The distribution of dry matter between the different bulblets of tulip is not markedly influenced by either changes in leaf area or the position of the leaf. On the contrary, total bulb yield is strongly affected.A reduction factor, S_c, for incomplete soil coverage, when the leaf area index (LAI) is less than 4, normally used for evaluation of planting density effects, can also be used for the effects of defoliation on dry matter increase. This LAI-dependent factor shows a distinctly asymptotic pathway closely resembling

$\text{S}{}_{\mathrm{c}}\text{=}\text{P}{}_{\mathrm{act}}\text{P}{}_{\mathrm{pot}}\text{=1?e}{}^{\mathrm{?k1LAI}}$

where k ～ 0.6 and in which P_act is the actual measured dry weight increase and $\text{P}\text{?}{}_{\mathrm{<mtext>pot</mtext>}}$ the potential net dry weight increase for a closed canopy.     

Effects of intracanopy lighting on photosynthetic characteristics in cucumber

Plants of cucumber (Cucumis sativus L. cv. Euphorbia) were grown in a traditional high-wire cultivation system to investigate the effects of three lighting regimes on photosynthetic characteristics, leaf area and yield. The lighting regimes included overhead lighting (OH), where all the lamps were mounted above the canopy and overhead + intracanopy lighting (OH + IC) which comprised 65% of overhead lamps and 35% of lamps mounted vertically along the plant rows. All overhead lighting was provided for 20 h day⁻¹ and intracanopy lighting was provided for either 20 h or 24 h day⁻¹ lighting period. Intracanopy lighting improved the light distribution in the canopy. Gas exchange measurements showed that intracanopy lighting increased net photosynthesis (P_N) and photosynthetic capacity (P_max). Parameters calculated from CO₂ response (A/C_i) curves showed that in vivo estimate of the maximum rate of Rubisco carboxylation (Vc_max) and the maximum rate of electron transport (J_max) were affected by light regime. Intracanopy light increased yield by 11% compared to traditional overhead light.     

The effect of intracanopy lighting on cucumber fruit yield—Model analysis

Intracanopy lighting is a recently developed supplementary lighting technique for high-wire grown vegetable production in greenhouses where a part of the lamps is mounted within instead of above the canopy. A potentially higher yield using intracanopy lighting compared with top-lighting, is based on three assumptions: (1) increased light-absorption by the crop; (2) a higher photosynthetic light use efficiency due to a more homogeneous vertical light distribution; (3) a preserved photosynthetic capacity of leaves deeper in the canopy. We used an explanatory crop model to quantify the relative importance of these assumptions for a cucumber crop during an experiment in winter in the Netherlands (Trouwborst et al., 2010). Photosynthesis and yield data of this intracanopy lighting experiment with light-emitting diodes (34% of supplemental PAR) in combination with top-lighting (66% of supplemental PAR) were used to parameterise our model. In that study intracanopy lighting did not result in an increased yield compared with 100% top-lighting due to extreme leaf curling and a lower dry matter partitioning to the fruits. Our model predicted an 8% increase in fruit yield for the intracanopy lighting treatment if there were to be no leaf curling and no lower dry matter partitioning. This increase can be largely explained by the change in light distribution and light absorption. The model further revealed unexpectedly large consequences of the lower dry matter partitioning to the fruits whereas the negative effect of leaf curling was small. The direct effect of a greater A_max at deeper canopy layers was slightly positive. The last however might have indirectly caused the greater partitioning to the leaves as the greater A_max was associated with a preserved leaf mass per area. Solutions for this problem are discussed. Our explanatory model allowed us to disentangle the interacting effects of intracanopy lighting on fruit yield. Overall, intracanopy lighting has been shown here to potentially increase the assimilation light use efficiency.