Effects of canopy manipulations on whole-vine photosynthesis: Results from pot and field experiments

A two-year study was conducted with potted and field-grown grapevines to examine the effects of canopy restriction and leaf removal on total vine assimilation (TVA). TVA was measured using a flow-through gas exchange system equipped with flexible plastic chambers enclosing the entire canopy. Canopy restriction was applied to potted bush-shaped (BS) and field-grown spur-pruned cordon (SPC) vines on trellises to force the foliage into the smallest canopy volume. Leaf removal was performed on free cordon (FC) and SPC-trained vines at different dates to eliminate internal leaves shaded to varying extent. Canopy restriction reduced TVA more severely in the BS canopies than in the trellised SPC vines. Leaf removal elicited varying responses depending upon canopy shape, initial canopy density and leaf/fruit ratio. The FC vine showed no decrease in TVA after 27 % of its total leaf area had been removed, suggesting the occurrence of active photosynthetic compensation. TVA decreased with defoliation in the SPC vine, although the effect was mostly due to the leaf removal applied earlier in the season. In the FC vine a regression of total leaf area versus TVA showed maximum TVA at 6.0-6.5 m(2) of leaf area per meter of canopy. In SPC vines this relationship indicated a linear increase of TVA with leaf area and the lack of a saturation threshold under our experimental conditions. Sugar accumulation in the grapes of SPC vines correlated closely to the ratios leaf area/fruit and TVA/yield

Gas-exchange response of grapevine leaves under fluctuating light

Gas exchange responses to lightflecks of different frequency and duration were studied in mature grapevine leaves. Light-response curves under intermittent light showed lower carbon exchange rate (CER) than continuous light at non-saturating PFD levels (10-500 µ molm-2 s-1). White-dark and white-green alternating light of equal bright and shade periods at 0.33-5.33 Hz systematically resulted in improved light utilization as compared to high continuous light. Transpiration (T) was slightly more limited than the CER under intermittent light, resulting in higher water use efficiency. No differences in carboxylation efficiency were found by comparing the high continuous light treatment to white-dark lightflecks at 0.33 and 2.67 Hz. Our results show that, under short-term alternating light, CER of the grapevine leaf fully responds to the mean PFD level resulting from light oscillations

Preliminary results on the use of a modified point quadrat method for estimating canopy structure of grapevine training systems

The reliability of a modified point quadrat method designed to describe the structure and seasonal canopy dynamics of the training systems simple curtain (SC) and traditional spur-pruned cordon (SPC) was tested in a two-year study. The method relies upon an unbiased sampling procedure as each canopy insertion is first identified within a ground-projected area by a random number generation routine (RND). From each insertion, the height of each contact with either leaves or clusters is then recorded along the vertical axis. Although the method suffered from a somewhat low percentage of effective insertions early in the season, the total leaf area-to-surface area ratio and the leaf layer number calculated for both canopy types are in accordance with those reported by others for high vigour canopies. Canopy dynamics showed an asymmetric growth in the SC starting at bloom. Both trellises resulted in similar canopy density indices and a high correlation was found between total leaf area and total number of leaf contacts

Row orientation effects on whole-canopy gas exchange of potted and field-grown grapevines

The effects of canopy orientation (North-South vs. East-West) on total canopy assimilation (TCA) and transpiration (TCE) were evaluated on potted grapevines mounted on wheeled platforms for full swivel relation. Eight vines were assembled in pairs to form four canopy walls 2 m long, 1.1 m tall and 0.25-0.30 m wide. TCA and TCE readings were also taken in the field on four NS-oriented, hedgerow cordon-trained grapevines. Diurnal trends of TCA recorded on potted vines showed little variability when related to row orientation. The TCE pattern for EW followed essentially that of light intensity, whereas a NS orientation induced a marked decrease in TCE at midday before recovering in mid-afternoon. As a result, water use efficiency (WUE) in NS rows was higher during the midday hours. Total canopy water loss in NS was linearly correlated with estimates of intercepted light, suggesting that water use was a function of both, light intensity and canopy geometry (i.e. more light lost to the ground at noon, hence less transpiration). The results for the NS-oriented field-grown canopies differed to some extent from those of the pot experiments. TCA showed a more marked afternoon decline and TCE flattened at noon, though with no apparent decrease. WUE efficiency was lowest at the highest evaporative demand. The daily water loss of field vines could not be predicted by total light interception estimates only, indicating a more complex regulation of canopy transpiration than recorded on potted plants

A custom-built simple system for conditioning and measurement of in situ whole-cluster transpiration

A custom-built, low-cost gas exchange system designed for conditioning of the cluster microclimate and for fully automated measurements of in situ whole-cluster transpiration is presented. Measurements were carried out on potted Sangiovese grapevines at the onset of veraison, To increase the range of variability in cluster transpiration, air streams of different vapor pressure deficits (VPD) were created by conditioning the temperature of the incoming flow. Heating was created and maintained for 10 d (26 June - 5 July) by air flow through a metal segment equipped with three 75 W (warm) or 100 W (hot) light bulbs, The cluster transpiration rates recorded for the unheated (control) clusters throughout the conditioning period varied from 0.18 to 0.28 mmol m-2 s-1. While the daily transpiration rates of clusters supplied with warm air were similar to those of the control, water loss began to decrease significantly in clusters treated with hot air from day 4 onward and stayed lower throughout the remaining conditioning period. The gas exchange system presented here proved sensitive enough to detect the typically low transpiration rates of berries during ripening; effects due to air heating could be separated from fluctuations caused by daily variation of weather.

Vine performance and leaf physiology of conventionally and minimally pruned Sangiovese grapevines

A three-year-study (1996-1998) was carried out on field-grown Sangiovese grapevines under the temperate, humid climate of the Po Valley (northern Italy) to assess their degree of adaptation to minimal pruning (NIT) as compared to conventional pruning (CP). Evaluation included canopy growth, yield, berry ripening and grape rot incidence. In 1996 leaf function was determined as net assimilation (A); seasonal total canopy light interception and percentage of canopy gaps were also measured. As compared to CP, over the 3-year period MP showed typical features of a more rapid canopy development and earlier growth cessation, higher shoot number with shorter shoots and smaller leaves, higher yields with smaller and looser clusters less susceptible to bunch rot. Must sugar concentration was significantly lowered. Seasonal rates of A recorded on single leaves of the two pruning treatments at different shoot positions were overall similar except for higher A in young MT leaves having a chronological age of about 8-10 d. MP also showed the tendency of retarded leaf senescence. The seasonal total light interception trends indicated a linear increase with formation of leaf area in CP, whereas total fight interception in MT augmented until about 50 % of canopy filling and then remained constant with further leaf area development. This suggests that about half the leaf area produced in the MP vines contributed mostly to mutual shading rather than enhancing light interception capability, and, hence, photosynthetic capacity. The overall data indicate that a satisfactory balance in the minimally pruned Sangiovese grapevines can only be reached with further adjustments of crop level to be performed either as partial winter and/or summer pruning. Nevertheless, in MP vines the consistent feature of looser clusters which are much less susceptible to bunch rot is crucial in an area usually characterized by abundant rainfall at pre-harvest.

Laser scanning estimation of relative light interception by canopy components in different grapevine training systems

The fractional light interception by different parts of vines trained to various systems was estimated by a modified point-quadrat method using an over-row solar are positioning device equipped with a laser to simulate sunbeam position and angle at any latitude and time of the day. Laser readings were also combined with total vine light interception estimates via a line sensor to calculate the total light intercepted by specific canopy components. At each sampling date (late June and September, corresponding to fruit set and full canopy), type and position of organs were directly detected by the laser beam. Regardless of sampling date, the relative amount of light captured by the renewal-fruiting area (nodes 1 to 6) of simple cordon (SC) and double curtain (GDC) was considerably higher than that of spur-pruned cordon (SPC), whose vegetative area (distal to node 6) received about two-thirds of the incoming light. Relative light interception by main and lateral leaves was rather constant for GDC, thus reflecting the negligible regrowth after topping. By contrast, SC and SPC showed a much stronger response to topping which caused an increase of light interception by laterals (19 % for SC and +21 % for SPC). Frequencies of relative intercepted light by main leaves as a function of node position showed a peak around nodes 6-8, a zone where maximum leaf size is attained in all systems and on all dates. Instead, lateral leaves predominantly exposed to light were within the three basal nodes of the lateral shoots. Estimates of relative and total light for different vine parts at any time during the season as detected by laser scanning can objectively assess important characteristics of grapevine training systems, e.g. cluster and basal node exposure to light

Manejo do dossel vegetativo e seu efeito nos componentes de produção da videira Merlot.

A poda verde é uma prática cultural utilizada para melhorar as condições do dossel vegetativo dos vinhedos, visando a favorecer a qualidade da uva e do vinho. Nesse sentido, realizou-se este experimento entre as safras de 1993/1994 e 1996/1997, com diferentes modalidades de poda verde, num vinhedo do cv. Merlot conduzido em latada. Houve 12 tratamentos e três repetições, sendo o delineamento experimental em blocos casualizados. Os tratamentos constituíram-se da testemunha e de 11 diferentes modalidades de poda verde, ou seja, desbrota, desponta e desfolha, algumas delas em diferentes épocas do ciclo vegetativo da videira. O componente principal 1, da análise de componentes principais (ACP) feita em cada ano, separadamente, mostra que o tratamento 10 (desbrota + desponta + desfolha realizada no início da floração, eliminando-se as folhas abaixo dos cachos) discriminou-se nos quatro anos, e os tratamentos 7 (desfolha realizada 21 dias antes da colheita, eliminando-se metade das folhas abaixo dos cachos) e 6 (desfolha realizada 21 dias antes da colheita, eliminando-se as folhas abaixo dos cachos), em três deles; a ACP da média dos quatro anos também evidencia essa discriminação entre eles. Constata-se que o tratamento 10 foi um dos que tiveram intensidade de poda verde mais intensa, caracterizando-se por variáveis indicativas de plantas com vigor e produtividade mais baixos que os demais

Ralentización del proceso de maduración en Bobal y Tempranillo mediante deshojado tardío y riego: efectos sobre la composición de la uva y del vino

Los efectos del cambio climático en la vitivinicultura mediterránea están resultando negativos, pues desacoplan la madurez tecnológica de la uva de la fenólica. Tal circunstancia afecta especialmente a variedades tintas, dando lugar a vinos de elevada graduación alcohólica y bajo contenido en compuestos fenólicos, aspectos que se asocian a baja calidad. El objetivo de este ensayo fue ralentizar las dinámicas de maduración de la uvas en las variedades Bobal y Tempranillo mediante la reducción del ratio fuente:sumidero, y así hacerlas coincidir con periodos más frescos. Para este fin, se estudiaron los efectos que las técnicas de riego deficitario frente al secano y del deshojado realizado antes de envero provocaron sobre el rendimiento de las cepas y la composición de la uva, durante dos años. Los resultados de las parcelas experimentales localizadas en Requena (Valencia) ponen en evidencia la gran influencia que el riego tiene sobre el estado hídrico de las cepas. A su vez, la reducción de área foliar tendió a atenuar el estrés hídrico. No obstante, estos incrementos no evitaron ligeras mermas productivas debidas a reducciones del tamaño de baya en algunos tratamientos deshojados. La respuesta al riego de la evolución en la acumulación de azúcares fue opuesta según la variedad. Sin embargo, el 40 % de reducción del área foliar la ralentizó significativamente en ambas variedades, retrasándose la vendimia como mínimo siete días. La concentración de antocianos y el índice de polifenoles totales en los mostos tendieron a reducirse en la variedad Bobal por el efecto del riego, y ligeramente en ambas variedades por los efectos del deshojado, así como en sus vinos. Por tanto, las dos técnicas resultaron eficaces para modular la evolución de la maduración de la uva de estas dos variedades tintas en condiciones semiáridas. Si bien, los resultados del deshojado tardío sobre la composición fenólica no fueron los esperados