Sap Flow Responses to Warming and Fruit Load in Young Olive Trees

The Ecophysiological Response of Olive Trees under Different Fruit Loads

Olive trees have a unique reproductive pattern marked by biennial fruiting. This study examined the repercussions of alternate fruit bearing on the water relations of olive trees and the associated ecophysiological mechanisms. The experiment spanned two consecutive years: the "ON" year, characterized by a high crop load, and the "OFF" year, marked by minimal fruit production. Key ecophysiological parameters, including sap flow, stomatal conductance, and photosynthetic rate, were monitored in both years. Pre-dawn water potential was measured using continuous stem psychrometers and the pressure chamber technique. Biochemical analyses focused on non-structural carbohydrate concentrations (starch, sucrose, and mannitol) and olive leaves' carbon-stable isotope ratio (δ13C). Results revealed a higher leaf gas exchange rate during the "ON" year, leading to an average 29.3% increase in water consumption and a 40.78% rise in the photosynthetic rate. Higher water usage during the "ON" year resulted in significantly lower (43.22% on average) leaf water potential. Sucrose and starch concentrations were also increased in the "ON" year, while there were no significant differences in mannitol concentration. Regarding the carbon-stable isotope ratio, leaves from the "OFF" year exhibited significantly higher δ13C values, suggesting a higher resistance to the CO2 pathway from the atmosphere to carboxylation sites compared to the "ON" year plants.

Influence of Experimental Warming on the Rate and Duration of Fruit Growth and Oil Accumulation in Young Olive Trees (cvs. Arbequina, Coratina)

Olive tree cultivation in new warmer areas and climate change have increased the global interest in understanding how air temperature affects both fruit growth and oil accumulation. The aims of this study were to evaluate the rate and duration of fruit growth and oil accumulation in response to experimental warming (+3) in a semiarid region of Argentina; and assess how warming affected fatty acid composition. Young, potted olive trees (cvs. Arbequina, Coratina) were warmed (T+) or maintained near ambient temperature (T0) inside open top chambers in the field during oil accumulation in 2014-2015 or 2015-2016 using different trees in each season. Warming reduced the rate of both fruit growth and oil accumulation in T+ compared to T0 in both cultivars. These rate reductions under T+ led to large decreases in final fruit dry weight and oil concentration. In contrast, the durations (i.e., days) of fruit growth and oil accumulation were most often not affected. Cultivar x temperature interactions were observed in 2014-2015 with warming decreasing oleic acid and increasing linoleic acid in cv. Arbequina, while cv. Coratina showed no response to warming. However, no interactions were found in 2015-2016. Studying how fruit growth and oil accumulation respond to adaptation strategies against increasing air temperatures should be a priority in both young and mature olive trees of numerous cultivars given crop expansion to new regions and future climate scenarios.

Influence of environmental growth temperature on tocopherol and sterol oil concentrations in olive fruit

BACKGROUND

Tocopherols and sterols are minor components of virgin olive oils that contribute to oil quality. Based on observations at different geographical locations, it has been suggested that environmental temperature during fruit growth affects tocopherol and sterol oil concentrations in olive fruit. However, controlled experiments have not been conducted to directly assess their responses to temperature. In this study, a manipulative experiment using open-top chambers (OTCs) was performed in the field to evaluate the responses of these oil components to a moderate air temperature increase during oil accumulation in young trees of two olive cultivars (Arbequina, Coratina). The two temperature levels in the OTCs were a control about 1 °C above ambient temperature (T0) and a heated treatment (T+) with a target temperature of 4 °C above T0.

RESULTS

Total tocopherol and sterol oil concentrations in olive fruit were generally higher in the T+ temperature treatment than in the control at the end of the oil accumulation period. The increase in total tocopherols in T+ appeared to be related to a decrease in fruit oil concentration with heating. Individual sterols showed both significant increases and decreases due to T+, and some differences in response occurred between the two cultivars.

CONCLUSION

These findings provide evidence that growth temperature affects tocopherol and sterol oil concentrations in olive fruit at the end of the oil accumulation period. Cultivars should be carefully chosen for new olive-growing regions, and the results could be relevant for global warming scenarios in existing growing regions. © 2021 Society of Chemical Industry.

Influence of Climate Change on Metabolism and Biological Characteristics in Perennial Woody Fruit Crops in the Mediterranean Environment

The changes in the state of the climate have a high impact on perennial fruit crops thus threatening food availability. Indeed, climatic factors affect several plant aspects, such as phenological stages, physiological processes, disease-pest frequency, yield, and qualitative composition of the plant tissues and derived products. To mitigate the effects of climatic parameters variability, plants implement several strategies of defense, by changing phenological trends, altering physiology, increasing carbon sequestration, and metabolites synthesis. This review was divided into two sections. The first provides data on climate change in the last years and a general consideration on their impact, mitigation, and resilience in the production of food crops. The second section reviews the consequences of climate change on the industry of two woody fruit crops models (evergreen and deciduous trees). The research focused on, citrus, olive, and loquat as evergreen trees examples; while grape, apple, pear, cherry, apricot, almond, peach, kiwi, fig, and persimmon as deciduous species. Perennial fruit crops originated by a complex of decisions valuable in a long period and involving economic and technical problems that farmers may quickly change in the case of annual crops. However, the low flexibility of woody crops is balanced by resilience in the long-life cycle.

Effects of prolonged elevated temperature on leaf gas exchange and other leaf traits in young olive trees

Despite the economic importance of long-lived crop species in the Mediterranean Basin and their expansion to new warmer regions, their potential responses to prolonged temperature increases have not been adequately addressed. The objectives of this study were to: (i) assess leaf gas exchange responses to prolonged elevated temperature in young olive trees; (ii) evaluate some additional leaf traits such as stomatal density and size under these same conditions; and (iii) determine whether photosynthetic acclimation to temperature was apparent. A field experiment with two temperature levels was conducted using well-irrigated, potted olive trees (cvs. Arbequina, Coratina) grown in open-top chambers during the summer and early fall in two growing seasons. The temperature levels were a near-ambient control (T0) and a heated (T+) treatment (+4 °C). Maximum photosynthetic rate (Amax), stomatal conductance (gs), transpiration (E) and chlorophyll fluorescence were measured. Stomatal size and density and trichome density were also determined. The Amax, gs and chlorophyll fluorescence were little affected by heating. However, leaf E was higher at T+ than T0 in the summer in both seasons due in large part to the moderate increase in vapor pressure deficit that accompanied heating, and consequently water-use efficiency was reduced in heated leaves. When reciprocal temperature measurements were conducted in mid-summer of the second season, Amax values of T0 and T+ leaves were higher under the temperature level at which they grew than when measured at the other temperature level, which suggests some thermal acclimation. Stomatal size and density were greater in T+ than in T0 grown leaves in some cases, which was consistent with a greater E in T+ leaves when measured at both temperature levels. These results suggest that acclimation to long-term changes in temperature must be carefully considered to help determine how olive trees will be influenced by global warming.

Mechanisms underlying photosynthetic acclimation to high temperature are different between Vitis vinifera cv. Syrah and Grenache

Photosynthesis acclimation to high temperature differs among and within species. Grapevine intra-specific variation in photosynthetic acclimation to elevated temperature has been scarcely assessed. Our objectives were to (i) evaluate the mechanisms underlying long-term acclimation of photosynthesis to elevated temperature in grapevine, and (ii) determine whether these responses are similar among two varieties. A warming experiment with well irrigated Grenache and Syrah field-grown plants was performed during two growing seasons comparing plants exposed at ambient temperature (control) with plants in open-top chambers (heating) that increased mean air temperature between 1.5 and 3.6°C. Photosynthetic acclimation was assessed through the response of net assimilation (An), Rubisco carboxylation rate (Vcmax) and electron transport rate (Jmax), at leaf temperatures from 20 to 40°C. Our results evidenced different mechanisms for photosynthetic acclimation to elevated temperature. Compared with control, Grenache heated increased An, maintaining higher Vcmax and Jmax at temperatures above 35°C. By contrast, Syrah heated and control presented similar values of An, Vcmax and Jmax, evidencing an adjustment of photosynthesis without increasing C assimilation. Both varieties increased the optimum temperature for An, but to a lesser extent when growth temperature was higher. Our study provides evidence that grapevine varieties present different acclimation mechanisms to expected warming.