Anpassungsstrategien an Klimawandelfolgen für den Obstbau im Mittelmeerklima – Wird der Obstbau zum Klimaschützer?

ZusammenfassungZur Abschlussveranstaltung des Adapt2Clima-EU-Projekts zu „Klimawandelfolgen für die Landwirtschaft im Mittelmeerraum und Adaptionsstrategien“ trafen sich fast 160 Klimaforscher aus über 30 Ländern am 24.–25. Juni 2019 in Heraklion – mit Klimamodellen und Risikoanalyse bzw. Vulnerabilität verschiedener Mittelmeerregionen. Bei den obstbaulichen Vorträgen stellte sich einmal die Witterung zur Blüte als besonders kritisch heraus, wobei zum einen kühl-nasse Witterung die Bestäubung durch ausbleibendes Fliegen der Honigbienen verhinderte und heiße Witterung die Pollen verklebten und zum anderen Unwetter mit Starkregenfällen im Laufe des Sommers, z. B. in Skopelos im August 2015, die Fruchtqualität bzw. die Ernte und auf Kreta im Frühling 2019 die Blüte bzw. den Fruchtansatz in Frage stellten. Als relativ klimaresilient erscheinen Gebirgsregionen wie Imathia, Pella und Pilion sowie Kreta und Zypern aufgrund der Kombination aus ausreichendem Kältereiz im Winter (Chilling), geringer Spätfrostgefahr, Zugang zu Wasser und weniger Hitzeschäden. Besonders betroffen von Klimawandelfolgen im Mittelmeerraum sind Wein, Tomate und Olive – in der Reihenfolge ihres Wasserbedarfs und ihrer Empfindlichkeit gegenüber Hitze und Trockenheit. Folgende Anpassungsstrategien wurden diskutiert: 1) Wasserauffang- und Rückhaltebecken; 2) Regelung der Wasserrechte; 3) Tröpfchenbewässerung, „deficit irrigation“ oder auch Verzicht auf Bewässerung; 4) Sorten mit hohem Wasserausnutzungsgrad (WUE); 5) geringe Pflanzdichten/extensiver Anbau; 6) Senkung der Evapotranspiration, z. B. durch Beschattung mit Schattier- oder Hagelnetzen; 7) Verzicht auf Bodenbearbeitung; 8) Kurzhalten des Grasaufwuchses oder cover crop im Winter aufgrund von Wasser- und Nährstoffkonkurrenz sowie Brandgefahr; 9) bei Oliven Einbringen von geschreddertem Schnittholz (statt Verbrennen) und 10) der Pressrückstände bzw. -kuchen sowie 11) im Weinbau Anbauverschiebung in nördliche Bergregionen. Ein Teil dieser Maßnahmen bedeutet einen Bruch mit althergebrachten Traditionen, da sowohl das Pflügen bzw. die Bodenbearbeitung als auch das Verbrennen von Schnittholz in Olivenhainen im Besitz der älteren Landbevölkerung in manchen Regionen Griechenlands nicht wegzudenken sind und aus einer Zeit stammen, als Schredder noch unbekannt waren. Die vielversprechenden Ansätze im Mittelmeerraum können auch ein Umdenken im Obstbau und den Beginn einer neuen Ära bedeuten, wenn neben der Erzeugung hochwertiger Früchte Klima- bzw. CO2-relevante Aspekte bei den Kultur- und Pflegemaßnahmen berücksichtigt und entlohnt werden.

GIS-Based Analysis and Mapping of the Winter Chilling Hours in Mainland Spain. Application to Some Sweet Cherry Cultivars

The knowledge of the chilling requirements for breaking rest and flowering of fruit trees is necessary to properly select cultivars and to avoid losses due to an inappropriate cultivar selection in a particular geographical location. With the aim of providing an analysis using three models (Chilling Hours, Utah Model, and Positive Utah Model) to estimate the accumulation of winter chilling, quantifying its spatial variability and representing the spatial pattern throughout mainland Spain, temperature data from 72 meteorological stations, considering the 1975–2015 period, were utilized. The statistical properties of values corresponding to each winter chilling model were assessed and, later, they were mapped by means of an integrated geographic information system (GIS) and a multivariate geostatistics (regression-kriging) and algebra map approach. The results show that measures obtained with the three chilling models were highly related, which were used to visualize the spatial variability of the accumulated winter chilling considering each model. Moreover, the fact that elevation and latitude are related to the chilling hours enables their use as auxiliary variables to better estimate at unsampled locations and generate more accurate maps. Knowledge of the spatial patterns of chill accumulation in different areas of mainland Spain is of great importance when appropriate fruit trees and cultivars have to be selected. Moreover, if a high probability of satisfying the chilling requirements in any area is considered, quantile maps can be used instead of maps based on mean values. Finally, the potential spatial distributions of three sweet cherry cultivars were delineated using the obtained maps.

Effects of winter chilling vs. spring forcing on the spring phenology of trees in a cold region and a warmer reference region

<p>Regions at high latitudes and high altitudes are undergoing a more pronounced winter warming than spring warming, and such asymmetric warming will affect chilling and forcing processes and thus the spring phenology of plants. We analyzed winter chilling and spring forcing accumulation in relation to the spring phenology of three tree species (Ulmus pumila, Populus simonii, and Syringa oblata) growing in a cold region (CR) compared with trees in a warmer reference region (WR, using the Dynamic Model and the Growing Degree Hour (GDH) model. We tested that forcing rather than chilling affects the spring phenology of trees in CR (hypothesis I), and that trees in CR have both lower chilling and lower forcing temperatures and thus longer accumulation periods than trees in WR (hypothesis II). In line with our hypotheses, forcing played a crucial role in spring phenology in CR, but chilling and forcing combined to determine spring phenology in WR. The temperatures during the chilling and forcing periods were lower and the accumulation period started earlier and ended later in CR than in WR. Moreover, the chilling accumulation was broken into two periods by the low deep winter temperature in CR. We conclude that asymmetric warming, with a stronger temperature increase in winter than in spring, could decrease the forcing accumulation effects and increase the chilling effects on the spring phenology of plants in CR. This change in the balance between chilling and forcing will lead to a shift in plant phenology, which will further have major impacts on biogeochemical cycles and on ecosystem functioning and services.</p>

Development of Peach Flower Buds under Low Winter Chilling Conditions

Here, we reviewed both endogenous and exogenous factors involved in the processes of flower bud formation and flower development in peach, analyzing how they can be affected by climatic change in temperate zones, explored the expansion of peach to tropical or subtropical zones. The process of flower bud formation in peach differs between low winter chilling and temperate conditions. Although the main steps of flower development are maintained, the timing in which each one occurs is different, and some processes can be altered under low winter chilling conditions, with a great impact on fruit production and crop management. Further studies on flower bud induction and differentiation under warmer conditions are fundamental for addressing the alterations in flower bud development that negatively impact on next season’s harvest. In the future, horticulturalists and scientists will face several challenges, mainly how high temperatures affect the expression of the main genes regulating flower formation and how to improve crop management in these conditions.

Evolution of the grapevine bud dormancy under different thermal regimes

Fluctuations in winter chilling availability impact bud dormancy and budburst. This study aimed to quantify the thermal requirements during dormancy for ‘Italia’ grape, under different thermal regimes. Cuttings of grapevines ‘Itália’ were collected in Veranópolis-RS, on April/2017, with zero chilling hours (CH). The cuttings were exposed to constant (7.2°C) or alternating (7.2 and 18°C for 12/12h, 12/12h or 18/6h) temperatures, or yet, a constant temperature (7.2°C) or alternating (7.2 and 18°C for 12/12h), combined with one or two days a week at 25°C. Periodically, part of the cuttings was transferred to 25°C for daily budburst evaluation. The induction of the endodormancy (dormancy induced by cold) occurred with 200 CH, independent of the thermal regime, and the overcoming with 300 HF, at 7.2°C. The alternating heat of 18°C in the middle of the cold did not affect the process of overcoming endodormancy. Heat waves during endodormancy resulted in an increased CH to overcome the bud dormancy. The negative effect of high temperature depended on the exposure time. Chilling was partly cancelled during dormancy when the heat wave lasted 36 continuous hours or more. These evidences serve as basis for new model adjustments for budburst prediction, especially for regions with mild and irregular winters, such as those of Southern Brazil.