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Premise: A comparison of methods using different materials to exclude light from stems to prevent stem CO2 exchange (i.e., photosynthesis), without affecting stem conductance to water vapor, surface temperature, and relative humidity, was conducted on stems of avocado trees in California. Methods and Results: The experiment featured three materials: aluminum foil, paper‐based wrap, and mineral‐based paint. We examined stem CO2 exchange with and without the light exclusion treatments. We also examined stem surface temperature, relative humidity, and photosynthetic active radiation (PAR) under the cover materials. All materials reduced PAR and stem CO2 exchange. However, aluminum foil reduced stem surface temperature and increased relative humidity. Conclusions: Methods used to study stem CO2 exchange through light exclusion have historically relied on methods that may induce experimental artifacts. Among the methods tested here, mineral‐based paint effectively reduced PAR without affecting stem surface temperature and relative humidity around the stem. [ABSTRACT FROM AUTHOR]

'Honeycrisp' apple is susceptible to bitter pit, which is associated with fruit mineral nutrient composition. Rootstock genotypes can affect nutrient acquisition, distribution, and fruit yields, which all affect fruit nutrient composition and bitter pit susceptibility. However, the changes of these traits among different rootstock genotypes in response to abiotic stress under semiarid conditions are relatively unknown. The objective of this study was to evaluate the influence of different rootstocks and irrigation on nutrient uptake and partitioning with 'Honeycrisp' apple grown in an irrigated, semiarid environment. 'Honeycrisp' apple trees were grafted on four different rootstocks, Geneva 41 ('G.41'), Geneva 890 ('G.890'), M.9-T337 ('M.9'), and Budagovsky 9 ('B.9'), and these were planted at high density (3000 trees/ha). Irrigation was applied as either a water-limited treatment where volumetric soil water content was maintained near 50% field capacity (FC) and a well-watered control where soil water content was maintained near 100% FC. 'G.890', the most vigorous rootstock, had lower nitrogen and higher potassium content in leaves, while 'B.9', the least vigorous rootstock, had lower potassium and higher nitrogen content. Rootstock genotype did not affect calcium uptake. Interestingly, water-limited conditions increased the nutrient content in root and stems but not in leaves. Water-limited trees partitioned more nitrogen and calcium to roots, while well-watered trees in the control partitioned more nutrients to the stems. Fruit size was the largest for 'G.890' and smallest for 'B.9'. Both 'G.41' and 'G.890' had higher bitter pit incidence, which was associated with higher potassium content in leaves and fruit. These results suggest that rootstock-induced vigor and irrigation can both contribute to nutrient imbalances in leaves and fruit that could affect the development of physiological disorders in 'Honeycrisp' apple. [ABSTRACT FROM AUTHOR]

Soil environment strongly contributes to tree growth and development, affecting nutrient and water uptake. Composite woody perennials, like apple, are a combination of two genetically different parts: a rootstock and a scion, and yet, the role of each part on nutrient uptake and distribution under differing soil environments has not been previously studied. We tested how water limitations and elevated soil temperatures, applied to different apple rootstocks and scions, affected mineral nutrient uptake and distribution on young apple trees. Two one-year-old potted apple cultivars were grown in a greenhouse, 'Honeycrisp' and 'Gala,' combined with four rootstocks: G890, G41, M9, and B9. Belowground abiotic environmental treatments were imposed for 60 days after trees reached approximately 45 cm height. Water limitations reduced aboveground biomass and, to a lesser extent, root biomass. 'Gala' and the rootstock G890 showed elevated mineral nutrient uptake compared to 'Honeycrisp' and the other rootstock genotypes. Additionally, G890 showed greater plasticity for both biomass and mineral nutrient accumulation. Elevated soil temperatures increased the ratios of K:Ca, N:Ca, Mg:Ca, and (N + K + Mg):Ca in leaf tissue of rootstock G41 and 'Honeycrisp'. These findings highlight the importance of the use of scion and rootstock genotypes that are adapted to specific soil environments to ensure optimal nutrient uptake. [ABSTRACT FROM AUTHOR]

Tree responses to fertilizer management are complex and are influenced by the interactions between the environment, other organisms, and the combined genetics of composite trees. Increased consumer awareness of the environmental impact of agriculture has stimulated research toward increasing nutrient-use efficiency, improving environmental sustainability, and maximizing quality. Here, we highlight recent advancements and identify knowledge gaps in nutrient dynamics across the soil–rhizosphere–tree continuum for fruit crops. Beneficial soil management practices can enhance nutrient uptake and there has been significant progress in the understanding of how roots, microorganisms, and soil interact to enhance nutrient acquisition in the rhizosphere. Characterizing root architecture, in situ, still remains one of the greatest research challenges in perennial fruit research. However, the last decade has advanced the characterization of root nutrient uptake and transport in plants but studies in tree fruit crops have been limited. Calcium, and its balance relative to other macronutrients, has been a primary focus for mineral nutrient research because of its important contributions to the development of physiological disorders. However, annual elemental redistribution makes these interactions complex. The development of new approaches for measuring nutrient movement in soil and plant systems will be critical for achieving sustainable production of high-quality fruit in the future. [ABSTRACT FROM AUTHOR]