| More than half of the apple production in China is from the Loess Plateau. Now, the widely used high density planting system with vigorous rootstock is going through trainsition to high density plating system with dwarf interstock. Moreover, with increasing shortage of available water for agriculture, the apple industry is facing threat from water stress. Fruit tree architecture has significant effecton light interception, transpiration and water transport, then dry matter production and fruit yield and quality. The transition of planting system and increasing water stress would affect tree architecture and ecophysiology. There are complex interactions among tree architecture, function and environment. So, the deep understanding of planting trainsition and water stress effect on tree architecture and function and the developing of a model framework which include tree architecture, function and environment in parallel would benefit the trainsition of planting system, tree architecture optimization, stratigies respond to water stress and determined fruit load using a modeling approach.In this study, characteristics of tree architecture and functions were analysed under different planting systems and water conditions, a functional-structural plant model for apple was firstly obstained. Research results are as follows:(1) We quantified the shootdemography characterics and virtual three-dimensional canopies were reconstructed accordingly for ‘Fuji’ and ‘Gala’ which grafted on a vigorous rootstock associated either with a dwarf M26 interstock or with a virgorous ‘Qinguan’ interstock. Those tree architecture factors favor light interception were determined. The shoot leaf area of long shoot can be estimated with a linear model and short shoot with a mean values and shoots should be considered based on cultivar, interstock and shoot types. Compared to vigorous interstock, vegetative growth in dwarf ineterstock was decreased by 50% and kept almost the same reproductive growth.The spatial distribution of leaf area density of vegetative short shoot was more uniform on dwarf interstock compared to the vigorous interstock. These improvements led to higher light interception efficiency in dwarf interstock trees. There were fewer poorly illuminated within-tree zones and shoots on dwarf interstock than on vigorous interstock. The dwarf interstock trees showed a 25% silhouette to total leaf area(STAR) increase for the whole-tree and 21% and 17% increases for fruiting shoots and vegetative short shoots, respectively. ‘Fuji’ foliage was more clumped than ‘Gala’, leading to lower light interception. The results indicate that dwarf interstocks can effectively improve light interception efficiency. The estimation of light interception can be refined by constructing virtual orchard.(2) The relationships of leaf function traits in apple trees were determined and the reason that the net photosynthesis rate was decreased in dwarf interstock was clarified. At leaf level, for the stomatal conductance model and photosynthesis model, the root mean square errors were 0.0318 mol H2O m-2 s-1 and1.7498 μmol CO2 m-2 s-1, respectively. The biases were 0.007and-0.0027, respectively. These model could accurately simulate stomatal comductnce and net photosynthesis rate at leaf level. Photosynthetic light acclimation in apple leaves resulted from the changes in leaf mass per area, area based nitrogen content and leaf nitrogen partitioning. At leaf level, compared to virgorous interstock trees, eventhe dwarf interstock trees showed 18%(‘Fuji’) and 13%(‘Gala’) increases inleaf area based nitrogen content, the nitrogen partitioned to carboxylation system showed-32%(‘Fuji’) and-31%(‘Gala’) decreases, leading to-15%(‘Fuji’)and-22%(‘Gala’) decreasses in net photosynthesis rate and-41%(‘Fuji’)and-22%(‘Gala’) decrease in water use efficienty and photosynthetic nitrogen use efficienty, respectively. The photosynthesis in vigorous interstock trees was inhibited by stomatal but by not-stomatal factors in dwarf interstock trees.(3) The functional-structural plant model RATP were parameterized for ‘Fuji’ and ‘Gala’ both grafted on a vigorous rootstock associated either with a dwarf M26 interstock or with a virgorous ‘Qinguan’ interstock, based on leaf functional parameters at leaf level. Contributions of leaf function and leaf distribution caused by cultivars or interstocks to tree functions at tree scale were clarified. At tree scale, the photosynthesis rate was significantly affected by cultivar-defined leaf function, and can be regulated by interstock-defined leaf distribution. The whole-tree transpiration rate was significantly affected both by cultivar-and interstock-defined leaf functions, but the extent of those effects depended on cultivars and interstocks. The net photosynthesis rate andwater use efficiency at tree scale were significantly improved by dwarf interstock-defined leaf distribution. Dwarf interstock-defined leaf function resulted an improvement of water use efficiency for ‘Gala’, but inverse effect on ‘Fuji’. Compared to ‘Fuji’, ‘Gala’-defined leaf function improved water use efficiency significantly, irrespective of interstocks.(4) The impact of long-term summer moderate water stress(7 years) on the fate of terminal and axillary buds was investigated in relation to flowering occurrence and production pattern(biennial vs. regular) in the ‘Granny Smith’ applecultivar. It was observed that water stress decreased the total number of shoots and flowers per branch, regardless of their type. Conversely, water stress did not modify the timing of the two successive developmental phases characterized by the production of long and medium shoots and an alternation of floral over time, respectively. The analysis of shoot successions over time using a variable-order Markov chain that included both the effects of the predecessor and water treatment revealed that water stress reduced the transition towards long and medium shoots and increased the transition towards floral, short and dead growth units. Water stress also slightly increased the proportion of axillary floral. The higher relative frequency of floral compared to vegetative ones reduced the tendency to biennial bearing under water stress. The accelerated ontogenetic trend observed under water stress suggests lower vegetative growth that could, in turn, be beneficial to floral induction.(5) A firsted resported functional-structural plant model for apple tree was established in our study. This model can simulate dynamic development of tree architecture, carbon assimilation and partitioning within one growing season. MappleT was used to generate architectures corresponding to the ‘Fuji’ cultivar with variability within and among trees. Architectures were input in QualiTree to simulate shoot and fruit growth during a growth cycle. The shoot type in QualiTree were modified to three shoot types(long, medium and short) based on apple and were characterized by different growth function parameters. The light interception model in Qualitree was adjusted to the shape of apple tree. Finally, the coupled model can simulate growth and architectural characteristics at the tree scale(plant leaf area, shoot number and types, harvest weight). At the shoot scale, mean fruit weight and its variability within tree was accurately simulated whereas the model tended to overestimate individual shoot leaf area and to underestimate its variability for each shoot type. Moreover, the model correctly applied with the crop load effect on organ growth. |
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