Photosynthetic carbon assimilation rates are highly dependent on environmental factors such as light availability and on metabolic limitations such as the demand for carbon by sink organs. The relative effects of light and sink demand on photosynthesis in perennial plants such as trees remain poorly characterized. The aim of the present study was therefore to characterize the relationships between light and fruit load on a range of leaf traits including photosynthesis, non-structural carbohydrate content, leaf structure, and nitrogen-related variables in fruiting (‘ON’) and non-fruiting (‘OFF’) ‘Golden Delicious’ apple trees. We show that crop status (at the tree scale) exerts a greater influence over leaf traits than the local light environment or the local fruit load. High rates of photosynthesis were observed in the ON trees. This was correlated with a high leaf nitrogen content. In contrast, little spatial variability in photosynthesis rates was observed in the OFF trees. The lack of variation in photosynthesis rates was associated with high leaf non-structural carbohydrate content at the tree level. Taken together, these results suggest that low carbon demand leads to feedback limitation on photosynthesis resulting in a low level of within-tree variability. These findings provide new insights into carbon and nitrogen allocations within trees, which are heavily dependent on carbon demand.

Trees participate in mitigating the urban heat island phenomenon thanks to their transpiration and shading. This cooling potential is highly dependent on leaf area. Nevertheless, leaf traits potentially vary across different land management practices in urban settings, thereby challenging the models used to estimate thermal budgets. The present study aims to investigate the variability of leaf area traits of linden (Tilia spp.) urban trees, and their effect on simulated tree transpiration. Reconstruction of the leaf area was undertaken at the tree scale at three different urban land management sites from three cities: London and Birmingham (UK) and Chantilly (France). The reconstruction combined allometric measurements at shoot and leaf scales, and a tree-scale 3D digitization with laboratory analysis using field data collected by citizen scientists. The management practices had a significant impact on leaf area, and on tree allometric relationships, which were propagated through the reconstruction process. Relative differences between the management practices ranged between 12% and 48% according to the city where the variable was considered (e.g., leaf area index, total leaf area, or tree transpiration). Trees in managed sites (i.e., individualized leaf crowns, frequent leaf litter removal, and standard thinning/pruning operations) develop a higher leaf area, thus promoting cooling potential. This study shows that the variability of leaf traits, and their responses to different land management, can be studied by comprehensive data collection through citizen science and lab-based modelling. It also highlights the importance of appropriate, well-designed urban planning, where landscaping using urban trees can play an even better role in climate proofing cities.

Mediterranean agroecosystems increasingly face prolonged summer drought, extended bare-soil periods and heat extremes, all of which constrain soil biota and threaten long-term soil functioning. Management practices maintaining plant cover during summer, such as cover crops, may alleviate these constraints but generally require irrigation in dry regions. However, the ecological consequences of combining summer cover crops with irrigation remain poorly quantified for soil fauna, particularly in heterogeneous agroforestry systems.,We monitored earthworm communities for six years (2019–2024) at the DIAMS experimental platform, a replicated Mediterranean alley-cropping agroforestry trial where an irrigated summer cover crop was implemented factorially. Earthworms were surveyed each winter across contrasted habitat types to assess delayed (legacy) effects of summer management. To isolate irrigation effects from spatial heterogeneity and interannual climatic variability, we applied a Difference-in-Differences framework complemented by event-study analyses.,Summer crop irrigation did not affect earthworm biomass or species richness but induced habitat-specific changes in abundance. Abundance increased in irrigated agroforestry crop alleys (×3.5 in AF_C and ×2.5 in AF_C1m), while no detectable effects occurred in monoculture or tree-dominated habitats. Communities were largely dominated by Microscolex dubius, suggesting that irrigation primarily enhanced the survival or recruitment of this disturbance-tolerant species. Irrigation effects were stronger following dry autumns, indicating climate-dependent legacy responses.,Overall, our results show that irrigation benefits for soil fauna are strongly context-dependent, emerging primarily in exposed crop habitats and shaped by habitat heterogeneity, seasonal legacy effects and interannual climatic variability.