Assessment of canopy leaf area and scale-dependent carbon-water flux responses in a desert shrub

The canopy leaf area (CLA) of desert shrubs is a key trait influencing canopy transpiration, while also regulating both oxygen release and carbon capture. However, precise quantification of diurnal whole canopy carbon-water fluxes remains difficult due to limitations in non-destructive CLA measurement.  Herein, we first employed diverse methods to estimate the CLA) of Caragana korshinskii across different ages. Subsequently, based on precise assessments of canopy leaf area, we quantified the daily-scale photosynthetic carbon assimilation and transpiration of the whole-canopy under lysimeter with or without groundwater. We found that the leaf area index (LAI) method underestimates CLA in younger C. korshinskii shrubs, whereas the basal diameter derivation (BDD) method overestimates CLA in older individuals, highlighting the limitations of both methods in accurately estimating the CLA of shrub across different ages. Further analysis identified key morphological traits of CLA, including total branch cross-sectional area, shrub canopy area, leaf area, and plant height. The multi-trait allometric relationships developed by the above morphological traits can accurately estimate the CLA of C. korshinskii shrubs, which were more accurate and reliable than other methods. Quantitative analysis revealed that a 2.41-fold difference in photosynthetic capacity (P_nDL) of C. korshinskii between with and without groundwater corresponded to a 5.2-fold difference in transpiration (T_rDL) at the leaf scale. However, at the canopy scale, groundwater increased the whole crown daily amount of transpiration (T_rD) 13.6-fold in C. korshinskii, but the whole crown daily amount of photosynthetic carbon assimilation (P_nD) only 6.2-fold. Our results indicated scale-dependent divergence in carbon–water flux responses, and revealed an adaptive strategy that enhances water use efficiency in arid habitats by maintaining minimal transpiration while maximizing photosynthetic carbon assimilation under drought. Our results highlighted that the multi-trait allometric relationships could more accurately estimate canopy leaf area of C. korshinskii, providing new methodological perspectives for quantifying shrub canopy dynamics and carbon-water fluxes in arid desert ecosystems.