Structural and functional adaptations of Cenchrus ciliaris to tree-specific overstory microenvironments in a forest ecosystem

Understory vegetation is a vital component of forest and agroforestry ecosystems, sustaining ecological processes such as nutrient cycling, microclimate regulation, soil stability, and biodiversity support. In semi-arid and arid regions, grasses like Cenchrus ciliaris a drought-tolerant C₄ perennial are particularly valuable due to their resilience, high forage potential, and ability to thrive under challenging conditions. However, the extent to which overstorey tree modulate the growth, physiology, and anatomy of understory vegetation remains insufficiently understood, especially in managed forestry systems. To address this gap, we conducted a field study in the Gatwala forest plantation, Punjab, Pakistan, sampling understory vegetation beneath ten overstorey tree. For each tree, three sites were selected, each containing three plots (5 quadrats per plot; 15 quadrats per species), ensuring robust replication. A two-way ANOVA with site × species interaction was performed to assess the key traits of Cenchrus ciliaris. Results showed that Morus nigra and Ficus religiosa enhanced grass performance most strongly, increasing shoot biomass by 42–47% and proline content by 38% compared to open controls, reflecting both productive and protective canopy effects. Ziziphus mauritiana improved osmotic regulation, with glycine betaine and soluble sugars rising by 25 and 31%, respectively, under its canopy. In contrast, Terminalia bellirica and Eucalyptus camaldulensis reduced grass height (−29%) and biomass (−34%), accompanied by declines in nitrogen and phosphorus uptake, suggesting inhibitory shading and allelopathic effects. Anatomical analysis revealed that populations beneath Casuarina obesa and Dalbergia sissoo developed vascular bundles 21–26% larger and epidermal layers up to 18% thicker than controls, enhancing hydraulic efficiency and mechanical stability. Moderate structural improvements were observed under Acacia nilotica and Broussonetia papyrifera , which produced narrower cortical zones and weaker vascular development. These findings demonstrate that overstorey species exert differential effects on C. ciliaris via light interception, nutrient cycling, and soil-water dynamics. These findings demonstrate that overstorey species exert differential effects on C. ciliaris via light interception, nutrient cycling, and soil–water dynamics. From a management perspective, Morus and Ficus appear as promising candidates for integration into silvopastoral systems, whereas Eucalyptus warrants caution due to its inhibitory influence on understory productivity. Functional traits of C. ciliaris , including epidermal thickening and vascular enlargement, provide useful indicators for identifying grass tree combinations suited to dryland agroforestry. These findings highlight species-specific canopy effects critical for designing silvopastoral systems in semi-arid regions