Effects of Fertilization and Defoliation on Growth Physiology and Leaf-Use Traits of Indocalamus herklotsii ‘Zongyezhu’ Under Moso Bamboo Forest

Objective: This study examined how fertilization and various defoliation regimes influence the growth physiology and leaf-use traits of Indocalamus herklotsii ‘Zongyezhu’ cultivated under a Moso bamboo (Phyllostachys edulis) forest, with emphasis on plant growth and leaf production. Methods: The experiment used a randomized block design with three replicates and six treatments: control (no fertilization, no defoliation), fertilization alone, fertilization + defoliation in October, fertilization + defoliation in December, fertilization + defoliation twice (June and October), and fertilization + defoliation twice (August and December). Over two consecutive years, we measured leaf physiological parameters, shoot emergence and culm quality, and biomass allocation, as well as the yield, grade, functional components and nutrient contents of harvested leaves. Results: The results showed the following: (1) Fertilization promoted the number and quality of newly emerged bamboo. Under fertilized conditions, defoliation significantly increased new shoot number and total biomass but decreased individual culm quality, reflecting a trade-off between new shoot number and individual culm quality. Defoliation also induced compensatory leaf growth, with greater biomass allocation to leaves. (2) Leaf harvesting twice per year produced higher total yield than a single harvest, but the proportion of grade-1 and grade-2 leaves decreased; the single defoliation in December gave the highest proportion of grade-1 and grade-2 leaves. Leaves harvested in June had the highest crude protein content, those in August the highest flavonoid content, and those in December the highest crude fiber and polysaccharide contents. (3) Both growth physiology and leaf-use trait scores were higher under defoliating twice than under defoliating once, and the August + December regime (defoliating twice) showed the best performance in both growth physiology and leaf-use traits among all tested treatments. Conclusions: Fertilization promoted the growth of I. herklotsii ‘Zongyezhu’, and under fertilized conditions defoliation further affected growth and leaf-use traits, with different defoliation regimes showing differential effects. For local production at the experimental site, the August + December defoliation-twice regime is recommended. This study provides a theoretical basis and practical reference for the scientifically oriented cultivation of understory Indocalamus for leaf production.