Abstract
Bamboo is an efficient silicon accumulator with diverse phytolith morphotypes and composition. The bamboo culm sheath, traditionally considered as a modified leaf, plays a key role in bamboo taxonomy and provides significant mechanical and physiological support for shoot development, but its silicon deposition and phytolith morphological variation remain underexplored. We investigated silicon variation and phytolith morphology in D. brandisii culm sheaths at different growth stages. The results showed that silicon deposition in D. brandisii culm sheaths at different growth stages was comparable to foliage leaves but significantly greater than branches as in previous research. Phytolith concentration in the culm sheath blades of D. brandisii was higher, associated with their greater silicon content than the sheath bodies. Silicon precipitated and phytoliths were produced as the culm sheath matured. Silicon and phytolith contents were significantly greater in upper culm sheath bodies. D. brandisii culm sheaths were characterized by a high proportion of rondel phytoliths, whereas bilobate and bulliform flabellate phytoliths were not observed. Circular and saddle phytoliths accounted for a very low proportion. Stomata phytoliths were abundant in culm sheaths at the shooting stage and increased with sheath maturation, which supported the transpiration, respiration and photosynthesis in culm sheaths of the shoots. Elongate and acute phytoliths were extremely abundant in D. brandisii culm sheaths and increased with sheath maturation, which enhanced the mechanical and protective role of the culm. The phytolith morphotypes in D. brandisii culm sheaths did not demonstrate a specific trend with sheath position. Saddle phytoliths showed insignificant variation in D. brandisii culm sheaths.