Morphological Characteristics And Physiological And Biochemical Mechanisms Of Degraded Bamboo Shoots Based On Rhizomes Breaking Treatment

Moso bamboo（Phyllostachys edulis）is a kind of clonal plant.Young bamboo develops from a shoot on the rhizomes.It has the characteristics of explosive growth,rapid timber formation,and strong carbon sequestration ability and plays an important role in the realization of rural revitalization and carbon neutrality strategies.During the explosive growth period,the nutrients required by the shoots are mainly come from the rhizomes and attached mature bamboos.However,a large number of shoots die and cannot develop into young bamboo,which greatly limits the productivity of Moso bamboo plantations.There is still no definite conclusion about the underlying mechanism of the occurrence of degraded shoots.The inadequate nutrient supply hypothesis is one of the widely accepted hypotheses,but there has been no clear evidence.To fill this knowledge gap,this study investigated the dynamic change of morphological,physiological and biochemical,and endogenous hormones of different parts（shoot tips,internodes,shoot roots,and culm necks）in the degraded bamboo shoots by artificially cutting the connected rhizomes of bamboo shoots was used to simulate insufficient nutrient supply in the Moso bamboo plantation.The mechanism of degraded bamboo shoots is revealed through the perspective of nutrient supply in Moso bamboo forests.The results of the study were as follows:（1）Although the height of bamboo shoots increased with rhizome breaking time（20.23-30.65cm）,which had a lower growth rate than that of normal growth shoots（18.98-25.09cm）.The phenomenon of spitting water at bamboo shoot tips gradually disappeared.The scabbard and epidermal hairs appear lodging and become disorganized.The sheath wrapping degree changed from tight to relaxation,the gap gradually became larger,the color of the tip leaves changed from green to yellow,the degree of curling increased,the texture gradually became brittle,and the color of the bamboo shoots changed from yellow-white to waxy yellow.The cytoplasmic shrinkage of shoot tips,internodes and shoot roots increased with rhizomes breaking time,the intercellular spaces changed from small to large,and the arrangement changed from tight and orderly to chaotic.（2）The concentrations of soluble protein,hydrogen peroxide（H₂O₂）,and malondialdehyde（MDA）,as well as the activities of sucrose synthase and catalase（CAT）of shoot tips,internodes,shoot roots,and culm necks significantly increased with the rhizomes breaking time（P<0.05）.The concentrations of starch and soluble sugar significantly decreased with the rhizome breaking time（P<0.05）.The activity of superoxide dismutase（SOD）significantly increased at first and then decreased with rhizome breaking time（P<0.05）.The lowest value of starch content(6.04mg·g^-1)and sucrose synthase activity(241.82μmol·min^-1·g^-1)and the highest values of H₂O₂ content(2.69μmg·g^-1)and CAT activity(113.63μmol·min^-1·g^-1)was observed in the shoot tips.The lowest concentrations of H₂O₂(1.16μmg·g^-1)and MDA(16.65nmg·g^-1)were observed in the internodes.The highest value of starch content(20.47mg·g^-1),sucrose synthase(443.45μmol·min^-1·g^-1)and SOD activities(465.16μmol·min^-1·g^-1)were observed in the culm necks.The lowest concentrations of soluble sugar(5.42mg·g^-1)and soluble protein(7.21mg·g^-1)were observed in shoot roots.The above changes did not change with rhizome breaking time.Soluble sugar and sucrose synthase showed a significant negative correlation（P<0.01）.Soluble protein and MDA were significantly and positively correlated with sucrose synthase（P<0.01）.H₂O₂ was significantly and positively correlated with sucrose synthase（P<0.05）.Starch and soluble sugar were significantly and negatively correlated with CAT（P<0.01）.Soluble protein,H₂O₂,and MDA were significantly and positively correlated with CAT（P<0.01）.Starch and MDA were significantly and positively correlated with SOD（P<0.01）.Soluble protein was significantly and positively correlated with SOD（P<0.05）.（3）The concentrations of indole acetic acid（IAA）and trans-zeatin riboside（t ZR）of shoot tips and culm necks significantly decreased with rhizomes breaking time（P<0.05）.The concentrations of abscisic acid（ABA）,jasmonic acid（JA）,and salicylic acid（SA）significantly increased with rhizome breaking time（P<0.05）.The values of IAA/ABA and t ZR/ABA significantly decreased with rhizome breaking time（P<0.05）.The concentrations of IAA(4.07ng·g^-1)and ABA(1.35ng·g^-1)were lower in the shoot tips than that in the culm necks,and the concentrations of JA(158.71ng·g^-1)were higher than that in the culm necks.In summary,these results showed that the morphology,physiology and biochemistry,and endogenous hormones of degraded bamboo shoots were significantly affected by rhizome breaking time,which was helpful to understand the regulation mechanism of degraded bamboo shoots and provide a scientific reference for improving the sustainable management of Moso bamboo plantations.