Effect of Waterlogging on Biomass Allocation and Allometric Pattern of Rhizome and Root System of Phyllostachys rivalis Physiological Response of Phyllostachys rivalis Rhizome Roots to Long-term Water Stress Adaptive adjustment to nutrient absorption and accumulation of Phyllostachys rivalis rhizome-roots under waterlogged conditions Effect of Long-term Flooded Conditions on Nutrient Stoichiometric Characteristics of Phyllostachys rivalis Rhizome Roots