Nutrient, chlorophyll and caloric dynamics of Phyllostachys pubescens leaves in Yongchun County, Fujian, China

Nutrient, chlorophyll and caloric dynamics of the mature and senescent leaves of Phyllostachys pubescens were studied in Yongchun County, Fujian, China, from April 2002 to March 2003. There were notable seasonal variations in nutrient concentrations in the mature and senescent leaves. Mature leaves had significantly higher N, P and K concentrations than senescent leaves, while senescent leaves had higher Ca concentration and Mg concentration changed little during senescence. Resorption efficiencies on leaf area basis of N, P and K were positive, and those of Ca and Mg were negative, suggesting that with leaf senescence, N, P and K were translocated out of senescing leaves to other parts of plant, while Ca and Mg accumulated in senescing leaves. Seasonal changes in Chl a, Chl b and total chlorophyll were curvilinear in style, with Chl a making up the major portion of total chlorophyll. Chl a increased substantially in winter in mature leaves only, reflecting that the photosynthetic apparatus of mature leaves adapted to changes in the environment (i.e., temperature), whilst senescent leaves were less sensitive to environmental changes. Chlorophyll content decreased but the Chl a/Chl b ratio increased during leaf senescence. Ph. pubescens leaves had relatively high ash contents, with 10.29 ± 2.59% for mature leaves and 10.82 ± 2.63% for senescent leaves respectively. There was an increasing trend (P = 0.0199) in the ash content during leaf senescence, showing that Ph. pubescens leaves possibly possessed the mechanism to maintain the nutrition balance. Gross caloric value and ash free caloric value remained almost constant during leaf senescence (P > 0.05), demonstrating that energy was not lost with leaf senescence.