Interactions between shoot age structure. nutrient availability and physiological integration in the giant bamboo Phyllostachys pubescens

The age structure of adult shoots, the nutrient availability of the habitat , and their interaction, are important factors influencing the productivity of bamboo groves. In a field fertilization experiment over two years we ex amined the impact of physiological integration on the emergence, growth, an d survival of new shoots of Phyllostachys pubescens, a giant woody bamboo. Impacts of physiological integration were compared using uniform and patchy fertilization treatments. The number of new shoots emerging per plot signi ficantly increased with the application of fertilizer (NPK), but the increa se was constrained by the age structure of adult shoots. In a year with a h igh proportion of shoots with new (first-year) leaves many more new shoots emerged than in a year with a low proportion of new leaves. Mean survivorsh ip of the new shoots was constant at 20% for all treatments in both years o f study. Surprisingly, fertilization did not increase DBH or height of the new shoots, suggesting that shoot size was fixed early in ontogeny. The pat tern of fertilizer application, either uniform or patchy, did not affect th e total number of new shoots produced. In the case of patchy application, m ore new shoots developed in unfertilized patches in comparison to uniformly unfertilized plots, probably because these parts of the clone received res ources via the rhizomes from the adult shoots in adjacent fertilized patche s. The production of new shoots in fertilized patches, in turn, was lower t han that in uniformly fertilized plots as a result of this physiological in tegration. The results are discussed in the general context of the impact o f integration on clonal plant performance in dense stands.