Morphology And Biomass Allocation Of Current-Year Shoots In Eight Deciduous Tree Species

Plants develop their growth through the repetition of their basic growth units-leaves, shoots, buds, flowers and roots, which is called module. The architecture is the research about integrated spatial structure to develop a plant and the characteristic of modules, and the relation between the growth and the environment. The architecture of plant is the arrangement and combination of the modules in spatial structure, being the expression of an equilibrium between endogenous growth processes and exogenous constraints exerted by the environment. The aim of architectural analysis is, by means of observation and sometimes experimentation, to identify and understand these endogenous processes and to separate from the plasticity of their expression resulting from external influences.Current-year shoots are fundamental units for tree crown development, and the relative importance of light-capture (i.e., leaf-display) and crown-expansion (i.e., space-acquisition) for current-year shoots is not uniform within a single tree. Therefore, the differentiation of current-year shoots for light-capture or crown-expansion is a significant expression of the differentiation of current-year shoots'function. Patterns of differentiation of current-year shoots are closely related to the productive strategies of trees. For example, the total amount of foliage and the leaf-stem balance of an assimilation system affect plant productivity. Meanwhile analysis of biomass allocation of current-year shoots is also important for studying the differentiation of current-year shoots, because the relative importance of functions for current-year shoots will be directly reflected in their biomass allocation.In this study, I examined patterns of the differentiation of current-year shoots in eight deciduous tree species (Acer buergerianum, Acer truncatum, Aesculus chinensis, Ginkgo biloba, Melia azedarach, Prunus cerasifera cv. Atropurpurea, P. lannesiana, and Sophora japonica). Through the analysis of patterns in size-related variation and biomass allocation of current-year shoots in the deciduous tree species, we achieved conclusions as follows:1) In all eight deciduous tree species examined in this study, longer current-year shoots displayed more leaf area than shorter current-year shoots. However, the pattern in the relationships between leaf display index (LDI) and shoot length (SL) was qualitatively different between M. azedarach and seven others. Moreover, the pattern was extreme in G. biloba and P. cerasifera cv. Atropurpurea among the latter seven species, indicating the existence of pattern of differentiation. In the seven species other than M. azedarach, the balance between leaf and stem in a current-year shoot was biased towards leaf in shorter current-year shoots and towards stem in longer current-year shoots, as has been suggested for species with apparent differentiation of short and long shoots. However, not all of these species showed apparent differentiation. The RLDI value and cLDI, value indicates that the structural difference between short and long shoots in G. biloba and P. cerasifera cv. Atropurpurea was much larger than those in the other five species. The large value for G. biloba and P. cerasifera cv. Atropurpurea indicates that, in comparison with the other five species, only dwarf current-year shoots (<0.3 cm) are light-capture-oriented.2) The negative correlation between cLDI and aSM,cLSR and aSM indicates that two types of shoot differentiation exist: type I, characterized by large cLDI and cLSR and small aSM, and type II, characterized small cLDI and cLSR and large aSM. In type I, shorter current-year shoots have a greater LDI than longer current-year shoots, and their stem thickness (i.e., [stem mass]/[shoot length]) is comparable to that of longer current-year shoots. In type II, shorter current-year shoots have a disproportionately smaller stem thickness than longer current-year shoots, and their LDI is comparable to that of longer current-year shoots. Type I has been reported for many tree species. Type II was newly found in recent years. Type I was typically found in G. biloba with dwarf shoots. Type II was found in M. azedarach. The other six species showed an intermediate pattern between type I and type II (referred as semi-type I differentiation).3) The correlation between b and cLSR implies that the proportion of the light-capture oriented shoots in more or less constant, irrespective of the type of differentiation, and accounts for the fact that there were no correlation between the type of differentiation and the leaf mass-stem mass balance in the population of current-year shoots.4) Under the matter-economic restriction, short current-year shoots in type I differentiation have stout stems for supporting offspring shoots in spite of severe self-shading, whereas short current-year shoots in type II differentiation avoid self-shading at the expense of stout stems. If a stout stem is necessary for short current-year shoots, type I should be preferable to type II; and if a stout stem is not necessary for short current-year shoots, type II should be preferable to type I.