Latitude is an important determinant of local environmental conditions that affect plant growth. Forty ecotypes of Arabidopsis thaliana were selected from a wide range of latitudes (from 16°N to 63°N) to investigate genetic variation in plant size and relative growth rate (RGR) along a latitudinal gradient. Plants were grown in a greenhouse for 31 days, during which period three consecutive harvests were performed. Plants from high latitudes tended to have smaller plant size in terms of seed size, cotyledon width, rosette size, number of rosette leaves, size (leaf area) of the largest leaves, total leaf area, and total dry weight per plant than those from low latitudes. The mean (±SE) RGR across ecotypes was 0.229 (±0.0013) day. There was, however, significant ecotypic variation, with RGR being negatively correlated with latitude. The two main components of RGR, leaf area ratio (LAR) and unit leaf rate (ULR), were also correlated with latitude: LAR increased with increasing latitude while ULR decreased with increasing latitude. It was also found that RGR tended to be negatively correlated with LAR, specific leaf area (SLA) and specific root length (SRL) but to be positively correlated with mean area per leaf (MAL) and ULR. The variation in RGR among ecotypes was relatively small compared with that in the other traits. RGR may be a conservative trait, whose variation is constrained by the trade-off between its physiological (i.e. ULR) and morphological (i.e. LAR) components.

Environmental heterogeneity has received wide attention in clonal plant research over the last decade. Most studies have focussed on the effects of spatial variation in environmental conditions on the performance of ramets and genets, while the effects of temporal heterogeneity have only occasionally been studied. As a consequence, our current knowledge about functional responses of clonal plants to habitat patchiness is biased towards spatial aspects of environmental heterogeneity. Nevertheless, temporal changes in biotic and abiotic conditions do occur in most natural habitats, and they are very likely to affect plant growth and performance, and to create positive selection pressures on traits that can buffer plants against unfavorable consequences of this variability. Storage of resources is a widespread phenomenon in clonal plant species. Typical clonal structures such as stolons, rhizomes and hibernacles serve as storage organs. However, the ecologic significance of storage in clonal plant structures remains partly unclear. We suggest that the lack of understanding with respect to resource storage in clonal plants be related to our poor knowledge of ecologic implications of temporal habitat heterogeneity in natural environments. Resource storage can be understood as a safety measure against temporal changes in the growing conditions of plants. This paper summarizes existing information about the ecologic relevance of storage in clonal plants and it tries to develop a framework for further investigation of resource storage as a strategy to enhance the performance of clonal plants in temporally variable environments.

The effects of understory dwarf bamboo ( Sasa kurilensis ) on soil water and the growth of overstory trees were studied in a dense secondary forest of Betula ermanii in northern Japan. Four plots were established in a Betula ermanii forest with Sasa kurilensis in the understory. The Sasa was removed in two of the plots. The annual increment of the trunk diameter for each tree was measured in the first two years from the commencement of the experiment. Soil water potential was similar in the plots following significant rainfall, but was found to be greater in the plot without Sasa between rainfall events. This suggests that the removal of Sasa slows the reduction of soil water after rainfall. The relative growth rate of the trunk diameter of Betula ermanii increased with tree size in all of the plots because taller trees strongly suppressed smaller ones in the dense forest. The growth rates of Betula ermanii were higher in the plots without Sasa . However, the difference in growth rates between all of the plots tended to be smaller in smaller size classes, possibly because smaller trees were strongly suppressed by larger ones, irrespective of the presence/absence of Sasa . Therefore, the removal of Sasa increased soil water and encouraged the growth of larger Betula ermanii in dense forest during the first two years after the Sasa was removed. The present study suggests that Sasa can reduce the growth of larger Betula ermanii in dense forest by limiting available soil water to these trees.

Festuca rubra , a clonal grass of mountain grasslands, possesses a considerable variability in traits related to spatial spreading (rhizome production, length and branching; tussock architecture). Since these traits highly influence the success of the species in a spatially heterogeneous system of grasslands, a combined field and growth chamber approach was adopted to determine the within‐population variation in these parameters. Clones were sampled in a mountain grassland (The Krkonoše Mts., Czech Republic); the environment (mean neighbour density) of individual clones varied highly. Before the clones were collected, shoot demography and tussock architecture within these clones were recorded in the field for four seasons. Their clone identity was determined using DNA RAPD. Vegetatively propagated plants from these clones were cultivated in a common garden experiment to demonstrate variation in tussock growth and architecture. Their response to change in red/far red light ratio was determined in the growth chamber. Highly significant variation among clones was found in almost all parameters. In the common garden, the clones differed in tussock growth (mean tillering rate), architecture (mean shoot angle, mean tussock density) and proportion of flowering shoots. In the growth chamber, both the aboveground parameters and parameters of the rhizome system were strongly affected by red/far red ratio; among‐clone variation was also almost always significant. The genotype × environment interaction was significant for tillering rate and rhizome architecture. The structure of the rhizome system (which is the major component of clonal spread in space) is a complex result of several components whose inter‐clone variations differ: (i) genetically determined mean rhizome system size, (ii) overall plasticity in rhizome system size (with no significant genetic variation in plasticity), and (iii) genetically determined plasticity in rhizome architecture. Because of the variation in plasticity in rhizome architecture, some c lones seemed to possess the ability to exploit a favourable habitat patch by producing short branches when there; whereas the remaining clones appeared to possess only a simple escape mechanism from unfavourable patches. Environmental variation in the light levels in the studied grassland is fine grained; horizontal growth rates of F. rubra are sufficient to make genets experience different patches in their lifetime. The high variation in both genotype means and plasticities is likely to be due to selection early in genet life in an environment which is heterogeneous at a fine scale.

This is the first study to detect local size hierarchies as a prelude to regular spacing using the mark correlation function. The results confirm that use of the mark correlation function together with the spatial autocorrelation function is an effective tool to analyse the development of a local size hierarchy of trees in a forest.