The response of clonal growth and ramet morphology to water depth (from 60 to 260 cm) and sediment type (sand versus organic clay) was investigated for the stoloniferous submersed macrophyte Vallisneria natans in an outdoor pond experiment. Results showed that water depth significantly affected clonal growth of V. natans in terms of clone weight, number of ramets, number of generations, clonal radius and stolon length. V. natans showed an optimal clonal growth at water depths of 110-160 cm, but at greater depths clonal growth was severely retarded. A high allometric effect was exhibited in ramet morphology. Along the sequentially produced ramet generations, ramet weight and plant height decreased while stolon length and the root:leaf weight ratio increased. When using ramet generations as covariate, sediment type rather than water depth more strongly affected the ramet characteristics. For plants grown in clay, ramet weight, ramet height and stolon length were greater, and plants exhibited lower root:leaf weight ratio. These data suggest that water depth and sediment type have differential effects on clonal growth of V. natans: Water depth appears primarily to affect numerical increase in ramets and spatial spread, whereas sediment type mainly affects biomass accumulation and biomass allocation.

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1. To test whether clonal macrophytes can select favourable habitats in heterogeneous environments, clonal fragments of the stoloniferous submerged macrophyte Vallisneria spiralis were subjected to conditions in which light intensity and substratum nutrients were patchily distributed. The allocation of biomass accumulation and ramet production of clones to the different patches was examined. 2. The proportion of both biomass and ramet number of clones allocated to rich patches was significantly higher than in poor patches. The greatest values of both clone and leaf biomass were produced in the heterogeneous light treatment, in which clones originally grew from light-rich to light-poor patches, while clones produced the most offspring ramets in the treatments with heterogeneous substratum nutrients. Similarly, root biomass had the highest values in nutrient-rich patches when clones grew from nutrient-rich to nutrient-poor patches.3. The quality of patches in which parent ramets established significantly influenced the foraging pattern. When previously established in rich patches, a higher proportion of biomass was allocated to rich patches, whereas a higher proportion of ramet number was allocated to rich patches when previously established in poor patches. 4. Results demonstrate that the clonal macrophyte V. spiralis can exhibit foraging in submerged heterogeneous environments: when established under resource-rich conditions V. spiralis remained in favourable patches, whereas if established in adverse conditions it could escape by allocating more ramets to favourable patches.

Altitudinal diversity of terrestrial plants has been widely studied, whereas little is known for the patterns of aquatic plants. Here, we used a standardised field dataset to quantify the altitudinal patterns in the diversity and structure of aquatic plant assemblages, as well as the relationships between diversity indices and environmental variables. Large‐scale field investigations were carried out in 128 sites ranging from 2,280 to 5,020 m above sea level across the southern part of Qinghai‐Tibet Plateau, China. In total, 102 species of aquatic plants were recorded, belonging to 67 genera, 31 families. Five taxonomic, phylogenetic, and functional indices were calculated for each collection site. We firstly examined altitudinal patterns of these diversity indices, then quantified the variations of indices across water areas, water flow, and soil matrix, respectively. We also explored the relationships between diversity indices and environmental variables using redundancy and variance partitioning analysis, to detect the ecological variables that drove the diversity. The results showed that taxonomic, phylogenetic, and functional diversity of aquatic plants decreased with increasing altitude. Net relatedness index of aquatic plants showed a hump pattern along the altitude gradient, with a peak around 3,800 m above sea level. There was no obvious trend in the net functional relatedness index of aquatic plants with altitude. Annual mean temperature was the most important variable associated with the taxonomic, phylogenetic, and functional diversity. Water area and water flow were significantly associated with functional structure, but not phylogenetic structure. Soil matrix also correlated with aquatic plant diversity. A large‐scale altitudinal gradient can influence aquatic plant diversity. Environmental filtering and niche convergence might have played dominant roles in the increasing and decreasing stages of phylogenetic structure of aquatic plant assemblages, respectively, along the altitudinal gradient. Phylogenetic and functional structure of aquatic plant assemblages showed different patterns along the altitudinal gradient, and the environmental variables better explained the change of functional structure than did the phylogenetic variables. This is the first comprehensive study on the species, phylogeny, and function of aquatic plant assemblages along a large‐scale altitudinal gradient. We found an altitudinal decline in the diversity of aquatic plants and different patterns in the phylogenetic and functional structures of aquatic plant assemblages. These findings indicate that functional traits have high phenotypic plasticity and are more affected by environments than phylogenetic relationships which are mainly shaped by evolutionary processes.

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