Nitrogen sharing strategies in six clonal species
Nitrogen is often a limiting factor for plant growth, and its availability is a major determinant of level of competition. In clonal plants, patterns of nitrogen translocation between ramets may be part of plant nitrogen economics, and, as such, may also be related to the typical availability of nitrogen. In nutrient-poor habitats, extensive nutrient sharing balancing resource availability may be important, whereas nutrient sharing between established ramets may not be beneficial in productive habitats. I tested the proposed nutrient sharing strategies on nitrogen translocation in six stoloniferous species that occur in habitats of varying productivity. Mother and daughter ramets of each species were grown either in a homogeneous nutrient-poor treatment or in a "nutrient-poor to nutrient-rich" treatment. I traced the translocation of nitrogen in both directions using stable isotope labelling when the daughter ramets were one month old. Surprisingly, I found no effect of nutrient treatment on nitrogen translocation. Instead, each species translocated nitrogen either acropetally, basipetally, or equally in both directions. There was no relationship between the direction of translocation and the productivity of the species habitats. However, net translocation seemed to be related to the relative size of daughters across species, and within Veronica officinalis. The results suggest that the relative size of plant parts is an important determinant of the strength of the sink for nitrogen they form, and that the growth habit of a species can affect its nitrogen translocation. Under certain conditions, such internally induced source-sink relationships may dominate over external nitrogen heterogeneity. I speculate that growth habit, together with nitrogen translocation patterns, may be part of adaptive growth strategies.