Kin selection or resource partitioning for growing with siblings: implications from measurements of nitrogen uptake

Kin selection and resource partitioning have been proposed to explain interactions between plants growing with siblings (from the same mother). These mechanisms have been examined by measurements of fitness, phenotype or allocation traits, but have seldom been tested with N acquisition traits. We determine if kin selection and resource partitioning are occurring using two annual species (Sorghum vulgare and Glycine max) with a short-term N-15 experiment. A mixture of ammonium, nitrate and glycine (1:1:1) was injected into soils around plants after they grew for 47 days. Only one nitrogen (N) form was N-15 labeled in each labeling solution. S. vulgare increased root allocation when growing with strangers (from the different mother), but not increase their N uptake. Although G. max strangers did not increase their root allocation, they significantly increased uptake of total N and the most abundant N form (nitrate) and decreased uptake of the least abundant (glycine). G. max siblings reduced competition due to chemical resource partitioning while S. vulgare showed kin selection. We concluded that processes related to kin selection and resource partitioning can occur simultaneously, resulting in different competitive ability. These findings can improve our understanding of plants growing with siblings or strangers