Plant roots have been recognized to be modu- lar, and a third order root cluster has been proposed to be the basic root module unit based upon the life cycle. This experiment examines root modularity of the nutrient-u...Plant roots have been recognized to be modu- lar, and a third order root cluster has been proposed to be the basic root module unit based upon the life cycle. This experiment examines root modularity of the nutrient-up- take function using stable isotope 15N. Solidago canadensis root clusters of second or third orders--from the same third or fourth order roots, respectively--were treated with 15NH15NO3, NH4NO3, and de-ionized water for 15 and 180 min. The δ15N values of the root clusters were then analyzed and compared. The 15N values of 15N-treated root clusters of both second and third orders were hundreds of times higher than that of the 15N untreated root clusters. However, the differences of the δ15N values among 15N untreated root clusters （though expressed some significant variations）, did not indicate the 15N shared by the sister root clusters came from a common higher-order root. These results demonstrated functional modularity of root nutrient uptake, revealed a second order root, perhaps even a first order root to be a base module unit in terms of root nutrient uptake. The results also suggested that the concept of root modularity is function-specific. This experiment further revealed the importance of treatment timing in stabilizing the internal 15N/14N ratio in roots and avoiding top-down transportation of 15N back into roots to secure unbiased measurements.展开更多
基金financially supported by the National Science Foundation of China(grants 30830024 and 30770330)
文摘Plant roots have been recognized to be modu- lar, and a third order root cluster has been proposed to be the basic root module unit based upon the life cycle. This experiment examines root modularity of the nutrient-up- take function using stable isotope 15N. Solidago canadensis root clusters of second or third orders--from the same third or fourth order roots, respectively--were treated with 15NH15NO3, NH4NO3, and de-ionized water for 15 and 180 min. The δ15N values of the root clusters were then analyzed and compared. The 15N values of 15N-treated root clusters of both second and third orders were hundreds of times higher than that of the 15N untreated root clusters. However, the differences of the δ15N values among 15N untreated root clusters （though expressed some significant variations）, did not indicate the 15N shared by the sister root clusters came from a common higher-order root. These results demonstrated functional modularity of root nutrient uptake, revealed a second order root, perhaps even a first order root to be a base module unit in terms of root nutrient uptake. The results also suggested that the concept of root modularity is function-specific. This experiment further revealed the importance of treatment timing in stabilizing the internal 15N/14N ratio in roots and avoiding top-down transportation of 15N back into roots to secure unbiased measurements.
