Document: JUA-3-30-17

Variation of root respiration rate with root diameter and nitrogen concentration.

LORETI, J.* and R.B.JACKSON

Duke University, Durham, NC 27708 USA ¹

Abstract:
Root respiration rate is an important variable for disciplines ranging from plant physiology to crop breeding to ecosystem modeling. It strongly depends on the type of activity that roots are performing, for example water uptake, nutrient uptake, and transport. In general, water and nutrient uptake are more important in finer roots, whereas coarser roots are devoted to transport. Hence, we expect a decrease of root respiration rate with increasing root diameter. In this study, we synthesized data from the literature with the aim of elucidating the effects of root diameter and root nitrogen concentration (%N) on root respiration rate. Our literature survey only considered studies that a) measured root respiration directly on intact or excised roots from field grown plants, and b) specified root diameter and/or nitrogen concentration. This selection procedure yielded 16 studies from an original list of 500 references related to roots and respiration. The selected studies included several temperate forest ecosystems and boreal shrublands and comprised a range of root diameters of 0.25 to 6.5 mm. All respiration values were corrected to 20^oC assuming a Q₁₀=2. Specific root respiration rate decreased in a logarithmic fashion with root diameter for trees as well as for shrubs (R²= 29% and 51% respectively; p < 0.01). When only respiration rates of roots < 2 mm diameter were analyzed, the relationship between these two variables still held for shrubs but was not significant for trees, suggesting that other factors may control the respiration rate of temperate tree roots finer than 2 mm diameter. Since a few papers reported data on respiration rate and root nitrogen concentration, we have been able to analyze the relationship only for roots thinner than 1 mm diameter of Acer saccharum, several Pinus species and a mixture of other species. Root respiration increased linearly with %N of roots for Pinus (R²=24%) as well as for a group of other species (R²= 23%) and A. saccharum (R²= 19%). This synthesis agrees with results of experiments we performed recently. It also indicates that a) root diameter explains the variation in respiration rate across a relatively large range of root diameters and b) %N of root tissue may be used to explain differences in respiration rate within a diameter class.

Keywords: root respiration, root diameter, nitrogen concentration

This abstract is being presented at: 3:30 PM in session:
ROOT PROCESSES