Determination of root biomasses of three species grown in a mixture using stable isotopes of carbon and nitrogen

Abstract

A method is evaluated that employs variation in stable C and N isotopes from fractionations in C and N acquisition and growth to predict root biomasses of three plant species in mixtures. Moench (C4) were grown together in separate, three-species combinations. Surface roots (0-10cm depth) of each species from each of the two combinations were mixed in various proportions, and the relative abundances of lSN and 14N and 13C and 12C in prepared mixtures, surface roots of single species, and roots extracted from the 80-cm soil profile in which each species combination was grown were analyzed by mass spectrometry. An algebraic determination which employed the 613C, % 15N, and C and N concentrations of root subsamples of individual species accounted for more than 95% of the variance in biomass of each species in prepared mixtures with G. max, G. hirsutum, and S. bicolor. A similar analysis demonstrated species-specific differences in rooting patterns. Root biomasses of the C 4 monocots in each combination, S. scoparium and S. bicolor, were concentrated in the upper 20 cm of soil, while those of G. hirsutum and the woody P. glandulosa were largest in lower soil strata. Analyses of stable C and N isotopes can effectively be used to distinguish roots of species which differ in ratios of 15N to ~4N and ~3C to ~2C and thus to study belowground competition between or rooting patterns of associated species with different C and N isotope signatures. The method evaluated can be extended to quantify aboveground and belowground biomasses of component species in mixtures with isotopes of other elements or element concentrations that differ consistently among plants of interest.

Species abundances influence the net biodiversity effect in mixtures of two plant species

“…All plant material was oven-dried to constant mass at 60 1C and weighed. The distinctive carbon (C) isotope signatures of C 3 forbs and C 4 grasses were used in a simple mixing model (Polley, Johnson, & Mayeux, 1992) to determine the relative contributions of each to root biomass recovered from grass/forb combinations (Sorghastrum/Ratibida and Bouteloua/Oenothera). The stable C isotope signature of each grass and forb was measured by mass spectometry (Isotope Services, Inc., Los Alamos, New Mexico, USA) on roots recovered from species monocultures.…”

Linking water uptake with rooting patterns in grassland species

“…Despite the recognized importance of water and its influence on patterns of aboveground net primary production (ANPP) in grasslands (Knapp and Smith 2001), ecological studies addressing belowground plant activity and functional rooting depth are rare, primarily because of the difficulty in assessing root growth, turnover and activity (Polley et al 1992;Craine et al 2002). An alternate approach to soil excavation and root mapping for inferring functional rooting depth and resource use has been to measure stable isotopic signatures of water.…”

Assessment of Root System Dynamics of Species Grown in Mixtures under Field Conditions using Herbicide Injection and 15N Natural Abundance Methods: A Case Study with Pea, Barley and Mustard

“…Nevertheless little information on differences in the rooting patterns of species grown in sole crops or in mixtures is available to understand how root systems of different component crops interact with each other under field conditions. Knowledge of root system dynamics in relation to partitioning of belowground resources among plants grown in mixtures has been limited by the inadequacies of methods used to distinguish roots according to species (Polley et al, 1992;Tofinga and Snaydon, 1992). Commonly used methods such as trench profile methods or soil cores cannot distinguish the roots of individual species in a mixture.…”

“…Svejcar and Boutton (1985) proposed a method based on large differences in stable carbon isotope composition of C 3 and C 4 plants in order to determine the fraction of the root biomass contributed by each type in a mixture. This method was further developed by Polley et al (1992) who used differences in 15 N natural abundance between legume and non-legume species to determine the contribution of each species to root biomass of the mixtures in a greenhouse experiment.…”