Root dynamics and global change: seeking an ecosystem perspective

Abstract

Changes in the production and turnover of roots in forests and grasslands in response to rising atmospheric CO # concentrations, elevated temperatures, altered precipitation, or nitrogen deposition could be a key link between plant responses and longer-term changes in soil organic matter and ecosystem carbon balance. Here we summarize the experimental observations, ideas, and new hypotheses developed in this area in the rest of this volume. Three central questions are posed. Do elevated atmospheric CO # , nitrogen deposition, and climatic change alter the dynamics of root production and mortality ? What are the consequences of root responses to plant physiological processes ? What are the implications of root dynamics to soil microbial communities and the fate of carbon in soil ? Ecosystem-level observations of root production and mortality in response to global change parameters are just starting to emerge. The challenge to root biologists is to overcome the profound methodological and analytical problems and assemble a more comprehensive data set with sufficient ancillary data that differences between ecosystems can be explained. The assemblage of information reported herein on global patterns of root turnover, basic root biology that controls responses to environmental variables, and new observations of root and associated microbial responses to atmospheric and climatic change helps to sharpen our questions and stimulate new research approaches. New hypotheses have been developed to explain why responses of root turnover might differ in contrasting systems, how carbon allocation to roots is controlled, and how species differences in root chemistry might explain the ultimate fate of carbon in soil. These hypotheses and the enthusiasm for pursuing them are based on the firm belief that a deeper understanding of root dynamics is critical to describing the integrated response of ecosystems to global change.

Underestimated role of legume roots for soil N fertility

“…Formowitz et al (2009) and Urquiaga et al (1998) supported that the positive effects of legume root residues in soil are small in a short term due to the slow mineralization rate, but this fact depends on the type of roots and climate. Mycorrhizal hyphae in thicker pasture roots is formed by chitin, a recalcitrant material which can account significantly for the stable organic matter pool, lasting for years in the soil (Norby and Jackson 2000), whereas non-mycorrhized roots as in grain legumes and fine roots in pasture legumes are fast-decomposing material. Depending on the climate characteristics, that fact may be positive in order to restrict the potential N losses out of the ecosystem.…”

Improving the representation of hydrologic processes in Earth System Models

“…Substantial evidence has accumulated that roots can be adaptive and dynamic [e.g., Harper et al, 1991] and that roots can be shaped by local variations in soil water, oxygen, and nutrient status [e.g., Hodge, 2004]. Additionally, the presence of a shallow groundwater may profoundly influence root structure and dynamics, the latter in turn shaping land hydrology and regulating water, energy, and biogeochemical pools and fluxes [Norby and Jackson, 2000]. This new body of knowledge is directly relevant to understanding ecosystem response-feedback to a rapidly changing global environment, and to improving global model capabilities to predict the possible trajectories of the coevolution of the ecosystems and the physical world [Fan, 2015].…”

Plant water relations at elevated CO2– implications for water‐limited environments

“…King, Thomas & Strain (1997) observed increased root surface area in Pinus taeda (loblolly pine) and P. ponderosa (Ponderosa pine) seedlings in elevated [CO 2 ], which was entirely attributable to whole-plant growth, not a redistribution of biomass. Increased fine root production and seasonal increases in fine root standing crop have also been observed in forest stands exposed to elevated [CO 2 ] (Norby & Jackson 2000;Matamala & Schlesinger 2000). However, in none of these cases has the increased fine root production been associated with increased water uptake.…”