Periodic carbon flushing to roots of Quercus rubra saplings affects soil respiration and rhizosphere microbial biomass

Abstract

Patterns of root/shoot carbon allocation within plants have been studied at length. The extent, however, to which patterns of carbon allocation from shoots to roots affect the timing and quantity of organic carbon release from roots to soil is not known. We employed a novel approach to study how natural short-term variation in the allocation of carbon to roots may affect rhizosphere soil biology. Taking advantage of the semi-determinate phenology of young northern red oak (Quercus rubra L.), we examined how pulsed delivery of carbon from shoots to roots affected dynamics of soil respiration as well as microbial biomass and net nitrogen mineralization in the rhizosphere. Young Q. rubra exhibit (1) clear switches in the amount of carbon allocated below-ground that are non-destructively detected simply by observing pulsed shoot growth above-ground, and (2) multiple switches in internal carbon allocation during a single growing season, ensuring our ability to detect short-term effects of plant carbon allocation on rhizosphere biology separate from longer-term seasonal effects. In both potted oaks and oaks rooted in soil, soil respiration varied inversely with shoot flush stage through several oak shoot flushes. In addition, upon destructive harvest of potted oaks, microbial biomass in the rhizosphere of saplings with actively flushing shoots was lower than microbial biomass in the rhizosphere of saplings with shoots that were not flushing. Given that plants have evolved with their roots in contact with soil microbes, known species-specific carbon allocation patterns within plants may provide insight into interactions among roots, symbionts, and free-living microbes in the dynamic soil arena.

Carbon allocation in forest ecosystems

“…NPP; g C m À2 yr À1 ; Odum, 1953). Our emphasis in this review is on annual fluxes, although flux can be measured on daily (Dickson, 1987), monthly or even phenological (Cardon et al, 2002) time scales.…”

Ecosystem photosynthesis regulates soil respiration on a diurnal scale with a short-term time lag in a coastal wetland

“…In principle, autotrophic soil respiration is a direct consequence of root respiration, so it is coupled to rates of photosynthesis (Baldocchi et al, 2006). Meanwhile, the flux of recent photosynthate supports substantial microbial activity in the rhizosphere, which can in turn influence the relative fraction of heterotrophic respiration (Cardon et al, 2002;Tang et al, 2005). Consequently, half or more of the soil respiration is driven directly by recent photosynthesis, which challenges the assumption that most of the soil respiration is derived from the decomposition of soil organic matter (Kuzyakov and Cheng, 2001;Bhupinderpal-Singh et al, 2003;Högberg and Read, 2006).…”

Early season root production in relation to leaf production among six diverse temperate tree species

“…For example, production of roots in early spring may be a competitive strategy by some species to occupy favorable soil layers and access water or nutrients before neighboring plants (Eissenstat and Caldwell 1988;Harris 1977). Other species may vary patterns of root production in response to timing of carbohydrate availability from recent photosynthesis or carbohydrate demand by other plant tissues (e.g., leaves, stems, or reproduction) (Cardon et al 2002;Dietze et al 2014). Overall, there have been relatively few observations that link root phenology with whole-plant or ecosystem processes.…”