Enhanced root exudation induces microbial feedbacks to N cycling in a pine forest under long-term CO2 fumigation.
By Richard P Phillips, A. Finzi, Emily S. Bernhardt. Ecology Letters, 2011
755 citations recorded by the source corpus.
The degree to which rising atmospheric CO(2) will be offset by carbon (C) sequestration in forests depends in part on the capacity of trees and soil microbes to make physiological adjustments that can alleviate resource limitation. Here, we show for the first time that mature trees exposed to CO(2) enrichment increase the release of soluble C from roots to soil, and that such increases are coupled to the accelerated turnover of nitrogen (N) pools in the rhizosphere. Over the course of 3 years, we measured in situ rates of root exudation from 420 intact loblolly pine (Pinus taeda L.) roots. Trees fumigated with elevated CO(2) (200 p.p.m.v. over background) increased exudation rates (μg C cm(-1) root h(-1) ) by 55% during the primary growing season, leading to a 50% annual increase in dissolved organic inputs to fumigated forest soils. These increases in root-derived C were positively correlated with microbial release of extracellular enzymes involved in breakdown of organic N (R(2) = 0.66; P = 0.006) in the rhizosphere, indicating that exudation stimulated microbial activity and accelerated the rate of soil organic matter (SOM) turnover. In support of this conclusion, trees exposed to both elevated CO(2) and N fertilization did not increase exudation rates and had reduced enzyme activities in the rhizosphere. Collectively, our results provide field-based empirical support suggesting that sustained growth responses of forests to elevated CO(2) in low fertility soils are maintained by enhanced rates of microbial activity and N cycling fuelled by inputs of root-derived C. To the extent that increases in exudation also stimulate SOM decomposition, such changes may prevent soil C accumulation in forest ecosystems.
Subfields: Global and Planetary Change, Plant Science, Soil Science
View Paper: https://www.semanticscholar.org/paper/3f532a32ff1af1ccd0aacb6478ccede26a2370ca
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Citations in the corpus
- Response of microbial diversity to C:N:P stoichiometry in fine root and microbial biomass following afforestation (2017, background): “Relative to N and P, root exudation greatly affects the availability of organic C and ultimately influences the soil nutrient balance (Phillips et al. 2011).”
- Functional guild classification predicts the enzymatic role of fungi in litter and soil biogeochemistry (2015, background): “This may be due to the absence of fresh plant photosynthate, if labile plant C primes enzyme production by ectomycorrhizal fungi (Phillips et al., 2011).”
- The mycorrhizal-associated nutrient economy: a new framework for predicting carbon-nutrient couplings in temperate forests. (2013, background): “, 2008a), exudation (Phillips et al., 2011) and mycorrhizal turnover (Pritchard et al.”
- Growth controls photosynthesis - mostly (2013, background): “), and one, the pine plantation at the Duke FACE site, ended up with trees supposedly mining extra nutrients (Phillips et al. 2011), facilitating extra growth, but obviously, such nutrient mining cannot be sustained in the long term (see discussion below).”
- Root-induced changes in nutrient cycling in forests depend on exudation rates (2014, positive): “In a companion study carried out in the same forest, cuvette-based measurements of exudation indicated that approximately half of the rhizosphere C flux, or 2.5% of NPP, was derived from root exudation (Phillips et al., 2011).”
- Plant clipping decelerates the mineralization of recalcitrant soil organic matter under multiple grassland species (2012, background): “For example, increased rates of fresh C inputs in soil by plants exposed to elevated atmospheric CO2 levels have been shown to accelerate SOM mineralization compared with plant-soil systems under ambient CO2 (Drake et al., 2011; Phillips et al., 2011).”
- Global change effects on humid tropical forests: Evidence for biogeochemical and biodiversity shifts at an ecosystem scale (2016, methodology): “At the Duke loblolly pine FACE experiment, root exudates, which may be a nutrient acquisition strategy, had positive effects on microbial decomposition and release of N after 11 years at 1.5 times ambient CO2 [Phillips et al., 2011].”
- Root exudates increase N availability by stimulating microbial turnover of fast-cycling N pools (2017, positive): “In the current study, we experimentally added root exudate solutions or extracellular enzymes to unfertilized and fertilized forest soil at the Duke Forest, NC, USA, as a means for better understanding how root-microbe interactions control N dynamics.”
- Paradigm shift in plant growth control. (2015, background): “In tree stands on undisturbed ground, greater effects will always be obtained in young, expanding, compared to more mature systems [29], which commonly end up with little if any growth stimulation [82,83 ,84] A pine plantation at the Duke FACE site, retained annual growth stimulation by elevated CO2”