ORCID Profile
0000-0002-4167-4672
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Publisher: Wiley
Date: 03-06-2021
Abstract: Elevated atmospheric carbon dioxide (eCO 2 ) can impact soil organic matter (SOM) dynamics by changing the rates of carbon (C) losses and gains. In the rhizosphere, these changes are usually assumed to be the result of root‐mediated eCO 2 impacts on saprotrophic microbes via altered below‐ground C allocation. This C allocation can also impact mycorrhizal fungi and their role in SOM dynamics. However, direct field quantifications of the influence of roots on both mycorrhizal fungi and saprotrophs together with SOM dynamics in forests exposed to eCO 2 are rare. This is especially true in phosphorus (P)‐limited systems, even though ecosystem responses to eCO 2 are known to depend on P availability. We assessed root mediation of eCO 2 impacts on saprotrophs, mycorrhizal fungi, and C dynamics of root litter and mineral soil C (SOM‐C) in a mature, P‐limited Eucalyptus woodland exposed to eCO 2 . We used a novel nested‐mesh‐bag method to manipulate roots access to the substrates in a 1‐year field incubation. We used an isotopic approach to trace C dynamics and performed a comprehensive microbial community analysis, along with nutrients and enzymatic activity measurements. Roots increased microbial biomass, fungal:bacterial ratio, plant‐derived C gains and substrate C losses while decreasing P availability and specific enzymatic activity. eCO 2 increased bacterial relative abundance in root litter and protozoa in SOM‐C, but it did not enhance root impacts or mycorrhizal fungi biomass. Our combination of in‐situ approaches allowed us to demonstrate that while roots have multiple impacts on soil microbial communities and C dynamics, they are not the main drivers of responses to eCO 2 in this P‐limited forest. Other factors beyond enhanced root‐derived below‐ground C inputs such as seasonality of nutrient and water availability, and shifts in plant communities may be more important in modulating eCO 2 impacts on soil dynamics in P‐limited systems. A free Plain Language Summary can be found within the Supporting Information of this article.
Publisher: Springer Science and Business Media LLC
Date: 10-09-2020
DOI: 10.1007/S10533-020-00699-Y
Abstract: It is uncertain how the predicted further rise of atmospheric carbon dioxide (CO 2 ) concentration will affect plant nutrient availability in the future through indirect effects on the gross rates of nitrogen (N) mineralization (production of ammonium) and depolymerization (production of free amino acids) in soil. The response of soil nutrient availability to increasing atmospheric CO 2 is particularly important for nutrient poor ecosystems. Within a FACE (Free-Air Carbon dioxide Enrichment) experiment in a native, nutrient poor Eucalyptus woodland (EucFACE) with low soil organic matter (≤ 3%), our results suggested there was no shortage of N. Despite this, microbial N use efficiency was high (c. 90%). The free amino acid (FAA) pool had a fast turnover time (4 h) compared to that of ammonium (NH 4 + ) which was 11 h. Both NH 4 -N and FAA-N were important N pools however, protein depolymerization rate was three times faster than gross N mineralization rates, indicating that organic N is directly important in the internal ecosystem N cycle. Hence, the depolymerization was the major provider of plant available N, while the gross N mineralization rate was the constraining factor for inorganic N. After two years of elevated CO 2 , no major effects on the pools and rates of the soil N cycle were found in spring (November) or at the end of summer (March). The limited response of N pools or N transformation rates to elevated CO 2 suggest that N availability was not the limiting factor behind the lack of plant growth response to elevated CO 2 , previously observed at the site.
Publisher: Cold Spring Harbor Laboratory
Date: 18-07-2021
DOI: 10.1101/2021.07.16.452715
Abstract: Enhanced soil organic matter (SOM) decomposition and organic phosphorus (P) cycling may help sustain plant productivity under elevated CO 2 (eCO 2 ) and P-limiting conditions. P-acquisition by arbuscular mycorrhizal (AM) fungi and their impacts on SOM decomposition may become even more relevant in these conditions. Yet, experimental evidence of the interactive effect of AM fungi and P availability influencing altered SOM cycling under eCO 2 is scarce and the mechanisms of this control are poorly understood. Here, we performed a pot experiment manipulating P availability, AM fungal presence and atmospheric CO 2 levels and assessed their impacts on soil C cycling and plant growth. Plants were grown in chambers with a continuous 13 C-input that allowed differentiation between plant- and SOM-derived fractions of respired CO 2 (R), dissolved organic C (DOC) and microbial biomass (MBC) as relevant C pools in the soil C cycle. We hypothesised that under low P availability, increases in SOM cycling may support sustained plant growth under eCO 2 and that AM fungi would intensify this effect. We found the impacts of CO 2 enrichment and P availability on soil C cycling were generally independent of each other with higher root biomass and slight increases in soil C cycling under eCO 2 occurring regardless of the P treatment. Contrary to our hypotheses, soil C cycling was enhanced with P addition suggesting that low P conditions were limiting soil C cycling. eCO 2 conditions increased the fraction of SOM-derived DOC pointing to increased SOM decomposition with eCO 2 . Finally, AM fungi increased microbial biomass under eCO 2 conditions and low-P without enhanced soil C cycling, probably due to competitive interactions with free-living microorganisms over nutrients. Our findings in this plant-soil system suggest that, contrary to what has been reported for N-limited systems, the impacts of eCO 2 and P availability on soil C cycling are independent of each other.
Publisher: Elsevier BV
Date: 04-2020
Publisher: Springer Science and Business Media LLC
Date: 07-06-2022
Publisher: Wiley
Date: 17-10-2022
DOI: 10.1111/GCB.16456
Abstract: Forest ecosystems are important global soil carbon (C) reservoirs, but their capacity to sequester C is susceptible to climate change factors that alter the quantity and quality of C inputs. To better understand forest soil C responses to altered C inputs, we integrated three molecular composition published data sets of soil organic matter (SOM) and soil microbial communities for mineral soils after 20 years of detrital input and removal treatments in two deciduous forests: Bousson Forest (BF), Harvard Forest (HF), and a coniferous forest: H.J. Andrews Forest (HJA). Soil C turnover times were estimated from radiocarbon measurements and compared with the molecular-level data (based on nuclear magnetic resonance and specific analysis of plant- and microbial-derived compounds) to better understand how ecosystem properties control soil C biogeochemistry and dynamics. Doubled aboveground litter additions did not increase soil C for any of the forests studied likely due to long-term soil priming. The degree of SOM decomposition was higher for bacteria-dominated sites with higher nitrogen (N) availability while lower for the N-poor coniferous forest. Litter exclusions significantly decreased soil C, increased SOM decomposition state, and led to the adaptation of the microbial communities to changes in available substrates. Finally, although aboveground litter determined soil C dynamics and its molecular composition in the coniferous forest (HJA), belowground litter appeared to be more influential in broadleaf deciduous forests (BH and HF). This synthesis demonstrates that inherent ecosystem properties regulate how soil C dynamics change with litter manipulations at the molecular-level. Across the forests studied, 20 years of litter additions did not enhance soil C content, whereas litter reductions negatively impacted soil C concentrations. These results indicate that soil C biogeochemistry at these temperate forests is highly sensitive to changes in litter deposition, which are a product of environmental change drivers.
Publisher: Informa UK Limited
Date: 26-04-2018
Location: Mexico
No related grants have been discovered for Laura Castañeda-Gómez.