Forest soils store large amounts of carbon (C) and nitrogen (N), yet how predicted shifts in forest composition will impact long‐term C and N persistence remains poorly understood. A recent hypothesis predicts that soils under trees associated with arbuscular mycorrhizas (
When aboveground materials are harvested for fuel production, such as with
- PAR ID:
- 10461696
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- GCB Bioenergy
- Volume:
- 11
- Issue:
- 8
- ISSN:
- 1757-1693
- Page Range / eLocation ID:
- p. 971-987
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract AM ) store less C than soils dominated by trees associated with ectomycorrhizas (ECM ), due to slower decomposition inECM ‐dominated forests. However, an incipient hypothesis predicts that systems with rapid decomposition—e.g. mostAM ‐dominated forests—enhance soil organic matter (SOM ) stabilization by accelerating the production of microbial residues. To address these contrasting predictions, we quantified soil C and N to 1 m depth across gradients ofECM ‐dominance in three temperate forests. By focusing on sites whereAM ‐ andECM ‐plants co‐occur, our analysis controls for climatic factors that covary with mycorrhizal dominance across broad scales. We found that whileECM stands contain moreSOM in topsoil,AM stands contain moreSOM when subsoil to 1 m depth is included. Biomarkers and soil fractionations reveal that these patterns are driven by an accumulation of microbial residues inAM ‐dominated soils. Collectively, our results support emerging theory onSOM formation, demonstrate the importance of subsurface soils in mediating plant effects on soil C and N, and indicate that shifts in the mycorrhizal composition of temperate forests may alter the stabilization ofSOM . -
Abstract Soils are an important source of
NO , particularly in dry lands because of trade‐offs that develop between biotic and abioticNO ‐producing processes when soils dry out. Understanding how drier climates may offset the balance of these trade‐offs as soils transition toward more arid states is, therefore, critical to estimating globalNO budgets, especially because drylands are expected to increase in size. We measuredNO emission pulses after wetting soils from similar lithologies along an altitudinal gradient in the Sierra Nevada,CA , where mean annual precipitation varied from 670 to 1500 mm. Along the gradient, we measured fieldNO emissions, and used chloroform in the laboratory to reduce microbial activity and partition between biotic and abioticNO ‐producing processes (i.e., chemodenitrification). FieldNO emission pulses were lowest in the acidic andSOM ‐rich soils (4–72 ngNO ‐N m−2s−1), but were highest in the high‐elevation barren site (~560 ngNO ‐N m−2s−1). In the laboratory,NO emission pulses were up to 19× greater in chloroform‐treated soils than in the controls, and these abiotic pulses increased with elevation aspH decreased (6.2–4.4) and soil organic matter (SOM ) increased (18–157 mg C g−1). Drought can shift the balance between the biotic and abiotic processes that produceNO , favoring chemodenitrification during periods when biological processes become stressed. Acidic andSOM ‐rich soils, which typically develop under mesic conditions, are most vulnerable to N loss viaNO as interactions betweenpH ,SOM , and drought stimulate chemodenitrification. -
Abstract Despite the large contribution of rangeland and pasture to global soil organic carbon (
SOC ) stocks, there is considerable uncertainty about the impact of large herbivore grazing onSOC , especially for understudied subtropical grazing lands. It is well known that root system inputs are the source of most grasslandSOC , but the impact of grazing on partitioning of carbon allocation to root tissue production compared to fine root exudation is unclear. Given that different forms of root C have differing implications forSOC synthesis and decomposition, this represents a significant gap in knowledge. Root exudates should contribute toSOC primarily after microbial assimilation, and thus promote microbial contributions toSOC based on stabilization of microbial necromass, whereas root litter deposition contributes directly as plant‐derivedSOC following microbial decomposition. Here, we used in situ isotope pulse‐chase methodology paired with plant and soil sampling to link plant carbon allocation patterns withSOC pools in replicated long‐term grazing exclosures in subtropical pasture in Florida,USA . We quantified allocation of carbon to root tissue and measured root exudation across grazed and ungrazed plots and quantified lignin phenols to assess the relative contribution of microbial vs. plant products to totalSOC . We found that grazing exclusion was associated with dramatically less overall belowground allocation, with lower root biomass, fine root exudates, and microbial biomass. Concurrently, grazed pasture contained greater totalSOC , and a larger fraction ofSOC that originated from plant tissue deposition, suggesting that higher root litter deposition under grazing promotes greaterSOC . We conclude that grazing effects onSOC depend on root system biomass, a pattern that may generalize to other C4‐dominated grasslands, especially in the subtropics. Improved understanding of ecological factors underlying root system biomass may be the key to forecastingSOC and optimizing grazing management to enhanceSOC accumulation. -
Abstract Temperature sensitivity of soil organic carbon (
SOC ) decomposition is one of the major uncertainties in predicting climate‐carbon (C) cycle feedback. Results from previous studies are highly contradictory with old soil C decomposition being more, similarly, or less sensitive to temperature than decomposition of young fractions. The contradictory results are partly from difficulties in distinguishing old from youngSOC and their changes over time in the experiments with or without isotopic techniques. In this study, we have conducted a long‐term field incubation experiment with deep soil collars (0–70 cm in depth, 10 cm in diameter ofPVC tubes) for excluding root C input to examine apparent temperature sensitivity ofSOC decomposition under ambient and warming treatments from 2002 to 2008. The data from the experiment were infused into a multi‐pool soil C model to estimate intrinsic temperature sensitivity ofSOC decomposition and C residence times of threeSOC fractions (i.e., active, slow, and passive) using a data assimilation (DA ) technique. As activeSOC with the short C residence time was progressively depleted in the deep soil collars under both ambient and warming treatments, the residences times of the wholeSOC became longer over time. Concomitantly, the estimated apparent and intrinsic temperature sensitivity ofSOC decomposition also became gradually higher over time as more than 50% of activeSOC was depleted. Thus, the temperature sensitivity of soil C decomposition in deep soil collars was positively correlated with the mean C residence times. However, the regression slope of the temperature sensitivity against the residence time was lower under the warming treatment than under ambient temperature, indicating that other processes also regulated temperature sensitivity ofSOC decomposition. These results indicate that oldSOC decomposition is more sensitive to temperature than young components, making the old C more vulnerable to future warmer climate. -
Summary Roots provide essential uptake of water and nutrients from the soil, as well as anchorage and stability for the whole plant. Root orientation, or angle, is an important component of the overall architecture and depth of the root system; however, little is known about the genetic control of this trait. Recent reports in
Oryza sativa (rice) identified a role for (DEEPER ROOTING 1 ) in influencing the orientation of the root system, leading to positive changes in grain yields under water‐limited conditions. Here we found thatDRO 1 andDRO 1 ‐related genes are present across diverse plant phyla, and fall within theDRO 1IGT gene family. TheIGT family also includes andTAC 1 , which are known to affect the orientation of lateral shoots. Consistent with a potential role in root development,LAZY 1 homologs in Arabidopsis and peach showed root‐specific expression. Promoter–reporter constructs revealed thatDRO 1At is predominantly expressed in both the root vasculature and root tips, in a distinct developmental pattern. Mutation ofDRO 1At led to more horizontal lateral root angles. Overexpression ofDRO 1At under a constitutive promoter resulted in steeper lateral root angles, as well as shoot phenotypes including upward leaf curling, shortened siliques and narrow lateral branch angles. A conserved C‐terminalDRO 1EAR ‐like motif found inIGT genes was required for these ectopic phenotypes. Overexpression ofPpe inDRO 1Prunus domestica (plum) led to deeper‐rooting phenotypes. Collectively, these data indicate a potential application for ‐related genes to alter root architecture for drought avoidance and improved resource use.DRO 1