Experimental Evaluation of Several Key Factors Affecting Root Biomass Estimation by 1500 MHz Ground-Penetrating Radar

Accurate quantification of coarse roots without disturbance represents a gap in our understanding of belowground ecology. Ground penetrating radar (GPR) has shown significant promise for coarse root detection and measurement, however root orientation relative to scanning transect direction, the difficulty identifying dead root mass, and the effects of root shadowing are all key factors affecting biomass estimation that require additional research. Specifically, many aspects of GPR applicability for coarse root measurement have not been tested with a full range of antenna frequencies. We tested the effects of multiple scanning directions, root crossover, and root versus soil moisture content in a sand-hill mixed oak community using a 1500 MHz antenna, which provides higher resolution than the oft used 900 MHz antenna. Combining four scanning directions produced a significant relationship between GPR signal reflectance and coarse root biomass (R2 = 0.75) (p \u3c 0.01) and reduced variability encountered when fewer scanning directions were used. Additionally, significantly fewer roots were correctly identified when their moisture content was allowed to equalize with the surrounding soil (p \u3c 0.01), providing evidence to support assertions that GPR cannot reliably identify dead root mass. The 1500 MHz antenna was able to identify roots in close proximity of each other as well as roots shadowed beneath shallower roots, providing higher precision than a 900 MHz antenna. As expected, using a 1500 MHz antenna eliminates some of the deficiency in precision observed in studies that utilized lower frequency antennas

Measuring soil frost depth in forest ecosystems with ground penetrating radar

Soil frost depth in forest ecosystems can be variable and depends largely on early winter air temperaturesand the amount and timing of snowfall. A thorough evaluation of ecological responses to seasonallyfrozen ground is hampered by our inability to adequately characterize the frequency, depth, durationand intensity of soil frost events. We evaluated the use of ground penetrating radar to nondestructivelydelineate soil frost under field conditions in three forest ecosystems. Soil frost depth was monitoredperiodically using a 900 MHz antenna in South Burlington, Vermont (SB), Sleepers River Watershed,North Danville, Vermont (SR) and Hubbard Brook Experimental Forest, New Hampshire (HBEF) duringwinter 2011–2012 on plots with snow and cleared of snow. GPR-based estimates were compared to datafrom thermistors and frost tubes, which estimate soil frost depth with a color indicating solution. In theabsence of snow, frost was initially detected at a depth of 8–10 cm. Dry snow up to 35 cm deep, enhancednear-surface frost detection, raising the minimum frost detection depth to 4–5 cm. The most favorablesurface conditions for GPR detection were bare soil or shallow dry snow where frost had penetrated to theminimum detectable depth. Unfavorable conditions included: standing water on frozen soil, wet snow,thawed surface soils and deep snow pack. Both SB and SR were suitable for frost detection most of thewinter, while HBEF was not. Tree roots were detected as point reflections and were readily discriminatedfrom continuous frost reflections. The bias of GPR frost depth measurements relative to thermistors wassite dependent averaging 0.1 cm at SB and 1.1 cm at SR, and was not significantly different than zero. Whenseparated by snow manipulation treatment at SR, overestimation of soil frost depth (5.5 cm) occurredon plots cleared of snow and underestimation (−1.5 cm) occurred on plots with snow. Despite somelimitations posed by site and surface suitability, GPR could be useful for adding a spatial component topre-installed soil frost monitoring networks

Biophysical controls on soil respiration in the dominant patch types of an old-growth, mixed-conifer forest

Little is known about biophysical controls on soil respiration in California’s Sierra Nevada oldgrowth, mixed-conifer forests. Using portable and automated soil respiration sampling units, we measured soil respiration rate (SRR) in three dominant patch types: closed canopy (CC), ceanothus-dominated patches (CECO), and open canopy (OC). SRR varied significantly among the patch types, ranging from 2.0 to 4.5 �μmol m�⁻² s�⁻¹ and from 0.9 to 2.9 �μmol m�⁻² s�⁻¹ during the 1999 and 2000 measuring periods, respectively, with the maximum in CECO and the minimum in OC. Multiple peaks of seasonal SRR were functions of soil temperature and moisture dynamics. The relationship between SRR and soil temperature switched from a positive to a negative correlation when soil moisture dropped from saturation to drought. Time lag, as a function of soil moisture, was included in an exponential model to assess the effects of soil moisture on SRR in this seasonal water-stressed ecosystem. The total soil C flux summed by an area-weighted average across all three patch types was 660 �± 163 g C m�⁻² from May to Oct. 2000. These results may be applicable to other water-stressed forests in the Mediterranean climate zone, and have implications for the conservation of soil carbon.Key Words: Soil CO₂ efflux, soil temperature, soil moisture, Sierra Nevada, California

Soil carbon sequestration and changes in fungal and bacterial biomass following incorporation of forest residues.

Sequestering carbon (C) in forest soils can benefit site fertility and help offset greenhouse gas emissions. However, identifying soil conditions and forest management practices which best promote C accumulation remains a challenging task. We tested whether soil incorporation of masticated woody residues alters short-term C storage at forested sites in western and southeastern USA. Our hypothesis was that woody residues would preferentially stimulate soil fungal biomass, resulting in improved C use efficiency and greater soil C storage. Harvest slash at loblolly pine sites in South Carolina was masticated (chipped) and either (1) retained on the soil surface, (2) tilled to a soil depth of 40 cm, or (3) tilled using at least twice the mass of organics. At comparative sites in California, live woody fuels in ponderosa pine stands were (1) masticated and surface applied, (2) masticated and tilled, or (3) left untreated. Sites with clayey and sandy soils were compared in each region, with residue additions ranging from 20 to 207 Mg ha_1. Total and active fungal biomass were not strongly affected by residue incorporation despite the high input of organics. Limited response was also found for total and active bacterial biomass. As a consequence, fungal:bacterial (F:B) biomass ratios were similar among treatments at each site. Total soil C was elevated at one California site following residue incorporation, yet was significantly lower compared to surface-applied residues at both loblolly pine sites, presumably due to the oxidative effects of tilling on soil organic matter. The findings demonstrated an inconsequential effect of residue incorporation on fungal and bacterial biomass and suggest a limited potential of such practices to enhance long-term soil C storage in these forests

Asbestos Burden Predicts Survival in Pleural Mesothelioma

Background: Malignant pleural mesothelioma (MPM) is a rapidly fatal asbestos-associated malignancy with a median survival time of &lt; 1 year following diagnosis. Treatment strategy is determined in part using known prognostic factors. Objective: The aim of this study was to examine the relationship between asbestos exposure and survival outcome in MPM in an effort to advance the understanding of the contribution of asbestos exposure to MPM prognosis. Methods: We studied incident cases of MPM patients enrolled through the International Mesothelioma Program at Brigham and Women’s Hospital in Boston, Massachusetts, using survival follow-up, self-reported asbestos exposure (n = 128), and a subset of cases (n = 80) with quantitative asbestos fiber burden measures. Results: Consistent with the established literature, we found independent, significant associations between male sex and reduced survival (p 1,099), suggested a survival duration association among these groups (p = 0.06). After adjusting for covariates in a Cox model, we found that patients with a low asbestos burden had a 3-fold elevated risk of death compared to patients with a moderate fiber burden [95% confidence interval (CI), 0.95–9.5; p = 0.06], and patients with a high asbestos burden had a 4.8-fold elevated risk of death (95% CI, 1.5–15.0; p < 0.01) versus those with moderate exposure. Conclusion: Our data suggest that patient survival is associated with asbestos fiber burden in MPM and is perhaps modified by susceptibility

The Effects of 11 Yr of CO2 Enrichment on Roots in a Florida Scrub-Oak Ecosystem

Uncertainty surrounds belowground plant responses to rising atmospheric CO2 because roots are difficult to measure, requiring frequent monitoring as a result of fine root dynamics and long-term monitoring as a result of sensitivity to resource availability. We report belowground plant responses of a scrub-oak ecosystem in Florida exposed to 11yr of elevated atmospheric CO2 using open-top chambers. We measured fine root production, turnover and biomass using minirhizotrons, coarse root biomass using ground-penetrating radar and total root biomass using soil cores. Total root biomass was greater in elevated than in ambient plots, and the absolute difference was larger than the difference aboveground. Fine root biomass fluctuated by more than a factor of two, with no unidirectional temporal trend, whereas leaf biomass accumulated monotonically. Strong increases in fine root biomass with elevated CO2 occurred after fire and hurricane disturbance. Leaf biomass also exhibited stronger responses following hurricanes. Responses after fire and hurricanes suggest that disturbance promotes the growth responses of plants to elevated CO2. Increased resource availability associated with disturbance (nutrients, water, space) may facilitate greater responses of roots to elevated CO2. The disappearance of responses in fine roots suggests limits on the capacity of root systems to respond to CO2 enrichment

Surface-based GPR underestimates below-stump root biomass

Aims: While lateral root mass is readily detectable with ground penetrating radar (GPR), the roots beneath a tree (below-stump) and overlapping lateral roots near large trees are problematic for surface-based antennas operated in reflection mode. We sought to determine if tree size (DBH) effects GPR root detection proximal to longleaf pine (Pinus palustris Mill) and if corrections for could be applied to stand-level estimates of root mass. Methods: GPR (1500 MHz) was used to estimate coarse root mass proximal to 33 longleaf pine trees and compared to the amount of biomass excavated from pits proportional in area to tree basal diameter. Lateral roots were excavated to a depth of 1 m and taproots were excavated in their entirety. Results: GPR underestimated longleaf pine below-stump mass and the magnitude of the underestimation increased with tree DBH. Non-linear regressions between GPR estimated root mass/excavated root mass and tree diameter at breast height (DBH) were highly significant for both below-stump (lateral + taproot) root mass (p < 0.0001, R² 0.77) and lateral coarse root mass (p < 0.0001, R² 0.65). Conclusions: GPR underestimates root mass proximal to trees, and this needs to be accounted for to accurately estimate stand-level belowground biomass.Keywords: GPR, Longleaf pine, Root mass, Lateral root, Below-stump, Pinus palustris, taprootThis is the publisher’s final pdf. The article is copyrighted by Springer and published for the Royal Netherlands Society of Agricultural Science. It can be found at: http://link.springer.com/journal/1110

ORIGINAL PAPER

Phenotypic analysis of first-year traits in a pseudo-backcross {(slash x loblolly) x slash} and the open-pollinated families of the pure-species progenitor