Root Ingrowth Bags Research Articles

Mycorrhizal roots slow the decay of belowground litters in a temperate hardwood forest.

There is increasing evidence that plant roots and mycorrhizal fungi, whether living or dead, play a central role in soil carbon (C) cycling. Root-mycorrhizal-microbial interactions can both suppress and enhance litter decay, with the net result dependent upon belowground nutrient acquisition strategies and soil nutrient availability. We measured the net effect of living roots and mycorrhizal fungi on the decay of dead roots and fungal hyphae in a hardwood forest dominated by either sugar maple (Acer saccharum) or white oak (Quercus alba) trees. Root and fungal litter were allowed to decompose within root-ingrowth bags and root-exclusion cores. In conjunction with root effects on decay, we assessed foraging responses and root induced changes in soil moisture, nitrogen (N) availability and enzyme activity. After 1 year, maple root production increased, and mycorrhizal fungal colonization decreased in the presence of decaying litter. In addition, we found that actively foraging roots suppressed the decay of root litter (-14%) more than fungal litter (-3%), and suppression of root decay was stronger for oak (-20%) than maple roots (-8%). Suppressive effects of oak roots on decay were greatest when roots also reduced soil N availability, which corresponded with reductions in hydrolytic enzyme activity and enhanced oxidative enzyme activities. These findings further our understanding of context-dependent drivers of root-mycorrhizal-microbial interactions and demonstrate that such interactions can play an underappreciated role in soil organic matter accumulation and turnover in temperate forests.

Organic carbon fractions in temperate mangrove and saltmarsh soils

Coastal wetlands, such as mangrove and saltmarsh environments, can store significant amounts of soil organic carbon (SOC); however, most studies focus on tropical and subtropical environments. We assessed SOC stocks and fractions in temperate mangrove (two sites) and saltmarsh (sites SM1, SM2 and SM3) environments in southern Australia. The SOC fractions were separated according to particulate organic carbon (POC), humic carbon (HC) and recalcitrant carbon (RC) by size fractionation. Saltmarsh sites generally had the highest SOC content (up to 12.4% SOC). The POC fraction was the highest at the surface in the saltmarsh site and decreased relative to the HC and RC fractions with depth. Conversely, the proportion of POC at the mangrove sites did not decrease with depth, forming up to 76% of the SOC. The vertical displacement of soil of up to 5.8 mm year–1 at the saltmarsh sites, measured using root ingrowth bags, suggest significant contributions of POC via root materials. Retention of these POC inputs are likely to be related to waterlogging, which decreases decomposition rates – with much lower soil moisture content at SM1, where the lowest POC content occurred below the surface, compared with SM2 and SM3.

Mangrove Damage, Delayed Mortality, and Early Recovery Following Hurricane Irma at Two Landfall Sites in Southwest Florida, USA

Mangrove forests along the coastlines of the tropical and sub-tropical western Atlantic are intermittently impacted by hurricanes and can be damaged by high-speed winds, high-energy storm surges, and storm surge sediment deposits that suffocate tree roots. This study quantified trends in damage, delayed mortality, and early signs of below- and aboveground recovery in mangrove forests in the Lower Florida Keys and Ten Thousand Islands following direct hits by Hurricane Irma in September 2017. Mangrove trees suffered 19% mortality at sites in the Lower Florida Keys and 11% in the Ten Thousand Islands 2–3 months post-storm; 9 months post-storm, mortality in these locations increased to 36% and 20%, respectively. Delayed mortality of mangrove trees was associated with the presence of a carbonate mud storm surge deposit on the forest floor. Mortality and severe branch damage were more common for mangrove trees than for mangrove saplings. Canopy coverage increased from 40% cover 1–2 months post-storm to 60% cover 3–6 months post-storm. Canopy coverage remained the same 9 months post-storm, providing light to an understory of predominantly Rhizophora mangle (red mangrove) seedlings. Soil shear strength was higher in the Lower Florida Keys and varied with depth; no significant trends were found in shear strength between fringe or basin plots. Rates of root growth, as assessed using root in-growth bags, were relatively low at 0.01–11.0 g m−2 month−1 and were higher in the Ten Thousand Islands. This study demonstrated that significant delayed mangrove mortality can occur 3–9 months after a hurricane has passed, with some mortality attributable to smothering by storm surge deposits.

The effect of heterogeneous soil bulk density on root growth of field-grown mangrove species

Mangroves harbour large organic carbon (C) reservoirs in their soils that are important in the global C cycle. The below-ground biomass of mangrove trees is a major contributor to these organic C stocks. Root system development tends to be highly plastic in response to environmental conditions such as soil bulk density (BD). Hence, this study aimed to assess the role of soil BD on mangrove root growth. Root in-growth bags filled with root-free soil ranging in BD from 0.2 to 1.2 g cm−3 were buried in the soil of three mangrove species. Root image analysis indicated that BD had a significant positive effect on root length and root biomass suggesting trees increase biomass allocation to roots and enhance root elongation, possibly to increase the acquisition of water and nutrients in dense soils. However, the responses to variation in BD were species-specific which was attributed to differences in species growth rates and the background soil conditions. Soil BD affects mangrove root growth with dense patches likely to have increased root growth and organic C sequestration potential compared to less dense soil patches.

Consequences of mixing Acacia mangium and Eucalyptus grandis trees on soil exploration by fine-roots down to a depth of 17 m

Fine-root functioning is a major driver of plant growth and strongly influences the global carbon cycle. While fine-root over-yielding has been shown in the upper soil layers of mixed-species forests relative to monospecific stands, the consequences of tree diversity on fine-root growth in very deep soil layers is still unknown. Our study aimed to assess the consequences of mixing Acacia mangium and Eucalyptus grandis trees on soil exploration by roots down to the water table at 17 m depth in a tropical planted forest. Fine roots (diameter < 2 mm) were sampled in a randomized block design with three treatments: monospecific stands of Acacia mangium (100A), Eucalyptus grandis (100E), and mixed stands with 50% of each species (50A50E). Root ingrowth bags were installed at 4 depths (from 0.1 m to 6 m) in the three treatments within three different blocks, to study the fine-root production over 2 periods of 3 months. Down to 17 m depth, total fine-root biomass was 1127 g m−2 in 50A50E, 780 g m−2 in 100A and 714 g m−2 in 100E. Specific root length and specific root area were 110–150% higher in 50A50E than in 100A for Acacia mangium trees and 34% higher in 50A50E than in 100E for Eucalyptus grandis trees. Ingrowth bags showed that the capacity of fine roots to explore soil patches did not decrease down to a depth of 6 m for the two species. Belowground interactions between Acacia mangium and Eucalyptus grandis trees greatly increased the exploration of very deep soil layers by fine roots, which is likely to enhance the uptake of soil resources. Mixing tree species might therefore increase the resilience of tropical planted forests through a better exploration of deep soils.

Fine root productivity varies along nitrogen and phosphorus gradients in high-rainfall mangrove forests of Micronesia

Belowground biomass is thought to account for much of the total biomass in mangrove forests and may be related to soil fertility. The Yela River and the Sapwalap River, Federated States of Micronesia, contain a natural soil resource gradient defined by total phosphorus (P) density ranging from 0.05 to 0.42 mg cm−3 in different hydrogeomorphic settings. We used this fertility gradient to test the hypothesis that edaphic conditions constrain mangrove productivity through differential allocation of biomass to belowground roots. We removed sequential cores and implanted root ingrowth bags to measure in situ biomass and productivity, respectively. Belowground root biomass values ranged among sites from 0.448 ± 0.096 to 2.641 ± 0.534 kg m−2. Root productivity (roots ≤20 mm) did not vary significantly along the gradient (P = 0.3355) or with P fertilization after 6 months (P = 0.2968). Fine root productivity (roots ≤2 mm), however, did vary significantly among sites (P = 0.0363) and ranged from 45.88 ± 21.37 to 118.66 ± 38.05 g m−2 year−1. The distribution of total standing root biomass and fine root productivity followed patterns of N:P ratios as hypothesized, with larger root mass generally associated with lower relative P concentrations. Many of the processes of nutrient acquisition reported from nutrient-limited mangrove forests may also occur in forests of greater biomass and productivity when growing along soil nutrient gradients.

Dynamics of phreatophyte root growth relative to a seasonally fluctuating water table in a Mediterranean-type environment

While seasonal redistribution of fine root biomass in response to fluctuations in groundwater level is often inferred in phreatophytic plants, few studies have observed the in situ growth dynamics of deep roots relative to those near the surface. We investigated the root growth dynamics of two Banksia species accessing a seasonally dynamic water table and hypothesized that root growth phenology varied with depth, i.e. root growth closest to the water table would be influenced by water table dynamics rather than surface micro-climate. Root in-growth bags were used to observe the dynamics of root growth at different soil depths and above-ground growth was also assessed to identify whole-plant growth phenology. Root growth at shallow depths was found to be in synchrony with above-ground growth phenophases, following increases in ambient temperature and soil water content. In contrast, root growth at depth was either constant or suppressed by saturation. Root growth above the water table and within the capillary fringe occurred in all seasons, corresponding with consistent water availability and aerobic conditions. However, at the water table, a seasonal cycle of root elongation with drawdown in summer followed by trimming in response to water table rise and saturation in winter, was observed. The ability to grow roots year-round at the capillary fringe and redistribute fine root biomass in response to groundwater drawdown is considered critical in allowing phreatophytes, in seasonally water-limited environments, to maintain access to groundwater throughout the year.

Impact of primary and secondary machinery tracks on fine root growth of sugar maple after selection cutting

Selection cutting, where approximately 30% of the trees are removed every 30 years, is the main silvicultural treatment used in temperate deciduous forests of Quebec (Canada). Concerns have been raised that the use of heavy machinery is creating soil disturbances that are negatively affecting the growth and survival of remaining trees. The aim of the study was to determine if heavy machinery is affecting the growth, morphology, and architecture of sugar maple (Acer saccharum Marsh.) fine roots in and around machinery tracks left after selection logging. The study site, a sugar maple dominated stand, was located in southern Quebec. Root ingrowth bags and standard root cores were used to compare fine root growth, morphology, and architecture in and around machinery tracks one year after logging. Fine root growth of maple was reduced fivefold in both primary (multiple trip) and secondary (only one trip) machinery tracks compared with the control. There was a nonstatistical reduction in fine root growth within 1 m of the tracks. Because machinery tracks cover between 15% and 25% of a stand after selection logging, such reduction in fine root growth could be significant for the growth and survival of the remaining mature maple trees.

EFFECTS OF MOBILE TREE ISLANDS ON ALPINE TUNDRA SOILS

Tree islands or krummholz found above tree line in the Front Range of Colorado are of interest because of their ability to migrate across the tundra landscape. This unique characteristic is caused by dieback of exposed, windward plant tissues, growth of the plant to the leeward, and the ability of these plants to produce new roots from branches buried in organic debris. This mobility also allows for the study of tree-induced changes on properties of soils initially formed by tundra vegetation. Soil characteristics, root productivity, decomposition of litter, and nitrogen flux in soils beneath mobile tree islands and adjacent alpine meadow tundra were studied to test whether tree islands modify the physical and chemical properties of soils formed in alpine tundra. Rates of surface decomposition of a standardized litter substrate were significantly increased leeward of tree islands and significantly decreased within these islands. Soil pH was not significantly reduced by tree island passage. We found significant reductions in amounts of soil organic matter (SOM) and KCl-extractable NH4+ in soils influenced by tree islands. No recovery in soil organic matter or NH4+ was observed at locations that correspond to 250-500 yr since the passage of a tree island. Cation exchange capacity was correlated with percentage SOM but was not reduced by tree island passage. Soil texture differences, when present, did not support the hypothesis that surface soils lose clay content with tree island passage but were consistent with a reduction in the depth of the A horizon of these locations. The soil carbon isotopic signature (6'3C) is only temporarily influenced by the passage of tree islands, suggesting that tree carbon is not stabilized in soils. Moreover while trees have numerous roots within the 0 horizon of soil, root ingrowth bags demonstrated large reductions in fine root production in the A horizons beneath trees (149 g.m-2-yr-' in tundra vs. 25 g.m-2 yr-1 beneath trees). Resin bag nitrogen collections indicated that soils beneath trees had higher NH4+ losses than adjacent tundra soils. Tree island passage therefore reduced SOM and the nitrogen storage potential of former tundra soils, and these effects likely persist for centuries following the passage of a tree island.

Effects of Mobile Tree Islands on Alpine Tundra Soils

Tree islands or krummholz found above tree line in the Front Range of Colorado are of interest because of their ability to migrate across the tundra landscape. This unique characteristic is caused by dieback of exposed, windward plant tissues, growth of the plant to the leeward, and the ability of these plants to produce new roots from branches buried in organic debris. This mobility also allows for the study of tree-induced changes on properties of soils initially formed by tundra vegetation. Soil characteristics, root productivity, decomposition of litter, and nitrogen flux in soils beneath mobile tree islands and adjacent alpine meadow tundra were studied to test whether tree islands modify the physical and chemical properties of soils formed in alpine tundra. Rates of surface decomposition of a standardized litter substrate were significantly increased leeward of tree islands and significantly decreased within these islands. Soil pH was not significantly reduced by tree island passage. We found significant reductions in amounts of soil organic matter (SOM) and KCl-extractable NH4+ in soils influenced by tree islands. No recovery in soil organic matter or NH4+ was observed at locations that correspond to 250–500 yr since the passage of a tree island. Cation exchange capacity was correlated with percentage SOM but was not reduced by tree island passage. Soil texture differences, when present, did not support the hypothesis that surface soils lose clay content with tree island passage but were consistent with a reduction in the depth of the A horizon of these locations. The soil carbon isotopic signature (δ13C) is only temporarily influenced by the passage of tree islands, suggesting that tree carbon is not stabilized in soils. Moreover while trees have numerous roots within the O horizon of soil, root ingrowth bags demonstrated large reductions in fine root production in the A horizons beneath trees (149 g·m−2·yr−1 in tundra vs. 25 g·m−2·yr−1 beneath trees). Resin bag nitrogen collections indicated that soils beneath trees had higher NH4+ losses than adjacent tundra soils. Tree island passage therefore reduced SOM and the nitrogen storage potential of former tundra soils, and these effects likely persist for centuries following the passage of a tree island.

Biomass production and species composition change in a tallgrass prairie ecosystem after long‐term exposure to elevated atmospheric CO2

AbstractTo determine the long‐term impact of elevated CO2 on primary production of native tallgrass prairie, we compared the responses of tallgrass prairie at ambient and twice‐ambient atmospheric CO2 levels over an 8‐year period. Plots in open‐top chambers (4.5 m diameter) were exposed continuously (24 h) to ambient and elevated CO2 from early April to late October each year. Unchambered plots were monitored also. Above‐ground peak biomass was determined by clipping each year in early August, and root growth was estimated by harvesting roots from root ingrowth bags. Plant community composition was censused each year in early June. In the last 2 years of the study, subplots were clipped on 1 June or 1 July, and regrowth was harvested on 1 October. Volumetric soil water content of the 0–100 cm soil layer was determined using neutron scattering, and was generally higher in elevated CO2 plots than ambient. Peak above‐ground biomass was greater on elevated CO2 plots than ambient CO2 plots with or without chambers during years with significant plant water stress. Above‐ground regrowth biomass was greater under elevated CO2 than under ambient CO2 in a year with late‐season water stress, but did not differ in a wetter year. Root ingrowth biomass was also greater in elevated CO2 plots than ambient CO2 plots when water stress occurred during the growing season. The basal cover and relative amount of warm‐season perennial grasses (C4) in the stand changed little during the 8‐year period, but basal cover and relative amount of cool‐season perennial grasses (C3) in the stand declined in the elevated CO2 plots and in ambient CO2 plots with chambers. Forbs (C3) and members of the Cyperaceae (C3) increased in basal cover and relative amount in the stand at elevated compared to ambient CO2. Greater biomass production under elevated CO2 in C4‐dominated grasslands may lead to a greater carbon sequestration by those ecosystems and reduce peak atmospheric CO2 concentrations in the future.

The effects of elevated CO2concentrations on the root growth of Lolium perenne and Trifolium repens grown in a FACE* system

AbstractLolium perenneandTrifolium repenswere grown in a Free Air CO2Enrichment (FACE) system at elevated (600 μimol mol‐1) and ambient (340 μmol mol‐1) carbon dioxide concentrations during a whole growing season. Using a root ingrowth bag technique the extent to which CO2enrichment influenced the growth ofL, perenneandT. repensroots under two contrasting nutrient regimes was examined. Root ingrowth bags were inserted for a fixed time into the soil in order to trap roots. It was also possible to follow the mortality of roots in bags inserted for different time intervals. Root ingrowth of bothL. perenneandT. repensincreased under elevated CO2conditions. InL. perenne, root ingrowth decreased with increasing nutrient fertilizer level, but forT. repensthe root ingrowth was not affected by the nutrient application rate. Besides biomass measurements, root length estimates were made forT, repens.These showed an increase under elevated CO2concentrations. Root decomposition appeared to decrease under elevated CO2concentrations. A possible explanation for this effect is the observed changes in tissue composition, such as the increase in the carbon: nitrogen ratio in roots ofL. perenneat elevated CO2concentrations.

Biomass Production in a Tallgrass Prairie Ecosystem Exposed to Ambient and Elevated CO"2.

Responses to elevated CO"2 have not been measured for natural grassland ecosystems. Global carbon budgets will likely be affected by changes in biomass production and allocation in the major terrestrial ecosystems. Whether ecosystems sequester or release excess carbon to the atmosphere will partly determine the extent and rate that atmospheric CO"2 concentration rises. Elevated CO"2 also may change plant community species composition and water status. We determined above- and belowground biomass production, plant community species composition, and measured and modeled water status of a tallgrass prairie ecosystem in Kansas exposed to ambient and twice-ambient CO"2 concentrations in open-top chambers during the entire growing season from 1989 through 1991. Dominant species were Andropogon gerardii, A. scoparius, and Sorghastrum nutans (C"4 metabolism) and Poa pratensis (C"3). Aboveground biomass and leaf area were estimated by periodic sampling throughout the growing season in 1989 and 1990. In 1991, peak biomass and leaf area were estimated by an early August harvest. Relative root production among treatments was estimated using root ingrowth bags which remained in place throughout the growing season. Latent heat flux was simulated with and without water stress. Botanical composition was estimated annually. Compared to ambient CO"2 levels, elevated CO"2 increased production of C"4 grass species, but not of C"3 grass species. composition of C"4 grasses did not change, but Poa pratensis (C"3) declined, and C"3 forbs increased in the stand with elevated CO"2 compared to ambient. Open-top chambers appeared to reduce latent heat flux and increase water-use efficiency similar to the elevated CO"2 treatment when water stress was not severe, but under severe water stress, the chamber effect on water-use efficiency was limited. In natural ecosystems with periodic moisture stress, increased water-use efficiency under elevated CO"2 apparently would have a greater impact on productivity irrespective of photosynthetic pathway.

Nitrogen and phosphorus dynamics of a tallgrass prairie ecosystem exposed to elevated carbon dioxide

ABSTRACTA tallgrass prairie ecosystem was exposed to ambient and twice‐ambient CO2 concentrations in open‐top chambers and compared to unchambered ambient CO2 during the entire growing season from 1989 through 1991. Dominant species were Andropogon gerardii (C4), A. scoparius (C4), Sorghastrum nutans (C4) and Poa pratensis (C3). Nitrogen and phosphorus concentrations in A. gerardii, P. pratensis and dicotyledonous herbs above ground biomass were estimated by periodic sampling throughout the growing season in 1989 and 1990. In 1991, N and P concentrations in peak biomass were estimated by an early August harvest. N and P concentrations in root production as a function of treatment were estimated using root ingrowth bags that remained in place throughout the growing season. Total N and P in above‐ and belowground biomass were calculated as products of concentration and peak biomass by species groups. N concentration in A. gerardii and dicotyledonous herb aboveground biomass was lower and total N higher in elevated CO2 plots than in ambient CO2 plots. N concentration in P. pratensis aboveground biomass was lower in elevated CO2 plots than in ambient, but total N did not differ among treatments in 2 out of 3 years. In 1990, N concentration in root ingrowth bag biomass was lower and total N greater in elevated CO2 than in ambient CO2 plots. Root ingrowth bag biomass N concentration did not differ among treatments in 1991, but total N was greater in elevated CO2 plots than in ambient CO2 plots. P concentration was lower under elevated CO2 compared to ambient in 1989, but did not differ substantially among treatments in 1990 or 1991. In all years, total P in aboveground A. gerardii and root ingrowth bag biomass was greater under elevated CO2 than ambient. P concentration and total P in P. pratensis was similar among treatments.

Seasonal Pattern of Fine Root Proliferation in a Tropical Dry Forest

The growth of fine roots (≤ 2 mm diameter) in a tropical dry forest on recent dune sand has been monitored for 2 years during the dry season-wet season transition, using root-ingrowth bags buried for short time intervals. In both years, most root growth was concentrated in one brief period after the beginning of rains, and it is estimated that the fine root system of the forest can be fully re-deployed before the start of water percolation through the soil. In an accompanying field experiment, root-ingrowth bags were protected from rainfall and treated with distilled water or simulated throughfall solution (...)