Soil Root Biomass Research Articles

The importance of soil and vegetation characteristics for establishing ground-nesting bee aggregations

Most bee species are ground-nesters, yet knowledge on the nesting behaviour of this diverse group remains sparse. Evidence on the effectiveness of ground-nesting bee species as crop pollinators is growing, but there is limited information on their nesting habits and preferences and how to manage habitats to enhance populations on farms. In this study, artificially prepared plots of bare soil were constructed with the aim to attract ground-nesting bees to nest in a commercial orchard in Kent, UK. Nine soil parameters were measured to determine their preferred soil properties: hydraulic conductivity, soil compaction, soil moisture, soil temperature, soil stoniness, soil organic matter, soil root biomass, soil texture and vegetation cover. Eighteen non-parasitic ground-nesting bee species (7 Andrena, 9 Lasioglossum, 1 Halictus and 1 Colletes spp.) were recorded in the study plots. Soil stoniness and soil temperature at 10cm depth were positively correlated, and vegetation cover and hydraulic conductivity were negatively correlated with the number of ground-nesting bees on the plots. We show that artificially created habitats can be exploited for nesting by several ground-nesting bee species. This study’s findings can inform management practices to enhance ground-nesting bee populations in agricultural and urban areas.

Increased precipitation enhances soil respiration in a semi-arid grassland on the Loess Plateau, China.

BackgroundPrecipitation influences the vulnerability of grassland ecosystems, especially upland grasslands, and soil respiration is critical for carbon cycling in arid grassland ecosystems which typically experience more droughty conditions.MethodsWe used three precipitation treatments to understand the effect of precipitation on soil respiration of a typical arid steppe in the Loess Plateau in north-western China. Precipitation was captured and relocated to simulate precipitation rates of 50%, 100%, and 150% of ambient precipitation.Results and DiscussionSoil moisture was influenced by all precipitation treatments. Shoot biomass was greater, though non-significantly, as precipitation increased. However, both increase and decrease of precipitation significantly reduced root biomass. There was a positive linear relationship between soil moisture and soil respiration in the study area during the summer (July and August), when most precipitation fell. Soil moisture, soil root biomass, pH, and fungal diversity were predictors of soil respiration based on partial least squares regression, and soil moisture was the best of these.ConclusionOur study highlights the importance of increased precipitation on soil respiration in drylands. Precipitation changes can cause significant alterations in soil properties, microbial fungi, and root biomass, and any surplus or transpired moisture is fed back into the climate, thereby affecting the rate of soil respiration in the future.

Drought in acid soil increases aluminum toxicity especially of the Al-sensitive wheat

In field conditions crops growth are usually under influence of many abiotic stresses that simultaneously affect their growth. Due to large areas of cultivated lands that are prone to anthropogenic or natural acidification and increasing frequency of drought events the exposure of crops to the simultaneous action of aluminum (Al) toxicity and water deficit is a serious threat decreasing food productivity. The effect of simultaneous soil drought and aluminum toxicity on wheat was studied to determine whether complex alteration within plants in response to drought affects the mechanism of Al tolerance in wheat.Al-tolerant (ET8) and Al-sensitive (ES8) wheat (Triticum aestivum L.) near isogenic lines (NILs) were grown in acid and limed soil under controlled laboratory conditions with precisely controlled water deficit.Although both NILs of contrasting resistivity to Al were characterized by similar root biomass in soil of pH 4.2, the tolerant line was characterized by 60% longer roots. This effect resulted from enhanced contribution of the thick root fractions in ES8. The NILs response to the drought in acid soil was characterized by the higher transpiration from ET8 than ES8 leaves irrespectively of leaf order and the effect was stronger with soil drying. The gap in the performance of both NILs in acid soil was increasing with the decrease in soil water potential.It was also shown that aluminum uptake through root surface area is increasing with the decrease in water uptake and the effect was most pronounced for sensitive line grown in acid soil.

Quantification of tree fine roots by real-time PCR

AimsTree roots contribute large quantities of biomass in forests and are important drivers of different ecosystem processes. However, estimation of root biomass remains a challenge. We have developed a method to quantify fine root biomass of trees, tested on Pinus sylvestris L. and Betula sp. in soils in natural environment, by applying specific qPCR primers to soil DNA extracts.MethodsWe first validated the molecular probes in the laboratory by constructing regression equations among known root biomass in soil and the number of gene copies obtained by qPCR. Then, to test the applicability of the method in an ecosystem setting and because Pinus and Betula are important components of boreal forests after wildfire, we quantified fine root biomass from these trees in soils from forests with different degrees of tree mortality after wildfire.ResultsThe new primers specifically amplified ITS (Internal Transcribed Spacer) markers from DNA extracted from fine roots of Pinus and Betula, and regression equations allowed us to calculate root biomass in soil from the number of gene copies obtained by qPCR. Root biomass of Pinus correlated positively with fire-induced canopy mortality, confirming the adequacy of the method. The biomass of Betula roots in soil did not differ across the fire severity gradient due to an overall low and stochastic presence of birch, and did not relate to the establishment of new birch seedlings.ConclusionsThis study shows that DNA-based qPCR methods can be used for rapid, quantitative and species-specific analysis of tree root biomass in natural forest ecosystems.

Soil organic carbon storage and its influencing factors in the riparian woodlands of a Chinese karst area

Riparian woodlands have recently been recognized as important carbon (C) storage regions with a considerable potential of sequestering C to mitigate global warming. Understanding soil organic carbon (SOC) storage in riparian woodland and the differences in SOC storage between riparian woodlands and other adjacent land types is important to effectively assess SOC storage in riparian woodlands and the influences of riparian land-use changes on SOC pool. Therefore, we thoroughly investigated C storage in the riparian woodlands along the Lijiang River watershed, located in a karst area in southwestern China. The goals of the study were to quantify the SOC density (SOCD) in the riparian woodland (0–20cm depth of upper soil) [N=54, the plot area was 1130.88±136.13m2 (mean value with standard deviation)]; to compare the differences in SOCD in the riparian woodland [bamboo-dominated (N=9) and non-bamboo-dominated woodlands (N=45)], the adjacent grasslands (N=13) and the farmlands [croplands (N=17) and orchards (N=17)]; and to assess the influence of soil texture, plant litter and soil root biomass on the SOCD of the riparian woodlands. The results showed that the average SOCD in the riparian woodlands of the Lijiang River watershed was 35.79±9.51t/ha. The SOCD in the non-bamboo-dominated woodland was 36.91±9.63t/ha, which was higher than that in the bamboo-dominated woodlands (29.86±4.90t/ha) by 7.05t/ha (about 23.59%) (p<0.05) and was higher than that in the adjacent grasslands (27.77±7.35t/ha), croplands (28.93±7.30t/ha) and orchards (21.26±8.20t/ha) by 32.91%, 27.58% and 73.61%, respectively (p<0.01). However, the SOCD in the bamboo-dominated woodlands was only higher than that in the orchard by 8.60t/ha (about 40.45%) (p=0.012). In the non-bamboo-dominated woodlands in the Lijiang riparian watershed, the SOCD showed a significant negative correlation with soil sand content (r=−0.69) and a significant positive correlation with the silt (r=0.59) and clay content (r=0.61) (p<0.01). The SOCD showed a significant positive correlation with plant litter (r=0.44) and soil root biomass (r=0.38) (p<0.05). Finally, the results indicate that the non-bamboo-dominated riparian woodland in the karst area stores more SOC compared with the adjacent grassland and farmland. However, converting riparian vegetation into bamboo woodland did not increase the accumulation of SOC and even caused some SOC loss in the Lijiang riparian area.

Root depth distribution and the diversity–productivity relationship in a long‐term grassland experiment

The relationship between plant diversity and productivity in grasslands could depend, partly, on how diversity affects vertical distributions of root biomass in soil; yet, no prior study has evaluated the links among diversity, root depth distributions, and productivity in a long‐term experiment. We used data from a 12‐year experiment to ask how plant species richness and composition influenced both observed and expected root depth distributions of plant communities. Expected root depth distributions were based on the abundance of species in each community and two traits of species that were measured in monocultures: root depth distributions and root‐to‐shoot ratios. The observed proportion of deep‐root biomass increased more than expected with species richness and was positively correlated with aboveground productivity. Indeed, the proportion of deep‐root biomass explained variation in productivity even after accounting for legume presence/abundance and greater nitrogen availability in diverse plots. Diverse plots had root depth distributions that were twice as deep as expected from their species composition and corresponding monoculture traits, partly due to interactions between C4 grasses and legumes. These results suggest that the productivity of diverse plant communities was partly dependent on belowground plant interactions that caused roots to be distributed more deeply in soil.

Seasonal variation in fire temperature and influence on soil CO2 efflux, root biomass, and soil water properties in a Sudanian savanna - woodland, West Africa

Savanna ecosystems are shaped mainly by fires, the consequences of which depend on both their intensities and the season in which they occur. The effects of fire disturbance on key soil parameters are still largely unknown, yet the knowledge of those effects are crucial to our understanding and management of savanna ecosystems. This study was aimed at determining seasonal variations in fire temperature and the influence of fire on soil respiration, root biomass, and soil water infiltration. It was conducted on long-term experimental plots established in 2006 in the savanna–woodland of Burkina Faso. Four fire treatments were applied: no fire, early fire, mid dry-season fire, and late dry-season fire. The results indicated that the average maximum temperature and the residence time of the lethal temperature varied significantly (P &lt; 0.05) depending on the season of fire occurrence, the location of the soil probe, and the interaction between these two factors. The duration of heating above the critical temperature threshold was generally longest at ground level. The season in which fire occurred significantly (P ≤ 0.001) affected soil respiration, soil root biomass, and soil water infiltration. In conclusion, although fire can be used as a management tool in the savanna, the effects of fire on soil should be considered.

New method to estimate root biomass in soil through root-derived carbon

Quantification of root biomass through the conventional root excavation and washing method is inefficient. A pot experiment was conducted to estimate root-derived carbon (C) in soil. Spring wheat ( Triticum aestivum L. cv. ‘Quantum’) was grown in plastic containers (6 L) filled with sterilized sandy soil in a greenhouse. Plants were enriched with 13CO 2 in a glass chamber twice at growth stages GS-37 and GS-59 for 70 min at each time. In one treatment, roots were separated from soil at crop maturity, washed and dried for the determination of biomass. Isotope ratios were then separately analyzed for roots and soil. In a second treatment, roots were thoroughly mixed with the whole soil and representative samples were analyzed for 13C abundance at crop maturity. Control plants were untreated with 13C, in which roots were separated from soil. The root biomass was calculated based on the root-derived C, which was measured through 13C abundance in the soil and root mixed samples. A substantial amount of root-derived C (24%) was unaccounted while separating the roots from soil. Similarly, about 36% of the root biomass was underestimated if conventional root excavation and washing method is used. It has been shown that root biomass can be estimated more accurately from the root-derived C using 13C tracer method than the estimates made by the conventional excavation and washing method. We propose this as an alternative method for the estimation of root-derived C in soil, based on which root biomass can be estimated.

Estimation of the fine root biomass in a Japanese cedar (Cryptomeria japonica) plantation using minirhizotrons

We estimated fine root biomass in a Japanese cedar (Cryptomeria japonica) plantation using a minirhizotron technique. Since data obtained from minirhizotrons are limited to the length and diameter of fine roots observed on minirhizotron tubes, data conversion is necessary to determine the fine root biomass per unit soil volume or unit stand area. We first examined the regression between diameter squared and weight per unit length of fine roots in soil core samples, and calculated the fine root biomass on minirhizotron tubes from their length and diameter. Then we determined conversion factors based on the ratio of the fine root biomass in soil core samples to that on minirhizotron tubes. We examined calculation methods, using a single conversion factor for total fine root biomass in the soil for depths of 0–40 cm (Cal1), or using four conversion factors for fine roots in the soil at 10-cm intervals (Cal2). Cal1 overestimated fine root biomass in the lower soil or underestimated that in the upper soil, while fine root biomass calculated using Cal2 better matched that in soil core samples. These results suggest that minirhizotron data should be converted separately for different soil depths to better estimate fine root biomass.

Fine Root Biomass and Soil N and P in North Queensland Rain Forests1

[Extract] The development of an extensive surface root mat is one of the major mechanisms that enhances nutrient conservation in tropical rain forest, particularly in ecosystems growing on nutrient-poor, heavily leached soils (Jordan & Herrera 1981, Cuevas & Medina 1988). In these root mats, it is the fine unsuberized roots that are primarily responsible for the retention of nutrients (Edwards & Grubb 1982, Gower 1987, Berish & Ewe1 1988). The level of development of these fine root mats has been found to be very variable within the tropics, with the biomass of roots <5-mm diameter in the top 40 cm of soil ranging from 1.1 t/ha to 123.4 t/ha (Sanford 1985, Gower 1987, Cavelier 1992). According to the source-sink theory of resource allocation, based on theorem three of Bloom et al. (1985), trees growing on infertile sites should allocate a greater proportion of their resources into fine root production than those growing on fertile sites, as this “investment” in nutrient acquisition should increase growth and/or reproduction. Vitousek and Sanford (1 986) found that the available data suggested that the biomass of functionally active roots was substantially greater on infertile sites. Soil nitrogen has been suggested as the major factor governing belowground carbon allocation in temperate forest ecosystems (Grier et al. 1981, Aber et al. 1985, Nadelhoffer et al. 1985); however, there is conflicting evidence of the role nitrogen plays in influencing fine root biomass in tropical rain forest. A nutrient amendment study in a tropical rain forest in Hawaii found that nitrogen addition resulted in a significant reduction in fine root biomass (Gower & Vitousek 1989). In contrast, the availability of nitrogen was not a significant factor influencing fine root biomass at two sites in Costa Rica (Gower 1987). At these sites, the availabilities of phosphorus and calcium were suggested to be the major factors influencing fine root biomass (Gower 1987). The aims of this study were to document the variation in fine root biomass in soils of differing fertility and to investigate the relationship between fine root biomass and soil nitrogen and available phosphorus in north Queensland tropical rain forests.

Infection of sweetpotato fibrous roots by Streptomyces ipomoeae: Influence of soil water potential

The effect of the matric component of soil water potential (Ψ m) on infection of fibrous roots of sweetpotato ( Ipomoeae batatas) cv. Jewel by Streptomyces ipomoeae and the influence of infection on water extraction by fibrous roots were examined. The severity of disease on fibrous roots was low in plants grown at constant Ψ m of 0, −1.0 or −2.5J kg −1 in non-fumigated or fumigated soils infested with S. ipomoeae. Disease severity increased with decreasing Ψ m and was greatest at Ψ m of −7.5 to −20J kg −1. Growth of S. ipomoeae in water-filled pores and subsequent infection may have been limited at Ψ m of 0, −1.0 and −2.5J kg −1. Root and shoot dry weights of sweetpotato were significantly lower in plants grown in infested soil than in non-infested soils at Ψ m between −5 and −20J kg −1, but were not affected by disease at Ψ m of 0, −1.0 or −2.5 J kg −1. The severity of disease on fibrous roots was low in plants drip-irrigated on a daily schedule, whereas the severity of disease on fibrous roots was significantly greater in plants irrigated on either a 4- or 6-day schedule. Total dry weights of roots were lower in plants grown for 4 weeks in infested than non-infested soil. However, total dry weights of roots were not affected by disease as compared to non-inoculated controls in plants grown for 8 weeks, thus suggesting that roots of cv. Jewel may be able to compensate for disease by production of additional root biomass in soil. Although root dry weight was not affected by disease in plants grown for 8 weeks, diseased plants extracted significantly less water from soil than healthy plants. Therefore, the effect of disease on water extraction from soil was not due solely to a reduction in root biomass. Limited growth of roots to inoculum in saturated soil, limited growth of the pathogen in saturated soil, or altered susceptibility of the host may explain the reduction of disease at high Ψ m.