Hooshang Majdi

Specific root length as an indicator of environmental change

Abstract Specific root length (SRL, m g−1) is probably the most frequently measured morphological parameter of fine roots. It is believed to characterize economic aspects of the root system and to be indicative of environmental changes. The main objectives of this paper were to review and summarize the published SRL data for different tree species throughout Europe and to assess SRL under varying environmental conditions. Meta-analysis was used to summarize the response of SRL to the following manipulated environmental conditions: fertilization, irrigation, elevated temperature, elevated CO2, Al-stress, reduced light, heavy metal stress and physical disturbance of soil. SRL was found to be strongly dependent on the fine root classes, i.e. on the ectomycorrhizal short roots (ECM), and on the roots <0.5 mm, <1 mm, <2 mm and 1 – 2 mm in diameter SRL was largest for ECM and decreased with increasing diameter. Changes in soil factors influenced most strongly the SRL of ECM and roots <0.5 mm. The variation in the SRL components, root diameter and root tissue density, and their impact on the SRL value were computed. Meta-analyses showed that SRL decreased significantly under fertilization and Al-stress; it responded negatively to reduced light, elevated temperature and CO2. We suggest that SRL can be used successfully as an indicator of nutrient availability to trees in experimental conditions.

Root sampling methods - applications and limitations of the minirhizotron technique

Applications and limitations of the minirhizotron technique (non-destructive) in relation to two frequently used destructive methods (soil coreing and ingrowth cores) is discussed. Sequential coreing provides data on standing crop but it is difficult to obtain data on root biomass production. Ingrowth cores can provide a quick estimate of relative fine-root growth when root growth is rapid. One limitation of the ingrowth core is that no information on the time of ingrowth and mortality is obtained.The minirhizotron method, in contrast to the destructive methods permits simultaneous calculation of fine-root length production and mortality and turnover. The same fine-root segment in the same soil space can be monitored for its life time, and stored in a database for processing. The methodological difficulties of separating excavated fine roots into living and dead vitality classes are avoided, since it is possible to judge directly the successive ageing of individual roots from the images. It is concluded that the minirhizotron technique is capable of quantifying root dynamics (root-length production, mortality and longevity) and fine-root decomposition. Additionally, by combining soil core data (biomass, root length and nutrient content) and minirhizotron data (length production and mortality), biomass production and nutrient input into the soil via root mortality and decomposition can be estimated.

Variation in fine root biomass of three European tree species: Beech (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.), and Scots pine (Pinus sylvestris L.)

Abstract Fine roots (<2 mm) are very dynamic and play a key role in forest ecosystem carbon and nutrient cycling and accumulation. We reviewed root biomass data of three main European tree species European beech, (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.), in order to identify the differences between species, and within and between vegetation zones, and to show the relationships between root biomass and the climatic, site and stand factors. The collected literature consisted of data from 36 beech, 71 spruce and 43 pine stands. The mean fine root biomass of beech was 389 g m−2, and that of spruce and pine 297 g m−2 and 277 g m−2, respectively. Data from pine stands supported the hypothesis that root biomass is higher in the temperate than in the boreal zone. The results indicated that the root biomass of deciduous trees is higher than that of conifers. The correlations between root biomass and site fertility characteristics seemed to be species specific. There was no correlation between soil acidity and root biomass. Beech fine root biomass decreased with stand age whereas pine root biomass increased with stand age. Fine root biomass at tree level correlated better than stand level root biomass with stand characteristics. The results showed that there exists a strong relationship between the fine root biomass and the above-ground biomass.

Root distribution in a Norway spruce (Picea abies (L.) Karst.) stand subjected to drought and ammonium-sulphate application

Results of the spatial distribution of fine roots are reported from a Norway spruce (Picea abies (L.) Karst.) in SW Sweden stand subjected to drought (D) and ammonium-sulphate application (NS). The sampling was carried out by excavating monoliths in segments of 0.5 × 0.5 × 0.1 m to a depth of one meter. Root data also included in the study were obtained by excavating whole trees and soil coring.The data suggest a fairly deep distribution pattern of fine roots (< 1 mm in diameter) in the study area compared with other forest sites in SW Sweden. The weight fraction of living fine roots in the LFH-horizon amounted to 53, 36 and 55% of the total fine-root biomass and 12, 30 and 32% of the total fine-root necromass (dead fine roots) in the control, D and NS-treatment areas respectively. Drought seemed to result in a redistribution of fine roots to deeper mineral soil horizons. Ammonium sulphate application led to the reverse, viz, a concentration of fine roots to the LFH-horizon. A significantly smaller fine-root necromass was indicated in the LFH-horizon of the control areas compared with both the D and NS-treatment areas, suggesting a high mortality of fine roots in these areas. A heavy dry matter fraction accumulates in roots > 1 mm in diameter and in stumps. These root fraction, were frequently found between the trees, although the stump constitutes an important fraction in terms of dry weight.

Demography of fine roots in response to nutrient applications in a Norway spruce stand in southwestern Sweden

Abstract:Effects of nitrogen and sulphur (ammonium sulphate [NS] application), nitrogen, other nutrients and water (liquid fertilization; LF), and N-free fertilizer (N-free) on fine root dynamics (...

Impact of tree species on soil carbon stocks and soil acidity in southern Sweden

Abstract The impact of tree species on soil carbon stocks and acidity in southern Sweden was studied in a non-replicated plantation with monocultures of 67-year-old ash (Fraxinus excelsior L.), beech (Fagus silvatica L.), elm (Ulmus glabra Huds.), hornbeam (Carpinus betulus L.), Norway spruce (Picea abies L.) and oak (Quercus robur L.). The site was characterized by a cambisol on glacial till. Volume-determined soil samples were taken from the O-horizon and mineral soil layers to 20 cm. Soil organic carbon (SOC), total nitrogen (TN), pH (H2O), cation-exchange capacity and base saturation at pH 7 and exchangeable calcium, magnesium, potassium and sodium ions were analysed in the soil fraction < 2 mm. Root biomass (<5 mm in diameter) and its proportion in the forest floor and mineral soil varied between tree species. There was a vertical gradient under all species, with the highest concentrations of SOC, TN and base cations in the O-horizon and the lowest in the 10–20 cm layer. The tree species differed with respect to SOC, TN and soil acidity in the O-horizon and mineral soil. For SOC and TN, the range in the O-horizon was spruce > hornbeam > oak > beech > ash > elm. The pH in the O-horizon ranged in the order elm > ash > hornbeam > beech > oak > spruce. In the mineral soil, SOC and TN ranged in the order elm > oak > ash = hornbeam > spruce > beech, i.e. partly reversed, and pH ranged in the same order as for the O-horizon. It is suggested that spruce is the best option for fertile sites in southern Sweden if the aim is a high carbon sequestration rate, whereas elm, ash and hornbeam are the best solutions if the aim is a low soil acidification rate.

Does liquid fertilization affect fine root dynamics and lifespan of mycorrhizal short roots

We studied effects of nitrogen, other nutrients and water (liquid fertilization; LF) on fine root dynamics (production, mortality) and life span of mycorrhizal short roots in a Norway spruce stand, using minirhizotrons. Data were collected and analyzed during a two-year period at depths of 0–20 cm, 21–40 cm and 41–85 cm, six years after the start of treatment. Relative to control (C), root production was lower in LF plots at depth 0–20 cm. Root production increased significantly at depth 41–85 cm. Fine root mortality in LF plots was higher at all depths. Life span of mycorrhizal short roots in LF plots was significantly lower than C plots and at the end of the study no mycorrhizal short roots were alive. It is suggested that the water and nitrogen input lower longevity of mycorrhizal short roots and promote fine root production at deeper soil layers.

Spatial distribution of fine roots, rhizosphere and bulk‐soil chemistry in an acidified Picea abies stand

Soil and fine‐root sampling were carried out in a Norway spruce (Picea abies (L.) Karst.) stand with high levels of atmospheric deposition of sulphur and nitrogen in south‐western Sweden. Living and dead fine roots in both LFH‐ and mineral horizons were excavated from soil cores. The bulk and rhizoshpere soil concentrations of Al, Ca, Mg, Fe, K and pH were measured in water extracts. The magnesium concentration was significantly higher in the rhizosphere than in the bulk soil except for in the deepest horizon. The Ca/Al‐ratio increased with depth in both the rhizosphere and bulk soils while it decreased with depth in fine roots. The ratio was lower in dead than in living fine roots. The amount of both living and dead fine roots decreased with depth. The necromass/biomass ratio was highest in the 10 to 20 cm mineral soil horizon.

Effects of ammonium sulphate application on the chemistry of bulk soil, rhizosphere, fine roots and fine-root distribution in a Picea abies (L.) karst. stand

The effect of ammonium sulphate application on the bulk and rhizosphere soil chemistry, elemental concentration of living fine roots (<2 mm in diameter), amounts of living and dead fine roots, root length density and specific root length density were investigated in a 28 year old Norway spruce stand in SW Sweden. The treatments started in 1988. Core samples of the LFH layer and mineral soil layers were sampled in control (C) and ammonium sulphate (NS) treatment plots in 1988, 1989 and 1990. Soil pH and NO3-S and SO4-S, Al, Ca, Mg, Mn and K concentrations were measured for both the bulk soil and rhizosphere soil.The pH-values of the bulk and rhizosphere soil decreased in 1989 and 1990 in NS plots compared to control plots, while the SO4-S concentration increased. The Ca, Mg and K concentration increased in the NS treatment in almost all layers in the bulk and the rhizosphere soil. Ammonium ions may have replaced these elements in the soil organic matter. The NS treatment reduced Mg concentration in fine roots in all layers in 1990. The Al concentrations in the rhizosphere and bulk soil were higher in NS plots in all layers, except at 0–10 cm depth, both in 1989 and 1990. The Al content of living fine roots was higher in NS plots than C plots but the differences were not significant. The NS addition did not affect the P and K contents of fine roots in any soil layer, but the S concentrations of fine roots were significantly higher in NS plots in 1989 and 1990. The fine root necromass was higher in NS than in C in 1990, in the LFH layer, indicating a gradual decrease in the vitality of the fine roots. It was suggested that the NS treatment resulted in displacement of Mg and K from exchange sites in the LFH layer leading to leaching of these cations to the mineral soil. Further application of ammonium sulphate may damage the fine roots and consequently adversely affect the water and nutrient uptake of root systems.

A comparison between minirhizotron and monolith sampling methods for measuring root growth of maize (Zea mays L.)

Transparent plastic minirhizotron tubes have been used to evaluate spatial and temporal growth activities of plant root systems. Root number was estimated from video recordings of roots intersecting minirhizotron tubes and of washed roots extracted from monoliths of the same soil profiles at the physiological maturity stage of a maize (Zea mays L.) crop. Root length was measured by the line intercept (LI) and computer image processing (CIP) methods from the monolith samples.There was a slight significant correlation (r=0.28, p<0.005) between the number of roots measured by minirhizotron and root lengths measured by the LI method, however, no correlation was found with the CIP method. Using a single regression line, root number was underestimated by the minirhizotron method at depths between 0–7.6 cm. A correlation was found between root length estimated by LI and CIP. The slope of estimated RLD was significant with depth for these two methods. Root length density (RLD) measured by CIP showed a more erratic decline with distance from the plant row and soil surface than the LI method.