Live Root Mass Research Articles

DNA based diagnostic for the quantification of sugarcane root DNA in the field

Plant root systems play many key roles including nutrient and water uptake, interface with soil microorganisms and resistance to lodging. As for other crops, large and systematic studies of sugarcane root systems have always been hampered by the opaque and solid nature of the soil. In recent years, methods for efficient extraction of DNA from soil and for species-specific DNA amplification have been developed. Such tools could have potential to greatly improve root phenotyping and health diagnostic capability in sugarcane. In this paper, we present a fast, specific and efficient method for the quantification of sugarcane live root cells in soil samples. Previous studies were typically based on mass and length, so we established a calibration to convert root DNA quantity to live root mass. This diagnostic was validated on field samples and used to investigate the fate of the root system after harvest prior to regrowth of the ratoon crop. Two weeks after harvest, the sugarcane roots from the previous crop were still viable. This raises the question of the role that the root system of the harvested crop plays in the performance of the next crop and demonstrates how this test can be used to answer research questions.

Extremely low fine root biomass in Larix sibirica forests at the southern drought limit of the boreal forest

Mongolia's Larix sibirica forests at the southern fringe of the Eurosiberian boreal forest belt are exposed not only to very low winter temperatures, but also to frequent summer droughts. It is not completely known how Siberian larch adapts to these stressors. We examined whether (i) these forests differ in their fine root bio- and necromass from more humid boreal forests further in the North and (ii) inter-annual fluctuations in fine root biomass are related to tree vitality. In two exceptionally dry summers, we found only 4–5g DM m−2 of fine root biomass (in 0–20cm depth), which is far less than typical conifer fine root biomass figures from boreal forests (c. 200–400gm−2) and the lowest forest fine root biomass reported worldwide; in a moist summer, fine root biomass was 20 fold higher. In contrast to fine root biomass, both necromass and non-tree root mass were high in all three years. From the large increase of fine root biomass in the moist summer and the generally high root necromass, we conclude that drought-induced fine root dieback was the likely cause of the very small amount of live root mass in the dry summers. Larch fine roots seem to be more drought-sensitive than shoots, since marked needle loss did not occur under the extreme conditions.

Early root morphology of jack pine seedlings grown in different types of container

This study compared the effects of container type on early root system morphology of jack pine (Pinus banksiana Lamb.) seedlings to determine impacts of container type on root characteristics that may be important for tree stability. Seedlings were grown for one season in Multipots®, Ventblocks®, Copperblocks®, Starpots® and Jiffy® pellets, and for a second season in sand culture in pots. After the first growing season, roots that had grown between Jiffy plugs were cut using a knife, either “early”, in September, or “late”, in November. Seedlings produced in non-pruning containers, Multipots and Ventblocks, had more vertical structural roots, less even root distribution and high shoot:root mass after a second season. Seedlings grown in pruning containers, Copperblocks, Starpots and Jiffy pellets, had more horizontal structural roots and more evenly distributed roots. Jiffy seedlings had high shoot:root mass after pruning, but ratios decreased to low levels similar to Starpots and Copperblocks after a second season in pots. Early pruning of Jiffy seedlings removed less root mass than late pruning, but total live root mass of early and late pruned seedlings was similar after the potting trial. Pruning containers thus produced structural root forms with more desirable characteristics for tree stability. These characteristics were evident after the first season and persisted after the second season in the potting trial.

Phosphorus status determines biomass response to elevated CO2 in a legume : C4 grass community

AbstractThirty‐six mesocosms, each containing a two‐species community of Trifolium repens (C3 legume) and Stenotaphrum secundatum (C4 grass), were grown in sand with three nutrient regimes, zero N low P, zero N high P and supplied N high P, under ambient (aCO2) and twice ambient CO2 (eCO2) for 15 months in two greenhouses. Aboveground annual production in the P limited mesocosms did not respond to eCO2 and was reduced by 50% relative to mesocosms with an adequate P supply, where dry‐matter production was increased by 12–24% under eCO2. The stimulation of production by eCO2 occurred throughout the year despite a clear seasonality in growth. There was no effect of eCO2 on leaf area index (LAI), which was larger under high P than low P. Live root mass at the end of the experiment was higher under eCO2 in all nutrient treatments, but the response of total belowground C (root+soil) to eCO2 depended on P treatment. Under limiting P, belowground C was not significantly changed by eCO2 (2–2.3 t belowground C ha−1). Under high P supply, both root and soil C pools increased under eCO2. Under aCO2, low P supply increased belowground C by 0.7–1 t C ha−1 above that added by the high P treatment. P is commonly limiting in Australian ecosystems and the majority of ecosystem N input is provided by biological N fixation. Consequently, the response of legumes to eCO2 is of particular importance. These results demonstrate that at low P availability, there is likely to be only a limited response of biomass production by T. repens to eCO2, which in turn may constrain any ecosystem response.

Organic Matter Dynamics on the Forest Floor of a Micronesian Mangrove Forest: An Investigation of Species Composition Shifts1

ABSTRACTSpecies composition shifts in mangrove forests may alter organic matter dynamics. The purpose of this study was to predict the effect of species replacements among mangrove trees on organic matter dynamics in a mangrove forest on the island of Kosrae, Federated States of Micronesia. We were particularly interested in elements of the carbon cycle that affect peat accumulation rates, organic matter exports to the estuary and coral reef systems, and soil microbiology. We compared organic matter production and decomposition rates among three mangrove species that commonly grow in similar hydrogeomorphic settings: Rhizophora apiculata BL, which is selectively harvested; Bruguiera gymnorrhiza, which may gradually replace Rhizophora; and Sonneratia alba, which is producing few mature fruits. Sonneratia had significantly higher rates of root production (estimated with ingrowth chambers) than Bruguiera or Rhizophora. Sonneratia foliage had significantly faster decomposition rates and significantly lower lignin:nitrogen ratios than Bruguiera foliage. Live root mass was positively correlated with ingrowth and soil carbon, although soil carbon and ingrowth were not significantly correlated with each other. Humic acid concentrations were significantly higher in Sonneratia rhizospheres than in either Bruguiera or Rhizophora rhizospheres and were positively correlated with root ingrowth. The species changes taking place on Kosrae are likely to result in lower rates of root production and foliage decomposition, and more refractory carbon pools in soil.

Organic Matter Dynamics on the Forest Floor of a Micronesian Mangrove Forest: An Investigation of Species Composition Shifts1

Species composition shifts in mangrove forests may alter organic matter dynamics. The purpose of this study was to predict the effect of species replacements among mangrove trees on organic matter dynamics in a mangrove forest on the island of Kosrae, Federated States of Micronesia. We were particularly interested in elements of the carbon cycle that affect peat accumulation rates, organic matter exports to the estuary and coral reef systems, and soil microbiology. We compared organic matter production and decomposition rates among three mangrove species that commonly grow in similar hydrogeomorphic settings: Rhizophora apiculata BL, which is selectively harvested; Bruguiera gymnorrhiza, which may gradually replace Rhizophora; and Sonneratia alba, which is producing few mature fruits. Sonneratia had significantly higher rates of root production (estimated with ingrowth chambers) than Bruguiera or Rhizophora. Sonneratia foliage had significantly faster decomposition rates and significantly lower lignin:nitrogen ratios than Bruguiera foliage. Live root mass was positively correlated with ingrowth and soil carbon, although soil carbon and ingrowth were not significantly correlated with each other. Humic acid concentrations were significantly higher in Sonneratia rhizospheres than in either Bruguiera or Rhizophora rhizospheres and were positively correlated with root ingrowth. The species changes taking place on Kosrae are likely to result in lower rates of root production and foliage decomposition, and more refractory carbon pools in soil.

The fate of carbon and fertiliser nitrogen when dryland wheat is grown in monoliths of duplex soil

Triticum aestivum L. (cv. Gutha), a short-season wheat, was grown to maturity in large monoliths of duplex soil (sand over sandy-clay) in a daylight phytotron mimicking field conditions. Either 15N-labelled ammonium sulphate ((NH4)2SO4) or urea was banded into the soil at a rate of 30 kg N ha−1: even though roots were about 20% heavier when grown in the presence of (NH4)2SO4 for 86 d (P<0.05), above-ground mass was not affected by the source of nitrogen. At four times through crop development up to grain-filling (50, 56, 70 and 86 d after sowing) shoots were labelled heavily with 14CO2 with two purposes. First, to trace `instantaneous' assimilate movement over 24 h, revealing relative sink strengths throughout plants. This, in turn, allowed precise measurements of live root mass and the proportion of recent photoassimilates deposited in the rhizosphere. Although root systems were sparse, even in surface soil layers, they were strong sinks for photoassimilates early in development (0–50 d), supporting the conversion of inorganic applied nitrogen (N) to soil organic forms. In the presence of roots, up to 28% of 15N was immobilised, whereas only 12% of labelled ammonium sulphate was immobilised in unplanted plots in spite of a favourable moisture status in both treatments. The effect of plants on rates of 15N transformation is ascribed to recently imported photoassimilates sustaining rhizosphere metabolism. Not more than 15% of recently fixed carbon imported by roots was recovered from the rhizoplane, suggesting that a highly localised microbial biomass supported vigorous immobilisation of soil N. Thus, more than twice as much applied N was destined for soil organic fractions as for root material. By these processes, root- and soil-immobilised N become substantial stores of applied N and together with shoot N accounted for all the applied N under dryland conditions.

EFFECTS OF NITROGEN AND PHOSPHORUS AVAILABILITY ON FINE-ROOT DYNAMICS IN HAWAIIAN MONTANE FORESTS

Although it is often assumed that root dynamics are similar to leaf dynamics in relation to nutrient availability, this hypothesis is rarely tested. Using sequential soil coring and a decomposition experiment, patterns of fine-root (,2 mm diameter) biomass, belowground net primary productivity, and root turnover rates were examined over a 1-yr period in three sites along a forest chronosequence in the Hawaiian Islands. These sites form a natural fertility gradient but have similar species composition, climate, and geology. The youngest site (300 yr old) was low in N availability, the oldest site (4.1 3 10 6 yr old) was low in P availability, and the intermediate-aged site (20 000 yr old) was higher in both N and P. The youngest and oldest sites also contained long-term fertilization plots that were fertilized with N or P, or were unfertilized (control). Along the natural fertility gradient, the oldest site generally differed from the other two sites; this site had the greatest standing stock of live root mass, the greatest root length density, the lowest belowground net primary productivity (BNPP), and the slowest root turnover rate. The 300-yr-old and 20 000-yr-old sites were similar in all of these variables, except that root turnover was slightly faster at the 300-yr-old site. The response of fine roots to fertilization was consistent with the response along the natural fertility gradient. Despite N limitation to aboveground growth at the 300-yr-old site, fertilization had small effects on root variables, with the only significant effects being a small increase in the standing stock of live root biomass in N-fertilized plots and an increase in root tissue P concentrations in P-fertilized plots. In contrast, fertilization at the 4.1 3 10 6 yr-old site altered root dynamics more than fertilization at the 300-yr-old site. In the P-fertilized plots, P concentrations increased, BNPP tended to be greater, and root turnover rates increased. These results suggest that root dynamics differ dramatically between ecosystems low in N and ecosystems low in P, even though each system is regarded as ''infertile.'' N availability had a smaller effect on root dynamics than did P availability, suggesting that the simple dichotomy between fertile and infertile sites that is often evoked to explain plant charac- teristics may be unjustified.

Effects of Nitrogen and Phosphorus Availability on Fine-Root Dynamics in Hawaiian Montane Forests

Although it is often assumed that root dynamics are similar to leaf dynamics in relation to nutrient availability, this hypothesis is rarely tested. Using sequential soil coring and a decomposition experiment, patterns of fine-root (<2 mm diameter) biomass, belowground net primary productivity, and root turnover rates were examined over a 1-yr period in three sites along a forest chronosequence in the Hawaiian Islands. These sites form a natural fertility gradient but have similar species composition, climate, and geology. The youngest site (300 yr old) was low in N availability, the oldest site (4.1 × 106 yr old) was low in P availability, and the intermediate-aged site (20 000 yr old) was higher in both N and P. The youngest and oldest sites also contained long-term fertilization plots that were fertilized with N or P, or were unfertilized (control). Along the natural fertility gradient, the oldest site generally differed from the other two sites; this site had the greatest standing stock of live root mass, the greatest root length density, the lowest belowground net primary productivity (BNPP), and the slowest root turnover rate. The 300-yr-old and 20 000-yr-old sites were similar in all of these variables, except that root turnover was slightly faster at the 300-yr-old site. The response of fine roots to fertilization was consistent with the response along the natural fertility gradient. Despite N limitation to aboveground growth at the 300-yr-old site, fertilization had small effects on root variables, with the only significant effects being a small increase in the standing stock of live root biomass in N-fertilized plots and an increase in root tissue P concentrations in P-fertilized plots. In contrast, fertilization at the 4.1 × 106 yr-old site altered root dynamics more than fertilization at the 300-yr-old site. In the P-fertilized plots, P concentrations increased, BNPP tended to be greater, and root turnover rates increased. These results suggest that root dynamics differ dramatically between ecosystems low in N and ecosystems low in P, even though each system is regarded as “infertile.” N availability had a smaller effect on root dynamics than did P availability, suggesting that the simple dichotomy between fertile and infertile sites that is often evoked to explain plant characteristics may be unjustified.

Spatial, Seasonal, and Annual Variation of Fine Root Mass in a Forested Wetland

live and dead fine root mass. Nylon mesh screens were used in the second year to determine if microtopographic position influenced rates of new root production. Samples were collected from 20 replicates each of three microsite types: well-drained hummocks, flats with intermediate drainage, and poorly-drained hollows. Overall live root mass was lower in the second year of the study, possibly because of greater flooding then. Within each year, microsites did not differ significantly in mean live root mass; however, hummocks had significantly less seasonal variation than did flats or hollows. When microsites were compared across years, seasonal fluctuations in live root mass overlapped more strongly in the second year. Dead root mass was significantly less in hollows than in hummocks in both years. Screen data showed that hummocks had the greatest productivity. Overall, results show that some spatial and seasonal patterns of root distribution are similar across years, while others change from year to year, possibly in response to hydrology.

Above- and below-ground biomass dynamics in a sole cropping and an alley cropping system withGliricidia sepium in the semi-deciduous rainforest zone of West Africa

A considerable amount of data is available about above-ground biomass production and turnover in tropical agroforestry systems, but quantitative information concerning root turnover is lacking. Above- and below-ground biomass dynamics were studied during one year in an alley cropping system withGliricidia sepium and a sole cropping system, on aPlinthic Lixisol in the semi-deciduous rainforest zone of the Cote d'Ivoire. Field crops were maize and groundnut. Live root mass was higher in agroforestry than in sole cropping during most of the study period. This was partly due to increased crop and weed root development and partly to the presence of the hedgerow roots. Fine root production was higher in the alleys and lower under the hedgerows compared to the sole cropping plots. Considering the whole plot area, root production in agroforestry and sole cropping systems was approximatly similar with 1000–1100 kg ha−1 (dry matter with 45% C) in 0–50 cm depth; about 55% of this root production occured in the top 10 cm. Potential sources of error of the calculation method are discussed on the basis of the compartment flow model. Above-ground biomass production was 11.1 Mg ha−1 in sole cropping and 13.6 Mg ha−1 in alley cropping, of which 4.3 Mg ha−1 were hedgerow prunings. The input of hedgerow root biomass into the soil was limited by the low root mass ofGliricidia as compared to other tree species, and by the decrease of live root mass of hedgerows and associated perennial weeds during the cropping season, presumably as a result of frequent shoot pruning.

Extracellular Acid Phosphatase Activities in Eriophorum vaginatum Tussocks: A Modeling Synthesis

Analyses of Eriophorum vaginatum tussocks provided mass and kinetic parameters for a Michaelis-Menten model of phosphatase activities in Alaskan tussock tundra. This model was used to simulate the temporal patterns of phosphatase activities, given a 90-d thawing season and organic phosphorus concentrations of 30 ,LM in the first and last 10-d intervals; 15 uM at other times. Results indicated that about 28% of the total annual tussock activity (155 mg P released) occurred during the brief period of high substrate availability in autumn; little occurred in spring because most of the tussock was frozen and live root mass was low. Phosphatases associated with living roots of E. vaginatum were responsible for about 4% of the total activity in tussocks (ca. 6 mg P), which is almost twice the annual plant demand (ca. 3.5 mg). These results suggest that (1) E. vaginatum may obtain much of its phosphorus requirement from the activities of root surface phosphatases, and (2) the timing of maximum plant phosphorus uptake (late in year) and growth (early in year) are asynchronous, i.e., E. vaginatum integrates nutrient availabilities across years. and is regrown each summer. Therefore, living root mass increases throughout the growing season. The total depth of soil thaw also increases during this period, expanding the potential rooting volume and stimulating enzyme activities. In addition, soil solution organic phosphorus concentrations change with time. For these reasons, any assessment of tussock phosphatase activities must account for these dynamically changing factors. The goals of this study were to evaluate the potential contributions of E. vaginatum root surface phosphatases to (1) total rhizosphere phosphatase activity and (2) satisfying plant phosphorus requirement. A combination of experimental and modeling approaches was used to address these objectives. The various components of E. vaginatum tussocks (e.g., live roots, dead roots, soil, etc.) were separated, quantified, and their associated phosphatase activities assayed. This information was then used to develop a model of rhizosphere enzyme activity, including the effects of soil thawing, root growth, and fluctuating organic phosphorus concentrations. Simulations were performed to elucidate the dynamics of tussock phosphatase activities throughout the growing season.

Soil invertebrate and plant responses to mowing and carbofuran application in a North American tallgrass prairie

Relationships between soil invertebrate populations and primary production of a tallgrass prairie were investigated using the insecticide-nematicide carbofuran and a range of mowing intensities to manipulate invertebrate densities and resource quantity and quality. The trophic composition of nematode populations was monitored through each of two growing seasons. Earthworm and macroarthropod densities and primary production were assessed at the end of the second season. Invertebrate densities were generally reduced in carbofuran-treated plots, although individual weights of surviving macroarth-ropod herbivores increased significantly (p<0.05). Carbofuran failed to affect estimates of above- or belowground plant biomass after two years of treatment. Changes in resource quantity and quality resulted in rapid responses by dominant invertebrate consumer populations. A 28% reduction in live root mass and a 24% increase in root detritus following two years of mowing was associated with a 54% decrease in herbivorous nematode densities, a 47% increase in microbivorous nematode densities, and a 41% increase in native earthworm biomass.