Belowground Root Research Articles

Response of carbon and nitrogen content in plants and soils to vegetation cover change in alpine Kobresia meadow of the source region of Lantsang, Yellow and Yangtze Rivers

We conducted this study in lightly and severely degraded Kobresia pygmaea meadow in Gande County, Qinghai Province of China. The purpose of this research was to compare carbon and nitrogen concentrations, content and dynamics of aboveground tissue, belowground roots and soil (0-40 cm) between lightly and severely degraded Kobresia meadow. The results showed that C and N concentrations and C:N ratio of the aboveground tissue were significantly higher in lightly degraded grassland than in severely degraded grassland. In addition, total carbon and nitrogen concentrations of the aboveground tissue were ranked in order of forbs > grasses > sedges in the same grassland type. Total carbon and nitrogen concentrations of belowground roots were significantly higher in severely degraded grassland than in lightly degraded grassland. Total carbon and nitrogen concentrations were higher in the aboveground tissue than in the belowground roots. Total soil organic carbon concentration in severely degraded grassland was significantly lower than that in lightly degraded grassland, and decreased with depth. C and N content per unit area was ranked in order of 0-40 cm soil depth > belowground roots > aboveground issue in the same grassland type. The total carbon content per unit area of aboveground tissue, roots and 0-40 cm soil depth declined by 7.60% after degradation from lightly (14669.2 g m −2) to severely degraded grassland (13554.3 g m −2), i.e., 0-40 cm soil depth declined by 4.10%, belowground roots declined by 59.97% and aboveground tissue declined by 15.39%. The nitrogen content per unit area of aboveground tissue, roots and 0-40 cm soil depth increased after degradation by 12.76% from lightly (3352.7 g m −2) to severely degraded grassland (3780.6 g m −2), i.e., 0-40 cm soil depth increased by 13.07%, belowground roots declined by 55.09% and aboveground tissue declined by 16.00%. As a result of grassland degradation, the total carbon lost by 11149 kg hm −2, and the total nitrogen increased by 4278 kg hm −2.

Coexistence of Typha Angustifolia and Impatiens Capensis in a tidal freshwater marsh

Several salt marsh plant species can oxygenate soils through their aerenchymous tissue and thereby facilitate the growth of neighboring species. Such positive interactions remain poorly understood for tidal freshwater marshes, yet may explain why species adverse to submerged roots are able to thrive in these marshes. Field observations showed a positive association between Typha angustifolia L. and Impatiens capensis Meerb., the two co-occuring dominant species in our study system, suggesting either that T. angustifolia facilitates I. capensis or that both species respond to environmental gradients the same way without interacting directly. We tested the facilitation hypothesis in a greenhouse experiment that measured the growth response of I. capensis with and without T. angustifolia as a neighbor species. Both species affected reduction-oxidation potential of the substrate, but facilitation of I. capensis was not observed. Typha angustifolia depleted soil nutrients in experimental mesocosms and negatively affected belowground root growth but not aboveground biomass of I. capensis; however, nutrient replenishment by tidal flushing may decrease the likelihood for competition in natural systems. Our greenhouse study suggests that abiotic conditions, dispersal events, or competitive biotic interactions, and not facilitation, are predominantly influencing the distribution of these two species in tidal freshwater marshes. Indeed, field measurements demonstrate that both species are positively associated with marsh surface elevation, which is related to frequency and length of water inundation of the marsh surface.

Domestication and Crop Physiology: Roots of Green-Revolution Wheat

Background and AimsMost plant scientists, in contrast to animal scientists, study only half the organism, namely above-ground stems, leaves, flowers and fruits, and neglect below-ground roots. Yet all acknowledge roots are important for anchorage, water and nutrient uptake, and presumably components of yield. This paper investigates the relationship between domestication, and the root systems of landraces, and the parents of early, mid- and late green-revolution bread wheat cultivars. It compares the root system of bread wheat and ‘Veery’-type wheat containing the 1RS translocation from rye.MethodsWheat germplasm was grown in large pots in sand culture in replicated experiments. This allowed roots to be washed free to study root characters.Key ResultsThe three bread wheat parents of early green-revolution wheats have root biomass less than two-thirds the mean of some landrace wheats. Crossing early green-revolution wheat to an F2 of ‘Norin 10’ and ‘Brevor’, further reduced root biomass in mid-generation semi-dwarf and dwarf wheats. Later-generation semi-dwarf wheats show genetic variation for root biomass, but some exhibit further reduction in root size. This is so for some California and UK wheats. The wheat–rye translocation in ‘Kavkaz’ for the short arm of chromosome 1 (1RS) increased root biomass and branching in cultivars that contained it.ConclusionsRoot size of modern cultivars is small compared with that of landraces. Their root system may be too small for optimum uptake of water and nutrients and maximum grain yield. Optimum root size for grain yield has not been investigated in wheat or most crop plants. Use of 1RS and similar alien translocations may increase root biomass and grain yield significantly in irrigated and rain-fed conditions. Root characters may be integrated into components of yield analysis in wheat. Plant breeders may need to select directly for root characters.

The impact of elevated CO2, increased nitrogen availability and biodiversity on plant tissue quality and decomposition

AbstractElevated CO2, increased nitrogen (N) deposition and increasing species richness can increase net primary productivity (NPP). However, unless there are comparable changes in decomposition, increases in productivity will most likely be unsustainable. Without comparable increases in decomposition nutrients would accumulate in dead organic matter leading to nutrient limitations that could eventually prohibit additional increases in productivity. To address this issue, we measured aboveground plant and litter quality and belowground root quality, as well as decomposition of aboveground litter for one and 2‐year periods usingin situlitterbags in response to a three‐way factorial manipulation of CO2(ambient vs. 560 ppm), N deposition (ambient vs. the addition of 4 g N m−2 yr−1) and plant species richness (one, four, nine and 16 species) in experimental grassland plots.Litter chemistry responded to the CO2, N and plant diversity treatments, but decomposition was much less responsive. Elevated CO2induced decreases in % N and % lignin in plant tissues. N addition led to increases in % N and decreases in % lignin. Increasing plant diversity led to decreases in % N and % lignin and an increase in % cellulose. In contrast to the litter chemistry changes, elevated CO2had a much lower impact on decomposition and resulted in only a 2.5% decrease in carbon (C) loss. Detectable responses were not observed either to N addition or to species richness.These results suggest that global change factors such as biodiversity loss, elevated CO2and N deposition lead to significant changes in tissue quality; however, the response of decomposition is modest. Thus, the observed increases in productivity at higher diversity levels and with elevated CO2and N fertilization are not matched by an increase in decomposition rates. This lack of coupled responses between production and decomposition is likely to result in an accumulation of nutrients in the litter pool which will dampen the response of NPP to these factors over time.

Belowground decomposition of mangrove roots in Florida coastal everglades

Mangrove root decomposition rates were measured by distributing mesh bags containing fine root material across six sites with different soil fertility and hydroperiod to compare ambient differences to substrate quality. Roots from a site with lower soil phosphorus concentration were used as a reference and compared to ambient roots at five other sites with increased phosphorus concentration. Four mesh bags of each root type (ambient versus reference), separated into four 10-cm replicate intervals, were buried up to 42 cm depth at each site and incubated for 250 d (initiation in May 2004). Mass loss of ambient mangrove roots was significant at all study sites and ranged from 17% to 54%; there was no significant difference with depth at any one site. Reference decomposition constants (−k) ranged from 0.0012 to 0.0018 d−1 among Taylor Slough sites compared to 0.0023–0.0028 d−1 among Shark River sites, indicating slower decomposition rates associated with lower soil phosphorous and longer flood duration. Reference roots had similar decomposition rates as ambient roots in four of the six sites, and there were no significant correlations between indices of root substrate quality and decomposition rates. Among these distinct landscape gradients of south Florida mangroves, soil environmental conditions have a greater effect on belowground root decomposition than root substrate quality.

Impact of heavy oil-polluted soils on reed wetlands

The impacts of heavy oil-contaminated soils on a reed wetland were studied during a 3-year field experiment in China's Liaohe Oilfield. Contaminated soils with a 30% heavy oil concentration were spread in the reed wetland in April of the first 2 years with 0.2, 2, 6, 18, and 0 kg of oil-polluted soil m −2 for 4 reed beds and a control. In the third year no polluted soil was spread in the wetland. Results indicated that removal efficiencies in 0–80 cm soil layers were between 88 and 92% in the first 2 years, and up to 96% in the third year. The soil profile analysis pointed out that in the third harvest season, there was little residual heavy oil in soil layers 60–80 cm deep, with most of heavy oils removed in the 0–20 cm surface layer, thus avoiding additional pollution of the deep soil layer. Furthermore, contaminated soils had beneficial impacts on soil physiochemical indices of chloride (Cl −), pH, and organic matter in the 0–20 cm surface layer, as well as allowing total nitrogen (TN) and total phosphorus (TP) in the 0–20 cm surface layer to recover within the last 2 years of operation. At the end of this experiment, all these indices in the soil profile (0–80 cm) followed the same trend as those in normal soil. During the first harvest season, reed biomass in the wetland increased with increasing heavy oil pollution loading. In the last two harvest seasons, reed biomass followed the same trend, i.e., at the highest and lowest contaminated soil levels (18 and 0.2 kg oil-polluted soil m −2 soil, respectively), reed biomass in reed beds increased with time, and resulted in levels higher than in the control. In contrast, at middle contaminated soil levels (2 and 6 kg oil-polluted soil m −2 soil) reed biomass followed an inverse trend similar to that experienced by the control. Reed health results suggested that contaminated soils had no obvious adverse effects on reed height and number of leaves, and no significant effect on the eco-physiological indices of reeds, including cellulose, pentose, lignose, length and width ratio of cellulose, and width of cellulose. There was also no effect on germination percentages from below-ground rhizomes, but some inhibition on the germination process. In order to analyze heavy oil uptake and distribution within reeds, a 14C-hexadecane tracer experiment was conducted in 2003. Results indicated that after a growing season, heavy oil concentrated mainly in the below-ground root of reeds.

Phenotypic plasticity rather than locally adapted ecotypes allows the invasive alligator weed to colonize a wide range of habitats

Both phenotypic plasticity and locally adapted ecotypes may contribute to the success of invasive species in a wide range of habitats. Here, we conducted common garden experiments and molecular marker analysis to test the two alternative hypotheses in invasive alligator weed (Alternanthera philoxeroides), which colonizes both aquatic and terrestrial habitats. Ninety individuals from three pairs of aquatic versus terrestrial populations across southern China were analyzed, using inter simple sequence repeat (ISSR) marker, to examine population differentiation in neutral loci. Two common gardens simulating aquatic and terrestrial habitats were set up to examine population differentiation in quantitative traits. We found no evidence of population differentiation in both neutral loci and quantitative traits. Most individuals shared the same ISSR genotype. Meanwhile, plants from different habitats showed similar reaction norms across the two common gardens. In particular, plants allocated much more biomass to the belowground roots in the terrestrial environment, where alligator weed may lose part or all of the aboveground shoots because of periodical or accidental disturbances, than those in the aquatic environment. The combined evidence from molecular marker analysis and common garden experiments support the plasticity hypothesis rather than the ecotype hypothesis in explaining the adaptation of alligator weed in a wide range of habitats.

Influence of fire on belowground root biomass and soil respiration dynamics in young brutian pine ( Pinus brutia) stands in north-western Turkey

Influence of fire on belowground root biomass and soil respiration dynamics in young brutian pine ( Pinus brutia) stands in north-western Turkey

Influences of canopy photosynthesis and summer rain pulses on root dynamics and soil respiration in a young ponderosa pine forest

Our first objective was to link the seasonality of fine root dynamics with soil respiration in a ponderosa pine (Pinus ponderosa P. & C. Lawson) plantation located in the Sierra Nevada of California. The second objective was to examine how canopy photosynthesis influences fine root initiation, growth and mortality in this ecosystem. We compared CO2 flux measurements with aboveground and belowground root dynamics. Initiation of fine root growth coincided with tree stem thickening and shoot elongation, preceding new needle growth. In the spring, root, shoot and stem growth occurred simultaneously with the increase in canopy photosynthesis. Compared with the other tree components, initial growth rate of fine roots was the highest and their growing period was the shortest. Both above and belowground components completed 90% of their growth by the end of July and the growing season lasted approximately 80 days. The period for optimal growth is short at the study site because of low soil temperatures during winter and low soil water content during summer. High photosynthetic rates were observed following unusual late-summer rains, but tree growth did not resume. The autotrophic contribution to soil respiration was 49% over the whole season, with daily contributions ranging between 18 and 87%. Increases in soil and ecosystem respiration were observed during spring growth; however, the largest variation in soil respiration occurred during summer rain events when no growth was observed. Both the magnitude and persistence of the soil respiration pulses were positively correlated with the amount of rain. These pulses accounted for 16.5% of soil respiration between Days 130 and 329.

Concentration, stock and transport rate of heavy metals in a tropical red mangrove, Natal, Brazil

This paper discusses distribution, dynamics and mass budget of heavy metals in a red mangrove forest of the Potengi River estuary, northern Brazil. Tidal hydrology, net primary productivity, decomposing rate of leaf and standing stock of leaf litter in a red mangrove forest were taken into consideration. The belowground roots represented the main mass budget of Fe, Zn and Pb (419.73 mol ha − 1 , 2.29 mol ha − 1 and 0.72 mol ha − 1 ). Differently, Al (683.05 mol ha − 1 ) was mostly present in aerial roots, Cd (1.33 mol ha − 1 ) in the branches and Ni in the trunks (4.43 mol ha − 1 ). Cr showed no significant difference among the structures of Rhizophora mangle (from 0.02 μmol ha − 1 to 0.96 mol ha − 1 ). The average litter fall value was 12.3 t ha − 1 year − 1 whereas the leaves contributed with 9.5 t ha − 1 year − 1 (78%), the reproductive parts with 1.4 t ha − 1 year − 1 (11%) and the branches with 1.4 t ha − 1 year − 1 (11%). The annual average transfer rates of heavy metals from the tree canopy to the sediment through leaf fall were: 0.56, 1.11, 0.01, 0.02 and 0.07 mol ha − 1 for Fe, Al, Pb, Zn and Ni respectively. Cu, Cr and Cd fluxes were less than 0.02 mol ha − 1 . An experiment on yellow leaf decomposition was carried out for different periods: 1, 2, 3, 7, 30, 60 and 90 days. The leaves in the litter bags lost 50% of their dry weight in 30 days. The rate of mass loss was faster in the first 7 days when the leaves lost 21.02% of their initial mass. Concentrations of heavy metals in the decomposing leaves showed a sharp rise from the beginning up to 90 days. However, since the residence time of leaves in the sediments was only 15 days, the leaf litter exported from the mangrove forest is still relatively low in metal concentrations. Considering that 7% of leaf fall (0.7 t ha − 1 year − 1 ) is exported to the marginal marine system, the average export of heavy metals through leaf litter is: 0.36, 0.02, 0.004, 0.01, 0.001, 0.005, 0.03 and 0.74 μmol ha − 1 year − 1 for Fe, Zn, Cr, Cu, Cd, Pb, Ni and Al, respectively. These data support the opinion that mangrove forest is an efficient biogeochemical barrier to the transport of heavy metals to Brazilian coastal areas.

Losses of nitrate from gaps of different sizes in a managed beech (Fagus sylvatica) forest

In the ongoing discussion about sustainable forestry, gap regeneration is suggested to reduce nitrate (NO3–) losses from forest ecosystems. The effect of gap formation and gap size on soil moisture and NO3– leaching was studied in two managed beech (Fagus sylvatica L.) stands in Denmark for about 2 years after formation of four gaps (approx. 20 and 30 m in diameter). Soil moisture content, soil solution NO3-N concentrations, and nitrogen (N) concentrations in throughfall and precipitation were measured along transects from the gaps into the surrounding forests. Losses of NO3-N were estimated using the water balance model WATBAL. Soil moisture content in gaps remained close to field capacity throughout the year, while it decreased to 50%–70% of field capacity under the closed canopy during the growing season. Drainage water fluxes, soil solution NO3-N concentrations, and NO3-N losses were increased in the gaps as compared to under the canopy. For the whole study period, losses of NO3-N were 3- to 13-fold higher in the gaps than in the surrounding forests. However, a significant effect of gap size was not found within the range of the investigated gap diameters and canopy heights. Presumably, not only the aboveground canopy gaps, but also the belowground root gaps affected soil moisture and thus drainage water fluxes and NO3- losses.

Defoliation increased above-ground productivity in a semi-arid grassland

In light of the continuing debate regarding overcompensation we studied the responses of above-ground biomass in a high-elevation, semi-arid grassland to defoliation, defoliation history, and livestock grazing. The above-ground annual net primary productivity (ANPP) was measured over 2 years in one-hundred twenty, 1-m2 plots that were exposed to single- and multi-year defoliation and grazing treatments. Plant communities showed an average increase in ANPP of 31%-45% due to a single defoliation event. The most conservative estimate of average ANPP of defoliated subplots was 29.4 g m-2 greater than the non-defoliated controls. A history of defoliation, due to clipping or grazing, lessened the magnitude of the compensatory response, but above-ground overcompensation of biomass was still observed, ranging on average from 17% to 26%. One dominant species, squirreltail grass [Elymus elymoides (Raf.) Swezeyi], accounted for nearly one-third of the community-level increases in ANPP. In contrast to above-ground patterns, below-ground root production of squirreltail did not increase in response to defoliation events. These results suggest that the above-ground production of high-elevation, semi-arid grasslands in the American Southwest may be temporarily increased through certain grazing events, and may help explain shifts in species dominance in grasslands exposed to long-term grazing by livestock.

Defoliation increased above-ground productivity in a semi-arid grassland

In light of the continuing debate regarding overcompensation we studied the responses of above-ground biomass in a high-elevation, semi-arid grassland to defoliation, defoliation history, and livestock grazing. The above-ground annual net primary productivity (ANPP) was measured over 2 years in one-hundred twenty, 1-m2 plots that were exposed to single- and multi-year defoliation and grazing treatments. Plant communities showed an average increase in ANPP of 31%–45% due to a single defoliation event. The most conservative estimate of average ANPP of defoliated subplots was 29.4 g m−2 greater than the non-defoliated controls. A history of defoliation, due to clipping or grazing, lessened the magnitude of the compensatory response, but above-ground overcompensation of biomass was still observed, ranging on average from 17% to 26%. One dominant species, squirreltail grass [Elymus elymoides (Raf.) Swezeyi], accounted for nearly one-third of the community-level increases in ANPP. In contrast to above-ground patterns, below-ground root production of squirreltail did not increase in response to defoliation events. These results suggest that the above-ground production of high-elevation, semi-arid grasslands in the American Southwest may be temporarily increased through certain grazing events, and may help explain shifts in species dominance in grasslands exposed to long-term grazing by livestock.

Allometry and partitioning of the mangrove, Rhizophora apiculata

This allometric data set gives total biomass in kg (log total biomass=2.523 log GBH −1.943 ); total above-ground biomass (log above-ground biomass=2.420 log GBH −1.832 ); total below-ground biomass (log below-ground biomass=2.611 log GBH −3.454 ) as well as stilts (log stilt biomass=2.546 log GBH −2.945 ); trunk (log trunk biomass=2.477 log GBH −2.050 ) and leaf biomass (log leaf biomass=0.133 log GBH −0.728 ), from girth at breast height (GBH, in cm) of the mangrove Rhizophora apiculata Blume. A comparison is made with three other previous studies. The below-ground data set is unique: there is only one other study on root biomass but the stilts were not separated from the below-ground roots. This is the second reported data set for total biomass and the two allometric regression equations are almost identical. Based on the few direct comparisons available, it is suggested that allometric equations for R. apiculata may not be very site specific but further studies would be needed to confirm this. Partitioning of biomass is very variable for the smaller trees (GBH<15 cm) but relatively constant for the larger trees. The ratio of all the components, except for trunk, to total biomass is larger and more variable for the smaller trees. For the larger trees, 4.5% is allocated to below-ground roots, 12.5% to stilts, 71.7% to trunk, 8.1% to branches, twigs and fruits and 3.2% to leaves, i.e. 17% is apportioned to roots and 11.3% to the canopy (branches, twigs, leaves, flowers and fruits), which is a bottom-heavy stable structure.

Seedling Establishment in Natural and Experimental Florida Scrub Gaps

PETRU, M. AND E. S. MENGES (Archbold Biological Station, P.O. Box 2057, Lake Placid, FL 33862). Seedling establishment in natural and experimental Florida scrub gaps. J. Torrey Bot. Soc. 130: 89-99. 2003.-Gaps are often important microhabitats for recruitment of herbaceous plants. In the Florida scrub, fires create gaps by top-killing resprouting shrubs. These natural gaps are aboveground gaps (without aboveground vegetation) that may also be complete gaps (if belowground roots and rhizomes are absent). Within three types of gaps (natural gaps, experimental aboveground and experimental complete gaps), we studied seedling recruitment and survival of spontaneous species and seven sown herbs for two years. We created aboveground gaps by clipping vegetation and complete gaps by removing shrub roots and rhizomes. These gaps occurred in two Florida scrub habitats: rosemary scrub and scrubby flatwoods. We also explored factors that can affect recruitment patterns in gaps, such as soil moisture, root water retention and light availability. In addition, we tested effects of supplemental watering on sown seeds in the field since drought in 2000 and 2001 suppressed natural seedling recruitment. The watering treatment increased recruitment in all types of gaps. Over half of all gaps were colonized, but there were few seedlings. Recruitment was highest in watered, complete gaps in scrubby flatwoods, where the soil moisture levels were higher and light levels lower than in the other gap types. Seedlings of a single spontaneously recruited species (Lechea deckertii) were more abundant than sown species. Locally common gap specialists were more abundant than generalists. Because many of these gap specialists are endangered plant species, understanding how disturbances create microsites for their regeneration is critical for conservation and management of the Florida scrub ecosystem. In small-scale conservation projects, artificially created gaps may substitute for post-fire gaps when prescribed burning is impossible.

Improving nitrogen and phosphorus use efficiencies through inclusion of forage cowpea in the rice–wheat systems in the Indo-Gangetic Plains of India

In high productivity zones of Indo-Gangetic Plains in south Asia, the rice–wheat system is stressed due to production fatigue as evidenced by declining soil organic matter content, low efficiency of fertilizer use and diminishing rates of factor productivity. We, therefore, conducted field experiments at Modipuram, India, to conserve soil organic carbon, improve N and P use efficiency, and increase yields of rice–wheat system through inclusion of forage cowpea during the summer before cultivating the rice–wheat system. Cowpea forage harvested at 50 days removed greater amounts of N and P through aboveground biomass than those recycled through belowground roots and nodules. The NO 3-N in soil profile below 45 cm depth after wheat harvest was greater under fallow during summer than under cowpea, suggesting that cowpea minimized NO 3-N leaching beyond 45 cm depth. Similarly, in the treatments receiving both 120 kg N and 26 kg P ha −1, NO 3-N in soil below 45 cm depth was lower compared to those receiving N or P alone. After three crop cycles, soil OC content in 0–15 and 15–30 cm depths was greater compared to initial OC in plots having cowpea. P applied at 26 kg ha −1 increased available P content over initial P content, and also over P content of soil under no P treatments. The available P content was, however, invariably low under summer cowpea plots as compared to that under no cowpea ones. With continuous rice–wheat cropping, the bulk density (BD) of soil increased over the initial BD at different profile-depths, more so at 30–45 cm depth in no cowpea plots, but inclusion of summer cowpea helped decreasing the BD in the surface (0–15 cm) and sub-surface (15–30 and 30–45 cm) soil layers. Summer cowpea grown on residual fertility after wheat harvest did not influence rice yield, but increased wheat grain yield ( P<0.05 during the terminal year), when both the crops received fertilizer N and P at recommended rates. Skipping of N or P or both, however, resulted in consistently low yield of these crops under summer cowpea treatments than those under no cowpea treatments, although the differences were not necessarily significant every year. The use efficiency of applied N and P fertilizers in rice and wheat, measured as agronomic efficiency and apparent recovery, was increased with the use of fertilizer N and P at recommended rates, and also with inclusion of summer cowpea.

Competition between Lolium perenne and Digitaria sanguinalis: Ecological consequences for harbouring an endosymbiotic fungus

Abstract This study examined the influence of the fungal endophyte Neotyphodium lolii on the competitive interactions between its perennial, cool season host, Lolium perenne (perennial ryegrass), and a warm season, annual grass, Digitaria sanguinalis (large crabgrass), in densely planted stands (>1000 plant.m−2) in the glasshouse. Endophyte infection had little or no effect on L. perenne tiller production, above- or below-ground biomass or root:shoot ratio in monoculture. However, endophyte infection significantly reduced L. perenne tiller production and above-ground biomass in mixtures with D. sanguinalis. Conversely, D. sanguinalis had significantly higher above-ground biomass and yielded more seed (g) when competing with endophyte infected L. perenne. An apparent trade-off between allocation of resources to reproductive vs root tissues was observed in D. sanguinalis – root:shoot ratio was significantly lower when competing with endophyte infected L. perenne. Results indicate negative ecological consequ...

Toppling in juvenile pines: A comparison of the root system characteristics of direct-sown seedlings, and bare-root seedlings and cuttings

Three-year radiata pine (Pinus radiata D. Don) direct-sown seedlings, bare-root seedlings and cuttings were excavated by hand from a planting trial in Taranaki, New Zealand. Eighteen trees were sampled, six of each plant type. Root system characteristics were compared by investigating differences in above- and below-ground biomass, root length, root size and root biomass distribution. No significant differences were found between plant types in total below-ground biomass, root:shoot ratio, tap root or sinker root biomass. Significant differences between plant types were found for total above-ground, branch, foliage, root bole and lateral root biomass. Additional significant differences were encountered for total root length, tap root and lateral root length. The study found the observed wind-firmness of direct-sown seedlings was unlikely to be because of the size or development of the tap root systems, the degree of symmetrical distribution of their lateral roots or higher root:shoot ratios, but could be associated with the greater proportion of total root biomass allocated to their near-stem lateral roots. It is proposed that the increase in biomass allocated to the near-stem portion of the root system, particularly on the leeward side of a tree, can be considered as an early indicator of emerging tree stability. A field-based method is suggested as a way of obtaining a measure of root anchorage. If plant types are to be developed for greater resistance to toppling, the results from this study would suggest that root stiffness, i.e. less root flexibility, should be a priority consideration in any selection or breeding programme.

Biostabilization of Mandaman dump slope, lndia

An integrated study of the biological stabilization of a coal-mine overburden dump slope has been carried out at Mandaman, 35 km from Dhanbad in eastern India. Native grasses—bamboo (Dendrocalmus strictus) and kashi (Saccharum spontaneum)—are important species that can stabilize the dump slopes. The grasses have good soil binding capacity and help to control soil erosion and improve dump stability. Field observation of their growth performance has indicated that the mean grass height and root depth are 232 (±74) cm and 46 (±5) cm, respectively, after three years and the below-ground root biomass is 474 (±69) g m-2. The mechanical and hydrogeological actions of the grass roots have improved the shear strength properties of the dump material. Numerical modelling has shown that the roots of these grasses increase the factor of safety of the dump slope from 1.2 to 1.4 and thus play a substantial role in the maintenance of long-term stability.

Photosynthesis and biomass under elevated CO2 in a semi-natural grassland - a six-years' field study

In a six years' field study (1995-2000) we have studied the effects of elevated CO2 on photosynthesis, above- and below-ground production and root dynamics in a species-rich semi-natural grassland with a long history of grazing in Central Sweden (59° 48'N, 17° 38'E, 10 m a.s.l.). We used open-top chambers with ambient (A, ca 350 µmol/mol) and elevated (E, ca 700 µmol/mol) CO2 treatments, and a control treatment consisting of rings without mounted chambers. Elevated CO2 was supplied to treatment E continuously during the field season (April-October/November). During each field season, elevated CO2 stimulated light-saturated leaf-level photosynthesis of Taraxacum vulgare and Plantago media. Although photosynthesis showed a significant decrease during each growing season, the CO2 effect (treatment E/A) was rather constant. We found no trend in photosynthesis or the effect of CO2 hereon over the years, but during the dry and extremely dry summers of 1996 and 1999, respectively, the CO2 effect on leaf-level photosynthesis was significantly larger than during rainy summers. Elevated CO2 stimulated above-ground production (standing crop in early August) in 1995-1997, but not in 1998-2000. Root production (measured with minirhizotrons and ingrowth-bags) was stimulated during each growing season. The lack of above-ground production response during the latter years may be explained by unusual weather circumstances (1998 and 2000 being extremely wet and overcast with only few sunny days, and 1999 being extremely dry). However, increasing nutrient limitation might also be involved.