Soil organic carbon dynamics 75 years after land-use change in perennial grassland and annual wheat agricultural systems

The dynamics of roots and soil organic carbon (SOC) in deeper soil layers are amongst the least well understood components of the global C cycle, but essential if soil C is to be managed effectively. This study utilized a unique set of land-use pairings of harvested tallgrass prairie grasslands (C₄) and annual wheat croplands (C₃) that were under continuous management for 75 years to investigate and compare the storage, turnover and allocation of SOC in the two systems to 1 m depth. Cropland soils contained 25 % less SOC than grassland soils (115  and 153 Mg C ha^?1, respectively) to 1 m depth, and had lower SOC contents in all particle size fractions (2000–250, 250–53, 53–2 and <2 μm), which nominally correspond to SOC pools with different stability. Soil bulk δ¹³C values also indicated the significant turnover of grassland-derived SOC up to 80 cm depth in cropland soils in all fractions, including deeper (>40 cm) layers and mineral-associated (<53 μm) SOC. Grassland soils had significantly more visible root biomass C than cropland soils (3.2 and 0.6 Mg ha^?1, respectively) and microbial biomass C (3.7 and 1.3 Mg ha^?1, respectively) up to 1 m depth. The outcomes of this study demonstrated that: (i) SOC pools that are perceived to be stable, i.e. subsoil and mineral-associated SOC, are affected by land-use change; and, (ii) managed perennial grasslands contained larger SOC stocks and exhibited much larger C allocations to root and microbial pools than annual croplands throughout the soil profile.     

Fine root biomass and turnover of two fast-growing poplar genotypes in a short-rotation coppice culture

Background and aims

The quantification of root dynamics remains a major challenge in ecological research because root sampling is laborious and prone to error due to unavoidable disturbance of the delicate soil-root interface. The objective of the present study was to quantify the distribution of the biomass and turnover of roots of poplars (Populus) and associated understory vegetation during the second growing season of a high-density short rotation coppice culture.

Methods

Roots were manually picked from soil samples collected with a soil core from narrow (75 cm apart) and wide rows (150 cm apart) of the double-row planting system from two genetically contrasting poplar genotypes. Several methods of estimating root production and turnover were compared.

Results

Poplar fine root biomass was higher in the narrow rows than in the wide rows. In spite of genetic differences in above-ground biomass, annual fine root productivity was similar for both genotypes (ca. 44 g DM m^?2 year^?1). Weed root biomass was equally distributed over the ground surface, and root productivity was more than two times higher compared to poplar fine roots (ca. 109 g DM m^?2 year^?1).

Conclusions

Early in SRC plantation development, weeds result in significant root competition to the crop tree poplars, but may confer certain ecosystem services such as carbon input to soil and retention of available soil N until the trees fully occupy the site.     

Factors controlling decomposition rates of fine root litter in temperate forests and grasslands

Background and aims

Fine root decomposition contributes significantly to element cycling in terrestrial ecosystems. However, studies on root decomposition rates and on the factors that potentially influence them are fewer than those on leaf litter decomposition. To study the effects of region and land use intensity on fine root decomposition, we established a large scale study in three German regions with different climate regimes and soil properties. Methods In 150 forest and 150 grassland sites we deployed litterbags (100 μm mesh size) with standardized litter consisting of fine roots from European beech in forests and from a lowland mesophilous hay meadow in grasslands. In the central study region, we compared decomposition rates of this standardized litter with root litter collected on-site to separate the effect of litter quality from environmental factors.

Results

Standardized herbaceous roots in grassland soils decomposed on average significantly faster (24?±?6 % mass loss after 12 months, mean ± SD) than beech roots in forest soils (12?±?4 %; p?Conclusions Grasslands, which have higher fine root biomass and root turnover compared to forests, also have higher rates of root decomposition. Our results further show that at the regional scale fine root decomposition is influenced by environmental variables such as soil moisture, soil temperature and soil nutrient content. Additional variation is explained by root litter quality.     

Fine root dynamics and soil carbon accretion under thinned and un-thinned Cupressus lusitanica stands in, Southern Ethiopia

Background and aims

Forest management activities influences stand nutrient budgets, belowground carbon allocation and storage in the soil. A field experiment was carried out in Southern Ethiopia to investigate the effect of thinning on fine root dynamics and associated soil carbon accretion of 6-year old C. lusitanica stands.

Methods

Fine roots (≤2 mm in diameter) were sampled seasonally to a depth of 40 cm using sequential root coring method. Fine root biomass and necromass, vertical distribution, seasonal dynamics, annual turnover and soil carbon accretion were quantified.

Results

Fine root biomass and necromass showed vertical and temporal variations. More than 70 % of the fine root mass was concentrated in the top 20 cm soil depth. Fine root biomass showed significant seasonal variation with peaks at the end of the major rainy season and short rainy season. Thinning significantly increased fine root necromass, annual fine root production and turnover. Mean annual soil carbon accretion, through fine root necromass, in the thinned stand was 63 % higher than that in the un-thinned stand.

Conclusions

The temporal dynamics in fine roots is driven by the seasonality in precipitation. Thinning of C. lusitanica plantation would increase soil C accretion considerably through increased fine root necromass and turnover.     

The impact of land degradation on the C pools in alpine grasslands of the Qinghai-Tibet Plateau

Aims

To determine the effect of grassland degradation on the soil carbon pool in alpine grassland.

Methods

In this study, we calculated the carbon pool in the above-and below-ground biomass, the soil microbial biomass carbon pool, the total organic carbon pool and the soil total carbon.

Results

Grassland degradation has resulted in decreases in biomass and carbon content and has changed the ratio of roots to shoots. However, there was less influence of degradation on dead root biomass. There was most likely a lag effect of changes in dead root biomass following grassland degradation. In the alpine grassland ecosystem, the carbon pool in soil accounts for more than 92 % of the total carbon both in vegetation and soil. The carbon in alpine grassland is stored primarily in the form of total organic carbon below-ground. As organic carbon decreases, the ratio of the microbial biomass carbon pool to the total organic carbon pool increases and then declines with increasing degradation level. Along the grassland degradation gradient, the total vegetation biomass (above-and below-ground) and the soil carbon pool (microbial biomass C, total organic C and total C) all decreased.     

Changes in some soil properties induced by re-conversion of cropland into grassland in the semiarid steppe zone of Inner Mongolia, China

Aims

“Grain for Green Program” (GGP), i.e., re-conversion of cropland into forest or grassland, initiated by Chinese government has a profound impact on mitigating environmental degradation. The objectives of this study were to assess the changes of some soil properties during the processes of re-conversion from cropland to grassland over time in the semiarid steppe region of north China.

Methods

Two sites with different ages of re-conversion were selected for measurements of organic matter (SOM), total nitrogen (TN) and phosphorus (TP), bulk density (BD) and grain size distribution. Saturated hydraulic conductivity was determined by the constant hydraulic head method and unsaturated hydraulic conductivity by disc infiltrometer at tensions of 30, 60 and 150 mm. Soil water content was measured using the gravimetric method. Wetting front depths in the soil after rainfall were also recorded at the study sites.

Results

Natural grasslands had higher belowground biomass than re-converted grasslands. Re-converted grasslands had lower SOM and TN at depths of 0–20 cm and higher saturated hydraulic conductivity at depths of 0–10 cm than natural grassland. The natural grassland soils had higher soil water contents in the surface soil (0–20 cm) and lower soil water contents at deeper depths than re-converted grassland soils. Soil aggregate stability reached the natural steppe level 12 years after re-conversion.

Conclusions

The recovery of soil properties after GGP appeared to be slow, and these properties did not return to natural grassland status before cultivation after 12 years of re-conversion.     

Chemistry and Microbial Functional Diversity Differences in Biofuel Crop and Grassland Soils in Multiple Geographies

We obtained soil samples from geographically diverse switchgrass (Panicum virgatum L.) and sorghum (Sorghum bicolor L.) crop sites and from nearby reference grasslands and compared their edaphic properties, microbial gene diversity and abundance, and active microbial biomass content. We hypothesized that soils under switchgrass, a perennial, would be more similar to reference grassland soils than sorghum, an annual crop. Sorghum crop soils had significantly higher NO₃ ^? -N, NH₄ ⁺ -N, SO₄ ^2? -S, and Cu levels than grassland soils. In contrast, few significant differences in soil chemistry were observed between switchgrass crop and grassland soils. Active bacterial biomass was significantly lower in sorghum soils than switchgrass soils. Using GeoChip 4.0 functional gene arrays, we observed that microbial gene diversity was significantly lower in sorghum soils than grassland soils. Gene diversity at sorghum locations was negatively correlated with NO₃ ^? -N, NH₄ ⁺ -N, and SO₄ ^2? -S in C and N cycling microbial gene categories. Microbial gene diversity at switchgrass sites varied among geographic locations, but crop and grassland sites tended to be similar. Microbial gene abundance did not differ between sorghum crop and grassland soils, but was generally lower in switchgrass crop soils compared to grassland soils. Our results suggest that switchgrass has fewer adverse impacts on microbial soil ecosystem services than cultivation of an annual biofuel crop such as sorghum. Multi-year, multi-disciplinary regional studies comparing these and additional annual and perennial biofuel crop and grassland soils are recommended to help define sustainable crop production and soil ecosystem service practices.     

Soil CO2 efflux in a bioenergy plantation with fast-growing Populus trees – influence of former land use, inter-row spacing and genotype

Aims

In this study we quantified the annual soil CO₂ efflux (annual SCE) of a short rotation coppice plantation in its establishment phase. We aimed to examine the effect of former (agricultural) land use type, inter-row spacing and genotype.

Methods

Annual SCE was quantified during the second growth year of the establishment rotation in a large scale poplar plantation in Flanders. Automated chambers were distributed over the two former land use types, the two different inter-row spacings and under two poplar genotypes. Additional measurements of C, N, P, K, Mg, Ca and Na concentrations of the soil, pH, bulk density, fine root biomass, microbial biomass C, soil mineralization rate, distance to trees and tree diameters were performed at the end of the second growth year.

Results

Total carbon loss from soil CO₂ efflux was valued at 589 g m^?2 yr^?1. Annual SCE was higher in former pasture as compared to cropland, higher in the narrow than in the wider inter-row spacings, but no effect of genotype was found.

Conclusions

Spatial differences in site characteristics are of great importance for understanding the effect of ecosystem management and land use change on soil respiration processes and need to be taken into account in modeling efforts of the carbon balance.     

The plasticity of the growth and proliferation of wheat root system under elevated CO2

Background and Aims

Understanding crop responses to increasing atmospheric CO₂ requires knowledge of how their root systems grow, proliferate and function. The effect of elevated CO₂ on the growth and proliferation of wheat root system (Triticum aestivum L.), was examined.

Methods

Two pairs of sister lines of wheat contrasting in vigour (CV97 and CV207) and tillering (7750N and 7750PF) were grown in rhizo-boxes under ambient (380 μl L^?1) and elevated CO₂ (700 μl L^?1), and the root growth and proliferation mapped.

Results

Elevated CO₂ effects on shoot and root biomass were observed in the lines contrasting for vigour, but not in the lines contrasting for tillering. Root biomass was reduced by 67 % in the high vigour line CV97, reducing total plant biomass by 26 % compared to the low vigour line, CV207. This was due to a reduction in root length down the 1 m soil profile and root proliferation in the top 0.2 m layer. The reduction in root biomass was not compensated by an increase in shoot biomass.

Conclusions

The reduction in root biomass under elevated CO₂ in the vigour line CV97 can be explained through its inability to increase the sink strength due to the failure to increase tiller number to which the plant presumably responded by increasing losses of the newly assimilated carbon by respiration.     

Differences in yield, Ellenberg N value, tissue chemistry and soil chemistry 15 years after the cessation of nitrogen addition

Background & Aims

The consequences of fertiliser addition to semi-natural grasslands are well understood, but much less is known about the consequences of cessation of nitrogen fertiliser regimes, including rates of recovery. This study aimed to investigate whether the effects of nitrogen (N) additions to a mesotrophic grassland were still apparent 15 years after the cessation of N inputs.

Methods

A long-term experiment at Tadham Moor, UK, received N additions at rates of 0, 25, 50, 100 and 200 kg N ha^?1 yr^?1 between 1986 and 1994. Fifteen years after the cessation of N additions soil chemistry, plant tissue chemistry, plant biomass and Ellenberg N values were assessed.

Results

KCl-extractable ammonium-N, total soil N, total organic carbon and microbial biomass N differed between the controls and the higher historic levels of N addition. Plant tissue chemistry showed no significant effects of previous N addition. Above-ground biomass was higher where N had been added, although this response was only weakly significant. The species composition of the vegetation showed effects of the N addition with mean Ellenberg N values significantly higher than the control in most treatments.

Conclusion

The effects of long-term N addition can be seen for many years.     

A randomization method for efficiently and accurately processing fine roots, and separating them from debris, in the laboratory

Background and Aims

We developed a method for processing roots from soil cores and monoliths in the laboratory to reduce the time and cost devoted to separating roots from debris and improve the accuracy of root variable estimates. The method was tested on soil cores from a California oak savanna, with roots from trees, Quercus douglasii, and annual grasses.

Methods

In the randomized sampling method, one isolates the sample fraction consisting of roots and organic debris?<?= 1 cm in length, and randomizes it through immersion in water and vigorous mixing. Sub-samples from the mixture are then used to estimate the percentage of roots in this fraction, thereby enabling an estimate of total sample biomass.

Results

We found that root biomass estimates, determined through the randomization method, differed from total root biomass established by meticulously picking every root from a sample with an error of 3.0 % +/? 0.6 %?s.e.

Conclusions

This method greatly reduces the time and resources required for root processing from soil cores and monoliths, and improves the accuracy of root variable estimates compared to standard methods. This gives researchers the ability to increase sample frequency and reduce the error associated with studying roots at the landscape and plant scales.     

Changes in soil organic carbon and total nitrogen stocks after conversion of meadow to cropland in Northeast China

Aims

Grassland conversion to cropland (GCC) may result in loss of a large amount of soil organic carbon (SOC). However, the assessment of such loss of SOC still involves large uncertainty due to shallow sampling depth, soil bulk density estimation and spatial heterogeneity. Our objectives were to quantify changes in SOC, soil total nitrogen (STN) and C:N ratio in 0–100 cm soil profile after GCC and to clarify factors influencing the SOC change.

Methods

A nest-paired sampling design was used in six sites along a temperature gradient in Northeast China.

Results

SOC change after GCC ranged from ?17 to 0 Mg ha^?1 in 0–30 cm soil layer, recommended by IPCC, across the six sites, but ranged from ?30 to 7 Mg ha^?1 when considering 0–100 cm. We found a linear relationship between SOC change in 30–100 cm and that in 0–30 cm profile (ΔC_30?100?=?0.35ΔC_0?30, P?<?0.001), suggesting that SOC change in 0–100 cm was averagely 35 % higher than that in 0–30 cm. The change in STN showed a similar pattern to SOC, and soil C:N ratio did not change at most of sites. On the other hand, SOC loss after GCC was greater in soils with higher initial SOC content or in croplands without applying chemical fertilizers. Furthermore, SOC loss after GCC decreased with falling mean annual temperature (MAT), and even vanished in the coldest sites.

Conclusions

The magnitude of SOC loss following GCC in Northeast China is lower than the global average value, partly due to low MAT here. However, the current low SOC loss can be intensified by remarkable climate warming in this region.     

Integrated effects of organic,inorganic and biological amendments on methane emission,soil quality and rice productivity in irrigated paddy ecosystem of Bangladesh: field study of two consecutive rice growing seasons

Aims

Effects of different soil amendments were investigated on methane (CH₄) emission, soil quality parameters and rice productivity in irrigated paddy field of Bangladesh.

Methods

The experiment was laid out in a randomized complete block design with five treatments and three replications. The experimental treatments were urea (220 kg ha^?1) + rice straw compost (2 t ha^?1) as a control, urea (170 kg ha^?1) + rice straw compost (2 t ha^?1) + silicate fertilizer, urea (170 kg ha^?1) + sesbania biomass (2 t ha^?1 ) + silicate fertilizer, urea (170 kg ha^?1) + azolla biomass (2 t ha^?1) + cyanobacterial mixture 15 kg ha^?1 silicate fertilizer, urea (170 kg ha^?1) + cattle manure compost (2 t ha^?1) + silicate fertilizer.

Results

The average of two growing seasons CH₄ flux 132 kg ha^?1 was recorded from the conventional urea (220 kg ha^?1) with rice straw compost incorporated field plot followed by 126.7 (4 % reduction), 130.7 (1.5 % reduction), 116 (12 % reduction) and 126 (5 % reduction) kg CH₄ flux ha^?1 respectively, with rice straw compost, sesbania biomass, azolla anabaena and cattle manure compost in combination urea and silicate fertilizer applied plots. Rice grain yield was increased by 15 % and 10 % over the control (4.95 Mg ha^?1) with silicate plus composted cattle manure and silicate plus azolla anabaena, respectively. Soil quality parameters such as soil organic carbon, total nitrogen, microbial biomass carbon, soil redox status and cations exchange capacity were improved with the added organic materials and azolla biofertilizer amendments with silicate slag and optimum urea application (170 kg ha^?1) in paddy field.

Conclusion

Integrated application of silicate fertilizer, well composted organic manures and azolla biofertilizer could be an effective strategy to minimize the use of conventional urea fertilizer, reducing CH₄ emissions, improving soil quality parameters and increasing rice productivity in subtropical countries like Bangladesh.     

Biomass of extramatrical ectomycorrhizal mycelium and fine roots in a young Norway spruce stand — a study using ingrowth bags with different substrates

Background and aims

The partitioning of below ground carbon inputs into roots and extramatrical ectomycorrhizal mycelium (ECM) is crucial for the C cycle in forest soils. Here we studied simultaneously the newly grown biomass of ECM and fine roots in a young Norway spruce stand.

Methods

Ingrowth mesh bags of 16 cm diameter and 12 cm height were placed in the upper soil and left for 12 to 16 months. The 2 mm mesh size allowed the ingrowth of fungal hyphae and roots whereas a 45 μm mesh size allowed only the ingrowth of hyphae. The mesh bags were filled with either EA horizon soil, pure quartz sand or crushed granite. Controls without any ingrowth were established for each substrate by solid tubes (2010) and by 1 μm mesh bags (2011). The fungal biomass in the substrates was estimated by the PLFA 18:2ω6,9 and ECM biomass was calculated as difference between fungal biomass in mesh bags and controls.

Results

The maximum ECM biomass was 438 kg ha^?1 in October 2010 in 2 mm mesh bags with EA substrate, and the minimum was close to zero in 2011 in 45 μm mesh bags with quartz sand. The high P content of the crushed granite did not influence the ECM biomass. Fine root biomass reached a maximum of 2,343 kg ha^?1 in October 2010 in mesh bags with quartz sand after 16 months exposure. In quartz sand and crushed granite, ECM biomass correlated positively with fine root biomass and the number of root tips, and negatively with specific root length.

Conclusion

The ratio of ECM biomass/fine root biomass in October ranged from 0.1 to 0.3 in quartz sand and crushed granite, but from 0.7 to 1.8 in the EA substrate. The results for the EA substrate suggest a large C flux to ECM under field conditions.     

Effect of wildfires on soil respiration in three typical Mediterranean forest ecosystems in Madrid, Spain

Background and Aims

Mediterranean forests are vulnerable to numerous threats including wildfires due to a combination of climatic factors and increased urbanization. In addition, increased temperatures and summer drought lead to increased risk of forest fires as a result of climate change. This may have important consequences for C dynamics and balance in these ecosystems. Soil respiration was measured over 2 successive years in Holm oak (Quercus ilex subsp. ballota; Qi); Pyrenean Oak (Quercus pyrenaica Willd; Qp); and Scots pine (Pinus sylvestris L.; Ps) forest stands located in the area surrounding Madrid (Spain), to assess the long term effects of wildfires on C efflux from the soil, soil properties, and the role of soil temperature and soil moisture in the variation of soil respiration.

Methods

Soil respiration, soil temperature, soil moisture, fine root mass, microbial biomass, biological and chemical soil parameters were compared between non burned (NB) and burned sites (B).

Results

The annual C losses through soil respiration from NB sites in Qi, Qp and Ps were 790, 1010, 1380 gCm^?2?yr^?1, respectively, with the B sites emitting 43 %, 22 % and 11 % less in Qi, Qp and Ps respectively. Soil microclimate changed with higher soil temperature and lower soil moisture in B sites after fire. Exchangeable cations and the pH also decreased. The total SOC stocks were not significantly altered, but 6–8 years after wildfires, there was still measurably lower fine root and microbial biomass, while SOC quality changed, indicated by lower the C/N ratio and the labile carbon and a relative increase in refractory SOC forms, which resulted in lower Q₁₀ values.

Conclusions

We found long term effects of wildfires on the physical, chemical and biological soil characteristics, which in turn affected soil respiration. The response of soil respiration to temperature was controlled by moisture and changed with ecosystem type, season, and between B and NB sites. Lower post-burn Q₁₀ integrated the loss of roots and microbial biomass, change in SOC quality and a decrease in soil moisture.     

Conventional tillage versus cover crops in relation to carbon fixation in Mediterranean olive cultivation

Background and Aims

For croplands, controversy persists concerning the adequacy of the soil use and the management of environmental problems such as soil erosion and fertility in a context of climate change. In this study, we used the RothC model to evaluate the capacity of carbon fixation by the soil in a Mediterranean olive grove for two different scenarios: the land-use change from native vegetation (NV) to conventional tillage (T) in the olive grove, and for the change in soil management from conventional tillage to cover crop (CC).

Methods

In three experimental olive groves in Andalusia (S Spain) two soil-management systems were sampled: T and CC. Areas of NV adjacent to the grove were also sampled as indicative of the initial state of the soil without olive trees. We measured the aboveground biomass production of the cover and the clay content, bulk density, and soil organic carbon (SOC) for 0–5, 5–15 and 15–30 cm depth.

Results

The removal of NV to implement T resulted in a significantly loss of SOC that depended mainly on the relief of the terrain. However, the use of CC increased the SOC because of greater inputs (above-and belowground plant inputs) to the soil. The final concentration at each location was related to the carbon inputs and the clay content. The CC resulted in carbon storage during the first year of 4.02?±?1.65 Mg C ha^?1, and a total carbon fixation by the soil of 5.91?±?2.06 Mg C ha^?1.

Conclusion

The use of cover crops in Mediterranean olive groves proved to be a suitable strategy to increase the carbon storage into the soil and then to decrease the CO₂ concentration in the atmosphere.     

Temporal variation in microbial and plant biomass during summer in a Mediterranean high-mountain dry grassland

Aims

We assessed the temporal changes on microbial biomass in relation to changes in soil moisture, dissolved organic carbon and plant biomass during the summer season in a Mediterranean high-mountain grassland.

Methods

Temporal variations were tested by two-way ANOVA. The relationships among microbial biomass, plant biomass, soil water content, soil organic carbon, dissolved organic carbon and total soil nitrogen during the summer season were assessed by means of structural equation modeling.

Results

Microbial biomass did not show variation, while dissolved organic carbon and root biomass decreased throughout the summer. Aboveground plant biomass peaked in the middle of the summer, when soil water content was at its minimum. Soil water content directly and negatively affected soil microbial biomass, and positively affected dissolved organic carbon. Moreover soil microbial biomass and dissolved organic carbon were negatively related. Plant biomass effects on soil microbial biomass were driven by root biomass, which indirectly affected soil microbial biomass through effects on soil organic carbon and soil nitrogen.

Conclusions

The temporal dynamic of microbial biomass during the summer season appeared to differ from previous observations in temperate alpine communities, and indicated the drought resistance of the microbial community during the summer in Mediterranean high-mountain grasslands. During the dry period, microbial biomass may play an alternative role in soil carbon conservation.     

Root elongation rate is correlated with the length of the bare root apex of maize and lupin roots despite contrasting responses of root growth to compact and dry soils

Background

We investigated interacting effects of matric potential and soil strength on root elongation of maize and lupin, and relations between root elongation rates and the length of bare (hairless) root apex.

Methods

Root elongation rates and the length of bare root apex were determined for maize and lupin seedlings in sandy loam soil of various matric potentials (?0.01 to ?1.6 MPa) and bulk densities (0.9 to 1.5 Mg m^?3).

Results

Root elongation rates slowed with both decreasing matric potential and increasing penetrometer resistance. Root elongation of maize slowed to 10 % of the unimpeded rate when penetrometer resistance increased to 2 MPa, whereas lupin elongated at about 40 % of the unimpeded rate. Maize root elongation rate was more sensitive to changes in matric potential in loosely packed soil (penetrometer resistances <1 MPa) than lupin. Despite these differing responses, root elongation rate of both species was linearly correlated with length of the bare root apex (r² 0.69 to 0.97).

Conclusion

Maize root elongation was more sensitive to changes in matric potential and mechanical impedance than lupin. Robust linear relationships between elongation rate and length of bare apex suggest good potential for estimating root elongation rates for excavated roots.     

Root dynamics of Carex stricta-dominated tussock meadows

Background and aims

The roots of tussock-forming plants contribute to the formation of microtopographic features in many ecosystems, but the dynamics of such roots are poorly understood. We examined the spatial heterogeneity of tussock fine root dynamics to investigate allocation patterns and the role of root productivity in the persistence of tussock structures.

Methods

We compared the spatial variability of fine root (<1 mm, 1–2 mm) density, biomass, % live, allocation, turnover rate (using bomb 14C), and productivity of four Carex stricta Lam.-dominated tussock meadows in the upper Midwest, USA (3 reference, 1 restored site).

Results

Relative to underlying microsites, tussocks were warm, dry, and high in root density, productivity, % live biomass, and turnover. Root productivity averaged 649 g?m^?2 yr^?1 (±208) in reference sites, comprised 57 % (±10) of total net production, and was concentrated in tussocks (70 %?±?4). Root turnover rate averaged 0.63 yr^?1 (±0.08), but tussocks had ~50 % faster root turnover than the underlying soil, and <1 mm roots turned over ~40 % faster than 1–2 mm roots.

Conclusions

Our detailed analysis of the spatial heterogeneity of tussock root dynamics suggests that high allocation and elevated turnover of tussock roots facilitates organic matter accumulation and tussock persistence over time.     

Perennial Grass Bioenergy Cropping on Wet Marginal Land: Impacts on Soil Properties,Soil Organic Carbon,and Biomass During Initial Establishment

The control of soil moisture, vegetation type, and prior land use on soil health parameters of perennial grass cropping systems on marginal lands is not well known. A fallow wetness-prone marginal site in New York (USA) was converted to perennial grass bioenergy feedstock production. Quadruplicate treatments were fallow control, reed canarygrass (Phalaris arundinaceae L. Bellevue) with nitrogen (N) fertilizer (75 kg N ha^?1), switchgrass (Panicum virgatum L. Shawnee), and switchgrass with N fertilizer (75 kg N ha^?1). Based on periodic soil water measurements, permanent sampling locations were assigned to various wetness groups. Surface (0–15 cm) soil organic carbon (SOC), active carbon, wet aggregate stability, pH, total nitrogen (TN), root biomass, and harvested aboveground biomass were measured annually (2011–2014). Multi-year decreases in SOC, wet aggregate stability, and pH followed plowing in 2011. For all years, wettest soils had the greatest SOC and active carbon, while driest soils had the greatest wet aggregate stability and lowest pH. In 2014, wettest soils had significantly (p?<?0.0001) greater SOC and TN than drier soils, and fallow soils had 14 to 20% greater SOC than soils of reed canarygrass + N, switchgrass, and switchgrass + N. Crop type and N fertilization did not result in significant differences in SOC, active carbon, or wet aggregate stability. Cumulative 3-year aboveground biomass yields of driest switchgrass + N soils (18.8 Mg ha^?1) were 121% greater than the three wettest switchgrass (no N) treatments. Overall, soil moisture status must be accounted for when assessing soil dynamics during feedstock establishment.