柠条细根的分布和动态及其与土壤资源有效性的关系

受土壤资源有效性时空异质性的影响,植物细根会表现出明显的垂直分布和季节变化特征。揭示这些特征对认识细根的养分和水分吸收规律,预测C在地下的分配特点具有重要意义。本研究运用Minirhizotron技术对晋西黄土丘陵区30年生柠条（Caragana korshinskii Kom.）人工林0-100cm土层深度范围内细根的密度( FRD, N cm-2)、根长密度( FRLD, mm cm-2)、平均直径(FRDi, mm)和根表面积(FRSA, mm2 cm-2)的垂直分布特征和季节动态进行了一个生长季的观测,并分析了这些参数与土壤温度、水分和有效氮之间的关系。结果表明：(1)FRD、FRLD和FRSA均表现出随土层深度增加而先增大后减小的趋势,以40-60cm土层之值最大(分别占总数的34.3%、35.5%和37.3%);而FRDi随土层深度增加而减小,其最大值为0.31970.0231mm,最小值为0.28840.0109 mm;(2)受土壤资源有效性季节变化的影响,FRD、FRLD和FRSA在不同土层(除0-20cm外)表现出相似的季节动态,即随季节变化而先增大后减小,春季小(分别为0.2204 N cm-2,1.8482 mm cm-2,2.2647 mm2 cm-2)而秋季大(分别为0.5316 N cm-2,4.4046mm cm-2,4.3007mm2 cm-2);FRDi则表现由粗逐渐变细的过程,春季最粗(0.3659mm)而秋季最细(0.2712mm);(3) 各细根参数与土壤温度、水分和有效氮在各土层存在不同程度的相关性。从简单相关分析来看,细根的季节性变化主要受土壤温度和水分的影响,有效氮的影响不明显。FRD、FRLD和FRSA在0-20cm土层主要受土壤水分影响(r=-0.729--0.914, p<0.05),而在20-100cm土层则主要受土壤温度的影响,且显著性随土层加深而增加(r=-0.028-0.832, p<0.05)。各土层细根与土壤有效资源间的相关性反映了细根功能的季节性差异。综合分析表明,各细根参数季节变化的54.0%-98.6%是由土壤温度和水分的交互作用而引起。     

Fine root dynamics along a 2,000-m elevation transect in South Ecuadorian mountain rainforests

Fine root turnover plays an important role in the cycling of carbon and nutrients in ecosystems. Not much is known about fine root dynamics in tropical montane rainforests, which are characterized by steep temperature gradients over short distances. We applied the minirhizotron technique in five forest stands along an elevational transect between 1,050 and 3,060 m above sea level in a South Ecuadorian montane rainforest in order to test the influence of climate and soil parameters on fine root turnover. Turnover of roots with diameter <?2.0 mm was significantly higher in the lowermost and the uppermost stand (0.9 cm cm^?1 year^?1) than in the three mid-elevation stands (0.6 cm cm^?1 year^?1). Root turnover of finest roots (d?<?0.5 mm) was higher compared to the root cohort with d?<?2.0 mm, and exceeded 1.0 cm cm^?1 year^?1 at the lower and upper elevations of the transect. We propose that the non linear altitudinal trend of fine root turnover originates from an overlapping of a temperature effect with other environmental gradients (e.g. adverse soil conditions) in the upper part of the transect and that the fast replacement of fine roots is used as an adaptive mechanism by trees to cope with limiting environmental conditions.     

Comprehensive assessments of root biomass and production in a Kobresia humilis meadow on the Qinghai-Tibetan Plateau

Alpine meadow covers ca. 700,000 km² with an extreme altitude range from 3200 m to 5200 m. It is the most widely distributed vegetation on the vast Qinghai-Tibetan Plateau. Previous studies suggest that meadow ecosystems play the most important role in both uptake and storage of carbon in the plateau. The ecosystem has been considered currently as an active “CO₂ sink”, in which roots may contribute a very important part, because of the large root biomass, for storage and translocation of carbon to soil. To bridge the gap between the potential importance and few experimental data, root systems, root biomass, turnover rate, and net primary production were investigated in a Kobresia humilis meadow on the plateau during the growing season from May to September in 2008 and 2009. We hypothesized that BNPP/NPP of the alpine meadow would be more than 50%, and that small diameter roots sampled in ingrowth cores have a shorter lifespan than the lager diameter roots, moreover we expected that roots in surface soils would turn over more quickly than those in deeper soil layers. The mean root mass in the 0–20 cm soil layer, investigated by the sequential coring method, was 1995?±?479 g?m^?2 and 1595?±?254 g?m^?2 in growing season of 2008 and 2009, respectively. And the mean fine root biomass in ingrowth cores of the same soil layer was 119?±?37 g?m^?2 and 196?±?45 g?m^?2 in the 2 years. Annual total NPP was 12387 kg?ha^?1?year^?1, in which 53% was allocated to roots. In addition, fine roots accounted for 33% of belowground NPP and 18% of the total NPP, respectively. Root turnover rate was 0.52 year^?1 for bulk roots and 0.74 year^?1 for fine roots. Furthermore, roots turnover was faster in surface than in deeper soil layers. The results confirmed the important role of roots in carbon storage and turnover in the alpine meadow ecosystem. It also suggested the necessity of separating fine roots from the whole root system for a better understanding of root turnover rate and its response to environmental factors.     

Variety specific relationships between effects of rhizobacteria on root exudation,growth and nutrient uptake of soybean

Aims

It has been increasingly recognized that only distal lower order roots turn over actively within the <2 mm fine root system of trees. This study aimed to estimate fine root production and turnover rate based on lower order fine roots and their relations to soil variables in mangroves.

Methods

We conducted sequential coring in five natural mangrove forests at Dongzhai Bay, China. Annual fine root production and turnover rate were calculated based on the seasonal variations of the biomass and necromass of lower order roots or the whole fine root system.

Results

Annual fine root production and turnover rate ranged between 571 and 2838 g m^?2 and 1.46–5.96 yr^?1, respectively, estimated with lower order roots, and they were increased by 0–30 % and reduced by 13–48 %, respectively, estimated with the whole fine root system. Annual fine root production was 1–3.5 times higher than aboveground litter production and was positively related to soil carbon, nitrogen and phosphorus concentrations. Fine root turnover rate was negatively related to soil salinity.

Conclusions

Mangrove fine root turnover plays a more important role than aboveground litter production in soil C accumulation. Sites with higher soil nutrients and lower salinity favor fine root production and turnover, and thus favor soil C accumulation.

     

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.     

Relation of fine root distribution to soil C in a Cunninghamia lanceolata plantation in subtropical China

Background and aims

Growth and distribution of fine roots closely depend on soil resource availability and affect soil C distribution in return. Understanding of relationships between fine root distribution and soil C can help to predict the contribution of fine root turnover to soil C accumulation.

Methods

A study was conducted in a subtropical Cunninghamia lanceolata plantation to assess the fine root mass density (FRMD), fine root C density (FRCD) of different fine root groups as well as their relations with soil C.

Results

The FRMD and FRCD of short-lived roots, dead roots and herb roots peaked in the 0–10 cm soil layer and decreased with soil depth, while FRMD, FRCD of long-lived roots peaked in the 10–20 cm soil layer. Soil C was positively related to FRMD and FRCD of total fine roots (across all three soil layers), dead roots (0–10 cm) and herb roots (10–20 cm) as well as FRCD of short-lived roots (20–40 cm) (P <0.05).

Conclusions

Soil C was mainly affected by herb roots in upper soil layers and by woody plant roots in deeper soil layers.     

Biological soil crusts influence carbon release responses following rainfall in a temperate desert,northern China

How soil cover types and rainfall patterns influence carbon (C) release in temperate desert ecosystems has largely been unexplored. We removed intact crusts down to 10 cm from the Shapotou region, China, and measured them in PVC mesocosms, immediately after rainfall. C release rates were measured in soils with four cover types (moss-crusted soil, algae-crusted soil, mixed (composed of moss, algae, and lichen)-crusted soil, and mobile dune sand). We investigated seven different rainfall magnitudes (0–1, 1–2, 2–5, 5–10, 10–15, 15–20, and >20 mm) under natural conditions. C release from all four BSCs increased with increasing rainfall amount. With a rainfall increase from 0 to 45 mm, carbon release amounts increased from 0.13 ± 0.09 to 15.2 ± 1.35 gC m^?2 in moss-crusted soil, 0.08 ± 0.06 to 6.43 ± 1.23 gC m^?2 in algae-crusted soil, 0.11 ± 0.08 to 8.01 ± 0.51 gC m^?2 in mixed-crusted soil, and 0.06 ± 0.04 to 8.47 ± 0.51 gC m^?2 in mobile dune sand, respectively. Immediately following heavy rainfall events (44.9 mm), moss-crusted soils showed significantly higher carbon release rates than algae- and mixed-crusted soils and mobile dune sands, which were 0.95 ± 0.02, 0.30 ± 0.03, 0.13 ± 0.04, and 0.51 ± 0.02 μmol CO₂ m^?2 s^?1, respectively. Changes in rainfall patterns, especially large rain pulses (>10 mm) affect the contributions of different soil cover types to carbon release amounts; moss-crusted soils sustain higher respiration rates than other biological crusts after short-term extreme rainfall events.     

Estimating the organic carbon stabilisation capacity and saturation deficit of soils: a New Zealand case study

The capacity of a soil to sequester organic carbon can, in theory, be estimated as the difference between the existing soil organic C (SOC) concentration and the SOC saturation value. The C saturation concept assumes that each soil has a maximum SOC storage capacity, which is primarily determined by the characteristics of the fine mineral fraction (i.e. <20 µm clay + fine silt fraction). Previous studies have focussed on the mass of fine fractions as a predictor of soil C stabilisation capacity. Our objective was to compare single- and multi-variable statistical approaches for estimating the upper limit of C stabilisation based on measureable properties of the fine mineral fraction [e.g. fine fraction mass and surface area (SA), aluminium (Al), iron (Fe), pH] using data from New Zealand’s National Soils Database. Total SOC ranged from 0.65 to 138 mg C g^?1, median values being 44.4 mg C g^?1 at 0–15 cm depth and 20.5 mg C g^?1 at 15–30 cm depth. Results showed that SA of mineral particles was more closely correlated with the SOC content of the fine fraction than was the mass proportion of the fine fraction, indicating that it provided a much better basis for estimating SOC stabilisation capacity. The maximum C loading rate (mg C m^?2) for both Allophanic and non-Allophanic soils was best described by a log/log relationship between specific SA and the SOC content of the fine fraction. A multi-variate regression that included extractable Al and soil pH along with SA provided the “best fit” model for predicting SOC stabilisation. The potential to store additional SOC (i.e. saturation deficit) was estimated from this multivariate equation as the difference between the median and 90th percentile SOC content of each soil. There was strong evidence from the predicted saturation deficit values and their associated 95 % confidence limits that nearly all soils had a saturation deficit >0. The median saturation deficit for both Allophanic and non-Allophanic soils was 12 mg C g^?1 at 0–15 cm depth and 15 mg C g^?1 at 15–30 cm depths. Improving predictions of the saturation deficit of soils may be important to developing and deploying effective SOC sequestration strategies.     

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.     

Phenotypic plasticity of the coarse root system of Prosopis flexuosa, a phreatophyte tree, in the Monte Desert (Argentina)

Prosopis flexuosa trees in the Monte Desert grow in dune and inter-dune valleys, where the water table is located at 6–14 m depth. We asked whether trees in the dunes, which are less likely to access the water table, present a coarse surface root architecture that might favor the exploration / exploitation of dune resources, compensating for water table inaccessibility. We characterized the architecture of surface roots of valley and dune trees, together with the soil environment. The dune held 50 % less and deeper gravimetric soil water (along a 4 m profile), 3-times less organic matter, 2-times less available phosphorous, and a sharper contrast of ammonium and nitrate concentration between plant canopies and uncovered soil than the valley. Coarse surface roots of dune trees were highly branched and grew tortuously at 0.56?±?0.16 m depth before sinking downward near the tree crown, suggesting an intensive exploitation of the ephemeral, deep, and canopy-linked resources. In contrast, trees from the valley spread their profuse and less branched surface roots mainly horizontally at 0.26?±?0.08 m depth, several meters outside the crown probably exploring this resource-rich site. A model for the environmental control of root architecture together with potential ecological effects is discussed.     

Nutrient resorption responses to water and nitrogen amendment in semi-arid grassland of Inner Mongolia, China

Litterfall and fine root production is a major pathway for carbon and nutrient cycling in forest ecosystems. We investigated leaf litterfall, fine-root mass, production and turnover rate in the upper soil (0–30 cm) under four major tree species (Leucaena leucocephala, Acacia nilotica, Azadirachta indica, Prosopis juliflora) of the semi-arid region of India. All the four tree species showed an unimodal peak of leaf litterfall with distinct seasonality. Leucaena leucocephala and Acacia nilotica had maximum leaf litterfall between September and December while Azadirachta indica and Prosopis juliflora shed most of their leaves between February and May. Annual leaf litterfall of the four species ranged from 3.3 Mg ha^?1 (Leucaena leucocephala) to 8.1 Mg ha^?1 (Prosopis juliflora). Marked seasonal variations in amount of fine root biomass were observed in all the four tree species. Fine root production was maximum in Prosopis juliflora (171 g m^?2 y^?1) followed by Azadirachta indica (169 g m^?2 y^?1), Acacia nilotica (106 g m^?2 y^?1) and Leucaena leucocephala (79 g m^?2 y^?1). Fine root biomass showed a seasonal peak after the rainy season but fell to its lowest value during the winter and dry summer season. Fine root turnover rate ranged from 0.56 to 0.97 y^?1 and followed the order Azadirachta indica > Leucaena leucocephala > Prosopis juliflora > Acacia nilotica. The results of this study demonstrated that Prosopis juliflora and Azadirachta indica had greater capability for maintaining site productivity as evidenced from greater leaf litterfall and fine root production.     

Root morphology and architecture respond to N addition in Pinus tabuliformis, west China

Belowground dynamics of terrestrial ecosystems are responding to global increases in anthropogenic N deposition with important consequences for productivity and ecosystem health. We compared root characteristics across five root orders in Pinus tabuliformis plantations treated for 3 years to a gradient of N addition (0–15 g m^?2 year^?1). In reference plots, the roots of P. tabuliformis were finer and with higher specific root length than reported for other pine species, suggesting severe N limitation. Addition of N resulted in slightly reduced fine root biomass and significant changes in root morphology, responses that were associated primarily with first and second order roots. In particular, root number, cumulative root length, individual root length, and specific root length all declined with increasing N addition for first and second order roots, with most of the responses elicited at <9 g m^?2 year^?1 N addition. These responses (1) support the concept of ephemeral root modules consisting of first and second orders and (2) are consistent with a change in functional demand from uptake to transport with increasing soil resource availability. Traditionally, fine roots have been identified by a somewhat arbitrary diameter cut-off (e.g., 1 or 2 mm); as an index of fine root function, diameter would fail to reveal most of the functional response.     

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.     

Embedded rock fragments affect alpine steppe plant growth,soil carbon and nitrogen in the northern Tibetan Plateau

Background and Aims

Rock fragments within topsoil have important effects on soil properties and plant growth. This study mainly aimed to investigate the relationships between rock fragments, soil carbon (C) and nitrogen (N) densities and vegetation biomass in an alpine steppe.

Methods

Rock fragments, plant and soil samples were collected from four topographic positions (top, upper, lower, and bottom) on a hillslope.

Results

Volumetric rock fragment content within the 0–30 cm soil profile varied from 17.8 to 30.5%, the upper position value was significantly greater (P < 0.05) than those at other positions. The highest aboveground biomass was observed at the lower position (921 kg ha^?1), while the highest belowground biomass within the 0–30 cm profile was found at the upper position (4460 kg ha^?1). More fine earth and plant litter input accompanied by lower C and N losses induced by rainfall erosion resulted in higher soil organic C and total N densities (28.6 Mg C ha^?1 and 2.87 Mg N ha^?1) at the lower position.

Conclusions

Rock fragments may promote root growth but limit aboveground biomass production, and can therefore change the biomass distribution pattern. Our findings provide more evidence for scientifically assessing alpine steppe productivity.

     

Fine Root Morphology,Biochemistry and Litter Quality Indices of Fast- and Slow-growing Woody Species in Ethiopian Highland Forest

Fine root turnover of trees is a major C input to soil. However, the quality of litter input is influenced by root morphological traits and tissue chemical composition. In this study, fine roots of ten tropical woody species were collected from an Afromontane forest in the northern highlands of Ethiopia. The fine roots were analysed for root morphological traits and tissue chemistry measured as proxy carbon fractionations. Based on stem increment, the 10 species were divided into faster- and slower-growing species. Faster-growing species exhibited higher specific root length (1362 cm g^?1) than slower-growing species (923 cm g^?1). Similarly specific root area was higher in faster-growing species (223 cm² g^?1) than in slower-growing species (167 cm² g^?1). Among the carbon fractions, the acid-insoluble fraction (AIF) was the highest (44–51%). The carbon content, AIF, and the lignocellulose index were higher for slower-growing species. Root tissue density was lower in faster-growing species (0.33 g cm^?3) than slower-growing species (0.40 g cm^?3) and showed a strong positive correlation with carbon content (r ² = 0.84) and the AIF (r _pearson = 0.93). The morphological traits of fine roots between faster- and slower-growing species reflect the ecological strategy they employ. Slower-growing species have a higher tissue density which may reflect a greater longevity.     

Effect of aboveground intervention on fine root mass, production, and turnover rate in a Chinese cork oak (Quercus variabilis Blume) forest

Aims

Fine root is an important part of the forest carbon cycle. The growth of fine roots is usually affected by forest intervention. This study aims to investigate the fine root mass, production, and turnover in the disturbed forest.

Methods

The seasonal and vertical distributions of fine root (diameter ≤2 mm) were measured in a Chinese cork oak (Quercus variabilis Blume) forest. The biomass and necromass of roots with diameters ≤1 mm and 1-2 mm in 0-40 cm soil profiles were sampled by using a sequential soil coring method in the stands after clear cutting for 3 years, with the stands of the remaining intact trees as the control.

Results

The fine root biomass (FRB) and fine root necromass (FRN) varied during the growing season and reached their peak in August. Lower FRB and higher FRN were found in the clear cutting stands. The ratio between FRN and FRB increased after forest clear cutting compared with the control and was the highest in June. The root mass with diameter ≤1 mm was affected proportionately more than that of diameter 1-2 mm root. Clear cutting reduced FRB and increased FRN of roots both ≤1 mm and 1-2 mm in diameter along the soil depths. Compared with the control, the annual fine root production and the average turnover rate decreased by 30.7 % and 20.7 %, respectively, after clear cutting for 3 years. The decline of canopy cover contributed to the dramatic fluctuation of soil temperature and moisture from April to October. With redundancy discriminate analysis (RDA) analysis, the first axis was explained by soil temperature (positive) and moisture (negative) in the control stands. Aboveground stand structure, including canopy cover, sprout height, and basal area, influenced FRB and FRN primarily after forest clear cutting.

Conclusions

This study suggested that the reduction of fine root biomass, production, and turnover rate can be attributed to the complex changes that occur after forest intervention, including canopy damage, increased soil temperature, and degressive soil moisture.     

Fine root production in three zones of secondary mangrove forest in eastern Thailand

Key message

High root productions, especially in the fine roots, estimated by ingrowth cores were confirmed in mangrove forests. The zonal variation in root production was caused by inundation regime and soil temperature.

Abstract

Mangrove forests have high net primary productivity (NPP), and it is well known that these trees allocate high amounts of biomass to their root systems. In particular, fine root production (FRP) comprises a large component of the NPP. However, information on root production remains scarce. We studied FRP in three zones (Avicennia, Rhizophora, and Xylocarpus) of a mangrove forest in eastern Thailand using ingrowth cores (0–30 cm of soil depth). The root biomass and necromass were periodically harvested from the cores and weighed during the one-year study. The FRP was determined by summation of the fine root biomass (FRB) and root necromass. The results showed that the FRB clearly increased in the wet and cool dry seasons. Magnitude of FRB in the Rhizophora and Xylocarpus zones was 1171.07 and 764.23 g/m²/30 cm, respectively. The lowest FRB (292.74 g/m²/30 cm) was recorded in the Avicennia zone locating on the river edge where there is a greater frequency of inundation than the other zones. Root necromass was high in the Rhizophora and Xylocarpus zones, and accumulated noticeably when soil temperatures rapidly declined during the middle of the wet season to cool dry season. However, root necromass in the Avicennia zone varied within a small range. We attributed the small accumulation of root necromass in the Avicennia zone to the relative high soil temperature that likely caused a high root decomposition rate. The average FRP (3.403–4.079 ton/ha/year) accounted for 74.4, 81.5, and 92.4 % of the total root production in the Avicennia, Rhizophora, and Xylocarpus zone, respectively. The root production and causative factors (i.e., soil temperature and inundation regime) are discussed in relation to the carbon cycle of a mangrove forest.

     

Standing fine root mass and production in four Chinese subtropical forests along a succession and species diversity gradient

Background and aims

The influences of succession and species diversity on fine root production are not well known in forests. This study aimed to investigate: (i) whether fine root biomass and production increased with successional stage and increasing tree species diversity; (ii) how forest type affected seasonal variation and regrowth of fine roots.

Methods

Sequential coring and ingrowth core methods were used to measure fine root production in four Chinese subtropical forests differing in successional stages and species diversity.

Results

Fine root biomass increased from 262 g·m^?2 to 626 g·m^?2 with increasing successional stage and species diversity. A similar trend was also found for fine root production, which increased from 86 to 114 g·m^?2 yr ^?1 for Cunninghamia lanceolata plantation to 211–240 g·m^?2 yr ^?1 for Choerospondias axillaries forest when estimated with sequential coring data. Fine root production calculated using the ingrowth core data ranged from 186 g·m^?2 yr ^?1 for C. lanceolata plantation to 513 g·m^?2 yr ^?1 for Lithocarpus glaber – Cyclobalanopsis glauca forest.

Conclusions

Fine root biomass and production increased along a successional gradient and increasing tree species diversity in subtropical forests. Fine roots in forests with higher species diversity exhibited higher seasonal variation and regrowth rate.     

Root and shoot growth, seed composition, and yield components of no-till rainfed soybean under variable potassium

Spatial soil-K availability for no-till soybean [Glycine max (L.) Merr.] has not been studied extensively. We characterize soybean growth- and yield-component and quantify root parameters as a function of soil depth in K-stratified soils with 1 M ammonium acetate extractable-K ranges 60–290 at 0–10 cm increment and 50–90 mg kg^?1 at the 10–20 cm increment. Shoots and roots (five depth increments to 50 cm) were collected during development and grain at harvest during 2 years. Soil K at or above the critical level (104 mg K kg^?1) increased early-season leaf area and root K-uptake rates early and late in reproductive development. Greater number of seeds plant^?1 increased yield for soils with K near the critical level. Soil-K above the critical level increased luxury K-uptake without improving yield, seed-K concentration and accumulation, or seed oil and protein concentration. Greater root length density (>41% of the total) in surface soil coupled with previous results showing greater water content throughout the season in surface soil compared to deeper layers illustrates K stratification caused by no-till may enhance soybean K-uptake.     

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.