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1.
Seasonal dynamics of fine root biomass, root length density, specific root length, and soil resource availability in a Larix gmelinii plantation 总被引:1,自引:0,他引:1
Cheng Yunhuan Han Youzhi Wang Qingcheng Wang Zhengquan 《Frontiers of Biology in China》2006,1(3):310-317
Fine root turnover is a major pathway for carbon and nutrient cycling in terrestrial ecosystems and is most likely sensitive
to many global change factors. Despite the importance of fine root turnover in plant C allocation and nutrient cycling dynamics
and the tremendous research efforts in the past, our understanding of it remains limited. This is because the dynamics processes
associated with soil resources availability are still poorly understood. Soil moisture, temperature, and available nitrogen
are the most important soil characteristics that impact fine root growth and mortality at both the individual root branch
and at the ecosystem level. In temperate forest ecosystems, seasonal changes of soil resource availability will alter the
pattern of carbon allocation to belowground. Therefore, fine root biomass, root length density (RLD) and specific root length
(SRL) vary during the growing season. Studying seasonal changes of fine root biomass, RLD, and SRL associated with soil resource
availability will help us understand the mechanistic controls of carbon to fine root longevity and turnover. The objective
of this study was to understand whether seasonal variations of fine root biomass, RLD and SRL were associated with soil resource
availability, such as moisture, temperature, and nitrogen, and to understand how these soil components impact fine root dynamics
in Larix gmelinii plantation. We used a soil coring method to obtain fine root samples (⩽2 mm in diameter) every month from May to October
in 2002 from a 17-year-old L. gmelinii plantation in Maoershan Experiment Station, Northeast Forestry University, China. Seventy-two soil cores (inside diameter
60 mm; depth intervals: 0–10 cm, 10–20 cm, 20–30 cm) were sampled randomly from three replicates 25 m × 30 m plots to estimate
fine root biomass (live and dead), and calculate RLD and SRL. Soil moisture, temperature, and nitrogen (ammonia and nitrates)
at three depth intervals were also analyzed in these plots. Results showed that the average standing fine root biomass (live
and dead) was 189.1 g·m−2·a−1, 50% (95.4 g·m−2·a−1) in the surface soil layer (0–10 cm), 33% (61.5 g·m−2·a−1), 17% (32.2 g·m−2·a−1) in the middle (10–20 cm) and deep layer (20–30cm), respectively. Live and dead fine root biomass was the highest from May
to July and in September, but lower in August and October. The live fine root biomass decreased and dead biomass increased
during the growing season. Mean RLD (7,411.56 m·m−3·a−1) and SRL (10.83 m·g−1·a−1) in the surface layer were higher than RLD (1 474.68 m·m−3·a−1) and SRL (8.56 m·g−1·a−1) in the deep soil layer. RLD and SRL in May were the highest (10 621.45 m·m−3 and 14.83m·g−1) compared with those in the other months, and RLD was the lowest in September (2 198.20 m·m−3) and SRL in October (3.77 m·g−1). Seasonal dynamics of fine root biomass, RLD, and SRL showed a close relationship with changes in soil moisture, temperature,
and nitrogen availability. To a lesser extent, the temperature could be determined by regression analysis. Fine roots in the
upper soil layer have a function of absorbing moisture and nutrients, while the main function of deeper soil may be moisture
uptake rather than nutrient acquisition. Therefore, carbon allocation to roots in the upper soil layer and deeper soil layer
was different. Multiple regression analysis showed that variation in soil resource availability could explain 71–73% of the
seasonal variation of RLD and SRL and 58% of the variation in fine root biomass. These results suggested a greater metabolic
activity of fine roots living in soil with higher resource availability, which resulted in an increased allocation of carbohydrate
to these roots, but a lower allocation of carbohydrate to those in soil with lower resource availability.
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Translated from Acta Phytoecologica Sinica, 2005, 29(3): 403–410 [译自: 植物生态学报, 2005, 29(3): 403–410] 相似文献
2.
为了阐明根区交替控制灌溉(CRDAI)条件下玉米根系吸水规律,通过田间试验,在沟灌垄植模式下采用根区交替控制灌溉研究玉米根区不同点位(沟位、坡位和垄位)的根长密度(RLD)及根系吸水动态。研究表明,根区土壤水分的干湿交替引起玉米RLD的空间动态变化,在垄位两侧不对称分布,并存在层间差异;土壤水分和RLD是根区交替控制灌溉下根系吸水速率的主要限制因素。在同一土层,根系吸水贡献率以垄位最大,沟位最低;玉米营养生长阶段,10—30 cm土层的根系吸水速率最大;玉米生殖生长阶段,20—70 cm为根系吸水速率最大的土层,根系吸水贡献率为43.21%—55.48%。研究阐明了交替控制灌溉下根系吸水与土壤水分、RLD间相互作用的动态规律,对控制灌溉下水分调控机理研究具有理论意义。 相似文献
3.
The Vertical Pattern of Rooting and Nutrient Uptake at Different Altitudes of a South Ecuadorian Montane Forest 总被引:1,自引:1,他引:0
The vertical pattern of root length densities (RLD) of fine roots (<2 mm in diameter) and nitrogen (N) uptake potential were determined at different altitudes (1,900, 2,400, and 3,000 m a.s.l.) of a tropical montane forest in order to improve our knowledge about the depth distribution of nutrient uptake in this ecosystem. At higher altitudes, precipitation rate and frequency of fog were higher than at lower altitudes while mean annual air temperature decreased with increasing altitude. Soils were always very acid with significantly lower pH at a depth of 0.0–0.3 m in mineral soil at 3,000 m (2.8–2.9) than at 1,900 and 2,400 m (3.1–3.5). The vertical distribution of RLD was very similar both during the dry and the rainy season. During the dry season the percentage of root length in the organic layer increased from 51% at 1,900 m to 61% at 2,400 m and 76% at 3,000 m. At 3,000 m, RLD was markedly higher in the upper 0.05 m than in the remaining organic layer, whereas at 1,900 m and 2,400 m RLD were similar in all depths of the organic layer. In mineral soil, RLD decreased to a greater degree with increasing soil depth at the upper two study sites than at 1,900 m. The relative N uptake potential from different soil layers (RNUP) was determined by 15N enrichment of leaves after application of 15N enriched ammonium sulphate at various soil depths. RNUP closely followed fine root distribution confirming the shallower pattern of nutrient uptake at higher altitudes. RNUP was very similar for trees, shrubs and herbs, but shallower for saplings which obtained N only from the organic layer at both altitudes. Liming and fertilizing (N, P, K, Mg) of small patches in mineral soil had no significant impact on fine root growth. We conclude that the more superficial nutrient uptake ability at higher altitudes may be partly related to increased nutrient input from canopy by leaching. However, the specific constraints for root growth in the mineral soil of tropical montane forests warrant further investigations. 相似文献
4.
A Dehesa is a structurally complex agro-silvo-pastoral system where at least two strata of vegetation, trees and herbaceous
plants coexist. We studied the root distribution of trees (Quercus ilex L.) and herbaceous plants, in order to evaluate tree and crops competition and complementarity in Dehesas of Central Western
Spain. 72 soil cores of 10 cm diameter (one to two metre deep) were taken out around 13 trees. Seven trees were intercropped
with Avena sativa L. and six trees were in a grazed pasture dominated by native grasses. Soil coring was performed at four distances from the
tree trunks, from 2.5 (beneath canopy) till 20 m (out of the canopy). Root length density (RLD) of herbaceous plants and trees
was measured using the soil core-break method. Additionally, we mapped tree roots in 51 profiles of 7 recently opened road
cuts, located between 4 and 26 m of distance from the nearest tree. The depth of the road cuts varied between 2.5 and 5.5 m.
Herbaceous plant roots were located mostly in the upper 30 cm, above a clayey, dense soil layer. RLD of herbaceous plants
decreased exponentially with depth until 100 cm depth. Holm-oak showed a much lower RLD than herbs (on average, 2.4 versus 23.7 km m−3, respectively, in the first 10 cm of the soil depth). Tree RLD was surprisingly almost uniform with depth and distance to
trees. We estimated a 5.2 m maximum depth and a 33 m maximum horizontal extension for tree roots. The huge surface of soil
explored by tree roots (even 7 times the projection of the canopy) could allow trees to meet their water needs during the
dry Mediterranean summers. The limited vertical overlap of the two root profiles suggests that competition for soil resources
between trees and the herbaceous understorey in the Dehesa is probably not as strong as usually assumed. 相似文献
5.
Summary In 1982 and 1983 root samples were taken by auger from potato crops grown on marine clay in the Flevo-Polder. The roots increased
their penetration depth throughout the periods of measurement, and ultimately reached depths between 80 cm and 100 cm below
the hills. Between 50 and 60 days after emergence, decay of roots commenced, starting in the upper horizons. In the hill mean
root length densities varied between 1 and 2 cm cm−3. Below the hills root density rarely exceeded 1 cm cm−3. The random variation in root density was equivalent to a coefficient of variation of 50%. There were significant effects
of the position of sampling (relative to the centre of the plant) on root density; densities were usually lowest beneath the
furrow. Depending on season and sampling date, total root length varied between 3.4 and 7.1 km m−2, and root dry mass varied between 33 and 77 g m−2. Representative figures for specific root length were 100–120 m g−1 dry weight. About 90% of the root diameters were smaller than 0.44 mm; the most frequent class (35%) were roots with diameters
between 0.12 and 0.20 mm. 相似文献
6.
Traits associated with improved P-uptake efficiency in CIMMYT's semidwarf spring bread wheat grown on an acid Andisol in Mexico 总被引:2,自引:1,他引:1
Manske G.G.B. Ortiz-Monasterio J.I. Van Ginkel M. González R.M. Rajaram S. Molina E. Vlek P.L.G. 《Plant and Soil》2000,221(2):189-204
Phosphorus deficiency is a major yield limiting constraint in wheat cultivation on acid soils. The plant factors that influence
P uptake efficiency (PUPE) are mainly associated with root characteristics. This study was conducted to analyze the genotypic
differences and relationships between PUPE, root length density (RLD), colonization by vesicular arbuscular and arbuscular
mycorrhizal (V)AM fungi and root excretion of phosphatases in a P-deficient Andisol in the Central Mexican Highlands. Forty-two
semidwarf spring-bread-wheat (Triticum aestivumL.) genotypes from CIMMYT were grown without (−P) and with P fertilization (+P), and subsequently in subsets of 30 and 22
genotypes in replicated field trials over 2 and 3 years, respectively. Acid phosphatase activity at the root surface (APASE)
was analyzed in accompanying greenhouse experiments in nutrient solution. In this environment, PUPE contributed more than
P utilization efficiency, in one experiment almost completely, to the variation of grain yield among genotypes. Late-flowering
genotypes were higher yielding, because the postanthesis period of wheat was extended due to the cold weather at the end of
the crop cycles, and postanthesis P uptake accounted for 40–45% of total P uptake. PUPE was positively correlated with the
numbers of days to anthesis (at −P r=0.57 and at +P r=0.73). The RLD in the upper soil layer (0–20 cm) of the wheat germplasm
tested ranged from 0.5 to 2.4 cm cm-3 at –P and 0.7 to 7.7 at +P. RLD was the most important root trait for improved P absorption, and it was positively genetically
correlated with PUPE (at –P r=0.42 and at +P r=0.63) and the number of spikes m-2 (at –P r=0.58 and at +P r=0.36). RLD in the upper soil layer was more important with P fertilizer application. Without P
fertilization, root proliferation in the deeper soil profile secured access to residual, native P in the deeper soil layer.
(V)AM-colonisation and APASE were to a lesser degree correlated with PUPE. Among genoptypes, the level of (V)AM-colonisation
ranged from 14 to 32% of the RLD in the upper soil layer, and APASE from 0.5 to 1.1 nmol s-1 plant-1 10-2.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
7.
On-line screening of soil VOCs exchange responses to moisture, temperature and root presence 总被引:1,自引:0,他引:1
The exchanges of volatile organic compounds (VOCs) between soils and the atmosphere are poorly known. We investigated VOC
exchange rates and how they were influenced by soil moisture, temperature and the presence of plant roots in a Mediterranean
forest soil. We measured VOC exchange rates along a soil moisture gradient (5%–12.5%–20%–27.5% v/v) and a temperature gradient
(10°C–15°C–25°C–35°C) using PTR-MS. Monoterpenes were identified with GC-MS. Soils were a sink rather than a source of VOCs
in both soil moisture and temperature treatments (−2.16 ± 0.35 nmol m−2 s−1 and −4.90 ± 1.24 nmol m−2 s−1 respectively). Most compounds observed were oxygenated VOCs like alcohols, aldehydes and ketones and aromatic hydrocarbons.
Other volatiles such as acetic acid and ethyl acetate were also observed. All those compounds had very low exchange rates
(maximum uptake rates from −0.8 nmol m−2 s−1 to −0.6 nmol m−2 s−1 for methanol and acetic acid). Monoterpene exchange ranged only from −0.004 nmol m−2 s−1 to 0.004 nmol m−2 s−1 and limonene and α-pinene were the most abundant compounds. Increasing soil moisture resulted in higher soil sink activity
possibly due to increases in microbial VOCs uptake activity. No general pattern of response was found in the temperature gradient
for total VOCs. Roots decreased the emission of many compounds under increasing soil moisture and under increasing soil temperature.
While our results showed that emission of some soil VOCs might be enhanced by the increases in soil temperature and that the
uptake of most soil VOCs uptake might be reduced by the decreases of soil water availability, the low exchange rates measured
indicated that soil-atmosphere VOC exchange in this system are unlikely to play an important role in atmospheric chemistry.
Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
8.
树木细根在森林生态系统C和养分循环中具有重要的作用。由于温带土壤资源有效性具有明显的季节变化, 导致细根生物量、根长密度 (Rootlengthdensity, RLD) 和比根长 (Specificrootlength, SRL) 的季节性变化。以 17年生落叶松 (Larixgmelini) 人工林为研究对象, 采用根钻法从 5月到 10月连续取样, 研究了不同土层细根 (直径≤ 2mm) 生物量、RLD和SRL的季节动态, 以及这些根系指标动态与土壤水分、温度和N有效性的关系。结果表明 :1) 落叶松细根年平均生物量 (活根 +死根 ) 为 189.1g·m-2 ·a-1, 其中 5 0 %分布在表层 (0~ 10cm), 33%分布在亚表层 (11~ 2 0cm), 17%分布在底层 (2 1~ 30cm) 。活根和死根生物量在 5~ 7月以及 9月较高, 8月和 10月较低。从春季 (5月 ) 到秋季 (10月 ), 随着活细根生物量的减少, 死细根生物量增加 ;2 ) 土壤表层 (0~ 10cm) 具有较高的RLD和SRL, 而底层 (2 1~ 30cm) 最低。春季 (5月 ) 总RLD和SRL最高, 分别为 10 6 2 1.4 5m·m-3 和 14.83m·g-1, 到秋季 (9月 ) 树木生长结束后达到最低值, 分别为 2 198.2 0m·m-3 和 3.77m·g-1;3) 细根生物量、RLD和SRL与土壤水分、温度和有效N存在不同程度的相关性。从单因子分析来看, 土壤水分和有效N对细根的影响明显大于温度, 对活根的影响大于死根。由于土壤资源有效性的季节变化, 使得C的地下分配格局发生改变。各土层细根与有效性资源之间的相关性反映了细根功能季节性差异。细根 (生物量、RLD和SRL) 的季节动态 (5 8%~ 73%的变异 ) 主要由土壤资源有效性的季节变化引起。 相似文献
9.
Mizue Ohashi Tomo’omi Kumagai Tomonori Kume Koichiro Gyokusen Taku M. Saitoh Masakazu Suzuki 《Biogeochemistry》2008,90(3):275-289
Although soil carbon dioxide (CO2) efflux from tropical forests may play an important role in global carbon (C) balance, our knowledge of the fluctuations
and factors controlling soil CO2 efflux in the Asian tropics is still poor. This study characterizes the temporal and spatial variability in soil CO2 efflux in relation to temperature/moisture content and estimates annual efflux from the forest floor in an aseasonal intact
tropical rainforest in Sarawak, Malaysia. Soil CO2 efflux varied widely in space; the range of variation averaged 17.4 μmol m−2 s−1 in total. While most CO2 flux rates were under 10 μmol m−2 s−1, exceptionally high fluxes were observed sporadically at several sampling points. Semivariogram analysis revealed little
spatial dependence in soil CO2 efflux. Temperature explained nearly half of the spatial heterogeneity, but the effect varied with time. Seasonal variation
in CO2 efflux had no fixed pattern, but was significantly correlated with soil moisture content. The correlation coefficient with
soil moisture content (SMC) at 30 and 60 cm depth was higher than at 10 cm depths. The annual soil CO2 efflux, estimated from the relationship between CO2 efflux and SMC at 30 cm depth, was 165 mol m−2 year−1 (1,986 g C m−2 year−1). As this area is known to suffer severe drought every 4–5 years caused by the El Nino-Southern Oscillation, the results
suggest that an unpredictable dry period might affect soil CO2 efflux, leading an annual variation in soil C balance. 相似文献
10.
Root growth,macro-nutrient uptake dynamics and soil fertility requirements of a high-yielding winter oilseed rape crop 总被引:2,自引:0,他引:2
P. B. Barraclough 《Plant and Soil》1989,119(1):59-70
Shoot growth, root growth and macro-nutrient uptake by a high-yielding (5t/ha grain) winter oilseed rape crop have been measured.
Maximum rooting density in the top 20cm of soil was 9.4 cm cm−3 and roots reached a depth of at least 1.8 m. Maximum nutrient uptakes were 364 kg ha−1 for N, 43 kg ha−1 for P, 308 kg ha−1 for K, 287 kg ha−1 for Ca and 16 kg ha−1 for Mg. A 30-day drought coincided with the flowering period and root and shoot growth, as well as nutrient uptake rates,
were reduced. Nutrient concentrations in the soil solution necessary to sustain the nutrient fluxes into the root system by
diffusive supply have been calculated. Peak values were in the range 10 μM for P to 87 μM for N, lower than the observed concentrations, and it was concluded that nutrient transport to roots was not a limitation
to uptake by this rape crop. 相似文献
11.
Root characteristics of representative Mediterranean plant species and their erosion-reducing potential during concentrated runoff 总被引:7,自引:1,他引:6
Gully erosion is an important soil degradation process in Mediterranean environments. Revegetation strategies for erosion
control rely in most cases on the effects of the above-ground biomass on reducing water erosion rates, whereas the role of
the below-ground biomass is often neglected. In a Mediterranean context, the above-ground biomass can temporally disappear
because of fire or overgrazing and when concentrated flow erosion occurs, roots can play an important role in controlling
soil erosion rates. Unfortunately, information on root characteristics of Mediterranean plants, growing on semi-natural lands,
and their effects on the topsoil resistance to concentrated flow erosion is lacking. Therefore, typical Mediterranean grass,
herb, reed, shrub and tree root systems of plants growing in habitats that are prone to concentrated flow erosion (i.e. in
ephemeral channels, abandoned fields and steep badland slopes) are examined and their erosion-reducing potential was evaluated.
Root density (RD), root length density (RLD) and root diameters are measured for 26 typical Mediterranean plant species. RD
values and root diameter distribution within the upper 0.10–0.90 m of the soil profile are then transformed into relative
soil detachment rates using an empirical relationship in order to predict the erosion-reducing effect of root systems during
concentrated runoff. Comparing the erosion-reducing potential of different plant species allows ranking them according to
their effectiveness in preventing or reducing soil erosion rates by concentrated flow. RD in the 0.10 m thick topsoil ranges
between 0.13 kg m−3 for Bromus rubens (L.) and 19.77 kg m−3 for Lygeum spartum (L.), whereas RLD ranges between 0.01 km m−3 for Nerium oleander (L.) and 120.43 km m−3 for Avenula bromoides ((Gouan) H. Scholz.) Relative soil detachment rates, compared to bare soils, range between 0.3 × 10-12 and 0.7 for the 0.10 m thick topsoil. The results show that grasses such as Helictotrichon filifolium ((Lag.) Henrard), Piptatherum miliaceum ((L.) Coss.), Juncus acutus (L.), Avenula bromoides ((Gouan) H. Scholz), Lygeum spartum (L.) and Brachypodium retusum ((Pers.) Beauv.) have the highest potential to reduce soil erosion rates by concentrated flow in the 0–0.1 m topsoil. But
also shrubs such as Anthyllis cytisoides (L.) and Tamarix canariensis (Willd.), having high root densities in the topsoil, can reduce erosion rates drastically. Among the species growing in channels,
Juncus acutus (L.) has the highest erosion reducing potential, whereas Phragmites australis (Cav.) is the least effective. On abandoned fields, Avenula bromoides ((Gouan) H. Scholz) and Plantago albicans (L.) are the most effective species in reducing concentrated flow erosion rates, while Thymelaea hirsuta (L. (Endl.)) and Bromus rubens (L.) perform the worst. On steep badland slopes, Helictotrichon filifolium ((Lag.) Henrard) and Anthyllis cytisoides (L.) perform the best in the analysis of erosion reducing potential, while Ononis tridentata (L.) is the least effective species. These findings have implications for ecological restoration and management of erosion-prone
slopes. 相似文献
12.
Root Respiration,Photosynthesis and Grain Yield of Two Spring Wheat in Response to Soil Drying 总被引:3,自引:0,他引:3
The effects of soil water regime and wheat cultivar, differing in drought tolerance with respect to root respiration and grain
yield, were investigated in a greenhouse experiment. Two spring wheat (Triticum aestivum) cultivars, a drought sensitive (Longchun 8139-2) and drought tolerant (Dingxi 24) were grown in PVC tubes (120 cm in length and 10 cm in diameter) under an automatic rain-shelter. Plants were subjected
to three soil moisture regimes: (1) well-watered control (85% field water capacity, FWC); (2) moderate drought stress (50%
FWC) and (3) severe drought stress (30% FWC). The aim was to study the influence of root respiration on grain yield under
soil drying conditions. In the experiment, severe drought stress significantly (p < 0.05) reduced shoot and root biomass, photosynthesis and root respiration rate for both cultivars, but the extent of the
decreases was greater for Dingxi 24 compared to that for Longchun 8139-2. Compared with Dingxi 24, 0.04 and 0.07 mg glucose m−2 s−1 of additional energy, equivalent to 0.78 and 1.43 J m−2 s−1, was used for water absorption by Longchun 8139-2 under moderate and severe drought stress, respectively. Although the grain yield of both cultivars decreased with declining
soil moisture, loss was greater in Longchun 8139-2 than in Dingxi 24, especially under severe drought stress. The drought tolerance cultivar (Dingxi 24), had a higher biomass and metabolic activity under severe drought stress compared to the sensitive cultivar (Longchun 8139-2), which resulted in further limitation of grain yield. Results show that root respiration, carbohydrates allocation (root:shoot
ratio) and grain yield were closely related to soil water status and wheat cultivar. Reductions in root respiration and root
biomass under severe soil drying can improve drought tolerant wheat growth and physiological activity during soil drying and
improve grain yield, and hence should be advantageous over a drought sensitive cultivar in arid regions. 相似文献
13.
Karibu Fukuzawa Hideaki Shibata Kentaro Takagi Fuyuki Satoh Takayoshi Koike Kaichiro Sasa 《Ecological Research》2007,22(3):485-495
We measured the vertical distribution and seasonal patterns of fine-root production and mortality using minirhizotrons in
a cool–temperate forest in northern Japan mainly dominated by Mongolian oak (Quercus crispula) and covered with a dense understory of dwarf bamboo (Sasa senanensis). We also investigated the vertical distribution of the fine-root biomass using soil coring. We also measured environmental
factors such as air and soil temperature, soil moisture and leaf area indices (LAI) of trees and the understory Sasa canopy for comparison with the fine-root dynamics. Fine-root biomass to a depth of 60 cm in September 2003 totaled 774 g m−2, of which 71% was accounted for by Sasa and 60% was concentrated in the surface soil layer (0–15 cm), indicating that understory Sasa was an important component of the fine-root biomass in this ecosystem. Fine-root production increased in late summer (August)
when soil temperatures were high, suggesting that temperature partially controls the seasonality of fine-root production.
In addition, monthly fine-root production was significantly related to Sasa LAI (P<0.001), suggesting that fine-root production was also affected by the specific phenology of Sasa. Fine-root mortality was relatively constant throughout the year. Fine-root production, mortality, and turnover rates were
highest in the surface soil (0–15 cm) and decreased with increasing soil depth. Turnover rates of production and mortality
in the surface soil were 1.7 year−1 and 1.1 year−1, respectively. 相似文献
14.
Eva Ritter 《Plant and Soil》2007,295(1-2):239-251
Afforestation has become an important tool for soil protection and land reclamation in Iceland. Nevertheless, the harsh climate
and degraded soils are growth-limiting for trees, and little is know about changes in soil nutrients in maturing forests planted
on the volcanic soils. In the present chronosequence study, changes in C, N and total P in soil (0–10 and 10–20 cm depth)
and C and N in foliar tissue were investigated in stands of native Downy birch (Betula pubescens Enrh.) and the in Iceland introduced Siberian larch (Larix sibirica Ledeb.). The forest stands were between 14 and 97 years old and were established on heath land that had been treeless for
centuries. Soils were Andosols derived from basaltic material and rhyolitic volcanic ash. A significant effect of tree species
was only found for the N content in foliar tissue. Foliar N concentrations were significantly higher and foliar C/N ratios
significantly lower in larch needles than in birch leaves. There was no effect of stand age. Changes in soil C and the soil
nutrient status with time after afforestation were little significant. Soil C concentrations in 0–10 cm depth in forest stands
older than 30 years were significantly higher than in heath land and forest stands younger than 30 years. This was attributed
to a slow accumulation of organic matter. Soil N concentrations and soil Ptot were not affected by stand age. Nutrient pools in the two soil layers were calculated for an average weight of soil material
(400 Mg soil ha−1 in 0–10 cm depth and 600 Mg soil ha−1 in 10–20 cm depth, respectively). Soil nutrient pools did not change significantly with time. Soil C pools were in average
23.6 Mg ha−1 in the upper soil layer and 16.9 Mg ha−1 in the lower soil layer. The highest annual increase in soil C under forest compared to heath land was 0.23 Mg C ha−1 year−1 in 0–10 cm depth calculated for the 53-year-old larch stand. Soil N pools were in average 1.0 Mg N ha−1 in both soil layers and did not decrease with time despite a low N deposition and the uptake and accumulation of N in biomass
of the growing trees. Soil Ptot pools were in average 220 and 320 kg P ha−1 in the upper and lower soil layer, respectively. It was assumed that mycorrhizal fungi present in the stands had an influence
on the availability of N and P to the trees.
Responsible Editor: Hans Lambers. 相似文献
15.
Numerous studies have explored the effect of environmental conditions on a number of plant physiological and structural traits,
such as photosynthetic rate, shoot versus root biomass allocation, and leaf and root morphology. In contrast, there have been
a few investigations of how those conditions may influence root respiration, even though this flux can represent a major component
of carbon (C) pathway in plants. In this study, we examined the response of mass-specific root respiration (μmol CO2 g−1 s−1), shoot and root biomass, and leaf photosynthesis to clipping and variable soil moisture in two C3 (Festuca idahoensis Elmer., Poa pratensis L.) and two C4 (Andropogon greenwayi Napper, and Sporobolus kentrophyllus K. Schum.) grass species. The C3 and C4 grasses were collected in Yellowstone National Park, USA and the Serengeti ecosystem, Africa, respectively, where they evolved
under temporally variable soil moisture conditions and were exposed to frequent, often intense grazing. We also measured the
influence of clipping and soil moisture on specific leaf area (SLA), a trait associated with moisture conservation, and specific
root length (SRL), a trait associated with efficiency per unit mass of soil resource uptake. Clipping did not influence any
plant trait, with the exception that it reduced the root to shoot ratio (R:S) and increased SRL in P. pratensis. In contrast to the null effect of clipping on specific root respiration, reduced soil moisture lowered specific root respiration
in all four species. In addition, species differed in how leaf and root structural traits responded to lower available soil
moisture. P. pratensis and A. greenwayi increased SLA, by 23% and 33%, respectively, and did not alter SRL. Conversely, S. kentrophyllus increased SRL by 42% and did not alter SLA. F. idahoensis responded to lower available soil moisture by increasing both SLA and SRL by 38% and 33%, respectively. These responses were
species-specific strategies that did not coincide with photosynthetic pathway (C3/C4) or growth form. Thus, mass-specific root respiration responded uniformly among these four grass species to clipping (no
effect) and increased soil moisture stress (decline), whereas the responses of other traits (i.e., R:S ratio, SLA, SRL) to
the treatments, especially moisture availability, were species-specific. Consequently, the effects of either clipping or variation
in soil moisture on the C budget of these four different grasses species were driven primarily by the plasticity of R:S ratios
and the structural leaf and root traits of individual species, rather than variation in the response of mass-specific root
respiration. 相似文献
16.
A. Q. Hurtado A. T. Critchley A. Trespoey G. Bleicher-Lhonneur 《Journal of applied phycology》2008,20(5):551-555
Kappaphycus striatum var. sacol was grown in two separate studies: (1) at two stocking densities, and (2) at four different depths, each for three different
durations of culture (30, 45 and 60 days) in order to determine the growth rate of the seaweed and evaluate the carrageenan
content and its molecular weight. The results demonstrated that stocking density, duration of culture and depth significantly
(P < 0.01) affected the growth rate, carrageenan content and molecular weight of K. striatum var. sacol. Decreasing growth rate was observed at both stocking densities and at four depths as duration of culture increased. A lower
stocking density (500 g m−1line−1) showed a higher growth rate for the shortest durations, i.e. 30 days, as compared to those grown at a higher density. Likewise,
decreasing growth rate was observed as depth increased, except at 50 cm after 60 days of culture. A 45-day culture period
produced the highest molecular weight at both stocking densities (500 g m−1line−1 = 1,079.5 ± 31.8 kDa, 1,000 g m−1line−1 = 1,167 ± 270.6 kDa). ‘Sacol’ grown for 30 days at 50 cm (1,178 kDa) to 100 cm (1,200 kDa) depth showed the highest values
of molecular weight of carrageenan extracted. The results suggested that K. striatum var. sacol is best grown at a stocking density of 500 g m−1line−1, at a depth of 50–100 cm, and for a duration of 30 days in order to provide the highest growth rate, carrageenan content
and molecular weight. 相似文献
17.
Root distribution and water uptake patterns of corn under surface and subsurface drip irrigation 总被引:14,自引:0,他引:14
Information on root distribution and uptake patterns is useful to better understand crop responses to irrigation and fertigation,
especially with the limited wetted soil volumes which develop under drip irrigation. Plant water uptake patterns play an important
role in the success of drip irrigation system design and management. Here the root systems of corn were characterized by their
length density (RLD) and root water uptake (RWU). Comparisons were made between the spatial patterns of corn RWU and RLD under
surface and subsurface drip irrigation in a silt loam soil, considering a drip line on a crop row and between crop rows. Water
uptake distribution was measured with an array of TDR probes at high spatial and temporal resolution. Root length density
was measured by sampling soil cores on a grid centered on crop row. Roots were separated and an estimation of root geometrical
attributes was made using two different image analysis programs. Comparisons of these programs yielded nearly identical estimates
of RLD. The spatial patterns of RWU and RLD distributions, respectively normalized to the total uptake and root length, were
generally similar only for drip line on a crop row, but with some local variations between the two measures. Both RLD and
RWU were adequately fitted with parametric models based on semi-lognormal and normal Gaussian bivariate density functions
(Coelho and Or, 1996; Soil Sci. Soc. Am. J. 60, 1039–1049). 相似文献
18.
Quanxiao Fang Qiang Yu Enli Wang Yuhai Chen Guoliang Zhang Jing Wang Longhui Li 《Plant and Soil》2006,284(1-2):335-350
There is a growing concern about excessive nitrogen (N) and water use in agricultural systems in North China due to the reduced
resource use efficiency and increased groundwater pollution. A two-year experiment with two soil moisture by four N treatments
was conducted to investigate the effects of N application rates and soil moisture on soil N dynamics, crop yield, N uptake
and use efficiency in an intensive wheat–maize double cropping system (wheat–maize rotation) in the North China Plain. Under
the experimental conditions, crop yield of both wheat and maize did␣not␣increase significantly at N rates above 200 kg N ha−1. Nitrogen application rates affected little on ammonium-N (NH4-N) content in the 0–100 cm soil profiles. Excess nitrate-N (NO3-N), ranging from 221 kg N ha−1 to 620 kg N ha−1, accumulated in the 0–100 cm soil profile at the end of second rotation in the treatments with N rates of 200 kg N ha−1 and 300 kg N ha−1. In general, maize crop has higher N use efficiency than wheat crop. Higher NO3-N leaching occurred in maize season than in wheat season due to more water leakage caused by the concentrated summer rainfall.
The results of this study indicate that the optimum N rate may be much lower than that used in many areas in the North China
Plain given the high level of N already in the soil, and there is great potential for reducing N inputs to increase N use
efficiency and to mitigate N leaching into the groundwater. Avoiding excess water leakage through controlled irrigation and
matching N application to crop N demand is the key to reduce NO3-N leaching and maintain crop yield. Such management requires knowledge of crop water and N demand and soil N dynamics as
they change with variable climate temporally and spatially. Simulation modeling can capture those interactions and is considered
as a powerful tool to assist in␣the␣future optimization of N and irrigation managements.
Section Editor: L. Wade 相似文献
19.
N2O, CH4 and CO2 emissions from seasonal tropical rainforests and a rubber plantation in Southwest China 总被引:2,自引:1,他引:1
Christian Werner Xunhua Zheng Janwei Tang Baohua Xie Chunyan Liu Ralf Kiese Klaus Butterbach-Bahl 《Plant and Soil》2006,289(1-2):335-353
The main focus of this study was to evaluate the effects of soil moisture and temperature on temporal variation of N2O, CO2 and CH4 soil-atmosphere exchange at a primary seasonal tropical rainforest (PF) site in Southwest China and to compare these fluxes with fluxes from a secondary forest (SF) and a rubber plantation (RP) site. Agroforestry systems, such as rubber plantations, are increasingly replacing primary and secondary forest systems in tropical Southwest China and thus effect the N2O emission in these regions on a landscape level. The mean N2O emission at site PF was 6.0 ± 0.1 SE μg N m−2 h−1. Fluxes of N2O increased from <5 μg N m−2 h−1 during dry season conditions to up to 24.5 μg N m−2 h−1 with re-wetting of the soil by the onset of first rainfall events. Comparable fluxes of N2O were measured in the SF and RP sites, where mean N2O emissions were 7.3 ± 0.7 SE μg N m−2 h−1 and 4.1 ± 0.5 SE μg N m−2 h−1, respectively. The dependency of N2O fluxes on soil moisture levels was demonstrated in a watering experiment, however, artificial rainfall only influenced the timing of N2O emission peaks, not the total amount of N2O emitted. For all sites, significant positive correlations existed between N2O emissions and both soil moisture and soil temperature. Mean CH4 uptake rates were highest at the PF site (−29.5 ± 0.3 SE μg C m−2 h−1), slightly lower at the SF site (−25.6 ± 1.3 SE μg C m−2 h−1) and lowest for the RP site (−5.7 ± 0.5 SE μg C m−2 h−1). At all sites, CH4 uptake rates were negatively correlated with soil moisture, which was also reflected in the lower uptake rates measured in the watering experiment. In contrast to N2O emissions, CH4 uptake did not significantly correlate with soil temperature at the SF and RP sites, and only weakly correlated at the PF site. Over the 2 month measurement period, CO2 emissions at the PF site increased significantly from 50 mg C m−2 h−1 up to 100 mg C m−2 h−1 (mean value 68.8 ± 0.8 SE mg C m−2 h−1), whereas CO2 emissions at the SF and RP site where quite stable and varied only slightly around mean values of 38.0 ± 1.8 SE mg C m−2 h−1 (SF) and 34.9 ± 1.1 SE mg C m−2 h−1 (RP). A dependency of soil CO2 emissions on changes in soil water content could be demonstrated for all sites, thus, the watering experiment revealed significantly higher CO2 emissions as compared to control chambers. Correlation of CO2 emissions with soil temperature was significant at the PF site, but weak at the SF and not evident at the RP site. Even though we demonstrated that N and C trace gas fluxes significantly varied on subdaily and daily scales, weekly measurements would be sufficient if only the sink/ source strength of non-managed tropical forest sites needs to be identified. 相似文献
20.
Calibration of minirhizotron data against root length density (RLD) was carried out in a field trial where three drip irrigation depths: surface (R0) and subsurface, 0.20 m (RI) and 0.40 m depth (RII) and two processing tomato cultivars: `Brigade' (CI) and `H3044' (CII) were imposed. For each treatment three minirhizotron tubes were located at 10, 37.5 and 75 cm of the way from one plant row to the next. Roots intersecting the minirizotrons walls were expressed as root length intensity (L
a) and number of roots per unit of minirhizotron wall area (N
ra). Root length density (RLD) was calculated from core samples taken for each minirhizotron tube at two locations: near the top of the minirhizotron (BI) and 15 cm apart from it, facing the minirhizotron wall opposite the plant row (BII). Minirhizotron data were regressed against RLD obtained at BI and BII and with their respective means. The results show that for all the situations studied, better correlations were obtained when RLD was regressed with L
a than with N
ra. Also was evident that the relationship between L
a and RLD was strongly influenced by the location of soil coring. RLD was correlated with L
a trough linear and cubic equations, having the last ones higher determination coefficients. For instance at 10 cm from the plant row when values from the top layer (0–40 cm) were analysed separately, L
a was significantly regressed with RLD measured at BII and described by the equations: RLD = 0.5448 + 0.0071 L
a (R
2 = 0.51) and RLD = 0.4823 + 0.0074L
a + 8×10–5
L
a
2 – 5×10–7
L
a
3 (R
2 = 0.61). Under the 40 cm depth the highest coefficients of determination for the linear and cubic equations were respectively 0.47 and 0.88, found when L
a was regressed with RLD measured at BI. For minirhizotrons located at 75 cm from the plant row and for location BI it was possible to analyse jointly data from all depths with coefficients of determination of 0.45 and 0.59 for the linear and cubic equations respectively. 相似文献