Impact of water depth on root morphology of Juncellus serotinus (Cyperaceae)

Root morphological adaptation is an important mechanism for wetland plants to adapt to environmental conditions. The objective of this study was to investigate the impact of water depth on biomass allocation and root morphology (including root mean diameter, root length, root surface area and root volume) of a wetland plant species, Juncellus serotinus (Cyperaceae). Four levels of water depth were chosen: 10, 30, 50 and 70 cm. Due to the enormous root system, and for easy observation, five groups were used according to the distance from the rhizome: 0–5, 5–10, 10–15, 15–20 and longer than 20 cm (> 20 cm). Results showed that with increasing water depth plant total biomass and root biomass decreased significantly (p < 0.05), and that biomass was mainly allocated to shoots resulting in decreased root to shoot ratio. Root morphology parameters also changed significantly with increasing water depth (p < 0.05). Root mean diameter in all treatments and all other root morphology parameters decreased with increasing distance from the rhizome, while maximum root length, root surface area and root volume in 10 and 30 cm occurred between 5 and 15 cm from the rhizome. The results indicate that shallow water (less than 30 cm in depth) is favorable for the development of J. serotinus root system, and that root morphological characteristics shift with increasing distance from the rhizome.     

中国结缕草属植物(Zoysia spp.)地下部分分布和形态类型的多样性

通过对分布于我国的结缕草属(ZoysiaWilld.)54份种质地下部分特点的研究,发现其地下茎分布都在15cm土层内,其中大部分在5cm深度的土层范围内(97.23%),很少达到15cm(0.29%);不定根一般可分布到40cm左右,但表层15cm内分布了不定根总量的81.62%,其下的25cm土层中分布的不定根只占不定根总量的18.38%。地下茎在10～15cm、不定根在30～40cm土层中各性状的变异都比较显著。相关分析表明,随着纬度的升高,地下茎在较深的土层(5～15cm)中分布密度有增加的趋势,而伴随着纬度升高不定根分布密度趋小。根据地下茎和不定根分布的特点,可将我国结缕草属植物地下部分划分为3大类型,即浅茎密根型、中茎密根型和深茎浅根型。     

Effect of mineral nitrogen on nitrogen nutrition and biomass partitioning between the shoot and roots of pea (Pisum sativum L.).

The effect of mineral N availability on nitrogen nutrition and biomass partitioning between shoot and roots of pea (Pisum sativum L., cv Baccara) was investigated under adequately watered conditions in the field, using five levels of fertiliser N application at sowing (0, 50, 100, 200 and 400 kg N ha^–1). Although the presence of mineral N in the soil stimulated vegetative growth, resulting in a higher biomass accumulation in shoots in the fertilised treatments, neither seed yield nor seed nitrogen concentration was affected by soil mineral N availability. Symbiotic nitrogen fixation was inhibited by mineral N in the soil but it was replaced by root mineral N absorption, which resulted in optimum nitrogen nutrition for all treatments. However, the excessive nitrogen and biomass accumulation in the shoot of the 400 kg N ha^–1 treatment caused crop lodging and slightly depressed seed yield and seed nitrogen content. Thus, the presumed higher carbon costs of symbiotic nitrogen fixation, as compared to root mineral N absorption, affected neither seed yield nor the nitrogen nutrition level. However, biomass partitioning within the nodulated roots was changed. The more symbiotic nitrogen fixation was inhibited, the more root growth was enhanced. Root biomass was greater when soil mineral N availability was increased: root growth was greater and began earlier for plants that received mineral N at sowing. Rooting density was also promoted by increased mineral N availability, leading to more numerous but finer roots for the fertilised treatments. However, the maximum rooting depth and the distribution of roots with depth were unchanged. This suggested an additional direct promoting effect of mineral N on root proliferation.     

Contribution of nitrogen fixation to first year Miscanthus × giganteus

Many characteristics make Miscanthus × giganteus an appealing bioenergy feedstock in temperate North America, but the degree to which this plant species interacts with nitrogen‐fixing bacteria remains understudied. Demonstration of associative nitrogen fixation in Miscanthus would support management with minimal fertilizer inputs that is demanded of long‐term biofuel sustainability. As a first step, we investigate the role of biological nitrogen fixation in nutrition of immature Miscanthus and temporal dynamics of plant‐associated nitrogen fixers. The contribution of biological nitrogen fixation to plant nitrogen acquisition in first year Miscanthus × giganteus was estimated using a yield‐dependent ¹⁵N isotope dilution model. Temporal changes in plant‐associated diazotroph relative abundance and community composition were analyzed with quantitative PCR and terminal restriction fragment length polymorphism of the nifH gene in rhizome and rhizosphere DNA extracts. We estimate 16% of new plant nitrogen was derived by nitrogen fixation during the growing season, despite non‐limiting soil nitrogen. Diazotroph communities from rhizome and rhizosphere changed with plant development and endophytic nitrogen fixers had significantly higher relative abundance and altered community composition at sampling dates in July and August. This study provides evidence for a small, but measurable, benefit of associative nitrogen fixation to first year Miscanthus × giganteus that underscores the potential and need for selection of breeding lines that maximize this trait.     

极端晚播对小麦籽粒产量、氮素吸收利用和籽粒蛋白质含量的影响

为探索小麦高产高效优质生产技术途径,指导小麦晚播生产实践,2012年10月—2014年6月,以弱春性小麦偃展4110和半冬性小麦矮抗58为材料进行连续2年的田间定位试验,设置了常规适播(10月中旬、240万株·hm^-2)和极端晚播(11月中旬、600万株·hm^-2)两种栽培模式,研究了极端晚播对0～40 cm土层土壤硝态氮含量、小麦氮素吸收利用、产量、籽粒蛋白质含量和氮素吸收效率的影响.结果表明: 与常规适播处理相比,两个生长季极端晚播处理均使拔节和开花期0～40 cm土壤硝态氮含量显著提高,从而促进拔节后小麦植株氮素吸收积累,成熟期穗部氮素的分配比例也得到提高,最终显著提高小麦籽粒蛋白质含量和偃展4110的蛋白质产量、氮素吸收效率,但对籽粒产量的影响因品种而异.其中,极端晚播处理使偃展4110的籽粒产量显著提高,而矮抗58的籽粒产量却显著降低.因此,极端晚播栽培模式可维持小麦拔节后的土壤氮供应,有利于提高小麦氮素吸收效率,从而提高小麦籽粒产量和蛋白质含量,是灌区小麦高产优质的有效途径之一.     

Root-induced changes in radial oxygen loss, rhizosphere oxygen profile, and nitrification of two rice cultivars in Chinese red soil regions

Aims

To evaluate the external and internal morphological differences of roots that might influence rice root radial oxygen loss (ROL) and the corresponding rhizosphere nitrification activity, growth characteristics and nitrogen nutrition of rice.

Methods

The root ROL and rhizosphere oxygen profile were determined using a miniaturised Clark-type oxygen microelectrode system, and the rhizosphere nitrification activity was studied with a short-term nitrification activity assay.

Results

The rice biomass, nitrogen accumulation and nitrogen use efficiency (NUE) of ZH (high yield) were significantly higher than those of HS (low yield). The root biomass, number, diameter and porosity of ZH were also much greater than those of HS. The inner and surface oxygen concentrations of the root of ZH were significantly higher than those of HS. The order of paddy soil oxygen penetration depth was ZH?>?HS?>?CK, and the order of the oxygen concentrations detected in the water layer and rhizosphere soil was the same. The rhizosphere nitrification activity and nitrate concentration of ZH were significantly higher than those of HS.

Conclusions

More porous and thicker roots improved the individual root ROL, and more adventitious root numbers enhanced the entire plant ROL and correspondingly improved the rhizosphere nitrification activity, which might influence the growth and nitrogen nutrition of rice.     

播种深度对夏玉米幼苗性状和根系特性的影响

选用郑单958(ZD958)和先玉335(XY335)为试验材料,在砂培和大田条件下设置3、5、7和9 cm 4个播种深度,并在大田条件下以不同播种深度混播作为对照(CK),研究播种深度对夏玉米幼苗性状和根系特性的影响.结果表明： 随着播种深度的增加,夏玉米的出苗率下降,出苗时间延长.ZD958和XY335播深9 cm的出苗率较3 cm的分别降低9.4%和11.8%,出苗时间较3 cm的均延长1.5 d.随着播种深度的增加,幼苗长度及幼苗整齐度显著降低,中胚轴长度显著增加,胚芽鞘长度差异不显著;初生胚根长度逐渐减小,次生胚根总长度逐渐增加,总根长度差异不显著;幼苗与中胚轴的总干质量增加,总根干质量差异不显著.随播种深度的增加,种子萌发时幼苗各部位可溶性糖含量增加,营养物质消耗量增加,幼苗根系生长速度增加,根系活力降低,总节根数及节根层数增加.播深增加后出苗率及幼苗活力的降低导致收获穗数的显著降低,最终影响产量形成.此外,播深一致有利于群体整齐度的提高和群体性状的改善,从而提高产量.     

Effect of inter-cropping bell-pepper with ginger on plant parasitic nematode populations and crop yields

During 1994 studies were undertaken to improve ginger (Zingiber officinale Roscoe) yield against the nematodes Pratylenchus penetrans, Meloidogyne incognita, Helicotylenchus dihystera and Tylenchorhynchus mashhoodi in Himachal Pradesh (HP) (India) by inter-cropping bell-pepper (Capsicum annum L) in eight different sequences (treatments). Inter-cropping of “one rhizome of ginger x one plant of bell-pepper” gave the highest ginger yield (600 g per rhizome). This treatment was completely free from P. penetrans and M. incognita. All treatments with bell-pepper plants equal to or higher in number to that of ginger rhizomes had higher ginger yields than treatments with ginger alone or with fewer bell-pepper plants. In the former, populations of P. penetrans and M. incognita were lower than in the latter treatments. The yield of ginger varied irrespective of population densities of H. dihystera and T. mashhoodi, indicating that P. penetrans and M. incognita are the major nematode problems of ginger in HP. Bell-pepper was a non-host to P. penetrans and non-preferred host to M. incognita. This helped to improve ginger yields by making the rhizosphere unfavourable for the development and multiplication of the major ginger nematode pests.     

Effects of Warming and Nitrogen Addition on Plant Photosynthate Partitioning in an Alpine Meadow on the Tibetan Plateau

Quantifying plant carbon (C) allocation among different pools is critical for understanding and predicting how C turnover responds to global climate change in terrestrial ecosystems. A field experiment with increasing warming and nitrogen (N) was established to investigate interactive effects on plant C allocation in alpine meadows. Open-top chambers (OTCs) were used to simulate warming. In OTCs, daytime air and soil temperature at 5 cm depth increased by 2.0 and 1.6 °C, respectively, compared with ambient conditions, but soil moisture at 5 cm depth decreased by 4.95% (v/v) from 2012 to 2014. Warming reduced aboveground biomass by 38, 36, and 43% in 2012, 2013, and 2014, respectively, and increased belowground biomass by 64% and 29% in 2013 and 2014, respectively, and the root-to-shoot ratio was significantly increased. Specifically, warming increased the proportion of plant roots in the deep layers (10–20 cm). Both N addition and its combination with warming substantially enhanced belowground biomass. Pulse-labeling experiments for ¹³C revealed that warming reduced the translocation of assimilated C to shoots by 8.8% (38.7% in warming, and 47.5% in the control [CK]), and increased the allocation to root by 12.2% (55.5% in warming, and 43.3% in CK) after 28 days labeling. However, N addition increased the proportion of assimilated C allocated to shoots by 6.5% (54.0% in N addition, and 47.5% in CK), whereas warming combined with N addition reduced this proportion by 10.9%. A decline in soil water content in the surface layer may be the main cause of plants allocating more newly fixed photosynthate to roots. Therefore, plants promoted root growth to draw water from deeper soil layers (10–20 cm). We concluded that climate warming will change the allocation patterns of plant photosynthates by affecting soil water availability, whereas N addition will increase plant photosynthates aboveground in alpine meadows and thus will significantly affect C turnover under future climate change scenarios.

     

Burial depth and diameter of the rhizome fragments affect the regenerative capacity of a clonal shrub

Clonal plants in highly disturbed habitats are often broken into small fragments of various sizes and buried at various soil depths. As a storage organ, rhizome fragments play an important role in enabling plants to survive in such habitats. But few studies have been concerned about the regenerative capacity of rhizome fragments of clonal shrubs of different rhizome diameter and at different burial depths. Here, we investigated whether deeper burial decreased, and diameter of the rhizome fragment increased, the regenerative capacity of a clonal shrub. Research samples of rhizome fragment (rhizome diameters of 2, 5, 10, 15, and 20 mm) of the clonal shrub Calligonum arborescens were buried at different depths (0, 1, 5, 10, and 20 cm). Increasing the diameter of the rhizome fragments significantly increased the survival rate of fragments, and increased the above-ground, below-ground and total biomass production of fragments. Vegetative reproduction ability also increased with an increase in diameter of the rhizome fragments. With an increase in sand burial depth, above-ground, below-ground, total biomass production and vegetative reproduction ability first decreased and then increased, and no fragments survived at the 0 cm burial depth. These results indicate that sand burial depth and diameter of the rhizome fragments significantly affected the regeneration capacity of C. arborescens. Sand burial is one of the essential prerequisites for C. arborescens rhizome fragments’ survival. Moderate burial depth (5 cm) and larger fragment diameter (20 mm diameter) were more suitable for biomass production and vegetative reproduction. These results indicate that reserves stored in rhizome fragments can contribute greatly to the regeneration capacity of the C. arborescens—responses that are very important for C. arborescens survival and establishment in frequently disturbed habitats.     

Fine Root and Soil Organic Carbon Depth Distributions are Inversely Related Across Fertility and Rainfall Gradients in Lowland Tropical Forests

Humid tropical forests contain some of the largest soil organic carbon (SOC) stocks on Earth. Much of this SOC is in subsoil, yet variation in the distribution of SOC through the soil profile remains poorly characterized across tropical forests. We used a correlative approach to quantify relationships among depth distributions of SOC, fine root biomass, nutrients and texture to 1 m depths across 43 lowland tropical forests in Panama. The sites span rainfall and soil fertility gradients, and these are largely uncorrelated for these sites. We used fitted β parameters to characterize depth distributions, where β is a numerical index based on an asymptotic relationship, such that larger β values indicate greater concentrations of root biomass or SOC at depth in the profile. Root β values ranged from 0.82 to 0.95 and were best predicted by soil pH and extractable potassium (K) stocks. For example, the three most acidic (pH?<?4) and K-poor (<?20 g K m^?2) soils contained 76?±?5% of fine root biomass from 0 to 10 cm depth, while the three least acidic (pH?>?6.0) and most K-rich (>?50 g K m^?2) soils contained only 41?±?9% of fine root biomass at this depth. Root β and SOC β values were inversely related, such that a large fine root biomass in surface soils corresponded to large SOC stocks in subsoils (50–100 cm). SOC β values were best predicted by soil pH and base cation stocks, with the three most base-poor soils containing 34?±?8% of SOC from 50 to 100 cm depth, and the three most base-rich soils containing just 9?±?2% of SOC at this depth. Nutrient depth distributions were not related to Root β or SOC β values. These data show that large surface root biomass stocks are associated with large subsoil C stocks in strongly weathered tropical soils. Further studies are required to evaluate why this occurs, and whether changes in surface root biomass, as may occur with global change, could in turn influence SOC storage in tropical forest subsoils.

     

氮肥运筹对免耕水稻根系生长、根际土壤特性及产量的影响

为探索氮肥运筹对免耕条件下水稻根系生长以及对根际土壤特性、产量的影响,以金优253为材料进行试验。结果表明：平衡施肥显著提高单株根系干重、根长、单株生物量、根半径、单株根表面积、根长密度及根系活力,实收单产高于重穗肥和重基肥处理,且与重基肥差异达95％的显著水平,主要是有效穗数、结实率的增加。平衡施肥显著提高0~10 cm土层的0~2 mm根际土壤有机质、碱解氮含量及脲酶、蔗糖酶活性。因此平衡施肥能明显促进免耕水稻根系生长和有效穗数的增加,对提高水稻产量具有促进作用。     

Strong regeneration ability from rhizome fragments in two invasive clonal plants (Solidagocanadensis and S. gigantea)

The two rhizomatous perennials Solidago canadensis and S. gigantea belong to the most widespread alien plants in Europe. Anecdotal observations suggest that they disperse also by rhizome fragments. For testing their resprouting ability, rhizome fragments of different sizes from both species were buried at four different soil depths (0, 5, 10 and 20 cm, respectively) in a common garden. Rhizome fragments of S. canadensis ranged 3–6 cm in length, those of S. gigantea 5–20 cm in length. Resprouting plants were harvested after 3 months and growth related traits measured to assess their vitality. Resprouting rate in S. gigantea was far higher than in S. canadensis (85 and 19%, respectively). In S. gigantea, fragments of all sizes resprouted from all soil depths whereas none rhizome of S. canadensis emerged from 20 cm burial depth. In S. gigantea, size related traits showed significant interactions between fragment size and burial depth, but not relative shoot growth rate. At all burial depths, vitality of plants emerging from small rhizomes was lower than plants emerging from large rhizomes. Effects of rhizome size became stronger with increasing burial depth. The results show that both species are able to resprout from buried rhizome fragments, and that succesful regeneration is more likely to occur in S. gigantea. Managing these species should avoid any activities promoting rhizome fragmentation and dispersal of fragments.     

Field observations on nitrogen catch crops

Nitrogen catch crops help to reduce the loss of nitrogen from arable cropping systems during autumn and winter. The ability of catch crops to absorb nitrogen from the soil profile is affected by rate and depth of colonization of the soil by roots. The aim of the current work was to analyze total root length and root length density of catch crops in relation to above ground growth, nitrogen supply and crop species. In two field experiments roots were sampled with an auger. Experimental factors included crop species (winter rye, Secale cereale and forage rape, Brassica napus ssp. oleifera (Metzg.) Sinsk., or oil radish, Raphanus sativus spp. oleiferus (DC.) Metzg.), two sowing dates S1 and S2 (end of August and three weeks later) and two nitrogen treatments: N0, no nitrogen applied, and N1, nitrogen applied at non-limiting rate.The natural logarithm of the total root length, measured in the top 40 cm, L_0–40 (km m^-2), was linearly related to natural logarithm of the dry weight of the shoot, W (g m^-2). There was no effect of species or sowing date on this relation. For a given W, N1 treatments showed lower values of L_0–40 than N0 treatments. The decline in root length density, D (cm cm^-3), with depth, X (cm), was described with the function ln D = ln D₀ – qX, where D₀ is the value of D at zero depth and q the linear coefficient. D₀ was linearly related to L_0–40, without effect of species, time of observation or N supply. The ratio D₀/q, an estimate of the absolute root length, was 1.24 × L_0–40.Together the relations enable estimates to be made of total root length and of root length distribution with depth using shoot dry weight of catch crops and its change with time as input. The generation of such estimates of root distribution is necessary for model studies in which the efficacy of catch crops to prevent N losses is evaluated in relation to sowing dates, distribution of N in the soil profile and the distribution of rainfall in the season.     

生姜水浸液对生姜幼苗根际土壤酶活性、微生物群落结构及土壤养分的影响

本文以生姜为材料,研究生姜不同部位（根茎、茎和叶）、不同浓度（10、20、40和80 g L-1）的水浸液对生姜幼苗根际土的微生物数量、土壤酶活性及土壤养分含量的影响,并通过HPLC定量分析了生姜各部位水浸液中所含酚酸类（香草酸、丁香酸、对羟基苯甲酸、香豆酸和阿魏酸）、香豆素类（伞花内脂和7-甲氧基香豆素）化合物的含量。结果表明：三种生姜水浸液对所测六种土壤酶活性均产生了不同程度的影响,其中影响最大的是酸性磷酸酶和蔗糖酶,在10 g L-1 时就达到了显著性差异水平,并且所有酶均有随着水浸液浓度的增加而呈增大的趋势;相同部位的水浸液随着浓度的增加,细菌和真菌的数量呈增加趋势,而放线菌的数量呈减少趋势;三种生姜水浸液均随着浓度的增加降低了土壤中有机质的含量,加剧了土壤中硝态氮含量的积累,根茎水浸液对土壤有效磷、速效钾和铵态氮均显示出低浓度提高其含量而高浓度降低其含量的趋势,而茎和叶水浸液则随着浓度的增加均降低了其含量。生姜水浸液中主要化感成分包括：根茎水浸液主要是丁香酸和伞花内脂;茎水浸液主要是阿魏酸,且其含量最高为73.4 ug/g;叶水浸液除了阿魏酸,其他六种物质均被检测出,但含量较高的主要有丁香酸、伞花内脂和香豆酸。     

Effect of Sowing Date and Cultivar on Root System Development in Pea (Pisum sativum L.)

In many species, root system development depends on cultivar and sowing date, with consequences for aerial growth, and seed yield. Most of the peas (Pisum sativum L.) grown in France are sown in spring or in mid-November. We analyzed the effect of two sowing periods (November and February) and three pea cultivars (a spring cultivar, a winter cultivar, a winter recombinant inbred line) on root development in field conditions. For all treatments, rooting depth at various dates seemed to be strongly correlated with cumulative radiation since sowing. Maximum root depth varied from 0.88 to 1.06 m, with the roots penetrating to greater depths for February sowing than for November sowing in very cold winters. The earlier the crop was sown, the sooner maximum root depth was reached. No difference in root dynamics between cultivars was observed. In contrast, the winter recombinant inbred line presented the highest root density in the ploughed layer. These findings are discussed in terms of their possible implications for yield stability and environmental impact.     

水稻根系通气组织与根系泌氧及根际硝化作用的关系

通过根箱土培试验研究了不同产量籼稻品种中旱22(ZH,高产品种)及禾盛10号(HS,低产品种)苗期根系生长、通气组织发育、根系径向泌氧量(radial oxygen loss,ROL)以及根表和根际土壤硝化强度差异。结果表明,除水稻播种40 d时二者根数量和根干重无显著差异外,ZH根直径、根数量和根干重均显著高于HS,二者差异尤其表现在根系生物量差异。两个水稻品种在距根尖20 mm处均可见辐射状通气组织,ZH皮层薄壁细胞已经完全崩溃形成连接中柱和外皮层的纵向气腔,而HS皮层薄壁细胞未发生完全离解,但仍能观察到明显的连接中柱和外皮层的纵向气腔的形成。同时ZH外皮层厚壁细胞体积较小,排列紧密,细胞壁增厚程度大;而HS外皮层厚壁细胞体积相对较大,排列疏松,细胞壁增厚程度相对较小。表明高产品种通气组织发育比低产品种更加完善,表现为ZH根孔隙度(porosity of root,POR)显著高于HS,且高产品种对水稻根系ROL的屏蔽作用较低产品种更强,为根系提供更充足的氧气供应,促进根系生长。除了水稻播种后40 d时ZH和HS单根ROL无显著差异外(P<0.05),ZH单株、单位重量以及单根ROL均显著高于HS(P<0.01)。两个水稻品种硝化强度均表现为根际土壤显著高于根表土壤 (P<0.01),前者大约是后者的3-6倍。两个品种根表土壤硝化强度无显著差异,而ZH根际土壤硝化强度均显著高于HS。相关性分析结果表明水稻根际土壤硝化强度和整株水稻ROL呈极显著正相关关系(r=0.803,P<0.01),和水稻POR也呈现极显著正相关关系(r=0.808,P<0.01),同时和根系直径、数量和干重均呈极显著正相关关系(P<0.01)。而根表土壤硝化强度和以上指标均无相关关系。由于硝化作用是好氧过程,因此高产品种由于根系发达,通气组织发育好,相应ROL也较大,造成根际土壤氧气含量高,从而可能导致根际土壤硝化强度显著高于低产品种。     

种皮和播种深度对辽东栎种子萌发和幼苗早期生长的影响

在玻璃温室内遮荫条件下,研究种皮和播种深度(0、2、5、10和15 cm)对辽东栎种子萌发和幼苗早期生长的影响.结果表明： 种皮对辽东栎种子萌发具有明显的抑制作用,去除种皮后,种子萌发率显著升高,不同播种深度处理种子萌发率平均升高19.4%,且萌发指数和活力指数显著增大,萌发进程加快.去皮种子和非去皮种子的萌发率均在2 cm播种深度下最大,分别为78.9%和62.2%;萌发指数和活力指数均在2 cm播种深度下最大,而萌发速率系数在5 cm播种深度下最大.去皮处理幼苗的单株叶面积和干质量与非去皮处理相比均显著增大,但比根长显著减小.去皮和非去皮处理幼苗株高均在5 cm播种深度下最大,分别为13.8和14.2 cm;基径随播种深度增加逐渐增大,而主根长、侧根数和最大侧根长均减小;幼苗干质量受播种深度影响较小.     

Belowground responses of <Emphasis Type="Italic">Picea asperata</Emphasis> seedlings to warming and nitrogen fertilization in the eastern Tibetan Plateau

The impacts of global climatic change on belowground ecological processes of terrestrial ecosystems are still not clear. We therefore conducted an experiment in the subalpine coniferous forest ecosystem of the eastern edges of the Tibetan Plateau to study roots of Picea asperata seedlings and rhizosphere soil responses to soil warming and nitrogen availability from April 2007 to December 2008. The seedlings were subjected to two levels of temperature (ambient; infrared heater warming) and two nitrogen levels (0 or 25 g m⁻²year⁻¹ N). We used a free air temperature increase from an overhead infrared heater to raise both air and soil temperature by 2.1 and 2.6°C, respectively. The results showed that warming alone significantly increased total biomass, coarse root biomass and fine root biomass of P. asperata seedlings. Both total biomass and fine root biomass were increased, but coarse root biomass was significantly decreased by nitrogen fertilization and warming combined with nitrogen fertilization. Warming induced a prominent increase in soil organic carbon (SOC) and NO₃ ⁻-N of rhizosphere soil, while nitrogen fertilization significantly decreased SOC and NH₄ ⁺-N of rhizosphere soil. The warming, fertilization and warming × N fertilization interaction decreased soil microbial C significantly, but substantially increased soil microbial N. These results suggest that nitrogen deposition combined with warmer temperatures under future climatic change possibly will have no effect on fine root production of P. asperata seedlings, but could enhance the nitrification process of their rhizosphere soils in subalpine coniferous forests.     

红壤区不同产量籼稻品种苗期根表和根际土壤硝化特征

以不同产量籼稻品种中旱22(ZH,高产品种)和禾盛10号(HS,低产品种)为材料,采用根际培养箱(三室)--速冻切片技术研究了红壤水稻土种植条件下,水稻苗期生长、氮素积累和氮素利用率(NUE)、根孔隙度(POR)、根际土壤矿质态氮含量和硝化强度.结果表明,ZH苗期生长、氮素吸收及NUE均显著优于HS,且ZH单株不定根数量及根系通气组织发育程度(用POR表示)均显著高于HS.ZH根际和土体土壤中铵(NH+4)含量始终低于HS,而硝(NO-3)含量则始终高于HS,但二者根表土壤NH+4和NO-3含量均无显著差异.ZH和HS硝化强度最大发生部位均是在距根表2 mm的根际土壤,分别为:0.48 μmol kg-1h-1和0.31 μmol kg-1h-1.随着距根表越远,硝化强度就越弱,直至距根表10～20 mm处土壤硝化强度就接近于土体土壤.ZH根际土壤硝化强度始终显著高于HS,但二者根表和土体土壤硝化强度均无显著差异.与不种水稻的CK相比,根际土壤硝化强度提高了约2～3.5倍.尽管红壤水稻土硝化作用很弱,但红壤区水稻根际硝化作用与水稻苗期生长和氮素营养密切相关.