Growth and Wood/Bark Properties of Abies faxoniana Seedlings as Affected by Elevated CO2

Growth and wood and bark properties of Abies faxoniana seedlings after one year's exposure to elevated CO2 concentration (ambient 350 (=1= 25) μmol/mol) under two planting densities (28 or 84 plants/mz) were investigated in closed-top chambers. Tree height, stem diameter and cross-sectional area, and total biomass were enhanced under elevated CO2 concentration, and reduced under high planting density. Most traits of stem bark were improved under elevated CO2 concentration and reduced under high planting density. Stem wood production was significantly increased in volume under elevated CO2 concentration under both densities, and the stem wood density decreased under elevated CO2 concentration and increased under high planting density. These results suggest that the response of stem wood and bark to elevated CO2 concentration is density dependent. This may be of great importance in a future CO2 enriched world in natural forests where plant density varies considerably. The results also show that the bark/wood ratio in diameter, stem cross-sectional area and dry weight are not proportionally affected by elevated CO2 concentration under the two contrasting planting densities. This indicates that the response magnitude of stem bark and stem wood to elevated CO2 concentration are different but their response directions are the same.     

Reproductive allocation patterns in different density populations of spring wheat

The effects of increased intraspecific competition on size hierarchies （size inequality） and reproductive allocation were investigated in populations of the annual plant, spring wheat （Triticurn aestivurn）. A series of densities （100, 300, 1 000, 3 000 and 10 000 plants/m^2） along a gradient of competition intensity were designed in this experiment. The results showed that average shoot biomass decreased with increased density. Reproductive allocation was negatively correlated to Gini coefficient （R^2 = 0.927）, which suggested that reproductive allocation is inclined to decrease as size inequality increases. These results suggest that both vegetative and reproductive structures were significantly affected by intensive competition. However, results also indicated that there were different relationships between plant size and reproductive allocation pattern in different densities. In the lowest density population, lacking competition （100 plants/m^2）, individual reproductive allocation was size independent but, in high density populations （300, 1 000, 3 000 and 10 000 plants/m^2）, where competition occurred, individual reproductive allocation was size dependent： the small proportion of larger individuals were winners in competition and got higher reproductive allocation （lower marginal reproductive allocation; MRA）, and the larger proportion of smaller individuals were suppressed and got lower reproductive allocation （higher MRA）. In conclusion, our results support the prediction that elevated intraspecific competition would result in higher levels of size inequality and decreased reproductive allocation （with a negative relationship between them）. However, deeper analysis indicated that these frequency- and size-dependent reproductive strategies were not evolutionarily stable strategies.     

Root growth of wetland plants with different root types

A wastewater culture system was designed to study the root growth of eight species of wetland plants with two different root types. The system included a plastic barrel for holding the wastewater and a foam plate for holding the plant. The results indicated that the root growth of the plants with fibril roots was faster than that of the plants with rhizomatic roots. The species with fibril roots had higher root number (1349 per plant) than species with rhizomatic roots (549 per plant) after ten weeks of cultivation. The average root biomass of plants with fibril roots was 11.3 g per plant, whereas that of plants with rhizomatic roots was 7.4 g per plant. Fine root biomass of diameter ≤ 1 mm constituted 51.9% of the total root biomass in plants with fibril roots, whereas it accounted for only 25.1% in plants with rhizomatic roots. The root surface area of the plants with fibril roots (6933 cm² per plant) was markedly larger than that of the species with rhizomatic roots (1897 cm² per plant). The species with rhizomatic roots showed a longer root lifespan (46.6 days) than those with fibril roots (34.8 days).     

Effect of planting date and nitrogen fertilization on photosynthesis and soluble carbohydrate contents of cotton in relation to silverleaf whitefly （Bemisia tabaci biotype “B”） populations

The impacts of planting date and nitrogen fertilization on cotton （Gossypium hirsutum L.） photosynthesis and soluble carbohydrate contents in relation to silverleaf whitefly, Bemisia tabaci （Gennadius） biotype “B”, populations were examined in field experiments. Cotton planted in late April and early June was treated with 0, 112, 168 and 224 kg/N hectare in soil using urea fertilizer. The mean photosynthetic rate of April-planted cotton was 4%-20% higher than that of June-planted cotton early in the season, but 10%- 18% lower than that of June-planted cotton late in the season. The photosynthetic rates for both planting dates were positively correlated with levels of added nitrogen. While levels of glucose for both planting dates were positively correlated with nitrogen levels, fructose and sucrose levels were not. The mean levels of fructose were up to 40% lower, while that of sucrose were up to 59% higher, in April-planted cotton than in June-planted cotton. Levels of photosynthetic rate or stomatal conductance were not correlated with adult whitefly densities for either planting date. Levels of glucose and fructose were positively correlated with whitefly densities only for June-planted cotton late in the season.     

Root Morphology and Zn^2＋ Uptake Kinetics of the Zn Hyperaccumulator of Sedum alfredii Hance

Root morphology and Zn^2＋ uptake kinetics of the hyperaccumulating ecotype （HE） and nonhyperaccumulating ecotype （NHE） of Sedum alfredii Hance were investigated using hydroponic methods and the radiotracer flux technique. The results indicate that root length, root surface area, and root volume of NHE decreased significantly with increasing Zn^2＋ concentration in growth media, whereas the root growth of HE was not adversely affected, and was even promoted, by 500μmol/L Zn^2＋. The concentrations of Zn^2＋ in both ecotypes of S. alfredii were positively correlated with root length, root surface area and root volumes, but no such correlation was found for root diameter. The uptake kinetics for ^65Zn^2＋ in roots of both ecotypes of S. alfredii were characterized by a rapid linear phase during the first 6 h and a slower linear phase during the subsequent period of investigation. The concentration-dependent uptake kinetics of the two ecotypes of S. alfredii could be characterized by the Michaelis-Menten equation, with the Vmax for ^65Zn^2＋ influx being threefold greater in HE compared with NHE, indicating that enhanced absorption into the root was one of the mechanisms involved in Zn hyperaccumulation. A significantly larger Vmax value suggested that there was a higher density of Zn transporters per unit membrane area in HE roots.     

Effect of Development Stage on the Artemisinin Content and the Sequence Characterized Amplified Region （SCAR） Marker of High-Artemisinin Yielding Strains of Artemisia annua L.

The effects of development states on the artemisinin content of clone S1 of Artemisia anuua L. grown in a greenhouse were investigated in the present study. The artemisinin content increased gradually during the phase of vegetative growth and reached its highest level at 8-9 mg/g dry weight （DW） when the S1 was 6 months old on a long day （LD） photoperiod. Treatment with 9-18 d of short day （SD） photoperiod resulted in the artemisinin content reaching and being maintained at a higher level （2.059-2.289 mg/g DW）, twofold that of control plants and plants of S1 presented at the pro-flower budding and flower-budding stages. The artemisinin content varied in different parts of the plant. The artemisinin content of leaves was higher than that of florets and branches. The artemisinin content in middle leaves was higher than that of bottom leaves, and then top leaves. Different densities of capitate glands （the storage organ of artemisinin） located on the surface of leaves, florets, and branches explained the variations in artemisinin content in these parts of the plant. The correlation coefficient between artemisinin content and density of capitate glands on the surface of different organs was 0.987. The genetic marker for artemisinin content was screened using random amplified polymorphic DNA （RAPD） and sequence characterized amplified region （SCAR） techniques. The random primer OPAl5 （5＇-TTCCGAACCC-3＇） could amplify a specific band of approximately 1 000 bp that was present in all high-artemisinin yielding strains, but absent in all low-yielding strains in three independent replications. This specific band was cloned and its sequence was analyzed. This RAPD marker was converted into a SCAR marker to obtain a more stable marker.     

Oxalate Accumulation as Regulated by Nitrogen Forms and Its Relationship to Photosynthesis in Rice （Oryza sativa L.）

Four-leaf rice seedlings (Oryza sativa L.), which had been cultivated in Kimura B complete nutrient solution, were treated with two nitrogen forms by replacing the nitrogen element in the complete solution with sole nitrate or ammonium (2.86 mmol/L). Nitrate-N nutrition tended to increase oxalate content in all parts of the plant, including the leaves, stems, roots, and root exudates, whereas ammonium had the opposite effect. Consequently, marked differences in oxalate content were observed between the two treatments throughout the time tested (0-12 d), with maximal differences of approximately 12-fold at 6d after treatment. Photosynthetic/respiratory parameters were examined over time simultaneously with changes in oxalate content. Net photosynthetic rate, chlorophyll fluorescence parameters (i.e. maximal photochemical efficiency (Fv/Fm) and photochemical quantum yields of photosystem (PS)II (ΦPSⅡ)), and respiratory rate were not significantly different between plants treated with the two nitrogen forms, although ammonium-fed plants had apparently higher leaf chlorophyll content than nitrate-fed plants. Leaf glucose content was altered little, but the content of fructose, sucrose, and total soluble sugar was significantly higher in the leaves of ammonium-fed plants than nitrate-fed plants. The results indicate that nitrate/ammonium may serve as efficient regulators of oxalate accumulation owing to regulation of metabolism in rice leaves rather than oxalate downward transfer and root excretion, and that photosynthetic metabolism is not directly correlated with the regulation of oxalate accumulation in rice plants.     

Much Improved Water Use Efficiency of Rice under Non-Flooded Mulching Cultivation

Water shortage is increasingly limiting the luxury use of water in rice cultivation. In this study, non-flooded mulching cultivation of rice only consumed a fraction of the water that was needed for traditional flooded cultivation and largely maintained the grain yield. We also investigated the growth and development of rice plants and examined grain yield formation when rice was subjected to non-flooded mulching cultivation. One indica hybrid rice combination was grown in a field experiment and three cultivation methods, traditional flooding （TF）, non-flooded straw mulching cultivation （SM） and non-flooded plastic mulching cultivation （PM）, were conducted during the whole season. Grain yield showed that there was no significant difference between SM and TF rice, but the grain yield of SM cultivation was significantly higher than that of PM. The tiller numbers were inhibited in the early stage under non-flooded mulching cultivation, but the situation was reversed at the later period. Both SM and PM rice reduced dry matter accumulation of shoot, but increased root dry weight, enhanced the remobilization of assimilates from stems to grains and increased the harvest index. During the middle and later grain filling period, mulched plants showed a faster decrease in chlorophyll concentrations, photosynthetic rates of flag leaves and root activity than TF rice, indicating that non-flooded mulching cultivation enhanced plant senescence. In comparison, SM treatment produced higher grain yield and, more dry matter accumulation and panicle numbers than the PM treatment. The overall results suggest that high yield of non-flooded mulching cultivation of rice can be achieved with much improved irrigaUonal water use efficiency.     

Effects of Local Nitrogen Supply on Water Uptake of Bean Plants in a Split Root System

To study the effects of local nitrogen supply on water and nutrient absorption, French bean （Phaseolus vulgaris L.） plants were grown in a split root system. Five treatments supplied with different nitrogen forms were compared： homogeneous nitrate （NN） and homogenous ammonium （AA） supply, spatially separated supply of nitrate and ammonium （NA）, half of the root system supplied with N-free nutrient solution, the other half with either nitrate （NO） or ammonium （AO）. The results showed that 10 d after onset of treatments, root dry matter （DM） in the nitratesupplied vessels treated with NA was more than two times higher than that in the ammonium-supplied vessels. Water uptake from the nitrate-supplied vessels treated with NA was 281% higher than under ammonium supply. In treatments NO and AO, the local supply of N resulted in clearly higher root DM, and water uptake from the nitratesupplied vessels was 82% higher than in the -N vessels. However, in AO plants, water uptake from the -N nutrient solution was 129% higher than from the ammonium-supplied vessels. This indicates a compensatory effect, which resulted in almost identical rates of total water uptake of treatments AA and AO, which had comparable shoot DM and leaf area. Ammonium supply reduced potassium and magnesium absorption. Water uptake was positively correlated with N, Mg and K uptake.     

棉花根系生长和空间分布特征

结合田间根钻取样和图像扫描分析方法, 研究了不同棉花品种根系的长度、直径和表面积动态及 0~ 10 0cm深和 0~ 4 0cm宽土壤范围内的空间分布特征。该方法与常规直尺测量结果相比相关系数R2 达到 0.899 (n =1318), 显示了较好的可靠性。研究结果表明, 棉花平均根长密度 (RLD) 在花铃期为 1.2 1~ 1.2 7mm·cm-3, 吐絮后降至 1.0 4~ 1.12mm·cm-3, 收花时为 0.76mm·cm-3 。棉花根平均直径在不同基因型间存在显著差异, 抗虫杂交棉的根直径最粗, 平均为 0.5 2mm ;早熟类型品种根直径较细, 平均为 0.36mm。在土壤深度上根直径的差异不显著, 但距棉行距离越远, 根的平均直径越小。在明确根系长度和直径动态规律的基础上, 提出了根表面积指数 (RAI) 的概念, 与地上部叶面积指数具有相似的含义和生物学意义, 且呈较好的指数相关关系 (R2 =0.779) 。RAI在生理发育时间 (PDT) 小于等于 4 0前, 其增长动态符合LOGISTIC生长规律 (R2 =0.84 9), 在PDT大于 4 0后, 呈线性递减趋势 (R2 =0.5 70~ 0.895 ), 且杂交抗虫棉的RAI在全生育期内均明显高于其它类型品种, 而早熟类型品种相对略低。RAI空间分布特征表现为, 开花前在浅根层内 (0~ 30cm) 分布最多, 花铃期以中层根系 (40~ 6 0cm) 为主, 吐絮后主要以深层 (70~ 10 0cm) 和距棉行较远的行间较多。研究结果为制定合理的施肥、灌溉措施提供了理论依据, 并量化了棉花根系的时空变化, 为进一步提高生长发育模拟模型的精度奠定了基础。     

Field performance of Solanum sisymbriifolium, a trap crop for potato cyst nematodes. II. Root characteristics

Hatching of potato cyst nematodes is induced by root exudates of Solanaceae, such as Solanum sisymbriifolium, and is therefore related to root length distribution of this crop. A mathematical model was derived to relate the hatching potential to root length density (RLD). A series of field experiments was carried out to study actual root length distribution of S. sisymbriifolium in relation to shoot properties and to provide input into the model. Using a modified Poisson distribution formula for the three‐dimensional distribution of roots in a volume of soil, the relation between the zone of influence of hatching agents and the RLD could be derived. On this basis, the minimal RLD was estimated, which is needed to expose 75%, 90% or 95% of cysts to root exudates, as a function of the length of the zone of influence of hatching agents on cysts. The logarithm of the total root length showed a linear relation with the logarithms of above‐ground biomass and with leaf area index. Root diameter distribution was the same for all crops examined and independent of soil depth. Fine roots (<0.4 mm in diameter) constituted around 50% of total root length. Using a zone of influence of 1.00, 0.75 and 0.50 cm around the centre of each root, a minimal RLD for sufficient soil exploration (75%) was estimated. Depth at which that minimal RLD was exceeded was linearly related to total root length (km m^?2) and to above‐ground crop biomass, enabling estimations being made of the potential hatching efficacy as related to measurable properties of S. sisymbriifolium crops. The proposed approach to derive potential hatching effects from crop properties needs further validation; particularly, the distance of influence of root exudates is a critical factor.     

Cultivar and planting date effects on soybean root growth

To avoid late summer drought, soybean [Gylcine max (L) Merrill] producers in many southern and border states of the USA modify their cropping systems. Options include use of unadapted cultivars and changing planting dates. Because root function is important to plant health and yield, this study was conducted to determine if planting date and soybean cultivar affect root growth and distribution. Seeds of one cultivar from each of four maturity groups (MG III, IV, V, and VI) were sown in mid-April, mid-May, and mid-June in 1992 and 1993 on a Tiptonville silt loam near Portageville, MO. Root observations were performed 30 and 60 days after emergence (DAE) using a minirhizotron system. Cultivars differed for root length density (RLD) only in the 15 to 28 cm depth in 1992 and in the 15 to 28 cm and 29 to 42 cm depths in 1993, but differences were not related to maturity classification of cultivar. Average RLD was 1.02 cm^–3 for MG III and IV cultivars and 1.21 cm cm^–3 for MG V and VI cultivars. Average RLD for the mid-June planting date was 1.65 cm cm^–3 but only 0.73 cm cm^–3 for the mid-April planting date. An increase in RLD between 30 and 60 DAE occurred at all soil depths. For both years, MG V and VI cultivars produced higher yields than the MG III cultivars. Earlier than normal planting dates inhibited early root growth, but did not reduce yield. Cultivars differed only slightly for the rooting characteristics measured in this study. These rooting characteristics may not be important criteria for cultivar selection.Abbreviations MG maturity group - VCR videocassette recorder - DAE days after emergence - RLD root length density - CRLD change in root length density Contribution from the Missouri Agric. Exp. Station Journal Series Number 12, 153Contribution from the Missouri Agric. Exp. Station Journal Series Number 12, 153     

Optimum plant densities for three semi-leafless combining pea (Pisum sativum) cultivars under contrasting field conditions

Yield and yield components of three semi-leafless pea (Pisum sativum) cultivars, of contrasting seed type/growth habit, were assessed at target planting densities of 40–140 plants/m² on nine sites over three years. Flat-topped parabolic/asymptotic yield/density relationships were obtained. The plant density required to maximise (p max) and optimise (p opt) yield differed between cultivars: Helka, small blue, p max 126 plants/m², p opt 101 plants/m²; Solara, large blue, p max 124 plants/m², p opt 94 plants/m²; and Countess, white-seeded, p max 104 plants/m², p opt 71 plants/m². Near-maximum yields were maintained between 70 and 140 plants/m² due to the ability of the pea crop to make compensatory increases in the number of pods per plant as density declined. Yield/density responses were influenced by site (e.g. soil type) more than by seasonal factors. The risk of yield reductions occurring at densities below 70 plants/m² was greater on a mineral soil than on a fertile organic soil. On the basis of agronomic and economic considerations, there was no evidence that target plant densities required to optimise yield should necessarily be higher for semi-leafless cultivars studied than for conventional leafed peas.     

樟树(Cinnamomum camphora)幼苗细根形态对氮磷添加和幼苗密度的响应

全球氮沉降对森林生态系统结构和功能的影响已成为现代生态学研究热点之一,我国华南地区氮沉降的增长引起了土壤酸化和磷限制加剧等一系列生态问题。密度制约着植物个体对环境资源的吸收利用,是自然界中十分重要的选择压力之一。因此研究樟树(Cinnamomum camphora)幼苗的细根形态对氮磷添加和密度的响应,有利于了解亚热带树木根系对氮沉降和磷添加与林分密度的响应过程和机制,并为全球变化背景下樟树林生态系统的管理提供依据。本研究以1年生樟树幼苗为试验材料,选择氯化铵(NH_4Cl)作为氮肥以模拟大气氮沉降,并且以二水合磷酸二氢钠(NaH_2PO_4·2H_2O)模拟磷添加,氮磷处理设置4个水平,即对照、施N、施P和施N+P;种植密度设置10、20、40和80株/m~2 4个水平。测定各处理樟树幼苗细根的根长、表面积、体积和根尖数,分析氮磷添加、密度和两者交互作用对樟树幼苗细根的影响。研究结果表明,与对照处理相比,N、P和N+P处理促进了幼苗细根长度、表面积、体积以及根尖数的增加。低密度条件下的N添加对幼苗根系形态的促进效果强于P添加。N+P处理对10、20、40株/m~2幼苗根系形态的促进效果最佳,而各处理对80株/m~2幼苗根系形态的促进效果均无显著性差异。随着种植密度的增大,幼苗细根长度、表面积、体积和根尖数均减少。樟树幼苗的细根长度、表面积、体积和根尖数在各密度间和不同氮磷添加处理间均有显著性差异,密度和氮磷处理间的交互作用对根系形态各指标均无显著影响。     

Seasonal dynamics of fine root biomass, root length density, specific root length, and soil resource availability in a Larix gmelinii plantation

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. __________ Translated from Acta Phytoecologica Sinica, 2005, 29(3): 403–410 [译自: 植物生态学报, 2005, 29(3): 403–410]     

Root length and biomass losses during sample preparation with different screen mesh sizes

Data are presented on the differences in root length density (RLD), dry matter (DM), and root diameter values determined on wheat and faba bean using sieves of different mesh size to separate roots from soil during sample preparation. Screens with 0.2, 1, and 2 mm (0.04, 1, and 4 mm²) aperture were used. Roots collected on the 2-mm sieve represented on average 55% of the weight and only 10% of the total length collected using a 0.2-mm sieve. With a 1-mm sieve 75% of weight was retained, but only 34% of the length. In the 0–20 cm soil layer average RLD and DM values ranged between 1.3 and 2.5 cm cm^-3 and 215 and 136 g m^-2 for faba bean and wheat respectively with 2 mm screens and 14.6 and 18.1 cm cm^-3 and 313 and 202 g m^-2 with 0.2 mm sieves. RLD was more affected than weight since losses from coarse screens were largely due to fine root fractions, although the 1-and 2-mm screens retained a small amount of fine roots that were long or attached to main structures. Variability was higher for measurements on coarser screens. The use of screens much coarser than the diameter of fine roots is not recommended for the study of surface-related phenomena in which root length quantification is necessary, while it may be acceptable for gross comparisons of root weight and spatial extent.     

Comparison of tomato root distributions by minirhizotron and destructive sampling

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.     

Short-Term Salinity Induced Changes in Two Wheat Cultivars at Different Growth Stages

Soluble sugars, proline, total chlorophyll contents and electrolyte leakage were measured in two wheat (Triticum aestivum L.) cultivars KRL 1-4 and HD 2009 at different growth stages [crown root initiation (CRI), flowering, and soft dough] under short term salinity (NaCl, CaCl₂ and Na₂SO₄). In control plants sugar contents were maximum at flowering stage. Proline and sugar concentrations increased in both cultivars under salinity with a maximum increase at CRI. Electrolyte leakage increased and chlorophyll content decreased with the plant age. A sharp increase of electrolyte leakage was noticed at salinity of 10 and 15 dS m^–1 in HD 2009 and KRL 1-4, respectively. The short-term salinity at CRI stage proved more detrimental as compared to salinity at flowering and soft dough stages in term of all biochemical changes induced. In wheat, plant resistance to salinity increased with the age of plant. The cultivar KRL 1-4 performed better under salinity as compared to HD 2009.     

宽窄行栽植模式下三倍体毛白杨根系分布特征及其与根系吸水的关系

采用剖面法对宽窄行栽植模式下三倍体毛白杨(triploid Populus tomentosa)的根系分布特征进行了研究;采用管式TDR系统对土壤剖面含水率变化动态进行了连续观测,并据此计算林木根系吸水速率,以探讨土壤含水率、根系分布和根系吸水分布之间的相关关系。研究结果表明:毛白杨的总平均根长密度在林带两侧和不同径向距离处非常接近(P>0.05);但在不同土层间变化很大(P<0.01),其中0-20和60-150 cm土层为根系主要分布区域,其根系所占比例共达86%;不同径阶间的根长密度差异显著(P<0.01),且其比例关系会随空间位置的改变而发生变化。不同栽植方位下,林带东侧毛白杨根系分布的浅层化程度高于西侧,且在径向240-280 cm内其0-0.5 mm的极细根显著多于西侧(P<0.05)。因此,宽窄行栽植模式下,深度和径阶是毛白杨根系分布的主要影响因子,而栽植方位会对其形态构型产生影响。毛白杨根系吸水模式受细根分布的影响,但会随土壤剖面水分有效性分布的变化而变化:当表土层水分有效性增加时,根系吸水主要集中在表土层;当表土层水分有效性降低时,深层土壤根系的吸水贡献率会逐渐增加;当土壤剖面水分条件异质性较高时,根系吸水主要集中在根系密度与水分有效性均较高的区域;当土壤剖面水分分布均匀且不存在水分胁迫时,根系吸水分布与细根分布最为一致。