Herbage yield, tiller number and root system activity after defoliation of prairie grass (Bromus catharticus Vahl)

The effects of defoliation upon root and shoot systems of prairie grass (Bromus catharticus Vahl) were examined in both field and pot studies. The varieties used were 78–32 (HY), a high-yielding variety; 79–42 (LY), a low-yielding variety; and the commercial variety Grasslands Matua. In the field, the presence of roots in early and late spring was estimated by measuring uptake of [³²P]phosphate by roots; herbage yields and tiller numbers were recorded. In a pot study, root and shoot dry-matter (DM) yields were analysed. In the field, roots were detected to a depth of 1·2 m. After defoliation to a height of 0·1 m, root presence decreased more than 50% at depths of 0·6 m for LY and 1·0 m for Matua in early spring and at several depths for each variety in late spring. After a second defoliation, the apparent growth rate of shoots decreased by 35% in relation to the first regrowth period. In pots, shoot DM and root DM of control plants (undefoliated) had the following allometric relationship of the form: In (shoot DM) = 0·61 + 1·14 ln (root DM) (r²= 0·81). After defoliation, compared with undefoliated controls, the relative growth rate of shoots and total herbage yields were higher, but root and stubble DM were lower in all three varieties. Pooled root DM means were 10·3 and 6·8 g plant^?1 and pooled stubble DM means were 12·7 and 7·6 g plant^?1 for control and defoliated plants respectively. HY produced heavier tillers than LY, pooled means being 0·94 and 0·53 g DM tiller^?1 (field study) and 3·44 and 2·05 g DM tiller^?1 (pot study) for HY and LY respectively. HY had 5–6 green leaves per tiller, whereas LY had 3–4. Developed green leaves were heavier in HY (58 g m^?2) than in LY (48 g m^?2). It is suggested that differences in both leaf parameters may be related to higher herbage yields for HY than LY.     

Physiological Response of Three Wheat Cultivars to High Shoot and Root Temperatures during Early Growth Stages

Abstract

Understanding wheat (Triticum aestivum L.) response to high shoot/root temperature during the early growth stages is important for successful production in tropical and subtropical environments. This study examined the physiological response of wheat cultivars to high shoot and/or root temperatures during early growth stages. Three cultivars; Imam, Fang and Siete Cerros were grown in soil and hydroponically at three shoot/root temperatures (23/23, 23/35 and 35/35ºC for the soil experiment; and 22/22, 22/38 and 38/38ºC for the hydroponic experiment). Leaf dry weight and leaf area plant-¹ were significantly decreased by high shoot/ root temperature (HS/HR, 35/35 and 38/38ºC) but was not affected by a normal shoot/high root temperature (NS/HR, 23/35 and 22/38ºC). The NS/HR (22/38ºC) and HS/HR (38/38ºC) treatments in the hydroponic experiment significantly decreased photosystem II quantum yield ( Φ_psii), photosynthetic rate (P_n) and specific leaf area (SLA) compared with the normal shoot/normal root (NS/NR, 22/22ºC) temperature treatment. Chlorophyll accumulation was significantly decreased by NS/HR, but increased significantly by HS/HR in most of the measuring dates. The heat-tolerant cultivar, Fang, always had the highest chlorophyll content, Φpsii and P_n under all temperature treatments, while the heat-sensitive cultivar, Siete Cerros, always had the greatest reduction in these traits especially towards the end of the experiment. Imam and Fang responded to HS/HR in the hydroponic experiment by immediate and greater reductions in leaf dry weight, total leaf area and SLA during the first wk of the treatments compared with Siete Cerros. The response changed with the treatments duration such that Imam showed the least reduction and Siete Cerros was the most affected cultivar towards the end of the experiment. Thus, wheat cultivars differentially responded to high shoot/root temperature by reducing the leaf weight and area and hence accumulating more chlorophyll in the diminished leaves. The failure to undergo such changes led to significantly lower chlorophyll accumulation, Φ_psii and P_n under high root temperature.     

Genotypic variation in patterns of root distribution, nitrate interception and response to moisture stress of a perennial ryegrass (Lolium perenne L.) mapping population

Genotypic variation in patterns of root distribution, nitrate interception and response to moisture stress were assessed in both parents and 198 progeny of a perennial ryegrass (Lolium perenne L.) full‐sibling mapping population. This was carried out in metre‐deep tubes of sand culture in a glasshouse experiment. The proportion of root dry matter (DM) weight in the top 10 cm of sand ranged from 0·33 to 0·75 and values of log₁₀(1 ? K), where K is the constant for an exponential model relating root DM weight and root depth, also showed wide variation among genotypes. The proportion of a pulse of ¹⁵N recovered in whole plants ranged from 0·124 to 0·431. There was a positive linear correlation between the proportion of ¹⁵N recovered and plant total DM weight, but no relationship between nitrate interception and patterns of distribution of DM weight of roots. Some genotypes responded to moisture stress by increasing root growth, and in others root growth was inhibited. It is concluded that this below‐ground variability in root variables may be an evolutionary adaptation by plant populations to survive heterogeneity in soil biotic and edaphic factors.     

施氮水平对7S亚基缺失大豆根系形态和结瘤固氮的影响

为有效推广功能型大豆7S亚基缺失品种,以7S亚基缺失大豆品系东富2号为研究对象,设置4种施氮水平(纯N),N0(0 mg·kg~(-1))、N1(25 mg·kg~(-1))、N2(50 mg·kg~(-1))、N3(75 mg·kg~(-1)),采用桶栽法研究大豆根系形态和结瘤固氮对不同施氮水平的响应。结果表明:N1(25 mg·kg~(-1))水平下根系干重加大,根冠比增大,根瘤固氮潜力高,单株产量较高。N2(50 mg·kg~(-1))水平下根长、根表面积、根体积在生育后期增长较快,根系干重较大,根冠比低,固氮酶活性最高,单株籽粒产量最高。N3(75 mg·kg~(-1))水平下植株干重较大,无效生长较多,根瘤数少,固氮潜力和根冠比低,单株产量不高。综合籽粒产量和根系特性指标,功能型大豆7S亚基缺失品系东富2号的适宜施肥量为25~50 mg·kg~(-1)。     

Effect of lowering the root/shoot ratio by pruning roots on water use efficiency and grain yield of winter wheat

A pot and a field experiment were conducted to assess the effects of root/shoot ratio (R/S) on the water use efficiency (WUE) and grain yield of winter wheat. The R/S was regulated by pruning the roots during the stem elongation stage, resulting in reduced root systems of the plants. At the heading stage, the root dry weight of root-pruned plants was less than that of intact-root plants, but their R/S was similar to that of intact-root plants under both experimental conditions. After tiller pruning, the R/S of root-pruned plants was significantly lower than that of intact-root plants (p < 0.05). Root pruning reduced the rate of leaf transpiration and lowered the number of tillers per plant (p < 0.05) during the vegetative stage. As a result, root-pruned wheat showed reduced water use when compared to intact-root plants before heading (p < 0.05). At anthesis, there was no significant difference in transpiration between plants with intact roots and those with pruned roots in the pots. However, under field conditions, transpiration of root-pruned plants was significantly higher than that of intact-root plants at anthesis. Additionally, at anthesis root-pruned plants had a higher rate of leaf photosynthesis and lower rate of root respiration, which resulted in a significantly higher grain yield at maturity when compared to plants with intact roots. Under both experimental conditions, there were no significant differences in shoot dry weight per plant between root-pruned and intact-root plants grown in monoculture. When root-pruned plants were grown with intact-root plants, the root-pruned wheat was less productive and had a lower relative shoot dry weight (0.78 and 0.86, respectively) than the intact-root plants (1.24 and 1.16, respectively). These results suggest that plants with pruned roots had a lower ability to compete and to acquire and use the same resources in the mixture when compared with intact-root plants. Root pruning improved the WUE of winter wheat under both experimental conditions. This suggests that appropriate management for the root system/tillers in wheat crops can be used to increase grain yield and water use efficiency. Specifically, lowering the R/S improved the grain yield and WUE of winter wheat significantly by lowering its competitive ability and improving root efficiency. Therefore, drought-resistance breeding to improve the grain yield and WUE, at least for wheat, should be made by targeted selection of less competitive progeny with a small R/S for cultivation in arid and semiarid areas.     

Effect of calcium silicate on growth and dry matter yield of Chloris gayana and Sorghum sudanense under two soil water regimes

The effects of five rates [0 (control), 1, 2, 4 and 6 Mg ha^?1] of calcium silicate on the growth and water consumption by rhodes grass (Chloris gayana Kunth) and sudan grass (Sorghum sudanense Piper) under wet and dry soil water regimes (60 g and 30 g H₂O kg^?1 soil respectively) were evaluated in a pot experiment. The effect of the application of silicate on plant biomass was similar to that of the control. However, the shoot and root dry mass varied significantly (P < 0.001) according to the soil water regime and plant species. During the first cut, the shoot dry mass was 5.7 g per pot under the wet soil moisture regime, significantly exceeding that under the dry soil water regime proportionately by 0.68. For sudan grass, the shoot dry mass varied from 3.6 g per pot in the control to 4.3 g per pot in the treatment that received 6 Mg ha^?1 of calcium silicate. Plant water demand decreased as the rate of calcium silicate application increased, suggesting that an application of calcium silicate could reduce drought stress and enhance water economy. For the soil under study, the reduction in plant water demand represents a water saving ranging from 0.076 to nearly 0.20.     

Changes in the physiology and feed quality of cocksfoot (Dactylis glomerata L.) during regrowth

Abstract A glasshouse study was undertaken to determine the physiological and morphological changes in cocksfoot (Dactylis glomerata L.) during regrowth after defoliation. Individual plants were arranged in a mini‐sward in a randomized complete block design. Treatments involved harvesting each time one new leaf had expanded (one‐leaf stage), up to the six‐leaf stage, with the plants separated into leaf, stubble (tiller bases) and roots. Stubble and root water‐soluble carbohydrate (WSC), stubble and leaf dry matter (DM), tiller number per plant and leaf quality (crude protein (CP), estimated metabolizable energy (ME) and mineral content) were measured to develop optimal defoliation management of cocksfoot‐based pastures. WSC concentration in stubble and roots was highest at the five‐ and six‐leaf stages. Mean WSC concentration (g kg^?1 DM) was greater in stubble than roots (32·7 ± 5·9 vs. 9·4 ± 1·5 respectively). There was a strong positive linear relationship between plant WSC concentration and leaf DM, root DM and tillers per plant after defoliation (Adj R² = 0·72, 0·88 and 0·95 respectively). Root DM plant^?1 and tiller DM tiller^?1 decreased immediately following defoliation and remained low until the three‐leaf stage, then increased from the four‐leaf stage. Tillers per plant remained stable until the four‐leaf stage, after which they increased (from 9·9 ± 0·5 to 15·7 ± 1·0 tillers plant^?1). Estimated metabolizable energy concentration (MJ kg^?1 DM) was significantly lower at the six‐leaf stage (11·01 ± 0·06) than at any previous leaf regrowth stage, whereas CP concentration (g kg^?1 DM) decreased with regrowth to the six‐leaf stage. Both the levels of ME and CP concentrations were indicative of a high quality forage throughout regrowth (11·37 ± 0·04 and 279 ± 8·0 for ME and CP respectively). Results from this study give a basis for determining appropriate criteria for grazing cocksfoot‐based pastures. The optimal defoliation interval for cocksfoot appears to be between the four‐ and five‐leaf stages of regrowth. Delaying defoliation to the four‐leaf stage allows time for replenishment of WSC reserves, resumption of root growth and an increase in tillering, and is before herbage is lost and quality falls due to onset of leaf senescence.     

耐盐促生菌筛选、鉴定及对盐胁迫小麦的效应

为利用盐碱地微生物促进植物适应盐逆境,从新疆玛纳斯河流域盐碱土壤中分离筛选出的耐盐菌株中,通过测定菌株生长特性及产吲哚乙酸(IAA)、铁载体、溶磷、固氮能力,得到1株耐盐高效促生菌株wp-8;结合形态观察、生理生化及16S rDNA鉴定了其种类;采用室内盆栽试验检测了其对盐胁迫小麦的效应。结果表明,菌株wp-8最适生长温度为30℃,最适生长pH为9,最适生长盐度为5%,吲哚乙酸分泌量为15.90 mg·L~(-1),铁载体相对含量为0.68,溶有机磷及无机磷量分别为0.34 mg·L~(-1)和1.10 mg·L~(-1);鉴定该菌为Nesterenkonia rhizosphaerae。在150 mmol·L~(-1)NaCl胁迫下,小麦种子接种wp-8生长50 d后,与对照相比,小麦株高、根长及根鲜重显著增加(P0.05),增长率分别为9.35%、27.15%、150%;单株鲜重也有所增加,但差异不显著;小麦幼苗根部丙二醛(MDA)含量显著降低(P0.05),超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性及叶片脯氨酸(Pro)含量显著增加,分别较对照增加160.63%、30.41%、44.93%、10.04%。说明菌株wp-8可缓解小麦盐胁迫并促进幼苗生长,尤其促进小麦根系的发育。     

Effect of plant age and severity of defoliation on regrowth of sheep's burnet during substrate moisture depletion

Regrowth of 3- and 4-month old (‘young’ and ‘old’ respectively) sheep's burnet [Sanguisorba minor ssp. muricata (Spach) Briq.] was studied under limiting and non-limiting moisture conditions in a glasshouse. Moisture deficits were imposed by using a single cycle of withholding moisture until first wilting. Plants of each age were defoliated severely at three levels which represented approximately 80–100% canopy removal. These levels were based on the proportion retained of the eight most mature leaves on each plant and were referred to as complete [0% residual leaf area (rLA)] and partial [50% rLA (four leaves) and 100% rLA (eight leaves)] defoliation. Vegetative growth and total non-structural carbohydrate (TNC) levels were studied. Leaf number (0-8 leaves), area (0-115 cm²) and dry weight (0-1·0 g) differed (P < 0·05) between defoliation intensities at the start of regrowth, while stubble (1·2 g) and root (12.·6 g) dry weights were similar. Soluble sugars [< 6% dry matter (DM)] and starch (< 1% DM) occurred in leaf, stubble and root. Old plants were morphologically and physiologically more developed than young plants. For example, stubble (2·0 g) and root (21·5 g) dry weights of old plants were greater (P < 0·05) than those of young plants (04 and 3·7 g respectively). Defoliation intensity had a major effect on regrowth, with completely defoliated plants at the final harvest having leaf numbers (forty-nine leaves) and areas (235 cm²) almost twice those of partially defoliated plants. Stubble soluble sugar levels (38% DM) were lower than those of partially defoliated plants (5·5% DM), and it was suggested that these contributed to regrowth. Moisture regime had a negligible influence on plant growth. However, plants in the dry regime had soluble sugar levels 1·4 (stubble) -1·7 (roots) times higher than those watered adequately, which suggested that plants adjusted to the water depletion. The effects of plant age on regrowth were similar for most characters, but the larger and physiologically more mature old plants would probably be more tolerant of successive defoliations.     

Effects of cutting frequency on plant production, N-uptake and N2 fixation in above- and below-ground plant biomass of perennial ryegrass–white clover swards

Nitrogen (N), accumulating in stubble, stolons and roots, is an important component in N balances in perennial ryegrass–white clover swards, and the effects of cutting frequency on the biomass of above‐ and below‐harvest height were studied during two consecutive years. Total dry matter (DM) and total N production, and N₂ fixation, were measured at two cutting frequencies imposed in the summers of two years either by cutting infrequently at monthly intervals to simulate mowing or by frequent cutting at weekly intervals to simulate grazing. Total DM production harvested was in the range of 3000–7000 kg DM ha^?1 with lower DM production associated with the frequent cutting treatment, and it was significantly affected by the different weather conditions in the two years. The higher cutting frequency also reduced the biomass below harvest height but the different weather conditions between years had less effect on stubble and, in particular, biomass of roots. The biomass of roots of white clover was significantly lower than that of roots of perennial ryegrass and remained at a relatively constant level (200–500 kg DM ha^?1) throughout the experiment, whereas the biomass of perennial ryegrass roots increased from 2400 kg DM ha^?1 in the year of establishment to 10 200 kg DM ha^?1 in the infrequent cutting treatment and 6650 kg DM ha^?1 in the frequent cutting treatment by the end of the experiment, giving shoot:root ratios of 4·7–16·6 and 0·5–1·6 for white clover and perennial ryegrass respectively. Annual N₂ fixation was in the range of 28–214 kg N ha^?1, and the proportion of N fixed in stolons and roots was on average 0·28. However, as weather conditions affect the harvested DM production and the shoot:root ratio, care must be taken when estimating total N₂ fixation based on an assumed or fixed shoot:root ratio.     

Comparative defoliation tolerance of temperate perennial grasses

The defoliation tolerance of cultivars of four temperate perennial pasture grasses, perennial ryegrass (Lolium perenne, cv. Yatsyn1), phalaris (Phalaris aquatica cv. Australian), tall fescue (Festuca arundinaceae cv. Demeter) and cocksfoot (Dactylis glomerata cv. Porto), was determined under controlled conditions over a period of 12 weeks. Undefoliated plants were compared with defoliated plants, where only half of one leaf was left intact at the initial defoliation, and leaf regrowth was harvested every 3–4 d. The growth responses measured were plant tiller number, dry weight, relative leaf regrowth rate, root:shoot ratio, sheath:stem ratio and specific leaf weight. All species showed morphological adaptations that potentially increased their ability to tolerate defoliation (e.g. increased allocation to shoot at the expense of roots and lower specific leaf weights) but cocksfoot was found to be the most defoliation‐tolerant and perennial ryegrass the least. The adaptation that favoured cocksfoot most strongly was high sheath:stem ratio, which, it is proposed, allowed it to maintain photosynthesis and a level of carbon supply sufficient to support regrowth throughout the experiment. The strategy of perennial ryegrass which favours leaf growth and leads to rapid leaf turnover rates made it particularly susceptible to defoliation under the conditions of this experiment. This highlights the likely importance of defoliation‐avoidance responses in explaining the well‐known grazing resistance of this species. Phalaris and tall fescue showed responses that were intermediate between the other two species. The importance of defoliation‐avoidance mechanisms and implications for grazing management are discussed.     

弱光胁迫下接种Glomus mosseae对玉米生长生理指标的影响

采用盆栽实验,以"云瑞47"为研究材料,Glomus mosseae(Gm)为接种菌剂,研究弱光和丛枝菌根真菌(AMF)对玉米生长生理的影响。结果表明,弱光作用下,玉米根系的AMF侵染率明显降低,叶片数、茎粗和总叶面积减少,植株地上部干重、地下部干重和总干重下降,株高增加,叶绿素a、叶绿素b、类胡萝卜素和总叶绿素含量上升,叶绿素a/b值降低,净光合速率减弱。弱光胁迫下接种Gm,能够增加玉米的叶片数、茎粗、株高和总叶面积,促进地上部干重、地下部干重和总干重的积累,提高叶片叶绿素a、叶绿素b、类胡萝卜素和总叶绿素含量,增强净光合速率。接种Gm真菌,能够缓解弱光对玉米生长产生的不良影响,促进植株生长。     

遮光和渍水对小麦幼苗形态和生长的影响

为了解遮光、渍水及其互作对小麦幼苗形态及生长性状的影响,以长江中下游不同年代小麦品种扬麦1号(20世纪70年代)、扬麦158(20世纪90年代)和扬辐麦4号(21世纪正在应用)为材料,通过盆栽试验研究了遮光、渍水后小麦幼苗主茎叶龄、单株茎蘖数、单株次生根数、苗高、叶面积、干物重、比叶重和根冠比的变化。结果表明,遮光处理显著延缓幼苗叶龄,抑制分蘖的发生,而渍水处理影响不显著;遮光和渍水处理均显著降低单株次生根数、叶面积、比叶重及地上部和根干重,遮光影响程度重于渍水,遮光和渍水同时处理仅对比叶重、地上部和根干重、根冠比表现出一定的累加效应。处理结束后经20d恢复,仅不遮光+渍水处理下叶龄、苗高和比叶重基本恢复到正常生长水平;不遮光+渍水处理下单株次生根数及各处理下根干重表现出恢复趋势。不同品种间幼苗形态和生长性状表现出显著的差异。扬辐麦4号和扬麦158单株次生根数和比叶重均显著高于扬麦1号。不同处理下扬辐麦4号幼苗形态和生长性状相比正常生长幼苗的变化幅度总体上小于其他品种,表现出较好的苗期抗渍及抗弱光能力。     

砷胁迫下磷用量对不同磷效率水稻苗生长、磷和砷吸收的影响

 通过盆栽试验研究了苗期砷胁迫下磷用量对磷高效水稻99011和磷低效水稻99056生长以及对P、As吸收的影响。试验设3个磷水平（0、30、150 mg/kg）和5个砷水平（0、25、50、100、200 mg/kg）。结果表明,苗期施砷显著增加了两个水稻品种地上部及地下部砷的含量,降低了两个水稻品种的株高、分蘖数、地上部及地下部干质量;施磷不但促进了两个水稻品种的生长,而且还增加了根系对砷的吸收量。当土壤砷浓度为25 mg/kg和50 mg/kg时,施用30 mg/kg磷抑制了两个水稻品种砷向地上部的转移,但施用150 mg/kg磷却促进了砷向地上部的转移。相同的处理,磷高效水稻99011地上部干质量和根干质量均显著高于磷低效水稻99056。施砷后,在30 mg/kg磷水平上磷低效水稻99056的砷转移系数最低。     

Physiology of the Potato: New Insights into Root System and Repercussions for Crop Management

Potato roots are concentrated mostly in the plow layer up to 30 cm in soil depth. Some roots extend up to 100 cm depth and the total root length throughout the soil profile reaches about 10–20 km m^?2 area. There are large differences in root mass (dry weight and length) in the plow layer between cultivars, breeding lines and wild relatives. The differences are generally stable across different environmental conditions, such as locations with different soil types, fertilizer rates and planting densities. Under favourable environmental conditions without severe shortage of water and nutrients, root mass differences between genotypes are related to maturity class: late genotypes continue root growth longer, and attain larger root mass and deeper rooting than early genotypes. Differences in root mass become clear at the start of flowering, much earlier than differences in shoot mass. Root mass is negatively correlated with early tuber bulking. However, root mass generally shows positive correlations with shoot mass and final tuber yield. Differences in root mass also exist amongst genotypes of the same maturity class. Using root mass in the plow layer and tuber yield as selection criteria, Konyu cultivars were bred in Japan. They showed significantly less reduction of leaf conductance and photosynthesis, leaf area and tuber yield than commercial cultivars under dry soil conditions. To assist breeding for root characters, new methods have been developed to assess the ability of roots to penetrate into hard soil layers using pots with paraffin-vaseline discs and the ability to absorb under low water potential in vitro. Physiological research on root characteristics contributed in the past, and will continue to do so in the future, to the development of new cultivars with high drought tolerance and to the improvement of irrigation practice.     

Effect of season and cutting frequency on root and shoot competition between Festuca pratensis and Dactylis glomerata

Abstract Plant competition strongly affects the species composition of managed grassland. To identify relevant processes, Festuca pratensis (Huds.) and Dactylis glomerata (L.) were grown as monocultures or mixtures in boxes placed in the field for two seasons and subjected to two cutting frequencies. Root and shoot competition effects were separated using soil and aerial partitions. Shoot competition was analysed by measuring the vertical distribution of the leaf area and root competition by analysing the absorption of tracers. Values of relative yield indicated that the two grasses fully competed for the same limiting resources under the experimental conditions. The competitive ability of F. pratensis was lower during both years relative to D. glomerata. This was mainly related to its consistently lower shoot competitive ability, which was associated with less leaf area in the upper layers of the canopy and shorter leaves. Root competitive ability of F. pratensis changed with season. It was similar to that of D. glomerata during spring and autumn, but less during summer. The lower root competitive ability in summer might be due to the lower root activity of F. pratensis, measured as rubidium (Rb) and strontium (Sr) absorption in July, 0·1 and 0·2 m below the ground. Cutting frequency did not greatly influence the relative importance of root and shoot competition during the first growing season. However, under infrequent defoliation, the competitive ability of F. pratensis decreased markedly in full competition during the second growing season. These results suggest that distinct differences in the canopy structure and root activity of different plant species can affect the relative importance of root and shoot competition during the season.     

Effects of Soil Moisture Conditions before Heading on Growth of Wheat Plants under Drought Conditions in the Ripening Stage: Insufficient Soil Moisture Conditions before Heading Render Wheat Plants More Resistant to Drought during Ripening

Abstract

Plants growing on soil with insufficient moisture need deep and dense roots to avoid water stress. In crop plants, the production of dry matter during ripening of grains is critically important for grain yield. We postulated that shoot growth would be suppressed but root growth would continue under an insufficient soil moisture condition before heading, while shoot growth would be more vigorous than root growth under a sufficient soil moisture condition. We anticipated that the plants growing under an insufficient soil moisture condition before heading would produce more dry matter and grain under an insufficient soil moisture condition during ripening. In order to examine our hypotheses and to determine the fundamental conditions for improving grain yield and efficient use of irrigated water under limited irrigation, we grew wheat plants (Triticum aestivum L., cv. Ayahikari) in pots (30 cm in diameter, 150 cm in height) with insufficient soil moisture (PD-D pots) or sufficient soil moisture (PW-D pots) for six weeks before heading followed by full irrigation, and then insufficient soil moisture condition during ripening. The growth of shoots was suppressed significantly but that of roots was not before heading in PD-D plants, with a higher resultant ratio of root to shoot than in PW-D plants. The former retained a high leaf water potential and, therefore, were able to produce more dry matter and grain during soil moisture depletion during ripening as compared with the latter plants. We also obtained similar results with field-grown plants.     

甲咪唑烟酸在土壤中的残留对后茬小麦幼苗生长和光合作用的影响

为探讨除草剂甲咪唑烟酸在土壤中的残留对后茬小麦幼苗生长和光合作用的影响,采用土壤添加法测定了在不同甲咪唑烟酸土壤残留浓度（0~1.2 mg·kg^-1）下麦苗根系和地上部生长、叶片光合参数的变化。结果表明,随着土壤中甲咪唑烟酸残留浓度的增加,麦苗的株高、单株鲜重和干重呈现降低的趋势,添加甲咪唑烟酸对根系生长的抑制作用大于地上部,导致麦苗根冠比下降和生长不均衡。甲咪唑烟酸处理均引起麦苗叶片叶绿素减少,暗呼吸速率上升。土壤中甲咪唑烟酸浓度较高时小麦光合速率显著受到抑制,1.2 mg·kg^-1处理的抑制率最大,达38.39%,净光合速率下降的原因主要是非气孔因素限制导致的。以上结果说明,甲咪唑烟酸土壤残留会对后茬小麦产生严重的影响,生产中应注意控制甲咪唑烟酸使用剂量和安全间隔期。     

Root System Development Including Root Branching in Cuttings of Cassava with Reference to Shoot Growth and Tuber Bulking

Summary

In spite of the important role it plays for water and nutrient acquisition, information on the root system development in cassava (Manihot esculenta Grantz) is limited. To examine the root length and branching pattern with reference to shoot growth and tuber bulking, we grew cassava plants in containers under natural climatic conditions in the southern end of Sumatra Island, Indonesia. One 20-cm length cutting of cassava (cv. Ardira IV) was planted in either a plastic bucket or a wooden box. The containers, which were filled with heavy clay soil, had different sizes depending on the growing period. At 30, 60, 100, 140, 180, and 270 days after planting (DAP), both the shoot and roots were sampled for quantitative analysis. The dry weight of both shoot and roots increased rapidly with the leaf area. The axile root number, however, decreased from 60 to 140 DAP as a result of the abscission of roots emerging from the basal part of the cutting during tuber bulking. The total root length reached its maximum at 60 DAP and significantly decreased thereafter because of decay and decomposition during tuber bulking. On the other hand, the root branching either increased the branching order or retained it, as determined from a topological point of view. The root branching during the later growing period compensated for the decrease in total root length and contributed to maintain a sufficient root surface area. The surviving roots with a well-developed branching pattern could absorb water and nutrients essential for tuber bulking.     

生物炭对土壤化学性质及水稻苗期生长的影响

研究表明,采用盆栽法,在土壤中添加油菜秸秆生物炭可极显著提高土壤的pH值和有机质含量,但对土壤全氮、碱解氮含量无显著影响;添加生物炭可显著或极显著增加水稻的根系活力、总根长、总根表面积、总根体积、分蘖数、叶面积、叶片叶绿素含量以及水稻各部位(根、茎、叶)干物质量.综上,添加生物炭有利于改善土壤肥力,进而促进水稻苗期根系...