Responses of Photosynthesis and Biomass Allocation of an Understorey Herb, Pteridophyllum racemosum, to Gradual Increases in Irradiance

In wave-regenerating Abies forests in central Japan, light availabilityon the forest floor of a mature-tree stand increases graduallyover 4 to 5 years during the senescence of trees. The understoreyevergreen perennialPteridophyllum racemosum Sieb. et Zucc. (Papaveraceae)is commonly found in such forests. To determine the acclimationcharacteristics of this species to gradual changes in lightavailability, leaf photosynthetic traits and biomass allocationpatterns were determined along a transect running from fullyshaded understorey to a canopy gap. Along the transect, thephoton flux density on the forest floor relative to full sun(RPFD) varied from 2.3–36.7%. The light-saturated netphotosynthetic rate of field-grown plants increased as the lightenvironment increased from 2.3–14.1% RPFD. However, aslight conditions increased from moderate (14.1%) to high (36.7%),the light-saturated net photosynthetic rate decreased to a levelcomparable to that exhibited by low-light grown plants. On theother hand, root mass per unit leaf area (RMA) increased withincreasing light conditions. A higher RMA contributes to a higherwater uptake capacity per unit leaf area which in turn supportshigher rates of photosynthesis and transpiration in high light.We conclude that in wave-regenerating forests P. racemosum cansurvive in high-light environments by avoiding a severe waterdeficit and heat load by increasing RMA. Copyright 2001 Annalsof Botany Company Biomass allocation, photosynthesis, Pteridophyllum racemosum, root mass per unit leaf area, wave regeneration     

Salt effects on functional traits in model and in economically important Lotus species

A common stress on plants is NaCl‐derived soil salinity. Genus Lotus comprises model and economically important species, which have been studied regarding physiological responses to salinity. Leaf area ratio (LAR), root length ratio (RLR) and their components, specific leaf area (SLA) and leaf mass fraction (LMF) and specific root length (SRL) and root mass fraction (RMF) might be affected by high soil salinity. We characterised L. tenuis, L. corniculatus, L. filicaulis, L. creticus, L. burtii and L. japonicus grown under different salt concentrations (0, 50, 100 and 150 mm NaCl) on the basis of SLA, LMF, SRL and RMF using PCA. We also assessed effects of different salt concentrations on LAR and RLR in each species, and explored whether changes in these traits provide fitness benefit. Salinity (150 mm NaCl) increased LAR in L. burtii and L. corniculatus, but not in the remaining species. The highest salt concentration caused a decrease of RLR in L. japonicus Gifu, but not in the remaining species. Changes in LAR and RLR would not be adaptive, according to adaptiveness analysis, with the exception of SLA changes in L. corniculatus. PCA revealed that under favourable conditions plants optimise surfaces for light and nutrient acquisition (SLA and SRL), whereas at higher salt concentrations they favour carbon allocation to leaves and roots (LMF and RMF) in detriment to their surfaces. PCA also showed that L. creticus subjected to saline treatment was distinguished from the remaining Lotus species. We suggest that augmented carbon partitioning to leaves and roots could constitute a salt‐alleviating mechanism through toxic ion dilution.     

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

Fine root tumover 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 Mav 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 (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 soil layer.RLD and SRL in May were the highestthe other months,and RLD was the lowest in Septemberdynamics 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.     

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]     

水曲柳根系生物量、比根长和根长密度的分布格局

采用连续钻取土芯法在生长季内对东北林业大学帽儿山实验林场17年生水曲柳人工林根系取样,研究水曲柳不同直径根系现存生物量、比根长和根长密度及垂直分布状况.结果表明,水曲柳人工林根系总生物量为1 637.6 g·m^-2,其中活根生物量占85%,死根占15%.在活根生物量当中,粗根(直径5～30 mm)占的比例最高（69.95%）,其次为活细根（直径<1 mm,13.53%）,小根(1～2 mm)和中等直径的根(2～5 mm)比例较小（分别为7.21%和9.31%）.直径<1 mm活细根的比根长为32.20 m·g^-1,直径5～30 mm粗根的比根长为0.08 m·g^-1.单位面积上活根的总长度为6 602.54 m·m^-2,其中直径<1 mm的细根占92.43%,其它直径等级则不到活根总长度的8%.直径<1 mm的细根生物量与根长密度具显著线性关系（R²=0.923）,但与比根长无显著相关关系（R²=0.134）.     

施肥对日本落叶松人工林细根直径、根长和比根长的影响

以辽宁东部山区16年生日本落叶松人工林为研究对象,探讨施肥对日本落叶松1～5级根序中细根直径、根长和比根长的影响.结果表明：随着根序等级的增加,日本落叶松细根平均直径和根长显著增加（P<0。05,P<0。01）、比根长则显著下降（P<0。01）.在日本落叶松的5级根序中,1级根的平均直径最细、根长最短、比根长最高,而5级根则相反;随着根序等级的增加,日本落叶松细根平均直径、根长和比根长的变异系数逐渐增大.除1级根外,土层对细根的平均直径、根长和比根长没有显著影响(P>0。05).与对照样地相比,施肥对各级细根平均直径、根长和比根长的影响主要表现在1～2级根上,对3级根序以上的细根影响不显著（P>0.05）.其中,施氮肥显著降低了1～2级根的平均直径（P<0.05）,施氮肥以及氮磷肥显著降低了表层土壤（0～10 cm）中1级根的平均根长（P<0.05）,表层土壤中细根的比根长在施氮肥的条件下显著增加（P<0.05）.     

Specific root length as an indicator of environmental change

Abstract

Specific root length (SRL, m g^?1) is probably the most frequently measured morphological parameter of fine roots. It is believed to characterize economic aspects of the root system and to be indicative of environmental changes. The main objectives of this paper were to review and summarize the published SRL data for different tree species throughout Europe and to assess SRL under varying environmental conditions. Meta-analysis was used to summarize the response of SRL to the following manipulated environmental conditions: fertilization, irrigation, elevated temperature, elevated CO₂, Al-stress, reduced light, heavy metal stress and physical disturbance of soil. SRL was found to be strongly dependent on the fine root classes, i.e. on the ectomycorrhizal short roots (ECM), and on the roots <0.5 mm, <1 mm, <2 mm and 1 – 2 mm in diameter SRL was largest for ECM and decreased with increasing diameter. Changes in soil factors influenced most strongly the SRL of ECM and roots <0.5 mm. The variation in the SRL components, root diameter and root tissue density, and their impact on the SRL value were computed. Meta-analyses showed that SRL decreased significantly under fertilization and Al-stress; it responded negatively to reduced light, elevated temperature and CO_2. We suggest that SRL can be used successfully as an indicator of nutrient availability to trees in experimental conditions.     

Long-term warming effects on root morphology, root mass distribution, and microbial activity in two dry tundra plant communities in northern Sweden

Effects of warming on root morphology, root mass distribution and microbial activity were studied in organic and mineral soil layers in two alpine ecosystems over>10 yr, using open-top chambers, in Swedish Lapland. Root mass was estimated using soil cores. Washed roots were scanned and sorted into four diameter classes, for which variables including root mass (g dry matter (g DM) m(-2)), root length density (RLD; cm cm(-3) soil), specific root length (SRL; m g DM(-1)), specific root area (SRA; m2 kg DM(-1)), and number of root tips m(-2) were determined. Nitrification (NEA) and denitrification enzyme activity (DEA) in the top 10 cm of soil were measured. Soil warming shifted the rooting zone towards the upper soil organic layer in both plant communities. In the dry heath, warming increased SRL and SRA of the finest roots in both soil layers, whereas the dry meadow was unaffected. Neither NEA nor DEA exhibited differences attributable to warming. Tundra plants may respond to climate change by altering their root morphology and mass while microbial activity may be unaffected. This suggests that carbon may be incorporated in tundra soils partly as a result of increases in the mass of the finer roots if temperatures rise.     

The effects of clipping and soil moisture on leaf and root morphology and root respiration in two temperate and two tropical grasses

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.     

Consequences of phenotypic plasticity vs. interspecific differences in leaf and root traits for acquisition of aboveground and belowground resources

Trade-offs between acquisition capacities for aboveground and belowground resources were investigated by studying the phenotypic plasticity of leaf and root traits in response to different irradiance levels at low nutrient supply. Two congeneric grasses with contrasting light requirements, Dactylis glomerata and D. polygama, were used. The aim was to analyze phenotypic covariation in components of leaf area and root length in response to above- and belowground resource limitation and the consequences of this variation for resource acquisition and plant growth. At intermediate shading (30 and 20% of full sunlight) the plants were able to maintain their total root length, despite a strongly increased total leaf area and a reduced biomass allocation to roots. This was associated with an unaltered or slightly increased nutrient uptake and growth. At 5.5% relative irradiance, growth was severely reduced, especially in the shade-tolerant D. polygama. The results show that constraints on acquisition capacities for aboveground and belowground resources, caused by biomass allocation, may be alleviated by plasticity in other traits such as tissue-mass density and thickness of roots and leaves. The results also suggest different adaptive constraints for phenotypic plasticity and for genetically determined interspecific variation. Phenotypic plasticity tends to maximize resource acquisition and growth rate in the short term, whereas the higher tissue-mass density and the longer leaf life-span of shade-tolerant species indicate reduced loss rates as a more advantageous species-specific adaptation to shade in the long term.     

黄土高原白羊草、沙棘和辽东栎细根比根长特性

以黄土高原地区典型草本（白羊草）、灌木（沙棘）和乔木（辽东栎）为对象,研究了3种植物细根比根长在不同土层的分布状况以及与其它细根参数和土壤物理因子之间的相关性。结果表明,3种植物细根比根长的变化范围为6～55ram／rag。在0,80cm土层,白羊草、沙棘和辽东栎细根比根长变化范围分别为18—55mm／mg,14—4JDmm／mg,6—33mm／mg。3种植物0--80cm土层平均细根比根长从大到小依次为白羊草〉沙棘〉辽东栎。3种植物0-10cm土层细根比根长依次为沙棘〉辽东栎〉白羊草,10-80cm依次为白羊草〉辽东栎〉沙棘,表明3种植物细根比根长不仅在这两土层中的分布不具一致性,而且与0-80cm土层平均比根长也不具有一致性,进一步说明3种植物沿土壤剖面的生物量分配策略不同。相关分析表明,3种植物细根比根长与其它细根参数之间的相互关系各不相同,制约程度存在差异。与土壤物理因子的相关分析表明,3种植物细根比根长均随土壤含水量的增加而减少。土壤各级水稳性团聚体和土壤颗粒对3种植物细根比根长并无一致的影响。     

羌塘高原降水梯度植物叶片、根系性状变异和生态适应对策

叶片和根系是植物获取资源的最重要的器官,其性状随环境梯度的变化反映了植物光合碳获取和水分与养分的吸收能力及其对环境变化适应的生态对策。羌塘高原降水梯度带高寒草地群落叶片和根系成对性状关系研究不仅能揭示环境梯度对植物性状的塑造作用,也可为理解寒、旱和贫瘠等极端环境下植物的适应策略提供依据。为此,选择3组具有代表性的叶片和根系成对性状:比叶面积(SLA)和比根长(SRL);单位质量叶氮含量(LN_(mass))和单位质量根氮含量(RN_(mass));单位面积叶氮含量(LN_(area))和单位长度根氮含量(RN_(length)),分析不同优势植物地上、地下成对性状变异特征及其与环境因子的关系,探讨植物性状对高寒生态系统水分和养分限制因素的适应策略。研究表明,区域气候和土壤环境导致的叶片性状变异大于根系性状的变异,干旱端的植物既具有高的SRL,又具有高的叶片和根系的养分含量(LN_(mass),LN_(area)和RN_(mass))。SLA-SRL、LN_(mass)-RN_(mass)、LN_(area)-RN_(length)均表现为权衡关系,在干旱端(年降雨量MAP 400 mm)的高寒草原、荒漠草原和极湿润端(MAP 600 mm)的高寒草甸这种权衡关系更为明显,而中间区域(400 MAP 600 mm)的高寒草甸养分和水分限制不是很强烈,叶片和根系性状更多地表现出协同关系。从植物功能类群来看,苔草和禾草类植物叶片和根系成对性状之间具有更强烈的权衡关系。干旱端植物通过增加SRL和叶片、根系养分含量来提高水分和养分的吸收能力,同时通过叶片高的氮含量提高光合碳获取能力,保障了根系生长的物质来源,表现出地上和地下同时投入的策略。干旱端植物保持较高的养分含量是抵御和适应严酷的寒、旱和贫瘠的环境胁迫的重要策略。而在湿润端植物则采取增加SLA,维持地上光合生产力的生态策略。     

青杨人工林根系生物量、表面积和根长密度变化

在植物生长季节,采用钻取土芯法对秦岭北坡50年生青杨人工林根径≤2 mm和2～5 mm根系的生物量、表面积和根长密度进行测定.结果表明：在青杨人工林根系(＜5 mm)中,根径≤2 mm根系占总生物量的77.8%,2～5 mm根系仅占22.2%;根径≤2 mm根系表面积和根长密度占根系总量的97%以上,而根径2～5 mm根系不足3%.随着土层的加深,根径≤2 mm根系生物量、表面积和根长密度数量减少,根径2～5 mm根系生物量、表面积和根长密度最小值均分布在20～30 cm土层.≤2 mm根系生物量、表面积和根长密度与土壤有机质、有效氮呈极显著相关,而根径2～5 mm根系的相关性不显著.     

Plasticity in above‐ and belowground resource acquisition traits in response to single and multiple environmental factors in three tree species

Functional trait plasticity is a major component of plant adjustment to environmental stresses. Here, we explore how multiple local environmental gradients in resources required by plants (light, water, and nutrients) and soil disturbance together influence the direction and amplitude of intraspecific changes in leaf and fine root traits that facilitate capture of these resources. We measured population‐level analogous above‐ and belowground traits related to resource acquisition, i.e. “specific leaf area”–“specific root length” (SLA–SRL), and leaf and root N, P, and dry matter content (DMC), on three dominant understory tree species with contrasting carbon and nutrient economics across 15 plots in a temperate forest influenced by burrowing seabirds. We observed similar responses of the three species to the same single environmental influences, but partially species‐specific responses to combinations of influences. The strength of intraspecific above‐ and belowground trait responses appeared unrelated to species resource acquisition strategy. Finally, most analogous leaf and root traits (SLA vs. SRL, and leaf versus root P and DMC) were controlled by contrasting environmental influences. The decoupled responses of above‐ and belowground traits to these multiple environmental factors together with partially species‐specific adjustments suggest complex responses of plant communities to environmental changes, and potentially contrasting feedbacks of plant traits with ecosystem properties. We demonstrate that despite the growing evidence for broadly consistent resource‐acquisition strategies at the whole plant level among species, plants also show partially decoupled, finely tuned strategies between above‐ and belowground parts at the intraspecific level in response to their environment. This decoupling within species suggests a need for many species‐centred ecological theories on how plants respond to their environments (e.g. competitive/stress‐tolerant/ruderal and response‐effect trait frameworks) to be adapted to account for distinct plant‐environment interactions among distinct individuals of the same species and parts of the same individual.     

光强对木麻黄幼苗根系形态、解剖结构及其碳氮含量的影响

对光环境的灵敏响应使得森林中常见的光照异质性成为影响植物自我更新的关键因素,然而植物地下根系结构对光照的响应较为难测而缺乏深入研究。为探究不同光强下木麻黄根系响应策略,以一年生木麻黄(Casuarina equisetifolia)幼苗为试验材料,模拟森林幼苗生长的林外(CK)、林缘(L1)、林窗(L2)和林下光环境(L3)设置4种光照强度,测定及分析木麻黄幼苗的生长、根系形态、细根解剖结构及碳氮含量等指标。结果表明:(1) L1下,幼苗采取维持高度,降低横向生长的方式,保证正常累积生物量,随光照强度的下降,株高、地径、叶片生物量及地上部分生物量逐渐下降。(2)在根系表型上,幼苗随光限制的加重呈现抑制纵伸但促进根系的横向生长,其中总根长、根平均直径及根体积达到显著差异。在径级结构上,细根发育程度随光照减弱而下降;而适当的遮光(L1)促进粗根生长但L3时除根尖数较CK上升外,根长度、根表面积、根体积均显著下降。(3)1-3级细根解剖变化较大,相较CK,1级细根皮层细胞面积显著增加,但根半径、维管柱结构、表皮厚度等指标则显著下降,2级细根根半径、皮层细胞面积、表皮厚度明显减少,但维管柱结构仅在L2、L3时显著下降;3级细根根半径、皮层细胞面积和维管柱面积均较CK显著增大,L1时维管柱结构下降,但随光照减弱加重,维管柱面积和中柱占比均明显增加。(4)在碳氮含量上,CK与L1无显著差异,TC在L2时显著下降,TN则在L2时显著上升,TC、TN均在L3达到最大,而C∶N随光强降低逐渐下降。综上所述,光限制时,木麻黄生物量及碳分配稳定根茎部分生长,采取“弱化吸收,强化储存”收缩型生长策略;当限制加重时,光合和呼吸作用失衡导致植物对细根投入养分的浪费,并最终造成林木死亡。研究结果为林下植被的更新提供理论参考。     

Effects of soil temperature on root and shoot growth traits and iron deficiency chlorosis in sorghum genotypes grown on a low iron calcareous soil

Iron deficiency chlorosis (FeDC) is a common disorder for sorghum [Sorghum bicolor (L.) Moench] grown on alkaline calcareous soils. Four sorghum genotypes were grown in growth chambers on a low Fe (1.3 g/g DTPA-extractable), alkaline (pH 8.0), calcareous (3.87% CaCO₃ equivalent) Aridic Haplustoll to determine effects of different soil temperatures (12, 17, 22 and 27°C at a constant 27°C air temperature) on various root and shoot growth traits and development of FeDC. As soil temperature increased, leaf chlorosis became more severe, and shoot and root dry weights, root lengths, and leaf areas increased markedly. Shoot/root ratios, shoot weight/root length, leaf area/shoot weight and leaf area/root weight and root length also increased while root length/root weight decreased as soil temperature increased. Severe FeDC developed in all genotypes even though genotypes had previously shown different degrees of resistance to FeDC. Genotypes differed in most growth traits, especially dry matter yields, root lengths, and leaf areas, but most traits did not appear to be related to genotype resistance to FeDC. The most FeDC resistant genotype had the slowest growth rate and this may be a mechanism for its greater resistance to FeDC.     

Influence of storage methods on corn root length measurements

This study evaluated the changes in root length, mass, and diameter after air drying and rehydration of corn (Zea mays L.) root samples. For corn roots washed from soil, rehydrated root length was not reduced when compared with fresh root length, but rehydrated root mass was reduced to about half of fresh root mass, and rehydrated root diameter was approximately 75% of fresh diameter. Three storage methods (air dried, 70% ethanol, and 5% formaldehyde solution) were also compared for corn roots grown in moist paper towels. Although root mass and diameter were significantly reduced by air drying, root length was not altered by any of the treatments.     

Allocation,within and between organs,and the dynamics of root length changes in two birch species

Spatial and temporal dynamics of biomass allocation within and between organs were investigated in seedlings of two birch species of contrasting successional status. Seedlings of Betula alleghaniensis Britt (yellow birch) and B. populifolia Marsh (gray birch) were grown for 6 weeks at two nutrient levels in rectangular plexiglass containers to allow non-destructive estimates of root growth, production and loss. Leaf area and production were simultaneously monitored. Yellow birch responded more to nutrient level than gray birch in terms of total biomass, shoot biomass, leaf area and root length. Yellow birch also flexibly altered within-organ allocation (specific leaf area, specific root length and specific soil amount). In contrast, gray birch altered between-organ allocation patterns (root length:leaf area and soil amount:leaf area ratios) more than yellow birch in response to nutrient level. Yellow birch showed greater overall root density changes within a very compact root system, while gray birch showed localized root density changes as concentric bands of new root production spread through the soil. Species differ critically in their responses of standing root length and root production and loss rates to nutrient supply. Early successional species such as gray birch are hypothesized to exhibit higher plasticity in varied environments than later successional species such as yellow birch. Our results suggest that different patterns of allocation, within and between plant organs, do not necessarily follow the same trajectories. To characterize thoroughly the nature of functional flexibility through ontogeny, within- and between-organ patterns of allocation must be accounted for.     

Leaf and fine root carbon stocks and turnover are coupled across Arctic ecosystems

Estimates of vegetation carbon pools and their turnover rates are central to understanding and modelling ecosystem responses to climate change and their feedbacks to climate. In the Arctic, a region containing globally important stores of soil carbon, and where the most rapid climate change is expected over the coming century, plant communities have on average sixfold more biomass below ground than above ground, but knowledge of the root carbon pool sizes and turnover rates is limited. Here, we show that across eight plant communities, there is a significant positive relationship between leaf and fine root turnover rates (r² = 0.68, P < 0.05), and that the turnover rates of both leaf (r² = 0.63, P < 0.05) and fine root (r² = 0.55, P < 0.05) pools are strongly correlated with leaf area index (LAI, leaf area per unit ground area). This coupling of root and leaf dynamics supports the theory of a whole‐plant economics spectrum. We also show that the size of the fine root carbon pool initially increases linearly with increasing LAI, and then levels off at LAI = 1 m² m^?2, suggesting a functional balance between investment in leaves and fine roots at the whole community scale. These ecological relationships not only demonstrate close links between above and below‐ground plant carbon dynamics but also allow plant carbon pool sizes and their turnover rates to be predicted from the single readily quantifiable (and remotely sensed) parameter of LAI, including the possibility of estimating root data from satellites.     

Does the photosynthetic light‐acclimation need change in leaf anatomy?

There is a strong correlation between leaf thickness and the light‐saturated rate of photosynthesis per unit leaf area (P_max). However, when leaves are exposed to higher light intensities after maturation, P_max often increases without increasing leaf thickness. To elucidate the mechanism with which mature leaves increase P_max, the change in anatomical and physiological characteristics of mature leaves of Chenopodium album, which was transferred from low to high light condition, were examined. When compared with leaves subjected to low light continuously (LL leaves), the leaves transferred from low to high light (LH leaves) significantly increased P_max. The transfer also increased the area of chloroplasts facing the intercellular space (S_c) and maintained a strong correlation between P_max and S_c. The mesophyll cells of LL leaves had open spaces along cell walls where chloroplasts were absent, which enabled the leaves to increase P_max when they were exposed to high light (LH). However, the LH leaves were not thick enough to allow further increase in P_max to the level in HH leaves. Thus leaf thickness determines an upper limit of P_max of leaves subjected to a change from low to high light conditions. Shade leaves would only increase P_max when they have open space to accommodate chloroplasts which elongate after light conditions improve.