隔离降水对杉木幼苗细根生物量和功能特征的影响

在福建三明陈大国有采育场杉木幼苗小区,采用土钻法和内生长环法,以非隔离降水为对照,对隔离降水50%处理一年的杉木幼苗细根生物量和形态、化学计量学、比根呼吸、非结构性碳水化合物等功能特征进行研究.结果表明: 与对照相比,隔离降水处理0～1 mm细根生物量显著降低,1～2 mm细根生物量差异不显著;隔离降水导致细根在形态上发生了适应性变化,0～1 mm和1～2 mm细根比根长分别增加21.1%和30.5%,0～1 mm细根组织密度显著降低,而比表面积显著增加.隔离降水导致细根氮的富集,但限制了对磷的吸收,氮磷比升高,导致营养失衡;隔离降水没有显著改变细根比根呼吸和非结构性碳水化合物含量,但导致1～2 mm细根可溶性糖、糖淀比显著降低,淀粉含量增加33.3%,表明其通过增加非结构性碳水化合物贮存比例以应对降水减少.     

杉木幼苗非结构性碳水化合物对遮阴及恢复光照的响应

该研究以盆栽杉木(Cunninghamia lanceolata)幼苗为研究对象,采用遮光率为60%的遮光网进行遮阴处理,以正常光照为对照,遮阴处理30 d后部分杉木幼苗进行20 d的光照恢复处理,测定分析遮阴及恢复光照处理后不同组织/器官的非结构性碳水化合物(NSC)浓度及其分配、以及NSC库的变化,以探讨杉木幼苗在遮阴及恢复光照后的NSC调控机制。结果显示:(1)遮阴能够显著降低杉木幼苗各组织/器官可溶性糖浓度,各组织/器官下降幅度依次为细根(71%)>当年生叶(68%)>一年生叶(58%)>树皮(57%)>木质部(55%)>粗根(45%);遮阴使淀粉浓度的下降程度显著高于可溶性糖,在所有组织/器官中粗根的淀粉浓度下降幅度最低(50%),其次是木质部(72%)细根的淀粉浓度下降最大。(2)遮阴处理使杉木幼苗各组织/器官的NSC浓度下降量均超过50%,但杉木幼苗的存活率依然为100%;遮阴后杉木幼苗的生物量变化无明显差异,但NSC库变小,NSC相对分配改变;遮阴后不同组织/器官的NSC下降程度不一,其中粗根的NSC浓度显著高于细根。(3)恢复光照处理后杉木幼苗各组织/器官的NSC浓度均可恢复到对照水平。研究证明,遮阴环境下杉木幼苗能够主动调节其NSC在各组织/器官的分配使其维持在一定范围,从而提高杉木幼苗对遮阴环境的适应性,而不是以牺牲生长为代价。     

Correlated responses of root growth and sugar concentrations to various defoliation treatments and rhythmic shoot growth in oak tree seedlings (Quercus pubescens)

Background and Aims

To understand whether root responses to aerial rhythmic growth and contrasted defoliation treatments can be interpreted under the common frame of carbohydrate availability; root growth was studied in parallel with carbohydrate concentrations in different parts of the root system on oak tree seedlings.

Methods

Quercus pubescens seedlings were submitted to selective defoliation (removal of mature leaves, cotyledons or young developing leaves) at appearance of the second flush and collected 1, 5 or 10 d later for morphological and biochemical measurements. Soluble sugar and starch concentrations were measured in cotyledons and apical and basal root parts.

Key Results

Soluble sugar concentration in the root apices diminished during the expansion of the second aerial flush and increased after the end of aerial growth in control seedlings. Starch concentration in cotyledons regularly decreased. Continuous removal of young leaves did not alter either root growth or apical sugar concentration. Starch storage in basal root segments was increased. After removal of mature leaves (and cotyledons), root growth strongly decreased. Soluble sugar concentration in the root apices drastically decreased and starch reserves in the root basal segments were emptied 5 d after defoliation, illustrating a considerable shortage in carbohydrates. Soluble sugar concentrations recovered 10 d after defoliation, after the end of aerial growth, suggesting a recirculation of sugar. No supplementary recourse to starch in cotyledons was observed.

Conclusions

The parallel between apical sugar concentration and root growth patterns, and the correlations between hexose concentration in root apices and their growth rate, support the hypothesis that the response of root growth to aerial periodic growth and defoliation treatments is largely controlled by carbohydrate availability.     

大气CO2浓度升高对红桦幼苗根系的影响

应用封闭式生长室系统,研究了CO2浓度升高对红桦(Betula albosinensis)幼苗的根/冠、粗根和细根的干质量、非结构性碳水化合物类含量、碳含量和碳/氮、氮和磷的含量及氮磷吸收量的影响。结果表明:CO2浓度升高使红桦幼苗粗根和细根的干质量增加,同时根/冠值显著升高,表明CO2浓度升高使红桦幼苗生物量向根系的分配增加;与对照相比,粗根的还原糖、蔗糖和总可溶性糖含量显著增加,而在细根中没有显著变化;粗根、细根的淀粉和总的非结构性碳水化合物含量显著增加;CO2浓度升高下粗根和细根的碳含量有升高的趋势但未达到显著水平,同时氮含量降低,碳/氮值升高;氮的吸收量在粗根和细根中均无显著变化。上述结果表明,CO2浓度升高下红桦幼苗根系氮含量下降是由非结构性碳水化合物(主要是淀粉)含量升高和(或)根系生物量增加产生的稀释效应引起的。     

Morphological and root carbohydrate responses of bald cypress to water level and water temperature regimes

1. 1. Reduced carbohydrate reserves have been suggested as a factor in the decline of bald cypress in swamp areas impacted by thermal effluents.

2. 2. Morphological characteristics and root carbohydrate concentrations were examined for bald cypress seedlings subjected to three temperature regimes (ambient, mid, and high) and three water levels (drained, saturated and flooded).

3. 3. Although few differences in total root carbohydrate concentrations existed after 3 weeks, the proportion of starch to sugar decreased with increasing temperature treatment.

4. 4. After senescence, mid saturated seedlings had the greatest aboveground and belowground biomass, whereas high flooded seedlings had the lowest concentration of root carbohydrates.

Effect of restricted watering and its combination with root pruning on root growth capacity,water status and food reserves ofPinus caribaea var.hondurensis seedlings

Summary Six-month oldPinus caribaea var.hondurensis seedling were subjected to various regimes of restricted watering and their combinations with root pruning to determine a suitable technique of producing seedlings with optimum physiological condition for successful bare-root planting.From the range of treatments tested, plants subjected to watering once every 9 days (D9) were found to be the hardest in terms of highest root growth capacity, leaf water content, root starch content and in having a moderately low transpiration rate.P. caribaea seedlings subjected to this preconditioning treatment may be more able to survive bare-root planting.     

Production of fine roots and the seasonality of their growth in a Mexican deciduous dry forest

Very limited information regarding fine-root growth and production of tropical dry forests is available. Fine roots and small roots are defined as rootlets with diameters < 1 mm and 1.1 to 5 mm, respectively. Live and dead fine-and small-root mass fluctuations were studied over one year by means of soil core analyses in the deciduous dry forest of Chamela, Mexico, at 19° 30, 2 km inland from the Pacific Ocean. By means of systematically varying the distance of soil core extraction points from tree stems, it was shown that random core collection is justified. A difference between fine-root biomass on south and north facing slopes was documented, although this difference was significant only during the rainy season. The live/dead ratio of fine roots was highest during the rainy period. The annual fine-root production for 1989 was estimated at 4.23 Mg ha^-1 by summing significant fine-root biomass changes between sampling dates. This value is higher than most of the comparable data from other ecosystems.     

Anatomical characteristics of individual roots within the fine-root architecture of Chamaecyparis obtusa (Sieb. & Zucc.) in organic and mineral soil layers

Nutrient availability and temporal variation of physical stress are usually higher in organic soil layers than in mineral soils. Individual roots within the fine-root system adjust anatomical, morphological, and turnover characteristics to soil conditions, for example nutrient availability and physical stresses. We investigated anatomical traits, including cork formation and passage and protoxylem cell numbers, in cross-sections of individual fine roots of the conifer Chamaecyparis obtusa (Siebold & Zucc.) growing under different soil conditions. The fine-root systems in different soil layers were compared by sampling ingrowth cores buried for 1 year and filled with organic and mineral soil substrates. The number of exodermal passage cells was lower in roots from organic soils than in those from mineral soils, suggesting that apical roots tend to be more stress-tolerant in the organic layer than in mineral soils. In contrast, both root tip and specific root tip density were higher in roots from organic soils than in those from mineral soil layers. The proportion of roots with two strands of protoxylem (diarch) was greater in organic (90%) than in mineral (25%) soils. Thus, although the absorptivity of individual apical roots decreases in organic layers, the absorptivity of the entire fine-root system of C. obtusa may be increased as a result of the increase in apical root density and the proportion of ephemeral roots. We found that the fine-root system had simultaneous plasticity in density, anatomy, and architecture in response to complex soil conditions.     

An approach for modelling the mean fine-root biomass of Norway spruce stands

The applicability of a heuristic model for estimating mean fine-root biomass of Norway spruce stands based on the coordinates and the diameters at breast height (diameter at a height of 1.3 m, dbh) of their trees was tested. The model was developed based on the following assumptions which were derived from the literature: (1) the maximum distance the roots of a tree can be found depends on the dimension of the tree and exceeds the edges of the crown; (2) fine-root biomass decreases with increasing distance from the tree trunk; (3) fine-root biomass increases with the dbh; (4) maximum fine-root biomass of a tree is not allocated directly around the trees trunk but at some distance from the stem. On the basis of these assumptions the model calculates a relative fine-root biomass at a given point within a stand. Four different versions of the model were compared, with each version differing with respect to the assumed decrease in fine roots with decreasing dbh and the approaches used to calculate the contribution of a subject tree to the fine-root biomass at a given point within a stand (additive versus consumptive). Using regression analysis we parameterised each model type with the data of 70 soil cores from a 75-year-old Norway spruce stand in southern Germany (Bavaria). The relative fine-root biomass calculated by the four different model types accounted for 62–72% of the variation of the measured fine-root biomass. The parameterised models were used to predict the fine-root biomass of 60 given points of a second Norway spruce stand based on its dbhs and stem coordinates. The comparison of measured and predicted mean fine-root biomasses of the second stand revealed no significant differences between the measured mean and the means estimated by three of the four model types. Whereas with two of the model types we achieved means and medians, respectively, nearly identical to the measured average, none of the model types was able to predict values as high as the measured maximum. Constraints of the models and points that need to be considered regarding the minimum number of soil cores needed for a reliable parameterisation of the model are discussed.     

CO2 and N-fertilization effects on fine-root length, production, and mortality: a 4-year ponderosa pine study

We conducted a 4-year study of juvenile Pinus ponderosa fine root (≤2 mm) responses to atmospheric CO₂ and N-fertilization. Seedlings were grown in open-top chambers at three CO₂ levels (ambient, ambient+175 μmol/mol, ambient+350 μmol/mol) and three N-fertilization levels (0, 10, 20 g m⁻² year⁻¹). Length and width of individual roots were measured from minirhizotron video images bimonthly over 4 years starting when the seedlings were 1.5 years old. Neither CO₂ nor N-fertilization treatments affected the seasonal patterns of root production or mortality. Yearly values of fine-root length standing crop (m m⁻²), production (m m⁻² year⁻¹), and mortality (m m⁻² year⁻¹) were consistently higher in elevated CO₂ treatments throughout the study, except for mortality in the first year; however, the only statistically significant CO₂ effects were in the fine-root length standing crop (m m⁻²) in the second and third years, and production and mortality (m m⁻² year⁻¹) in the third year. Higher mortality (m m⁻² year⁻¹) in elevated CO₂ was due to greater standing crop rather than shorter life span, as fine roots lived longer in elevated CO₂. No significant N effects were noted for annual cumulative production, cumulative mortality, or mean standing crop. N availability did not significantly affect responses of fine-root standing crop, production, or mortality to elevated CO₂. Multi-year studies at all life stages of trees are important to characterize belowground responses to factors such as atmospheric CO₂ and N-fertilization. This study showed the potential for juvenile ponderosa pine to increase fine-root C pools and C fluxes through root mortality in response to elevated CO₂.     

The importance of nitrogen and carbohydrate storage for plant growth of the alpine herb Veratrum album

We examined whether nitrogen (N) and carbohydrates reserves allow Veratrum album, an alpine forb, to start spring growth earlier than the neighbouring vegetation and to survive unpredictable disturbances resulting in loss of above-ground biomass. * Seasonal dynamics of plant reserves, soil N availability and vegetation growth were monitored. Veratrum album shoots were experimentally removed when carbohydrate reserves were at a seasonal minimum and the subsequent changes in biomass and reserves were compared with those in control plants. Reserves did not give V. album a competitive advantage in spring; however, they did function as a buffer against the impact of calamities. Shoot removal resulted in significantly lower root dry weight, higher N concentration in rhizome and roots and lower starch concentrations in rhizome and roots but no plant mortality was observed. Veratrum album used stored N reserves to supplement N uptake and establish high leaf N concentrations, which facilitated a rapid refilling of depleted carbohydrate reserves. The primary function of N reserves appears to be to allow V. album to complete the growing cycle in as short a period as possible, thus minimizing exposure to above-ground risks.     

Effect of a strong cold storage induced desiccation on metabolic solutes,stock quality and regrowth,in seedlings of two oak species

Bare-root seedlings of pedunculate oak (Quercus robur L.) and northern red oak (Quercus rubra L.) were lifted in January and stored at 1.8°C, at 82% relative humidity, until their fresh weight declined by 33%. Root growth potential (RGP), fine root electrolyte leakage (REL), fine root water content (RWC), shoot tip water content (SWC), starch and metabolic solute contents in root and shoot, were measured just after lifting and after treatment. Survival of treated seedlings was also assessed in a field trial. RWC, SWC, REL, RGP were dramatically affected by desiccation during cold storage. In both species, root soluble carbohydrate level, inositol level and isocitrate level increased, whereas root starch level and shoot soluble carbohydrate level decreased. In northern red oak, treated seedlings had higher root contents of soluble carbohydrates, inositol and proline than in pedunculate oak. Moreover, treatment induced proline accumulation only in northern red oak roots. These differences could explain why field survival of treated seedlings was significantly better in northern red oak than in pedunculate oak.     

Seasonal changes in carbohydrate reserves in mature northern<Emphasis Type="Italic"> Populus tremuloides</Emphasis> clones

To assess the changes in seasonal carbohydrate status of Populus tremuloides, sugar and starch concentrations were monitored in roots, stem xylem and phloem and branches of ten different clones. Time of root growth was assessed by extraction of roots from in-growth cores collected five times during the season. Overall the results showed that the main period of root growth in these northern clones was shifted from spring to late summer and fall likely due to the microclimatic conditions of the soil. This increase in root growth was associated with a decline in total non-structural carbohydrate content in the roots during this period. This study also found that the carbohydrate reserves in these clones were being stored as close as possible to the organs of annual growth (leaves and roots). At the time of leaf flush, the largest reduction in stored carbohydrates (3% of dry weight) was observed in the branches of the trees, compared to a slight decline in the stem and roots. Starch and sugar reserves in most tissues were very low in early summer. This suggests that reserves that might be used for the regrowth of foliage after insect defoliation or other disturbances, are relatively small compared to the portion that is needed for maintenance and typical growth developments such as leaf flush.     

Carbohydrate supply and n(2) fixation in soybean : the effect of varied daylength and stem girdling

When arrival of shoot supplied carbohydrate to the nodulated root system of soybean was interrupted by stem girdling, stem chilling, or leaf removal, nodule carbohydrate pools were utilized, and a marked decline in the rates of CO₂ and H₂ evolution was observed within approximately 30 minutes of treatment. Nodule excision studies demonstrated that the decline in nodulated root respiration was associated with nodule rather than root metabolism, since within 3.5 hours of treatment, nodules respired at less than 10% of the initial rates. Apparently, a continuous supply of carbohydrate from the shoot is required to support nodule, but not root, function. Depletion of nodular carbohydrate pools was sufficient to account for the (diminishing) nodule respiration of girdled plants. Of starch and soluble sugar pools within the whole plant, only leaf starch exhibited a diurnal variation which was sufficient to account for the respiratory carbon loss of nodules over an 8 hour night. Under 16 hour nights, or in continuous dark, first the leaf starch pools were depleted, and then nodule starch reserves declined concomitant with a decrease in the rates of CO₂ and H₂ evolution from the nodules. Nodule soluble sugar levels were maintained in dark treated plants but declined in girdled plants. The depletion of starch in root nodules is an indicator of carbohydrate limitation of nodule function.     

沙地樟子松幼苗干旱致死过程中非结构性碳水化合物的变化

以2年生沙地樟子松幼苗为对象,通过持续自然干旱处理,研究当土壤含水量下降到田间持水量的60%、40%、30%、20%和15%时幼苗叶片水势及不同器官(一年生叶、当年生叶、茎、粗根和细根)的可溶性糖、淀粉和非结构性碳水化合物(NSC)的含量,分析沙地樟子松幼苗在干旱致死过程中各器官NSC的分配规律及其适应机制.结果表明: 土壤含水量从田间持水量的40%下降到15%,幼苗叶片凌晨及正午水势无显著变化.当土壤含水量从田间持水量的60%下降到30%,各器官可溶性糖、淀粉、NSC含量和可溶性糖/淀粉先下降后上升.从30%下降到20%,当年生叶、一年生叶、茎和细根可溶性糖、淀粉和NSC含量降低,而粗根可溶性糖含量增加,淀粉和NSC含量减少.从20%下降到15%,当年生叶、一年生叶和茎可溶性糖、淀粉和NSC含量降低,粗根可溶性糖和NSC含量下降,淀粉含量上升,细根可溶性糖含量减少,淀粉和NSC含量增加.沙地樟子松幼苗通过不断调整各器官NSC及其组分含量变化以适应不同干旱环境,土壤含水量下降到田间持水量的30%后,幼苗可溶性糖和NSC含量总体呈下降趋势,淀粉在粗根和细根中积累,幼苗可能因碳耗竭而死亡.     

Effects of shading and of seasonal differences in weather on the growth, sugar content and sugar yield of sugar-beet crops

In 1967 and 1968 plots of sugar beet in two identically grown crops were shaded for successive four week periods starting on 13 June, 18 July and 22 August, and the growth of the plants compared with that on unshaded plots. At the beginning of each period in 1967 some shaded and unshaded plants received additional nitrogen, and in 1968 plants continuously shaded from June to September were compared with unshaded plants irrigated to equalize their water losses with those of the shaded plants. The weather in 1967 was sunny and dry and that in 1968 dull and wet, but the yields of dry matter, and particularly of sugar, of the unshaded crop in the 2 years were similar because, although net assimilation rate (E) was greater in 1967 than 1968, mean leaf area index (L) in 1968 was almost double that in the 1967 crop. Shading decreased the incoming radiation by 56%; it decreased E proportionally in 1967, increasing L slightly, but it decreased both E (by 44%) and L in 1968. The weights of dry matter and sugar in the roots of the shaded crop were consistently smaller at the end of shading and at final harvest in October in both years, and their weights, but not those of the tops or the whole plant, at final harvest over all shading treatments in both years were proportional to the amount of radiation received by the crop between June and September. Although shading greatly decreased the supply of photosynthate to the roots, it did not change the sugar content percentage of dry matter, except in the early stages of growth when the sugar content was rapidly increasing. Sugar content percentage of fresh weight of the roots was consistently decreased by shading, wholly because water content was increased relative to dry matter. Therefore the sugar yield of shaded plants was less because the dry weights of the roots were less, not because the partition of photosynthate between sugar storage and root growth changed. There appears to be a mechanism within the root operating over a wide range of photosynthate supply that maintains a nearly constant proportion of sucrose to non-sugar, contrary to the hypothesis that sugar stored in the roots is photosynthate in excess of what can be used in growth of the plant. However, in the extreme condition of continuous shading which drastically decreased the dry weights of all parts of the plant, sugar percentage of dry matter in the roots was decreased, but only from 80 to 70%. In 1967 extra nitrogen applied at the start of shading increased L and the dry weight of the tops in all periods, but had no effect on the dry weight of roots. Because 1968 was a wet year the irrigation treatment had no effect on E or L except for a slight increase in L during the first period; it had no effect on plant dry weight. Both irrigation and additional nitrogen decreased the sugar content percentage of fresh weight of the roots only by altering their water content; sugar percentage of dry matter was unaffected. None of these changes persisted until the final harvest in October.     

Cassava Response to Water Deficit in Deep Pots: Root and Shoot Growth, ABA, and Carbohydrate Reserves in Stems, Leaves and Storage Roots

Cassava (Manihot esculenta, Crantz) is an important staple crop for tropical climates worldwide, including drought-prone environments where it is valued for its reliable yield. The extent to which stress tolerance involves regulation of growth and carbon balance aided by remobilization of carbohydrate from various plant parts was investigated. Plants were grown in 1-meter high pots to permit observation of deep rooting while they were subjected to four soil water regimes over a 30-d period. Transpiration declined abruptly in conjunction with leaf ABA accumulation and severe leaf abscission. In water stressed plants, growth of all plant parts decreased substantially; however, a basal rate of leaf growth continued to provide some new leaves, and although growth of fibrous lateral roots was reduced, main root elongation to deeper regions was only modestly decreased by stress. In leaf blades and petioles, sugars were the predominant form of nonstructural carbohydrate and about one third was in starch; these reserves were depleted rapidly during stress. In contrast, stems and storage roots maintained relatively high starch concentrations and contents per organ until final harvest. Stems gradually lost starch and had sufficient reserves to serve as a prolonged source of remobilized carbohydrate during stress. The amount of starch stored in stems represented about 35 % of the reserve carbohydrate in the plant at the onset of water stress (T₀), and 6 % of total plant dry mass. We suggest that this pool of carbohydrate reserves is important in sustaining meristems, growing organs, and respiring organs during a prolonged stress and providing reserves for regrowth upon resumed rainfall.     

Fine-root mass, growth and nitrogen content for six tropical tree species

Although fine roots might account for 50% of the annual net primary productivity in moist tropical forests, there are relatively few studies of fine-root dynamics in this biome. We examined fine-root distributions, mass, growth and tissue N and C concentrations for six tree species established in 16-year-old plantations in the Caribbean lowlands of Costa Rica in a randomized-block design (n = 4). The study included five native species (Hyeronima alchorneoides, Pentaclethra macroloba, Virola koschnyi, Vochysia ferruginea and Vochysia guatemalensis) and one exotic (Pinus patula). Under all species >60% of the total fine-root mass to 1 m deep was located in the uppermost 15 cm of the soil. Fine-root live biomass and necromass (i.e., the mass of dead fine-roots) varied significantly among species but only within the uppermost 15 cm, with biomass values ranging from 182 g m⁻² in Pinus to 433 g m⁻² in Hyeronima plots, and necromass ranging from 48 g m⁻² in Pinus to 183 g m⁻² in Virola plots. Root growth, measured using ingrowth cores, differed significantly among species, ranging from 304 g m⁻² year⁻¹ in Pinus to 1,308 g m⁻² year⁻¹ in Hyeronima. These growth rates were one to five times those reported for moist temperate areas. Turnover rates of fine-root biomass ranged from 1.6 to 3.0 year⁻¹ in Virola and Hyeronima plots, respectively. Fine-root biomass was significantly and positively correlated with fine-root growth (r = 0.79, P < 0.0001), but did not correlate with fine-root turnover (r = 0.10, P = 0.20), suggesting that fine-root accumulation is a function of growth rate rather than mortality. Fine-root longevity was not correlated (r = 0.20, P = 0.34) and growth was negatively correlated with root N concentration across species (r = −0.78, P < 0.0001), contrary to reported trends for leaves, perhaps because N was relatively abundant at this site.     

Heterorhizy can lead to underestimation of fine-root production when using mesh-based techniques

This study investigates the relationship between fine-root morphology and net mesh size in fine-root production (FRP) measurements (ingrowth core and net method). The data collected show that when a fine root has an apical diameter equal or bigger than the mesh size, the degree of difficulty in passing through the net determines a response that arrests growth or deviation from the initial direction of growth. Both reactions prevent the root from crossing the net and induce the fine root to produce new laterals with thinner diameters. The investment in biomass necessary to form the new laterals is smaller than that needed to support the parental fine root and this leads to determines an underestimation of FRP. In particular, a considerable reduction of fine-root biomass in the area outside the netting was detected with a mesh size below 1.5 mm. The choice of net mesh size to be used for FRP measurement cannot be arbitrary, but should be evaluated through a preliminary analysis of fine-root morphology of experimental species prior to net installation.     

遮荫对水曲柳幼苗细根衰老的影响

细根周转对森林生态系统碳地下分配和养分循环具有重要影响,而衰老是细根周转过程中最重要的阶段。根据“源-汇”理论,细根衰老受碳向细根分配的影响。为此,该研究通过控制水曲柳(Fraxinus mandshurica)苗木向根系的碳分配的遮荫处理试验,采用树木生理分析技术,重点研究了在光合产物供应停止情况下水曲柳幼苗根系的生理变化(即根尖、1级根到3级根的细胞活力、可溶性糖含量、可溶性蛋白含量和膜透性的变化)。目的是从生理水平上证实:1)碳分配对细根衰老产生怎样的影响;2)细根衰老的顺序是否与分支顺序相反。实验结果表明,遮荫处理使细根活力、可溶性糖含量、可溶性蛋白含量显著降低和膜透性增大,导致细根出现明显衰老。从根系顶端向基部随着根序增加,细胞活力、可溶性糖含量和可溶性蛋白含量提高,膜透性降低,从生理水平上表明细根衰老具有逐渐变化的顺序性,并且这种顺序性与根发育的顺序性相反。