Patterns of photosynthesis and starch allocation in seedlings of four bottomland hardwood tree species subjected to flooding

Effects of short-term (32 days) flooding on photosynthesis, stomatal conductance, relative growth rate and tissue starch concentrations of flood-intolerant Quercus alba L. (white oak), bottomland Quercus nigra L. (water oak), bottomland Fraxinus pennsylvanica Marshall. (green ash) and flood-tolerant Nyssa aquatica L. (water tupelo) seedlings were studied under controlled conditions. Net photosynthetic rates of flooded N. aquatica seedlings were reduced by 25% throughout the 32-day flooding period. Net photosynthetic rates of flooded Q. alba seedlings fell rapidly to 25% of those of the control seedlings by Day 4 of the flooding treatment and to 5% by Day 16. In F. pennsylvanica and Q. nigra, net photosynthetic rates were reduced to 50% of control values by Day 8 but remained at approximately 30 and 23%, respectively, of control values by Day 32. Leaves of flooded Q. alba seedlings accumulated approximately twice as much starch as leaves of non-flooded control plants, whereas root starch concentrations decreased to 67% of those of control plants by the end of the 32-day flooding treatment. In contrast, flooding caused only a small increase in leaf starch concentrations of N. aquatica plants, but it increased root starch concentrations to 119% of those of the control plants by the end of the experiment. The co-occurring bottomland species, Fraxinus pennsylvanica and Q. nigra, differed from each other in their patterns of stomatal conductance and root starch concentrations. We conclude that the maintenance of low leaf starch concentrations, and high pre-flood root tissue starch concentrations are important characteristics allowing flood-tolerant species to survive in flooded soils.     

Growth,morphology and gas exchange responses of two-year-old Quercus castaneifolia seedlings to flooding stress

Tolerance to flooding is crucial when thinking in promissory species for restoration of ecosystems prone to suffer soil water excess. In this study, we tested the flooding tolerance of two-years-old seedlings of Chestnut-leaved oak (Quercus castaneifolia C.A.Mey.) to determine whether it can be recommended for use in wetland restoration programs. Seedlings of Q. castaneifolia were subjected to three treatments: (1) control (C), (2) flooding for 60 days followed by a 42-day recovery period (F?+?R) and (3) continuous flooding for 102 days (F). Physiological performance, plant morphological changes and biomass accumulation were assessed. Results showed that, although net photosynthetic rates, stomatal conductance and transpiration decreased with prolonged flooding, when flood waters were removed, plants were able to recover their physiological activity (49–80% compared to controls). By contrast, when plants were continually flooded, their physiological activity decreased as well as the leaves experienced precocious senescence and wilting. Biomass responses paralleled physiological responses: leaf and root biomass were 42–49% higher under F?+?R treatment than under continuous flooding, and all plants under the F?+?R survived. Therefore, Q. castaneifolia appears as a promising species to be further studied when thinking re-vegetation of riverine areas and other temporarily flooded wetlands.     

Effects of drought and rewatering on growth and transpiration in European beech seedlings late in the growing season

Drought stress is one of the most important environmental factors affecting plant growth and survival. To date, most studies aim at understanding of post-stress physiological and anatomical adaptation to drought stress; however only few studies focus on plant recovery. In the present study, transpiration, shoot water potential, and anatomical and morphological measurements were performed on 4-year-old European beech seedlings with fully developed leaves. The seedlings were exposed to three levels of soil water potential (well-watered, moderate drought stress and severe drought stress) and followed by rewatering under greenhouse conditions. Reduced transpiration rates were observed in the stressed seedlings as a response to drought stress, whereas anatomical and morphological variables remained unchanged. Three days after rewatering, transpiration rates in both moderately and severely stressed seedlings recovered to the levels of those of well-watered seedlings. Drought stress promoted leaf budding, resulting in higher shoot dry mass of stressed seedlings. Our findings indicate that anatomical and morphological adaptations of European beech seedlings to drought stress are visibly limited during late-season growth stages. These results will help us to further understand factors involved in drought adaptation potential of European beech seedlings faced with expected climate-related environmental changes. To complete our findings, further experiments on plant recovery from drought stress should be focused on different periods of growing season.     

Assessing the effect of late-season fertilization on Holm oak plant quality: insights from morpho–nutritional characterizations and water relations parameters

Forest restoration projects with Holm oak (Quercus ilex) have had limited success, mostly due to water stress after planting and poor plant quality. Recent studies indicated that large and nutrient rich plants perform better in Mediterranean areas, suggesting that late-season fertilization may improve plant quality and field performance. The purpose of this study was to assess the effect of late-season fertilization on the quality of Holm oak seedlings, as determined by morphological, nutritional, and water relations analyses. We grew Holm oak nursery seedlings under 5 different late-season fertilization regimes and then analyzed morphological characteristics, nutritional status, and water relations parameters of the fertilization groups at the end of the nursery period. We also analyzed the effect of fertilization on nutritional status by use of vector nomograms. Our results indicated that late-season NPK fertilization improved shoot and root growth, and the overall nutritional status of seedlings. The lack of late-season fertilization leads to nutrient deficiency in plants, whilst the application of imbalanced fertilization treatments may trigger nutrient luxury consumption and nutrient dilution, pointing out the importance of NPK proportions in the fertilizer. Moreover, late-season fertilization with nitrogen might improve the drought resistance of seedling by enhancing their osmotic adjustment.     

Drought tolerance and transplanting performance of holm oak (Quercus ilex) seedlings after drought hardening in the nursery

Drought stress is the main cause of mortality of holm oak (Quercus ilex L.) seedlings in forest plantations. We therefore assessed if drought hardening, applied in the nursery at the end of the growing season, enhanced the drought tolerance and transplanting performance of holm oak seedlings. Seedlings were subjected to three drought hardening intensities (low, moderate and severe) for 2.5 and 3.5 months, and compared with control seedlings. At the end of the hardening period, water relations, gas exchange and morphological attributes were determined, and survival and growth under mesic and xeric transplanting conditions were assessed. Drought hardening increased drought tolerance primarily by affecting physiological traits, with no effect on shoot/root ratio or specific leaf mass. Drought hardening reduced osmotic potential at saturation and at the turgor loss point, stomatal conductance, residual transpiration (RT) and new root growth capacity (RGC), but enhanced cell membrane stability. Among treated seedlings, the largest response occurred in seedlings subjected to moderate hardening. Severe hardening reduced shoot soluble sugar concentration and increased shoot starch concentration. Increasing the duration of hardening had no effect on water relations but reduced shoot mineral and starch concentrations. Variation in cell membrane stability, RT and RGC were negatively related to osmotic adjustment. Despite differences in drought tolerance, no differences in mortality and relative growth rate were observed between hardening treatments when the seedlings were transplanted under either mesic or xeric conditions.     

Long- and short-term flooding effects on survival and sink-source relationships of swamp-adapted tree species

About 95% of swamp tupelo (Nyssa sylvatica var. biflora (Walt.) Sarg.) and sweetgum (Liquidambar styraciflua L.) seedlings survived continuous root flooding for more than two years, whereas none of the swamp chestnut oak (Quercus michauxii Nutt.) and cherrybark oak (Q. falcata var. pagodifolia Ell.) seedlings survived one year of flooding. Death of oak seedlings occurred in phases associated with periods of major vegetative growth, e.g., after bud burst in spring, after summer stem elongation, and during the winter deciduous stage, suggesting that stored reserves and sources were inadequate to maintain the seedlings when vegetative sinks were forming. Additional evidence that flooding induced a source deficiency in oak was that leaves of flooded oak were 65 to 75% smaller than leaves of nonflooded oak. Flooded swamp tupelo seedlings had a normal leaf size and patchy stomatal opening compared with nonflooded seedlings. Flooding caused increases in alcohol dehydrogenase (ADH) specific activity in taproot cambial tissues and increases in starch concentrations of swamp tupelo seedlings that were reversed when seedlings were removed from flooding. Flooding had little effect on soluble sugar concentrations in swamp tupelo or sweetgum. In the long-term flood-dry-flood treatment, in which all species had survivors, upper canopy leaf photosynthetic rates were higher in all species during the dry period than in nonflooded controls, whereas their starch and soluble sugars concentrations were similar to those of nonflooded controls. Based on seedling survival and the sink-source relationships, the order of flood tolerance was: swamp tupelo > sweetgum > swamp chestnut oak > cherrybark oak.     

Physiological responses of seedlings of two oak species to flooding stress

The physiological responses of 2-year-old seedlings of Nuttall＇s oak （Quercus nuttallii） and Southern red oak （Q.falcata） with two treatments i.e., deep-drowning and shallow-drowning, were studied. Taxodium distichum was selected as a control. The survival rates of seedlings were calculated, the photosynthetic indices were detected by Licor-6400 photosynthetic system instrument, and the root activities of seedlings were tested by the method of triphenyltetrazolium chloride （TTC）. Results showed that： 1） By experiencing flooding for 76 d and recovering for 60 d after water was drained off, all seedlings survived under the shallow-drowning treatment. None of Q. falcata seedlings died in the deep-drowning treatment until the 49th day. The survival rate of Q. falcata in the deep-drowning treatment was 30%. 2） Within 61 d of waterlogging treatments, the net photosynthetic rate （Pn）, stomatal conductance （gs） and transpiration rate （Tr） showed a tendency of declining, but intercellular concentration of CO2 （Ci） increased. With the prolongation of flooding stress, the extents of variation for all indices under deep-drowning treatment were larger than those under the shallow-drowning treatment. The variation of Q. falcata in flooding stress was larger than that of Q. nuttallii. 3） The root vigor and alcohol dehydrogenase （ADH） activities were detected at the 61st day in flooding stress. Waterlogging obviously inhibited root activities. Shallow-drowning made root vigor of Q. nuttallii decreased by 11.7%, and for Q. falcata, by 51.88%. Shallow-drowning treatment had no remarkable effects on ADH activities of seedlings, but deep-drowning increased those of Q. nuttallii seedlings by 227.24%, and decreased those of Q. falcata seedlings by 59.22% in the meantime. We conclude that Q. nuttallii had a stronger waterlogging resistance than Q. falcata, but weaker than T. distichum.     

Responses of black spruce (Picea mariana) and tamarack (Larix laricina) to flooding and ethylene

Black spruce (Picea mariana (Mill.) BSP) and tamarack (Larix laricina (Du Roi) K. Koch) are the predominant tree species in the boreal peatlands of Alberta, Canada, where low nutrient availability, low soil temperature and a high water table limit their growth. Effects of flooding for 28 days on morphological and physiological responses were investigated in greenhouse-grown black spruce and tamarack seedlings in a growth chamber. Flooding reduced root hydraulic conductance, net assimilation rate and stomatal conductance, and increased water-use efficiency (WUE) and needle electrolyte leakage in both species. Although flooded black spruce seedlings maintained higher net assimilation rates and stomatal conductance than flooded tamarack seedlings, flooded tamarack seedlings were able to maintain higher root hydraulic conductance than flooded black spruce seedlings. Needles of flooded black spruce developed tip necrosis and electrolyte leakage after 14 days of flooding, and these symptoms were subsequently more prominent than in needles of flooded tamarack seedlings. Flooded tamarack seedlings exhibited no visible injury symptoms and developed hypertrophied lenticels at their stem base. Application of exogenous ethylene resulted in a significant reduction in net assimilation, stomatal conductance and root respiration, whereas root hydraulic conductivity increased in both species. Thus, although flooded black spruce seedlings maintained a higher stomatal conductance and net assimilation rate than tamarack seedlings, black spruce did not cope with the deleterious effects of prolonged soil flooding and exogenous ethylene as well as tamarack.     

Effects of flooding depth on growth,morphology and photosynthesis in <Emphasis Type="Italic">Alnus japonica</Emphasis> species

The present study deals with effects of flooding depth on growth, morphology and photosynthesis in Alnus japonica species thorough one field study and two controlled experiments. In the field study performed in Kushiro Mire, Hokkaido Island, Japan, tree heights and stem diameters decreased with an increase in water depth accompanied with the reduction of soil redox potential. In contrast, the rate of multiple stems per individual tree increased. In the controlled experiments for seedlings flooding suppressed the shoot elongation and biomass increment in roots. However, diameter increment around water levels, epicormic shoot development and adventitious root formation were enhanced in flooded seedlings. The photosynthetic rate and stomatal conductance of flooded seedlings also were lowered with an increase in flooding depth. The recovery of the reduced photosynthetic rate and stomatal conductance occurred simultaneously with the advancement of adventitious root formation in the flooded seedlings. These results indicate the importance of a series of morphological changes occurring on stems around water levels in flood tolerance in A. japonica species.     

淹水胁迫对两种栎树生长的影响

对纳塔栎、南方红栎的2 a生苗在深度淹水约20 cm、浅度淹水(完全水饱和)、对照3种水平下持续76 d的生长进行研究,其中又以抗涝性极强的落羽杉作为参照.主要测定了各树种的生物量和株高,并对外部形态特征及叶片内部解剖结构的变化进行了观察.结果表明:浅淹没有造成苗木死亡,深度淹水第49天南方红栎开始出现枯死植株,第76天纳塔栎出现轻微受害症状,落羽杉没有出现受害症状.与各自对照相比,浅淹水平对落羽杉、纳塔栎的高生长及生物量的累积均具有促进作用,且对落羽杉影响较显著,而对南方红栎影响不显著;深淹水平对落羽杉、纳塔栎的'高生长及生物量的累积影响不显著,但对南方红栎具有显著的抑制作用.同时,发现淹水对落羽杉、纳塔栎的叶片解剖性状影响不显著,而深淹水平下,数据显示南方红栎的叶片内部细胞间隙明显增大.综合表明两种栎树都具有较强的耐水性,而纳塔栎更优于南方红栎,仅次于落羽杉.     

Physiological, morphological and anatomical responses of Fraxinus mandshurica seedlings to flooding

Two-year-old Fraxinus mandshurica Rupr. var. japonica Maxim. seedlings were flooded to 8 cm above soil level for 70 days. The flooding treatment altered the growth, morphology, stem anatomy and ethylene production of the seedlings. Although flooding did not affect height growth, it stimulated diameter growth of the submerged stems by increasing both the number and size of wood fibers produced; however, the thickness of the cell walls of the wood fibers was reduced by flooding. In response to the flooding treatment, the seedlings formed abundant hyperhydric tissues, originating from the vicinity of lenticels on the surface of the flooded stems, and adventitious roots, which grew through the hyperhydric tissues. Aerenchyma tissues were observed in the bark of the adventitious roots. The flooding treatment did not affect dry weight increment of leaves and stems, but it reduced the total dry weight increment of the root system even though it promoted adventitious root formation. Flooding also enhanced ethylene production in the submerged portions of stems. The potential roles of flood-induced ethylene in cambial growth and adventitious root formation in flooded plants are discussed.     

Water movement in yellow-cedar seedlings and rooted cuttings: comparison of whole plant and root system pressurization methods

One-year-old yellow-cedar (Chamaecyparis nootkatensis (D. Don) Spach) seedlings and rooted cuttings were taken from cold-storage facilities and grown in aerated water in a controlled environment room for 21 days. Root areas of seedlings and rooted cuttings were initially comparable, but after 21 days seedlings had produced more than twice as much new root area as rooted cuttings. Water flow resistance through the plant-atmosphere continuum decreased in both stock types over the 21-day period. In both seedlings and rooted cuttings, transpirational flux density increased in a curvilinear manner as new root area increased. Root resistance to water movement decreased sharply with increasing new root area up to 20 cm(2) in both seedlings and rooted cuttings. Further increases in new root area did not result in further changes in root resistance of either stocktype. Plant water movement was measured by both the whole plant and the root system pressurization methods with results differing between the two techniques.     

Ecophysiological acclimatization to cyclic water stress in Eucalyptus

Drought is considered the main environmental factor limiting productivity in eucalyptus plantations in Brazil. However, recent studies have reported that exposure to water deficit conditions enables plants to respond to subsequent stresses. Thus, this study investigates the ecophysiological acclimatization of eucalyptus clones submitted to recurrent water deficit cycles. Eucalyptus seedlings were submitted to three recurrent water deficit cycles and anatomical, morphological and physiological changes were analyzed. The results were:(1) Eucalyptus seedlings responded to water deficits by directing carbohydrates to root and stem growth;(2) Size and number of stomata were reduced;(3) Stomatal conductance decreased which allowed the plants to reduce water losses through transpiration,increasing instantaneous water use efficiency;(4) The relationship between gas exchanges and available water contents allowed the seedlings to uptake the retained soil water athigher tensions;and,(5) Physiological recovery from subsequent water deficits became faster. As a result of these changes, the eucalyptus seedlings recovered from the same degree of water stress more rapidly.     

The effects of flooding on several hybrid poplar clones in Northern China

The ecophysiological, morphological, and growth characteristics of 14 poplar clones were studied during 37 days of flooding and a 13-day recovery period. Cuttings were subjected to three soil water regimes, viz. drained (control), shallow flooding to 10 cm above the soil, and deep flooding to a depth of 120 cm. All hybrids modified their ecophysiological and morphological patterns to decrease carbon loss and maintain water balance. In response to flooding, all 14 hybrids reduced their expansion and initiation of new leaves, reduced height and root collar growth, and reduced the number of leaves. For shallowly flooded plants, adventitious roots developed by day 14, and their number increased with flooding duration; net photosynthesis, stomatal conductance, and growth decreased significantly compared with the control; dry weights of roots, leaves, and total biomass decreased and the allocation of growth to shoots and roots changed. After flooding ended, net photosynthesis recovered, but stomatal conductance recovered before net CO₂ assimilation since photosynthesis was limited by stomatal factor at the initial stage of stress and it was limited by non-stomatal factors over relatively long periods of stress. Transpiration and the amount of water obtained from the roots both decreased. In the deeply flooded plants, similar but often more severe changes were observed. Based on our results, we classified the hybrids into three types using hierarchical cluster analysis. Clones 15-29, 196-522, 184-411, 306-45, 59-289, DN-2, DN-182, DN-17, DN-14274, NE-222, DTAC-7, and R-270 were flood-tolerant, clone NM-6 was flood-susceptible, and clone 328-162 was moderately flood-tolerant.     

容器苗质量评定指标研究

对大叶樟、猴欢喜、木莲3种容器苗的多个形态指标进行测定，并研究其根系水势和根生长潜力的关系，结果表明，容器苗地径和全苗干重与各形态指标间显著相关，是反映容器苗质量的重要形态指标；苗木根系水势和根生长潜力回归极显著，是苗木质量评价重要的生理指标和活力指标。     

Fall lifting and long-term freezer storage of ponderosa pine seedlings: effects on post-storage leaf water potential, stomatal conductance, and root growth potential

Post-storage water relations, stomatal conductance, and root growth potential were examined in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) seedlings from high- and low-elevation seed sources that had been lifted either in October or November and freezer stored, or in March, and then grown hydroponically in a greenhouse for 31 days. Seedlings lifted in October had poor root initiation (< 17 new roots per seedling), low predawn leaf water potentials (< -1.5 MPa), and low stomatal conductance (7.10 mmol m(-2) s(-1)) compared with seedlings lifted in November or March. There was little difference in post-storage water relations and stomatal conductance between seedlings lifted in November and those lifted in March. Throughout the 31-day test, seedlings from the high-elevation seed source produced 3-9 times more new roots, had higher predawn leaf water potentials (-0.6 to -0.7 MPa versus -1.1 to -1.6 MPa), and 1.3-5 times greater stomatal conductance than seedlings from the low-elevation seed source. For all seedlings on Day 31, the number of new roots was significantly related to predawn leaf water potential (r(2) = 0.65) and stomatal conductance (r(2) = 0.82). Similarly, the dry weight of new roots per seedling on Day 31 accounted for a significant amount of the variation in predawn leaf water potential (r(2) = 0.81) and stomatal conductance (r(2) = 0.49).     

Photosynthetic light response of flooded cherrybark oak (Quercus pagoda) seedlings grown in two light regimes

Two-year-old cherrybark oak (Quercus pagoda Raf.) seedlings raised in full or partial (27%) sunlight were flooded for 30 days to study the effects of light availability and root inundation on photosynthetic light response. Compared with seedlings receiving full sunlight, seedlings receiving partial sunlight developed leaves with 90% greater blade area, 26% less mass per unit volume, and 35% lower nitrogen (N) concentration per unit area, leading to a 15% reduction in leaf photosynthetic capacity when carbon exchange rates were based on blade area. However, when carbon exchange rates were based on leaf mass, leaves acclimated to partial sunlight exhibited a 15% greater photosynthetic capacity realized primarily through an increased initial slope of the photosynthetic light response (A/PPFD) curve and increased net photosynthesis at leaf saturation (Amax). Short-term flooding increased leaf mass per unit area more than 19%, reduced foliar N concentrations per unit dry mass by 19%, and initiated reductions in Amax and apparent quantum yield (phi) of seedlings in both light regimes. Greatest impairment of Amax (56% area basis, 65% mass basis) and phi (40%) were observed in leaves receiving full sunlight, and the declines were concomitant with a 35% decrease in chlorophyll concentration. Flooding also depressed instantaneous photosynthetic N-use efficiency (PPNUE) such that Amax decreased 54%, and the initial slope of PPNUE/PPFD curves decreased 33 and 50% for leaves acclimated to partial and full sunlight, respectively. The A/PPFD patterns indicated that the magnitude of flood-induced inhibition of the photosynthetic mechanism of cherrybark oak seedlings is determined partly by the light environment.     

Changes in root growth and relationships between plant organs and root hydraulic traits in American elm (Ulmus americana L.) and red oak (Quercus rubra L.) seedlings due to elevated CO2 level

The relationships between plant organs and root hydrological traits are not well known and the question arises whether elevated CO2 changes these relationships. This study attempted to answer this question. A pseudo-replicated experiment was conducted with two times 24 American elm (Ulmus americana L.) and 23 and 24 red oak (Quercus rubra L.) seedlings growing in ambient CO2 (around 360 μmol·L–1) and 540 ± 7.95 μmol·L–1 CO₂ in a greenhouse. After 71 days of treatment for American elm and 77 days for red oak, 14 American elm and 12 red oak seedlings from each of the two CO2 levels were randomly selected in order to examine the flow rate of root xylem sap, root hydraulic conductance, total root hydraulic conductivity, fine root and coarse root hydraulic conductivity. All seedlings were harvested to investigate total plant biomass, stem biomass and leaf biomass, leaf area, height, basal diameter, total root biomass, coarse root biomass and fine root biomass. The following conclusions are reached: 1) plant organs respond to the elevated CO2 level earlier than hydraulic traits of roots and may gradually lead to changes in hydraulic traits; 2) plant organs have different relationships with hydraulic traits of roots and elevated CO2 changes these relationships; the changes may be of importance for plants as means to acclimatize to changing environments; 3) biomass of coarse roots increased rather more than that of fine roots; 4) Lorentzian and Caussian models are better in estimating the biomass of seedlings than single-variable models.     

Leaf physiology and sugar concentrations of transplanted Quercus rubra seedlings in relation to nutrient and water availability

Newly planted seedlings incur transplant stress resulting from poor root-soil contact, which limits access to soil moisture and nutrients and reduces growth for one or more growing seasons. Controlled release fertilizer (CRF) applied at planting may reduce transplant stress by augmenting rhizosphere nutrient availability yet with potential risk of root system damage due to elevated fertilizer salt concentrations, which may be further exacerbated by drought. Under controlled conditions, we examined northern red oak (Quercus rubra L.) leaf physiological parameters and soluble sugar concentrations in response to varying nutrient levels (via CRF application) and moisture availability gradients ranging from drought to flooding. Net photosynthetic rates, transpiration rates, and chlorophyll fluorescence parameters responded positively to CRF application, and no interactions were observed between CRF and moisture availability; however, CRF did not increase soluble sugar concentrations. No effects of short-term drought were observed, but flooding exerted a rapid negative influence on net photosynthetic rates, transpiration rates, and chlorophyll fluorescence parameters; flooding also elevated soluble sugar concentrations, indicative of disrupted carbon partitioning and a much greater sensitivity to root-zone hypoxia than to drought in this species. Lack of interactions between CRF application and soil moisture availability indicates relatively similar responses of fertilized seedlings across moisture gradients.     

水曲柳苗木根系形态和解剖结构对不同氮浓度的反应

采用温室沙培方法,在不同氮浓度处理下,研究1年生水曲柳苗木整株根系和前3级根形态,以及前3级根形态与解剖结构的关系,探讨不同氮浓度导致细根形态变化的原因。结果表明:1)随着氮浓度的增加,整株根系的总面积、总长度和比根长增加,但是总的平均直径减小,前3级根也具有相同的变化规律。根表面积和比根长从低氮到高氮增加与直径和根长的变化有关。2)氮浓度引起直径和根长变化与解剖特征变化有密切关系。低氮条件下直径增加与横切面皮层细胞直径和皮层厚度的增加有关,而高氮条件下皮层细胞直径减小和皮层厚度缩窄有关。在纵切面上,根长度从低氮到高氮增加可能与细胞数量增加有关。研究结果对解释施肥导致细根形态变化原因具有重要意义。