Does the root to shoot ratio show a hormetic response to stress? An ecological and environmental perspective

Root/shoot(R/S)ratio is an important index for assessing plant health,and has received increased attention in the last decades as a sensitive indicator of plant stress induced by chemical or physical agents.The R/S ratio has been discussed in the context of ecological theory and its potential importance in ecological succession,where species follow different strategies for above-ground growth for light or below-ground competition for water and nutrients.We present evidence showing the R/S ratio follows a biphasic dose–response relationship under stress,typical of hormesis.The R/S ratio in response to stress has been widely compared among species and ecological succession classes.It is constrained by a variety of factors such as ontogeny.Furthermore,the current literature lacks dose-response studies incorporating the full dose–response continuum,hence limiting scientific understanding and possible valuable application.The data presented provide an important perspective for new-generation studies that can advance current ecological understanding and improve carbon storage estimates by R/S ratio considerations.Hormetic response of the R/S ratio can have an important role in forestry for producing seedlings with desired characteristics to achieve maximum health/productivity and resilience under plantation conditions.

Effects of Soil Moisture on Dynamic Distribution of Dry Matter Between Winter Wheat Root and Shoot

The dynamic relationship of dry matter accumulation and distribution between winter wheat root and shoot was studied under different soil water conditions. The dry matter accumulation in root was greatly influenced by water stress, so as to the final root weight of the treatment with 40% field moisture capacity(FMC) was less than 1/4 of that of the treatment with 80% FMC on average. Water stress during the 3-leaf stage to the tillering stage had the greatest influence on root, and the influence of water stress during the jointing stage to the booting stage on shoot was greater than root. However, water stress during the tillering stage to the booting stage had a balanced effect on root and shoot, and the proportion of dry matter that distributed to root and shoot was almost the same after rewatering. Water recovery during the jointing stage to booting stage could promote R/S, but the increasing degree was related to the duration of water limitation. Soil water condition had the lowest effect on R/S during the flowering stage to the filling stage and the maximal effect on R/S during the jointing stage to the heading stage, R/S of 40% FMC treatment was 20.93 and 126.09% higher than that of 60% FMC and 80% FMC treatments respectively at this period.

The Equilibrium and Growth Stability of Winter Wheat Root and Shoot Under Different Soil Water Conditions

The equilibrium between root, shoot and growth stability under different soil water conditions were investigated in a tube experiment of winter wheat. The water supplying treatments included： sufficient irrigation at whole growth phase, moderate deficiency irrigation at whole growth phase, serious deficiency irrigation at whole growth phase, sufficient irrigation at jointing stage, tillering stage, flowering stage, and fillering respectively, after moderate and serious water deficit during their previous growth stage. Root and shoot biomass were measured. On the basis of the cooperative root-shoot interactions model, the equilibrium and growth stability were studied on the strength of the kinetics system theory. There was only one varying equilibrium point between the root and shoot over the life time of the winter wheat plant. Water stress prolonged the duration of stable growth, the more serious the water deficit, the longer the period of stable growth. The duration of stable growth was shortened and that of unstable growth was prolonged after water recovery. The growth behavior of the plants exposed to moderate water deficit shifted from stable to unstable until the end of the growth, after rewatering at flowering. In the life-time of the crop, the root and shoot had been adjusting themselves in structure and function so as to maintain an equilibrium, but could not achieve the equilibrium state for long. They were always in an unbalanced state from the beginning to the end of growth. This was the essence of root-shoot equilibrium. Water stress inhibited the function of root and shoot, reduced root shoot interactions, and as a result, the plant growth gradually tended to stabilize. Rewatering enhanced root shoot interactions, prolonged duration of instable growth. Rewatering at flowering could upset the inherent relativity during the long time of stable growth from flowering to filling stage, thus leading to unstable growth and enhanced dry matter accumulating rate in the whole plant.

Root-shoot relationships of Fraxinus mandchurica

In this paper, root-shoot relationships of seedlings of Manchurican ash (Fraxinus mandchurica) in pots is studied in green house. The results show that roots and shoots have the co-ordination of growth and roots and shoots of ash have the same growth dynamics. There are very close relationships between toall root mass and total shoot mass, between fine root mass and leaf mass in this experiments. At the end growing season, ash root-shoot mass ratio and fine root-leaf mass ratio are 1 .85 and 2.01 respectively. These ratios are difference during growth season. There are larger roots than shoots on seedling stage. Low nitrogen and phosphorus produce higher root-shoot ratio, and high nutrient concentrations decrease the ratios.

Regulation of phytohormones on root primordium initiation and adventitious root formation in the etiolated shoots of Paeonia suffruticosa'Yinfen Jinlin'

Tree peony is well known and sought after for its large, colorful flowers. Its propagation is via vegetative methods. Mech- nisms of the adventitious rooting and the regulation of rooting processes are the principles and techniques of plant propagation and improvement. Microstructures and fluctuations of phytohormones in the adventitious rooting were studied with the etiolated soft- wood shoots of Paeonia suffkuticosa ＇Yinfen Jinlin＇. There are no pre-primordia in the shoots of the cultivar. Adventitious roots are produced in five stages： shoot selection, primordium initiation, primordium growth, conducting tissue differentiation and root protru- sion. Primordia initiated in the cortex. The contents of the endogenous hormones, IAA, ABA and GA, were 5.842, 0.873 and 1.043 nmol·g^-1 FW on the bases of shoots, respectively. CTKs which included isopentenyl adenine （iPA）, zeatin riboside （ZR） and dihy- drozeatin riboside （DHZR） were 0.949, 0.695 and 2.034 nmol·g^-1 FW, respectively. DHZR is active among CTKs. The ratio of IAA to GA, CTK and ABA clearly increased at the stage of primordium initiation, while they showed low levels at the stages of primor- dium growth. The ratios were restored at the shoot levels at the stage of root protrusion. IBA provoked primordia initiation in the cortex, the vascular cambium, the pith and even in the callus induced on the base of shoots. ]AA levels in the treated shoots increased gradually to its highest level （three times of control） at the stage of conducting tissue differentiation. The ratios of IAA to GA, CTK and ABA clearly decreased at the stage of primordium initiation. The ratio of IAA to ABA is regulated at 10：1.

Variations in shoot and root growth of three provenances of Faidherbia albida in clay and sand soil

The variation in shoot and root seedling growth traits was compared among three Faidherbia albida （Del）. A. Chev. provenances originating from Kenya （Taveta）, Malawi （Bolero） and Ghana （Bolgatanga）; representing east, south and west Africa, respectively. Bulked seeds from three provenances were grown in two soil types （clay and sand） at the World Agroforestry Centre nursery, Nairobi. Seedlings grown in clay soil had high shoot growth and shoot to root ratios but shorter root length, lower number of nodules and specific root length compared to seedlings in sand soil. Shoot to root ratios reduced with time and this was more pronounced in sand soil. Overall, the Bolero and Taveta provenances had higher growth than the Bolgatanga provenance. This was probably because plants grown in nutrient-rich clay soil invest more in shoot growth as compared to root growth. Longer root growth in sand soil shows a better adaptive mechanism that increases competitive ability and survival in nutrient-poor systems. Variations observed among the seedling variables such us shoot and root growth could be used for early selection for reforestation and agroforestry in predominantly clay and sand soil areas.

Water Deficit Stress Effects on Corn (<i>Zea mays</i>, L.) Root:Shoot Ratio

A study was conducted at Akron, CO, USA, on a Weld silt loam in 2004 to quantify the effects of water deficit stress on corn (Zea mays, L.) root and shoot biomass. Corn plants were grown under a range of soil bulk density and water conditions caused by previous tillage, crop rotation, and irrigation management. Water deficit stress (Dstress) was quantified by the number of days when the water content in the surface 0.3 m deviated from the water content range determined by the Least Limiting Water Range (LLWR). Root and shoot samples were collected at the V6, V12, and R1 growth stages. There was no significant correlation between Dstress and shoot or root biomass at the V6 growth stage. At the V12 and R1 growth stages, there were negative, linear correlations among Dstress and both root biomass and shoot biomass. The proportional decrease of shoot biomass was greater than the proportional decrease in root biomass, leading to an increase in the root:shoot ratio as water deficit stress increased at all growth stages. Determining restrictive soil conditions using the LLWR may be useful for evaluating improvement or degradation of the soil physical environment caused by soil management.

Establishment of Somatic Cell Clones in Thesium chinense Turcz and Its in vitro Rooting Technique

[Objective] The aim of this study is to establish the rapid micro-propagation system in Thesium chinense Turcz.[Method]With stem fragments of wild Thesium chinense Turcz as explants,different culture media were designed to conduct induction culture,strengthening plantlet culture and in vitro rooting.[Result]The optimum medium for inducing clustered shoots was determined to be MS medium appended with 1.5 mg/L 6-BA,0.01 mg/L NAA and 0.3 mg/L 2,4-D;in addition,60 mg/kg ABT was suitable for rooting,by which the percentage of rooted plantlets reached 76.6%.[Conclusion]This study simplified the procedures of tissue culture in Thesium chinense Turcz and enhanced the proliferation rate,providing basis for artificial cultivation and resource protection of Thesium chinense Turcz.

The Role of Nitrogen Fertilizers in Sugarcane Root Biomass under Field Conditions

Sugarcane is used worldwide for sugar, ethanol and energy production. In Brazil, the shift from burned to unburned harvest systems resulted in increases in nitrogen fertilization rates, which can impact root architecture and biomass. The expectation is also an increase in sugarcane biomass. The study hypothesized that high N rates applied to sugarcane fields increases root growth and N stored in roots, promoting higher biomass and N accumulated in shoots. Two experiments were set up in Southeastern Brazil, on a Typic Kandiudox (TK) and Rhodic Eutrudox (RE). Four treatments were studied 1) N application in the plant-cane (0 and 120 kg·ha-1 N) and 2) N application in the ratoon (0 and 150 kg·ha-1 N). The shoot biomass and the root density (by the core method up to 0.6 m) were evaluated over the first ratoon crop cycle, and the N content in those compartments was also examined. There was no carry over effect on N applied at planting in root and shoot biomass in the ratoon crop cycle. At the RE site, the ratoon N fertilization increased root density in the superficial soil layer (0 - 0.2 m) and close to the plants (<0.3 m). The effect of N addition on root biomass, and biomass and N accumulated in shoot was limited in both sites. Increasing N rates in unburned sugarcane fields do not consistently increases root and shoot biomass under Brazilian field conditions.

Root distribution of three co-occurring desert shrubs and their physiological response to precipitation

Root distribution of three desert shrubs,Tamarix ramosissima Ledeb.,Haloxylon ammodendron(C.A.Mey.) Bunge and Reaumuria soongorica(Pall.) Maxim.was investigated under co-occurring conditions using a method for excavating the whole root system.Assimilation shoot water potential and transpiration rates were monitored during the wet-dry cycle.Leaf-specific apparent hydraulic conductance and the index of water stress impact for the three species were calculated from shoot water potential and transpiration rate.The results showed that,along the soil profile,the root system of T.ramosissima mainly distributed at 50 to 310 cm interval,with an average total absorbing root-surface area of 30,249.2 cm2 per plant;the root system of H.ammodendraom distributed at 0 to 250 cm interval with an average total absorbing root-surface area of 12,847.3 cm2 per plant;the root system of R.soongorica distributed at 0-80 cm interval,with an average total absorbing root-surface area of 361.8 cm2.The root distribution shows the following:T.ramosissima uses groundwater as its main water source;H.ammodendraom uses both groundwater and rainwater;and R.soongorica uses rainwater only.During the wet-dry cycle,the hydraulic parameters of T.ramosissima showed no responses to precipitation.R.soongorica responded most significantly,and the responses of H.ammodendraom were intermediate.In conclusion,the plant response to rain events is closely related to their root distribution and plant water-use strategy.

Water adaptive traits of deep-rooted C_3 halophyte(Karelinia caspica(Pall.) Less.) and shallow-rooted C_4 halophyte(Atriplex tatarica L.) in an arid region,Northwest China

This paper focused on the water relations of two halophytes differing in photosynthetic pathway, phe- notype, and life cycle： Karelinia caspica （Pall.） Less. （C3, deep-rooted perennial Asteraceae grass） and Atriplex tatarica L. （C4, shallow-rooted annual Chenopodiaceae grass）. Gas exchange, leaf water potential, and growth characteristics were investigated in two growing seasons in an arid area of Xinjiang to explore the physiological adaptability of the two halophytes. Both K. caspica and A. tatarica showed midday depression of transpiration, in- dicating that they were strong xerophytes and weak midday depression types. The roots of A. tatarica were con- centrated mainly in the 0-60 cm soil layer, and the leaf water potential （~L） increased sharply in the 0-20 cm layer due to high soil water content, suggesting that the upper soil was the main water source. On the other hand, K. caspica had a rooting depth of about 1.5 m and a larger root/shoot ratio, which confirmed that this species uptakes water mainly from deeper soil layer. Although A. tatarica had lower transpiration water consumption, higher water use efficiency （WUE）, and less water demand at the same leaf water potential, it showed larger water stress impact than K. caspica, indicating that the growth of A. tatarica was restricted more than that of K. caspica when there was no rainfall recharge. As a shallow-rooted C4 species, A. tatarica displayed lower stomatal conductance, which could to some extent reduce transpiration water loss and maintain leaf water potential steadily. In contrast, the deep-rooted C3 species K. caspica had a larger root/shoot ratio that was in favor of exploiting groundwater. We concluded that C3 species （K. caspica） tapes water and C4 species （A. tatarica） reduces water loss to survive in the arid and saline conditions. The results provided a case for the phenotype theory of Schwinning and Ehleringer on halophytic plants.

Potential of Plant Growth Regulators on Modulating Rooting of <i>Rosa centifolia</i>

Rosa centifolia is grown for its flowers which are used for essential oil extraction. It is vegetatively propagated through its cuttings which are difficult to root. This study was designed to increase the rooting percentage of cuttings by applying plant growth regulators (PGRs) with different levels. In total 31 treatments with different concentrations (450 ppm, 700 ppm and 950 ppm) of indole butyric acid (IBA), indole acetic acid (IAA), naphthalene acetic acid (NAA) alone, in combination and with same concentrations of 6-benzylamino purine (BAP) were used. Healthy similar sized cutting of R. centifolia was treated in solution of PGRs by quick dip method and planted in polythene bags. The data for shoot length, shoot dry weight, number of roots, root length and root dry weight were recorded. All three levels (450 ppm, 700 ppm and 950 ppm) of IBA alone produced maximum results in case of all parameters as compared to all other treatments. Among three levels of IBA, 450 ppm concentration produced maximum shoot length (10.67 cm), shoot dry weight (3.02 g), number of roots (14.00), root length (11.90 cm) and root dry weight (0.50 g). Lower concentrations of plant growth regulators produced better results as compared to higher concentrations.

Non-aerated liquid culture promotes shoot organogenesis in Eucalyptus globulus Labill

Eucalyptus is very recalcitrant to in vitro culture.In this research, an efficient shoot organogenesis system was developed using 60-day-old plants of Eucalyptus globulus grown in vitro and non-aerated liquid medium to improve shoot proliferation. Cultures were initiated with hypocotyls and leaf segments from plantlets cultivated on semisolid 1/2 MS modified medium supplemented with 4.44 μM 6-Benzyladenine(BA) and 16.1 μM 1-Naphthaleneacetic acid(NAA). Calli were transferred to shoot induction medium, with either 0.5 or 2.7 μM NAA. Shoot multiplication was carried out on 4.44 μM BA + 0.5 μM NAA medium, and semisolid and non-aerated liquid systems were compared for improving shoot proliferation.Rooting of adventitious shoots was evaluated on medium containing NAA or Indole-3-butyric acid-IBA(5 and16 μM). Callogenesis was obtained from both types of explants, although shoot formation was only obtained from leaf-derived calli. Shoot proliferation on 4.44 μM BA+0.5 μM NAA resulted in the most shoots/callus.Non-aerated liquid medium was more efficient in promoting shoot multiplication(53.5 shoots/callus) than was semisolid medium(28.5 shoots/callus). Levels of phenolic compounds were significantly reduced in the shoots cultivated in liquid medium. Efficient rooting(76%) was obtained using 16 μM IBA.

旱、渍胁迫对夏玉米根冠比及籽粒灌浆源库关系的影响

利用河北固城站电动防雨棚,遮去自然降水,人工控制灌水形成土壤渍水、高湿、干旱和对照,夏玉米开花后通过测定籽粒灌浆进程和地上生物量以及产量构成要素、根冠结构和根冠比等,探究不受阴雨和低温胁迫影响下的土壤旱、渍胁迫对夏玉米籽粒灌浆及产量形成的影响。分析夏玉米籽粒灌浆干物质的源库关系,结果表明:夏玉米籽粒灌浆对旱、渍胁迫的响应不同,渍水时灌浆持续日数延长,较对照延长7~8 d,重旱时缩短,较对照缩短5~6 d;对于平均灌浆速率,高湿最大,较对照偏大9.19%~9.85%,重旱最小,较对照偏小24.80%~25.26%,中度旱次小,较对照偏小6.89%~7.45%。旱、渍胁迫对夏玉米产量形成都有负效应:渍水、高湿减产率为1.83%~8.43%,干旱处理减产率为32.73%~81.96%,重旱近乎绝收,干旱危害程度比渍水、高湿影响大得多。旱、渍胁迫对夏玉米灌浆期穗位叶光合生理特性的影响不同,净光合速率(Pn)渍水比对照偏高0.91%~9.10%,高湿比对照偏低1.75%~9.13%;干旱比对照显著偏低,中度旱偏低55.76%~59.08%,重旱偏低92.16%~92.75%。夏玉米籽粒灌浆的干物质主要来源于灌浆期绿叶等光合作用形成的光合产物,成熟期地上干物质籽粒分配率减少,收获期秸秆存量大,导致收获指数降低。干旱胁迫刺激、诱导玉米根系增生须根,须根重增加显著,导致其根冠比提高,尤其重旱较渍水、高湿和对照提高近10倍以上,揭示出玉米根系尤其须根系对土壤水分逆境胁迫的应急响应生理调节机制和适应逆境条件的生存机理。实际生产管理中可利用土壤干湿交替变化刺激、诱发根系生长发育,提升优化根冠结构。研究结果为评估旱、涝灾害对北方旱区农作物生长发育和产量形成的影响提供数据支撑和参考。

苹果砧木新品种鲁砧1号离体叶片高效不定植株再生

【目的】建立苹果半矮化砧木新品种鲁砧1号离体叶片高效不定梢再生技术体系,为该砧木快繁和遗传改良奠定技术基础。【方法】以鲁砧1号无菌苗离体叶片为外植体,研究碳源、细胞分裂素种类和质量浓度对叶片不定梢再生的影响;以不定梢为试材,研究基本培养基、蔗糖质量浓度对不定梢生根的影响。【结果】MS添加较低质量浓度(0.6 mg·L^(-1))细胞分裂素(TDZ)时,碳源物质为D-山梨醇的叶片不定梢再生率显著高于蔗糖;其他激素处理下,D-山梨醇和蔗糖之间叶片不定梢再生率无显著差异。两种碳源上的平均每叶不定芽(梢)数,都表现较高细胞分裂素质量浓度处理高于或显著高于较低细胞分裂素质量浓度处理,以TDZ质量浓度为1 mg·L^(-1)时产生的不定芽数最多,平均每叶不定芽数为3.8~4个。在不定芽诱导培养基上,6-苄基氨基嘌呤(BA)比TDZ更容易诱导产生直接伸长生长的不定梢。不定梢生根率和平均每株生根条数,两种基本培养基及两个蔗糖质量浓度之间都表现差异不显著,但以1/4MS基本培养基和20 g·L^(-1)蔗糖组合的生根培养基上获得的生根率和单株生根条数最高,分别超过93%和5.8。【结论】鲁砧1号离体叶片容易诱导再生不定芽和不定梢生根,诱导叶片不定芽再生最佳培养基为MS添加1 mg·L^(-1)TDZ、0.3 mg·L^(-1)IBA和30 g·L^(-1)蔗糖,最佳生根培养基为1/4MS添加0.3~0.5 mg·L^(-1)IBA和20 g·L^(-1)蔗糖。

杜梨组培快繁及组培苗微扦插技术研究

以种子来源的4个杜梨株系组培苗为试材,采用植物组织培养和组培苗微扦插的方法,研究了不同浓度细胞分裂素6-BA和IBA处理对杜梨丛生芽增殖的影响以及不同浓度IBA和生长素(NAA)处理对杜梨组培苗离体生根和微扦插生根的影响,以期为稳定高效杜梨组培快繁体系的建立提供参考依据。结果表明:基因型和6-BA浓度对杜梨增殖系数具有极显著影响,IBA浓度对增殖系数具有显著影响;低浓度的生长素更适合用于杜梨组培苗的生根诱导。综合考虑组培苗增殖和生根情况,DL30株系表现最优,其适宜的增殖培养基为MS+1.0 mg·L^(-1)6-BA+0.2 mg·L^(-1)IBA,增殖系数为3.4±0.35,适宜的生根培养基为1/2MS+0.2 mg·L^(-1)IBA,生根率达60.0%±20.0%。IBA和NAA蘸根处理对杜梨组培苗微扦插生根有显著影响,杜梨株系DL30组培苗通过1000 mg·L^(-1)的IBA蘸根处理后微扦插生根率为46.7%±8.8%。

西南桦立木生物量模型的研建

基于2019—2020年在云南省境内采集并测定的157株西南桦立木生物量(其中地上生物量106株、全树生物量51株),建立地上、地下生物量一元(二元)独立模型W=a×D^(b)、W=a×D^(b)×HC,并采用相容性生物量模型建立西南桦地上总生物量与树枝、树叶、树干各分项生物量之和相容的西南桦立木生物量模型,采用根茎比建立地下生物量模型。结果表明:对于西南桦地上生物量,一元、二元模型分别选用权函数W=1/(D^(2))、W=1/(D^(2)H),对于西南桦地下生物量,一元、二元模型分别选用权函数W=1/(D^(0.5))、W=1/(D^(0.5)H^(0.5)),进行加权回归求解模型参数,可明显减小异方差影响及提高模型稳定性;相容性生物量模型解决了立木树枝、树叶、树干等分项生物量之和与地上总生物量不相等问题;从评价指标来看,西南桦地上总生物量和树干生物量模型预估精度均在94%以上;树枝、树叶生物量模型预估精度在92%以上,地下生物量模型预估精度在87%以上。总之,各模型预估精度均达到了国家相关精度要求;研究成果可应用于西南桦生物量的估算。

不同浓度矮壮素、萘乙酸和烯效唑对大葱苗期生长的影响

为探究不同植物生长调节剂对大葱苗期徒长的控制效果,研究了矮壮素、萘乙酸和烯效唑3种植物生长调节剂对大葱苗期生长的影响。结果表明,喷施3种植物生长调节剂均能显著增加大葱幼苗的根系数量、茎粗、壮苗指数和根冠比;矮壮素和烯效唑处理显著降低株高,萘乙酸处理则增加株高;矮壮素和萘乙酸处理的叶绿素含量增加,干质量增加,而喷施不同浓度烯效唑的叶片和假茎干质量在处理后35 d时分别较对照降低7.56%~31.59%和27.95%~47.33%。综合考虑大葱幼苗的形态指标和干物质分配比例,500 mg·L^(-1)烯效唑处理对大葱幼苗控制徒长的效果最好,壮苗指数和根冠比分别较对照提高111.00%和91.30%。

播期推迟对棉花根系生长发育特征及产量的影响

【目的】研究推迟播期对棉花根系生长发育特征和产量的影响,为黄河流域棉区棉花适期播种提供依据。【方法】2022―2023年在河北农业大学威县试验站开展田间试验,设置常规播期(4月15日)和推迟播期(5月1日)2个处理,分析推迟播期对棉花品种冀农大23号的根系分布、根系生长速率、根冠比、干物质积累量和产量等的影响。【结果】与常规播期相比,推迟播期条件下,棉花根系长度和生物量的最大增长速率分别增加2.92~5.35 cm·d^(-1)和0.40~0.76 mg·d^(-1);深层土壤中棉花根系占比提高,其中30~60 cm土层根系长度占比和根系生物量占比分别增加2.99~3.55百分点和3.94~4.42百分点;生育后期棉株地上部干物质积累量和根冠比无明显差异;根系载荷能力显著降低6.43%~17.69%;2022年籽棉产量无显著差异,2023年单位面积铃数和籽棉产量分别显著增加9.72%和7.66%。相关分析表明,0~60 cm土层根长密度、0~60 cm土层根系生物量密度、根系生物量最大增长速率和30~60 cm土层根系长度占比均与籽棉产量极显著正相关。【结论】黄河流域棉区推迟播期(5月1日)可通过提高棉花根系生长速率、深层土壤中根系长度和根系生物量的占比,增强根系吸收功能以保障地上部干物质的积累,促进棉花高产。

光竞争对杉木幼苗生长、生物量分配及叶片化学计量特征的影响

通过研究杉木幼苗在不同光竞争条件下的生长特性及叶片C、N、P化学计量响应策略,以探究光竞争环境下杉木叶片营养利用及生长适应性规律。选择生长均一杉木无性系幼苗,采用室内盆栽试验,通过调整相邻盆栽容器高度差以模拟相邻杉木获得不同光资源优势,形成具有明显光资源竞争优势植株(优势木)及竞争劣势的相邻植株(竞争木),根据调整后的高度差共设置3个光竞争强度:强度光竞争(高度差0 cm)、中度光竞争(高度差8 cm)、轻度光竞争(高度差16 cm),通过测定分析光竞争模拟处理1 a后参试幼苗苗高和地径、各器官生物量以及叶片C、N、P含量的差异性,分析各元素间化学计量比特征。结果表明,随着光竞争强度的减小,竞争木苗高比优势木高6.04%,地径比优势木小17.51%,根冠比增大,根系生物量分配比例增大至40.0%。随着光竞争强度的减小,竞争木植株叶片N含量增多达21.63 g/kg;优势木叶片C、P含量变化趋势相同,均随光竞争强度的减小先减小后增大,且显著大于竞争木(P<0.05);优势木C/N、C/P均随着光竞争强度的减小先增大后减小,竞争木C/P随光竞争强度的减小而增大。优势木叶生物量与P含量呈显著正相关,竞争木茎生物量与叶生物量呈显著正相关,与P含量呈显著正相关。不同光资源竞争位置杉木幼苗生长特性及叶片化学计量特征对不同光竞争强度适应策略有差异,表现为随光竞争强度的减小,处于光竞争劣势的竞争木生物量主要分配于地下根系,幼苗株形呈现“细高”的生长趋势;与之相反,光资源竞争的优势木则将生物量分配倾向于叶片,同时C、P含量明显减小,株形呈现“矮粗”的生长趋势。