三峡库区岸边共存松栎树种水分利用策略比较

对三峡库区木鱼岛上马尾松(Pinus massoniana)、槲栎(Quercus aliena)和栓皮栎(Q. variabilis)组成的针阔混交林成林和幼林的光合速率(P_n)、气孔导度(G_s)、清晨和中午水势(ψ_pd和ψ_md)以及叶片稳定碳同位素(δ¹³C)进行了测定。实验结果表明:针叶树马尾松P_n、G_s均低于阔叶树槲栎和栓皮栎(差异达到极显著水平,p<0.001),但马尾松内在水分利用效率(WUE_i, P_n/G_s)却高于槲栎(p=0.003)和栓皮栎(p=0.025)。反映了裸子植物和被子植物木质部不同的水力特性。针阔叶树幼树的P_n和G_s高于成年树,但WUE_i和δ¹³C却低于成年树。表明水分利用效率与水分在树体内传输的距离有关。幼树属于挥霍型水分利用策略,成年树属保守型水分利用策略。三峡大坝的建设所造成的生态环境的改变可能会对三峡库区针阔混交林的演替产生一定的影响,但这需要长期的研究。     

不同基因型冬小麦旗叶的稳定碳同位素比值及其与产量和水分利用效率的关系

以我国北方12个冬小麦(Triticum aestivum)品种(系)和美国德克萨斯州3个冬小麦品种(系)为供试材料, 在甘肃陇东黄土高原旱作和拔节期有限补灌条件下, 比较研究了不同基因型冬小麦之间产量、水分利用效率(WUE)和灌浆期旗叶稳定碳同位素比值(δ¹³C)的差异, 以及δ¹³C值与产量和WUE的关系。旨在通过分析δ¹³C值与产量和WUE的关系, 明确δ¹³C值在评价植物WUE方面的可靠性, 为抗旱节水品种的筛选提供理论依据。结果表明: 不论旱作还是有限补灌, 不同基因型冬小麦之间产量、WUE、旗叶δ¹³C值存在显著差异, 随着灌浆过程的进行, 旗叶δ¹³C值呈缓慢增大的趋势, 而且旗叶δ¹³C值旱作高于有限补灌。不论旱作还是补灌条件, 旗叶δ¹³C值在4个测定时期的平均值与籽粒产量、WUE呈显著正相关关系(R²= 0.527 3-0.691 3)。小麦拔节期补灌100 mm水分后, 不同基因型小麦表现出明显的水分超补偿效应。说明冬小麦灌浆期旗叶δ¹³C值在旱作条件下和在补灌条件下均可较好地评价WUE, 可将冬小麦灌浆期旗叶δ¹³C值作为筛选高效用水品种的参考指标之一。     

晋西黄土区典型乔灌木短期水分利用效率对环境因子的响应

为明确晋西黄土区植物的水分利用规律及对半干旱区的适应策略, 提高黄土地区植被建设效益, 该研究对该地区典型乔灌木短期水分利用效率随环境因子的变化进行了探究。以典型乔木油松(Pinus tabuliformis)、刺槐(Robinia pseudoacacia)及其林下灌木黄刺玫(Rosa xanthina)、杠柳(Periploca sepium)为研究对象, 测定叶片可溶性糖稳定碳同位素比值(δ¹³C_leaf)与枝条渗出液稳定碳同位素比值(δ¹³C_branch), 使用δ¹³C_leaf推导计算7-10月叶片尺度下植物短期水分利用效率(WUE_leaf)变化趋势, 使用δ¹³C_branch明确植物光合作用后分馏情况, 确定半干旱区植物在生长季的水分变化规律对环境因子变化的响应。结果表明: (1) 7-10月4种植物δ¹³C_leaf总体呈现降低趋势, δ¹³C_branch呈现先升高后降低趋势。δ¹³C_leaf在种间和生活型中均存在差异。具体表现为: 灌木>乔木, 常绿乔木(油松) >落叶乔木(刺槐)。研究过程中未发现明显的碳同位素在光合作用后发生分馏的情况。(2) 4种植物WUE_leaf在7-8月保持稳定, 9-10月逐渐升高。21.5 ℃、0.9 kPa、52.4%分别为WUE_leaf随温度(T_a)、饱和水汽压差(VPD)、相对湿度(RH)变化的突变点, 突变点之后4种植物WUE_leaf均表现出稳定的变化趋势, 不再随T_a、VPD、RH升高而降低。(3) WUE_leaf与T_a、RH、VPD之间存在显著负相关关系, T_a通过非气孔因素, 即酶的作用改变光合速率, 引起WUE_leaf变化。RH、VPD等水分因子则通过改变气孔开度, 影响蒸腾, 进而改变WUE_leaf。随着土壤含水量(SWC)的升高, WUE_leaf呈现先升高后降低的趋势。油松林和刺槐林在SWC分别达到15%-18%、13%-14%时, WUE_leaf达到最高值。经过混合线性模型(LMM)分析得到, 油松和刺槐WUE_leaf主导环境因子分别为RH和VPD, 黄刺玫和杠柳WUE_leaf主导环境因子均为T_a。该研究得到了黄土地区典型乔灌木生长季水分利用效率变化的规律和主要环境影响因子, 明确了黄土地区植物对气候因子变化的适应机制。     

中国区域478种C3植物叶片碳稳定性同位素组成与水分利用效率

目前, 在中国区域关于植物碳稳定性同位素组成(δ¹³C)已经有了很多的研究, 同时, δ ¹³C作为植物水分利用效率(WUE)的替代指标, 得到了越来越广泛的应用。而这些研究多集中在站点或小的区域尺度, 那么在整个中国区域尺度上, δ¹³C能否作为植物WUE的替代指标值得探讨。该文通过对文献资料的收集整理, 研究了中国区域187个采样点478种C₃植物叶片的δ¹³C, 统计分析结果表明δ¹³C的变化范围为-33.50‰- -22.00‰, 均值为-(27.10 ± 1.70)‰。在乔木、灌木和草本3种不同的生活型间, 叶片δ¹³C的差异达到极显著水平, 其中以草本的δ¹³C最高, 乔木最低, 这与在站点或小的区域尺度上的研究结果不同。对不同系统发育类型的植物而言, 种子植物的δ¹³C极显著地大于蕨类植物; 祼子植物与被子植物间的差异未达到显著水平; 单子叶植物极显著地大于双子叶植物。叶片δ¹³C值随经度的变化没有明显的规律, 但是随纬度的增加, δ ¹³C极显著地升高。随年均温度和年均降雨量的降低, 叶片δ¹³C值极显著升高。年均降雨量与δ¹³C间的这种极显著的负相关关系, 与WUE和降水量间的关系一致, 这表明在大的区域尺度上, δ¹³C可以作为植物WUE的指示指标。     

增强UV-B辐射对暖温带落叶阔叶林土庄绣线菊水分利用效率、气孔导度、叶氮素含量及形态特性的影响

在北京东灵山暖温带森林生态系统中,选择常见灌丛土庄绣线菊(Spiraea pubescens),建立UV-B控制实验。连续3个生长季每天增补9.4 kJ·m^-2的辐射剂量,模拟臭氧衰减17%时近地表面UV-B辐射的增强。该实验的目的是在野外环境下观测,长时间人工增强UV-B辐射对土庄绣线菊叶片的气孔导度、碳同位素比率(δ¹³C)、叶含水量、叶面积、特别是水分利用效率(WUE)和叶片全氮含量等指标的影响。实验结果表明,增强UV-B辐射显著减少了土庄绣线菊的叶面积(50.1%),提高了叶片全氮含量(102%)。同时,UV-B辐射还在一定程度上(尽管统计显示不显著)降低了气孔导度(16.1%)、胞间CO₂浓度与大气CO₂浓度之比(C_i/C_a) (4.0%)、提高了碳同位素比率(δ¹³C)(20.5‰)、叶含水量(3.1%)及比叶重(SLW)(5.2%),从而导致WUE的增加(4.1%)和植物的抗旱能力增强。值得注意的是,深层土壤(30~40 cm)含水量变化会影响气孔导度、δ¹³C和WUE对紫外辐射的响应程度:在土壤干旱的季节(6月和9月),气孔导度、δ¹³C、WUE这些指标处理和对照的差异很小,但是当土壤水分充足时(7月和8月),处理和对照的差异就较为显著。另外,随着实验处理时间的延长,UV-B的效应变得不显著。相关分析表明,UV-B辐射降低了土壤含水量(30~40 cm)与土庄绣线菊叶含水量、δ¹³C、C_i/C_a和气孔导度的相关系数,增强了WUE与土壤含水量的相关性,这也许是由于UV-B辐射增强了WUE对土壤水分变化的敏感性。该研究的结果表明UV-B辐射对土庄绣线菊的形态和生长有显著的影响,但对主要水分生理指标影响不显著。     

贝壳堤岛旱柳光合效率的土壤水分临界效应及其阈值分级

为阐明黄河三角洲贝壳堤岛旱柳(Salix matsudana)叶片光合效率对土壤水分的适应机制, 明确其水分阈值效应, 以二年生旱柳为材料, 采用人工给水与自然耗水相结合获取系列水分梯度的方法, 测定分析贝壳砂生境下旱柳叶片光合效率参数对土壤水分的响应特征及其生产力分级。结果表明: 旱柳叶片净光合速率(P_n)、蒸腾速率(T_r)、水分利用效率(WUE)及光合光响应参数具有明显的水分临界效应。(1) P_n、T_r、WUE和潜在水分利用效率均随土壤水分的降低先升高后下降, 但各指标水分临界值表现不同步, 其中P_n水分气孔限制转折点和水分补偿点分别出现在相对含水量(W_r)为42.9%和14.4%时; P_n和T_r的水分饱和点为73.1%和68.9%, WUE水分高效点为80.1%; (2)水分胁迫下旱柳叶片具有明显的光抑制现象, 可通过减弱对光的利用来适应水分逆境。随土壤水分的增加, 表观量子效率(AQY)、光饱和点(LSP)和最大净光合速率(P_nmax)表现为先升高后降低, 但光补偿点(LCP)相反。P_n、AQY、LSP、P_nmax和暗呼吸速率(R_d)均表现为渍水胁迫明显高于干旱胁迫。W_r为69.1%时, LCP达到较低值(18.6 µmol∙m ^-2∙s^-1), AQY最高(0.05), 利用弱光能力较强。W_r为80.9%时, LSP达到最高(1775 µmol∙m ^-2∙s^-1), 光照生态幅最宽, 光能利用效率最高, 水分对光强的补偿效应显著; (3)采用临界值分类法确定出贝壳砂生境下旱柳光合效率的5级水分阈值, 73.1%_r<80.1%范围内为高产高效水, 此时旱柳具有较高的光合能力和高效生理用水特性。贝壳砂生境内旱柳表现出一定的耐水湿而不耐干旱的适应特性, 在干旱缺水的贝壳堤岛滩脊地带栽植时需充分考虑其水分环境。     

帽儿山17个种源落叶松针叶的水分利用效率比较

研究环境变化下的树木水分利用效率对探讨森林生态系统碳水耦联关系及其对气候变化的响应和适应对策具有重要意义。落叶松(Larix gmelinii)为我国北方森林的建群种之一。将水热条件不同的17个种源落叶松种植在帽儿山森林生态系统研究站的同质园内30年后, 测定其针叶水分利用效率(WUE)及其相关因子。结果表明: WUE、净光合速率(P_n)、蒸腾速率(T_r)、气孔导度(G_s)、比叶面积(SLA)和叶片氮含量(N_L)均存在显著的种源差异(p < 0.05)。WUE和G_s呈显著指数相关关系, 当G_s < 0.2时WUE随G_s的增大而明显增大, 而当G_s > 0.2时WUE趋于稳定。WUE和SLA及N_L分别呈线性负相关和正相关关系, 且随种源原地的干燥度指数(AI)的增大其相关性明显增强。WUE和种源原地年平均气温、平均年降水量及AI分别呈线性负相关、负相关和正相关关系, 并且相关系数依次增大; T_r则仅和种源原地年平均气温呈线性正相关关系, 而P_n和种源原地AI呈线性正相关关系。不同种源落叶松由于对种源原地环境条件的适应而存在针叶结构和生理特征的显著差异, 并因此引起针叶水分利用效率的差异。     

毛白杨杂种无性系叶片δ13C差异与气体交换参数

在苗木生长的不同时期对13个毛白杨(Populus tomentosa)杂种无性系叶片碳同位素δ¹³C和气体交换参数(净光合速率P_n、蒸腾速率T_r、瞬时水分利用效率WUE_i、气孔导度G_s和胞间CO₂浓度C_i)的差异进行研究, 分析不同无性系间δ¹³C与气体交换参数的相互关系, 目的在于探求δ¹³C在筛选高光合及高水分利用效率毛白杨杂种无性系中的应用价值。结果表明: 不同生长时期和不同无性系间δ¹³C、T_r、WUE_i、G_s和C_i的差异均显著, δ¹³C和WUE_i表现为9月>7月, T_r、G_s和C_i表现为7月>9月, P_n在不同生长时期差异不显著。季节变化是引起毛白杨杂种无性系叶片δ¹³C差异的主要原因。同一时期, 无性系间δ¹³C和WUE_i表现出较好的一致性, 即WUE_i较高的无性系30、42、46、83、BL2和BL5, 其δ¹³C值也较高, WUE_i较低的无性系B331和TG34, 其δ¹³C值也较低, 且不同时期(7月和9月) δ¹³C和WUE_i呈较强的正相关, 相关系数r分别为0.739 0和0.545 8, 高δ¹³C可以作为筛选高WUE_i毛白杨的有效指标, 且在苗木生长旺盛时期选育能得到更为可靠的结果。对毛白杨而言, 高WUE_i的无性系, 一般具有适中或较低的G_s和C_i, 但不一定具有很高的P_n, 气孔调节使得毛白杨在不影响光合作用的同时保持较高的WUE。     

生产力调控对翌年苹果园土壤水分和苹果叶片光合特性的影响

以盛果期‘长枝富士’为试验材料, 以生产力调控翌年苹果(Malus pumila)树坐果期为主要观测期, 对不同生产力水平下果园土壤水分状况及苹果叶片光合特性进行了研究。结果表明: 在生产力调控范围内, 土壤剖面各个层次土壤含水量均随着生产力水平的减小而增加, 其中在60 cm处达到最大增量, 为31.02%; 而在600 cm范围内土壤贮水量最大能够提高15.41%。随着生产力水平的降低, “光合午休”现象减弱, 净光合速率(P_n)增加, 最大增幅为25.71%, 下午时段的蒸腾速率(T_r)下降迅速, 水分利用效率(WUE)最大提高34.12%。通过相关分析表明, 土壤贮水量(WSC)与P_n、T_r、WUE之间均达到显著相关, 其相关系数分别为: 0.973^**、-0.543^*和0.992^**。土壤贮水量(x)与水分利用效率(y)之间符合y = 0.002 3x - 1.480 6, R²= 0.984 4^**的回归模型。通过生产力调控可以改善土壤水分状况和果树光合能力, 提高WUE。     

基于年降水、生长季降水和生长季蒸散的高寒草地水分利用效率

水分利用效率是深入理解生态系统碳、水循环间耦合关系的重要指标。以前研究青藏高原的水分利用效率多基于年降水量(AP)来分析, 但植物对水分的利用主要在生长季。该研究采用以AP、生长季降水量(GSP)和生长季蒸散量(ET_gs)分别计算的年降水利用效率(PUE_a)、生长季降水利用效率(PUE_gs)和生长季水分利用效率(WUE_gs), 分析了2000-2010年间青藏高原两种主要植被类型高寒草甸和高寒草原PUE_a、PUE_gs和WUE_gs的差异及其与降水量、蒸散量和气温的关系。结果表明: (1)高寒草甸的PUE_a、PUE_gs均大于高寒草原, 但两种草地类型的WUE_gs无显著差别, 这说明两种草地类型可能存在相似的内在的水分利用效率。(2)从年际动态来看, PUE_a和PUE_gs的波动范围相似, 而WUE_gs的波动范围更大, 说明以蒸散为依据的WUE_gs可能比PUE_a和PUE_gs更敏感, 因而可能更好地反映生态系统的水分利用能力。(3)高寒草甸和高寒草原的PUE_a、PUE_gs和WUE_gs分别与AP、GSP和ET_gs呈单调递减趋势, 表明3种水分利用效率均随降水量或蒸散量的增加而降低。高寒草原的3种水分利用效率中仅WUE_gs随着气温的增加而增加, 而高寒草甸的3种水分利用效率均与气温无显著关系, 这说明相比高寒草甸, 高寒草原的水分利用效率对气温更加敏感。     

Morphological traits and physiological characteristics in drought tolerance in 20 shrub species on the Qinghai-Xizang Plateau

Aims Providing indispensably theoretical evidence for establishing indices of evaluation on drought tolerance in shrubs, and screening for tree species that are drought tolerant for afforestation in arid regions or for matching their characteristics with suitable habitat conditions are the key to vegetation restoration in the Qinghai-Xizang Plateau. However, these issues are not adequately addressed in recent research due to lack of systematic methods. Therefore, our objective was to make a comprehensive evaluation on drought tolerance in 20 shrub species collected from different areas in Qinghai-Xizang Plateau, and to study their underlying mechanisms in drought tolerance.
Methods We made measurements on variables depicting root characteristics, including the root length (TRL), surface area (TRSA), volume (TRV), and tips number (TRTN) of all roots, the root length (FRL), surface area (FRSA), volume (FRV), and tips number (FRTN) of fine roots (d≤2 mm), and derived plant characteristic indices including thickness of cuticle (CT), thickness of palisade tissue (TPT), thickness of spongy tissue (TST), TPT/TST, thickness of leaf (LT), palisable tissue cell density, and tissue structural tense ratio (CTR = TPT/LT × 100%) and spongy tissue loosened ratio (SR = TST/LT × 100%) of leaf anatomical structure, root to shoot ratio (RSR), leaf transpiration rate (T_r), instantaneous water use efficiency (WUE_i), and carbon isotopic composition (δ¹³C) of the 20 shrub species through field experiments. Correlation analysis and principal component analysis were performed on the 19 variables and indices.
Important findings Different shrubs had different mechanisms of drought tolerance. In this study, the character- istics of drought tolerance were mainly categorized into 6 types, involving modifications of (1) root systems, (2) leaf anatomical structure, (3) leaf pattern, and (4) biomass allocation, or via (5) low water-consumption and (6) high WUE_i. Different genera or different tree species within the same genus clearly differed in drought tolerance. The species of the genus Hippophae were relatively poorly tolerant to drought, whereas several shrubs including Potentilla fruticosa, Berberis julianae, Caragana arborescens, Spiraea salicifolia and Hippophae rhamnoides ssp. mongolica occurred to be more drought tolerant than other shrub species investigated in this study. On the other hand, there were highly significant correlations among the characteristics of root systems and among characteristics of leaf anatomical structure. The results of principal component analysis on 19 variables and indices showed that TRL, TRSA, TRV, TRTN, FRL, FRSA, FRV, FRTN, CT, TPT, TST and WUE_i could be effective indicators of drought tolerance of shrubs in the Qinghai-Xizang Plateau. In addition, the drought tolerance of shrubs had a close connection with their origin of collections; the shrubs collected from Xining prefecture in Qinghai Province were more drought tolerant than those from Tianshui Prefecture in Gansu and Lasa Prefecture in Xizang.     

Traits of shrubs in forests and bushes reveal different life strategies

灌木是森林和灌丛生态系统的重要组成部分, 探究森林与灌丛灌木功能性状的差异, 可揭示灌木在不同生境的适应策略。该研究以金华北山森林群落林下灌木层、低山灌丛和山顶灌丛共24个样地中的优势灌木为研究对象, 分析叶片和小枝9个功能性状在3种生境下的总体差异, 以及种间、种内变异和不同生活型的差异。结果表明: 1) 9个性状在3种不同生境下存在差异。林下灌木具有较大的叶面积和比叶面积, 较小的叶干物质含量、叶和小枝的组织密度, 低山灌丛相较于山顶灌丛具有较大的叶厚度、叶组织密度和较小的比叶面积、小枝干物质含量。2)林下灌木的比叶面积、小枝直径、小枝组织密度和小枝干物质含量的种内种间变异系数最大, 低山灌丛的比叶面积、叶和小枝的干物质含量、叶和小枝的组织密度的种内种间变异系数最小。3)不同生活型间, 林下常绿灌木的叶厚度、叶组织密度、叶干物质含量显著高于落叶灌木, 落叶灌木的比叶面积显著高于常绿灌木, 而山顶灌丛叶厚度和比叶面积的差异规律与林下灌木相同, 叶组织密度和叶干物质含量的差异与其相反。4)影响灌木性状的主要因素是物种以及物种和生境的交互作用。总之, 森林群落林下灌木形成较大叶面积和比叶面积, 较小叶和小枝组织密度、叶干物质含量的性状组合, 以快速生长而适应光照较弱、竞争作用强的林下环境, 是资源获取型策略; 低山灌丛和山顶灌丛具有较大叶厚度、组织密度、干物质含量和小枝组织密度和较小叶面积、比叶面积等一系列储存养分、慢速生长的性状组合, 属于资源保守型策略。灌木植物性状的不同组合及其所反映的不同生活策略, 对亚热带地区退化植被的生态恢复具有指导意义。     

森林与灌丛的灌木性状揭示不同的生活策略

灌木是森林和灌丛生态系统的重要组成部分, 探究森林与灌丛灌木功能性状的差异, 可揭示灌木在不同生境的适应策略。该研究以金华北山森林群落林下灌木层、低山灌丛和山顶灌丛共24个样地中的优势灌木为研究对象, 分析叶片和小枝9个功能性状在3种生境下的总体差异, 以及种间、种内变异和不同生活型的差异。结果表明: 1) 9个性状在3种不同生境下存在差异。林下灌木具有较大的叶面积和比叶面积, 较小的叶干物质含量、叶和小枝的组织密度, 低山灌丛相较于山顶灌丛具有较大的叶厚度、叶组织密度和较小的比叶面积、小枝干物质含量。2)林下灌木的比叶面积、小枝直径、小枝组织密度和小枝干物质含量的种内种间变异系数最大, 低山灌丛的比叶面积、叶和小枝的干物质含量、叶和小枝的组织密度的种内种间变异系数最小。3)不同生活型间, 林下常绿灌木的叶厚度、叶组织密度、叶干物质含量显著高于落叶灌木, 落叶灌木的比叶面积显著高于常绿灌木, 而山顶灌丛叶厚度和比叶面积的差异规律与林下灌木相同, 叶组织密度和叶干物质含量的差异与其相反。4)影响灌木性状的主要因素是物种以及物种和生境的交互作用。总之, 森林群落林下灌木形成较大叶面积和比叶面积, 较小叶和小枝组织密度、叶干物质含量的性状组合, 以快速生长而适应光照较弱、竞争作用强的林下环境, 是资源获取型策略; 低山灌丛和山顶灌丛具有较大叶厚度、组织密度、干物质含量和小枝组织密度和较小叶面积、比叶面积等一系列储存养分、慢速生长的性状组合, 属于资源保守型策略。灌木植物性状的不同组合及其所反映的不同生活策略, 对亚热带地区退化植被的生态恢复具有指导意义。     

Correlation between vein density and water use efficiency of Salix matsudana in Zhangye Wetland,China

Aims The correlation between vein density and water use efficiency (WUE) affects the balance between water supply and demand of plant leaves, which is significant for comprehending the ecological adaptation strategies of plants. The objective of this study was to study how Salix matsudana modulated vein density and WUE along a soil moisture gradient in Zhangye Wetland, China. Methods The study was conducted in floodplain wetland near Heihe River in Zhangye City, Gansu Province, China. Three sample plots, at a spatial interval of 70 m, were set up along a soil moisture gradient ordinally from the area near the water body to the wetland edge, plot I (69.23%), spot II (48.38%) and spot III (35.27%). Community traits were investigated by using diagonal method, and all individuals of S. matsudana were used for measurements of height and canopy. At each plot, 5 individuals of S. matsudana at 4 vertices and diagonal intersection were selected for measurements of vein density, WUE, net photosynthetic rate (P_n), transpiration rate (T_r), photosynthetically active radiation (PAR), saturated vapor pressure differences (VPD), specific leaf area, stomatal conductance (G_s) and intercellular CO₂ concentration (C_i). We used mathematical methods of correlation analysis and standardized major axis to investigate relationships between vein density and WUE. Important findings With decreasing soil moisture, the height, canopy, specific leaf area, G_s and C_i of S. matsudana decreased gradually, while the vein density, WUE, P_n, T_r, PAR and VPD increased gradually. The correlation between vein density and WUE was positive in all the three plots, but the relationship varied along the soil moisture plots gradient. There was a highly significant positive correlation (p < 0.01) between the vein density and WUE at plot I and III, whereas the correlation only reached a significant level (p < 0.05) at plot II; The correlation coefficient between vein density and WUE is significantly smaller than 1 at plot I (p < 0.05), while the correlation coefficient is significant greater than 1 at plot II and III (p < 0.05). We can conclude that varied relationships between vein density and WUE of S. matsudana along a soil moisture gradient could reflect plant acclimation.     

Biomass estimation models and allocation patterns of 14 shrub species in Mountain Luya,Shanxi, China

Aims Shrub species have evolved specific strategies to regulate biomass allocation among various organs or between above- and belowground biomass and shrub biomass model is an important approach to estimate biomass allocation among different shrub species. This study was designed to establish the optimal estimation models for each organ (leaf, stem, and root), aboveground and total biomass of 14 common shrub species in Mountain Luya, Shanxi Province, China. Furthermore, we explored biomass allocation characteristics of these shrub species by using the index of leaf biomass fraction (leaf to total biomass), stem biomass fraction (stem to total biomass), root biomass fraction (root to total biomass), and root to shoot mass ratio (R/S) (belowground to aboveground biomass).
Methods We used plant height, basal diameter, canopy diameter and their combination as variables to establish the optimal biomass estimation models for each shrub species. In addition, we used the ratios of leaf, stem, root to total biomass, and belowground to aboveground biomass to explore the difference of biomass allocation patterns of 14 shrub species.
Important findings Most of biomass estimation models could be well expressed by the exponential and linear functions. Biomass for shorter shrub species with more stems could be better estimated by canopy area; biomass for taller shrub species with less stems could be better estimated by the sum of the square of total base diameter multiply stem height; and biomass for the rest shrub species could be better estimated by canopy volume. The averaged value for these shrub species was 0.61, 0.17, 0.48, and 0.35 for R/S, leaf biomass fraction, stem biomass fraction, and root biomass fraction, respectively. Except for leaf biomass fraction, R/S, stem biomass fraction, and root biomass fraction for shrubs with thorn was significantly greater than that for shrubs without thorn.     

Physiological responses of the legume model Medicago truncatula cv. Jemalong to water deficit

In Medicago truncatula Gaertn. cv. Jemalong plants some mechanisms involved in drought resistance were analysed in response to a progressive water deficit imposed by suppression of soil irrigation. Withholding water supply until the soil had reached one-half of its maximum water content had no significant effect on leaf RWC, gas exchanges or chlorophyll fluorescence parameters. Under severe drought conditions, the plants resistance to water shortage involved mainly drought avoidance mechanisms through a decrease in stomatal conductance. The consequent decrease in the internal CO₂ concentration (C_i) should have limited the net CO₂ fixation (A). Since A decreased slightly more than C_i under severe water deficit, non-stomatal limitations of photosynthesis may have also occurred. Analysis of A/C_i curves showed reduced carboxylation efficiency due to limitations in RuBP regeneration and Rubisco activity, confirming the presence of non-stomatal limitations of photosynthesis. Drought tolerance mechanisms involving osmotic adjustment and an increase in cell membrane integrity were also present. Altogether, these mechanisms allowed M. truncatula cv. Jemalong plants to still maintain a quite elevated level of net CO₂ fixation rate under severe water deficit conditions. These results may contribute to identify useful physiological traits for breeding programs concerning drought adaptation in legumes.     

苗期干旱及复水条件下不同花生品种的光合特性

为探索不同花生(Arachis hypogaea)品种的旱后恢复能力, 研究花生品种耐旱性与光合特性的关系, 通过盆栽土壤水分控制实验, 测定了12个花生品种苗期对干旱胁迫与复水过程的光合响应特征, 并讨论了所测各性状参数与抗旱性强弱的关系, 包括对水分胁迫伤害的修复能力。结果表明, 根据苗期生物量抗旱系数, ‘山花11号’、‘如皋西洋生’、‘A596’、‘山花9号’、‘农大818’的抗旱性较强, 且复水后植株产生超补偿生长效应, 补偿生长能力与抗旱性呈极显著正相关。叶片净光合速率(P_n)、气孔导度(G_s)、胞间CO₂浓度(C_i)、最大光化学效率(F_v/F_m)、实际光化学效率(Φ_PSII)、光化学猝灭系数(q_P)随干旱进程逐渐降低, 复水后逐渐增加, 抗旱性强的花生品种变幅较小。干旱7天, 大多数花生品种的光合参数值未有显著性差异。干旱14天, 抗旱性越强的花生品种光合参数值越高, 不同抗旱性花生品种的光合参数值有显著差异。‘山花11号’、‘如皋西洋生’、‘A596’、‘山花9号’的P_n、G_s、Φ_PSII、F_v/F_m、q_P在复水5天时恢复至对照水平, 复水10天时超过对照, ‘79266’、‘ICG6848’、 ‘白沙1016’、‘花17’在复水10天时仍未达到对照水平, 复水过程中抗旱性强的品种的光合参数显著高于抗旱性弱的品种。相关分析表明, 干旱胁迫14天和复水5天后, 花生的P_n、Φ_PSII、F_v/F_m、q_P与品种抗旱性呈极显著正相关。因此, 可在苗期用40%土壤相对含水量胁迫14天及复水5天时花生的P_n、Φ_PSII、F_v/F_m、q_P鉴定品种的干旱伤害程度及修复能力, ‘山花11号’可作为强干旱适应性鉴定的标准品种。     

QTLs affecting morph-physiological traits related to drought tolerance detected in overlapping introgression lines of rice (Oryza sativa L.)

Plant photosynthetic traits such as net photosynthetic rate (P_n), stomata conductance (g_s), transpiration rate (T_r), and intercellular CO₂ concentration (C_i), are known to relate to drought tolerance in plants, but the genetic basis of these traits remains largely uncharacterized because of the difficulty in phenotyping physiological traits in a large mapping population. In this study, a set of 55 overlapping introgression lines (ILs) in the Teqing (indica) background were used to genetically dissect several morph-physiological traits and their relationship with grain yield under water stress and non-stress conditions. These traits included specific leaf weight (SLW), chlorophyll content (CC), leaf stomata frequency (SF), P_n, g_s, T_r, and C_i. A total of 40 QTLs affecting the measured traits were identified and mapped to 21 genomic regions in the rice genome. Clustered QTLs affecting P_n, g_s, T_r, and C_i in the same genomic regions suggest common genetic bases for the physiological traits. Low or no phenotypic correlations between leaf morphological traits and photosynthetic traits and between morph-physiological traits and grain yield (GY) appeared to be due to inconsistence in QTL effect for clustered QTLs, unlinked QTLs affecting different traits, and to possible epistasis that could not be adequately addressed in this study. Our results indicate that improving drought tolerant (DT) of rice by selecting any single secondary traits is not expected to be effective and the identified QTLs for GY and related morph-physiological traits should be carefully confirmed before to be used for improving DT in rice by MAS.     

林分密度对马尾松林下植物与土壤种子库多样性的影响

林分密度是影响林下植物多样性的重要因子。本研究以马尾松人工林为对象,设置低密度(1575株·hm^-2,D₁)、中密度(2474株·hm^-2,D₂)和高密度(3550株·hm^-2,D₃)3个林分密度,分析林下植物和土壤种子库多样性及二者的关系,为马尾松人工林实现多目标可持续发展提供科学依据。结果表明: 3种林分密度林下草本与灌木植物共有42科62属70种,D₁密度以喜光植物种类分布较多,而D₂、D₃密度以耐阴植物为主;3种林分密度间的草本、灌木的Margalef (M)、Shannon (H)、Simpson (D)、Pielou (J_sw)、Alatalo (Al)指数均随林分密度增加而呈下降趋势,且在草本与灌木层中对密度的响应不同。在草本层中,D₁与D₃的H、D、J_sw、Al指数均存在显著差异;在灌木层中,不同林分密度J_sw和Al指数存在显著差异,H和D指数差异不显著。土壤种子库H、D、J_sw和Al指数均随林分密度增加呈先下降后升高趋势,D₁密度的物种丰富度及多样性最高;不同林分密度下土壤种子库Jaccard与Sorensen相似性系数均较低。草本层M与J_sw指数呈显著正相关;灌木层林分密度与H、D、J_sw、Al指数的相关性大于草本层,而草本、灌木层的林分密度与J_sw指数均呈显著负相关。林分密度1575株·hm^-2是马尾松林下植被生长发育较为合适的密度,能够维持林下植物多样性,有利于马尾松人工林的可持续经营。     

Influence of flood-preconditioning and drought on leaf gas exchange and plant water relations in seedlings of pecan

Four-month old seedlings of pecan [Carya illinoensis (Wangenh) C. Koch] were either not flooded or flooded for 14 days, then transferred to well-drained conditions for 23 days. Water was withheld from one-half of the trees for 6 days, then trees were rewatered, and water was withheld from all trees. Leaf expansion, leaf dry weight, and the number of new leaves that developed were reduced by flooding, but not trunk or root dry weights. Evapotranspiration rates of flooded trees after transfer to well-drained conditions were initially higher than those of unflooded trees, but decreased to rates of control trees after 12 days. Flooding had no effect on photosynthesis after trees had been transferred to well-drained conditions for 23 days. Drought-stressed trees with leaf water potentials as low as − 1.93 MPa had lower leaf photosynthetic CO₂ assimilation rate (A), transpiration (E), and leaf conductance to CO₂ (g_L) as compared to wellwatered trees. Leaf internal CO₂ concentration (c_i) was reduced only by the most severe water-stress treatment. Water use rates and relative water content were lower at the permanent wilting point during a second drought stress when trees had been exposed previously to drought stress.