八个树种叶水力性状对水分条件的响应及其驱动因素

树木叶片的水力效率和安全性会对水分条件的改变做出一定的响应, 进而影响树木的生长和分布, 然而叶导水率(K_leaf)和叶水力脆弱性(P₅₀)对不同水分条件的响应模式及其影响因素尚不清楚。该研究选取了晋西北关帝山和黑茶山两种水分条件下的8种树种, 测量其水力性状、叶片导管和形态性状, 比较两地不同树种的K_leaf和P₅₀的变化, 分析叶片水力效率和安全性之间的权衡关系, 并探讨叶片水力性状在不同树种及水分条件下的响应模式及其驱动因素。结果表明: 对同一树种而言, 湿润的关帝山叶最大导水率(K_max)和P₅₀均高于干旱的黑茶山; 对同一地区而言, 从在高水分条件下生长的树种到在易干旱环境生长的树种, K_max和P₅₀均逐渐下降。K_max、P₅₀、膨压丧失点水势(TLP)之间均存在显著相关关系。两地叶片P₅₀与导管密度、导管塌陷预测值((t/b)³)、叶片厚度、比叶质量显著正相关, 与导管直径、叶面积显著负相关, 不同树种的K_leaf和P₅₀与叶导管性状的关系大于叶形态性状。同一树种的关帝山到黑茶山P₅₀变化量(δP₅₀)与比叶质量和叶干物质含量在两地的变化量显著正相关, 同一树种δP₅₀与叶形态性状变化量的关系大于与叶导管性状的。以上结果表明: 随着水分条件变差, 叶片水力效率降低, 水力安全性提高, 不同树种叶片水力效率与安全性之间存在一定的权衡关系, 不同树种叶水力性状的差别受叶导管性状影响的程度大于受叶形态性状的影响, 同一树种叶水力安全性对水分条件变化的响应主要依靠叶形态性状的驱动, 树木在提高自身叶水力安全的同时增加了叶构建的碳投资。     

Leaf hydraulic traits of larch and ash trees in response to long-term nitrogen addition in northeastern China

兴安落叶松和水曲柳叶片水力性状对长期氮添加的响应 大气氮沉降影响树木水力结构，进而影响树木的生长和生存。然而，目前关于叶片水力性状对氮沉降的响应尚不明确，而且该响应可能与物种或植物功能型有关。本研究以中国东北地区水曲柳 (Fraxinus mandshurica，阔叶被子植物)和兴安落叶松(Larix gmelinii，针叶裸子植物)人工林为研究对象，利用长达16年的施氮(10 g N m⁻² yr⁻¹)试验研究了氮添加对两种树种叶片水力性状的影响。用自然干燥法测定了叶片压力-容积曲线，用复水动力学法量化了叶片最大水力导度(K_{leaf_max})和抗栓塞阻力(P_50leaf)。研究结果表明，与水曲柳相比，兴安落叶松具有较高的K_{leaf_max}和较强的干旱容忍性(即较低的质壁分离点的相对含水量(RWC_tlp)和弹性模量(ε)，较负的P_50leaf)。此外，氮添加增加了水曲柳的叶膨压损失点水势(π_tlp)、叶饱和含水量时的渗透势(π₀)和叶水容(C_{leaf_mass})，但对兴安落叶松的这些性状影响不显著，表明水曲柳对氮添加更敏感。氮添加增加了水曲柳和兴安落叶松的K_{leaf_max}和P_50leaf。水曲柳的π_tlp和π₀均与叶密度(LD)正相关，而C_{leaf_mass}与LD负相关。兴安落叶松的K_{leaf_max}与LD正相关，P_50leaf与LD负相关。两个树种的K_{leaf_max}与P_50leaf均呈负相关关系。我们的研究表明，长期氮添加降低了这两个重要造林树种的叶片干旱容忍性，这一发现加深了我们对氮沉降背景下树木水力表现的理解。     

美国海滨桤木和薄叶桤木水分生理特性的比较

采取盆栽、人工控水的方式, 研究并比较了美国本土海滨桤木(Alnus maritima)和薄叶桤木(A. incana)的气孔导度(G_s)、叶片水势(ψ_leaf)以及渗透调节能力对土壤水分条件的响应, 以探讨引起两种桤木生态分布差异巨大的生理生态原因。结果表明: 1)正常水分条件下, 海滨桤木的G_s低于薄叶桤木, 其与大气温度、相对湿度和水蒸气亏缺等气象因子的相关性低于薄叶桤木; 干旱胁迫下, 海滨桤木的G_s对其自身ψ_leaf下降信号的敏感度低于薄叶桤木; 复水后, 其G_s恢复更为缓慢。2)正常水分条件下, 海滨桤木的ψ_leaf高于薄叶桤木, 且引起气孔关闭的ψ_leaf临界值较高; 干旱胁迫下, 海滨桤木的ψ_leaf下降幅度高于薄叶桤木。3)正常水分条件下, 海滨桤木和薄叶桤木的渗透调节能力无显著差异; 干旱胁迫下, 尽管两种桤木均表现出饱和状态渗透势(ψ_s^sat)下降、膨压与水势关系的最大变化率降低、初始失膨点渗透势(ψ_s^tlp)增加、细胞渗透调节能力范围(ψ_s^sat-ψ_s^tlp, Dψ_s)减小的趋势, 但与薄叶桤木相比, 海滨桤木的ψ_s^tlp较高, Dψ_s较小。从以上生理生态指标可以看出, 较高的叶片水势、较低的气孔调节能力、干旱下较低的渗透调节能力是造成海滨桤木分布范围狭小的重要原因。     

环境因子对常绿阔叶树种脱耦联系数及冠层气孔导度估算的影响

精确模拟冠层气孔导度(G_S)对于评估区域蒸散具有重要意义。该研究选择两种常见的人工阔叶树种尾叶桉(Eucalyptus urophylla, 外来种)和木荷(Schima superba, 本地种)作为研究对象, 利用K?stner法和修订的Penman-Monteith公式计算冠层平均气孔导度(分别定义为G_S1和G_S2)。研究还分析了环境因子对冠层脱耦联系数(Ω)的影响, 并用其来评价两种方法模拟的冠层气孔导度的合理性。结果表明, 两个树种冠层气孔导度均与气象条件耦合较好(尾叶桉: Ω = 0.10 ± 0.03, 木荷: Ω = 0.17 ± 0.03)。主成分分析显示, 光合有效辐射(PAR)以及水汽压亏缺(D)显著影响Ω的大小, 而风速(u)的影响较小。单因素分析则发现各环境因子与Ω之间的相关性并不显著。边界线分析表明D和PAR的增加使得Ω最终趋向于一个与树种有关的稳定值(木荷≈ 0.20, 尾叶桉≈ 0.05), 而Ω随u的增加呈幂指数下降。与木荷相比, 尾叶桉具有更高的气孔导度(尾叶桉和木荷的G_S2年平均值分别为(33.42 ± 9.37) mmol·m ^-2·s ^-1和(23.40 ± 2.03) mmol·m ^-2·s ^-1), 并且尾叶桉和木荷的G_S1与G_S2的线性拟合斜率分别为0.92 (R ² ≈ 0.70)和0.98 (R ² ≈ 0.76) , 表明G_S1比G_S2高估了冠层气孔导度。另外, G_S1和G_S2对水汽压亏缺的敏感性与参比气孔导度(G_Siref, D = 1 kPa时的气孔导度)的比值Pi与Ω紧密相关。根据统计, 尾叶桉和木荷的G_S1估计值在Ω = 0.05-0.15 (83.1%的数据)和0.10-0.20 (47.8%的数据)之间时是相对可靠的。     

九种维管植物水力性状的演化趋势

维管植物从蕨类植物、裸子植物到被子植物的演化过程中, 生理结构和功能都被认为更趋向于适应干旱的环境。但是关于3类植物是否提升了水分传导和水分利用效率的研究目前多基于叶脉和气孔的形态结构推断, 而对水分传导速率的直接测量则集中于被子植物内部。因此, 同时测定3类植物叶片和枝条尺度的水力性状, 可以研究维管植物水力性状的演化趋势和协同演化关系。该研究测定了中国科学院华南植物园内的蕨类植物(芒萁(Dicranopteris pedata)、华南毛蕨(Cyclosorus parasiticus)、乌毛蕨(Blechnum orientale)), 裸子植物(罗汉松(Podocarpus macrophyllus)、竹柏(Podocarpus nagi)、落羽杉(Taxodium distichum))和被子植物(海南木莲(Manglietia fordiana var. hainanensis)、东京油楠(Sindora tonkinensis)、羊蹄甲(Bauhinia purpurea))共9种植物的水力结构与功能的相关性状。发现9种植物从原始到更演化物种的枝条比导水率(K_S)、叶片比导水率(K_L)和叶片水力导度(K_leaf)依次升高; 叶片蒸腾速率(E)和潜在水分利用效率(WUE_i)升高趋势不显著; 气孔面积指数(SPI)和木材密度(WD)在3个类群间无明显变化趋势。水力功能性状在枝条(K_S)和叶片(K_L、K_leaf和E)尺度显著相关, 但和两个结构性状并无显著相关性。对显著相关的性状进行系统发育独立差分析发现相关性依然存在, 表明枝条导水和叶片导水、叶片失水的协同性独立于系统发育而存在。该文以9种维管植物为例, 发现演化过程中水分传导相关的功能性状有显著提升, 且导水和失水的性状存在着协同演化关系。上述维管植物水力性状演化趋势的结论需要对更多物种、更精细的水力结构性状的进行测定验证。     

立地条件和树龄对刺槐和小叶杨叶水力性状及抗旱性的影响

以形成黄土高原“小老树”的2种典型树种刺槐和小叶杨为对象,研究了立地条件(沟谷台地和沟间坡地)和树龄对两种树木叶水力学性质和抗旱性的影响,探讨“小老树”形成的水力生理机制.结果表明: 水分较好的沟谷台地上生长的两种树木的叶最大水力导度(K_max)明显大于水分较差的沟间坡地,叶水力脆弱性(P₅₀)也较高;随树龄增加,两种树木的K_max明显下降,但P₅₀差异不大.台地上生长的两种树木的叶表皮导度和PV曲线参数(膨压损失点时的相对含水量RWC_tlp、膨压损失点时的水势ψ_tlp、饱和含水量时的渗透势ψ_sat)均大于坡地;随树龄增加,两种树木的叶表皮导度显著下降,PV曲线参数出现不同程度的下降.两种树木K_max与ψ_tlp呈显著正相关,P₅₀与PV曲线参数之间存在一定的相关性,表明K_max与抗旱性之间存在一种权衡关系,P₅₀是反映两种树木的抗旱性特征之一.     

Changes in hydraulic traits of nine vascular plants from different evolutionary lineages

维管植物从蕨类植物、裸子植物到被子植物的演化过程中, 生理结构和功能都被认为更趋向于适应干旱的环境。但是关于3类植物是否提升了水分传导和水分利用效率的研究目前多基于叶脉和气孔的形态结构推断, 而对水分传导速率的直接测量则集中于被子植物内部。因此, 同时测定3类植物叶片和枝条尺度的水力性状, 可以研究维管植物水力性状的演化趋势和协同演化关系。该研究测定了中国科学院华南植物园内的蕨类植物(芒萁(Dicranopteris pedata)、华南毛蕨(Cyclosorus parasiticus)、乌毛蕨(Blechnum orientale)), 裸子植物(罗汉松(Podocarpus macrophyllus)、竹柏(Podocarpus nagi)、落羽杉(Taxodium distichum))和被子植物(海南木莲(Manglietia fordiana var. hainanensis)、东京油楠(Sindora tonkinensis)、羊蹄甲(Bauhinia purpurea))共9种植物的水力结构与功能的相关性状。发现9种植物从原始到更演化物种的枝条比导水率(K_S)、叶片比导水率(K_L)和叶片水力导度(K_leaf)依次升高; 叶片蒸腾速率(E)和潜在水分利用效率(WUE_i)升高趋势不显著; 气孔面积指数(SPI)和木材密度(WD)在3个类群间无明显变化趋势。水力功能性状在枝条(K_S)和叶片(K_L、K_leaf和E)尺度显著相关, 但和两个结构性状并无显著相关性。对显著相关的性状进行系统发育独立差分析发现相关性依然存在, 表明枝条导水和叶片导水、叶片失水的协同性独立于系统发育而存在。该文以9种维管植物为例, 发现演化过程中水分传导相关的功能性状有显著提升, 且导水和失水的性状存在着协同演化关系。上述维管植物水力性状演化趋势的结论需要对更多物种、更精细的水力结构性状的进行测定验证。     

太行山南麓栓皮栎和刺槐光合作用-CO2响应模拟

采用便携式光合仪(Li-6400XT)对太行山南麓栓皮栎、刺槐2个树种叶片光合作用-CO₂响应曲线进行测定,利用直角双曲线模型(RH)、非直角双曲线模型(NRH)以及直角双曲线的修正模型—叶子飘模型(YZP)进行曲线拟合,并对3种光合模型的拟合参数(最大净光合能力A_max、初始羧化速率η、光呼吸速率R_p、CO₂补偿点CCP和CO₂饱和点CSP)进行比较.结果表明: 与NRH和YZP模型相比,RH模型所得的A_max、η、R_p和CCP较高,分别高出实测值59.8%、128.6%、133.4%和19.8%.与RH模型和YZP模型相比,NRH模型拟合得出的A_max较大,高于实测值11.1%,η、R_p和CCP接近于实测值.YZP模型能较好地模拟光合作用对CO₂的饱和现象,在A_max和CSP的拟合效果上较好.栓皮栎阴叶的A_max、R_p和CCP比阳叶分别低31.3%、5.2%和14.3%.刺槐阴叶的A_max、R_p和CCP分别高出阳叶23.5%、11.0%和5.4%.栓皮栎、刺槐阴叶的η分别比阳叶高6.9%和7.0%.刺槐叶片的R_p和CCP与温度、光强均具有显著线性关系,η与气孔导度(g_s)具有显著线性关系.栓皮栎叶片的η与光强和气孔导度具有显著线性关系,CCP主要受温度和湿度影响.栓皮栎叶片的A_max与相对湿度和g_s具有显著的正线性相关关系.     

祁连山水源区主要树种耐旱性研究

应用P-V技术对祁连山水源涵养林主要树种水分参数进行测定分析.结果表明,不同水分参数在树种上的变化规律各异,反映了植物耐旱机理的复杂性;对10项水分参数的主成分分析结果显示,以|φπ₁₀₀-φπ₀ |、RCV、ROWC₀和ε_max分析植物的耐旱性能具有可靠性.用两种几何数学方法的分析结果表明,按照耐旱性大小可将供试树种分为耐旱性强树种(青海云杉和千里香杜鹃)、耐旱性较强树种(祁连圆柏、烈香杜鹃、头花杜鹃和青海杜鹃)、耐旱性较弱树种(金露梅、绣线菊和红桦)和耐旱性弱树种(青杨).苗木清晨叶水势与土壤含水率间变化趋势可以用双曲线方程、幂函数式(或指数函数式)取得满意的拟合.通过逐步聚类分析,按照树种主要耐旱机理可分为高水势延迟脱水耐旱树种(红桦和青海杜鹃)、亚高水势延迟脱水型树种(青海云杉、千里香杜鹃和头花杜鹃)、亚低水势忍耐脱水耐旱树种(祁连圆柏)与低水势忍耐脱水型耐旱树种(金露梅、绣线菊和烈香杜鹃).     

毛乌素沙地油蒿叶建成成本及相关叶性状沿降水梯度的变化

干旱区植物在如何提高水分利用效率与降低叶建成成本之间可能存在一种权衡。我们假设: 与湿润区植物相比, 干旱区植物能通过调节叶功能性状之间的关系(如通过提高单位面积叶氮含量(N_area)), 实现在相同的叶建成成本下具有更高的水分利用效率。为了验证这一假设, 该研究以毛乌素沙地的广布物种油蒿(Artemisia ordosica)为研究对象, 分析了油蒿叶建成成本沿降水梯度的变化规律及其与比叶面积(SLA)、单位质量叶氮含量(N_mass)、N_area和叶碳稳定同位素比率(δ ¹³C)的关系。结果表明: 油蒿单位质量叶建成成本(CC_m)在不同降水条件下差异不显著, 而单位面积叶建成成本(CC_a)在不同降水条件下虽有显著差异, 但并未随降水减少而明显增加。油蒿CC_m与SLA无显著相关性, 与叶δ ¹³C值呈显著正相关关系。油蒿叶建成成本与N_area呈显著正相关关系, 但这种关系格局在低降水量(264 mm)区与高降水量(310-370 mm)区之间存在策略位移现象——即在相同叶建成成本下, 低降水量区植物比高降水量区植物具有更高的N_area。以上结果表明, 尽管高水分利用效率与高叶建成成本相关, 但与高降水量区植物相比, 低降水量区植物具有较高的N_area并没有导致其叶建成成本增加。     

Forest resilience to drought varies across biomes

Forecasted increase drought frequency and severity may drive worldwide declines in forest productivity. Species‐level responses to a drier world are likely to be influenced by their functional traits. Here, we analyse forest resilience to drought using an extensive network of tree‐ring width data and satellite imagery. We compiled proxies of forest growth and productivity (TRWi, absolutely dated ring‐width indices; NDVI, Normalized Difference Vegetation Index) for 11 tree species and 502 forests in Spain corresponding to Mediterranean, temperate, and continental biomes. Four different components of forest resilience to drought were calculated based on TRWi and NDVI data before, during, and after four major droughts (1986, 1994–1995, 1999, and 2005), and pointed out that TRWi data were more sensitive metrics of forest resilience to drought than NDVI data. Resilience was related to both drought severity and forest composition. Evergreen gymnosperms dominating semi‐arid Mediterranean forests showed the lowest resistance to drought, but higher recovery than deciduous angiosperms dominating humid temperate forests. Moreover, semi‐arid gymnosperm forests presented a negative temporal trend in the resistance to drought, but this pattern was absent in continental and temperate forests. Although gymnosperms in dry Mediterranean forests showed a faster recovery after drought, their recovery potential could be constrained if droughts become more frequent. Conversely, angiosperms and gymnosperms inhabiting temperate and continental sites might have problems to recover after more intense droughts since they resist drought but are less able to recover afterwards.     

九种不同材性的温带树种叶水力性状及其权衡关系

不同材性树种的解剖、叶脉分布等结构性状差异会影响树木的水分运输效率和水分利用策略, 进而限制树木的生存、生长和分布。然而, 材性对叶导水率、水力脆弱性及其潜在的权衡关系的影响尚不清楚。该研究选择东北温带森林中不同材性的9种树种(散孔材: 山杨(Populus davidiana)、紫椴(Tilia amurensis)、白桦(Betula platyphylla); 环孔材: 蒙古栎(Quercus mongolica)、水曲柳(Fraxinus mandshurica)、胡桃楸(Juglans mandshurica); 无孔材: 红皮云杉(Picea koraiensis)、樟子松(Pinus sylvestris var. mongolica)、红松(Pinus koraiensis), 测量其基于叶面积和叶质量的叶导水率(K_area和K_mass)、水力脆弱性(P₅₀)、膨压丧失点水势(TLP)及叶结构性状, 以比较不同材性树种叶水力性状的差异, 并探索叶水力效率与安全的权衡关系。结果表明: 3种材性树种的K_area、K_mass和P₅₀均差异显著(p < 0.05)。无孔材树种的K_area和K_mass最低, 而散孔材和环孔材树种差异不显著; 环孔材树种P₅₀最高, 而散孔材和无孔材树种差异不显著。K_area和K_mass均与P₅₀显著负相关(p < 0.05), 但散孔材、环孔材和无孔材树种的相关关系分别呈线性、幂函数和指数函数关系。这表明叶水力效率与安全之间存在一定的权衡关系, 但该关系受树木材性的影响。K_mass与TLP显著负相关(p < 0.01), 其中散孔材和环孔材树种呈线性负相关, 无孔材树种呈负指数函数关系; P₅₀随TLP的增加而增加, 这表明树木在面临水分胁迫时, 其质外体和共质体抗旱阻力共同协调保护叶片活细胞, 防止其水分状况到达临界阈值。K_mass与叶干物质含量、叶密度、比叶重均显著负相关, 而P₅₀与之显著正相关(p < 0.01, P₅₀与比叶重的关系除外), 表明树木叶水力特性的变化受相同叶结构特性驱动, 树木增加对水力失调的容忍需要在叶水力系统构建上增加碳投资。     

Leaf hydraulic traits and their trade-offs for nine Chinese temperate tree species with different wood properties

Aims Trees with different wood properties display variations in xylem anatomy and leaf vein structure, which may influence tree water transport efficiency and water-use strategy, and consequently constrain tree survival, growth and distribution. However, the effects of wood properties on leaf hydraulic conductance and vulnerability and their potential trade-offs at leaf level are not well understood. Our aims were to examine variations in leaf hydraulic traits of trees with different wood properties and explore potential trade-offs between leaf hydraulic efficiency and safety.
Methods Nine tree species with different wood properties were selected for measuring the leaf hydraulic traits, including three diffuse-porous species (Populus davidiana, Tilia amurensis, Betula platyphylla), three ring-porous species (Quercus mongolica, Fraxinus mandshurica, Juglans mandshurica), and three non-porous species (Picea koraiensis, Pinus sylvestris var. mongolica, Pinus koraiensis). Four dominant and healthy trees per species were randomly selected. The hydraulic traits measured included leaf hydraulic conductance on leaf area (K_area) and dry mass (K_mass) basis, leaf hydraulic vulnerability (P₅₀), and leaf water potential at turgor loss point (TLP), while the leaf structural traits were leaf dry mass content (LDMC), leaf density (LD) and leaf mass per unit area (LMA).
Important findings The K_area, K_mass, and P₅₀ differed significantly among the tree species with different woody properties (p < 0.05). Both K_area and K_mass were the lowest for the non-porous trees, and did not differ significantly between the diffuse-porous and ring-porous trees. The ring-porous trees had the highest P₅₀ values, while the diffuse-porous and non-porous trees showed no significant differences in P₅₀. Both K_area and K_mass were negatively correlated with P₅₀ (p < 0.05) for all the trees, and the relationships for the diffuse-porous, ring-porous, and non-porous trees were fitted into linear, power, exponential functions, respectively. This indicates that significant trade-offs exist between leaf hydraulic efficiency and safety. The K_mass was correlated (p < 0.01) with TLP in a negative linear function for the diffuse- and ring-porous trees and in a negative exponential function for the non-porous trees. The P₅₀ increased with increasing TLP. These results suggest that apoplastic and symplastic drought resistance are strictly coordinated in order to protect living cells from approaching their critical water status under water stresses. The K_mass was negatively correlated (p < 0.01) with LDMC, LD, or LMA, while the P₅₀ was positively correlated with LDMC and LD; this suggests that variations in K_mass and P₅₀ are driven by similar changes in structural traits regardless of wood traits. We conclude that the tree tolerance to hydraulic dysfunction increases with increasing carbon investment in the leaf hydraulic system.     

Tree mortality across biomes is promoted by drought intensity,lower wood density and higher specific leaf area

Drought events are increasing globally, and reports of consequent forest mortality are widespread. However, due to a lack of a quantitative global synthesis, it is still not clear whether drought‐induced mortality rates differ among global biomes and whether functional traits influence the risk of drought‐induced mortality. To address these uncertainties, we performed a global meta‐analysis of 58 studies of drought‐induced forest mortality. Mortality rates were modelled as a function of drought, temperature, biomes, phylogenetic and functional groups and functional traits. We identified a consistent global‐scale response, where mortality increased with drought severity [log mortality (trees trees^?1 year^?1) increased 0.46 (95% CI = 0.2–0.7) with one SPEI unit drought intensity]. We found no significant differences in the magnitude of the response depending on forest biomes or between angiosperms and gymnosperms or evergreen and deciduous tree species. Functional traits explained some of the variation in drought responses between species (i.e. increased from 30 to 37% when wood density and specific leaf area were included). Tree species with denser wood and lower specific leaf area showed lower mortality responses. Our results illustrate the value of functional traits for understanding patterns of drought‐induced tree mortality and suggest that mortality could become increasingly widespread in the future.     

润楠属植物叶片和枝条水力特征的协同关系

以润楠属(Machilus) 7种植物成年个体为材料,对其进行生理指标测定,并对它们的叶片水分供需关系以及木质部纹孔特征和导水效率之间的关联进行分析。结果显示,润楠属7种植物相比原始被子植物具有更高的叶脉密度(VD),叶脉密度为9.8～14.1 mm/mm~2;气孔密度(SD)与叶脉密度呈显著正相关,说明叶片水分供需存在协同关系;气孔密度与气孔大小(GLC)呈负相关;气孔越大的叶片其膨压丧失点(TLP)的绝对值越低。枝条边材比导率(Ks)较低,为0.13～1.87 kg·m~(-1)·s~(-1)·MPa~(-1),且种间差异较大。叶脉和气孔密度均与边材比导率呈正相关。边材比导率与纹孔膜面积、纹孔口面积以及纹孔口长短轴比例相关性不显著。研究结果表明润楠属植物虽然叶脉密度较高,且木质部水分供应和叶片结构具有协同关系,但木质部解剖结构较为原始,导管多具梯形穿孔板,导水效率低,只能适应比较湿润的生境。     

润楠属广布种和狭域种幼苗生理生态特征

润楠属植物属于基部被子植物类群,大部分物种局限分布于热带亚热带森林的潮湿生境,但也有些物种分布范围较广。本研究以润楠属11个物种的幼苗为材料,测定了一系列植物叶片水力学性状和解剖结构,包括:比叶重、叶片密度、气孔密度、叶脉密度、膨压丧失点水势、栅栏组织和海绵组织厚度等。结果表明:与其它分布在热带亚热带地区的被子植物相比,润楠属植物的叶脉密度较低,推测叶脉密度受强烈的进化限制;该属植物叶脉密度与气孔密度、栅栏和海绵组织的比值呈显著的正相关,表明该属植物能够维持叶片水平的水分供需平衡;广布种比狭域种具有更低的叶片膨压丧失点和更高的叶片密度,耐旱能力更强,但是比叶重差异不显著;叶片的膨压丧失点与物种的最大树高呈反比,即更高的物种叶片耐失水能力更强,说明植物叶片耐旱性与植物本身的遗传特性有关。本研究结果显示,叶片水力学性状可以较好地用于解释润楠属植物的地理分布。     

Hydraulics and life history of tropical dry forest tree species: coordination of species' drought and shade tolerance

Plant hydraulic architecture has been studied extensively, yet we know little about how hydraulic properties relate to species' life history strategies, such as drought and shade tolerance. The prevailing theories seem contradictory. We measured the sapwood (K(s) ) and leaf (K(l) ) hydraulic conductivities of 40 coexisting tree species in a Bolivian dry forest, and examined associations with functional stem and leaf traits and indices of species' drought (dry-season leaf water potential) and shade (juvenile crown exposure) tolerance. Hydraulic properties varied across species and between life-history groups (pioneers vs shade-tolerant, and deciduous vs evergreen species). In addition to the expected negative correlation of K(l) with drought tolerance, we found a strong, negative correlation between K(l) and species' shade tolerance. Across species, K(s) and K(l) were negatively correlated with wood density and positively with maximum vessel length. Consequently, drought and shade tolerance scaled similarly with hydraulic properties, wood density and leaf dry matter content. We found that deciduous species also had traits conferring efficient water transport relative to evergreen species. Hydraulic properties varied across species, corresponding to the classical trade-off between hydraulic efficiency and safety, which for these dry forest trees resulted in coordinated drought and shade tolerance across species rather than the frequently hypothesized trade-off.     

东北5种温带人工林表层土壤碳氮含量的分异

造林是固碳(C)的有效方法之一,也深刻地影响土壤氮(N)动态,然而不同造林树种对土壤C和N收支的影响及其机制尚不明确.本研究采用同质园试验方法,测定了东北温带水曲柳、胡桃楸、白桦、落叶松和樟子松5个主要造林树种造林后第3年和第11年表层(0～10 cm)土壤有机C(C_soil)、全N含量(N_soil)的变化,以及植被特性和土壤微生物等相关因子,探究了不同树种造林对土壤C、N的影响及驱动因子.结果表明: 试验期间,5个树种纯林的C_soil、N_soil均显著降低,C_soil与N_soil变化量呈显著正相关,并且C_soil减少速率(2.6%·a^-1～4.8%·a^-1)显著高于N_soil减少速率(0.8%·a^-1～2.8%·a^-1).阔叶树种纯林C_soil、N_soil减少量显著小于针叶树种纯林.树种特征、微生物特性共同解释了C_soil变化率的68.5%、N_soil变化率的90.9%,C_soil、N_soil变化率随凋落叶C/N及微生物生物量C/N的增大而减小,但随着细根生物量、微生物生物量C及微生物获取C酶与获取N酶之比的增加而增大;N_soil变化率还随凋落叶产量及微生物代谢熵的增大而减小.这些温带人工林在造林11年后表层土壤C、N含量显著减少,而树种间的不同变化强度主要是由树种特征和土壤微生物特性的差异引起的.     

Ecological differentiation in xylem cavitation resistance is associated with stem and leaf structural traits

Cavitation resistance is a critical determinant of drought tolerance in tropical tree species, but little is known of its association with life history strategies, particularly for seasonal dry forests, a system critically driven by variation in water availability. We analysed vulnerability curves for saplings of 13 tropical dry forest tree species differing in life history and leaf phenology. We examined how vulnerability to cavitation (P₅₀) related to dry season leaf water potentials and stem and leaf traits. P₅₀‐values ranged from ?0.8 to ?6.2 MPa, with pioneers on average 38% more vulnerable to cavitation than shade‐tolerants. Vulnerability to cavitation was related to structural traits conferring tissue stress vulnerability, being negatively correlated with wood density, and surprisingly maximum vessel length. Vulnerability to cavitation was negatively related to the Huber‐value and leaf dry matter content, and positively with leaf size. It was not related to SLA. We found a strong trade‐off between cavitation resistance and hydraulic efficiency. Most species in the field were operating at leaf water potentials well above their P₅₀, but pioneers and deciduous species had smaller hydraulic safety margins than shade‐tolerants and evergreens. A trade‐off between hydraulic safety and efficiency underlies ecological differentiation across these tropical dry forest tree species.     

人工长白落叶松立木叶面积预估模型

叶面积影响着树木干物质的生产,进而影响树木乃至整个林分的生长,而叶面积准确估计对分析树木和林分生长具有重要作用.本研究基于黑龙江省长白落叶松人工林中76株解析木数据,分别建立枝条层面和单木层面的叶面积预估模型.结果表明: 考虑样木层次随机效应的最优枝条叶面积混合效应模型包含lnBD(BD为枝条基径)、lnRDINC(RDINC为相对着枝深度)和lnCR(CR为冠长率)3个随机效应参数,具体形式为:lnBLA=β₁+(β₂+b₂)lnBD+(β₃+b₃)lnRDINC+β₄lnDBH+β₅lnHT/DBH+(β₆+b₆)lnCR,其中:β_i和b_i分别是模型的固定效应参数和随机效应参数;DBH为树木胸高处直径;HT/DBH为树高与胸径的比值.模型的修正决定系数(R_a²)为0.90,均方根误差(RMSE)为0.5477,平均偏差(ME)为-0.03,平均绝对偏差(MAE)为0.24,预测精度(P)为91%,枝条叶面积预估模型的预估效果较好.以枝条叶面积预估模型为基础,计算树冠叶面积并建立树冠叶面积预估模型,最终形式为:lnCLA=γ₀+γ₁lnDBH+γ₂CR,其中,γ_i为模型参数.似然比检验结果(P>0.05)说明该模型不用考虑样地层次的随机效应.本研究所建立的立木树冠叶面积预估模型的决定系数(R²)为0.87,RMSE为0.3847,拟合效果好,可以很好地预测人工长白落叶松立木树冠叶面积,为以后叶面积分布和光合作用的研究提供了理论基础.