秦岭东段栓皮栎枝条非结构性碳水化合物含量的季节动态

枝条是碳供应器官和碳需求器官的连接者, 研究其非结构性碳水化合物(NSC)含量的季节变化对理解树木体内的碳分配至关重要。该研究以秦岭东段栓皮栎(Quercus variabilis)优势群落为研究对象, 于2016年5月至2017年5月, 在其分布的海拔上下限(650 m和970 m), 通过在展叶期采用旬尺度和在非展叶期采用月尺度相结合的周期性取样方法(共计12次), 测定栓皮栎枝条NSC组分及含量, 并观测同期叶片物候变化。结果表明: (1)栓皮栎枝条NSC含量随季节波动较小, 变化差异不显著。但枝条可溶性糖含量(高海拔)或淀粉含量(低海拔)在一定生境条件下, 均存在明显的季节波动, 说明栓皮栎枝条可溶性糖和淀粉之间存在动态转化过程。(2)栓皮栎枝条NSC组成以可溶性糖为主(61%), 这可能是该树种在暖温带季风气候区所采取的生长策略。(3)土壤含水量(正相关)和饱和水汽压差(负相关)分别是在高海拔和低海拔影响栓皮栎枝条NSC含量的主导环境因子, 说明相比高海拔, 低海拔的栓皮栎可能对高温引起的水分胁迫更敏感。(4)结合叶片物候发现, 栓皮栎枝条NSC含量最大值出现在萌芽前(3月中下旬, 11%左右), 最小值出现在展叶后期(4月末, 5%左右), 叶片萌芽展叶后枝条NSC含量下降。总体而言, 枝条NSC含量在高低海拔不存在显著差异, 但春季萌芽前后存在显著差异, 海拔引起的叶片物候时间差极可能是造成这一现象的主要原因。研究结果说明, 栓皮栎叶片物候会直接影响枝条NSC含量的季节变化, 枝条NSC含量对叶片萌芽生长至关重要, 研究结果有助于加深对栓皮栎树体内碳调配机制的理解。     

秦岭东段栓皮栎枝条非结构性碳水化合物含量的季节动态

枝条是碳供应器官和碳需求器官的连接者,研究其非结构性碳水化合物(NSC)含量的季节变化对理解树木体内的碳分配至关重要。该研究以秦岭东段栓皮栎(Quercus variabilis)优势群落为研究对象,于2016年5月至2017年5月,在其分布的海拔上下限(650m和970m),通过在展叶期采用旬尺度和在非展叶期采用月尺度相结合的周期性取样方法(共计12次),测定栓皮栎枝条NSC组分及含量,并观测同期叶片物候变化。结果表明:(1)栓皮栎枝条NSC含量随季节波动较小,变化差异不显著。但枝条可溶性糖含量(高海拔)或淀粉含量(低海拔)在一定生境条件下,均存在明显的季节波动,说明栓皮栎枝条可溶性糖和淀粉之间存在动态转化过程。(2)栓皮栎枝条NSC组成以可溶性糖为主(61%),这可能是该树种在暖温带季风气候区所采取的生长策略。(3)土壤含水量(正相关)和饱和水汽压差(负相关)分别是在高海拔和低海拔影响栓皮栎枝条NSC含量的主导环境因子,说明相比高海拔,低海拔的栓皮栎可能对高温引起的水分胁迫更敏感。(4)结合叶片物候发现,栓皮栎枝条NSC含量最大值出现在萌芽前(3月中下旬, 11%左右),最小值出现在展叶后期(4月末, 5%左右),叶片萌芽展叶后枝条NSC含量下降。总体而言,枝条NSC含量在高低海拔不存在显著差异,但春季萌芽前后存在显著差异,海拔引起的叶片物候时间差极可能是造成这一现象的主要原因。研究结果说明,栓皮栎叶片物候会直接影响枝条NSC含量的季节变化,枝条NSC含量对叶片萌芽生长至关重要,研究结果有助于加深对栓皮栎树体内碳调配机制的理解。     

秦岭东段不同海拔栓皮栎粗根非结构性碳水化合物含量的季节动态

掌握树木根部碳存储规律对于准确估算碳在地上器官与地下器官间的分配非常必要。本研究以栓皮栎(Quercus variabilis Blume)为对象,在2016年5月—2017年6月,通过周期性采样方法(共计采样14次),测定了高、低海拔(970和650 m)栓皮栎粗根非结构性碳水化合物(non-structural carbohydrates,NSC)及其组分(可溶性糖和淀粉)含量的年内动态变化。结果表明:除高海拔淀粉外,栓皮栎粗根NSC及其组分含量均随季节变化差异显著(P<0.05)。粗根NSC含量呈现生长季初期(3月)下降,非生长季(2月)达到最高值的变化趋势;栓皮栎粗根NSC组成以淀粉为主,高、低海拔淀粉含量占比分别为61%和71%,这可能与栓皮栎适应区域环境特征有关。不同海拔间,栓皮栎粗根NSC及其组分含量的差异出现在生长季初期(3月,P<0.05)。高海拔(10.26%)栓皮栎粗根NSC含量小于低海拔(13.96%)。栓皮栎粗根NSC含量存在明显的季节波动,粗根在生长季末及非生长季积累的NSC对下一年树木生长启动非常重要,研究结果有助于理解树木地下器官对树木生长的碳供应机制。     

祁连山优势树木碳水化合物资源分配的海拔和树种效应

海拔梯度造成的温度、水分和土壤肥力等环境异质性会影响树木的生长, 但是不同树木的生理差异也决定了树木资源分配权衡还存在很多不确定性。为探明祁连山地区青海云杉(Picea crassifolia)和祁连圆柏(Juniperus przewalskii)非结构碳水化合物(NSC)含量的海拔和树种效应差异, 该研究以祁连山两个优势针叶树种青海云杉和祁连圆柏为研究对象, 分别设置了高海拔(3 300 m)和低海拔(2 850 m)两个采样高度, 采用t检验和多因素方差分析比较了不同海拔两个树种NSC及其组分(可溶性糖、淀粉)含量的差异, 分析叶、树干、粗根和细根间的NSC及其组分含量的资源分配权衡特征, 明晰不同海拔青海云杉和祁连圆柏生长限制因素和生理生态适应机理。结果表明: (1)低海拔青海云杉整株和各器官NSC及其组分含量均显著高于高海拔青海云杉; 而低海拔祁连圆柏整株和各器官NSC及其组分含量均显著低于高海拔祁连圆柏; (2)不同海拔两个优势针叶树种可溶性糖主要投资在叶, 而淀粉主要投资在粗根和树干; (3)高海拔青海云杉的可溶性糖与淀粉的比值显著高于低海拔青海云杉, 说明高海拔青海云杉将更多的碳用于生长, 而低海拔青海云杉将更多的碳用于储存; (4)海拔、树种、器官以及它们的交互作用显著地影响NSC及其组分含量及可溶性糖:淀粉, 其中树种分别解释了NSC、淀粉总变异的38%和37%; 器官分别解释了可溶性糖、可溶性糖:淀粉总变异的68%和42%。该研究结果阐明了不同海拔青海云杉和祁连圆柏的生长限制因素及其资源分配权衡, 为理解不同海拔和不同树种的生态适应机理以及祁连山森林生态系统的保护提供了科学参考。     

圆叶玉兰叶片非结构性碳水化合物与氮、磷含量对海拔的响应

非结构性碳水化合物(non-structural carbohydrates, NSC)、氮(N)和磷(P)是植物生长的重要能源物质和影响植物分布的限制生长因子,圆叶玉兰(Magnolia sinensis)是四川省特有的珍稀濒危极小种群野生植物,研究其NSC、N和P可以反映它的营养供应水平及对环境的适应策略。选取芦山6个海拔梯度(1840,1960,2070,2170,2270,2390 m)的圆叶玉兰为对象,研究不同海拔下圆叶玉兰叶片中NSC与N、P及其化学计量间的关系。结果表明,圆叶玉兰叶片可溶性糖含量在2390 m处显著高于1840 m处, NSC含量在不同海拔差异极显著,随海拔增加呈"低-高-低"的单峰变化,2170 m处叶片NSC含量最高,碳水化合物供应充足;可溶性糖/淀粉的比值随海拔升高呈增大趋势,N含量和N/P比都随海拔上升而下降,且N/P比在各海拔上均小于14,NSC/N比在2390 m处显著高于1840 m处。总之,圆叶玉兰叶片的可溶性糖和NSC含量显著不受海拔的影响,较高的可溶性糖含量有利于抵御低温环境,其生长主要受氮元素限制而不受碳限制,反映了濒危植物圆叶玉兰在其有限的分布范围内NSC及N、P的保护策略,为圆叶玉兰的碳代谢和生长适应对策提供数据基础。     

巴郎山大叶醉鱼草叶片非结构性碳水化合物和氮分配的海拔响应

为深入认识和探讨植物对环境变化的生理生态响应和适应,以分布在川西巴郎山的大叶醉鱼草(Buddleja davidii)为研究对象,沿海拔梯度对植物叶片中非结构性碳水化合物(NSC)、可溶性糖和淀粉含量,氮含量和氮分配比例(光合系统氮分配比例P_P、细胞壁氮分配比例P_CW和其他组分氮分配比例P_other)等参数进行对比分析,探讨其沿海拔的变化趋势,以及叶片NSC、可溶性糖和淀粉含量与氮分配间的相关关系。结果显示：大叶醉鱼草叶片NSC、可溶性糖、淀粉和单糖含量随海拔的升高而增加,而可溶性糖/淀粉比值未发生显著变化,表明高海拔较高的NSC含量的累积是由可溶性糖和淀粉含量共同决定的,而可溶性糖含量的增加主要由单糖含量的变化引起。叶片氮含量和P_P在海拔间差异不显著,但P_CW和P_other分别随海拔升高而降低和升高。此外,随海拔升高,叶片NSC/N比值随之增加,这主要归因于随海拔升高而增加的NSC含量而非海拔间差异不显著的氮含量。NSC含量和可溶性糖含量均与P_...     

三种温带树种非结构性碳水化合物的分配

树体中的非结构性碳水化合物(NSC)浓度、含量及其分配反映了树木整体的碳供应状况, 是决定树木生长和存活的关键因子, 也是构建树木碳平衡模型的关键参数。温带树种的NSC尚缺乏系统研究。该文测定了特性各异的3种温带树种在生长盛期的NSC及其组分的浓度和含量以及分配格局的种间种内变异。结果表明, NSC及其组分的浓度在树种和组织之间差异显著, 可溶性糖、淀粉和总NSC浓度分别在0.65-8.45、1.96-5.95和3.00-13.90 g·100 g^-1 DM之间波动。NSC及其组分含量的大小依次为: 兴安落叶松(Larix gmelinii) >蒙古栎( Quercus mongolica) >红松( Pinus koraiensis), 其中叶和根中的浓度较高。树干中的NSC及其组分浓度的纵向变化不显著, 但其心材与边材之间的浓度差异却随树种和NSC组分而异, 表现为心边材的可溶性糖浓度差异不显著, 但其淀粉和总NSC浓度差异显著。不同直径根系的NSC及其组分浓度在2种针叶树种中差异不显著, 但在蒙古栎中差异显著。蒙古栎将可溶性糖主要投资到地上生长, 而2种针叶树将更多的可溶性糖投资到根系生长。淀粉的主要储存库为树干, 其在树体内的分布格局与可溶性糖正相反, 因而使总NSC在树根和树枝中的分配趋于较平衡状态。在树干中, 除了2种针叶树的可溶性糖库以边材为主外, 心材是淀粉和总NSC的主要储存库。在树根中, 粗根是NSC及其组分的优势储存库。该研究中3种温带树种的NSC及其组分的浓度和含量的种间和种内变化, 反映了这些树种的生长对策和体内碳源汇强度的差异。     

不同地理种源栓皮栎幼苗生长与物质分配的变化趋势

该研究通过收集栓皮栎5个地理种源(北京平谷、河南内乡、江西永修、湖北秭归和湖南城步)种子并在栓皮栎自然分布南界以南(广东鹤山)进行培育,考察自然增温对不同地理种源栓皮栎当年生幼苗的生长性状、非结构性碳水化合物(NSC)的积累以及迁移和养分分配的影响,探讨在未来气候变暖情景下不同地理种源树木在生长与物质分配方面是否存在某种地理趋势。结果表明:(1)栓皮栎全株NSC浓度随种源地纬度增加而呈显著上升趋势,且该趋势以叶片NSC浓度(特别是可溶性糖浓度)所主导;不同器官间,叶片可溶性糖和根系淀粉浓度均随种源地纬度增加而增加,而根系可溶性糖浓度则相反;茎NSC及其组分无明显地理趋势。(2)在养分方面,栓皮栎不同器官N浓度及叶片P浓度均随种源地纬度的增加而增加,叶片氮磷比则随种源地纬度增加而显著下降;除叶片外,不同器官的N利用效率和P利用效率均随种源地纬度的增加而呈现微弱下降趋势。(3)栓皮栎幼苗的相对生长速率随种源地纬度增加而呈显著下降趋势,且与全株可利用碳库(主要指NSC)呈极显著负相关关系。结合已有研究,初步认为栓皮栎幼苗生长及物质分配的地理格局主要受遗传因素所控制。     

温带12个树种新老树枝非结构性碳水化合物浓度比较

非结构性碳水化合物(NSC)是树木存活的重要碳储备。以温带12个树种(红松、樟子松、红皮云杉、兴安落叶松、蒙古栎、春榆、水曲柳、胡桃楸、山杨、大青杨、白桦和紫椴)为对象,在不同物候期取样7次以比较新枝和老枝的NSC浓度的季节动态,分析新枝和老枝的可溶性糖和淀粉浓度的关系,探索引起树枝NSC种间差异的原因。结果表明:除了山杨和大青杨之外,其它树种的新枝和老枝NSC浓度具有相似的季节动态,且新枝NSC浓度普遍高于老枝。常绿树种发芽前老枝TNC(总非结构性碳水化合物,即糖和淀粉之和)浓度快速上升,发芽后TNC变化较小,秋季TNC略有回升。落叶树种展叶前多数树种老枝TNC浓度下降;完全展叶后新枝和老枝TNC浓度均逐渐升高;秋季新枝和老枝的TNC大量积累,在休眠季节部分淀粉转化为可溶性糖。所有树种的新老枝中可溶性糖和淀粉均具有显著的线性关系;而可溶性糖、淀粉和TNC在新枝和老枝之间也均有显著的相关性。除了红皮云杉、春榆(缺乏数据)和蒙古栎(夏季出现两次生长)之外,其它9个树种老枝的TNC浓度的季节平均值、最大值和储存能力均随枝长生长期的延长而显著下降,说明枝长生长期与TNC存储功能之间相关联。     

沙地樟子松幼苗干旱致死过程中非结构性碳水化合物的变化

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

Early season cuticular conductance and gas exchange in two oaks near the western edge of their range

Seasonal changes in minimum leaf conductance to water vapor (g_min), an estimate of cuticular conductance, and photosynthetic gas exchange in two co-occurring oak species in north-east Kansas (USA) were examined to determine if leaf gas exchange characteristics correlated with differences in tree distribution. Bur oak (Quercus macrocarpa Michx.) is more abundant in mesic gallery forest sites, whereas chinquapin oak (Quercus muehlenbergii Englm.) is more abundant in xeric sites. Early, during leaf expansion, g_min was significantly lower in chinquapin oak than in bur oak, though midday water potentials were similar. After leaves had fully expanded, g_min decreased to seasonal minimum values of 4.57 (±0.274) mmol m^-2 s^-1 in bur oak, and 2.66 (±0.156) mmol m^-2 s^-1 in chinquapin oak. Water potentials at these times were significantly higher in chinquapin oak. As leaves were expanding, photosynthesis (A_net) was significantly higher in chinquapin oak than in bur oak. Later in the growing season, A_net and gleaf increased dramatically in both species, and were significantly higher in bur oak relative to chinquapin oak. We concluded that bur and chinquapin oak have a number of leaf gas exchange characteristics that minimize seasonal water loss. These characteristics are distinct from trees from more mesic sites, and are consistent with the distribution patterns of these trees in tall-grass prairie gallery forests.     

Non-structural carbon compounds in temperate forest trees

The current carbon supply status of temperate forest trees was assessed by analysing the seasonal variation of non‐structural carbohydrate (NSC) concentrations in leaves, branch wood and stem sapwood of 10 tree species (six deciduous broad‐leafed, one deciduous conifer and three evergreen conifer trees) in a temperate forest that is approximately 100 years old. In addition, all woody tissue was analysed for lipids (acylglycerols). The major NSC fractions were starch, sucrose, glucose and fructose, with other carbohydrates (e.g. raffinose and stachyose) and sugar alcohols (cyclitols and sorbitol) playing only a minor quantitative role. The radial distribution of NSC within entire stem cores, assessed here for the first time in a direct interspecific comparison, revealed large differences in the size of the active sapwood fraction among the species, reflecting the specific wood anatomy (ring‐porous versus diffuse‐porous xylem). The mean minimum NSC concentrations in branch wood during the growing season was 55% of maximum, and even high NSC concentrations were maintained during times of extensive fruit production in masting Fagus sylvestris. The NSC in stem sapwood varied very little throughout the season (cross species mean never below 67% of maximum), and the small reductions observed were not significant for any of the investigated species. Although some species contained substantial quantities of lipids in woody tissues (‘fat trees’; Tilia, Pinus, Picea, Larix), the lipid pools did not vary significantly across the growing season in any species. On average, the carbon stores of deciduous trees would permit to replace the whole leave canopy four times. These data imply that there is not a lot of leeway for a further stimulation of growth by ongoing atmospheric CO₂ enrichment. The classical view that deciduous trees rely more on C‐reserves than evergreen trees, seems unwarranted or has lost its justification due to the greater than 30% increase in atmospheric CO₂ concentrations over the last 150 years.     

Seasonal variations of gas exchange, photosynthetic pigments, and antioxidants in Turkey oak (Quercus cerris L.) and Hungarian oak (Quercus frainetto Ten.) of different age

Seasonal changes in physiological and biochemical parameters were studied in 35-, 55- and 140-year-old trees of Turkey oak (Quercus cerris L.) and Hungarian oak (Q. frainetto Ten.), growing in natural stands in Eastern Balkan Mountains (Bulgaria). During the seasonal drought period (August), assimilation activity, transpiration rate, stomatal conductance and water potential had a seasonal minimum in all the studied tree ages and species. The foliar concentrations of glutathione, ascorbate, α-tocopherol, as well as photosynthetic pigments in oak leaves were significantly affected by season. With the increasing age of the studied trees, we observed a decrease of the physiological activity and an increase of the antioxidants’ accumulation. Both the species were drought tolerant and anisohydric, where Q. frainetto exhibited higher rates of gas exchange than Q. cerris. Moreover, they differed in the extent of increase in the foliar antioxidants and carotenoids.     

古尔班通古特沙漠梭梭木射线径向运输特征研究

以古尔班通古特沙漠地区优势植物种梭梭（Haloxylon ammodendron）为试验材料,通过观察测定不同树龄、不同季节梭梭木质部解剖结构,计算梭梭木质部非结构性碳水化合物（NSC）及其组分的径向运输速率,分析NSC运输特征与木质部射线和导管解剖结构之间的相关性。结果表明：（1）随着树龄的增加,梭梭导管和射线解剖特征均表现出增加趋势;5月梭梭导管长度和导管直径高于其他季节,10月梭梭射线高度、射线宽度和射线细胞壁厚度均高于其他季节。（2）梭梭木质部NSC、可溶性糖和淀粉的径向运输速率随树龄增长呈显著递增趋势,但13年生与18年生树龄间的NSC、可溶性糖和淀粉的径向运输速率差异不显著。（3）5月和10月的梭梭木质部NSC径向运输速率显著高于7月（P<0.05）;可溶性糖径向运输速率表现为5月最高、7月最低;淀粉径向运输速率从5月到10月呈显著递减趋势。（4）相关分析结果显示,可溶性糖径向运输速率与导管长度（P＜0.05）、导管直径和射线高度呈显著正相关关系（P＜0.01）;淀粉径向运输速率与导管长度、导管直径间呈极显著正相关关系（P＜0.01）;NSC径向运输速率与导管直径、射线高度间呈极显著正相关关系。研究认为,梭梭木质部径向运输功能与木射线和导管解剖结构有关,且呈明显季节动态变化。     

Global patterns of mobile carbon stores in trees at the high‐elevation tree line

Aim Across all latitudes, high‐elevation tree lines represent a drastic change in the dominant plant life‐form, from upright trees to low‐stature alpine plants. Although associated with low temperatures, the physiological mechanisms controlling this boundary are still not clear. The growth‐limitation hypothesis assumes a direct low‐temperature restriction of tissue formation at otherwise sufficient photoassimilation. In order to test this hypothesis, we present a global synthesis of previously published and new data on tree carbon supply status at high‐elevation tree lines. Location Global; 13 regions between 68° N and 45° S. Methods Late‐season concentrations of non‐structural carbohydrates (NSC) in foliage and branch wood were measured at three elevations across the tree line ecotones, from upper tall forests (timber line) to the edges of aborescent tree growth (tree line). Year‐round records of ?10 cm soil temperatures were taken at the tree line. Results Despite large differences in elevation and season length, the mean growing season temperature at the tree line was similar (approximately 6.6 °C) between all sites. NSC concentrations were not depleted at any of the elevation gradients between timber line and tree line, indicating no shortage of C at the uppermost tree stands. Tested across all sites, NSC concentrations in fact significantly increased with elevation. On average, NSC increased by 18% in leaves and 26% in branch wood from the lowest to the highest stands, primarily due to higher starch concentrations rather than free sugars. Hence, these responses do not reflect osmotic adjustments to lower temperatures at the end of the growing season. Main conclusions This global data set contributes to a mechanistic understanding of tree line formation based on biological principles across climatic zones and tree genera. No evidence of C shortage was found at the high‐elevation tree line in either seasonal and non‐seasonal regions. The increasing trend of NSC concentrations with elevation is in line with the growth‐limitation hypothesis.     

Prey distribution,foliage structure,and foraging behavior of insectivorous birds in two oak species (<Emphasis Type="Italic">Quercus serrata</Emphasis> and <Emphasis Type="Italic">Q. variabilis</Emphasis>)

We examined foraging behaviors of four insectivorous bird species (Great Tit Parus major, Varied Tit P. varius, Long-tailed Tit Aegithalos caudatus and Japanese White-eye Zosterops japonica) on the two oak species (Q. serrata and Q. variabilis) in relation to fine-scale foliage structures, abundance, and distribution of folivorous insects and physical and chemical characteristics of leaves. There was no difference in the mean number of insects for each oak species, but there was a significant difference in the mean biomass. The distance from twigs or branches to leaf tips or blade-petiole junctions showed that leaves of Q. variabilis were more dispersed than those of Q. serrata. The different size distribution of insects influenced insect sizes selected and foraging maneuvers used by each bird species. Parus major and P. varius fed on beetles (low energy gain) with perch-gleaning (the most energy-saving maneuver) from the upper side of leaves on Q. variabilis, whereas they fed on large lepidopteran larvae (high energy gain) from the lower side of leaves on Q. serrata using a variety of maneuvers (including energy-consuming ones). Both A. caudatus and Z. japonica fed on insects from the lower side of leaves by hang-gleaning and reach-gleaning, respectively. These species appeared to be morphologically adapted to the energy-consuming but more effective maneuvers used to take preys from the undersides of leaves. We hypothesize that differences in foliage structures between closely related species of trees have evolved as a balance between defense against folivorous insects and attraction of insectivorous birds.     

Large seasonal fluctuations in whole-tree carbohydrate reserves: is storage more dynamic in boreal ecosystems?

Background and AimsCarbon reserves are a critical source of energy and substrates that allow trees to cope with periods of minimal carbon gain and/or high carbon demands, conditions which are prevalent in high-latitude forests. However, we have a poor understanding of carbon reserve dynamics at the whole-tree level in mature boreal trees. We therefore sought to quantify the seasonal changes in whole-tree and organ-level carbon reserve pools in mature boreal Betula papyrifera.MethodsNon-structural carbohydrate (NSC; soluble sugars and starch) tissue concentrations were measured at key phenological stages throughout a calendar year in the roots, stem (inner bark and xylem), branches and leaves, and scaled up to estimate changes in organ and whole-tree NSC pool sizes. Fine root and stem growth were also measured to compare the timing of growth processes with changes in NSC pools.Key ResultsThe whole-tree NSC pool increased from its spring minimum to its maximum at bud set, producing an average seasonal fluctuation of 0.96 kg per tree. This fluctuation represents a 72 % change in the whole-tree NSC pool, which greatly exceeds the relative change reported for more temperate conspecifics. At the organ level, branches accounted for roughly 48–60 % of the whole-tree NSC pool throughout the year, and their seasonal fluctuation was four to eight times greater than that observed in the stemwood, coarse roots and inner bark.ConclusionsBranches in boreal B. papyrifera were the largest and most dynamic storage pool, suggesting that storage changes at the branch level largely drive whole-tree storage dynamics in these trees. The greater whole-tree seasonal NSC fluctuation in boreal vs. temperate B. papyrifera may result from (1) higher soluble sugar concentration requirements in branches for frost protection, and/or (2) a larger reliance on reserves to fuel new leaf and shoot growth in the spring.     

Seasonal variation in leaf chemistry of the coast live oak Quercus agrifolia and implications for the California oak moth Phryganidia californica

Summary The perennial foliage of the California coast live oak (Quercus agrifolia Nee) permits herbivores to feed on this oak species throughout the year. Patterns of herbivory for a two-year period on Q. agrifolia were observed in relation to seasonal and age-related changes in the nutritional and defensive characteristics of leaves. Nitrogen and phosphorus contents were higher in new leaves compared to mature foliage. Structural compounds (e.g., cellulose) in leaves rapidly increased with age. Concentrations of tatal phenolics (Folin-Denis) and astringency were higher in new foliage, and concentrations of condensed tannins gradually increased as the leaves matured. Peaks of herbivore damage were observed in June and in September–October, and were caused by outbreaks of the California oak moth (Phryganidia californica). P. californica, a bivoltine oak specialist, exhibited feeding preferences in June for old leaves over emerging leaves, and showed no preferences for leaf classes in September. These results suggest that P. californica is adapted to survive on nutritionally poor foliage and to circumvent quantitative defenses such as condensed tannins.