牛姆林自然保护区3种栲属树种热值与碳含量研究

对福建永春牛姆林自然保护区内22a生的闽粤栲(Castanopsis fissa)、丝栗栲(Castanopsis fargesii)、拉氏栲(Castanopsis lamonteii)不同器官的灰分含量、去灰分热值和碳含量进行对比分析,并估算各树种人工林的碳储量和能量现存量。结果表明:3种栲属树种各器官灰分含量总体表现为叶根枝干,各器官平均灰分含量则表现为拉氏栲丝栗栲闽粤栲;各树种各器官去灰分热值总体表现为叶枝干根,各器官平均去灰分热值则表现为拉氏栲闽粤栲丝栗栲;各树种各器官碳含量均表现为干枝根叶,各器官平均碳含量则表现为闽粤栲丝栗栲拉氏栲;各树种各器官间的灰分含量、去灰分热值和碳含量总体差异均达到显著水平(t检验,P0.01);除了碳含量与去灰分热值呈极显著正相关外,其他各指标间无显著相关性;3种栲属树种人工林碳储量和能量现存量表现为为闽粤栲丝栗栲拉氏栲,在低产低效林分改造中可优先考虑闽粤栲。     

川西亚高山岷江冷杉和铁杉年轮对气候因子的响应

研究四川卧龙亚高山森林岷江冷杉和铁杉树木年轮与气候因子的关系.结果表明:川西亚高山针叶林树木径向生长主要受气温的制约,卧龙地区岷江冷杉树轮宽度序列与当年2和4月月平均气温显著正相关(P≤0.05),而与多数月平均降水量和月平均相对湿度负相关;铁杉树轮宽度序列与上一年7月和当年2--4月月平均气温显著正相关(P≤0.05),与上一年10月和当年5月月平均降雨量显著正相关(P≤0.05),而与上一年7月及当年4和9月月平均相对湿度显著负相关(P≤0.05).     

川西亚高山森林岷江冷杉树轮碳稳定同位素对气候要素的响应

利用四川卧龙亚高山暗针叶林岷江冷杉树木年轮样本资料,建立树轮宽度年表,对比宽度年表,提取树木年轮(简称树轮)碳稳定同位素(δ13C)序列和去趋势序列(DS),研究岷江冷杉树轮碳稳定同位素序列对气候要素的响应关系.结果表明:岷江冷杉(1904-2009年)树轮碳稳定同位素变化范围为-23.33‰～-26.31％‰,平均值为-24.91‰,变异系数为-0.025;相关分析表明,岷江冷杉δ13C序列(DS)与前一年11月和当年1月的月平均气温显著正相关(P≤0.05),与前一年1月和当年2,11月的月平均气温极显著正相关(P≤0.01),冬季平均气温对岷江冷杉树轮碳稳定同位素的响应最为敏感,是研究过去环境变化的良好载体,与当年1月降水量显著正相关(P≤0.05),与全年的月平均相对湿度相关性不显著(P≥0.05).     

99种栲属类常绿阔叶树种叶片功能性状研究

以南北样带栲属树种和常绿阔叶树种(包括栲属)为试验材料,测定了栲属树种的净光合速率、叶氮和磷含量、叶厚度、比叶重和常绿阔叶树种的比叶重、叶厚度、干物质含量。通过检验叶片功能性状指标之间相关关系得到,栲属植物的单位面积最大净光合速率与单位面积叶氮含量、比叶重彼此呈正相关,单位质量最大净光合速率与比叶重、叶厚度呈负相关,同时,无论是基于面积还是基于质量叶氮和磷含量都呈正相关关系。99种常绿阔叶树种的比叶重、叶厚度、干物质含量彼此呈正相关。     

不同海拔梯度川滇高山栎林土壤颗粒组成及养分含量

分析卧龙自然保护区皮条河上游巴郎山3个海拔梯度川滇高山栎林的土壤颗粒组成、总有机碳含量和全氮含量.结果表明:巴郎山川滇高山栎林土壤颗粒组成以粉粒为主,属中质地土壤;3个海拔梯度表层土(0～15cm)土壤总有机碳和全氮含量均高于亚层土(15～30cm);在表层土壤中总有机碳含量随海拔增加呈现由低到高,再变低的趋势,亚层土则随海拔升高呈增加趋势;表层和亚层土壤全氮含量均随海拔降低而减少;巴郎山高山栎林土壤碳氮比值较小,平均为12.77;在2个土层中,总有机碳含量与全氮含量的相关性随海拔梯度递减由极显著正相关(P＜0.01)到不相关;表层土壤中总有机碳和全氮含量在海拔3549m处与粗粉粒含量呈极显著正相关(P＜0.01),与粘粒呈显著负相关(P＜0.05),3091m处与粗粉粒含量正相关性显著(P＜0.05),2551m处与细砂粒含量呈显著正相关(P＜0.05);亚层土壤全氮含量只在海拔2551m处与细粉粒含量呈显著负相关(P＜0.05).     

四川省不同气候类型核桃氨基酸含量研究

以四川省26个县的182份核桃优树的风干种仁为材料,采用相关分析、聚类分析和多重比较研究了四川省不同气候类型核桃种仁的氨基酸含量,及其与气候因子的相关性。结果表明：核桃仁氨基酸总量在16％-18％左右,共含有18种氨基酸,其中人体必需氨基酸9种。除胱氨酸外,不同气候类型核桃仁中各种氨基酸含量及氨基酸总量差异显著（P〈0．05）,说明气候条件对核桃氨基酸含量影响较大。气候类型Ⅱ的核桃各种氨基酸含量及氨基酸总量均最高。氨基酸总量、缬氨酸、异亮氨酸、色氨酸、亮氨酸、苯丙氨酸、脯氨酸、丙氨酸、苏氨酸、丝氨酸、酪氨酸、天冬氨酸、组氨酸和精氨酸与7月平均气温、年降水量、大于10℃年积温、年平均气温和年平均相对湿度呈极显著（P〈0．01）或显著（P〈0．05）的正相关关系。说明7月平均气温、年降水量、大于10℃年积温、年平均气温和年平均相对湿度越高,越有利于氨基酸总量、缬氨酸、异亮氨酸、色氨酸、亮氨酸、苯丙氨酸、脯氨酸、丙氨酸、苏氨酸、丝氨酸、酪氨酸、天冬氨酸、组氨酸和精氨酸的形成。蛋氨酸、甘氨酸和胱氨酸与年降水量、7月平均气温和年平均相对湿度呈极显著（P〈O．01）或显著（P〈0．05）的正相关关系。说明年降水量、7月平均气温和年平均相对湿度越高,越有利于蛋氨酸、甘氨酸和胱氨酸的形成,谷氨酸与年降水量呈显著的正相关关系（P〈0．05）。赖氨酸与大于10℃年积温、7月平均气温呈极显著的正相关关系（P〈0．05）。7月平均气温与各种氨基酸含量均呈极显著或显著的正相关关系,表明核桃仁中氨基酸的积累可能取决于核桃成熟期的温度情况,核桃成熟期温度越高,越有利于氨基酸的积累。     

黑龙江省造林树种含碳率与土壤性质研究

为研究造林树种的碳汇效应,采用生长锥取样法对黑龙江省5个造林树种进行含碳率分析,并考察了含碳率与土壤性质的相关性。结果表明:5个造林树种含碳率在0.490±0.014(樟子松,S朝向)~0.439±0.018(杨树,N朝向)之间变化,在S(南)和N(北)朝向上,樟子松的含碳率均较高,其次为白桦和落叶松且含碳率相差不多,红松和杨树的含碳率较低。造林树种含碳率与土壤性质相关性研究表明:S朝向,樟子松含碳率与土壤容重呈显著正相关(R=0.571,P0.05),与土壤总碳呈显著负相关(R=-0.552,P0.05);白桦含碳率与土壤总碳之间呈显著正相关(R=0.558,P0.05)。     

天山北坡7种野生果树幼苗的功能性状分析

以分布在天山北坡的7种野生果树幼苗为研究对象,测定比叶面积( SLA)、木材密度、叶片厚度、茎皮厚度及根、茎、叶器官的N,P,K含量等功能性状指标,分析影响植物功能性状的环境因子.结果表明:7种野生果树幼苗各项功能性状测定指标均差异显著(P＜0.05),新疆野苹果木材密度最小,酸枣木材密度和比叶面积均最大,但叶片厚度和茎皮厚度均最小,胡桃比叶面积最小,但茎皮厚度最大;SLA与叶N含量呈显著正相关(P＜0.05);不同树种的根、茎、叶器官的N,P,K含量,除茎P含量差异不显著外(P＞0.05),其他均差异显著(P＜0.05);酸枣和新疆桃的根、茎、叶器官N,P,K含量均相对较高,辽宁山楂和胡桃各器官养分含量均相对较低.7个树种的叶N含量平均为28.4 mg·g-1,较报道的国内外陆地植物叶片N含量平均水平高,叶P含量平均为2.20 mg·g-1,也相对高于国内陆地植物叶片P含量平均水平,近似于全球平均水平;新疆桃和酸枣的养分利用率较低,辽宁山楂和胡桃的养分利用率较高,其他3个树种居中.     

长沙市城乡交错带4种人工林土壤养分及其相关性研究

以长沙市城乡交错带4种人工林为研究对象,对各林分林下土壤理化性质进行比较分析,揭示了土壤养分间的相互关系,结果表明:土壤物理性质指标垂直分布规律明显,同一林分内土壤容重基本上随土层深度增加而增大,毛管孔隙度、总孔隙度和自然含水率相反;土壤容重与毛管孔隙度、总孔隙度呈极显著的负相关(P<0.01),与自然含水率呈显著的负相关(P<0.05);毛管孔隙度与总孔隙度呈极显著的正相关(r=0.943,P<0.01);自然含水率与总孔隙度呈显著正相关(P<0.05),与毛管孔隙度呈极显著正相关(r=0.815,P<0.01);各林分内不同土层土壤各化学性质指标垂直分布规律明显,基本上随土层深度增加而减小;土壤pH值与土壤养分因子的相关系数值均为负数,与速效氮含量显著负相关(r=-0.661,P<0.05),土壤有机质与全氮、全磷、全钾、速效钾含量相关性显著(P<0.05),与速效氮呈极显著正相关(r=0.760,P<0.01);土壤全量养分与有效养分间均呈显著的正相关。     

人工修复植被对锰矿区废弃地土壤酶活性的影响

以自然修复的矿区废弃地土壤为对照,从土壤酶活性的垂直分布、季节动态特征及其与土壤养分含量、重金属含量相关性研究了人工修复的栾树Koelreuteria paniclata、杜英Elaeocarpus decipens混交林(修复地)对湘潭锰矿区废弃地土壤酶活性的影响.结果表明:0～60 cm土层中,随着土层深度的增加,土壤酶活性逐渐下降;同一土层中,修复地土壤脲酶、蔗糖酶、过氧化氢酶活性均高于对照地,且脲酶、过氧化氢酶活性的差异均达到了极显著差异(P＜0.01),0～20 cm土层中蔗糖酶酶活性的差异达到显著水平(P＜0.05);同一季节修复地土壤脲酶、过氧化氢酶活性均显著或极显著高于对照地(P＜0.05),秋、冬季修复地土壤蔗糖酶活性显著高于对照地(P＜0.05),夏季差异不显著(P＞0.05),而春季修复地显著低于对照地(P＜0.05);土壤酶活性与土壤有机质、全N、Mg含量呈极显著(P＜0.01)或显著(P＜0.05)的正相关性,与土壤微生物数量之间均呈极显著或显著的正相关;土壤中重金属对土壤酶活性多表现为抑制作用,且以脲酶活性最敏感,其次是过氧化氧酶活性.人工修复植被能明显提高锰矿区废弃地土壤的酶活性.     

Leaf optical properties in Venezuelan cloud forest trees

Leaf optical properties and related leaf characteristics were compared for thirteen cloud forest tree species differing in successional status. Sun leaves were sampled for the eight pioneer species and sun and shade leaves were sampled for the five climax species. Sun leaves had a slightly higher absorptance than shade leaves, although differences were small. Sun leaves had a higher leaf mass per unit area (LMA) and a lower chlorophyll concentration per unit leaf mass, resulting in similar chlorophyll concentrations per unit leaf area and hence similar light harvesting capacities as shade leaves. However, shade leaves realized a higher efficiency of absorptance per unit leaf biomass than sun leaves. There were few differences in leaf characteristics of sun leaves between the climax and pioneer species. Absorptance values of cloud forest species were comparable with values reported for rain forest and more seasonal forest species. Intraspecific variation in leaf absorptance was largely the result of variation in LMA, whereas interspecific variation in leaf absorptance was largely a result of variation in chlorophyll concentration per unit leaf area.     

Leaf-trait variation explained by the hypothesis that plants maximize their canopy carbon export over the lifespan of leaves

Measured values of four key leaf traits (leaf area per unit mass, nitrogen concentration, photosynthetic capacity, leaf lifespan) co-vary consistently within and among diverse biomes, suggesting convergent evolution across species. The same leaf traits co-vary consistently with the environmental conditions (light intensity, carbon-dioxide concentration, nitrogen supply) prevailing during leaf development. No existing theory satisfactorily explains all of these trends. Here, using a simple model of the carbon-nitrogen economy of trees, we show that global leaf-trait relationships and leaf responses to environmental conditions can be explained by the optimization hypothesis (MAXX) that plants maximize the total amount of carbon exported from their canopies over the lifespan of leaves. Incorporating MAXX into larger-scale vegetation models may improve their consistency with global leaf-trait relationships, and enhance their ability to predict how global terrestrial productivity and carbon sequestration respond to environmental change.     

Relative importance of photosynthetic physiology and biomass allocation for tree seedling growth across a broad light gradient

Studies of tree seedling physiology and growth under field conditions provide information on the mechanisms underlying inter- and intraspecific differences in growth and survival at a critical period during forest regeneration. I compared photosynthetic physiology, growth and biomass allocation in seedlings of three shade-tolerant tree species, Virola koschynii Warb., Dipteryx panamensis (Pittier) Record & Mell and Brosimum alicastrum Swartz., growing across a light gradient created by a forest-pasture edge (0.5 to 67% diffuse transmittance (%T)). Most growth and physiological traits showed nonlinear responses to light availability, with the greatest changes occurring between 0.5 and 20 %T. Specific leaf area (SLA) and nitrogen per unit leaf mass (N mass) decreased, maximum assimilation per unit leaf area (A area) and area-based leaf N concentration (N area) increased, and maximum assimilation per unit leaf mass (A mass) did not change with increasing irradiance. Plastic responses in SLA were important determinants of leaf N and A area across the gradient. Species differed in magnitude and plasticity of growth; B. alicastrum had the lowest relative growth rates (RGR) and low plasticity. Its final biomass varied only 10-fold across the light gradient. In contrast, the final biomass of D. panamensis and V. koschynii varied by 100- and 50-fold, respectively, and both had higher RGR than B. alicastrum. As light availability increased, all species decreased biomass allocation to leaf tissue (mass and area) and showed a trade-off between allocation to leaf area at a given plant mass (LAR) and net gain in mass per unit leaf area (net assimilation rate, NAR). This trade-off largely reflected declines in SLA with increasing light. Finally, A area was correlated with NAR and both were major determinants of intraspecific variation in RGR. These data indicate the importance of plasticity in photosynthetic physiology and allocation for variation in tree seedling growth among habitats that vary in light availability.     

Canopy dynamics and aboveground production of five tree species with different leaf longevities

Canopy dynamics and aboveground net primary production (ANPP) were studied in replicated monospecific and dual-species plantations comprised of species with different leaf longevities. In the monospecific plantations, leaf longevity averaged 5, 6, 36, 46 and 66 months for Quercus rubra L., Larix decidua Miller, Pinus strobus L., Pinus resinosa Ait. and Picea abies (L.) Karst., respectively. Specific leaf area, maximum net photosynthesis per unit mass (A/mass), leaf N per unit mass (N(leaf)/mass) and maximum net photosynthesis on a leaf N basis (A/N(leaf)) were inversely correlated to leaf longevity (r(2) = 0.92-0.97, 0.91, 0.88 and 0.80, respectively). Maximum net photosynthesis per unit area (A/area) was not correlated to leaf longevity, whereas leaf N per unit area (N(leaf)/area) was positively correlated to leaf longevity (r(2) = 0.95). For a similar-diameter conifer, species with long-lived foliage supported a greater foliage mass than species with short-lived foliage; however, Quercus rubra did not follow this pattern. At the stand level, total foliage mass ranged from 3.3 to 30.5 Mg ha(-1) and was positively correlated (r(2) = 0.97) to leaf longevity. Leaf area index (LAI) was also positively correlated (r(2) = 0.82) to leaf longevity. Production efficiency (ANPP/LAI) was inversely related to leaf longevity and positively related to A/mass. Aboveground biomass and net primary production differed significantly (P < 0.05) among the five species but were not correlated to leaf longevity, total foliage mass or leaf area. In monospecific plantations, stem NPP for Larix decidua was 17% greater than for Pinus strobus and 14% less than for Picea abies, but in mixed-species plantations stem NPP for Larix decidua was 62 and 85% greater than for Pinus strobus and Picea abies, respectively. Similar aboveground net primary production rates can be attained by tree species with different leaf longevities because of trade-offs resulting from different structural and physiological leaf and canopy characteristics that are correlated to each other and to leaf longevity.     

Influence of photosynthetic photon flux density on growth and transpiration in seedlings of Fagus sylvatica

Beech seedlings (Fagus sylvatica L.) were grown in various combinations of three photosynthetic photon flux densities (PPFD, 0.7, 7.3 or 14.5 mol m(-2) day(-1)) for two years in a controlled environmental chamber. Dry mass of leaves, stem and roots, leaf area and number of leaves, and unit leaf rate were affected by both previous-year and current-year PPFD. Number of shoots and length of the main shoot were affected by previous-year PPFD but not by current-year PPFD. Number of leaves per shoot did not change with PPFD, whereas leaf dry mass/leaf area ratio was mainly affected by current-year PPFD. During the first 10 days that newly emerged seedlings were grown at a PPFD of 0.7 or 14.5 mol m(-2) day(-1), transpiration rate per unit leaf area declined. Thereafter, transpiration increased to a constant new rate. Transpiration rate per seedling was closely related to leaf area but the relationship changed with time. In two-year-old seedlings grown at various PPFD combinations of 0.7, 7.3 and 14.5 mol m(-2) day(-1) during Years 1 and 2, leaf area and transpiration rate per seedling were closely correlated at Weeks 7 and 11 after bud burst. Weak correlations were found between root dry mass and transpiration rate per seedling. During Year 2, transpiration rate per leaf area was higher at a particular PPFD in seedlings grown at a previous-year PPFD of 0.7 mol m(-2) day(-1) than in seedlings grown at a previous-year PPFD of 14.5 mol m(-2) day(-1). After transfer of two-year-old seedlings at the end of the experiment to a new PPFD (7.3 or 14.5 mol m(-2) day(-1)) for one day, transpiration rates per leaf area, measured at the new PPFD, were correlated with leaf area and root dry mass, irrespective of former PPFD treatment.     

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.     

Photosynthetic nitrogen-use efficiency in evergreen broad-leaved woody species coexisting in a warm-temperate forest

Photosynthetic nitrogen-use efficiency (PNUE, photosynthetic capacity per unit leaf nitrogen) varies among species from different habitats and correlates with several ecological characteristics such as leaf life span and leaf mass per area. We investigated eight evergreen broad-leaved woody species with different leaf life spans that coexist in a warm-temperate forest. We determined photosynthetic capacity at ambient CO(2) concentration in saturated light, nitrogen concentration, and the concentration of ribulose-1,5-bisphosphate carboxylase (RuBPCase), a key enzyme of photosynthesis and the largest sink of nitrogen in leaves. Each species showed a strong correlation between photosynthetic capacity and RuBPCase concentration, and between RuBPCase concentration and nitrogen concentration. Photosynthetic capacity of leaves decreased with increasing leaf life span, whereas PNUE did not correlate significantly with leaf life span. There was a twofold variation in PNUE among species. This relatively small variation in PNUE is consistent with the argument that species that coexist in a single habitat maintain a similar PNUE. The two components of PNUE-photosynthetic rate per unit RuBPCase and RuBPCase per unit leaf nitrogen-were not significantly correlated with other leaf characteristics such as leaf life span and leaf mass per area. We conclude that differences in PNUE are relatively small among coexisting species and that differences in absolute amounts of photosynthetic proteins lead to differences in photosynthetic productivity among species.     

Effects of elevated CO(2) concentration on leaf characteristics and photosynthetic capacity of beech (Fagus sylvatica) during the growing season

Two-year-old beech (Fagus sylvatica L.) saplings were planted directly in the ground at high density (100 per m(2)), in an experimental design that realistically mimicked field conditions, and grown for two years in air containing CO(2) at either ambient or an elevated (ambient + 350 ppm) concentration. Plant dry mass and leaf area were increased by a two-year exposure to elevated CO(2). The saplings produced physiologically distinct types of sun leaves associated with the first and second growth flushes. Leaves of the second flush had a higher leaf mass per unit area and less chlorophyll per unit area, per unit dry mass and per unit nitrogen than leaves of the first flush. Chlorophyll content expressed per unit nitrogen decreased over time in plants grown in elevated CO(2), which suggests that, in elevated CO(2), less nitrogen was invested in machinery of the photosynthetic light reactions. In early summer, the photosynthetic capacity measured at saturating irradiance and CO(2) was slightly but not significantly higher in saplings grown in elevated CO(2) than in saplings grown in ambient CO(2). However, a decrease in photosynthetic capacity was observed after July in leaves of saplings grown in CO(2)-enriched air. The results demonstrate that photosynthetic acclimation to elevated CO(2) can occur in field-grown saplings in late summer, at the time of growth cessation.     

Leaf physiological versus morphological acclimation to high-light exposure at different stages of foliar development in oak

We investigated light acclimation in seedlings of the temperate oak Quercus petraea (Matt.) Liebl. and the co-occurring sub-Mediterranean oak Quercus pyrenaica Willd. Seedlings were raised in a greenhouse for 1 year in either 70 (HL) or 5.3% (LL) of ambient irradiance of full sunlight, and, in the following year, subsets of the LL-grown seedlings were transferred to HL either before leaf flushing (LL-HLBF plants) or after full leaf expansion (LL-HLAF plants). Gas exchange, chlorophyll a fluorescence, nitrogen fractions in photosynthetic components and leaf anatomy were examined in leaves of all seedlings 5 months after plants were moved from LL to HL. Differences between species in the acclimation of LL-grown plants to HL were minor. For LL-grown plants in HL, area-based photosynthetic capacity, maximum rate of carboxylation, maximum rate of electron transport and the effective photochemical quantum yield of photosystem II were comparable to those for plants grown solely in HL. A rapid change in nitrogen distribution among photosynthetic components was observed in LL-HLAF plants, which had the highest photosynthetic nitrogen-use efficiency. Increases in mesophyll thickness and dry mass per unit area governed leaf acclimation in LL-HLBF plants, which tended to have less nitrogen in photosynthetic components and a lower assimilation potential per unit of leaf mass or nitrogen than LL-HLAF plants. The data indicate that the phenological state of seedlings modified the acclimatory response of leaf attributes to increased irradiance. Morphological adaptation of leaves of LL-HLBF plants enhanced photosynthetic capacity per unit leaf area, but not per unit leaf dry mass, whereas substantial redistribution of nitrogen among photosynthetic components in leaves of LL-HLAF plants enhanced both mass- and area-based photosynthetic capacity.     

Effects of crown development on leaf irradiance,leaf morphology and photosynthetic capacity in a peach tree

The three-dimensional (3-D) architecture of a peach tree (Prunus persica L. Batsch) growing in an orchard near Avignon, France, was digitized in April 1999 and again four weeks later in May 1999 to quantify increases in leaf area and crown volume as shoots developed. A 3-D model of radiation transfer was used to determine effects of changes in leaf area density and canopy volume on the spatial distribution of absorbed quantum irradiance (PAR(a)). Effects of changes in PAR(a) on leaf morphological and physiological properties were determined. Leaf mass per unit area (M(a)) and leaf nitrogen concentration per unit leaf area (N(a)) were both nonlinearly related to PAR(a), and there was a weak linear relationship between leaf nitrogen concentration per unit leaf mass (N(m)) and PAR(a). Photosynthetic capacity, defined as maximal rates of ribulose-1,5-bisphosphate carboxylase (Rubisco) carboxylation (V(cmax)) and electron transport (J(max)), was measured on leaf samples representing sunlit and shaded micro-environments at the same time that the tree crown was digitized. Both V(cmax) and J(max) were linearly related to N(a) during May, but not in April when the range of N(a) was low. Photosynthetic capacity per unit N(a) appeared to decline between April and May. Variability in leaf nitrogen partitioning between Rubisco carboxylation and electron transport was small, and the partitioning coefficients were unrelated to N(a). Spatial variability in photosynthetic capacity resulted from acclimation to varying PAR(a) as the crown developed, and acclimation was driven principally by changes in M(a) rather than the amount or partitioning of leaf nitrogen.