Alterations of chemical composition,construction cost and payback time in needles of Masson pine (Pinus massoniana L.) trees grown under pollution

Previous studies show that Masson pine (Pinus massoniana L.) stands grown at the industrially-polluted site have experienced unprecedented growth decline, but the causal mechanisms are poorly understood. In this study, to understand the mechanisms of growth decline of Mason pine strands under pollution stresses, we determined the reactive oxygen species levels and chemical composition of the current-year (C) and one-year-old (C + 1) needles, and calculated the needle construction costs (CC_mass) of Masson pine trees grown at an industrially-polluted site and an unpolluted remote site. Pine trees grown at the polluted site had significantly higher levels of hydroxyl radical and superoxide anion in their needles than those grown at the unpolluted site, and the former trees eventually exhibited needle early senescence. The contents of lipids, soluble phenolics and lignins in C and C + 1 needles were significantly higher at the polluted site than at the unpolluted site, but the total amounts of non-construction carbohydrates were lower in non-polluted needles than in polluted needles. Elevated levels of the reactive oxygen species and early senescence in polluted needles together led to significant increases in CC_mass and a longer payback time. We infer that the lengthened payback time and needle early senescence under pollution stress may reduce the Masson pine tree growth and consequently accelerate tree decline.     

Variability of photosynthetic capacity and water relations of <Emphasis Type="Italic">Pinus sylvestris</Emphasis> L. in the field

Measurements of dependence of photosynthetic electron transport on irradiance and analyses of stable isotope ratios (δ¹⁸O, δ¹³C, δ¹⁵N) were performed on 4 to 6-year-old pine trees (Pinus sylvestris L.) in the primeval forest reserve of Białowieża and on 21-year-old pine trees of a plantation of different provenances at the Sękocin Forest Station near Warsaw, Poland. Small differences in maximum photosynthetic electron transport rates, ETR_max were related to growth. Stable isotope analyses suggest that water relations play an important role for the performance of P. sylvestris at the sites studied. The intraspecific comparisons showed a very high variability of photosynthetic capacity between needles of given trees and between individual trees under similar conditions. Differences between specific provenances were also observed. This is relevant for ecological niche occupation in a wide geographical growth range, where P. sylvestris is actually occurring. The high physiological plasticity demonstrated reveals a conspicuous trait of this tree species.     

华南地区固氮与非固氮豆科树种叶片养分利用策略的对比研究

为探究富氮环境中固氮(nitrogen-fixing leguminous trees,NLT)与非固氮豆科树种(non-nitrogen-fixing leguminous trees,n-NLT)的叶片养分利用策略差异,以华南地区5种NLT植物[水黄皮(Pongamia pinnata)、大叶相思(Acacia auriculiformis)、朱樱花(Calliandra haematocephala)、海南红豆(Ormosia pinnata)、台湾相思(Acacia confusa)]和3种n-NLT植物[油楠(Sindora glabra)、中国无忧花(Saraca dives)、银珠(Peltophorum tonkinense)]为对象,测定其单位质量叶片碳(C)、氮(N)和磷(P)含量及其比值、单位面积叶片最大净光合速率(Aarea)和叶片光合氮、磷利用效率(PNUE、PPUE)等功能性状。结果表明,NLT的单位质量叶片N、P含量和Aarea均显著高于n-NLT,而两者PNUE和PPUE无显著差异;尽管两类植物单位质量叶片C含量无显著差异,但NLT的叶片C:N和C:P显...     

Seasonal differences in leaf-level physiology give lianas a competitive advantage over trees in a tropical seasonal forest

Lianas are an important component of most tropical forests, where they vary in abundance from high in seasonal forests to low in aseasonal forests. We tested the hypothesis that the physiological ability of lianas to fix carbon (and thus grow) during seasonal drought may confer a distinct advantage in seasonal tropical forests, which may explain pan-tropical liana distributions. We compared a range of leaf-level physiological attributes of 18 co-occurring liana and 16 tree species during the wet and dry seasons in a tropical seasonal forest in Xishuangbanna, China. We found that, during the wet season, lianas had significantly higher CO₂ assimilation per unit mass (A _mass), nitrogen concentration (N _mass), and δ¹³C values, and lower leaf mass per unit area (LMA) than trees, indicating that lianas have higher assimilation rates per unit leaf mass and higher integrated water-use efficiency (WUE), but lower leaf structural investments. Seasonal variation in CO₂ assimilation per unit area (A _area), phosphorus concentration per unit mass (P _mass), and photosynthetic N-use efficiency (PNUE), however, was significantly lower in lianas than in trees. For instance, mean tree A _area decreased by 30.1% from wet to dry season, compared with only 12.8% for lianas. In contrast, from the wet to dry season mean liana δ¹³C increased four times more than tree δ¹³C, with no reduction in PNUE, whereas trees had a significant reduction in PNUE. Lianas had higher A _mass than trees throughout the year, regardless of season. Collectively, our findings indicate that lianas fix more carbon and use water and nitrogen more efficiently than trees, particularly during seasonal drought, which may confer a competitive advantage to lianas during the dry season, and thus may explain their high relative abundance in seasonal tropical forests.     

Spatial patterns of photosynthetic characteristics and leaf physical traits of plants in the Loess Plateau of China

The spatial patterns of photosynthetic characteristics and leaf physical traits of 171 plants belonging to nine life-forms or functional groups (trees, shrubs, herbs, evergreen trees, deciduous trees, C₃ and C₄ herbaceous plants, leguminous and non-leguminous species) and their relationships with environmental factors in seven sites, Yangling, Yongshou, Tongchuan, Fuxian, Ansai, Mizhi and Shenmu, ranging from south to north in the Loess Plateau of China were studied. The results showed that the leaf light-saturated photosynthetic rate (P_max), photosynthetic nitrogen use efficiency (PNUE), chlorophyll content (Chl), and leaf mass per area (LMA) of all the plants in the Loess Plateau varied significantly among three life-form groups, i.e., trees, shrubs and herbs, and two groups, i.e., evergreen trees and deciduous trees, but leaf nitrogen content differed little among different life-form groups. For the 171 plants in the Loess Plateau, leaf P_max was positively correlated with PNUE. The leaf nitrogen content per unit area (N_area) was positively correlated but Chl was negatively correlated with the LMA. When controlling the LMA, the N_area was positively correlated with the Chl (partial r = 0.20, P < 0.05). With regard to relationships between photosynthetic characteristics and leaf physical traits, the P_max was positively correlated with N _area, while the PNUE was positively correlated with the Chl and negatively correlated with the N_area and LMA. For all the species in the Loess Plateau, the PNUE was negatively correlated with the latitude and annual solar radiation (ASR), but positively correlated with the mean annual rainfall (MAR) and mean annual temperature (MAT). With regard to the leaf physical traits, the leaf Chl was negatively correlated with the latitude and ASR, but positively correlated with the MAR and MAT. However, the N_area and LMA were positively correlated with the latitude and ASR, but negatively correlated with the MAR and MAT. In general, leaf N_area and LMA increased, while PNUE and Chl decreased with increases in the latitude and ASR and decreases in MAR and MAT. Electronic supplementary material The online version of this article () contains supplementary material, which is available to authorized users.     

Vertical gradients in photosynthetic physiology diverge at the latitudinal range extremes of white spruce

Light availability drives vertical canopy gradients in photosynthetic functioning and carbon (C) balance, yet patterns of variability in these gradients remain unclear. We measured light availability, photosynthetic CO₂ and light response curves, foliar C, nitrogen (N) and pigment concentrations, and the photochemical reflectance index (PRI) on upper and lower canopy needles of white spruce trees (Picea glauca) at the species' northern and southern range extremes. We combined our photosynthetic data with previously published respiratory data to compare and contrast canopy C balance between latitudinal extremes. We found steep canopy gradients in irradiance, photosynthesis and leaf traits at the southern range limit, but a lack of variation across canopy positions at the northern range limit. Thus, unlike many tree species from tropical to mid-latitude forests, high latitude trees may not require vertical gradients of metabolic activity to optimize photosynthetic C gain. Consequently, accounting for self-shading is less critical for predicting gross primary productivity at northern relative to southern latitudes. Northern trees also had a significantly smaller net positive leaf C balance than southern trees suggesting that, regardless of canopy position, low photosynthetic rates coupled with high respiratory costs may ultimately constrain the northern range limit of this widely distributed boreal species.     

Frost hardening and photosynthetic performance of Scots pine (Pinus sylvestris L.) needles. I. Seasonal changes in the photosynthetic apparatus and its function

Photosynthetic CO₂ uptake, the photochemical efficiency of photosystem II, the contents of chlorophyll and chlorophyll-binding proteins, and the degree of frost hardiness were determined in three-year-old Scots pine (Pinus sylvestris L.) trees growing in the open air but under controlled daylength. The following conditions were compared: 9-h light period (short day), 16-h light period (long day), and natural daylength. Irrespective of induction by short-day photoperiods or by subfreezing temperatures, frost hardening of the trees was accompanied by a long-lasting pronounced decrease in the photosynthetic rates of one-year-old needles. Under moderate winter conditions, trees adapted to a long-day photoperiod, assimilated CO₂ with higher rates than the short-day-treated trees. In the absence of strong frost, photochemical efficiency was lower under short-day conditions than under a long-day photoperiod. Under the impact of strong frost, photochemical efficiency was strongly inhibited in both sets of plants. The reduction in photosynthetic performance during winter was accompanied by a pronounced decrease in the content of chlorophyll and of several chlorophyll-binding proteins [light-harvesting complex (LHC)IIb, LHC Ib, and a chlorophyll-binding protein with MW 43 kDa (CP 43)]. This observed seasonal decrease in photosynthetic pigments and in pigment-binding proteins was irrespective of the degree of frost hardiness and was apparantly under the control of the length of the daily photoperiod. Under a constant 9-h daily photoperiod the chlorophyll content of the needles was considerably lower than under long-day conditions. Transfer of the trees from short-day to long-day conditions resulted in a significantly increased chlorophyll content, whereas the chlorophyll content decreased when trees were transferred from a long-day to a short-day photoperiod. The observed changes in photosynthetic pigments and pigment-binding proteins in Scots pine needles are interpreted as a reduction in the number of photosynthetic units induced by shortening of the daily light period during autumn. This results in a reduction in the absorbing capacity during the frost-hardened state. Received: 3 March 1997 / Accepted: 16 July 1997     

Photosynthesis, leaf morphology and chemistry of Pinus koraiensis and Quercus mongolica in broadleaved Korean pine mixed forest

Leaf traits and physiology are species-specific and various with canopy position and leaf age. Leaf photosynthesis, morphology and chemistry in the upper and lower canopy positions of Pinus koraiensis Sieb. et Zucc and Quercus mongolica Fisch. ex Turoz in broadleaved Korean pine forest were determined in September 2009. Canopy position did not significantly affect light-saturated photosynthetic rate based on unit area (P _area) and unit dry mass (P _mass), apparent quantum yield (α), light compensation point (LCP), light saturation point (LSP); total nitrogen (N_m), phosphorus (P_m), carbon (C_m), and chlorophyll content (Chl_m) per unit dry mass; leaf dry mass per unit area (LMA) and photosynthetic nitrogen-use efficiency (PNUE) for P. koraiensis current-year needles and Q. mongolica leaves. While in P. koraiensis one-year-old needles, P _area, P _mass, α and LCP in the upper canopy were lower than those in the lower canopy. The needles of P. koraiensis had higher Cm and LMA than leaves of Q. mongolica, but P _mass, Chl_m and PNUE showed opposite trend. There were no differences in P _area, LSP, N_m, and P_m between the two species. Needle age significantly influenced photosynthetic parameters, chemistry and LMA of P. koraiensis needles except LCP, LSP and C_m. In contrast to LMA, P _area, P _mass, N_m, P_m, Chl_m, and PNUE of one-year-old needles were significantly lower than those of current-year needles for P. koraiensis. The negative correlations between LMA and P _mass, N_m, P_m, Chl_m, and positive correlations between P _mass and N_m, P_m, Chl_m were found for P. koraiensis current-year needles and Q. mongolica leaves. Our results indicate that leaf nitrogen and phosphorus contents and nutrient absorption from soil are similar for mature P. koraiensis and Q. mongolica growing in the same environment, while difference in carbon content between P. koraiensis and Q. mongolica may be attributed to inherent growth characteristics.     

Photosynthesis or persistence: nitrogen allocation in leaves of evergreen and deciduous Quercus species

Photosynthetic nitrogen use efficiency (PNUE, photosynthetic capacity per unit leaf nitrogen) is one of the most important factors for the interspecific variation in photosynthetic capacity. PNUE was analysed in two evergreen and two deciduous species of the genus Quercus. PNUE was lower in evergreen than in deciduous species, which was primarily ascribed to a smaller fraction of nitrogen allocated to the photosynthetic apparatus in evergreen species. Leaf nitrogen was further analysed into proteins in the water‐soluble, the detergent‐soluble, and the detergent‐insoluble fractions. It was assumed that the detergent‐insoluble protein represented the cell wall proteins. The fraction of nitrogen allocated to the detergent‐insoluble protein was greater in evergreen than in deciduous leaves. Thus the smaller allocation of nitrogen to the photosynthetic apparatus in evergreen species was associated with the greater allocation to cell walls. Across species, the fraction of nitrogen in detergent‐insoluble proteins was positively correlated with leaf mass per area, whereas that in the photosynthetic proteins was negatively correlated. There may be a trade‐off in nitrogen partitioning between components pertaining to productivity (photosynthetic proteins) and those pertaining to persistence (structural proteins). This trade‐off may result in the convergence of leaf traits, where species with a longer leaf life‐span have a greater leaf mass per area, lower photosynthetic capacity, and lower PNUE regardless of life form, phyllogeny, and biome.     

Control of Adventitious Root Production and Hypocotyl Hypertrophy of Sunflower (Helianthus annuus) in Response to Flooding

Needles of 20-year-old Scots pine trees (Pinus silvestris L.) were permitted to photoassimilate ¹⁴CO₂ for 1 h on different dates during the growing season. The loss of radioactivity from current, 1-year-old, and 2-year-old needles was followed, and the translocation of photoassimilated ¹⁴CO₂ from older needle age-classes to the elongating new needles studied. The effects of good mineral and water supply on translocation were also considered. In the spring, 1-year-old and 2-year-old needles accumulated ¹⁴C. These reserves, together with current photosynthate, were utilized when the trees started growing. The 1-year-old needles exported ¹⁴C to the current needles during the first weeks of elongation of the later, while no such translocation occurred from the 2-year-old needles. Removal of the 1-year-old needles resulted in translocation of assimilates from the 2-year-old needles to the current needles. The general pattern of translocation observed in the control trees was not changed when the trees were fertilized and irrigated. The new needles started to export assimilates in the middle of July when the photosynthetic rate per needle was comparable with that of the older age-classes. This occurred about 4 weeks after positive net photosynthesis was first measured for the current shoot. The current needles of trees with good nutrient and water supply seemed to become self-sufficient in photoassimilates earlier than the current needles of the control trees.     

Plant biodiversity in a larch plantation from the view point of photosynthetic nitrogen use efficiency in northeast China

Forest floor of larch species often provides growth habitat for many kinds of understory species because of relatively sparse structure in a larch canopy. A rich flora of forest understory species may play an essential role in maintaining fertility of a larch stand. An attempt was made to evaluate photosynthetic nitrogen use efficiency (PNUE) of many understory and overstory species according to their Raunkiaer lifeform. By studying 72 perennial deciduous species in a larch plantation in northeast China, marked photosynthetic differences between phanerophytes (Ph) and other three lifeforms of chamaephytes (Ch), hemicryptophytes (He), and cryptophytes (Cr) were found, with marginal differences found among Ch, He, and Cr. Ph species had much lower PNUE, and much lower values of rate of nitrogen allocation to chlorophyll (Chl./N) and nitrogen allocation to carboxylation processes (V _cmax/N) were concurrently observed in Ph compared with the other three lifeforms. Ph had much lower leaf nitrogen per unit of projection area (N _area) and specific leaf area (SLA, cm² g^–1). At lower SLA, for Ph species the change of PNUE with SLA was small, but these changes became very large at higher SLA for Ch, He, and Cr species. Our findings indicate that leaf morphological change is important for clarifying photosynthesis differences among species with different lifeform.     

Photosynthetic capacity of loblolly pine (Pinus taeda L.) trees during the first year of carbon dioxide enrichment in a forest ecosystem

Our objective was to assess the photosynthetic responses of loblolly pine trees (Pinus taeda L.) during the first full growth season (1997) at the Brookhaven National Lab/Duke University Free Air CO₂ Enrichment (FACE) experiment. Gas exchange, fluorescence characteristics, and leaf biochemistry of ambient CO₂ (control) needles and ambient + 20 Pa CO₂ (elevated) needles were examined five times during the year. The enhancement of photosynthesis by elevated CO₂ in mature loblolly pine trees varied across the season and was influenced by abiotic and biotic factors. Photosynthetic enhancement by elevated CO₂ was strongly correlated with leaf temperature. The magnitude of photosynthetic enhancement was zero in March but was as great as 52% later in the season. In March, reduced sink demand and lower temperatures resulted in lower net photosynthesis, lower carboxylation rates and higher excess energy dissipation from the elevated CO₂ needles than from control needles. The greatest photosynthetic enhancement by CO₂ enrichment was observed in July during a period of high temperature and low precipitation, and in September during recovery from this period of low precipitation. In July, loblolly pine trees in the control rings exhibited lower net photosynthetic rates, lower maximum rates of photosynthesis at saturating CO₂ and light, lower values of carboxylation and electron transport rates (modelled from A–C_i curves), lower total Rubisco activity, and lower photochemical quenching of fluorescence in comparison to other measurement periods. During this period of low precipitation trees in the elevated CO₂ rings exhibited reduced net photosynthesis and photochemical quenching of fluorescence, but there was little effect on light- and CO₂-saturated rates of photosynthesis, modelled rates of carboxylation or electron transport, or Rubisco activity. These first-year data will be used to compare with similar measurements from subsequent years of the FACE experiment in order to determine whether photosynthetic acclimation to CO₂ occurs in these canopy loblolly pine trees growing in a forest ecosystem.     

Experimental drought and heat can delay phenological development and reduce foliar and shoot growth in semiarid trees

Higher temperatures associated with climate change are anticipated to trigger an earlier start to the growing season, which could increase the terrestrial C sink strength. Greater variability in the amount and timing of precipitation is also expected with higher temperatures, bringing increased drought stress to many ecosystems. We experimentally assessed the effects of higher temperature and drought on the foliar phenology and shoot growth of mature trees of two semiarid conifer species. We exposed field‐grown trees to a ~45% reduction in precipitation with a rain‐out structure (‘drought’), a ~4.8 °C temperature increase with open‐top chambers (‘heat’), and a combination of both simultaneously (‘drought + heat’). Over the 2013 growing season, drought, heat, and drought + heat treatments reduced shoot and needle growth in piñon pine (Pinus edulis) by ≥39%, while juniper (Juniperus monosperma) had low growth and little response to these treatments. Needle emergence on primary axis branches of piñon pine was delayed in heat, drought, and drought + heat treatments by 19–57 days, while secondary axis branches were less likely to produce needles in the heat treatment, and produced no needles at all in the drought + heat treatment. Growth of shoots and needles, and the timing of needle emergence correlated inversely with xylem water tension and positively with nonstructural carbohydrate concentrations. Our findings demonstrate the potential for delayed phenological development and reduced growth with higher temperatures and drought in tree species that are vulnerable to drought and reveal potential mechanistic links to physiological stress responses. Climate change projections of an earlier and longer growing season with higher temperatures, and consequent increases in terrestrial C sink strength, may be incorrect for regions where plants will face increased drought stress with climate change.     

Temporal variation in leaf nitrogen partitioning of a broad-leaved evergreen tree, <Emphasis Type="Italic">Quercus myrsinaefolia</Emphasis>

We examined temporal changes in the amount of nitrogenous compounds in leaves from the outer and inner parts of the crown of Quercus myrsinaefolia growing in a seasonal climate. Throughout the leaf life span, metabolic protein and Rubisco content closely correlated with total nitrogen content, while structural protein content was relatively stable after full leaf expansion. Chlorophyll content was affected by shading as well as total nitrogen content in outer leaves that were overtopped by new shoots in the second year. Outer leaves showed a large seasonal variation in photosynthetic nitrogen-use efficiency (PNUE; the light-saturated photosynthetic rate per unit leaf nitrogen content) during the first year of their life, with PNUE decreasing from the peak in summer towards winter. Outer and inner leaves both showed age-related decline in PNUE in the second year. There were no such drastic changes in leaf nitrogen partitioning that could explain seasonal and yearly variations in PNUE. Nitrogen resorption occurred in overwintering leaves in spring. Metabolic protein explained the majority of nitrogen being resorbed, whereas structural protein, which was low in degradability, contributed little to nitrogen resorption.     

Phytohormones in needles of healthy and declining silver fir (Abies alba Mill.): I. Indole-3-acetic acid

 Levels of indole-3-acetic acid (IAA) were determined in needles from silver fir (Abies alba Mill.) trees in the northern Black Forest. IAA was quantified by gas chromatography (GC) as 1-heptafluorobutyryl-IAA-methylester (HFB-IAA-ME) using electron capture detection. Prior to GC analysis, extensive purification of needle extracts was performed employing two HPLC steps. Peak identity of HFB-IAA-ME was confirmed by combined gas chromatography-mass spectrometry in selected samples. Levels of IAA in needles belonging to different needle age-classes exhibited a cyclic seasonal pattern with highest concentrations in winter and lowest levels in spring when bud-break occurred. Such a cyclic seasonal pattern of IAA levels was also observed in needles from declining fir trees or fir trees suffering from a strong sulfur impact (S-impact) in the field due to a local SO₂ source. Levels of IAA increased with increasing needle age. This age dependency of IAA concentrations was most pronounced in late autumn when IAA levels were high and nearly disappeared in spring when IAA levels reached their minimum. In needles from declining fir trees or fir trees suffering from a strong S-impact in the field, IAA levels hardly increased with increasing needle age. It is suggested that in healthy trees high levels of IAA protect older needles from abscission and that the considerable losses of older needles of declining fir trees or of fir trees under S-impact are a consequence of the low levels of IAA found in older needles of such trees. Received: 4 May 1995 / Accepted: 29 August 1995     

Carbon isotope discrimination and stomatal responses of mature Pinus sylvestris L. trees exposed in situ for three years to elevated CO2 and temperature

The Climate Change Experiment (CLIMEX) is a unique large scale facility in which an entire undisturbed catchment of boreal vegetation has been exposed to elevated CO₂ (560 ppm) and temperature (+3°C summer, +5°C winter) for the past three years with all the soil-plant-atmosphere linkages intact. Here, carbon isotope composition and stomatal density have been analysed from sequential year classes of needles of mature Scots pine trees (Pinus sylvestris L.) to investigate the response of time-integrated water-use efficiency (UWE) and stomatal density to CO₂ enrichment and climate change. Carbon isotope discrimination decreased and WUE increased in cohorts of needles developing under increased CO₂ and temperature, compared to needles on the same trees developing in pretreatment years. Mid-season instantaneous gas exchange, measured on the same trees for the past four years, indicated that these responses resulted from higher needle photosynthetic rates and reduced stomatal conductance. Needles of P. sylvestris developing under increased CO₂ and temperature had consistently lower stomatal densities than their ambient grown counterparts on the same trees. The stomatal density of P. sylvestris needles was inversely correlated with δ¹³C-derived WUE, implying some effect of this morphological response on leaf gas exchange. Future atmospheric CO₂ and temperature increases are therefore likely to improve the water economy of P. sylvestris, at least at the scale of individual needles, by affecting stomatal density and gas exchange processes.     

Effects of Season,Needle Age,and Elevated Atmospheric CO2 on Chlorophyll Fluorescence Parameters and Needle Nitrogen Concentration in Scots Pine (Pinus sylvestris)

Six-year-old Scots pine (Pinus sylvestris L.) seedlings were grown in open top chambers (OTCs) at ambient (AC) or elevated (ambient + 400 µmol mol^–1; EC) CO₂ concentration for three years (1996–1998). Chlorophyll (Chl) a fluorescence of current and one-year-old needles was measured in the field at two-weekly intervals in the period July–October 1998. In addition, Chl, carbon (C), and nitrogen (N) concentrations in both needle age classes were determined monthly during the same period. Chl fluorescence parameters were not significantly affected by EC, suggesting there was no response of the light reactions and the photochemical efficiency of photosystem 2. Chl concentrations were not significantly different but a reduced N concentration was observed in needles of EC treatment. Significant differences between needle age classes were observed for all parameters, but were most apparent under EC and toward the end of the growing season, possibly due to an acclimation process. As a result, significant interactions between CO₂ treatment, needle age class, and season were found. This study emphasizes the importance of repeated measures including different leaf/needle age classes to assess the photosynthetic response of trees under EC.     

Relationship between δ13C and photosynthetic parameters and their responses to leaf nitrogen content in six broadleaf tree species

Stable carbon isotope composition (δ¹³C), net photosynthetic rate (P _N), actual quantum yield of photosystem 2 (PS2) electron transport (ΦPS2), nitrogen content (N_c), and photosynthetic nitrogen use efficiency (PNUE) in the leaves of six broadleaf tree species were determined under field environmental conditions. The six tree species were Magnolia liliflora Desr., M. grandiflora Linn., M. denudata Desr., Prunus mume (Sieb.) Sieb. et Zucc. cv. Meiren Men, P. mume (Sieb.) Sieb. et Zucc. f. alphandii (Carr.) Rehd., and P. persica (L.) Batsch. var. rubro-plena. The relationships among δ¹³C, Φ_PS2, P _N, and PNUE, as well as their responses to N_c in the six species were also studied. Both P _N and δ¹³C negatively correlated with N_c, but Φ_PS2 positively correlated with N_c. This indicated that with N_c increase, P _N and δ¹³C decreased, while Φ_PS2 increased. There were weak negative correlations between δ¹³C and PNUE, and strong negative correlations (p<0.01) between Φ_PS2 and PNUE. According to the variance analysis of parameters, there existed significant interspecific differences (p<0.001) of δ¹³C, P _N, Φ_PS2, PNUE, and N_c among the tree seedlings of the six tree species, which suggests that the potential photosynthetic capacities depend on plant species, irradiance, and water use capacity under field conditions.     

Growth and physiological activity in <Emphasis Type="Italic">Larix kaempferi</Emphasis> seedlings inoculated with ectomycorrhizae as affected by soil acidification

To evaluate the effect of ectomycorrhizal colonization on growth and physiological activity of Larix kaempferi seedlings grown under soil acidification, we grew L. kaempferi seedlings with three types of ectomycorrhizae for 180 days in acidified brown forest soil derived from granite. The soil had been treated with an acid solution (0 (control), 10, 30, 60, and 90 mmol H⁺ kg⁻¹). The water-soluble concentrations of Ca, Mg, K, Al, and Mn increased with increasing amounts of H⁺ added to the soil. Ectomycorrhizal development significantly increased in soil treated with 10 and 30 mmol H⁺ kg⁻¹ but was significantly reduced in soil treated with 60 and 90 mmol H⁺ kg⁻¹. The concentrations of Al and Mn in needles or roots increased with increasing H⁺ added to the soil. The total N in seedlings significantly increased with increasing H⁺ in soil and colonization with ectomycorrhiza. The maximum net photosynthetic rate at light and CO₂ saturation (P _max) was greater in soil treated with 10 mmol H⁺ kg⁻¹ than in controls, and was less is soils treated with greater than with 30 mmol H⁺ kg⁻¹, especially with 60 and 90 mmol H⁺ kg⁻¹. However, colonization with ectomycorrhiza significantly reduced the concentration of Al and Mn in needles or roots and increased the values of P _max and total dry mass (TDM). The relative TDM of L. kaempferi seedlings was approximately 40% at a (BC, base cation)/Al ratio of 1.0. However, ectomycorrhizal seedlings had a 100–120% greater TDM at a BC/Al ratio of 1.0 than non-ectomycorrhizal seedlings, even though the acid treatment reduced their overall growth.     

Photosynthesis–nitrogen relationships in species at different altitudes on Mount Kinabalu, Malaysia

In situ photosynthetic nitrogen-use efficiency (PNUE, photosynthetic capacity per unit leaf nitrogen) was investigated in species that commonly distributed at different altitudes (600–3700m above sea level) on Mount Kinabalu. Photosynthetic nitrogen-use efficiency was lower in species at higher altitudes, with a mean PNUE at 3700m being one-third as large as that at 600m. This difference in PNUE was larger than that explained by the biochemical response to lower air pressures only. Across altitudes a negative correlation between ¹³C abundance (¹³C) and PNUE was found. Species at higher altitudes tended to have higher ¹³C, suggesting that they had a lower conductance for CO₂ diffusion from the air to chloroplasts. The lower conductance might be responsible for the lower PNUE in species at higher altitudes. Although leaf nitrogen content per unit area tended to be higher at higher altitudes, it did not seem to contribute to increasing photosynthetic rates. Thus, the idea that a higher nitrogen content at higher altitudes is a compensation for a lower PNUE was not supported. In contrast to the large difference in PNUE among altitudes, PNUE tended to converge within a narrow range among species growing at the same altitude.