Long-term effects of elevated CO2 and nutrients on photosynthesis and rubisco in loblolly pine seedlings

The effects of long-term CO₂ enhancement and varying nutrient availability on photosynthesis and ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) were studied on loblolly pine (Pinus taeda L.) seedlings grown in two atmospheric CO₂ partial pressures (35 and 65 Pa) and three nutrient treatments (low N, low P, and high N and P). Measurements taken in late autumn (November) after 2 years of CO₂ enrichment and nutrient addition showed that photosynthetic rates were higher for plants grown at elevated CO₂ only when they received supplemental N. Total rubisco activity and rubisco content decreased at elevated CO₂, but there was an increase in activation state. At elevated CO₂, proportionately less N was found in rubisco and more N was found in the light reaction components. These results demonstrate acclimation of photosynthetic processes to elevated CO₂ through reallocation of N. Loblolly pine grown in nutrient conditions similar to native soils (low N availability) had lower needle N and chlorophyll content, lower total rubisco activity and content, and lower photosynthetic rates than plants grown at high N and P. This suggests that the magnitude of the photosynthetic response to a future, high-CO₂ environment will be dependent on soil fertility in the system.     

不列颠·哥伦比亚省北部小杆松及白云杉立地指数与生态立地质量的关系

为在ＰｒｉｎｃｅＲｕｐｅｒｔ林区的“亚北方”部分建立生态立地质量与森林生产力的联系,对从９３个小杆松林分和７７个白云杉林分获得的数据进行了分析．所研究的林分处于两个气候状况、８个土壤水分状况以及５个土壤养分状况．这些气候、土壤水分和养分状况被视为等级变量用于林地分类和回归分析．小杆松和白云杉的立地指数随土壤水分和养分状况变化而变化,但不依赖于气候变化．与土壤水分相关的变化格局对两个种来说很相似,但与土壤养分相关的变化格局则全然不同．在所建立的５类回归模型中,土壤小区模型对于两个种都显示出立地指数与土壤水分和养分状况具有很强的相互关系（Ｒ２＞０．８０,ＳＥＥ≤１．６ｍ）．可以认为土壤水分和养分的等级度量在大范围内可作为小杆松和白云杉立地指数的预测预报因子．     

Natural regeneration of Pinus resinosa on burned and unburned sites in Newfoundland

Abstract. Natural regeneration of Pinus resinosa (red pine) seedlings around mature trees was studied in burned and unburned stands. Growth inhibitory effects of the forest organic matter on red pine seedlings was tested by a stair-step experiment using leachate of forest soil monoliths and also by a seed germination bio-assay using forest floor substrates. To test if higher burning temperatures can remove the allelopathic effects of red pine-Kalmia organic matter, a laboratory bio-assay was conducted by germinating red pine seeds on the organic matter burned at 200, 400, 600 and 800°C. Deposition of dry needles and a thick duff layer under red pine stands affected seedling establishment. Red pine seedling establishment increased with the decreasing thickness of duff layer away from the stump of the seed-bearing trees. Wildfire helped in removing the duff layer and increased seedling establishment. A high fuel load within a 0 - 1 m radius around the tree stump caused a deep burn of the organic matter including part of the soil seed reserve. On a burned-over surface, more seedlings established in a band between 1 and 2 m around the stump than inside and outside the band. Primary root growth of red pine was severely inhibited when the seedlings were grown in unburned forest floor organic matter where Kalmia was the principal understory species. Water leachate of a Pinus resinosa-Kalmia soil monolith was inhibitory to red pine seedling growth. In greenhouse conditions, the seedlings grew well in burned-over soil from a Pinus resinosa stand. Burned organic matter from a red pine forest showed an increase in pH with a burning temperature of 600°C. Primary root growth of red pine seedlings was similarly increased with increasing temperature up to 600°C; at higher temperatures the root length of seedlings did not increase any further.     

High resolution radiocarbon spike confirms tree ring dating with low sample depth

Radiocarbon (¹⁴C) has been used to date carbon-rich objects in Earth science, archeology, and history since the 1940s. New methods, using spikes in ¹⁴C caused by solar proton events, can be used to annually date wood when crossdating is not possible, such as when sample size is low, samples are floating in time, or external disturbances lead to insecure dates. Here, we use a spike in radiocarbon during a solar energetic particle (SEP) event in 774/775 CE to confirm crossdating of a poorly-replicated King Billy pine (Athrotaxis selaginoides) chronology. Low sample depth between 1498 and 1523 CE (two trees) prevented confident dating of the early period of the chronology. Three core samples with strong correlation with the master chronology that likely included the 774/775 CE Miyake SEP event were identified for radiocarbon isotope analysis. We sectioned segments centered on the estimated 774/775 CE date and then isolated the holocellulose in each sample. Samples were sent to an accelerator mass spectrometry (AMS) for radiocarbon measurements. The AMS data confirmed the crossdating accuracy of the tree ring series and reinforces the applicability of this technique to anchor poorly dated tree ring series in time. In addition, we found sample processing with a microtome proved superior for holocellulose extractions and yielded more accurate ¹⁴C measurements. We recommend sampling with a microtome, processing at least three samples per year, and including sample masses greater than 100 ug C to confirm dating using radiocarbon spikes.     

Optimization of in vitro bud induction and plantlet formation from mature embryos of Aleppo pine (Pinus halepensis Mill.)

Summary Studies were undertaken to optimize tissue culture conditions for micropropagation of Aleppo pine (Pinus halepensis Mill.) from mature embryos and various explants of the embryo. Over 90% of the embryo explants gave rise to adventitious buds within 4 wk. Intact embryos were the most suitable explants for shoot bud induction. Both isolated cotyledons and hypocotyls produced adventitious buds, but these developed slowly and failed to elongate. N⁶-Benzyladenine (BA) alone at 5.0μM was the most effective cytokinin when added to gelled to gelled von Arnold and Eriksson’s (AE) medium containing 3% sucrose. Adventitious bud development was achieved on hormone-free AE medium, and shoot elongation was optimum on three quarter-strength Bornman’s MCM medium, with 0.1% conifer-derived activated charcoal. Shoots were multiplied on three-quarter strength MCM medium, containing 5μM BA. To induce adventitious roots on the elongated shoots, pulse treatment with 1 mM IBA for 6 h, followed by the transfer of the shoots to sterile peat:vermiculite (1:1) mixture, was beneficial. After acclimatization for 3 to 4 wk under mist, almost all the rooted shoots could be transplanted successfully to the greenhouse, where the plants exhibited normal growth habit. Histologic studies on the ontogeny of adventitious shoot formation from mature embryo explants revealed temporal structural changes in different parts of the explant. Induction of mitotic divisions on the shoot-forming medium resulted in the formation of meristemoids in the epidermal and subepidermal layers of the explant, located initially at both the tips of the cotyledons and the axils of adjacent cotyledons. Shoot buds arising in the axils of adjacent cotyledons were due to new cell division and not to any preexisting meristem.     

安徽马尾松人工林营养元素分配格局的研究

本文系统地研究了马尾松人工林营养元素的分配格局。结果表明马尾松不同器官营养元素含量是叶>枝皮>干皮>枝木>干木;同化器官——针叶中营养元素含量规律为N>K>Ca>Mg>P,非同化器官为Ca>N>K>Mg>P;不同器官营养元素的贮量为干木>干皮>叶>枝木>枝皮,同化器官对不同营养元素的贮量呈N>K>Ca>Mg>P,非同化器官为Ca>N>K>Mg>P;不同立地条件下,马尾松林生产1t干物质所贮存的营养元素不同,立地条件愈好,营养元素效率愈高,贮存愈少;母岩、土层厚度和养分总量是影响马尾松林地上各器官,特别是针叶营养元素含量的重要因子,土壤N、P含量越高,马尾松人工林生物量越大。     

Soil-surface carbon dioxide efflux and microbial biomass in relation to tree density 13 years after a stand replacing fire in a lodgepole pine ecosystem

The effects of fire on soil‐surface carbon dioxide (CO₂) efflux, F_S, and microbial biomass carbon, C_mic, were studied in a wildland setting by examining 13‐year‐old postfire stands of lodgepole pine differing in tree density (< 500 to > 500 000 trees ha^?1) in Yellowstone National Park (YNP). In addition, young stands were compared to mature lodgepole pine stands (～110‐year‐old) in order to estimate ecosystem recovery 13 years after a stand replacing fire. Growing season F_S increased with tree density in young stands (1.0 µmol CO₂ m^?2 s^?1 in low‐density stands, 1.8 µmol CO₂ m^?2 s^?1 in moderate‐density stands and 2.1 µmol CO₂ m^?2 s^?1 in high‐density stands) and with stand age (2.7 µmol CO₂ m^?2 s^?1 in mature stands). Microbial biomass carbon in young stands did not differ with tree density and ranged from 0.2 to 0.5 mg C g^?1 dry soil over the growing season; C_mic was significantly greater in mature stands (0.5–0.8 mg C g^?1 dry soil). Soil‐surface CO₂ efflux in young stands was correlated with biotic variables (above‐ground, below‐ground and microbial biomass), but not with abiotic variables (litter and mineral soil C and N content, bulk density and soil texture). Microbial biomass carbon was correlated with below‐ground plant biomass and not with soil carbon and nitrogen, indicating that plant activity controls not only root respiration, but C_mic pools and overall F_S rates as well. These findings support recent studies that have demonstrated the prevailing importance of plants in controlling rates of F_S and suggest that decomposition of older, recalcitrant soil C pools in this ecosystem is relatively unimportant 13 years after a stand replacing fire. Our results also indicate that realistic predictions and modeling of terrestrial C cycling must account for the variability in tree density and stand age that exists across the landscape as a result of natural disturbances.     

Feeding by the pine weevil Hylobius abietis in relation to sun exposure and distance to forest edges

Abstract 1 The intensity of feeding by adult pine weevils Hylobius abietis (L.) on the stem bark of Norway spruce Picea abies (L.) Karst. seedlings planted in rows with a north–south orientation across a clear‐cutting, was measured throughout a growth season. The feeding was then correlated to light interception, soil temperature and distance to the nearest forest edge. 2 Feeding was at least twice as intense on seedlings in the central part of the clear‐cutting compared to those at the edges. The decline began approximatety 15 m from the edge and was of similar proportions on both the sun‐exposed and shaded sides. 3 Measures of global radiation and soil temperature correlated well with consumption on the shaded side. However, on the sun‐exposed side, there were no apparent correlations with global radiation or soil temperature that could explain the decline in consumed bark area. 4 We conclude that the decline in feeding towards the forest edges was mainly due to factors other than the microclimate variables we monitored. We suggest that the presence of roots of living trees along the forest edge may reduce damage to seedlings, since they provide an alternative source of food for the weevils. This alternative‐food hypothesis may also explain why seedlings in shelterwoods usually suffer less damage from pine weevils than seedlings in clear‐cuttings.     

The Liphook Forest Fumigation Project: an overview

The aim of the Liphook Project was to assess the effects of SO₂ and O₃, singly and in combination, on coniferous forest ecosystems. More than 4000 trees of Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and Sitka spruce (P. sitchensis) were fumigated for nearly 4 years using an open-air fumigation technique especially developed for the purpose. The technique eliminated artifacts due to chambers and enabled a variety of effects of the pollutant gases on forest ecosystems to be studied. Most symptoms of forest decline did not occur, but each species reacted in a different way to SO₂ stress, providing no evidence for universal forest decline symptoms. However, some of the mechanisms hypothesized to underlie forest declines were observed as an effect of SO₂ treatment, though others were not, notably any major effect of O₃. The results are assessed against proposed regulatory standards (critical loads and levels) for the protection of forest ecosystems against pollution.     

Effect of open-air fumigation with sulphur dioxide and ozone on phyllosphere and endophytic fungi of conifer needles

The phyllosphere microbial populations inhabiting the needles of three conifer species, Scots pine (Pinus sylvestris L.), Sitka spruce (Picea sitchensis L.) and Norway spruce (Picea abies (L.) Karst.), exposed to SO₂ and O₃, in an open-air fumigation experiment were analysed over a 3 year period using serial dilution after washing, direct plating and a fluorescein diacetate (FDA) enzyme assay. Total fungal populations ranged from 10² to 10⁵ colonyforming units (CPU) g^?1 fresh weight of needles. The dominant fungi isolated from needles varied with tree species and isolation technique; Aureobasidium pullulans (de Bary) Arnaud was most common on Scots pine and Norway spruce and white yeasts on Sitka spruce using the dilution plating method. However, direct plating of needle segments onto culture media indicated that Sclerophoma pythiophila (Corda) Hohnel was dominant on Scots pine and A. pullulans on Sitka and Norway spruce. Green needles of Sitka spruce were found to be endophytically colonized by Rhizosphaera kalkhoffii Bubak, but seldom by Lophodermium piceae (Fuckel) Hohn during extensive sampling in 1990. Statistical analyses revealed significant differences (P<0.05) between plots in the 3 year mean of the total fungal populations or the fungal biomass (FDA assay) on all three tree species. Differences between plots were also observed for a number of dominant component species. Data were also analysed for treatment effects. A significant effect of SO₂ treatment was observed on the total fungal populations on Sitka spruce (P<0.05) which were reduced markedly by the low-SO₂ treatment, while the O₃ treatment caused a significant increase in total fungal numbers on Scots pine (P<0.05). The FDA activity on needles of both Scots pine and Sitka spruce was noticeably higher in the 0₃-only treatment plot, but the overall O₃ effect was not significant. Treatment effects were also detected on the occurrence of component species. The serial dilution method revealed an SO₂ effect (P<0.05) of a reduction in the occurrence of pink yeasts on Sitka spruce and an O₃ effect (P<0.05) of an increase in the occurrence of S. pythiophila on Sitka spruce (P<0.01) but a decrease of Epicoccum nigrum Link and Cladosporium spp. on Scots pine. The direct-plating method revealed an SO₂ effect of an increase in S. pythiophila on Norway spruce (P<0.05). Ozone treatment caused a significant increase in the isolation of a black strain of A. pullulans on Norway spruce (P<0.05). Endophytic colonization of Sitka spruce needles by R. kalkhoffii was found to be increased on two occasions by O₃ exposure.