Effects of nitrogen supply on photosynthetic and anatomical changes in current-year needles of <Emphasis Type="Italic">Pinus koraiensis</Emphasis> seedlings grown under two irradiances

We investigated the responses of photon-saturated photosynthesis rate (P _sat) and its simultaneous acclimation of anatomy and nitrogen use patterns of current needles of Korean pine (Pinus koraiensis) seedlings grown under factorial combinations of two nitrogen levels and irradiances. Although N supply resulted in a significant increase of N content in needles under both irradiances, the increase of P _sat tended to be suppressed only in shade (S). The significant increase of P _sat in full sunlight (O) was associated with the increase of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and chlorophyll (Chl) contents. In contrast, small increase of Chl content and no increase of RuBPCO content were found in S (90 % cut of full irradiance), which would result in a small increase of P _sat. This result suggests that extra N is stocked in needles under shade for the growth in next season. With N supply, a significant decrease of specific leaf area (SLA) was detected only in O. This decrease of SLA was due to the increase of density of needle. Furthermore, the increase of needle density was not due to the increased number and size of mesophyll cells, but the increased density of each mesophyll cell. Therefore, although SLA changed in O, the change did not involve anatomical adaptation to use increased N effectively, at least observable by light microscopy. Hence, even though the SLA would change, N deposition will improve the photosynthetic capacity of Korean pine seedlings, not through the development of needle anatomy but through improvement of the allocation of N in both irradiances.     

模拟氮沉降对温带典型森林土壤有效氮形态和含量的影响*

通过室内模拟氮沉降试验,研究了氮沉降对温带典型森林土壤有效氮的影响.结果表明:试验期间,与对照相比,经过氮沉降处理的土壤铵态氮、硝态氮和有效氮均呈增长的趋势,增加的程度取决于森林类型、土层、氮处理类型和氮处理的持续时间.氮沉降对不同林型土壤有效氮形态和含量的影响不同,氮沉降对混交林的影响弱于阔叶林,强于针叶人工纯林;土壤A层对氮沉降的敏感程度大于土壤B层;铵态氮形态沉降对土壤铵态氮含量的影响比对土壤硝态氮含量的影响大,而硝态氮形态沉降对土壤硝态氮含量的影响比对土壤铵态氮含量的影响大,混合形态的氮沉降对二者均有促进作用,且增加幅度更高;氮沉降对土壤有效氮的影响存在累加效应.     

酸沉降下铝毒对森林的影响(综述)

回顾了酸沉降的研究历史,总结了酸沉降对森林生态系统的影响。在此基础上综述了近二十年来酸沉降下铝毒与森林衰亡关系方面的一些研究成果,阐明铝毒是引起森林衰亡的一个重要的因素,并提出了酸沉降影响下铝毒与森林衰亡研究中存在的一些问题。     

The effects of a 9-year nitrogen and water addition on soil aggregate phosphorus and sulfur availability in a semi-arid grassland

Previous studies have demonstrated that higher nitrogen (N) and water availability affect both above- and below-ground communities, soil carbon and N pools, and microbial activity in semi-arid grasslands of Inner Mongolia. However, how soil phosphorus (P) and sulfur (S) pools, and related soil enzyme activities (as indicators of P and S cycles) respond to long-term N and water addition has still remained unclear. Since 2005, a field experiment with urea and water amendments has been conducted to examine their effects on total and available P and S concentrations and alkaline phosphomonoesterase (PME) and aryl-sulfatase (ArS) activities in three soil aggregate fractions: large macroaggregates (>2 mm), small macroaggregates (0.25–2 mm), and microaggregates (<0.25 mm) in an Inner Mongolia semi-arid grassland. Normalized to aggregate mass, microaggregates retained the highest total P and S concentrations. Both N and water additions increased the available P (by up to 84.5%) and the available S (by up to 150%) in the soil aggregate fractions. Soil acidification, as a result of the N addition, decreased both alkaline PME and ArS activities by up to 62.9% and 39.6%, respectively, while the water addition increased their activities. Our observations revealed that soil acidification (under the N addition) and elevated enzyme activity (under the water addition) played important roles in the levels of soil available P and S. The depression of P- and S-acquiring enzymes with soil acidification may decrease P and S availability, potentially impacting ecosystem processes and limiting the restoration of these grassland systems. The water addition was shown to be a more effective practice than the urea amendment for improving soil structure, supplying available P and S, and maintaining the sustainability of this semi-arid grassland.     

Nitrogen addition reduces soil respiration in a mature tropical forest in southern China

Response of soil respiration (CO₂ emission) to simulated nitrogen (N) deposition in a mature tropical forest in southern China was studied from October 2005 to September 2006. The objective was to test the hypothesis that N addition would reduce soil respiration in N saturated tropical forests. Static chamber and gas chromatography techniques were used to quantify the soil respiration, following four‐levels of N treatments (Control, no N addition; Low‐N, 5 g N m^?2 yr^?1; Medium‐N, 10 g N m^?2 yr^?1; and High‐N, 15 g N m^?2 yr^?1 experimental inputs), which had been applied for 26 months before and continued throughout the respiration measurement period. Results showed that soil respiration exhibited a strong seasonal pattern, with the highest rates found in the warm and wet growing season (April–September) and the lowest rates in the dry dormant season (December–February). Soil respiration rates showed a significant positive exponential relationship with soil temperature, whereas soil moisture only affect soil respiration at dry conditions in the dormant season. Annual accumulative soil respiration was 601±30 g CO₂‐C m^?2 yr^?1 in the Controls. Annual mean soil respiration rate in the Control, Low‐N and Medium‐N treatments (69±3, 72±3 and 63±1 mg CO₂‐C m^?2 h^?1, respectively) did not differ significantly, whereas it was 14% lower in the High‐N treatment (58±3 mg CO₂‐C m^?2 h^?1) compared with the Control treatment, also the temperature sensitivity of respiration, Q₁₀ was reduced from 2.6 in the Control with 2.2 in the High‐N treatment. The decrease in soil respiration occurred in the warm and wet growing season and were correlated with a decrease in soil microbial activities and in fine root biomass in the N‐treated plots. Our results suggest that response of soil respiration to atmospheric N deposition in tropical forests is a decline, but it may vary depending on the rate of N deposition.     

Silica deposition in relation to ageing of leaf tissues in Sasa veitchii (Carriere) Rehder (Poaceae: Bambusoideae)

BACKGROUND AND AIMS: Silica deposition is one of the important characteristics of plants in the family Poaceae. There have been many investigations into the distribution, deposition and physiological functions of silica in this family. Two hypotheses on silica deposition have been proposed based on these studies. First, that silica deposition occurs passively as a result of water uptake by plants, and second, that silica deposition is controlled positively by plants. To test these two apparently contradictory hypotheses, silica deposition in relation to the ageing of leaf tissues in Sasa veitchii was investigated. METHODS: Tissues were examined using a light microscope and a scanning electron microscope equipped with an energy dispersive X-ray microanalyser. KEY RESULTS: The deposition process differed depending on cell type. In mesophyll tissue, fusoid cells deposited large amounts of silica depending on leaf age after maturation, while chlorenchyma cells deposited little. In epidermal tissue, comprised of eight cell types, only silica cells deposited large amounts of silica during the leaf's developmental process and none after maturation. Bulliform cells, micro-hairs and prickle hairs deposited silica densely and continuously after leaf maturation. Cork cells, guard cells, long cells and subsidiary cells deposited silica at low levels. CONCLUSIONS: The significance of these observations is discussed in relation to the two hypotheses proposed for silica deposition in Poaceae. The results of the present study clearly indicate that both hypotheses are compatible with each other dependent on cell types.     

Uniform and Residue-specific 15N-labeling of Proteins on a Highly Deuterated Background

A general method for stable-isotope labeling of large proteins is introduced and applied for studies of the E. coli GroE chaperone proteins by solution NMR. In addition to enabling the residue-specific (15)N-labeling of proteins on a highly deuterated background, it is also an efficient approach for uniform labeling. The method meets the requirements of high-level deuteration, minimal cross-labeling and high protein yield, which are crucial for NMR studies of structures with sizes above 150 kDa. The results obtained with the new protocol are compared to other strategies for protein labeling, and evaluated with regard to the influence of external factors on the resulting isotope labeling patterns. Applications with the GroE system show that these strategies are efficient tools for studies of structure, dynamics and intermolecular interactions in large supramolecular complexes, when combined with TROSY- and CRINEPT-based experimental NMR schemes.     

Towards high-resolution solid-state NMR on large uniformly 15N- and [13C,15N]-labeled membrane proteins in oriented lipid bilayers

Based on exact numerical simulations, taking into account isotropic and conformation-dependent anisotropic nuclear spin interactions, we systematically analyse the prospects for high-resolution solid-state NMR on large isotope-labeled membrane proteins macroscopically oriented in phospholipid bilayers. Using the known X-ray structures of rhodopsin and porin as models for large membrane proteins with typical -helical and -barrel structural motifs, the analysis considers all possible one- to six-dimensional spectra comprised of frequency dimensions with evolution under any combination of amide ¹H, amide ¹⁵N, and carbonyl ¹³C chemical shifts as well as ¹H-¹⁵N dipole-dipole couplings. Under consideration of typical nuclear spin interaction and experimental line-shape parameters, the analysis provides new insight into the resolution capability and orientation-dependent transfer efficiency of existing experiments as well as guidelines as to improved experimental approaches for the study of large uniformly ¹⁵N- and [¹³C,¹⁵N]-labeled membrane proteins. On basis of these results and numerical optimizations of coherence-transfer efficiencies, we propose several new high-resolution experiments for sequential protein backbone assignment and structure determination.     

X-ray microanalytical studies of mineral localization in the needles of white pine (Pinus strobus L.)

Eastern white pine (Pinus strobus L.) shoots from mature trees were collected from two sites of contrasting soil pH: the Glendon campus of York University in Toronto, Ontario (pH 6.7 at 40 cm); and Muskoka near Huntsville, Ontario (pH 4.2 at 40 cm). Needles of ages 1-3 years were removed from the shoots, and the percentage of ash and silica was determined for all ages. Other needles were frozen in liquid nitrogen and kept in a cryo-biological storage system before x-ray microanalysis. Percentages of ash and silica were higher in the needles from Muskoka. Ash and silica increased with needle age for trees from the Muskoka site, but less so at the Toronto site. Of the 13 elements (Na, Mg, Al, Si, P, S, Cl, K, Ca, Mn, Fe, Cu and Zn) detected by microanalysis, Mn, Fe, Cu and Zn were detected in small amounts in the epidermis, endodermis and transfusion tissue (the layer of tracheids and parenchyma immediately surrounding the vascular bundles), and K, P, S and Cl were almost ubiquitous in distribution. Sodium was occasionally detected in the transfusion tissue, and magnesium was concentrated in the endodermal cells. The epidermal walls, transfusion tissue and endodermis were major sites of calcium localization. Silicon was concentrated in the extreme tips of the needles in all tissues, but particularly in the transfusion tissue, and more so in the Muskoka samples. Microanalysis revealed a higher Al content in the Muskoka needles, that Al was concentrated in the needle tips and that the transfusion tissues were major sites of accumulation.     

Pine Forest Floor Carbon Accumulation in Response to N and PK Additions: Bomb <Superscript>14</Superscript>C Modelling and Respiration Studies

The addition of nitrogen via deposition alters the carbon balance of temperate forest ecosystems by affecting both production and decomposition rates. The effects of 20 years of nitrogen (N) and phosphorus and potassium (PK) additions were studied in a 40-year-old pine stand in northern Sweden. Carbon fluxes of the forest floor were reconstructed using a combination of data on soil ¹⁴C, tree growth, and litter decomposition. N-only additions caused an increase in needle litterfall, whereas both N and PK additions reduced long-term decomposition rates. Soil respiration measurements showed a 40% reduction in soil respiration for treated compared to control plots. The average age of forest floor carbon was 17 years. Predictions of future soil carbon storage indicate an increase of around 100% in the next 100 years for the N plots and 200% for the NPK plots. As much as 70% of the increase in soil carbon was attributed to the decreased decomposition rate, whereas only 20% was attributable to increased litter production. A reduction in decomposition was observed at a rate of N addition of 30 kg C ha^–1 y^–1, which is not an uncommon rate of N deposition in central Europe. A model based on the continuous-quality decomposition theory was applied to interpret decomposer and substrate parameters. The most likely explanations for the decreased decomposition rate were a fertilizer-induced increase in decomposer efficiency (production-to-assimilation ratio), a more rapid rate of decrease in litter quality, and a decrease in decomposer basic growth rate.