Nitrate reductase in needles,roots and trunk wood of spruce trees [Picea abies (L.) Karst.]

Summary Nitrate reductase (EC 1.6.6.2) activity (NRA), as measured by an in vivo assay, is present in needle leaves and mycorrhizal fine root tips of adult Norway spruce [Picea abies (L.) Karst.] in at least equal amounts on a fresh weight basis, in both adult and 5-year-old trees. NRA could also be demonstrated in trunk wood of deroted trees after fertilization with 5 mM , exhibiting a longitudinal profile in the trunk. Inducibility in needles can more efficiently be achieved by NO₂ (100 g·m^-3) than by 5 mM nitrate, which is effective only in root-amputated trees. A remarkably high level of needle-NRA in unfertilized trees, which are characterized by a very low level of nitrate in the xylem sap, suggests that NRA in spruce needles may in part be constitutive. Organic-N is a major nitrogen source for the needles even in root-amputated trees, indicating pronounced exchange processes between ray parenchyma and trunk xylem, which in turn are modified by the nitrogen source fed to the trunk stump. Intact trees exhibit a very similar amino acid composition of the xylem sap, regardless of whether or has been fed. The amino acid pattern of the needles is not thrown out of balance by flooding with and , which occurs in fertilized derooted trees. This indicates a distinct potential for homoeostasis of nitrogen entrance-metabolism (i.e. NRA and glutamine synthetase activity) in the needles. In the ectomycorrhiza/fine root-system (EMC), marked differences in NRA were observed depending on root-tip diameter and along the longitudinal profile of the fine roots. EMC-nitrate reductase is strongly enhanced by . Needle-NRA exhibits a circannual rhythm. An early summer maximum is followed by a December minimum. This activity pattern matches well the transitory increase of soluble nitrogen in spring and the total protein maximum in winter. In an indirect way assimilatory NRA may well contribute to nitrogen overfertilization (by consumption of NO_X) as one possible cause of the contemporary decline of spruce populations.     

Ammonium and nitrate uptake rates and rhizosphere pH in non-mycorrhizal roots of Norway spruce [Picea abies (L.) Karst.]

Summary Relationships between root zone temperature, concentrations and uptake rates of NH ₄ ⁺ and NO ₃ ^– were studied in non-mycorrhizal roots of 4-year-old Norway spruce under controlled environmental conditions. Additionally, in a forest stand NH ₄ ⁺ and NO ₃ ^– uptake rates along the root axis and changes in the rhizosphere pH were measured. In the concentration (C_min) range of 100–150 M uptake rates of NH ₄ ⁺ were 3–4 times higher than those of NO ₃ ^– The preference for NH ₄ ⁺ uptake was also reflected in the minimum concentration (C_min) values. Supplying NH₄NO₃, the rate of NO ₃ ^– uptake was very low until the NH ₄ ⁺ concentrations had fallen below about 100 M. The shift from NH ₄ ⁺ to NO ₃ ^– uptake was correlated with a corresponding shift from net H⁺ production to net H⁺ consumption in the external solution. The uptake rates of NH ₄ ⁺ were correlated with equimolar net production of H⁺. With NO ₃ ^– nutrition net consumption of H⁺ was approximately twice as high as uptake rates of NO ₃ ^– In the forest stand the NO ₃ ^– concentration in the soil solution was more than 10 times higher than the NH ₄ ⁺ concentration (<100 M), and the rhizosphere pH of non-mycorrhizal roots considerably higher than the bulk soil pH. The rhizosphere pH increase was particularly evident in apical root zones where the rates of water and NO ₃ ^– uptake and nitrate reductase activity were also higher. The results are summarized in a model of water and nutrient transport to, and uptake by, non-mycorrhizal roots of Norway spruce in a forest stand. Model calculations indicate that delivery to the roots by mass flow may meet most of the plant demand of nitrogen and calcium, and that non-mycorrhizal root tips have the potential to take up most of the delivered nitrate and calcium.     

Effects of acid irrigation and liming on two clones of Norway spruce

Summary The effect of acid irrigation on the growth of rooted cuttings ofPicea abies (L.) Karst, was investigated in a pot experiment lasting 3 years. It involved two clones of Norway spruce, H 253 Bogstad I and H 254 Bogstad II. Irrigation water of pH 5.4, 4.0, 3.0 and 2.5 was used. Liming was included in the experiment.After the experimental period, the plants of all treatments were growing reasonably well. However, those plants irrigated at pH 2.5 were slightly discoloured. The plant mortality was only 3% throughout the experiment, and was not connected to acid irrigation. The limiting growth factor was N. All other nutrient elements measured in the plants were close to optimal concentration. Plants irrigated at pH 2.5, and to some extent at pH 3, contained excessively high concentrations of Al, t-S and SO₄. The total amount of Ca, Fe and Mn taken up by the plants decreased with increasing soil acidity. The increased growth of clone H 254 relative to H 253, produces a corresponding impression on soil characteristics. Soil acidity is governed by acid irrigation and CaCO₃ application, but the clonal effects are also of importance. Norway spruce appears to be tolerant to Al concentrations as high as 50 mmol/kg in the needles.     

Assessing the response of forest productivity to climate extremes in Switzerland using model–data fusion

The response of forest productivity to climate extremes strongly depends on ambient environmental and site conditions. To better understand these relationships at a regional scale, we used nearly 800 observation years from 271 permanent long‐term forest monitoring plots across Switzerland, obtained between 1980 and 2017. We assimilated these data into the 3‐PG forest ecosystem model using Bayesian inference, reducing the bias of model predictions from 14% to 5% for forest stem carbon stocks and from 45% to 9% for stem carbon stock changes. We then estimated the productivity of forests dominated by Picea abies and Fagus sylvatica for the period of 1960–2018, and tested for productivity shifts in response to climate along elevational gradient and in extreme years. Simulated net primary productivity (NPP) decreased with elevation (2.86 ± 0.006 Mg C ha^?1 year^?1 km^?1 for P. abies and 0.93 ± 0.010 Mg C ha^?1 year^?1 km^?1 for F. sylvatica). During warm–dry extremes, simulated NPP for both species increased at higher and decreased at lower elevations, with reductions in NPP of more than 25% for up to 21% of the potential species distribution range in Switzerland. Reduced plant water availability had a stronger effect on NPP than temperature during warm‐dry extremes. Importantly, cold–dry extremes had negative impacts on regional forest NPP comparable to warm–dry extremes. Overall, our calibrated model suggests that the response of forest productivity to climate extremes is more complex than simple shift toward higher elevation. Such robust estimates of NPP are key for increasing our understanding of forests ecosystems carbon dynamics under climate extremes.     

Linking variability of tree water use and growth with species resilience to environmental changes

Tree growth is an indicator of tree vitality and its temporal variability is linked to species resilience to environmental changes. Second-order statistics that quantify the cross-scale temporal variability of ecophysiological time series (statistical memory) could provide novel insights into species resilience. Species with high statistical memory in their tree growth may be more affected by disturbances, resulting in lower overall resilience and higher vulnerability to environmental changes. Here, we assessed the statistical memory, as quantified with the decay in standard deviation with increasing time scale, in tree water use and growth of co-occurring European larch Larix decidua and Norway spruce Picea abies along an elevational gradient in the Swiss Alps using measurements of stem radius changes, sap flow and tree-ring widths. Local-scale interspecific differences between the two conifers were further explored at the European scale using data from the International Tree-Ring Data Bank. Across the analysed elevational gradient, tree water use showed steeper variability decay with increasing time scale than tree growth, with no significant interspecific differences, highlighting stronger statistical memory in tree growth processes. Moreover, Norway spruce displayed slower decay in growth variability with increasing time scale (higher statistical memory) than European larch; a pattern that was also consistent at the European scale. The higher statistical memory in tree growth of Norway spruce in comparison to European larch is indicative of lower resilience of the former in comparison to the latter, and could potentially explain the occurrence of European larch at higher elevations at the Alpine treeline. Single metrics of resilience cannot often summarize the multifaceted aspects of ecosystem functioning, thus, second-order statistics that quantify the strength of statistical memory in ecophysiological time series could complement existing resilience indicators, facilitating the assessment of how environmental changes impact forest growth trajectories and ecosystem services.     

洮河上游紫果云杉种群结构特征

该研究以洮河上游尕海-则岔自然保护区、卡车林区和冶力关林区的紫果云杉(Picea purpurea)天然种群为研究对象, 通过样地调查和数据统计, 绘制种群结构图, 编制静态生命表, 拟合并分析存活曲线, 运用数量化方法研究种群动态, 揭示种群生存现状, 预测种群发展趋势, 以期为该物种的保护、管理及结构恢复提供理论依据。结果显示: 3个林区紫果云杉种群自然更新能力强, 幼苗、幼树储量丰富, 幼小龄期死亡率普遍偏高; 尕海-则岔种群存活曲线符合Deevey-III型, 种群稳定结构完整, 卡车林区和冶力关林区种群存活曲线均符合Deevey-II型, 且均出现了局部衰退; 3个林区种群动态指数均大于0, 说明种群均属于增长型, 增长潜力为尕海-则岔>卡车>冶力关; 受随机干扰时卡车林区紫果云杉最敏感, 冶力关次之, 尕海-则岔种群最稳定。该研究表明: 竞争和自疏作用是造成紫果云杉幼小龄级个体存活率偏低的普遍因素, 3个林区不同的生存状况反映了紫果云杉种群在不同生境及生活史下生存能力的差异, 保护幼苗生存环境并提高幼苗质量和存活率是种群更新和发展的关键。尕海-则岔紫果云杉生存良好, 种群生存状况主要受自身生物学特性和环境因子的影响; 卡车林区主要受人为影响, 种群结构遭到破坏; 冶力关林区受分布限制, 造成种群结构不稳定, 须采取一定的人工措施来促进种群更新与增长。     

增温、施肥与种内竞争的交互作用对云杉根系属性的影响

增温、施肥与种内竞争的交互作用对云杉根系属性的影响 物种竞争、气温和土壤养分是青藏高原东部高寒地区影响树木生长的重要因素。虽然已开展了大量关于物种竞争、气温、施肥单因素对树木生长的影响研究,但关于这三者的交互作用对根系生长的影响还知之甚少。因此,本研究拟通过测量根系属性(细根长、根表面积、比根长、比表面积、根尖数、根系分支数等)、根生物量,以及根系养分吸收,研究施肥和增温对物种竞争的影响,并进一步探讨施肥、增温与物种竞争的交互作用对云杉(Picea asperata)生长的影响机制以及所采取的适应策略。研究结果表明,增温、施肥和竞争均提高了细根的氮、钾浓度,但并未影响细根生物量和根长、根表面积、根尖数和根分支数等根系特征。然而,无论是增温、施肥,或是它们的联合作用,与物种竞争进行交互时,均增加了根长、根表面积、根尖数、根系分支数和养分吸收。此外,施肥降低了根比表面积、比根长和单位面积的根尖数和根分支数,增温和竞争的交互作用使根比表面积、比根长下降,其他参数不受温度和竞争的影响。该结果表明,云杉在物种竞争、气候变暖、施肥及其交互作用下保持着保守的营养策略。该研究加强了对树木应对全球变化的生理和生态适应性的理解。     

Direct response of tree growth to soil water and its implications for terrestrial carbon cycle modelling

Wood growth constitutes the main process for long‐term atmospheric carbon sequestration in vegetation. However, our understanding of the process of wood growth and its response to environmental drivers is limited. Current dynamic global vegetation models (DGVMs) are mainly photosynthesis‐driven and thus do not explicitly include a direct environmental effect on tree growth. However, physiological evidence suggests that, to realistically model vegetation carbon allocation under increased climatic stressors, it is crucial to treat growth responses independently from photosynthesis. A plausible growth response function suitable for global simulations in DGVMs has been lacking. Here, we present the first soil water‐growth response function and parameter range for deciduous and evergreen conifers. The response curve was calibrated against European larch and Norway spruce in a dry temperate forest in the Swiss Alps. We present a new data‐driven approach based on a combination of tree ring width (TRW) records, growing season length and simulated subdaily soil hydrology to parameterize ring width increment simulations. We found that a simple linear response function, with an intercept at zero moisture stress, used in growth simulations reproduced 62.3% and 59.4% of observed TRW variability for larch and spruce respectively and, importantly, the response function slope was much steeper than literature values for soil moisture effects on photosynthesis and stomatal conductance. Specifically, we found stem growth stops at soil moisture potentials of ?0.47 MPa for larch and ?0.66 MPa for spruce, whereas photosynthesis in trees continues down to ?1.2 MPa or lower, depending on species and measurement method. These results are strong evidence that the response functions of source and sink processes are indeed very different in trees, and need to be considered separately to correctly assess vegetation responses to environmental change. The results provide a parameterization for the explicit representation of growth responses to soil water in vegetation models.     

Pollen Phenology of the Most Important Trees in Finland

The pollen frequency of Alnus correlated negatively at the 10% level with the daily mean temperature and at the 5% level with the temperatures of the previous day, and of the same week in 1975; and with the same levels of chance with humidity in 1974. The pollen frequency of Betula correlated positively with the mean temperature both of the same and previous day. Because of the rainy year 1974, birch pollen amount correlated very significantly negatively with humidity. The correlations showed the same tendencies in the other two years. The Pinus pollen frequency correlated positively with the mean daily temperature either at the 0.1% or 1% level, and in the same way with the mean temperature of the previous day. The correlation ofPinus to humidity was negative. Pine pollen showed fairly significant negative correlation with the snow cover thickness in 1974 and 1976. In 1975, there was less snow in S. Finland than normally, and Pinus had no significant correlations to this factor.