Shoot nitrate reductase activities of field‐layer species in different forest types. II

Analysis of in vivo shoot nitrate reductase activity (NRA) of the grass Deschampsia flexuosa (L.) Trin. has been proposed as a method of indicating the availability of nitrate in northern temperate forest soils. We report the seasonal variation in NRA and the influence of temperature on the NRA assay. Studies were performed in the field or on natural populations on topsoil monoliths in a greenhouse.

The induced in vivo NRA as measured at 28°C was higher in plants grown at lower than at higher temperatures within the range 4–20°C, although the induction was faster at higher temperatures. When the assay was performed at various temperatures, enzyme activity was much lower at lower temperatures. The accumulation of organic nitrogen in shoots showed that reduction actually increased with temperature. Transfer of monoliths from high to low temperature led to an increase of in vivo NRA within a day, whereas the decline caused by the reverse began after six days. Variations in temperature accounted for between 0 and 80% of the seasonal variation in NRA in the field, depending on the influence of the variability in nitrate supply.

Maximally induced NRA after application of nitrate was mostly higher in a clearfelling than in a closed forest. In the forest, there was a close correlation between current and maximally induced NRA. One interpretation of this result is that low availability of nitrogen may have been a cause of the lower maximally induced NRA there. This is supported by results from other studies.

We conclude that variations in temperature and availability of nitrogen, particularly nitrate, are largely responsible for seasonal variations in NRA. The influence of temperature can be adjusted for.     

Impact of sod-cutting and choppering on nutrient budgets of dry heathlands

Heathlands are endangered by both atmospheric nutrient deposition and natural succession. High-intensity management measures are considered necessary, as low-intensity measures (e.g. mowing, prescribed burning) are not able to compensate for atmospheric nutrient loads. Choppering (i.e. the near-complete removal of the O-layer) has several advantages over sod-cutting, including less waste material, faster vegetation recovery and lower costs. This raises the question addressed in this study as to the extent to which choppering and sod-cutting affect nutrient budgets in dry heathlands.We compared the quantities of N, Ca, K, Mg, and P removed by choppering and sod-cutting in the Lueneburg Heath (NW Germany). Nutrient balances were calculated by analysing atmospheric inputs, elevated leaching rates following management, and output due to the removal of above-ground biomass and humus horizons.Nutrient loss was particularly high after removal of O- and A-horizons. In contrast, increased leaching after management was of minor importance for nutrient budgets. Although considerably more nutrients were removed by sod-cutting than by choppering (e.g. N: 1712/1008 kg ha⁻¹), nutrient output by choppering was still sufficient to compensate for 60.7 years of net N-input. Choppering was able to remove more N per volume unit than sod-cutting due to higher N-contents in the organic layer than in the A-horizon. For this reason, choppering is more economical than sod-cutting and, thus, should be considered the preferable method at sites not dominated by Molinia caerulea. A combination of high-intensity measures with prescribed burning would appear to be suitable as this would ensure more selective removal of N.     

Snow mould caused by a Pythium sp.: a potential vascular plant pathogen in the maritime Antarctic

The pathogenicity of an isolate of a Pythium species from Signy Island in the South Orkney Islands was tested against the Antarctic hairgrass Deschampsia antarctica. The isolate was found to infect plants at 8ºC and to cause foliar and root symptoms similar to those seen in other Pythium infections in grasses. Analysis of ribosomal RNA sequences placed it, together with another isolate from Antarctica, in a clade that included the known snow moulds caused by Pythium spp. Sporangia and oogonia were produced in culture, but the isolate differed from other Pythium spp. in producing chlamydospores in older cultures and plant tissue. This is the first report of a pathogen of an eukaryotic vascular plant in the maritime Antarctic region.     

水分逆境对发草脯氨酸及其代谢途径的影响

本研究以发草为研究对象,通过盆栽模拟水分胁迫,研究干旱、水涝胁迫下发草地上部分及根系中脯氨酸(Pro)积累状况及其代谢途径中底物、中间产物和关键酶的变化.结果显示:1)干旱胁迫和水涝胁迫均使发草Pro含量显著升高(P<0.05),相同的水分处理下发草地上部分及根系中Pro含量相差不大.2)干旱胁迫和水涝胁迫下,发草地上...     

黄河源区发草适生地植物群落特征及其土壤因子解释

本研究以黄河源区发草作为研究对象,通过生境地植物群落物种结构组成、多样性分布、土壤理化特性等调查,采用相关分析和RDA排序法分析了黄河源区玛沁县5个发草适生地植物群落多样性特征和土壤影响因子及其关系,以期揭示影响发草种群在复杂多样高寒沼泽异质生境中适应性的关键环境因子.结果表明:1)不同发草适生地植物群落结构、组成和多...     

Seasonal variations and effects of nutrient applications on N and P and microbial biomass under two temperate heathland plants

Eutrofication is a threat against nutrient-poor habitats as increased amounts of nutrients in ecosystems may cause changes in the vegetation. Nitrogen (N) deposition leads to conversion of Calluna heathlands into graminoid dominated heath, but low availability of P may hinder or slow down this process.In this study the soil properties under two dominant heathland plants, the dwarf shrub Calluna vulgaris and the grass Deschampsia flexuosa, were investigated, with focus on nutrient content in the organic top soil and soil microbes during the main growing season and effects of nutrient amendments. The concentration of inorganic and dissolved organic N was significantly higher under D. flexuosa than C. vulgaris all though there were the same amounts of total N in the soil below the two species. N and P amendment enhanced available N and P in the soil, but added nutrients had little direct effects on microbes. The microbial biomass on the other hand was positively related to soil water content in fertilized plots indicating that this was due to an indirect effect of enhanced nutrient availability. Microbial N and P pools were respectively 1000 and 100 times higher than the pool of inorganic N and P, and microbes therefore may play an important role in regulating plant nutrient supply. Judged from responses of inorganic and microbial N and P concentrations to added N and P, N seemed to limit C. vulgaris and soil microbes below while P seemed to limit D. flexuosa and soil microbes below this species. There were lower rates of net nitrification, net ammonification and DOC and DON production rates during winter in the soil under C. vulgaris than below D. flexuosa, although all these rates were equal under the two species on an annual basis. This indicates that these microbial processes were taking place during winter but were affected by exudates from C. vulgaris.     

底质与水深对大叶藻和丛生大叶藻分布的影响

考察了烟台玉岱山、担子岛和荣成褚岛海域106个采样点的大叶藻种类的分布及各采样点不同表层底质（深度3 cm以内）、根部底质（深度3～15 cm）和水深等级。对不同底质与水深条件下大叶藻Zostera marina和丛生大叶藻Z.caespitosa的出现频率进行χ2检验。结果表明：不同大叶藻的分布与表层底质、根部底质变化呈极显著相关关系（P〈0.01）,列联系数分别为0.612和0.640;与水深等级变化的相关性虽然显著,但列联系数仅为0.338。在表层底质、根部底质和水深等级3种因素中,两物种的分布与根部底质类型相关性最大,与表层底质类型相关性次之。研究表明,两种大叶藻在不同底质上分布的差异明显,大叶藻偏好泥与泥沙底质,而丛生大叶藻偏好沙与砾石底质。     

Comparison of Four Different Extraction Methods to Assess Plant Availability of Some Metals in Organic Forest Soil

Abstract

The objective was to find an uncomplicated test giving the best correlation between calcium (Ca), magnesium (Mg), manganese (Mn), copper (Cu), zinc (Zn), and lead (Pb) extracted from humic forest soil and the total concentration of the element in some understorey forest plants using well‐known extractants. The elements were selected because Ca, Mg, Mn, Cu, and Zn are essential nutrients to plants and Zn and Pb are potentially harmful heavy metals received over the years in the southern parts of Norway by long‐range atmospheric transport. Extraction of organic podzolic surface soil (Oe and Oa horizon) from 17 different pine forests in central and southern Norway was carried out with four different reagents to evaluate uptake of Ca, Mg, Mn, Cu, Zn, and Pb in the understorey plants Deschampsia flexuosa, Vaccinium myrtillus (leaves and stems), and Vaccinium vitis‐idaea (leaves and stems). The NH₄OAc, NH₄NO₃, HCl, and EDTA solutions used to extract the soil in addition to concentrated HNO₃, demonstrated variability in capacity to extract the different elements from the soil. The extractants yielded significant relations between concentrations of Ca, Mn, and Pb in the Oe or Oa horizon and some of the plants or plant compartments, even though distinct correlation was more dependent on species and plant part than the actual extractant used. In the case of Zn, Cu, and Mg only a few sporadic correlations were observed between the different plant/plant compartments and the element concentrations in the soil extracts. Altogether none of the extractants was shown to be superior to the others in providing the best correlation with the elements concentrations in selected plant/plant compartments. In the case of Ca, Mn, and Pb all the extractants including concentrated HNO₃ provided significant correlations with at least some of the selected plant/plant compartments.     

Effects of habitat management on heathland response to atmospheric nitrogen deposition

A field experiment was carried out to investigate the impact of four different management treatments on the response of Calluna-dominated heathland to nitrogen additions of 0 or 30 kg ha⁻¹ yr⁻¹ at a lowland heath in Surrey, England. Post-management Calluna regeneration, growth and canopy development were significantly affected by both the form of management and by nitrogen addition. The effect of nitrogen on shoot growth was lower, in absolute terms, in those plots which had undergone more intensive management treatments. Seedling establishment was higher in plots which received a simulated accidental burn treatment, reflecting the greater proportion of bare ground and the high degree of physical disturbance associated with this treatment. Invasion by Deschampsia seedlings was increased by nitrogen addition, particularly in simulated accidental burn plots. In the long term, the need to maintain a low nutrient environment to favour Calluna dominance, particularly in the face of elevated nitrogen deposition, favours the use of managements which result in the export of a significant proportion of the organic nitrogen stores. However, further study is required to ensure that initial enhancement of seedling invasion by grass and other species, associated with these more intense managements, does not outweigh the long term benefits of associated nutrient removal.     

发草栽培驯化研究初报

对果洛州玛沁县野生草种发草进行了驯化栽培的初步研究,结果表明∶发草在海拔高度3800m左右的果洛地区人工栽培条件下第2年起能完成整个生育期,生育天数为130d;栽培当年生长缓慢,第2年起生长迅速,第3年长势达到高峰,株高可达81.6cm,盖度达到98.0%,越冬率达到99.0%,干草产量和种子产量分别为4426.2kg/hm^2和482.8 kg/hm^2,表现出了良好的生态性能和栽培性能;发草叶量丰富,适口性好,适合刈牧兼用,喜潮湿地带生长,可作为高寒草甸(尤其是高寒沼泽草甸)退化草地植被恢复与重建的优良草种和先锋草种。