Showing papers by "Ernst Detlef Schulze published in 2003"

The role of plant diversity and composition for nitrate leaching in grasslands

Abstract: The relationship between plant diversity and nitrate leaching into groundwater was investigated in a mid-European semi-natural grassland ecosystem. An experimental approach was used to directly manipulate plant diversity in the field, while holding other environmental factors constant. Species loss was simulated by establishing grassland communities of 16, 8, 4, 2, 1, and 0 plant species, composed of 3, 2, or 1 functional groups (grasses, legumes, and non-legume herbs). Every diversity treatment was replicated with several different species mixtures. Nitrate leaching was determined by continuous extraction of soil solution below the rooting zone and modeling of seepage rates. The concentration of nitrate in the soil solution was highly variable within each level of diversity. In bare ground plots and several low-diversity mixtures containing legumes, nitrate concentrations were higher than the official European Union threshold value for drinking water of 50 mg/L, with maximum values of up to 350 mg/L measured in Trifolium pratense monocultures. Total annual loss of nitrate was unaffected by the number of plant species or functional groups, but it was highly dependent on the specific species composition of the communities, and plots with legumes lost significantly more nitrate than plots without them. Aboveground biomass had no influence on nitrate loss, whereas leaching was negatively correlated with increasing root biomass. The abundance of legumes within a community, litter decomposition rates, and net nitrification were all positively correlated with total nitrate loss. However, in those communities containing legumes, leaching decreased with increasing diversity, because higher species richness led to a reduction in legume dominance, to a reduced nitrate supply through nitrification, and to a complementary uptake of nitrate by grasses and non-leguminous herbs. Based on these results, we expect that increasing the diversity of non-leguminous species or functional groups would reduce the risk of nitrate leaching in low-diversity grass–clover mixtures of ley-farming systems, while allowing for a more efficient exploitation of the beneficial fertilization effect provided by legumes. Corresponding Editor: M. Loreau.

How surface fire in Siberian Scots pine forests affects soil organic carbon in the forest floor: Stocks, molecular structure, and conversion to black carbon (charcoal)

Abstract: [1] In boreal forests, fire is a frequent disturbance and converts soil organic carbon (OC) to more degradation-resistant aromatic carbon, i.e., black carbon (BC) which might act as a long-term atmospheric-carbon sink. Little is known on the effects of fires on boreal soil OC stocks and molecular composition. We studied how a surface fire affected the composition of the forest floor of Siberian Scots pine forests by comparing the bulk elemental composition, molecular structure (13C-MAS NMR), and the aromatic carbon fraction (BC and potentially interfering constituents like tannins) of unburned and burned forest floor. Fire reduced the mass of the forest floor by 60%, stocks of inorganic elements (Si, Al, Fe, K, Ca, Na, Mg, Mn) by 30–50%, and of OC, nitrogen, and sulfur by 40–50%. In contrast to typical findings from temperate forests, unburned OC consisted mainly of (di-)O-alkyl (polysaccharides) and few aromatic structures, probably due to dominant input of lichen biomass. Fire converted OC into alkyl and aromatic structures, the latter consisting of heterocyclic macromolecules and small clusters of condensed carbon. The small cluster size explained the small BC concentrations determined using a degradative molecular marker method. Fire increased BC stocks (16 g kg−1 OC) by 40% which translates into a net-conversion rate of 0.7% (0.35% of net primary production) unburned OC to BC. Here, however, BC was not a major fraction of soil OC pool in unburned or burned forest floor, either due to rapid in situ degradation or relocation.

Microbial characteristics of soils on a latitudinal transect in Siberia

Abstract: Soil microbial properties were studied from localities on a transect along the Yenisei River, Central Siberia. The 1000 km-long transect, from 56°N to 68°N, passed through tundra, taiga and pine forest characteristic of Northern Russia. Soil microbial properties were characterized by dehydrogenase activity, microbial biomass, composition of microbial community (PLFAs), respiration rates, denitrification and N mineralization rates. Relationships between vegetation, latitude, soil quality (pH, texture), soil organic carbon (SOC) and the microbial properties were examined using multivariate analysis. In addition, the temperature responses of microbial growth (net growth rate) and activity (soil respiration rate) were tested by laboratory experiments. The major conclusions of the study are as follows: 1. Multivariate analysis of the data revealed significant differences in microbial activity. SOC clay content was positively related to clay content. Soil texture and SOC exhibited the dominant effect on soil microbial parameters, while the vegetation and climatic effects (expressed as a function of latitude) were weaker but still significant. The effect of vegetation cover is linked to SOC quality, which can control soil microbial activity. 2. When compared to fine-textured soils, coarse-textured soils have (i) proportionally more SOC bound in microbial biomass, which might result in higher susceptibility of SOC transformation to fluctuation of environmental factors, and (ii) low mineralization potential, but with a substantial part of the consumed C being transformed to microbial products. 3. The soil microbial community from the northernmost study region located within the permafrost zone appears to be adapted to cold conditions. As a result, microbial net growth rate became negative when temperature rose above 5 °C and C mineralization then exceeded C accumulation. (Less)

Age-dependence of the antioxidative system in tobacco with enhanced glutathione reductase activity or senescence-induced production of cytokinins

Abstract: Tobacco leaves of plants with enhanced glutathione reductase activity (GR46-27, Nicotiana tabacum L. cv. Samsun) or with autoregulated senescence-induced production of cytokinins (P SAG12 -IPT, N. tabacum L. cv. Wisconsin) were studied during the course of leaf development and senescence by measuring photosynthesis, chlorophyll and protein content, the antioxidants ascorbate, glutathione and α-tocopherol as well as the antioxidative enzymes ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2) and superoxide dismutase (SOD, EC 1.15.1.1). The photosynthetic rate, as well as the chlorophyll and protein content, dropped with increasing leaf age after having reached a maximum at the end of the exponential growth phase. The concentrations of the water-soluble antioxidants ascorbate and glutathione fell continuously with age, whereas the concentration of the lipophilic a-tocopherol increased. The activities of the antioxidative enzymes APX, GR and SOD reached their maximum at the beginning of leaf development, but were reduced in senescing leaves. The age-dependent course of the measured leaf parameters in GR46-27 leaves was similar to the one in wild-type leaves, with the exception of an overall enhanced GR activity. In contrast, in old leaves of P SAG12 -IPT plants, which possess a much higher life span, the chlorophyll and protein content, the photosynthetic rate, the antioxidant concentrations of ascorbate and glutathione as well as the activities of the antioxidative enzymes were higher than in wild-type leaves. The results show that the capacity of the antioxidative system to scavenge radicals is sufficiently balanced with the plant metabolism, and its decline with increasing age is not the cause, but a consequence of senescence and ageing in plants.

Spruce forests (Norway and Sitka spruce, including Douglas fir): Carbon and water fluxes, Balances, Ecological and ecophysiological determinants

Abstract: Natural forests with a high percentage of spruce will be found in Europe only in subalpine and alpine regions or in the boreal forests of Scandinavia and Russia. Nevertheless, spruce belongs to the most important European tree species. Due to its favorable architecture and rapid growth, management practices have led to widespread monospecific spruce forests in a latitude band between 45 and 55°N. Only recently have other species such as beech and oak been included in afforestation efforts at former pure spruce sites. So today spruce is still an important forestry tree in central Europe, with a coverage for instance of about 33 % of all forested areas in Germany (Bundesministerium fur Ernahrung, Landwirtschaft und Forsten 1999).

Making Deforestation Pay Under the Kyoto Protocol

Abstract: Current pressures to change the reforestation time limit of the Kyoto Protocol for Clean Development Mechanism sinks will create the conditions to generate carbon credits from recent deforestation of pristine tropical forests.

Conclusions: The role of Canopy Flux Measurements in Global C-Cycle Research

Abstract: The carbon cycle is central to the Earth System, being inextricably coupled with climate, the water cycle, the nutrient cycles, and the production of bio-mass by photosynthesis on land and in the oceans. Over the past century, the Earth’s carbon cycle experienced large perturbations. Since the beginning of the industrial revolution, the mean global carbon dioxide (C02) concentra-ion has risen from about 280 ppm to over 368 ppm (Conway et al. 1994; Keeling and Whorf 2002). The worldwide rise in atmospheric C02 concentration is occurring due to an imbalance between the rate at which anthropogenic and natural sources emit C02 (by burning fossil fuel and respiring) and the rate at which biospheric and oceanic sinks remove C02 from the atmosphere by photosynthesis and physio chemical processes. Superimposed on the overall trend regarding C02 is a record of great interannual variability of sources and sinks in the rate of growth of atmospheric C02. Typical values are on the order of 0.5 to 3 ppm year-1. On a mass basis, these values correspond to 1 and 5 Gt C year-1, respectively. Potential sources of year-to-year changes in C02 remain a hot topic of debate. Such variation has been attributed to El Nino/La Nina events, which cause regions of droughts or excessive rainfall (Conway et al. 1994; Keeling et al. 1995), and alterations in the timing and length of the growing season (Myneni et al. 1997; Randerson et al. 1997).

A Method of Theoretical and Experimental Evaluation of Carbon Accumulation in Bog Ecosystems

Abstract: Bog ecosystems occupy a significant part of Russia and play an important role in the turnover of major biogenic elements [1, 4]. According to latest estimates, the rate of long-term deposition of carbon from the atmosphere provided by bogs is comparable to the rate of carbon deposition provided by basic types of ecosystems [4, 8]. The annual rate of carbon deposition in a sphagnum column can be measured quantitatively if the rates of annual growth and degradation of sphagnum in layers of different ages are known. However, it is very difficult to obtain such data, because the necessary measurements should be performed for many years in bog ecosystems from different natural and climatic zones [2, 3]. Various methods are used to solve this problem. The net ecosystem efficiency of carbon accumulation (NEE) averaged over many years (hundreds and thousands of years) is calculated from peat layer thickness and basal age as determined using the radiocarbon method [4]. In contrast, direct measurements of carbon fluxes over bog ecosystems revealed annual variation in the NEE value [6]. The mean rate of peat accumulation averaged over many years is often determined using the model of vertical growth of bogs, which is based on questionable assumptions [10]. In this work, we suggest a method of estimation of this parameter. This method combines theoretical and experimental approaches to the problem and has the following specific features: (1) it can be applied to a large number of bog ecosystems and (2) it is based on the peatland characteristics that can be measured relatively easily.