Dirk Gansert

Root respiration and its importance for the carbon balance of beech saplings (Fagus sylvatica L.) in a montane beech forest

Root respiration of 10-year-old beech saplings (Fagus sylvatica L.) grown in the understorey (UND) and in a natural gap (GAP) of a mature beech forest in the Solling mountains, FRG, was investigated from April until December, 1990. Respiration rates of fine, medium and coarse roots were measured in situ by a PC-controlled cuvette system. Fine root respiration rates were in the range of 0.5–9.8 nmol CO2 gDW−1 s−1 at both sites, but respiration rates of UND saplings were higher, compared to those of GAP saplings. The dependence of respiratory activity on soil temperature proved to be highly significant (p<0.001) for both plots, following a quasi-Arrhenius type curve. Fine root respiration rates of UND saplings were highly significantly, negatively correlated with the water content of the attached organic material, whereas respiration rates of GAP saplings did not show such a correlation. Further, a significant correlation (p<0.01) between mycorrhizal biomass and respiration rate was detected at the UND site, but not at the GAP site. Medium and coarse root respiration rates were very similar and no significant differences between the two sites were detected. Maximum respiration rates of 3.1 nmol CO2 gDW−1 s−1 were reached in the middle of July. Due to low light intensities in the under storey, daily net CO2 assimilation rates of UND saplings were much smaller than those of GAP saplings. At both sites, net CO2 assimilation rates varied more than respiration rates and thus the carbon balance of beech saplings was more affected by the rate of carbon fixation than by the rate of respiratory carbon loss.

Storage and mobilization of nonstructural carbohydrates and biomass development of beech seedlings (Fagus sylvatica L.) under different light regimes

Abstract Beech seedlings were grown under 8%, 13%, 23% and 100% relative light intensity for 2 years after germination. Starch, sucrose and monosaccharides from the bark and wood parenchyma of shoots and roots were analyzed during the course of the second year. The annual allocation pattern of starch revealed five successive phases: starch disintegration in November (1) was paralleled by high monosaccharide concentrations in the shoot cortex (≤ 33.4 mg/g DW). Seedlings of all light variants reached maximum sucrose concentrations (≤ 82.8 mg/g DW) during starch disintegration in January (2) that coincided with decreased monosaccharide contents. Up to mid-April, resynthesis of starch (3) occurred in most shaded and unshaded seedlings. In May, starch was converted into monosaccharides in all storage tissues (4). Seedlings grown under 13% light intensity showed de novo synthesis of starch (5) 4 weeks after bud burst. These seedlings reached 98% maximum starch storage capacity of the shoot and 89% of the root in July. In mid-October, the maximum starch concentration of the roots increased with light intensity, and this corresponded with an increase of lateral root growth. The variation of shoot and root dry weight was closely related to the content of nonstructural carbohydrates during the second year. The shift of shoot growth to the first half of the growing season and the suppression of lateral root growth during the second half is assumed to be a strategy of young beech to survive under light limiting conditions.

The inhibiting effect of nitrate fertilisation on methane uptake of a temperate forest soil is influenced by labile carbon

Upland soils are the most important terrestrial sink for the greenhouse gas CH4. The oxidation of CH4 is highly influenced by reactive N which is increasingly added to many ecosystems by atmospheric deposition and thereby also alters the labile C pool in the soils. The interacting effects of soil N availability and the labile C pool on CH4 oxidation are not well understood. We conducted a laboratory experiment with soil columns consisting of homogenised topsoil material from a temperate broad-leaved forest to study the net CH4 flux under the combined or isolated addition of NO3− and glucose as a labile C source. Addition of NO3− and glucose reduced the net CH4 uptake of the soil by 86% and 83%, respectively. The combined addition of both agents led to a nearly complete inhibition of CH4 uptake (reduction by 99.4%). Our study demonstrates a close link between the availability of C and N and the rate of CH4 oxidation in temperate forest soils. Continued deposition of NO3− has the potential to reduce the sink strength of temperate forest soils for CH4.

Treelines of the Japanese Alps – altitudinal distribution and species composition under contrasting winter climates

Summary In Japan, contrasting winter climate conditions between the Sea of Japan and the Pacific Ocean side have created conspicuous differences in species composition and altitudinal distribution of subalpine forests and treeline ecotones. In the Japanese Alps the altitudinal distribution of principal subalpine and treeline tree species was investigated along the slopes of four mountain ranges, two located in snowy regions facing the Sea of Japan (Mt. Hakusan, Mt. Naeba), and two with little snow cover located near the Pacific Ocean (Mt. Akaishi, Mt. Fuji). On Mt. Fuji many years of temperature records at different altitudes up to the treeline and at the summit provided the database for calculation of monthly lapse rates of air temperature, particularly the decrease of absolute and mean minima. High and prolonged snow cover causes the descent of the upper distribution limit of the subalpine coniferous forest by 800 to 1000 m altitude towards the Sea of Japan. A subalpine deciduous broad-leaved woodland of 500 m of vertical spread is formed only on snowy mountains, and does not exist on the Pacific Ocean side. With reference to Betula ermanii, the thermal upperdistribution limit of treelines in the Japanese Alps unimpaired by snow is determined by two periods of minimum temperature: (1) periods of subzero temperature which determine the occurrence of spring frost injury and affect the onset of the growing season, (2) minimum temperatures during the growing season which affect the thermal-time requirement (TTR) for fully differentiated tissues in overwintering plant organs. It is suggested to quantify TTR as thermal sum [(t–5.5), given in day-degrees], where t is the daily minimum air temperature above 5.5°C during the growing season. For B. ermanii the TTR is 210 day-degrees, which corresponds to 82 d of growing season length at the species’ upper distribution limit at 2800 m altitude. The descent of deciduous treelines on snowy mountains in humid northeastern Asia below the general thermal forest line of the Northern Hemisphere is discussed in terms of a hypoxia-induced carbohydrate limitation hypothesis. Tree survival will be im-paired by high and prolonged snow cover if oxygen deprivation causes hypoxia in wood parenchymas, which in turn will accelerate the depletion of nonstructural carbohydrate reserves. The impact of oxygen deprivation will increase towards spring, when most of the nonstructural reserve carbohydrates have been consumed so that enhanced ATP demand of live tissues at that time cannot be further compensated.

Seasonal variation of branch respiration of a treeline forming (Betula ermanii Cham.) and a montane (Fagus crenata Blume) deciduous broad-leaved tree species on Mt. Fuji, Japan

Summary In this study we focus on four particular aspects in the field of ecological studies of woody tissue respiration: 1) the application of the non-destructive soda lime technique to the in situ measurement of CO 2 efflux rates from branches or stems of standing trees all year round; 2) the investigation of respiration rates of branches of similar diameter but different positions in the canopy; 3) the comparative study of seasonal variation and long-term thermal acclimation of branch respiration along an altitudinal transect up to the treeline; 4) the comparison of branch respiration between a treeline forming ( Betula ermanii ) and a montane ( Fagus crenata ) deciduous broad-leaved tree species in order to evaluate the relevance of woody tissue respiration to tree survival in low temperature climates. No qualitative differences in respiratory behaviour between the treeline forming B. ermanii and the montane F. crenata were found in this study. Significantly higher respiration rates of upper crown branches of both tree species were due to biogenic factors which were spatio-temporally unevenly effective within the crown. In early spring, branch respiration rose independently of xylem temperature. This was caused by an increase in metabolic activity of branch parenchymatous tissues associated with the phenological development of the buds. During summer, the CO 2 efflux of upper crown branches reached up to sixfold higher rates than that of lower crown branches. This was associated with secondary thickening being more pronounced in the upper crown. During winter, higher rates of maintenance respiration in the upper crown reflected different physiological states of branches, probably with respect to protein metabolism involved in processes of cold resistance of live branch tissues. As shown in this study, thermal acclimation of branch respiration is occuring at a similar level as was reported for leaves of herbaceous alpine plants. The tendency for a lower activation energy for respiration towards low temperature climatic conditions points to a physiologically driven increase in respiratory capacity in branches of B. ermanii and F. crenata . In treeline forming tree species a decrease in activation energy may contribute to keep respiratory activity relatively unaffected by large daily temperature fluctuations of more than 25°C during the cold season. In this study, no evidence was found that branch respiration may act as an ecophysiologically limiting parameter for the survival of Betula ermanii at its present upper distribution limit in the Japanese Alps.

Modelling the influence of climatic variability on carbon and water budgets of beech saplings (Fagus sylvatica L.) based on field data

Abstract A simulation model of perennial courses of carbon and water budgets of beech saplings from a temperate deciduous forest is presented. It is based on empirical results from steady-state field measurements of the rates of net assimilation, transpiration and respiration in the Solling area, Germany. The driving climatic variables (distribution of radiation, temperature and moisture in air and soil) were determined in 32 complete diurnal courses at the site. To get a complete data set covering the entire growing season, the relationship between in-canopy conditions and standard weather data supported by a nearby meteorological station was studied. By harvesting six sample trees the model output was related to dry matter of the plant compartments leaf (14.4 g), stem (57.1 g), main root (19.9 g), and lateral roots (17.9 g on average), respectively. Climate-induced differences of seasonal gross/net carbon uptake, relative growth rate and water-use efficiency were calculated using data of three years with different mean weather conditions (intermediate, wet/cold, dry/warm) for the simulation run. The model gave seasonal rates of relative growth, which were highest in the intermediate year (77%) and, due to large respiration losses, lowest in the warm/dry year (58%). Mostly affected was the seasonal transpiration coefficient showing highest value in the warm/dry year (416 g H 2 O g −1 dry matter produced) and lowest in the cold/wet year (242 g H 2 O g −1 dry matter).

The Use of Planar Optodes in Root Studies for Quantitative Imaging

The present state-of-the-art optical sensors – planar optodes – as a technology for noninvasive bioprocess analysis for rhizosphere research are presented. The measuring principle of planar optodes is described very briefly and their advantage over conventional techniques is discussed. The different ways of application of planar optodes for the quantitative imaging of rhizospheric parameters like pH, O2, CO2, or ammonium concentration are described. The core of this chapter is a review of the application of planar optodes in rhizosphere research since the first approach 5 years ago, highlighting the great potential of this technology.

Organismic Interactions and Plant Water Relations

Plants normally function as physiological units that respond to ambient conditions regulating their water relations, mostly independent of other organisms that co-occur in the same habitat. However, water consumption from the soil and vapor transpiration into the atmosphere can influence local pedospheric and atmospheric conditions in a rather specific manner. Feedback can occur in this way, from a plant community as part of the biotic component of an ecosystem, to the abiotic parameters of the habitat. Competition for soil water reserves results from these interactions, and the canopy microclimate that influences transpiration rates can deviate drastically from the conditions that would control latent heat exchange of a solitary plant under the temperature and humidity conditions of the mixed layer of the atmosphere. Moreover, quite often plant water relations are influenced directly by other organisms that interact with a plant individual in mutualistic, parasitic or symbiotic ways. Other plant individuals, fungi and microorganisms as well as animals are such interacting partners.

Root and Stem Respiration of Beech Saplings in the Understorey — Studies of Carbon Balance in a Montane Beech Forest ( Fagus sylvatica L. ) in the Solling Area, FRG.

In cool temperate forests, the total respiration of trees is estimated to be 40–60% of gross photosynthesis (3,6,8,9). Root and stem respiration of a one hundred year-old beech tree (F. sylvatica) was calculated as being 27–30% of net photosynthesis (7). Investigations on the respiration of beech fine roots done in 1972/73 yielded a release of 0.41 mmol CO 2 * g DW -1 *d -1 as an annual mean value (4). This release was calculated as being 36% of daily net assimilation rate (7).