Search

Aims: Shrub expansion is common in the tundra biome and has been linked to climate warming. However, the underlying mechanisms are still not fully understood. This study aimed to investigate the seasonal and vertical rooting patterns of different plant functional types, which is important for predicting tundra vegetation dynamics. Methods: We harvested root samples by soil coring and investigated seasonal changes in root biomass and vertical root distribution across a vegetation gradient, focusing on the differences between graminoids and dwarf shrubs, at a northeastern Siberian tundra. Results: Graminoid fine root biomass increased significantly during the growing season, whereas that of shrubs was already high at the beginning and did not change later on. Shrubs had a much shallower rooting pattern than graminoids. Also, shrub roots did not respond to increases in permafrost thawing depth over the growing season, whereas graminoids grew fine roots in deeper, recently thawed soil layers during the growing season. Conclusions: Our results show that shrubs are predominantly shallow-rooted and grow roots earlier than graminoids, which allows shrubs to take advantage of the nutrient pulse after snowmelt in the early growing season. In contrast, the deep-rooted graminoids can access the nutrients in deeper soil and may profit from increasing permafrost thawing depth. The outcome of the competitive interactions between graminoids and shrubs in tundra may depend on the balance between the benefits associated with earlier root growth and deeper root distribution, respectively. The shrub expansion with climate warming observed in recent decades suggests that earlier root growth in the upper soil layer may be more important than increased rooting depth later in the growing season. [ABSTRACT FROM AUTHOR]

Cover crops are plants that are integrated in the crop rotation between two cash crops. The main objectives of cover cropping are organic matter input, mitigation of nitrate leaching and reduction of soil erosion. These benefits will only be achieved efficiently if the selected cover crop species are adapted to local environmental conditions and appropriate for the defined agro-ecological target. Therefore, a main limitation in cover cropping is the lack of a comprehensive species description. An improved cover crop characterization could be achieved with quantitative parameters derived from growth functions. Here, we show the use of this approach to assess plant traits relevant for erosion control by cover cropping. An experiment with four cover crop species (phacelia, vetch, rye and mustard) was performed over two years at a semi-arid site in Eastern Austria. Canopy cover was measured four times over the vegetation period. Root length density measurements were made to 40 cm soil depth before winter. Canopy dynamics were characterized by parameters from the asymptotic Gompertz function and from an extended logistic model that includes a parameter for decay after maximum coverage. Our results show that vetch had the lowest early vigor after dry conditions at sowing, with +45% longer time to attain maximum growth rate (parameter t) than the other species. Drought during the later autumn growing period led to the highest reduction in maximum canopy cover (parameter y) for phacelia (−41%). The rooting pattern was assessed by parameters from the exponential distribution function of Gerwitz and Page. The most intense rooting near the soil surface (parameter L) was found for phacelia (9.7 cm cm). Vetch had the lowest L (4.6 cm cm) but highest root allocation to deeper soil layers. Mustard combined high average values in y (76%) and L (6.3 cm cm) with a stable growth over both years. The potential strengths of phacelia and vetch were more dependent on the particular year. Rye showed a stably high L (8.6 cm cm), but had only a low average value of ymax (55.1%). The quantitative parameter sets we derived for plant traits required for erosion control improved cover crop comparison and analysis of their local adaptation. Based on this extended species description our approach allows a better evaluation of cover crops and can be used for the optimization of management and decision support. [ABSTRACT FROM AUTHOR]

Above-ground plant growth is widely known in terms of structural diversity. Likewise, the below-ground growth presents a mosaic of heterogeneous structures of differing complexity. In this study, root system structures of heterogeneous plant communities were recorded as integral systems by using the trench profile method. Fractal dimensions of the root images were calculated from image files by the box-counting method. This method allows the structural complexity of such associations to be compared between plant communities, with regard to their potentials for soil resource acquisition and utilization. Distinct and partly significant differences are found (fractal dimension between 1.46?±?0.09 and 1.71?±?0.05) in the below-ground structural complexity of plant communities, belonging to different biotope types. The size of the heterogeneous plant community to be examined has an crucial influence on the fractal dimension of the root system structures. The structural heterogeneity becomes particularly evident (fractal dimensions between 1.32 and 1.77) when analysing many small units of a complex root system association. In larger plant communities, a broad variety of below-ground structures is recorded in its entirety, integrating the specific features of single sub-structures. In that way, extreme fractal dimensions are lost and the diversity decreases. Therefore, the analysis of larger units of root system associations provides a general knowledge of the complexity of root system structures for heterogeneous plant communities. [ABSTRACT FROM AUTHOR]

In a 2-year experiment, the evergreen shrubs Erica tetralix and Calluna vulgaris (dominant on nutrient-poor heathland soils) and the perennial deciduous grass Molinia caerulea (dominant on nutrient-rich heathland soils) were grown in replacement series in a factorial combination of four competition types (no competition, only aboveground competition, only belowground competition, full competition) and two levels of nutrient supply (no nutrients and 10 g N+2 g P+10 g K m yr). Both in the unfertilized and in the fertilized treatments Molinia allocated about twice as much biomass to its root system than did Erica and Calluna. In all three species the relative amount of biomass allocated to the roots was lower at high than at low nutrient supply. The relative decrease was larger for Molinia than for Erica and Calluna. In the fertilized monocultures biomass of all three species exceeded that in the unfertilized series. Molinia showed the greatest biomass increase. In the unfertilized series no effects of interspecific competition on the biomass of each species were observed in either of the competition treatments. In the fertilized mixtures where only belowground competition was possible Molinia increased its biomass at the expense of both Erica and Calluna. When only aboveground competition was possible no effects of interspecific competition on the biomass of the competing species were observed. However, in contrast with the evergreens, Molinia responded by positioning its leaf layers relatively higher in the canopy. The effects of full competition were similar to those of only belowground competition, so in the fertilized series belowground competition determined the outcome of competition. The high competitive ability of Molinia at high nutrient supply can be attributed to the combination of (1) a high potential productivity, (2) a high percentage biomass allocation to the roots, (3) an extensive root system exploiting a large soil volume, and (4) plasticity in the spatial arrangement of leaf layers over its tall canopy. In the species under study the allocation patterns entailed no apparent trade-off between the abilities to compete for above- and belowground resources. This study suggests that this trade-off can be overcome by: (1) plasticity in the spatial arrangement of leaf layers and roots, and (2) compensatory phenotypic and species-specific differences in specific leaf area and specific root length. [ABSTRACT FROM AUTHOR]