Dorte Bodin Dresbøll

Spatial variation in root system activity of tomato (Solanum lycopersicum L.) in response to short and long-term waterlogging as determined by 15N uptake

Background and aimRoot system activity is affected by abiotic stresses, which often creates spatial differences in root conditions. This is expected to influence plants ability to cope with suboptimal conditions.MethodsChanges in root system activity were determined as 15N root uptake in top and bottom layers of potted tomato plants (Solanum lycopersicum L.), after waterlogging the bottom layer for 24 h or 5 d. The plants were grown in peat-based media; non-compacted or highly-compacted, resulting in differences in gas diffusion, air permeability and oxygen availability.ResultsThe roots were affected by short-term waterlogging (24 h) by decreasing uptake in the bottom layer and increasing uptake in the pot top layer. Long-term waterlogging (5 d) decreased the 15N root uptake more in both layers. Root uptake recovered fast (within 6 h) after short-term waterlogging, whereas recovery of long-term waterlogged roots took more than 24 h, suggesting production of new root biomass. Despite affecting physical properties, medium compaction did not affect root uptake. Aboveground biomass was affected by waterlogging by increasing the dry matter percentage, decreasing nitrogen (N) percentage and increasing starch content.ConclusionsThe results confirmed that root uptake in different layers of small pots could be distinguished by the 15N technique, which was applicable under potentially denitrifying conditions. The results demonstrated that during short-term stress in part of the root system plants increased uptake from the non-affected parts of the root system, probably as compensation for suboptimal conditions.

Spatial root distribution of plants growing in vertical media for use in living walls

Background and AimsFor plants growing in living walls, the growth potential is correlated to the roots ability to utilize resources in all parts of the growing medium and thereby to the spatial root distribution. The aim of the study was to test how spatial root distribution was affected by growing medium, planting position and competition from other plants.MethodsFive species (Campanula poscharskyana cv. ‘Stella’, Fragaria vesca cv. ‘Småland’, Geranium sanguineum cv. ‘Max Frei’, Sesleria heufleriana and Veronica officinalis cv. ‘Allgrün’) were grown in three growing media (coir and two of rockwool) in transparent boxes under greenhouse conditions. Root frequency was registered and the activity of individual root systems was studied via 15N uptake and plant dry weight was measured.ResultsPlants in coir had stronger root growth in all parts of the medium than plants in rockwool. Upwards root growth was limited for plants in the middle or lower parts of the medium and 15N measurements confirmed that only plants in the bottom of the box had active roots in the bottom of the medium. The species differed in root architecture and spatial root distribution.ConclusionsThe choice of growing medium, plant species and planting position is important for a living wall as it affects the spatial root growth of the plants.

Yields and the extent and causes of damage in cauliflower, bulb onion, and carrot grown under organic or conventional regimes

Summary The effects of organic vs. conventional growing practices on yield, pest attacks, N uptake, and NO3– contents of three vegetable crops were examined. A range of cultivars of cauliflower (Brassica oleracea L. cv. Botrytis), bulb onion (Allium cepa L.), and carrot (Daucus carota L.) were grown organically and conventionally in a sandy-loam soil. Ranking of cultivars according to yield and susceptibility towards insect attack and fungal disease was similar in the two systems. Yields of cauliflower and onion were 20% and 45% higher, respectively, when grown conventionally. No differences in carrot yields and discard rates were observed between the two systems. Generally, the reasons for discarding varied between the two systems. In organically grown cauliflower, damage by slugs was the main reason for discarding, with 9% discarded, while hollow stem was more prevalent in conventionally grown cauliflowers, where 7% was discarded. No statistically significant differences were found between discard rates or causes in bulb onions grown organically or conventionally. Conventionally grown carrots were significantly more damaged by carrot root fly with 5% of carrots discarded, even though the flies were also present in the organic system. In contrast, more carrots with morphological defects were seen in the organic system, where 29% were discarded. The lower yields in organically grown vegetables can be explained mainly by the management practices specific to the organic system that are designed to facilitate weed and pest management. In addition, inadequate early nutrient supply provides a possible explanation for the lower yields in organically grown cauliflowers and onions, as well as the lower planting density of onions.

Long-Term Stability and Mineralization Rate Of Compost is Influenced by Timing of Nutrient Application During Composting of Plant Residues

The long-term nitrogen mineralization and stability of compost based on easily available plant residues were examined. Four different composts were prepared from wheat straw and clover-grass hay, one treatment receiving all material initially (100/0), two treatments where addition of 75% of the clover-grass was postponed for 3 weeks (25/75,3w) respectively, 8 weeks (25 / 75,8w) and one treatment receiving only 25% of the clover-grass added to the other treatments (25/0). Mineralization and structural stability of the compost was followed for 24 weeks in leaching tubes, leached regularly by 0.01 M CaCl2. Postponing the addition of the clover-grass hay for 3 weeks (25/75,3w) during composting had a significant effect on the N mineralization rate leading to more mineralized N during the leaching period. Postponing the addition for 8 weeks (25/75,8w) did not affect mineralization pattern. Most of the decomposition in this treatment occurred in the leaching tubes after the composting step and no temperature increase (thermophilic phase) was observed here. Thus, the decomposition was seemingly dominated by different microorganisms compared to the thermophilic phases during composting observed in i.e. the 100/0 and 25/75,3w treatments. When only 25% of the clover-grass hay was added (25/0) decomposition was so N limited that almost no net mineralization occurred. Postponing the addition for 3 weeks (25/75,3w) increased the structural stability of the compost during the initial 14 weeks of incubation probably because more slowly decomposable compounds were degraded; however, after 24 weeks of incubation losses were similar to losses in the treatment receiving all the material from the start. Thus, the postponed addition was shown to alter the mineralization pattern and structural stability of the compost in a long-term scale. This has implications for production of growing media: A disadvantage of the postponed addition is the higher mass loss during composting. However, the 25/75,3w treatment with the supplementary addition postponed for 3 weeks remained stable for a longer period than the other treatments and might be a functional improvement as growing medium for plants with a shorter growth period.