Tom Ericsson

Growth and shoot: root ratio of seedlings in relation to nutrient availability

The influence of mineral nutrient availability, light intensity and CO2 on growth and shoot:root ratio in young plants is reviewed. Special emphasis in this evaluation is given to data from laboratory experiments with small Betula pendula plants, in which the concept of steady-state nutrition has been applied.

Physiology of carbon allocation in trees

Abstract The influence of mineral nutrients, light, carbon dioxide, ozone, ammonia, water, temperature, soil texture and soil acidity on carbon allocation in trees is reviewed. The growth rhythms of the different plant parts on a seasonal basis are examined as well as the change in source-sink balance caused by plant age and genetic constitution. The exact outcome of all these factors on plant growth and carbon allocation is difficult to predict. However, one distinct pattern with regard to carbon allocation, and important for plant survival, becomes evident from this evaluation. Root growth is always decreased when plants become carbon limited, independently of whether this situation is caused by reduced photosynthesis (O3, low light, or shortage of K, Mg or Mn) or competition between root growth and NH4+ as sinks for carbon skeletons (atmospheric NH3 and root uptake of NH4+). Low soil temperatures as well as competition from intensive shoot growth affect root development in a similar way. Inhibition of mycorrhizal development after exposure to O3, NH3, and low availability of Mg can also be explained by the same mechanisms.

Growth and nutrition of birch seedlings in relation to potassium supply rate

SummaryGrowth of hydroponically cultivated birch seedlings (Betula pendula Roth.) at sub- and supra-optimum potassium supply rates was investigated. Potassium was supplied either as a relative addition rate (rk = 5, 10, 15 and 20% increase day-1) or as fixed concentrations (0.2, 3, 6, 12 and 15 mM) in the culture solution. After an acclimation period the growth rate of the seedlings in the suboptimum treatments reached values close to the treatment variable, the relative rate of K-addition. Deficiency symptoms, in the form of chlorosis and necroses along the leaf margins, developed initially in all suboptimum treatments, but very few new symptoms appeared once the seedlings had reached the phase of steady-state nutrition and growth. At supra-optimum K-supply levels, i.e. at 0.2–15 mM K in the culture solution, no symptoms of deficiency or toxicity developed, and the relative growth rate of the seedlings remained maximum. The relative growth rate of the seedlings was linearly related to the plant K-status for K contents ranging from 0.2 to 1.0% of dry weight (DW). At higher internal K-concentrations, 1.0–3.0% DW, no further increase in relative growth rate was achieved. A shortage of K resulted in a decrease in the net assimilation rate. This effect was counterbalanced by the absence of shift in he leaf weight ratio as well as by the production of relatively thin leaves. The fraction of dry matter allocated to roots decreased in K-limited plants, as did the leaf contents of soluble carbohydrates and starch.

Nutrient cycling in energy forest plantations

Abstract Knowledge about growth and nutrient uptake dynamics within and between seasons, internal nutrient cycling, decomposition and mineralization of litter as well as nutrient losses due to harvest and leakage in energy forest plantations are reviewed. These topics, especially in connection to willow plantations, will be presented and discussed, and where possible, comparisons with other fast growing deciduous tree species like grey alder and poplar will be made. A nitrogen budget during the two first rotations of a willow plantation on good agricultural soil is presented. It is concluded that the fertilizer need in well established and high yielding (⪢12 tonnes stems, dry weight, ha −1 year −1 ) stands is small, about 30 kg N ha −1 yr −1 , due to an efficient recycling of N from litter and the relatively low nutrient content in the harvested biomass (stems).

Seasonal variation of macronutrients in leaves, stems and roots of Salix dasyclados Wimm. grown at two nutrient levels

Abstract In order to obtain a more compete understanding of the macronutrient dynamics in coppiced willow plantations, a pot experiment with Salix dasyclados was performed. In this study, the seasonal variation in concentration and amounts of N, P, K, Mg, Ca and S in roots, cutting, stem and leaves were determined. Plants were grown in pots containing 1 l of washed sand under outdoor conditions. Nutrients were given during the first 3–4 weeks at two relative addition rates, 0.08 (−Nutr) and 0.12 (+Nutr) day−1, respectively. Nine harvests were performed and covered a whole seasonal cycle. At each harvest, leaf area (growing season only), dry weight and macronutrient concentrations in roots, cutting, stem and leaves (growing season only) were determined. Plants in the +Nutr treatment continued to grow 2 weeks longer in the autumn than −Nutr plants and started to grow 1 week earlier the following spring. The leaf area and the weight of the different plant parts were significantly higher in the +Nutr plants. Between 40% and 50% of N and about 60% of P was withdrawn from the leaves prior to abscission and stored mainly in the above-ground perennial organs. Retranslocation of K and S from senescing leaves was only observed in −Nutr plants. No seasonal trends and no retranslocation from senescing leaves were observed for Ca and Mg. At bud break, N stored in all perennial organs was used for growth of new shoots.

Effects of Demand-driven Fertilization on Nutrient Use, Root:Plant Ratio and Field Performance of Betula pendula and Picea abies

Norway spruce [Picea abies (L.) Karst.] and silver birch (Betula pendula Roth) seedlings were grown for one season under three different fertilization regimens in the forest nursery. During the first 50 days the seedlings were grown in a glasshouse, and thereafter outdoors until the beginning of September. Finally, the plants were exposed to 16 h nights in the glasshouse throughout September. When the seedlings were supplied with fertilizers at a rate adjusted to expected plant demand (RO), less than half as much of each nutrient was applied as in a conventional regimen (RC), in which equal amounts were supplied per unit time during the growth season, yet the plants still looked healthy. Utilization of N increased by almost 50% in spruce when supply was adjusted to plant demand. In the third treatment (RL), nutrients were supplied as in the RO treatment, but at a growth-limiting rate. These plants were loaded with nutrients at the end of the season and had higher root:plant ratios, i.e. root weight in relation to total plant weight, compared with the other treatments. The nutrient status of the plants was not growth limiting at the end of the growing season in any of the treatments. The plants given the different treatments differed in size at planting out, but they had similar heights after 3 yrs in the field. This indicates that the root:plant ratio may be important for growth performance, provided that nutrient status is not at a growth-limiting level. This study suggests that the use of fertilizers can be considerably reduced in Swedish forest nurseries.

Interfamily variation in nitrogen productivity of pinus sylvestris seedlings

Open‐pollinated families from 21 Pinus sylvestris L. clones from a seed orchard in central Sweden were cultivated in growth chambers in mineral wool for two growth periods. Two nitrogen treatments were applied: high N availability, free access to all nutrient elements and low N availability aimed at 1/3 of the potential requirement under prevailing external conditions. The second treatment was realized by daily additions of nutrient solution containing nitrogen in amounts adjusted to plant size and actual growth rate. Two types of nitrogen productivity were estimated for plants from the low‐N treatment‐one called nitrogen productivity, expressed per day and based only on the period of the intensive growth during the second growth period, the other, called nitrogen productivity per growth period, based on growth increment during the entire second growth period. Nitrogen productivity varied between 7.8 and 10.3 mg plant DW (mg needle‐N)−1 day−1, whereas the nitrogen productivity per growth period varied bet...

Levels of IAA, ABA and carbohydrates in source and sink leaves of Betula pendula Roth.

Young birch (Betula pendula Roth) seedlings were grown in hydroponic cultures to which nutrients were added in amounts that increased exponentially over time. The nutrient additions were adjusted to give three different suboptimal, but stable, relative growth rates (RGR). Levels of glucose, fructose, sucrose and starch and the hormones 3‐Indolyl acetic acid (IAA) and abscisic acid (ABA) were determined in immature (sink) and mature (source) leaves and related to the measured RGR of the seedlings. The results show that ABA increased and IAA decreased in the sink leaves as the RGR of the plants decreased. This occurred in concert with a decrease in soluble sugar levels and starch accumulation in the source leaves. These observations suggest that ABA and IAA may be involved in source‐sink communication in the seedlings, although such causal relationships remain to be proven.

Demand-driven fertilization. Part I: Nitrogen productivity in four high-maintenance turf grass species

Abstract The effect of four nitrogen (N) availabilities on growth, leaf N concentration, N productivity (dry matter production per unit time and unit N taken up), shoot:root ratio and carbohydrate storage was studied in velvet bentgrass (Agrostis canina ‘Legendary’), creeping bentgrass (A. stolonifera ‘Independence’), slender creeping red fescue (Festuca rubra ssp. trichophylla ‘Cezanne’) and chewings fescue (F. rubra ssp. commutata ‘Center’). In growth chamber experiments, plants were grown for 3 weeks in sand with 12.5, 25, 50 or 200 mg N L−1 in the irrigation water and at two mowing intensities, cut at 5 mm twice per week or uncut. It proved possible to control important turf grass traits such as shoot growth rate, shoot:root ratio, leaf morphology and carbohydrate storage through leaf N concentration. The relationship between leaf N concentration and aboveground growth was linear for both cut and uncut turf. The relative N demand of the studied species, based on their N productivity, was 1:0.67:0.67:0.37 for creeping bentgrass, velvet bentgrass, chewings fescue and slender creeping red fescue, respectively. Clipping significantly reduced N productivity, and hence turf N demand. The lowest possible leaf N concentration without adverse effects on plant health and appearance was between 3.1 and 3.5% of dry matter (DM) in both bentgrasses and fescues. This value can be used as a target in minimizing fertilizer usage and N leaching losses. In conclusion, fertilization based on the influence of leaf N concentration on growth-related processes offers possibilities to control growth in a predictable and desirable manner under varying climate and growth conditions. This could provide more environmentally friendly and economic fertilization regimes and also better playing quality.

Demand-driven fertilization. Part II: Influence of demand-driven fertilization on shoot nitrogen concentration, growth rate, fructan storage and playing quality of golf turf

Abstract The ability of demand-driven fertilization, based on the growth potential provided by solar radiation and temperature, to regulate golf turf characteristics such as growth rate, leaf nitrogen (N) concentration, carbohydrate storage and playing quality was investigated in a 2-year field experiment at Landvik, Norway. Three N regimes (100, 60 and 40% of the estimated N requirement for maximum growth) were applied on a sand-based green with a turf cover consisting of creeping bentgrass, colonial bentgrass, velvet bentgrass, slender creeping red fescue or chewings fescue. In the 100% treatment, this corresponded to 3 (creeping bentgrass), 2.1 (colonial and velvet bentgrass) and 1.5 (chewings and slender creeping red fescue) kg N 100 m−2 yr−1. The weekly liquid fertilizer dose basically followed the potential growth curve provided by solar radiation and temperature from early April to late October. The turf was exposed to artificial wear and daily maintenance followed conventional standards. Growth, leaf N concentration, carbohydrate storage in clippings, green appearance and playing quality were determined once per month. The results indicated that solar radiation and temperature can successfully be used as driving variables when quantifying turf fertilizer requirements from early spring to late autumn. The desired leaf N concentration, i.e. growth rate, and the resulting effects on fructan content and playing quality can be achieved by raising or lowering the seasonal fertilizer curve. A leaf N level of 3.1–3.5% was indicated as the lower limit for producing healthy-looking turf with high playing quality.