Growth, nutrition, and nitrogen fixation in grey alder at varied rate of nitrogen addition

Seedlings of grey alder (Alnus incana Moench), nodulated or unnodulated, were investigated at varied relative addition rate of nitrogen. Nitrogen fixation alone, without addition of mineral nitrogen, resulted in an almost optimum nitrogen status but only about half the maximum relative growth rate, probably mainly because of energy costs of nodulation and fixation. The growth deficit due to nodulation was much more than can be explained by the theoretical energy requirement for the amount of nitrogen fixed. Thus, the nitrogen fixation process was not very efficiently used. The nitrogen fixation rate was strongly stimulated by increasing nitrogen addition rate up to high levels. The fixation rate decreased rapidly close to optimum (maximum relative growth rate) and was negligible at maximum growth. A feed-back of mineral nitrogen on photosynthesis increased fixation rate with time, and the relative importance of fixation over mineral nitrogen nutrition increased. However, nitrogen fixation, also at maximum rate, supplied only a small proportion of the nitrogen amount required for maximum growth. The optimum nutrient solutions contained comparatively high nitrogen concentrations to secure free access to nitrogen. The nodules were damaged by this treatment, and it is concluded that the nitrogen additions must be adjusted to the current consumption of the plants to avoid an increased external nitrogen concentration. Strong linear regressions were found between relative growth rate, nitrogen status expressed as percentage content of fresh weight, and relative growth rate in unnodulated seedlings. There was a greater variability in nodulated seedlings than in unnodulated ones, because of the nitrogen fixation. The reactions of unnodulated grey alder were largely the same as previously reported for birch seedlings, but the maximum growth capacity was lower in grey alder. During an initial period of change in the internal nitrogen status, deficiency symptoms appeared, especially in unnodulated seedlings. As in birch, the leaves turned green again at stable nitrogen status, independent of level. The results are in sharp contrast to data from the literature where the external nitrogen concentration was used as the driving variable for the internal nitrogen status. The measured fixation rates for grey alder are much higher than those previously reported. Still, the maximum fixation rate observed is small compared to the total nitrogen uptake rate required for maximum growth, in contrast to reported relationships. These comparisons indicate that increased external nitrogen concentration obscures the real relations between mineral and fixed nitrogen, on one hand because of rapid inhibition of nitrogen fixation and, on the other hand, because of failure to obtain stable optimum nutrition and maximum growth by means of this treatment variable.     

Nutrition and growth of coniferous seedlings at varied relative nitrogen addition rate

The growth of two provenances of Pinus sylvestris L. were compared with two provenances of Picea abies (L.) Karst. and with Pinus contorta Dougl. when grown in solution cultures with low nutrient concentrations. Nitrogen was added at different exponentially increasing rates, and the other nutrients were added at a rate high enough to ensure free access of them to the seedlings. During an initial period of the culture (a lag phase), when the internal nutrient status was changing from optimum to the level of the treatment, deficiency symptoms appeared. The needles yellowed and the root/shoot ratio increased. The initial phase was followed by a period of exponential growth and steady-state nutrition. The needles turned green again, and the root/shoot ratio stabilized at a level characteristic of the treatment. These patterns were the same as previously reported for other tree species. The relative growth rate during exponential growth was numerically closely equal to the relative nitrogen addition rate. The maximum relative growth rates were about 6 to 7.5% dry weight increase day^-1. This is a much lower maximum than for broad-leaved species (about 20 to 30% day^-1) under similar growth conditions. The internal nitrogen concentrations of the seedlings and the relative growth rates were stable during the exponential period. Close linear relationships were found between these parameters and the relative addition rate up to maximum growth. During steady state the relative growth rates of the different plant parts were equal. However, there were large differences between genotypes in absolute root growth rate at the same seedling size because of differences in root/shoot ratio. Lodgepole pine had the highest root growth rate, whereas that of Norway spruce, especially the southern provenance, was remarkably low. Yet, Norway spruce had a high ability to utilize available nutrients. In treatments with free nutrient access, growth allocation to the shoot had a high priority in all genotypes, but there was still a marked tendency for luxury uptake of nutrients. Nitrogen productivity (growth rate per unit of nitrogen) was lower than in broadleaved species and highest in lodgepole pine. The relevance of the dynamic factors, i.e. maximum relative growth rate, nutrient uptake rate, nitrogen productivity, growth allocation and root growth rate, are discussed with regard to conifer characteristics and selection value.     

氮过量吸收对地肤暗呼吸速率及相对生长速率的影响

为研究N过量吸收对植物生长的作用,以耐盐植物地肤(Kochia scoparia)作为研究对象,设置3个不同的施N处理,测量了不同生长时期的N含量、暗呼吸速率、生物量和相对生长速率(RGR)。结果表明:在N过量吸收的情况下,多余的N对暗呼吸速率并没有显著的影响,导致了暗呼吸中N的利用效率变低;单位质量暗呼吸速率与相对生长速率(RGR)有很好的线性相关,并且直线的斜率和截距并不受氮素过量吸收的影响,表明单位质量暗呼吸速率与RGR的关系不受施氮水平的影响;暗呼吸速率与总N的异速关系中,幂指数的大小与施N量相关,施N量越大对应的幂指数越小。     

Nutrition and growth of birch seedlings at varied relative phosphorus addition rates

Birch ( Betula pendula Roth.) was investigated under steady state nutrition and growth at different relative addition rates of phosphorus (R_p). Phosphorus deficiency symptoms appeared on the leaves when the internal phosphorus concentration decreased, but disappeared again under steady state nutrition, independent of the stress level. The increased root/shoot ratio and the exploratory type of root systems developed during the adjustment stage remained under steady state conditions. At nonoptimum and close to optimum relative addition rates, independent of the rate, the phosphorus concentration of the culture solution did not exceed 2 μmol dm⁻³ and was generally < 1 μmol dm⁻³ immediately after phosphorus additions. The phosphorus concentration just before additions was generally < 0.5 μmol dm⁻³. The nutrition/growth relationships were similar to those for nitrogen, with relative growth rate (R_g) closely related to the R_p applied and with a strong linear relationship between internal phosphorus concentration and R_g. Regression was much steeper than that for nitrogen. The slope of the optimum nutrition was attained at a lower phosphorus weight proportion to nitrogen (8–10 P: 100 N) than previously estimated (= 13 P: 100 N), but a higher relative phosphorus requirement was observed under stress conditions. Birch seedlings had a strong tendency to consume phosphorus in excess of immediate requirements with a small effect on growth above optimum. This resulted in rapidly decreasing phosphorus productivity (P_p, growth rate per unit of phosphorus) with increasing internal phosphorus concentrations above optimum.     

Nutrient requirements and stress response of Populus simonii and Paulownia tomentosa

The aim of this investigation was to estimate the optimum nutrient requirements and responses to low relative nutrient addition rates of seedlings of two important broadleaf tree species in China, Populus simonii Carr. and Paulownia tomentosa (Thunb.) Steud. In preliminary experiments the optimum nutrient proportions were estimated under high concentration conditions. The nutrients consumed were replaced by means of daily additions determined by pH and conductivity titrations without changing the nutrient solutions. A relatively high K level was needed in relation to nitrogen; higher than in birch or grey alder seedlings. To obtain a high relative growth rate, suitable proportions by weight were 100 N:70 K:14 P:7 Ca:7 Mg for the Populus seedlings and 100 N:75 K:20 P:8 Ca:9 Mg for the Paulownia seedlings.
In studies of nutrient stress responses the relative nutrient addition rate was used as the treatment variable under low conductivity conditions. The responses and relationships were similar to those described for birch, grey alder and Salix . The relative addition rate, and there was also a strong linear regression between relative growth rate and nitrogen status. Relative growth rates were high and the maximum weight increase was about 19% day⁻¹ in Populus and over 25% day⁻¹ in Paulownia . The nitrogen productivity of Paulownia was very high, 0.26 g dry weight (g N)⁻¹ h⁻¹, and for Populus it was 0.16 g dry weight (g N)⁻¹ h⁻¹.     

Growth and nutrition of three Salix clones in low conductivity solutions

The effect of replacing 50% or 95% of the potassium by sodium on growth and on potassium and sodium levels in three genotypes of sugar beet (MONOHILL; ADA; FIA) has been studied in water culture over a period from 2 to 9 weeks.
In all three genotypes there was a preferential uptake of potassium compared to sodium. Nevertheless, at high sodium supply most of the potassium was replaced by sodium, particularly in the leaves. At the same supply the accumulation of sodium in the leaves increased in the following order: ADA < MONOHILL < FIA. Even with high dominance of sodium in the medium, the youngest leaves of FIA held about 0.5 mmol potassium per g dry matter, and potassium was evidently translocated from old leaves to the new growth.
Effects of sodium on growth became more important with time. After 9 weeks, 50% replacement of potassium by sodium increased growth of all plant organs of the three genotypes. Replacing 95% of potassium by sodium depressed growth of the storage root in MONOHILL and particularly in ADA, with simultaneous enhancement of leaf growth in the latter. In FIA, however, this treatment further stimulated both leaf and, particularly, storage root growth. Sodium in comparison with potassium increased the sucrose concentration in leaves and storage roots. The highest sucrose concentration in the storage roots of ADA and FIA was obtained in the treatment with 95% sodium.
The results demonstrate pronounced genotypic differences in sugar beet with respect to the response to sodium. FIA has the most natrophilic behaviour and might be a promising genotype for breeding programmes for adaptation of sugar beet plants to soils high in sodium.     

Interaction of nitrogen and phosphorus nutrition in determining growth

In this paper we discuss the differences and similarities in the growth response of tomato plants to N and P limitation, and to their interaction. Two detailed growth experiments, with varied N or P supply, were conducted in order to unravel the effects of N and P limitation on growth of young tomato plants (Lycopersicon esculentum Mill.). Relative growth rate (RGR) initially increased sharply with increasing plant P concentration but leveled off at higher plant P concentrations. In contrast, RGR increased gradually with increasing plant N concentration before it leveled off at higher plant N concentrations. The relationship of RGR with organic leaf N and P showed the same shape as with total N and P concentrations, respectively. The difference in response is most likely due to the different roles of N and P in the machinery of the plant's energy metabolism (e.g., photosynthesis, respiration). Plant N concentration decreased with increasing P limitation. We show that this decrease cannot be explained by a shift in dry-mass partitioning. Our results suggest that the decrease in N concentration with increasing P limitation may be mediated by a decrease in leaf cytokinin levels and is less likely due to decreased energy availability at low P conditions. Dry-mass partitioning to the roots was closely linearly related to the leaf reduced-N concentration. However, treatments that were severely P limited deviated from this relationship.     

A method for establishing ectomycorrhiza on conifer seedlings in steady-state conditions of nutrition

Scots pine ( Pinus sylvestris L.), and Norway spruce ( Picea abies (L.) Karst.) seedlings, inoculated with Suillus bovinits (L. ex Fr.) O. Kuntze and Paxillus involutus (Batsch) Fr., were grown on sloping plastic plates in growth units. A circulating nutrient solution flowed continuously over the plates. Nutrients in balanced proportions previously found to be appropriate for conifers, were added at a specified relative addition rate, in exponentially increasing amounts. The conductivity of the solution was kept low and stable (<50 μS cm⁻¹). No carbohydrates were added.
Seedling nitrogen concentration and relative growth rate attained steady states in both inoculated and uninoculated treatments. The fungi infected the short roots within a few days and formed typical mantles and Hartig nets. This occurred in all treatments, including conditions of free access to nutrients, in which the nutrient concentration of the seedlings was optimal. The growth rate of the extramatrical mycelium was very high.     

The application of ethephon (an ethylene releaser) increases growth, photosynthesis and nitrogen accumulation in mustard (Brassica juncea L.) under high nitrogen levels

Ethephon (2-chloroethyl phosphonic acid), an ethylene-releasing compound, influences growth and photosynthesis of mustard (Brassica juncea L. Czern & Coss.). We show the effect of nitrogen availability on ethylene evolution and how this affects growth, photosynthesis and nitrogen accumulation. Ethylene evolution in the control with low N (100 mg N kg(-1) soil) was two-times higher than with high N (200 mg N kg(-1) soil). The application of 100-400 microl x l(-1) ethephon post-flowering, i.e. 60 days after sowing, on plants receiving low or high N further increased ethylene evolution. Leaf area, relative growth rate (RGR), photosynthesis, leaf nitrate reductase (NR) activity and leaf N reached a maximum with application of 200 microl x l(-1) ethephon and high N. The results suggest that the application of ethephon influences growth, photosynthesis and N accumulation, depending on the amount of nitrogen in the soil.