Increased Plant Dry Weight Research Articles

Correction - Studies in the nodulation of Kenya white clover (Trifolium semipilosum) under field conditions in south-east Queensland

The nodulation of Kenya white clover (Trifolium semipilosum) was examined under field conditions to evaluate reported establishment problems attributed to poor nodulation. Two isolates of Rhizobium identified as strain CB782 were obtained from nodules of T. semipilosum located in separate field sowings each of which was considered an establishment failure but which had recovered to healthy stands at the time of sampling. The two isolates were compared with a laboratory maintained culture of CB782 for nodulation and nitrogen fixation. Both isolates and the original strain were equally effective in N-fixation and all three increased plant dry weight, per cent plants with effective (pink) nodules and amount of nitrogen fixed compared with an uninoculated control. Increasing the level of seed application of inoculum up to the normal rate increased effective nodulation, but excess inoculum levels resulted only in greater numbers of smaller effective (pink) nodules without any increase in nodule dry weight. High inoculum levels decreased the number of white and green nodules compared with the control. Over 50 per cent effective nodulation was obtained with less than 50 Rhizobium seed-1 at sowing. Serological identification and effectiveness tests of strains in nodules confirmed that most white and green nodules on T. semipilosum resulted from infection by naturally occurring white clover rhizobia. These were ineffective in nitrogen fixation with T. semipilosum but fully effective on T. repens. Serological typing of nodules also indicated that normal levels of inoculation resulted in more than 80 per cent of nodules being formed by the specific inoculum strain. We conclude that field sowings of T. semipilosum can be effectively nodulated by the specific inoculum strain CB782 which is both effective and persistent under south-east Queensland conditions. We suggest that most reported nitrogen deficiency symptoms of establishing T. semipilosum are due to infection by Rugose Leaf Curl Virus.

Changes in starch, reducing sugars, and total nitrogen in cotyledons of two cultivars ofPhaseolus vulgarisL. during seedling development

SummarySignificant changes in starch, total nitrogen and dry weight occurred 4, 5, 6, 7, 8 and 11 days after planting in the cotyledons of developing bean seedlings, cv. Greenpod 478. These changes were significantly correlated with increases in plant dry weight and an increase in top : root ratio from 2.8 : 1 at emergence (4 days) to 5.6 : 1 at cotyledon senescence (11 days). Although 57% of the cotyledons of cv. Slimgreen were cracked, the pattern of changes in the constituents and associated plant growth was similar to that for Greenpod 478, but the magnitude was generally smaller. Subsequent tests to determine the effect of cracking on changes in cotyledon constituents showed marked influences of this type injury on the starch and total nitrogen contents in cotyledons and on top growth.

The Effect of Nitrogen on the Growth and Sugar Content of Sugar-beet

Nitrogen fertilizer applied to sugar-beet increased plant and root dry weight and leaf area, and decreased the sugar content of the roots per cent of both fresh and dry weight. Change in leaf area accounted wholly for the increase in plant dry weight produced by nitrogen, because net assimilation rate was unaffected. Nitrogen did not alter the partition of the total assimilate between roots and shoots, but increased the fraction of total assimilate entering the roots that was used in growth, at the expense of that stored as sugar. Thus, plants with more nitrogen had a smaller proportion of their root dry weight as sugar because more was metabolized in growth of the roots, and not because less entered the roots. The heavier roots of plants given more nitrogen were larger in cross-sectional area because the areas of both parenchyma and vascular zones of each peripheral ring within the root were larger; the number of rings was not increased. Nitrogen increased the areas of the tissues in these zones by enlarging cell volumes, not by increasing the number of cells within the tissues. Increase in cell volume was accompanied by proportional increases in the weights of non-sugar dry matter per cell and water per cell, but the amount of sugar per cell was proportional to cell volume only during the initial stage of cell expansion up to cell volumes of about 15 X io~8 cm3; thereafter it was less than proportional, so that sugar per cent of both fresh and dry weight decreased as cell size increased beyond 15 X io~8 cm3. The relation of sugar per cell to cell volume was the same with both amounts of nitrogen given. This implies that increase in nitrogen supply made the sugar concentration of the root less by increasing the size of the root cells and not by a specific effect on sugar storage.

Growth Rates in Lolium temulentum as influenced by Previous Regimes of Light Energy

THE relationships between the vegetative growth of single plants and the intensity of incident light have been extensively studied in various dicotyledonous species1,2, and less extensively in herbage grasses3,4. These and other investigations assessed plant growth in terms of relative growth rate (rate of increase in plant dry weight per unit of dry weight already present, RGR) and its components leaf area ratio (photosynthetic surface per unit dry weight, LAR) and net assimilation rate (rate of increase in dry weight per unit of photosynthetic surface, NAR). As in most other species, decreasing the amount of light incident on grass plants generally leads to decreased RGR for, although LAR increases in these conditions, this is more than offset by a fall in NAR.