Climate, nitrogen and grass. 3. Some effects of light intensity on nitrogen metabolism.

Between 18 May and 29 June 1966, a 2-year-old sward of perennial ryegrass was grown at normal (390), low (88) or high (711 cal/cm2 day) light intensity and given 20-160, 40-320 and 80-360 kg N/ha at the 3 light intensities, respectively. At low rates of N, high light intensity exhausted the nitrate reserves of perennial ryegrass, diminished the CP content, but greatly increased the percentage of water-soluble carbohydrates. With high N, high light intensity decreased nitrate content but increased both CP and water-soluble-carbohhdrate content. (Abstract retrieved from CAB Abstracts by CABI’s permission

Prediction of forage digestibility from some laboratory procedures. 2. Comparison of in vivo digestibility at two institutes.

For part 1 see Abst. 1564, Vol. 40. 2. The relation between digestibilities of organic matter in vivo and in vitro did not differ significantly between the institutes at Hoorn and Wageningen. No difference was found in digestibility of the cell wall constituents in relation to the lignin content, nor was there a significant difference in the relation between the percentage of digestible cell contents and the percentage of cell contents in forage from well managed pastures. Twelve forages of highly digestible perennial ryegrass deviated from these farm forages at Wageningen, showing smaller excretion of bacterial and endogenous residue. Comparison of the 2 lignin procedures showed that 72% sulfuric acid lignin gave consistent residual standard deviations of digestibility of cell wall constituents; permanganate lignin gave smaller errors in forages at Wageningen but greater errors in forages at Hoorn. (Abstract retrieved from CAB Abstracts by CABI’s permission

Climate, nitrogen and grass. 6. Comparison of yield and chemical composition of some temperate and tropical grass species grown at different temperatures.

For part 5 see NAR 43, 148. 6. Lolium perenne, Festuca arundinacea and 2 tropical grasses, Axonopus compressus and Brachiaria ruziziensis, were grown in pots under day/night temperatures of 19 deg /12 deg , 24 deg /18 deg , 28 deg /23 deg and 34 deg /30 deg C and regrowth was cut after 18 and 35 days. The stemmy Brachiaria was much more productive than the others which remained vegetative. The optimum production temperature was 24 deg or less for the temperate grasses but >30 deg for the others. Yield was greatest after 35 days and with high N fertilization. Lolium had the highest average content of N, soluble carbohydrates and digestibility in vitro and Brachiaria the lowest. Digestibility declined with increase in temperature and age, most for Brachiaria. These effects were caused by an increase in content of cell-wall constituents and a decrease in their digestibility. N fertilization had no effect on digestibility. Results support the hypothesis that the low digestibility of tropical grasses is mainly due to the high temperature during growth but may be improved appreciably if stem formation is suppressed. ADDITIONAL ABSTRACT: Lolium perenne, Festuca arundinacea, Axonopus compressus and Brachiaria ruziziensis were grown in pots in a glasshouse under day/night temperatures of 19/12, 24/18, 28/23 or 34/30 deg C with intermediate or high N and regrowth was harvested after 18 and 35 days. Reproductive B. ruziziensis was much more productive than the other vegetative species. Optimum day temperature for production was 24 deg or lower for temperate grasses but >30 deg for tropical species. L. perenne had the highest contents of N and soluble carbohydrates and in vitro digestibility and B. ruziziensis the lowest, differences being smallest at the low temperature. There was a consistent decline in digestibility of all species with increase in temperature and age which was correlated with an increase in cell wall constituents but was not related to amount of N applied. [For Part 5 see HbA 43, 1557] (Abstract retrieved from CAB Abstracts by CABI’s permission

Climate, nitrogen and grass. 4. The influence of age on chemical composition and in vitro digestibility of maize (Zea mays L.) and tall fescue (Festuca arundinacea Schreb.).

In a field experiment with maize it was found that in vitro digestibility of leaves decreased somewhat during undisturbed growth, whereas digestibility of stems decreased appreciably. This decrease in leaf digestibility was caused by a lower digestibility of later-developed leaves and by a slight decrease in digestibility during ageing of each individual leaf. In a pot experiment with tall fescue grown at 15/10, 20/15 and 25/20 deg C, it was found that a higher temperature resulted in higher concentrations of cell-wall constituents and lower digestibility, whereas during ageing the percentage of cell-wall constituents remained constant or even decreased, digestibility decreasing slightly. Results suggested that in a constant climate the effect of age on digestibility would be small, and that the great effect of age on forage quality in spring is mainly due to rising temperature and stem formation. (Abstract retrieved from CAB Abstracts by CABI’s permission

The influence of defoliation and nitrogen on the regrowth of Rhodes grass (Chloris gayana Kunth). 2. Etiolated growth and non-structural carbohydrate, total-N and nitrate-N content.

Data are given on the chemical composition of Rhodes grass cv. Common grown in a heated glasshouse [see HbA 42, 1910]. Plants given high N (8.29 meq/100 g soil) contained about 30% less carbohydrate in the stubble and roots than those given low N (1.43 meq/100g). The carbohydrate content of plants cut every 28 days was generally lower than that of plants cut every 14 days. Amounts of etiolated growth in darkness after cutting were positively correlated with the carbohydrate level in the roots and in the stubble. The percentage of tillers exhibiting regrowth in darkness increased linearly up to about 60% with increase in the amount of etiolated growth. Contents of total N in roots and in stubble were almost double at the high rate of N. Amounts of nitrate as a proportion of total N were about 12% in low-N plants and up to 47% in high-N plants. The nitrate contents of shoots, stubble and roots were negatively correlated with the carbohydrate levels in each of these tissues. The overall difference in carbohydrate level between shoots, stubble and roots was relatively small. It was concluded that Rhodes grass had a limited capacity to accumulate reserve material when grown under conditions favouring rapid growth. (Abstract retrieved from CAB Abstracts by CABI’s permission

From plasmodesma geometry to effective symplasmic permeability through biophysical modelling

Regulation of molecular transport via intercellular channels called plasmodesmata (PDs) is important for both coordinating developmental and environmental responses among neighbouring cells, and isolating (groups of) cells to execute distinct programs. Cell-to-cell mobility of fluorescent molecules and PD dimensions (measured from electron micrographs) are both used as methods to predict PD transport capacity (i.e., effective symplasmic permeability), but often yield very different values. Here, we build a theoretical bridge between both experimental approaches by calculating the effective symplasmic permeability from a geometrical description of individual PDs and considering the flow towards them. We find that a dilated central region has the strongest impact in thick cell walls and that clustering of PDs into pit fields strongly reduces predicted permeabilities. Moreover, our open source multi-level model allows to predict PD dimensions matching measured permeabilities and add a functional interpretation to structural differences observed between PDs in different cell walls