Microbial biomass and activity along a natural pH gradient in forest soils in a karst region of the upper Yangtze River,China

Mountain closure, considered an effective and economic measure for natural restoration of degraded forest ecosystems, has been widely carried out in the karst region of southwest China. The aim of this study was to evaluate microbial aspects of soil quality after mountain closure by analyzing soil microbial biomass, basal respiration, metabolic quotient, and relationships with basic chemical properties in Guizhou Province, a karst region of the upper Yangtze River. Soil quality was considered poor from the low levels of microbial biomass carbon (MBC), nitrogen (MBN), and microbial quotient (MBC/total C and MBN/total N), but high metabolic quotient (qCO₂). Soil pH, showing marked variation from 4.1 to 7.9 in this karst region, was proved to significantly affect soil microbial biomass and activity. Soil microbial biomass, microbial quotient, and soil basal respiration declined significantly with decreasing soil pH, while qCO₂ showed an apparently increasing, but not statistically significant, trend. The changes in microbial biomass and activity following the change in soil pH could possibly be because of a change in soil microbial composition, and more detailed research is necessary. Compared with soil pH, soil organic matter content was another, more important, factor that directly restricted microbial growth because of the serious loss as a result of disturbance. As a practical application based on microbial aspects, introduction of some N-fixing tree species may be an active and effective measure to improve soil fertility and thus to accelerate restoration of the forest ecosystem in the karst region.     

Investigations on the radioactive contamination of crop plants as a result of H-bomb detonation (Part 2) Root and foliage uptake of “Bikini ash”

The Foliar Uptake by Squash Plant

The radioactive ash for experimental use, hereafter referred to as “Bikini ash”, was prepared by igniting the heavily contaminated substances on board No. 5 Fukuryu Maru at about 650°C, followed by sifting through a 100 mesh sieve. On ignition some parts of the fission products, particularly iodine, ruthenium and tellurium would have possibly been lost to the air.     

Changes in soil chemical and physical characteristics in Japanese cypress (Chamaecyparis obtusa Endl.) stands by mixture of deciduous broad-leaved trees in the northern Kanto region of Japan

In order to clarify the effects of a mixture of deciduous broad-leaved trees on soil fertility, we investigated litter biomass accumulation, mineral soil chemical and physical characteristics, characteristics of nitrogen mineralization, and the mutual relationships between them in Japanese cypress (Chamaecyparis obtusa) stands mixed with deciduous broad-leaved trees at different ratios (mixture ratio; MR = 0, 16, 33, 43, 100% by basal area) in the northern Kanto region of Japan. Litter biomass in the forest floor and mineral soil was 19.1 Mg ha⁻¹ in MR 0% and decreased approximately 60 % in MR 33%, MR 43% and MR100%. The permeability at 0–5 cm soil depth in MR100% was twice as much as that in MR 0%. Increases in soil permeability were likely due to larger soil pores in the higher MR with much accumulated deciduous broad-leaves. At 0–5 cm soil depth, the differences in carbon concentration among the plots were not clear. On the other hand, carbon concentrations at 5–10 cm depth increased from 90 g kg⁻¹ to 147 g kg⁻¹ with increases in MR from 0% to 100%. Concentrations of exchangeable bases increased two to four times with increases in MR from 0 to 100% at 0–10 cm depth. Soil pH (H₂O) generally increased with increases in MR at each depth. The rates of net nitrogen mineralization at 0–5 cm depthin vitro increased from 25 to 87 mg kg⁻¹ 2 weeks⁻¹ with increases in MR from 0 to 100%. However, increases in nitrification with increases in MR were not clear compared with nitrogen mineralization. These results indicated that a mixture of deciduous broad-leaved trees in a Japanese cypress stand was effective in preventing soil fertility decline. This study was supported by a grant from the Showa Shell Sekiyu Fundation for Promotion of Environmental Research. A part of this study was presented at the 7th International Congress of Ecology (1998).     

Asparagine test in relation with the nitrogen nutritional status of crop plants: V

The previous (1) investigation on this crop brought two very interesting results which include the presence of nitrate in detectable quantity under waterlogged soil condition and quite different role of different forms of nitrogen towards the appearance of asparagine. It created a new interest in the Asparagine Test study and it was considered essential to obtain confirmatory results with the present investigation. However, the plan of the experiment previously adopted was modified to some extent to get, in addition, informations on the results obtained in the previous investigation. The experiment was aimed to include a completely reduced condition in combination with ammonium and nitrate nitrogen as basal application. Also, urea was excluded from the topdressing forms of nitrogen and only nitrate and ammonium form nitrogens were studied in greater detail.     

Effect of organic matter on the growth,nodulation, and nitrogen fixation of soybean grown under acid and saline conditions

Abstract

A field experiment was conducted to examine the effects of two organic materials (Bark and Tenporon composts) on the growth, nodulation and nitrogen fixation (measured as acetylene-reducing activity) of soybean plants (Glycine max L.) under acid and saline conditions. These organic materials were incorporated into acid and saline (induced by irrigating the soil with a NaCl solution) soils at 4% rate of application.

These composts tended to improve nodule formation in soybean under acid and saline conditions, especially in the plants treated with Bark compost. Acetylene-reducing activity was significantly (P<0.05) increased by these composts under acid condition.

These composts also tended to improve shoot growth under acid and saline conditions, presumably due to the improvement of the soil moisture status of the soils and nutrient uptake. These results suggest that the growth of soybean could be improved by the application of organic matter under acid and saline conditions.     

Asparagine test in relation with the nitrogen nutritional status of crop plants II

In the previous paper it was reported that the early panicle formation is the most important period of top dressing for rice plant, and to determine the requirement of top dressing asparagine test may be used.     

Use of optical spectrograpiuc 15N-analyses to trace nitrogen applied at tile heading stage of rice

In the recent decades experimental work has led to the accumulation of vast quantities of valuable data on mineral nutrition of plants through the use of isotopic tracers. However, only limited research has been done with nitrogen presumably because of the high costs of instrumentation and isotopes. A few Investlgatlons on the distribution and accumulation of nitrogen have been reported using mass spectrographic method. For example, Ozaki et al. (1) observed a larger distribution of ammonical nitrogen administered before heading, Into ears, culms, and boot leaves in contrast with other plant parts. They further noted that 35% of the nitrogen applied after heading was found in the ears (2).     

The uptake,distribution, and accumulation of 15N-labelled ammonium and nitrate nitrogen top-dressed at different growth stages of rice

A pot experiment with soil culture was carried out to trace ¹⁵N-labelled nitrogen top-dressed at different growth stages of rice. The study involves the use of a modified vacuum system for determining total nitrogen by gu volumetric measurement, and the N₂ gas sampled in the discharge tube was analysed for nitrogen-15 by the optical spectrographic technique.

The plants took up more nitrogen from (¹⁵NH₄)₂SO₄ than from Na¹⁵NO₃, irrespective of the stage of dressing, and the uptake of both forms was much higher when the planta were top-dressed at the young panicle formation stage as compared with the later dressings. At full maturity the plants had the highest accumulation of labelled nitrogen from both ammonium and nitrate sources when they are top-dressed at the young panicle formation stage. More than 80% ot the labelled nitrogen taken up by the plants waa distributed in the brown rice and this trend was more remarkable when top-dressing was carried out at the milk stage. The distribution patterns of ammonium and nitrate nitrogen were similar in brown rice but differed in leaves and stem.

Nitrogen transported from other parts to the panicle was utilized for the formation ot the husk until the booting stage, and then for brown rice development. With the completeness of husk formation, at the milk stage, nitrogen transported to the grain might have been utilized for brown rice development more rapidly. In the brown rice, nitrogen from ammonium was translocated maximally to the inner part of the endosperm from dressing at the booting stage, and to the embryo from that at the milk stage, whereas that from nitrate was translocated maximally to the embryo from the dressings at both stages.     

Anatomical responses of root tips to boron deficiency II. Effect of boron deficiency on the cellular growth and development in root tips

Changes induced in the tissue structure and the cellular patterns of young tomato root tips by the absence of boron in the nutrient solution were investigated.

Boron deficiency caused primarily the inhibition of cell division and cell elongation in root apices, and the cells of boron-deficient root tips were fully vacuolated. The cell wall in the apical region was thickened by boron deficiency and the intercellular spaces insufficiently developed.

Boron deficiency also caused the radial enlargement of cortical cells, especially of endodermis, but this enlargement was not accompanied by an increase in water imbibition. In the advanced stage of boron deficiency, the disintegration of tissue structure had occurred.

Primordia of lateral roots arose closely in root apices. Maturation of the vascular system, especially of the primary xylem, was exasperated abnormally, and frequently there occurred a differentiation of cambial layers close to the apical initials.

Anatomical effects of boron deficiency appeared particularly in the root apex and not clearly in the region of successive maturation. The results are discussed with regards to the role of boron in cellular growth at apical growing points.

The results are discussed with regards to the role of boron in cellular growth at apical growing points.     

Amino acid metabolism in plant leaf

¹⁴C-labelled sodium bicarbonate and ¹⁵N-labelled ammonium sulfate were simultaneously vacuum-infiltrated into detached sunflower leaves, and the incorporation of ¹⁴C and ¹⁵N into free amino acids was chased during 60-min period in the light and in the dark.

In the light, the ue specific activity of aspartic acid, alanine, serine and glycine rapidly increased for 5 min and thereafter decreased. On the other hand, that of gultamic acid continued to increase slowly during the entire 60-min period. In the dark, aspartic acid most actively incorporated ¹⁴C. The difference of changes in ¹⁴C specific activity between glutamic acid and other amino acids was also observed in the dark as in the light. These results suggest that the carbon skeleton of glutamic acid is synthesized from aspartic acid, alanine, serine and glycine.

¹⁵N content of glutamine was the highest of all amino acids investigated in the light, and it was followed by glutamic acid. alanine, aspartic acid, serine and glycine, in this order. In the dark, ¹⁵N content of glutamic acid fell remarkably and was lower than that of alanine up to 5 min. From these ¹⁵N tracer experiments, it is suggested that the incorporation of ammonium into glutamic acid is strictly dependent on light and that alanine incorporates ammonium by the direct amination besides the transamination from glutamic acid.