Interaction between two decomposer basidiomycetes and a collembolan under Sitka spruce: Grazing and its potential effects on fungal distribution and litter decomposition

The hypothesis that selective grazing by Onychiurus latus Gisin altered the outcome of competition between two basidiomycetes, Mycena galopus (Pers. ex Fr.) Kummer and Marasmius androsaceus (L. ex Fr.) Fr. on Sitka spruce litter was tested. Without grazing M. androsaceus had the higher colonizing ability of litter in the laboratory whereas with grazing the position was reversed. Field exclusion experiments also suggested that higher densities of O. latus resulted in a reduction in the activity of M. androsaceus and an increase in that of M. galopus and vice versa. It is suggested that selective grazing may be an important factor determining the field distribution of these fungi, since M. androsaceus, the preferred food source, was restricted to the L litter horizon where the density of O. latus was not high enough to alter the outcome of competition whereas M. galopus predominated in the F₁ horizon. The rate of decomposition of Sitka spruce litter in the laboratory caused by M. androsaceus (17% dry weight loss over 6 months at 11°C) increased by 4–14% in the presence of grazing by O. latus whereas that of M. galopus (11.5%) decreased by 12–16%.     

Polycyclic Aromatic Hydrocarbon Oxidation from Concentrates Issued from an Attrition Process of Polluted Soil Using the Fenton Reagent and Permanganate

This study was conducted to determine the optimal conditions for PAH degradation from highly contaminated attrition sludge (PAC) using a Fenton process or successive permanganate (KMnO₄) oxidation and Fenton processes. The following parameters were studied to optimize the Fenton oxidation process: the amounts of reactants based on the stoichiometric oxidant demand (SOD), the reactant addition protocol and number of doses, and the solid/liquid ratio (S/L). The results showed that the following conditions were optimum: TS?=?30%, 7.5 times SOD, H₂O₂/Fe²⁺ ratio?=?10, and added five times during 60 min, which allowed the degradation of 43% of total 27 PAHs from the PAC. Successive Fenton and KMnO₄ oxidation processes were also tested. PAH degradation using a sequential Fenton process followed by KMnO₄ oxidation (or KMnO₄ followed by Fenton) was higher than for the use of Fenton or KMnO₄ treatment alone. Up to 71% of the total 27 PAHs were degraded when using a combination of both processes. It appeared that the sequential treatment is a viable method for the significant degradation of 27 PAHs from PAC (t value?>?2.77).     

Non nutritional factors affecting the growth of Trichoderma in culture

Species of Trichoderma typical of cool geographic regions possessed lower temperature optima and maxima than species from warm climatic regions. T. viride Pers. ex S.F. Gray and T. polysporum (Link ex Pers.) Rifai had temperature maxima ranging from 28–31°C and grew much better than other species at 7°C. The temperature maxima of T. koningii Oud. ranged from 32–35°C, T. hamatum (Bon.) Bain. from 30–35°C, T. harzianum Rifai from 30–38°C and T. pseudokoningii Rifai and T. saturnisporum Hammill from 40–41°C.Isolates of Trichoderma varied in their responses to CO₂-enriched atmospheres and the response was pH dependent. The largest responses were obtained on a medium of pH 7.5 as compared to an acid medium of pH 4.4. As the CO₂ level increased from 2 to 10 per cent, growth was reduced on an acid medium and increased on the alkaline medium as compared to cultures incubated in air. In air the optimum pH for Trichoderma ranged between 3–7 and 4.7. However, as the CO₂ concentration was increased to 10 per cent, growth was nearly as good at pH 7.5 as at pH 4.4.The addition of HCO₃^? to an alkaline medium strongly inhibited Trichoderma while having little effect on fungi isolated from roots or a strongly alkaline habitat. Low moisture content of litter was shown to have a variable effect on Trichoderma species and may be important in the ecology of Trichoderma. Salt (NaCl) concentration is not considered to be an important ecological factor.     

Carbon and nitrogen turnover in response to warming and nitrogen addition during early stages of forest litter decomposition—an incubation experiment

Purpose

Little is known about the interactive effects of temperature, nitrogen (N) supply, litter quality, and decomposition time on the turnover of carbon (C) and N of forest litter. The objective of this study was to investigate the interactive effects of warming, N addition and tree species on the turnover of C and N during the early decomposition stage of litters in a temperate forest.

Materials and methods

A 12-week laboratory incubation experiment was carried out. The leaf litters including two types of broadleaf litters (Quercus mongolica and Tilia amurensis), a needle litter (Pinus koraiensis), and a mixed litter of them were collected from a broad-leaved Korean pine mixed forest ecosystem in northeastern China in September 2009. Nine treatments were conducted using three temperatures (15, 25, and 35 °C) combined with three doses of N addition (equal to 0, 75, and 150 kg?·?ha^?1?a^?1, respectively, as NH₄NO₃).

Results and discussion

After 12 weeks of incubation, the mass loss ranged between 12 and 35 %. The broadleaf litters had greater mass loss and cumulative CO₂–C emission than the needle litter. Temperature and N availability interacted to affect litter mass loss and decomposition rate. The dissolved organic carbon (DOC) and nitrogen (DON) concentrations in litter leachate varied widely with litter types. DOC increased significantly with increased temperature but decreased significantly with increased N availability. DON increased significantly with increased N availability but showed a higher level at the moderate decomposition temperature. The amounts of CO₂ and N₂O emission were significantly higher at 25 °C than those at 15 and 35 °C, and were significantly increased by the N addition.

Conclusions

The present study indicated relatively intricate temperature and N addition effects on C and N cycling during early stages of litter decomposition, implying that future increases in temperature and N deposition will directly affect C and N cycling in broad-leaved Korean pine mixed forest ecosystem, and may indirectly influence the ecosystem composition, productivity, and functioning in NE China. It is, therefore, important to understand the interactive effects of biotic and abiotic factors on litter decomposition in field conditions in order to assess and predict future ecosystem responses to environmental changes in NE China.     

Competitiveness and effectiveness of strains of Rhizobium phaseoli isolated from the sonoran desert

Four strains of Rhizobium phaseoli were examined for N₂ fixation effectiveness and for competitiveness for nodule occupancy by utilizing strain-specific fluorescent antibodies. Competition studies in Leonard jars held in a growth chamber showed strain KIM-5 (a cool season isolate from Kimberly, Idaho) consistently occupied the majority of nodules on bean plants (Phaseolus vulgaris L.) cv. Kentucky Wonder, when applied as a mixed inoculant with desert strains (K-1, 36 or 90). Competitiveness of KIM-5 was relatively independent of cell numbers as shown by the high recovery of KIM-5 from nodules, even when extensively outnumbered in the inoculant. KIM-5 out-competed the desert strains regardless of whether they were ineffective (strains 36 and 90) or highly effective (K-1). Although KIM-5 was more competitive than K-l, no difference in infectiveness (as shown by nodule mass) or effectiveness (as shown by % N, total plant N, C₂H₂ reduction and total plant weight) was observed.In YEM broth, strain K-l showed increasing growth rates when the temperature was increased from 27° to 35°C, and was viable at 40°C. These data indicate K-1 to be an unusually heat-tolerant strain. Growth rates of KIM-5 were constant from 27° to 35°C and the organism was not viable at 40°C. Both strains produced acid in a defined broth medium.The effectiveness of KIM-5 and K-l was also evaluated under field conditions using single strain inoculants with two cultivars of pinto beans (P. vulgaris L.) ev. Mexicali 80 and Delicias 71. Inoculation with K-1 resulted in yield increases with both cultivars over uninoculated plants, whereas there was little difference between KIM-5 inoculated and uninoculated plants.     

Effect of Waterborne Zinc on Survival, Growth, and Feed Intake of Indian Major Carp, Cirrhinus mrigala (Hamilton)

The effect of waterborne zinc on survival, growth, and feed intake of Indian major carp, Cirrhinus mrigala (Hamilton), advanced fry was studied under laboratory condition. Survival rates of C. mrigala advanced fry (2.71?±?0.49 g) after 30 days exposure to control (0.01), 0.03, 0.06, 0.10, and 0.15 mg/L zinc using the static renewal method in freshwater at pH 7.3?±?0.2, temperature 26?±?2°C, and total hardness 114?±?16 mg/L as CaCO₃ were 100%. Growth of the fish exposed to 0.10 and 0.15 mg/L of zinc was significantly lower (P?<?0.05) than in control (0.01), 0.03, and 0.06 mg/L of zinc after 30 days of exposure. However, there were no significant differences (P?>?0.05) in fish growth between 0.03 and 0.06 mg/L zinc concentrations. Feed intake rates were significantly (P?<?0.05) reduced in the fish exposed to 0.10 mg/L and higher levels of zinc. The zinc accumulation in the whole body of the fish increased with increasing concentrations of the metal.     

Carbon dioxide production and oxygen consumption during the early decomposition of different litter types over a range of temperatures in soil‐inoculated quartz sand

Oat straw, hay, and alfalfa litter, differing in microbial colonization and recalcitrance, were added to organic matter–free quartz sand (5 mg C [g material]^–1) and incubated in the laboratory at 5°C, 10°C, 15°C, 20°C, and 25°C. Different incubation periods were chosen so that theoretically the same amounts of CO₂ would be produced and the same amounts of O₂ would be consumed for each litter type. It was investigated whether Q₁₀ values (change in respiration rate between two temperatures) increase with decreasing temperature and how much these Q₁₀ values and also the respiratory quotient (RQ: mol CO₂/mol O₂) depend on the litter type. The sums of CO₂‐C evolved and O₂ consumed, but also the contents of microbial biomass C and microbial biomass N showed a nearly 7‐fold increase in the order oat straw < hay < alfalfa litter. In contrast, the ratio of the fungal cell‐membrane component ergosterol to microbial biomass C was highest in the oat straw (4.1‰) and lowest in the alfalfa litter (0.2‰). This ratio reached a similar level between 5°C and 15°C (1.9‰), significantly higher (p = 0.01) than the level at 20°C (0.9‰). Respiration was similar between 20°C and 25°C, with a mean Q₁₀ value of 1.9. The use of temperature rate‐modifying factors suggested by the carbon‐turnover model ROTHC revealed that the incubation period for similar respiration rates was underestimated at 5°C and overestimated at 25°C. The lignin‐poor and protein‐rich alfalfa litter showed the highest Q₁₀ values of the three litter types in the medium temperature range of 10°C to 20°C. In contrast, the lignin‐rich and protein‐poor oat straw showed significantly highest Q₁₀ values at 5°C and 25°C in comparison with the other two litter types. The RQ was significantly highest in the hay litter (1.05) and in comparison with alfalfa litter (0.97) and oat straw (0.92). Strong temperature‐dependent variations in Q₁₀ values and respiratory quotients suggest interactions between litter quality, microbial colonization of litter, and temperature, which warrants further investigation.     

不同森林植被下土壤活性有机碳的含量及动态变化

Soil organic matter （SOM） in forest ecosystems is not only important to global carbon （C） storage but also to sustainable management of forestland with vegetation types, being a critical factor in controlling the quantity and dynamics of SOM. In this field experiment soil plots with three replicates were selected from three forest vegetation types： broadleaf, Masson pine （Pinus massoniana Lamb.）, and Chinese fir （Cunninghamia lanceolata Hook.）. Soil total organic C （TOC）, two easily oxidizable C levels （EOC1 and EOC2, which were oxidized by 66.7 mmol L^-1 K2Cr2O7 at 130-140℃ and 333 mmol L^-1 KMnO4 at 25 ℃, respectively）, microbial biomass C （MBC）, and water-soluble organic C （WSOC） were analyzed for soil samples. Soil under the broadleaf forest stored significantly higher TOC （P ≤ 0.05）. Because of its significantly larger total soil C storage, the soil under the broadleaf forest usually had significantly higher levels （P ≤ 0.05） of the different labile organic carbons, EOC1, EOC2, MBC, and WSOC; but when calculated as a percentage of TOC each labile C fraction of the broadleaf forest was significantly lower （P ≤ 0.05） than one of the other two forests. Under all the three vegetation types temperature as well as quality and season of litter input generally affected the dynamics of different organic C fractions in soils, with EOC1, EOC2, and MBC increasing closely following increase in temperature, whereas WSOC showed an opposite trend.     

Microbial biomass and activity in soil and litter underPinus sylvestris, Picea abies andBetula pendula at originally similar field afforestation sites

Microbial biomass C and N, and activities related to C and N cycles, were compared in needle and leaf litter, and in the uppermost 10 cm of soil under the litter layer in Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.) and silver birch (Betula pendula L.) stands, planted on originally similar field afforestation sites 23–24 years ago. The ground vegetation was differentiated under different tree species, consisting of grasses and herbs under birch and pine, and mosses or no vegetation with a thick layer of needles under spruce. The C:N ratio of the soils was 13–21 and the soil pH_{CaCl 2} 3.8–5.2. Both showed little variation under different tree species. Microbial biomass C and N, C mineralization, net ammonification, reduction) did not differ significantly in soil under different tree species either. Birch leaf litter had a higher pH_{CaCl 2} (5.9) than spruce and pine needle litter (pH 5.0 and 4.8, respectively). The C:N ratio of spruce needles was 30, and was considerably higher in pine needles (69) and birch leaves (54). Birch leaves tended to have the highest microbial biomass C and C mineralization. Spruce needles appeared to have the highest microbial biomass N and net formation of mineral N, whereas formation of mineral N in pine needles and birch leaves was negligible. Microbial biomass C and N were of the same order of magnitude in the soil and litter samples but C mineralization was tenfold higher in the litter samples.     

Potential for Quantification of Biologically Active Soil Carbon with Potassium Permanganate

Oxidation of soils with 333 mM potassium permanganate (KMnO₄) has been identified as a means to quantify labile soil carbon (C) and may have potential for rapid measurement of biologically active soil C. In the current study, active C pools in several soils were estimated by oxidation with a range of KMnO₄ concentrations and compared to estimates determined from carbon dioxide evolution during 28‐d incubations. Digestion with 333 mM KMnO₄ identified larger active C pools than did incubation data. However, shaking soils for 15 min with 2.5 mM KMnO₄ provided estimates of active C that accounted for 1.5 to 1.9% of the total C pools and were not significantly different than those estimated using incubation data. Oxidation with dilute KMnO₄ appears to be feasible to rapidly quantify active soil C pools. However, measurements are dependent on KMnO₄ concentration and shaking time, so great care is needed to assure consistent results.     

Foliar sensitivity of pinto bean and soybean to ozone as affected by temperature,potassium nutrition and ozone dose

Pinto bean (Phaseolus vulgaris L.) and soybean [Glycine max (L.) Merv.] were exposed to O₃ to determine the interactions of growth temperature, exposure temperature, K nutrition and doses of O₃ on their foliar sensitivity. Pinto bean developed more foliar injury than soybean. Pinto bean were most sensitive when grown and exposed at 28°C. Growth and exposure temperature interacted in the development of foliar injury on pinto bean, but only growth temperature influenced the amount of foliar injury on soybean. Both species developed more foliar injury when grown with low K nutrition. There was no relationship between foliar injury and reducing sugars or sucrose content of the leaves.     

Kinetics of glucose uptake by soil microorganisms

The kinetics of glucose uptake by soil microorganisms was investigated. Soil amended with an inorganic nutrient solution containing C glucose at concentrations of 2.5, 5.0, 10.0 or 20.0 mmol 1⁻¹ was maintained at 4, 12 or 25°C for varying times. The soil was analyzed for glucose, soluble ^14C, total organic ¹⁴C and evolved ¹⁴CO₂ to develop a carbon balance for the system and to define Michaelis-Menten kinetic parameters (K_m and V_max) for glucose uptake at each temperature.Glucose uptake rates, as measured by the depletion of glucose or soluble ¹⁴C from solution, were similar in soils maintained at 12 or 25°C. Based on the depletion of soluble ¹⁴C, values for K_m were 2.25 and 2.43 mmol I⁻¹ at 12 and 25°C, respectively, while V_max values were 0.25 and 1.61 h¹⁴', respectively. Glucose depletion at 4°C was faster than at 12C, while soluble ¹⁴C was removed at a significantly slower rate, suggesting soluble-C intermediates were produced in the 4°C system. Based on Chromatographie techniques and GC-MS, a soluble ¹⁴C-compound accumulating in the 4°C system was identified as maltose. The conversion of glucose to maltose resulted in K_m and V_max values of 17.29 mmol I⁻¹ and 0.12h⁻¹, respectively, for soluble ¹⁴C depletion and 4.96mmol1⁻¹ and 0.43 h⁻, respectively, for glucose depletion at 4δC. These results demonstrate the need to differentiate uptake rates for the parent compound as well as for transitory intermediates excreted into the growth medium. Evolution of CO₂ was shown to be a poor indicator of the rapid disappearance of glucose in soils.     

Effects of litter (beech and stinging nettle) and earthworms (Octolasion lacteum) on carbon and nutrient cycling in beech forests on a basalt-limestone gradient: A laboratory experiment

Effects of leaf litter of beech (Fagus sylvatica L.) and stinging nettles (Urtica dioica L.) and of the endogeic earthworm species Octolasion lacteum (Örley) on carbon turnover and nutrient dynamics in soil of three beechwood sites on a basalt hill (Hesse, Germany) were investigated in a laboratory experiment lasting for about 1 year. The sites were located along a gradient from basalt (upper part of the hill) to limestone (lower part of the hill) with an intermediate site in between (transition zone). At the intermediate site U. dioica dominated in the understory whereas at the other sites Mercurialis perennis L. was most abundant. The amount and composition of organic matter was similar in soil of the basalt (carbon content 5.9%, C/N ratio 13.8) and intermediate site (carbon content 5.6%, C/N ratio 14.3) but the soil of the intermediate site produced more CO₂ (in total +17.5%) and more nitrogen (as nitrate) was leached from this soil (in total +55.6%). It is concluded that the soil of the intermediate site contains a large mobile carbon and nitrogen pool and the formation of this pool is ascribed to the input of U. dioica litter. Leaf litter of U. dioica strongly increased NO₃ ^–-N leaching immediately after the litter had been added, whereas nitrogen was immobilized due to addition of beech litter. Despite the very fast initial decomposition of nettle litter, the increase in CO₂ production due to this litter material was only equivalent to 20.1% of the amount of carbon added with the nettle litter; the respective value for beech litter was 34.8%. Earthworms altered the time course of carbon and nitrogen mineralization in each of the treatments. In general, earthworms strongly increased mineralization of nitrogen but this effect was less pronounced in soil of the intermediate site (treatments without litter), which is ascribed to a depleted physically protected nitrogen and carbon pool. In contrast, their effect on the total amount of nitrogen mobilized from nettle litter was small. Earthworms significantly reduced CO₂ production from soil of the intermediate site (treatments without litter) and it is concluded that earthworm activity contributes to the restoration of the depleted physically protected carbon pool at this site.     

Decomposition of tree leaf litter and crop residues from ginkgo agroforestry systems in Eastern China: an in situ study

Purpose

Litter decomposition is a crucial biogeochemical process linking nutrient cycling and carbon (C) storage in ecosystems, but few studies have investigated this process in agroforestry systems, where tree leaf litter is mixed with intercrop residues.

Materials and methods

A 360-day in situ litter bag decomposition experiment was conducted in three ginkgo (Ginkgo biloba L.) plantation systems (a ginkgo-corn (Zea mays L.)-wheat (Triticum aestivum L.) system, ginkgo-rape (Brassica napus L.)-soybean (Glycine max (L.) Merr.) system, and pure ginkgo system).

Results and discussion

Ginkgo leaves decomposed fastest in the ginkgo-corn-wheat system, followed by the ginkgo-soybean-rape system, and the pure ginkgo system. Among all litter species, corn leaves and a ginkgo-corn mixture in the ginkgo-corn-wheat system decomposed fastest and wheat straw most slowly. The Olson’s litter exponential decay model showed the same results; approximately 9 months and slightly less than 27 months was required to decompose 50 and 95% of the litter, respectively. Compared to single-species litter, mixed litters accelerated litter decomposition, except for the ginkgo-wheat mixture. Litter nitrogen (N) loss varied dramatically among litter species during the 360-day in situ incubation.

Conclusions

The agroforestry system, litter quality, and mixed effects play important roles in litter decomposition. The Ca content, organic carbon, and living vegetation should be taken into account when studying litter decomposition in agroforestry. Analysis during the litter decomposition process clearly indicated that litter N loss changes dramatically.

     

How gypsy moth eggs freeze

Although eggs of the gypsy moth Lymantria dispar (L.) supercool, a steady and substantial portion freezes and dies at a steady temperature below ?26°C. The rate of freezing at steady temperature is about 1% per min at ?27°C and changes about tenfold per degree. The freezing of the eggs at varying temperature is predicted by integration of the rates observed at steady temperature.     

Growth,transpiration, root‐born cytokinins and gibberellins,and nutrient compositional changes in sesame exposed to low root‐zone temperature under different ratios of nitrate: Ammonium supply

The growth of sesame (Sesamum indicum L.) was studied at three root temperature regimes (25/25, 20/10 and 15/15°C day/night) factorially combined with three NO₃ ^‐: NH₄ ⁺ ratios (mM ratios, 10:0, 8:2, or 6:4), as a source of nitrogen (N), in the irrigation solution. The air temperature was kept constant at 30°C. Transpiration, nutrient composition, and level of root‐born cytokinins and gibberellins in the xylem exudate were monitored. The two low root temperature regimes, 15/15 and 20/10°C, restricted the growth of sesame, reduced transpiration and increased the accumulation of soluble carbohydrates in the shoot and in the roots compared to the 25/25°C regime. The NO₃:NH₄ ⁺ ratios had no effect on growth. Nutrient contents in the shoot at low root temperatures, particularly K⁺, NO₃ ^‐, and H₂PO₄ ^‐ were decreased markedly, but Na⁺ increased relative to it's content in the 25/25°C regime. Increasing NH₄ ⁺ proportion in the irrigation solution raised total N concentration in the plant tissues at all root temperatures. The amounts of cytokinins and gibberellins in the xylem exudate decreased at the low root temperature regimes relative to the 25/25°C regime. Low root temperature reduced xylem transport of nutrients and root born‐phytohormones, most probably because of reduced water flow through the plant relative to the 25/25°C regime.     

Growth and reproduction of the vermicomposting earthwormPerionyx excavatus as influenced by food materials

An outdoor study was undertaken using polyethylene containers to assess the suitability of different organic residues, soybean straw (Glycine max L. Merril.), wheat straw (Triticum aestivum L.), maize stover (Zea mays L.), chickpea straw (citer arietinum L.) and city garbage, as food for the tropical epigeic earthwormPerionyx excavatus, and to assess the influence of this earthworm on the decomposition of these materials. Maize stover was found to be the most suitable of the food materials used. Population growth ofP. excavatus was enhanced by addition of these organic materials in the temperature range 24°-30°C, while the population was adversely affected above 30°C in a vermiculture system. Addition of earthworms accelerated the breakdown of residues, which ultimately resulted in a lowering of the C:N ratio, water-soluble carbon and carbohydrates, and increased ash percentage and cation exchange capacity compared with their respective controls.     

Phytoremediation of High-Phosphorus Soil by Annual Ryegrass and Common Bermudagrass Harvest

Removal of soil phosphorus (P) in crop harvest is a remediation option for soils high in P. This 4-year field-plot study determined P uptake by annual ryegrass (ARG, Lolium multiflorum Lam.) and common bermudagrass (CB, Cynodon dactylon (L.) Pers.) from Ruston soil (fine-loamy, siliceous, thermic Typic Paleudult) enriched in P by five previous annual applications of poultry litter, and related P removed to Bray 2 P in surface (0–15 cm) soil. Decreases in surface soil Bray 2 P were largely attributable to uptake. Phosphorus uptake was positively related to Bray 2 P but approached a limit. Mass of P removed in harvest closely approximated the decrease in mass of surface soil Bray 2 P. Maximum Bray 2 P drawdown per harvest (ARG and CB, average) was ?3 mg kg^?1 at Bray 2 P ? 300 mg kg^?1, generally consistent with measured decreases in Bray 2 P.     

Light and temperature modulated expolinear growth model for potato (Solanum tuberosum L.)

Expolinear growth equations are robust and simple models for the early and middle stages of crop growth. Those proposed by Greenwood and by Monteith were compared for potato (Solanum tuberosum L.) crop biomass in well-managed fields in the Central Wisconsin Sand Plain, and the Monteith equation found preferable. A time-derivative form of the Monteith equation was coupled to daily solar radiation and air temperature. Solar radiation was linked to daily maximum absolute growth through light use efficiency, and daily maximum relative growth rate was made a function of temperature by assuming a doubling of biological processes with every 10 °C increase (Q₁₀=2). The modified model predicted dynamic dry matter accumulation variation from year to year, and showed improved prediction of potato growth until senescence.     

Seasonal effects on photoassimilated carbon-14 in the root system of blue grama and associated soil organic matter

Blue grama (Bouteloua gracilis (H.B.K.) Lag.) was grown at day (14 h) and night temperatures of 25° and 15°C, respectively, in a ¹⁴CO₂-atmosphere during the last 31 of the 55 days from germination to seed set (period 1). An air-tight seal separated the shoot and root spheres. This period was followed by 21 days of a 14°C day (10 h) and 38°C night regime, and 29 days of continuous ?5°C (period 2), and 26 days of the original temperature and light conditions (period 3). Distribution of the assimilated ¹⁴C at the end of period 1 was: roots 33%; root-derived organic matter in the soil 23%; and 22% was released as CO₂. The washed root mass to root-derived soil organic matter ratio of the labelled ¹⁴C was 60 to 40. A root mass decrease of 45% over the cool and frost period changed this ratio to 23 to 77. Polysaccharides and 0.1 n NaOH-extractable organic matter decreased while potential dehydrogenase activity and total organic P increased during this same period, thereby confirming field related observations. Measured dehydrogenase activity overwinter may have two different origins. As total C content of the soil did not increase under the conditions of the experiment, it was postulated that a portion of the observed increase in total C in the field overwinter was of inorganic rather than organic origin.