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61.
Effect of salinisation of soil on growth and macro- and micro-nutrient accumulation in seedlings of Acacia catechu (Mimosaceae) 总被引:3,自引:0,他引:3
The effects of salinisation of soil on Acacia catechu (Mimosaceae) were studied by means of emergence and growth of seedlings and pattern of mineral accumulation. A mixture of chlorides and sulphates of Na, K, Ca and Mg was added to the soil and salinity was maintained at 4.1, 6.3, 8.2,10.1 and 12.2 dSm−1. A negative relationship between proportion of seed germination and salt concentration was obtained. Seedlings did not emerge when soil salinity exceeded 10.1 dSm−1. Results suggested that this tree species is salt tolerant at the seed germination stage. Seedlings survived and grew up to soil salinity of 10.1 dSm−1, which suggests that this species is salt tolerant at the seedling stage too. Elongation of stem and root was retarded by increasing salt stress. Among the tissues, young roots and stem were most tolerant to salt stress and were followed by old roots and leaves, successively. Leaf tissue exhibited maximum reduction in dry mass production in response to increasing salt stress. However, production of young roots and death of old roots were found to be continuous and plants apparently use this process as an avoidance mechanism to remove excess ions and delay onset of ion accumulation in this tissue. This phenomenon, designated “fine root turnover”, is of importance to the mechanisms of salt tolerance. Plants accumulated Na in roots and were able to regulate transfer of Na ions to leaves. Stem tissues were a barrier for translocation of Na from root to leaf. Moreover, K was affected in response to salinity; it rapidly decreased in root tissues with increased salinisation. Nitrogen content decreased in all tissues (leaf, stem and root) in response to low water treatment and salinisation of soil. Phosphorus content significantly decreased, while Ca increased in leaves as soil salinity increased. Changes in tissue and whole plant accumulation patterns of the other elements tested, as well as possible mechanisms for avoidance of Na toxicity in this tree species during salinisation, are discussed. 相似文献
62.
Mercury evaporation from undisturbed iron‐humus podzol lysimeters was measured over 3 months after treatment with HgCl2 spiked with radioactive 203Hg. The relative evaporation rate from HgCl2 treated soils followed the sum of two exponential functions. Because evaporation asymptotically approaches zero with time, the integral of the fit curve represents the evaporative loss in percent of atmospheric deposition. For the soil investigated, about 5% of atmospheric Hg deposition was reemitted into the atmosphere. It is hypothesized that mercury evaporation can decrease the leaching of mercury in and from soil significantly; this effect is probably increasing with decreasing rain acidity or soil acidity. Mercury deposited as soluble salt remains susceptible to reemission to air for 300 d after incorporation into the soil matrix. Indications are found that Hg evaporation from soils in geological background areas predominantly derives from recent atmospheric Hg deposition and not from geological sources. 相似文献
63.
J. H. Lawton D. E. Bignell G. F. Bloemers P. Eggleton M. E. Hodda 《Biodiversity and Conservation》1996,5(2):261-273
Theoretically, there are three principal ways in which ecosystem processes might respond to reductions in species richness. These theories are reviewed, and then considered in the context of a study of the diversity of soil nematodes and termites in near-primary forest sites at Mbalmayo, Cameroon, and the contribution made by these two taxa to carbon fluxes (CO2 and CH4) from the forest floor. Nematode abundances average 2.04 × 106 m-2, and termites between 2933 and 6957 m-2. The site is the most species-rich yet investigated for both groups anywhere in the world, so that a very large number of species contribute to carbon fluxes. We speculate about how much redundancy might be built into the functioning of both assemblages, and point out the enormous difficulties of resolving such questions, and of producing such detailed species-inventories. 相似文献
64.
Atmospheric carbon dioxide enrichment and increasing nitrogen deposition are often predicted to increase forest productivity based on currently available data for isolated forest tree seedlings or their leaves. However, it is highly uncertain whether such seedling responses will scale to the stand level. Therefore, we studied the effects of increasing CO2 (280, 420 and 560 μL L-1) and increasing rates of wet N deposition (0, 30 and 90 kg ha-1 y-1) on whole stands of 4-year-old spruce trees (Picea abies). One tree from each of six clones, together with two herbaceous understory species, were established in each of nine 0.7 m2 model ecosystems in nutrient poor forest soil and grown in a simulated montane climate for two years. Shoot level light-saturated net photosynthesis measured at growth CO2 concentrations increased with increasing CO2, as well as with increasing N deposition. However, predawn shoot respiration was unaffected by treatments. When measured at a common CO2 concentration of 420 μL L-1 37% down-regulation of photosynthesis was observed in plants grown at 560 μL CO2 L-1. Length growth of shoots and stem diameter were not affected by CO2 or N deposition. Bud burst was delayed, leaf area index (LAI) was lower, needle litter fall increased and soil CO2 efflux increased with increasing CO2. N deposition had no effect on these traits. At the ecosystem level the rate of net CO2 exchange was not significantly different between CO2 and N treatments. Most of the responses to CO2 studied here were nonlinear with the most significant differences between 280 and 420 μL CO2 L-1 and relatively small changes between 420 and 560 μL CO2 L-1. Our results suggest that the lack of above-ground growth responses to elevated CO2 is due to the combined effects of physiological down-regulation of photosynthesis at the leaf level, allometric adjustment at the canopy level (reduced LAI), and increasing strength of below-ground carbon sinks. The non-linearity of treatment effects further suggests that major responses of coniferous forests to atmospheric CO2 enrichment might already be under way and that future responses may be comparatively smaller. 相似文献
65.
TheAnticarsia gemmatalisnuclear polyhedrosis virus (AgNPV) was released in two soybean plots in September, 1991; the soil in the plots was then sampled periodically through July, 1992, to determine the effects of normal agricultural soil manipulations and precipitation on vertical distribution of the polyhedral occlusion bodies (POBs). The amount of AgNPV increased at all depths down to 37.5–50 cm as long as there was virus-contaminated plant matter, even dead soybean refuse, above the soil surface. Agricultural operations (disking, harrowing, mowing, planting, cultivating) had no effect on the amount or vertical distribution of AgNPV in soil. After the crop refuse was disked into the soil in November, the amount of POBs began decreasing at all depths; these decreases continued over winter and at times appeared to be associated with precipitation. The POBs were no longer detected below 37.5 cm by April, 1992, or below 25 cm by July, 1992. However, in July there were still 274 POBs/g in the top 2.5 cm of soil. Thus, agricultural operations should not hinder contamination of soybean leaves by AgNPV from its soil reservoir. 相似文献
66.
Parietochloris incisa comb. nov. (Trebouxiophyceae, Chlorophyta) 总被引:3,自引:0,他引:3
Shin Watanabe Seishiro Hirabayashi Sammy Boussiba Zvi Cohen Avigad Vonshak Amos Richmond 《Phycological Research》1996,44(2):107-108
A coccoid green alga, Myrmecia incisa Reisigl, was isolated from the soil of Mt Tateyama, Japan. Electronmicroscopy revealed that the organism has pyrenoids sparsely covered with starch segments and traversed by many parallel thylakoid membranes, and zoo-spores with counterclockwise basal body orientation. Due to the presence of these features, we have proposed a reclassification of M. incisa into the genus Parietochloris, Trebouxiophyceae. 相似文献
67.
Stomatal responses to increased CO2 : implications from the plant to the global scale 总被引:9,自引:5,他引:4
Increased atmospheric CO2 often but not always leads to large decreases in leaf conductance. Decreased leaf conductance has important implications for a number of components of CO2 responses, from the plant to the global scale. All of the factors that are sensitive to a change in soil moisture, either amount or timing, may be affected by increased CO2. The list of potentially sensitive processes includes soil evaporation, run-off, decomposition, and physiological adjustments of plants, as well as factors such as canopy development and the composition of the plant and microbial communities. Experimental evidence concerning ecosystem-scale consequences of the effects of CO2 on water use is only beginning to accumulate, but the initial indication is that, in water-limited areas, the effects of CO2-induced changes in leaf conductance are comparable in importance to those of CO,2-induced changes in photosynthesis. Above the leaf scale, a number of processes interact to modulate the response of canopy or regional evapotran-spiration to increased CO2. While some components of these processes tend to amplify the sensitivity of evapo-transpiration to altered leaf conductance, the most likely overall pattern is one in which the responses of canopy and regional evapotranspiration are substantially smaller than the responses of canopy conductance. The effects of increased CO2 on canopy evapotranspiration are likely to be smallest in aerodynamically smooth canopies with high leaf conductances. Under these circumstances, which are largely restricted to agriculture, decreases in evapotranspiration may be only one-fourth as large as decreases in canopy conductance. Decreased canopy conductances over large regions may lead to altered climate, including increased temperature and decreased precipitation. The simulation experiments to date predict small effects globally, but these could be important regionally, especially in combination with radiative (greenhouse) effects of increased CO2. 相似文献
68.
69.
In this paper we present a conceptual model of integrated plant-soil interactions which illustrates the importance of identifying the primary belowground feedbacks, both positive and negative, which can simultaneously affect plant growth responses to elevated CO2. The primary negative feedbacks share the common feature of reducing the amount of nutrients available to plants. These negative feedbacks include increased litter C/N ratios, and therefore reduced mineralization rates, increased immobilization of available nutrients by a larger soil microbial pool, and increased storage of nutrients in plant biomass and detritus due to increases in net primary productivity (NPP). Most of the primary positive feedbacks share the common feature of being plant mediated feedbacks, the only exception being Zak et al.'s hypothesis that increased microbial biomass will be accompanied by increased mineralization rates. Plant nutrient uptake may be increased through alterations in root architecture, physiology, or mycorrhizal symbioses. Further, the increased C/N ratios of plant tissue mean that a given level of NPP can be achieved with a smaller supply of nitrogen.Identification of the net plant-soil feedbacks to enhanced productivity with elevated CO2 are a critical first step for any ecosystem. It is necessary, however, that we first identify how universally applicable the results are from one study of one ecosystem before ecosystem models incorporate this information. The effect of elevated CO2 on plant growth (including NPP, tissue quality, root architecture, mycorrhizal symbioses) can vary greatly for different species and environmental conditions. Therefore it is reasonable to expect that different ecosystems will show different patterns of interacting positive and negative feedbacks within the plant-soil system. This inter-ecosystem variability in the potential for long-term growth responses to rising CO2 levels implies that we need to parameterize mechanistic models of the impact of elevated CO2 on ecosystem productivity using a detailed understanding of each ecosystem of interest. 相似文献
70.
We conducted a set of in situ incubations to evaluate patterns of N availability among dominant land uses in the shortgrass
steppe region of Colorado, USA, and to assess recovery of soil fertility in abandoned fields. Replicated 30 d incubations
were performed in 3 sets of native (never cultivated), abandoned (cultivated until 1937), and currently cultivated, fallow
fields. Net N mineralization and the percentage of total N that was mineralized increased in the order: native, abandoned,
cultivated. Higher soil water content in fallow fields is the most likely reason for greater mineralization in cultivated
fields, while higher total organic C and C/N ratios in native and abandoned fields may explain differences in mineralization
between these land uses. Recovery of soil organic matter in abandoned fields appears to involve accumulation of soil C and
N under perennial plants, but probable methodological artifacts complicate evaluation of the role of individual plants in
recovery of N availability. Higher N mineralization and turnover in cultivated fields may make them more susceptible to N
losses; recovery of N cycling in abandoned fields appears to involve a return to slower N turnover and tighter N cycling similar
to native shortgrass steppe. 相似文献