Autumn growth and cold hardening of winter wheat under simulated climate change

Abstract

Plant responses to elevated CO₂ are governed by temperature, and at low temperatures the beneficial effects of CO₂ may be lost. To document the responses of winter cereals grown under cold conditions at northern latitudes, autumn growth of winter wheat exposed to ambient and elevated levels of temperature (+2.5°C), CO₂ (+150 µmol mol^?1), and shade (?30%) was studied in open-top chambers under low light and at low temperatures. Throughout the experiment, temperature dominated plant responses, while the effects of CO₂ were marginal, except for a positive effect on root biomass. Increased temperature resulted in increased leaf area, total biomass, total root biomass, total stem biomass, and number of tillers, but also a lower content of total sugars and a weaker tolerance to frost. The loss of frost tolerance was related to the larger size of plants grown at elevated temperature. The 30% light reduction under shading did not affect the growth, sugar content, or frost tolerance of winter wheat. At the low temperatures found at high latitudes during autumn, the atmospheric CO₂ increase is unlikely to enhance autumn growth of winter wheat to any significant extent, while a temperature increase may have important and major effects on its development and growth.     

Influence of elevated CO2 and mild water stress on nonstructural carbohydrates in field-grown cotton tissues

Root, stem and leaf tissues, from cotton plants exposed to CO₂ at ambient (370 μmol mol⁻¹ (control)) or elevated (550 μmol mol⁻¹ (FACE; free-air carbon dioxide enrichment)) levels in the field during the 1990 and 1991 growing seasons, were analyzed for nonstructural carbohydrates (glucose, fructose, sucrose and starch). Besides the FACE treatment, these plants were also exposed to two irrigation levels: 100% and 67% replacement of evapotranspiration. FACE had a greater effect upon cotton plant nonstructural carbohydrates than did irrigation treatments. Leaf carbohydrate content was increased by FACE, but this increase was much more pronounced in the stems and roots. Starch and soluble sugars in leaves in FACE plots tended to be consistently greater than in control leaves, without much change in carbohydrate content during the growing season. In contrast, root and stem, starch and soluble sugar pools were strongly increased by FACE and fluctuated strongly during the growing season. In both seasons, stem and taproot nonstructural carbohydrate content passed through a minimum during periods of heavy boll set. The fluctuations in stem and root carbohydrate content were therefore probably caused by the varying metabolic demands of the developing plant. These results suggest that a significant effect of CO₂ enrichment on starch-accumulating plants is an increase of nonstructural carbohydrate, especially starch, in nonleaf storage pools. This buildup occurs somewhat independently of the water status of the plant, and these enlarged pools can be drawn upon by the growing plant to maintain growth during periods of high metabolic demand.     

Effect of carbon dioxide on sorghum yield,root growth,and water use

The concentration of atmospheric carbon dioxide (CO₂) is rising. The effect of higher than ambient levels of CO₂ on plants grown in the sub-humid central Great Plains of the U.S.A. has not been investigated. Therefore, an experiment was conducted at Manhattan, Kansas, to study the effect of elevated levels of CO₂ on grain sorghum [Sorghum bicolor (L.) Moench]. During the summer of 1984, the sorghum was grown in rhizotrons in which root and shoot growth could be monitored throughout the growth cycle. The tops of the plants were enclosed in plastic chambers, which contained one of four concentrations of CO₂ : 330 (ambient), 485, 660, and 795 μl 1⁻¹.Enriched CO₂ delayed the boot, half bloom, and soft dough stages. Sorghum grown at elevated concentrations of CO₂ yielded more roots and shoots than plants grown with 330 μl 1⁻¹. At all soil-profile depths, root numbers and weights were higher at elevated CO₂ than at ambient CO₂. However, water use per unit dry matter of leaf, stem, root, and grain was decreased 13, 30, 31, and 29%, respectively, in plants grown at 795 μl 1⁻¹ CO₂ compared to plants at 330 μl 1⁻¹ CO₂. Although elevated CO₂ levels increased the stomatal resistance and leaf temperature, an increase in leaf area indices resulted in a lower canopy resistance.     

Impact of a biochar or a biochar-compost mixture on water relation, nutrient uptake and photosynthesis of Phragmites karka

Soil water and nutrient status are both of major importance for plant appearance and growth performance. The objective of this study was to understand the effect of biochar (1.5%) and a biochar-compost mixture (1.5% biochar + 1.5% compost) on the performance of Phragmites karka plants grown on a synthetic nutrient-poor sandy clay soil (50% sand, 30% clay, and 20% gravel). Indicators of plant performance, such as growth, lignocellulosic biomass, water status (leaf water potential, osmotic potential, and turgor potential), mineral nutrition status, leaf gas exchange, and chlorophyll fluorescence, and soil respiration (carbon dioxide (CO₂) flux) were assessed under greenhouse conditions. Biochar-treated plants had higher growth rates and lignocellulosic biomass production than control plants with no biochar and no compost. There was also a significant increase in soil respiration in the treatments with biochar, which stimulated microbial interactions. The increase in soil water-holding capacity after biochar amendment caused significant improvements in plant water status and plant ion (K⁺, Mg²⁺, and Ca²⁺) contents, leading to an increase in net photosynthesis and a higher energy-use efficiency of photosystem II. Biochar-treated plants had lower oxidative stress, increased water-use efficiency, and decreased soil respiration, and the biochar-compost mixture resulted in even greater improvements in growth, leaf turgor potential, photosynthesis, nutrient content, and soil gas exchange. Our results suggest that biochar and compost promote plant growth with respect to nutrient uptake, water balance, and photosynthetic system efficiency. In summary, both the soil amendments studied could increase opportunities for P. karka to sequester CO₂ and produce more fodder bio-active compounds and biomass for bio-energy on nutrient-poor degraded soils.     

二氧化碳升高与干旱对植物生理、土壤碳及土壤酶活的影响

Global climate models have indicated high probability of drought occurrences in the coming future decades due to the impacts of climate change caused by a mass release of CO2.Thus,climate change regarding elevated ambient CO2 and drought may consequently affect the growth of crops.In this study,plant physiology,soil carbon,and soil enzyme activities were measured to investigate the impacts of elevated CO2 and drought stress on a Stagnic Anthrosol planted with soybean (Glycine max).Treatments of two CO2 levels,three soil moisture levels,and two soil cover types were established.The results indicated that elevated CO2 and drought stress significantly affected plant physiology.The inhibition of plant physiology by drought stress was mediated via prompted photosynthesis and water use efficiency under elevated CO2 conditions.Elevated CO2 resulted in a longer retention time of dissolved organic carbon (DOC) in soil,probably by improving the soil water effectiveness for organic decomposition and mineralization.Drought stress significantly decreased C:N ratio and microbial biomass carbon (MBC),but the interactive effects of drought stress and CO2 on them were not significant.Elevated CO2 induced an increase in invertase and catalase activities through stimulated plant root exudation.These results suggested that drought stress had significant negative impacts on plant physiology,soil carbon,and soil enzyme activities,whereas elevated CO2 and plant physiological feedbacks indirectly ameliorated these impacts.     

Root biomass dynamics in a semi-natural grassland exposed to elevated atmospheric CO2 for five years

The effects of elevated atmospheric CO₂ on root dynamics were studied in a semi-natural grassland in central Sweden during five consecutive summer seasons. Open-top chambers were used for ambient and elevated (+350 μmol mol^?1) concentrations of CO₂, and chamberless rings were used for control. Root dynamics were observed in situ with minirhizotrons during the five summers and root biomass production was measured with root in growth cores during the last two years, from which total root biomass was estimated for each of the five years. The elevated CO₂ treatment showed both a greater increase in root numbers during the early summer and a greater decline in root numbers during autumn and winter than the ambient CO₂ treatment. Mean root production under elevated CO₂ was 50% greater than ambient CO₂ during the five years, and the difference increased from +25% in the first year to +80% in the last two years. Conversely, during the same period, the elevated to ambient CO₂ difference in shoot biomass decreased from +50% to +5%. This resulted in a dramatic change in root to shoot ratios in elevated CO₂ compared with the ambient treatment, which increased from ?15% in 1996 to +70% in 2000. Similar differences were seen between elevated CO₂ and the chamberless grown control plants, where root to shoot ratios increased steadily from ?47% in 1996 to +27% in 2000. Less dynamically, the root to shoot ratios of ambient CO₂ grown plants compared with the chamberless control plants were consistently ?29%±6% during the experimental period. In conclusion, during the 5 years this grassland was studied, there was a clear shift in plant biomass partitioning from above to below ground for plants exposed to elevated CO₂.     

Response of determinate- and semi-determinate-types of common bean to elevated CO2 concentration in the atmosphere

The growth of determinate-type and semi-determinate -type plants of common beam (Phaseolus vulgaris L.) was studied at elevated (700 μL L^-1) and ambient (350 μL L^p-1) CO, concentrations in an open-top chamber. Successive changes in dry matter production and in the number of stems and branches were investigated. To evaluate the sink-source balance at different CO₂ concentrations, ¹³CO₂ was introduced to the leaves during the pod filling stage and the ¹³C distribution profile was analyzed. In the elevated CO₂ treatment, no significant differences in dry matter production were observed for the determinate -type plants, unlike in the semi-determinate-type ones, where the volume was 1.3 times bigger than those in the ambient CO₂ treatment. This enhanced growth in the semi-determinatetype plants mainly involved the branches. Starch accumulation in leaves at elevated CO₂ concentratton was up to 200 and 300 mg glucose g DML^-1 for determinate- and semi-determinate-types, respectively. Though the increased accumulation of starch under elevated CO₂ treatment was more pronounced in the semi-determinate-type plants, it appeared that photosynthesis was not down-regulated. The net assimilation rate of the semi-determinate-type plants in the elevated CO₂ treatment was generally higher than that in the ambient CO₂ treatment. The semi-determinate-type plants could take advantage of the elevated CO₂ treatment for the distribution of photosynthates to branches, while in the determinate-type plants the growth of the branches could not be expanded, and consequently plant growth was not enhanced by elevated CO₂ treatment.     

Effect of elevated carbon dioxide and water stress on gas exchange and water use efficiency in corn

CO₂ has been predicted to increase in the future, and thus leading to possible changes in precipitation patterns. The objectives of this study were to investigate water use and canopy level photosynthesis of corn plants, and to quantify water use efficiency in corn plants under two different CO₂ levels combined with four different water stress levels. Corn plants were planted in sunlit plant growth chambers and a day/night temperature of (28/18 °C) was applied. From 21 days after emergence (DAE), the eight treatments including two levels of carbon dioxide concentrations (400 and 800 μmol mol⁻¹) and four levels of water stress (well-watered control, “mild”, “moderate”, and “severe” water stress) treatments at each CO₂ level were imposed. Height, number of leaves, leaf lengths, and growth stages of corn plants were monitored from nine plants twice a week. Corn plants were separately collected, dried, and analyzed for the biomass accumulation at 21 and 60 DAE. Soil water contents were monitored by a time domain reflectometry (TDR) system (15 probes per chamber). The “breaking points” (changes from high to low rates of soil water uptake) were observed in the bottom of soil depth for the water stressed conditions, and the “breaking points” under ambient CO₂ appeared 6-9 days earlier than under elevated CO₂. Although approximately 20-49% less water was applied for the elevated CO₂ treatments than for ambient CO₂ from 21 DAE, higher soil water contents were recorded under elevated CO₂ than under ambient CO₂. However, corn growth variables such as height, leaf area, and biomass accumulation were not significantly different in CO₂ or water stressed treatments. This result may be explained by considering that significant differences in canopy level gross photosynthesis among the water stress treatments was observed only toward the end of the experiment. The higher soil water contents observed under elevated CO₂ resulted mainly from less water use than under ambient CO_2. WUE (above ground biomass per water use since 21 DAE) at the final harvest was consistently higher and varied with a smaller range under elevated CO₂ than under ambient CO₂. This study suggests that less water will be required for corn under high-CO₂ environment in the future than at present.     

Elevated CO2 concentrations increase leaf nitrate reduction by strengthening sink activity in soybean plants

An experiment was conducted to examine the effect of CO₂ enrichment on the nitrate uptake, nitrate reduction activity, and translocation of assimilated-N from leaves at varying levels of nitrogen nutrition in soybean using ¹⁵N tracer technique. CO₂ enrichment significantly increased the plant biomass, apparent leaf photosynthesis, sugar and starch contents of leaves, and reduced-N contents of the plant organs only when the plants were grown at high levels of nitrogen. A high supply of nitrogen enhanced plant growth and increased the reduced-N content of the plant organs, but its effect on the carbohydrate contents and photosynthetic rate were not significant. However, the combination of high CO₂ and high nitrogen levels led to an additive effect on all these parameters. The nitrate reductase activity increased temporarily for a short period of time by CO₂ enrichment and high nitrogen levels. ¹⁵N tracer studies indicated that the increase in the amount of reduced-N by CO₂ enrichment was derived from nitrate-N and not from fixed-N of the plant. To examine the translocation of reduced-N from the leaf in more detail, another experiment was conducted by feeding the plants with ¹⁵NO₃-N through a terminal leaflet of an upper trifoliated leaf under depodding and/or CO₂ enrichment conditions. The export rate of ¹⁵N from the terminal leaflet to other plant parts decreased by depodding, but it increased by CO₂ enrichment. CO₂ enrichment increased the percentage of plant ¹⁵N in the stem and / or pods. Depodding increased the percentage of plant ¹⁵N in the leaf and stem. The results suggested that the increase in the leaf nitrate reduction activity by CO₂ enrichment was due to the increase of the translocation of reduced-N from leaves through the strengthening of the sink activity of pods and / or stem for reduced-N.     

Phosphorus‐deficiency effects on response of symbiotic N2 fixation and carbohydrate status in soybean to atmospheric CO2 enrichment

The impact of phosphorus (P) deficiency on response of symbiotic N₂ fixation and carbohydrate accumulation in soybean (Glycine max [L.] Merr.) to atmospheric CO₂ enrichment was examined. Plants inoculated with Bradyrhizobium japonicum MN 110 were grown in growth chambers with controlled atmospheres of 400 and 800 μL CO₂ L^‐1 and supplied either 1.0 mM‐P (P‐sufficient) or 0.05 mM‐P (P‐deficient) nitrogen (N)‐free nutrient solution. When plants were supplied with sufficient P, CO₂ enrichment significantly increased whole plant dry mass (83%), nodule mass (67%), total nitrogenase activity (58%), and N (35%) and P (47%) accumulation at 35 days after transplanting (DAT). Under sufficient P supply, CO₂ enrichment significantly increased starch concentrations in nodules compared to the normal atmospheric CO₂ treatment. Under normal CO₂ levels (400 μL L^‐1) nonstructural carbohydrate concentration (starch plus soluble sugar) was significantly higher in leaves of P‐deficient plants than in leaves of P‐sufficient plants in which nonstructural carbohydrate concentration exhibited a strong diurnal pattern. Under deficient P supply whole plant dry mass, symbiotic N₂‐fixation parameters, and N and P accumulation were not enhanced by atmospheric CO₂ enrichment. Phosphorus deficiency decreased nonstructural carbohydrate accumulation in nodules at the end of a 10‐day period in which functional activity was developing by 86% relative to P‐sufficient controls. While P deficiency elicited significant increases in the nonstructural carbohydrate concentration in leaves, it caused significant decreases in the nonstructural carbohydrate concentration in nodules over the diurnal cycle from 30 to 31 DAT. Collectively, these results indicate that the lack of a symbiotic N₂‐fixation response to atmospheric CO₂ enrichment by P‐deficient plants may be related to the decreased carbohydrate status of nodules.     

Elevated CO2 reduces whole transpiration and substantially improves root production of cassava grown under water deficit

We evaluated the possibility of elevated CO₂ concentration ([CO₂]) to reduce the negative effect of drought on growth and physiological parameters of cassava (Manihot esculenta Crantz). Plants were grown with 390 ppm or 750 ppm of CO₂, under well-watered or under water deficit conditions. The study was conducted in a climate-controlled greenhouse using 14 L pots, for 100 days. For any value of fraction of transpirable soil water (FTSW) the carbon assimilation was always higher for plants grown under elevated [CO₂]. Still, elevated [CO₂] reduced the negative effect of drought on transpiration, water use efficiency, all growth measures and harvest index. Elevated [CO₂] increased the dry matter of tuber roots (DMTR) of well-watered plants by 17.4%. The DMTR of plants grown under water deficit were 124.4 g and 58.9 g, respectively, for plants under elevated and ambient CO₂, an increase of 112%. Thus, the CO₂ effect was relatively stronger to the production of tuberous roots when cassava were subjected to water-deficit. Our results suggest that cassava tuber production might be resilient to changes in precipitation that will accompany higher atmospheric CO₂ and reinforce cassava as a specie that can significantly contribute to mitigate hunger in a changing climate environment.     

Availability of soil nitrogen and phosphorus under elevated [CO2] and temperature in the Taihu Lake region,China

Global climate change affects the availability of soil nutrients, thereby influencing crop productivity. This study examined the effects of elevated [CO₂] and temperature on the availability of soil N and P in a paddy field in the Taihu Lake region, China. Winter wheat (Triticum aestivum L.) was planted at two levels of atmospheric [CO₂] (375 μmol L^–1 ambient; 575 μmol L^–1 elevated) and two temperature levels (ambient; ambient + 2°C). The results were as follows: Compared to ambient, the interaction effects of elevated [CO₂] and temperature significantly decreased soil NH$ _4^+ $ ‐N contents by 20.3%, 20.6%, and 18.7% in the jointing, heading, and ripening stages (p < 0.05), respectively, while soil NO₃^–‐N content had no clear variation trend under different [CO₂] and temperature conditions. Elevated [CO₂] significantly increased soil available P content by 14.3% in the jointing stage, and elevated temperature significantly decreased soil available P content by 18.8% in the jointing stage. Compared with ambient [CO₂], elevated [CO₂] significantly increased wheat biomass in jointing and heading stages (p < 0.05). The positive effect of elevated [CO₂] on wheat biomass was more significant at ambient temperature (AT) than at elevated temperature (ET) in the middle and late plant growth stages. These results explained that the availability of soil N and P varied under elevated [CO₂] and temperature conditions. The application of N and P should be adjusted to meet the need of wheat plants after the wintering stage.     

Effects of carbon dioxide enrichment on cotton nutrient dynamics

The rise in atmospheric carbon dioxide (CO₂) concentration is predicted to have positive effects on agro‐ecosystem productivity. However, an area which requires further study centers on nutrient dynamics of crops grown under elevated CO₂ in the field. In 1989 and 1990, cotton [Gossypium hirsutum (L.) ‘Deltapine 77'] was grown under two CO₂ levels [370 umol mol^‐1=ambient and 550 μmol mor^‐1=free‐air CO₂ enrichment (FACE)]. At physiological maturity, nutrient concentration and content of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) were determined for whole plant and individual plant organs. While the effects of added CO₂ on whole plant nutrient concentrations and contents were consistent, some differences among plant organs were observed between years. FACE often decreased tissue nutrient concentration, but increased total nutrient accumulation. Results indicate that under elevated CO₂, field grown cotton was more nutrient efficient in terms of nutrient retrieval from the soil and nutrient utilization in the plant. This implies more efficient fertilizer utilization, better economic return for fertilizer expenditures, and reduced environmental impact from agricultural fertilization practices in the future.     

Elevated carbon dioxide level along with phosphorus application and cyanobacterial inoculation enhances nitrogen fixation and uptake in cowpea crop

Climate change, as a result of increase in the concentration of greenhouse gases, influences growth and productivity of leguminous crops. A study was carried out to analyse the impacts of elevated carbon dioxide (CO₂) and cyanobacterial inoculation on growth, N₂ fixation and N availability and uptake in cowpea crop, under different doses of phosphorus. Cowpea crop was grown under ambient (400 µmol mol^?1) and elevated (550 ± 20 µmol mol^?1) CO₂ levels using Free-Air Carbon dioxide Enrichment facility. Elevated CO₂ level increased chlorophyll content in leaves, improved nodulation and nitrogen fixation by the crop. Increase in P dose up to 16 mg kg^?1 soil enhanced nodule development and N₂ fixation under high CO₂ condition. Cyanobacterial inoculation increased nodule weight, leghaemoglobin content in nodules and total nitrogenase activity. Although nitrogen concentration in cowpea seeds decreased in high CO₂ treatment, higher N uptake was recorded. Under elevated CO₂ condition, cyanobacterial inoculation and higher P doses led to enhanced root growth and N₂ fixation and availability of soil nitrogen. The study illustrated the synergistic effect of high CO₂ and cyanobacterial inoculation in enhancing crop growth and availability of soil N, mediated by biological N₂ fixation in cowpea under different levels of P.     

High night temperature stimulates photosynthesis,biomass production and growth during the vegetative stage of rice plants

Abstract

The effects of night temperature on biomass accumulation and plant morphology were examined in rice (Oryza sativa L.) during vegetative growth. Plants were grown under three different night temperatures (17, 22 and 27°C) for 63 days. The day temperature was maintained at 27°C in all treatments. The final biomass of the plants was greatest in the plants grown at the highest night temperature. Total leaf area and tiller number were also the greatest in this treatment. Growth analysis indicated that the relative growth rate in the 27°C night-temperature treatment was maximal between days 21–42 and this was caused by increases in leaf area ratio, leaf weight ratio and specific leaf area. Plant total nitrogen contents did not differ among treatments. However, nitrogen allocation to the leaf blades was highest and the accumulation of sucrose and starch in the leaf blades and sheaths was the lowest in the 27°C night-temperature treatment by day 42. Despite this, dark respiration was also highest, and both the gross and net rates of CO₂ uptake at the level of the whole plant at day 63 were the highest in the 27°C night-temperature treatment. Thus, high night temperature strongly stimulated the growth of leaf blades during the early stage of rice plant growth, leading to increased biomass during the vegetative stage of the rice plants. As the CO₂ uptake rate per total leaf area was higher, photosynthesis at the level of the whole plant was also stimulated by a high night temperature.     

Rapid response of soil protozoa to elevated CO2

Short-term changes in bacterial and protozoan populations from the soil of plants grown under elevated atmospheric CO₂ were quantified. We grew Brassica nigra at either ambient or twice-ambient CO₂ levels within open-top chambers in the field for 4 weeks. Plant biomass, above- and belowground, was unaffected by elevated CO₂. Direct count bacterial density was unchanged under elevated CO₂. Flagellate density tended to increase, whereas amoebal density significantly declined under elevated CO₂. This change in protozoan community structure suggests trophic transfer of the elevated CO₂ fertilization effect through the soil food chain. Received: 20 August 1996     

Effect of elevated carbon dioxide on growth,nutrient partitioning,and uptake of major nutrients by soybean under varied nitrogen application levels

Rising carbon dioxide (CO₂) concentration causes fertilization effects resulting in enhanced crop biomass and yields and thus likely enhances nutrient demand of plants. Hence, this field study was carried out to investigate the effects of elevated CO₂ and N on biomass yield, nutrient partitioning, and uptake of major nutrients by soybean (Glycine max L.) using open‐top chambers (OTCs) of 4 m × 4 m size. Soybean was grown in OTCs under two CO₂ [ambient and elevated (535 ± 36.9 mg L^?1)] and four N levels during July to October 2016. The four N levels were N₀, N₅₀, N₁₀₀, and N₁₅₀ referring to 0, 50, 100, and 150% recommended dose of N. Both CO₂ and N significantly affected biomass and grain yield, though the interaction was non‐significant. CO₂ enrichment produced 30–65% higher biomass and 26–59% higher grain yield under various N levels. As compared to the optimum N application (N₁₀₀), the CO₂‐mediated increment in biomass yield decreased with either lower or higher N application, with the response being lowest at N₁₅₀. As compared to ambient concentration, elevated CO₂ resulted in significant reduction of seed P concentration at all N application levels but at N₁₅₀, an opposite trend was observed. The decrease in seed P was maximum at N₀ and N₅₀ (7–9%) and by 3% at N₁₀₀, whereas there was a gain of 7.5% at N₁₅₀. The seed N and K concentrations were not affected either by CO₂ or N application. Total N, P, and K uptake at harvest were significantly affected by CO₂ and N, but not by CO₂ × N interaction. Elevated CO₂ resulted higher uptake of N by 18–61%, P by 23–62%, and K by 22–62% under various N treatments.     

两种氮水平下CO2浓度升高对冬小麦生长和氮磷浓度的影响

预计到 2 1世纪末期大气CO2 浓度将会比目前水平增加 1倍 ,约 70 0 μmolmol- 1 左右。因此CO2 浓度升高对作物的影响研究十分重要。本文探讨在两种氮 (N)水平下 ,CO2 浓度升高对冬小麦 (TriticumaestivumL cv Xinong 872 7)生长和地上部N、磷 (P)浓度的影响及原因。试验设 3 5 0 μmolmol- 1 和 70 0 μmolmol- 1 两种CO2 浓度水平和 45kghm- 2 和 90kghm- 2 两种N肥施用水平。结果表明 ,CO2 浓度升高 ,冬小麦株高和叶面积指数 (LAI)均增加 ,净同化率 (NAR)值增加 ,叶面积比率 (LAR)下降 ,比叶重 (SLW )不增加。高CO2 浓度对相对生长率 (RGR)的影响因施N水平而异 ,低N时RGR不增加 ,高N时明显增加。CO2 浓度增加 ,小麦抽穗提早 7～ 8d ,叶鞘、茎杆和地上部干物重提高 ,叶片、叶鞘和茎杆N、P浓度降低 ,但叶片、叶鞘和茎杆N、P吸收量增加均不明显。CO2 浓度升高 ,氮磷利用效率 (NUE和PUE)提高 ,而对相对氮磷累积速率 (RNAR和RPAR)影响不大。高CO2 浓度冬小麦体内N、P浓度下降是由于稀释效应以及NUE和PUE提高之故。     

EXPOSURE TO ENVIRONMENTALLY RELEVANT LEVELS OF CADMIUM PRIMARILY IMPACTS TRANSPIRATION IN FIELD-GROWN SOYBEAN

Cadmium (Cd) is a toxic heavy metal released into agricultural settings primarily due to human activities. Cadmium is readily taken up by plants from the soil and has been shown to result in numerous changes to plant growth and physiology. In this study we examined the physiological effect of environmentally relevant levels of cadmium on field-grown soybean (Glycine max). No significant differences in carbon dioxide (CO₂) assimilation response to leaf internal CO₂ concentration, chlorophyll fluorescence, or growth parameters were observed. However, we did observe an increase in sap flow, a real-time measure of transpiration. Consistent with increased sap flow there was a significant increase in total daily sap flow and peak sap flow between the control and cadmium-treated plants. Our results suggest that treatment with environmentally relevant levels of cadmium primarily impacts transpiration.     

Elevated atmospheric CO2 changes phosphorus fractions in soils under a short rotation poplar plantation (EuroFACE)

Future high levels of atmospheric carbon dioxide (CO₂) may increase biomass production of terrestrial plants and hence plant requirements for soil mineral nutrients to sustain a greater biomass production. Phosphorus (P), an element essential for plant growth, is found in soils both in inorganic and in organic forms. In this work, three genotypes of Populus were grown under ambient and elevated atmospheric CO₂ concentrations (FACE) for 5 years. An N fertilisation treatment was added in years 4 and 5 after planting. Using a fractionation scheme, total P was sequentially extracted using H₂O, NaOH, HCl and HNO₃, and P determined as both molybdate (Mo) reactive and total P. Molybdate-reactive P is defined as mainly inorganic but also some labile organic P which is determined by Vanado-molybdophosphoric acid colorimetric methods. Organic P was also measured to assess all plant available and weatherable P pools. We tested the hypotheses that higher P demand due to increased growth is met by a depletion of easily weatherable soil P pools, and that increased biomass inputs increases the amount of organic P in the soil. The concentration of organic P increased under FACE, but was associated with a decrease in total soil organic matter. The greatest increase in the soil P due to elevated CO₂ was found in the HCl-extractable P fraction in the non-fertilised treatment. In the NaOH-extractable fraction the Mo-reactive P increased under FACE, but total P did not differ between ambient and FACE. The increase in both the NaOH- and HCl-extractable fractions was smaller after N addition. The results showed that elevated atmospheric CO₂ has a positive effect on soil P availability rather than leading to depletion. We suggest that the increase in the NaOH- and HCl-extractable fractions is biologically driven by organic matter mineralization, weathering and mycorrhizal hyphal turnover.