Photosynthetic and growth responses of <Emphasis Type="Italic">Camelina sativa</Emphasis> (L.) Crantz to varying nitrogen and soil water status

Water and nitrogen (N) deficiency are two major constraints limiting the yield and quality of many oilseed crops worldwide. This study was designed to assess the response of Camelina sativa (L.) Crantz to the availability of N and water resources on photosynthesis and yield parameters. All the measured variables, which included plant height, root and shoot dry matter, root:shoot ratio, xylem pressure potential (XPP), yield components, photosynthetic parameters, and instantaneous water-use efficiency (WUE) were remarkably influenced by water and nitrogen supply. Net photosynthetic rate (P _N) and yield components were significantly decreased more by water deficit than by N deficiency. XPP, stomatal conductance (g _s), and intercellular CO₂ concentration (C _i) decreased substantially as the water deficit increased irrespective of the level of N application. WUE at the high N supply [100 and 150 kg(N) ha⁻¹] dropped in a large degree as the increased water deficit due to a larger decrease in P _N than transpiration rate (E). The results of this study suggest that the regulative capacity of N supply on photosynthetic and plant growth response is significantly affected by soil water status and C. sativa is more sensitive to water deficit than N supply.     

漓江上游毛竹生理生态特征对不同土壤水分的响应

漓江上游毛竹林面积大,是我国毛竹最南端产区。该研究针对当地季节性干旱问题,通过模拟降水使土壤水分变化,共设立了5个毛竹水分处理小区(CK.对照;A.无降水+覆膜;B.降水5 mm+覆膜;C.降水10mm+覆膜;D.降水20 mm+覆膜),并与HM(木荷Schima superba)(自然状态)进行对比。结果表明:土壤水分变化影响了毛竹叶片水势和叶绿素的变化,叶片白天水势下降,傍晚均可恢复到凌晨水势。C处理的毛竹午间水势下降值最小,叶绿素含量也最高。本研究区位于最南端产区,毛竹的光合生产力也属偏低水平。适当的土壤水分亏缺,毛竹表现出相对的高净光合速率(P_(n))、高蒸腾速率(Tr)、低水分利用效率(WUE)的特点;过多或过少土壤水分,则为低P_(n)和Tr,但高WUE。毛竹叶片的P_(n)与气孔导度Gs呈极显著的正相关关系,说明毛竹的光合速率受气孔调节明显;Tr与午时叶水势呈负相关(符合二项式函数)关系,土壤水分问题造成的叶片水分不足同时也影响了毛竹的Tr。水分亏缺,P_(n)主要由气孔调节,但水分过多导致P_(n)的下降应该是由气孔导度的下降和叶肉细胞光合能力的下降共同作用的结果。水分过少或过多均对毛竹生理生态过程产生负效应。相对于木荷,毛竹的P_(n)较高,但同时也消耗更多的水分。     

Comparison of two chickpea varieties regarding their responses to direct and induced Fe deficiency

The effects of Fe deficiency (whether direct or bicarbonate-induced) on plant morphology, growth parameters, photosynthesis-related pigment contents, gas exchange, and water relations were addressed in two contrasting chickpea varieties (INRAT88 and Chetoui, respectively tolerant and sensitive to Fe deficiency). A marked decrease in the whole plant Fe content was observed in the Fe deprived plants of both varieties, especially the bicarbonate-treated ones, which showed a slower growth development and water deficit stress symptoms (increased leaf tissue osmolality associated with decreased shoot height, increased leaf mass to area ratio, and decreased water content). Both Fe shortage and bicarbonate addition resulted in both varieties in the decline of the photosynthetic pigment contents, contributing to lower photosynthetic efficiency (φ_c) and lower net photosynthesis (A). Fe deficiency reduced the water use efficiency and physiological availability of water too. However, INRAT88 was more tolerant to Fe deficiency than Chetoui, by maintaining a higher growth rate associated with lower respiration rate (R_D), higher chlorophyll a and b concentrations, higher A, lower transpiration rate (E) and a higher water use efficiency (A/E). The present data suggest that the efficient utilisation of Fe for the synthesis of chlorophyll together with the effective control of electron-transport chains at chloroplasts (high A) and mitochondria (low R_D) may account for the higher tolerance of INRAT88 to direct Fe deficiency. Further investigations with respect to oxidative stress and ROS generation, or about photorespiration would be helpful for a better understanding of their interaction with Fe deficiency in this grain legume.     

Transpiration of spring barley under nitrogen and phosphorus deficiency during leaf wilting

In an open gas exchange system with a thermocouple psychrometer the transpiration rate of the first leaf in 8-day plants of spring barley was measured in dependence on the water saturation deficit (ΔW _sat). The plants were cultivated in Richter’s nutrient solution, either complete, or deficient in nitrogen or phosphorus. The cuticular transpiration (as measured in the dark) was unaffected by N and P deficiency. The N deficiency reduced the transpiration rate by increasing stomatal resistance since full water saturation of the leaf (67% rate of the control variant) up to stomatal closing at Δ W_sat = 14%. The P deficiency does not affect the transpiration rate at initial phases of wilting, but the stomata close only at a higher Δ W_sat (25%) than those in the control.     

The influence of CO2 enrichment, phosphorus deficiency and water stress on the growth, conductance and water use of Pinus radiata D. Don

Abstract. Seedlings of Pinus radiata D. Don were grown in growth chambers for 22 weeks with two levels of phosphorus, under either well-watered or water-stressed conditions at CO₂ concentrations of either 330 or 660mm³ dm^?3. Plant growth, water use efficiency and conductance were measured and the relationship between these and needle photosynthetic capacity, water use efficiency and conductance was determined by gas exchange at week 22. Phosphorus deficiency decreased growth and foliar surface area at both CO₂concentrations; however, it only reduced the maximum photosynthetic rates of the needles at 660 mm³ CO₂ dm^?3 (plants grown and measured at the same CO₂ concentration). Water stress reduced growth and foliar surface area at both CO₂ concentrations. Increases in needle photosynthetic rates appeared to be partly responsible for the increased growth at high CO₂ where phosphorus was adequate. This effect was amplified by accompanying increases in needle production. Phosphorus deficiency inhibited these responses because it severely impaired needle photosynthetic function. The relative increase in growth in response to high CO₂ was higher in the periodically water-stressed plants. This was not due to the maintenance of cell volume during drought. Plant water use efficiency was increased by CO₂ enrichment due to an increase in dry weight rather than a decrease in shoot conductance and, therefore, transpirational water loss. Changes in needle conductance and water use efficiency in response to high CO₂ were generally in the same direction as those at the whole plant level. If the atmospheric CO₂ level reaches the predicted concentration of 660 mm³ dm^?3 by the end of next Century, then the growth of P. radiata will only be increased in areas where phosphorus nutrition is adequate. Growth will be increased in drought-affected regions but total water use is unlikely to be reduced.     

Growth and Leaf Gas Exchange Characteristics in Dalbergia sissoo Roxb. and D. latifolia Roxb. Under Water Deficit

Forty two-month-old plants of Dalbergia sissoo and D. latifolia were subjected for 56 d to water deficit induced by withholding water. Drought stress caused a significant reduction in plant height, stem diameter, net photosynthetic rate (P _N), transpiration rate (E), and stomatal conductance (g _s) in both species, but the reduction was greater in D. sissoo than in D. latifolia. Water use efficiency (P _N/E) was adversely affected due to water stress only in D. latifolia, and intrinsic water use efficiency (P _N/g _s) was increased in both species. There was a slight effect of water stress on variable to maximum fluorescence (F_v/F_m) (quantum yield of photosystem 2) in both species, but the species did not differ significantly in this attribute.     

Photosynthesis and Growth Responses of Parthenocissus quinquefolia (L.) Planch to Soil Water Availability

Photosynthesis and growth characteristics of Parthenocissus quinquefolia were measured under differing soil water availability within a pot. Decreased soil moisture significantly reduced the leaf relative water content (RWC) and the above- and below-ground biomass. However, more biomass was allocated to the root than to the leaf. Net photosynthetic rate (P _N), stomatal conductance (g _s), and transpiration rate (E) were also significantly decreased but water use efficiency (WUE) was increased. Midday depressions in P _N and g _s were not evident for the well-irrigated plants. With the lower water availability, midday reductions in P _N and g _s were much more marked and the duration of the depression was longer. Additionally, the P _N-irradiance response curves also indicated that water supply affected photosynthesis capacity. The growth and photosynthetic response of P. quinquefolia to water supply indicated that this species could resilient to water availabilities and adapt to Hunshandak conditions very well.     

Measured and modeled interactive effects of potassium deficiency and water deficit on gross primary productivity and light‐use efficiency in Eucalyptus grandis plantations

Global climate change is expected to increase the length of drought periods in many tropical regions. Although large amounts of potassium (K) are applied in tropical crops and planted forests, little is known about the interaction between K nutrition and water deficit on the physiological mechanisms governing plant growth. A process‐based model (MAESPA) parameterized in a split‐plot experiment in Brazil was used to gain insight into the combined effects of K deficiency and water deficit on absorbed radiation (aPAR), gross primary productivity (GPP), and light‐use efficiency for carbon assimilation and stem biomass production (LUE_C and LUE_s) in Eucalyptus grandis plantations. The main‐plot factor was the water supply (undisturbed rainfall vs. 37% of throughfall excluded) and the subplot factor was the K supply (with or without 0.45 mol K m^?2 K addition). Mean GPP was 28% lower without K addition over the first 3 years after planting whether throughfall was partly excluded or not. K deficiency reduced aPAR by 20% and LUE_C by 10% over the whole period of growth. With K addition, throughfall exclusion decreased GPP by 25%, resulting from a 21% decrease in LUE_C at the end of the study period. The effect of the combination of K deficiency and water deficit was less severe than the sum of the effects of K deficiency and water deficit individually, leading to a reduction in stem biomass production, gross primary productivity and LUE similar to K deficiency on its own. The modeling approach showed that K nutrition and water deficit influenced absorbed radiation essentially through changes in leaf area index and tree height. The changes in gross primary productivity and light‐use efficiency were, however, driven by a more complex set of tree parameters, especially those controlling water uptake by roots and leaf photosynthetic capacities.     

Enhanced drought tolerance in transgenic Leymus chinensis plants with constitutively expressed wheat TaLEA3

Leymus chinensis is an important grassland perennial grass. However, its drought tolerance requires to be improved. LEA (late embryogenesis abundant) genes are believed to confer resistance to drought and water deficiency. Using Agrobacterium-mediated transformation, a wheat LEA gene, TaLEA ₃ , was integrated into L. chinensis. The transgenic lines showed enhanced growth ability under drought stress during which transgenic lines had increased the relative water content, leaf water potential, relative average growth rate, but decreased the malondialdehyde content compared with the non-transgenic plant. Thus, transgenic breeding is an efficient approach to enhance drought tolerance in L. chinensis.     

Effect of phosphorus deficiency on the photosynthetic characteristics of rice plants

The effects of phosphorus deficiency on the photosynthetic characteristics were studied in rice seedlings (Oryza sativa L.) every 8 days after treatment. P deficiency caused a significant reduction in the net photosynthesis rate (P _N) in rice plants. During the first 16 days of P deficiency, the maximum efficiency of PSII photochemistry (F _v/F _m), the effective PSII quantum yield (ϕ_PSII), the electron transport rate (ETR) as well as photochemical quenching (qP) in the P-limited rice plants kept close to the control, but the excitation energy capture efficiency of PSII reaction centers (F′_v/F′_m) was significantly declined in the P-deficient rice leaves. Meanwhile, in the stressed leaves, we also found a significant increase in nonphotochemical quenching (NPQ) as well as in the activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX). It was indicated that a series of photoprotective mechanisms had been initiated in rice plants in response to short-term P deficiency. Therefore, PSII functioning was not affected significantly under such stress. As P deficiency continued, the excess excitation energy was accumulated in excess of the capacity of photoprotection systems. When the rice suffered from P deficiency more than 16 days, ϕ_PSII, ETR, and qP were decreased more rapidly than that in the control plants, although NPQ still kept higher in the stressed plants. These results were also consistent with the data on the distribution of excitation energy. The excess energy induced the generation of reactive oxygen species, which might lead to the further damage to PSII functioning. This text was submitted by the authors in English.     

Gibberellic acid affects growth and flowering of Philodendron‘Black Cardinal’

Changes in net photosynthetic rate (P_N), stomatal conductance (g_s), intercellular CO₂ concentrations (C_i), transpiration rate (E) and water use efficiency (WUE) were measured in Plantago major L. plants grown under sufficient soil water supply or under soil water stress conditions. The plants had high P_N in a wide range of soil water potential and temperature regimes. Soil water had little effect on P_N under ambient CO₂ concentrations, which was explained by a high carboxylation rate, but increased the dark respiration rate. Carboxylation activity at low C_i depended on RuBP regeneration, whereas at high C_i it depended on the phosphate regeneration rate. The g_s and E values were low in plants under stress as compared to the controls that resulted in an increase of WUE. The results obtained show that Plantago major plants have different ways of adaptation to soil water deficit conditions.     

Fluctuations in nitrate reductase activity,and nitrate and organic nitrogen concentrations of succulent plants under different nitrogen and water regimes

The CAM (Crassulacean acid metabolism) succulent species Kalanchoe daigremontiana, K. tubiflora and Crassula argentea, and the succulent C₃ species Peperomia obtusifolia, were cultivated in pure culture in open-air conditions under two different regimes of nitrogen and water supply. At specified intervals during the course of vegetative growth, biomass, nitrate reductase activity (NRA), nitrate concentration, and organic nitrogen concentration of whole plants were measured. After 100 days of cultivation the leaf conductance of Crassula and Peperomia was measured at intervals for the duration of a day. Behaviour of all four species was strongly influenced by the cultivation regime. This was apparent in terms of productivity and variable flucturations in NRA, nitrate concentration, and organic nitrogen concentration during the vegetative period. Increase in biomass was mostly connected with a decrease in all other investigated parameters, especially under conditions of water and/or nitrogen deficiency. The typical reaction of the CAM species Crassula to limited netrogen but adequate soil water was to reduce leaf conductance during light, whereas the C₃ plant Peperomia increased conductance in comparison with plants having a nitrogen suppy. The NRA of all plant species was reduced by both soil nitrate deficiency and drought. The succulent plant species, which are specially adapted to drought, neither took up nor used nitrate when water was limited. This was particularly the case for the CAM species, but less so for the C₃ Peperomia, which showed very high concentrations of nitrate and organic nitrogen, but low NRA and biomass gain. A formula was derived to express the nitrogen use efficiency (NUE) of the species, i.e. the ability of a plant to use nitrogen over a specific period of growth. NUE was shown to increase with age for the crassulacean species but to decrease for the C₃ Peperomia. Furthermore, NUE varied with the different nutrient levels in a species-specific manner, with high values for NUE not necessarily coupled to high productivity, and with NUE of the C₃ species generally higher than that of CAM species.     

缺钼对旺长期烤烟光合色素和荧光日变化及亚显微结构的影响

以模式作物烟草(Nicotiana tabacum)为试材,采用水培试验,以营养液含钼0.20mg·kg-1作为对照(CK),0mg·kg-1为缺钼处理(T),研究缺钼对旺长期烟草光合色素、叶绿素荧光日变化和叶片细胞亚显微结构的影响,以揭示钼对旺长期烟草光合作用影响及其作用机理。结果显示:(1)缺钼处理烟叶的叶绿素和类胡萝卜素含量显著低于施钼烟叶。(2)缺钼烟叶的日净光合速率(Pn)下降早于对照,而且回升较慢;施钼烟叶的Pn呈典型双峰日变化。(3)施钼烟叶的最大光化学效率(Fv/Fm)比较稳定;光合电子传递速率(ETR)和光合有效量子产量(Y)在14:00较低,16:00略有回升;初始荧光(F0)和非光化学猝灭系数(NPQ)在12:00~14:00略微增加,18:00恢复到8:00的水平。缺钼烟叶Fv/Fm在12:00明显降低,16:00后开始有所回升;10:00后,其ETR和Y开始下降,F0和NPQ急剧增加,16:00后开始有所降低,18:00未恢复到8:00的水平。(4)缺钼烟叶细胞亚显微结构的基粒片层和基质片层膨胀变形、松散,淀粉粒少而且发育差;施钼烟叶片层结构排列整齐,淀粉粒发育好。研究表明,旺长期缺钼烟叶的光合色素含量降低,细胞结构发育不良,叶绿素荧光受强光和高温反应敏感,净光合速率降低,光合碳同化产物减少。     

PdERECTA,a leucine-rich repeat receptor-like kinase of poplar,confers enhanced water use efficiency in <Emphasis Type="Italic">Arabidopsis</Emphasis>

Water deficiency causes a dramatic reduction in crop production globally. Breeding crop varieties that are more efficient in their water use is one strategy to overcome this predicament. In this study, a member of the LRR-RLKs family, the Populus nigra × (Populus deltoides × Populus nigra) ERECTA (PdERECTA) gene was cloned. To study the biological functions of PdERECTA, transgenic Arabidopsis plants (35S:PdERECTA) that constitutively expressed the PdERECTA gene were constructed. Overexpression of PdERECTA resulted in early seedling establishment, longer primary roots, and larger leaf areas. Notably, transgenic Arabidopsis overexpressing PdERECTA resulted in enhanced long-term water use efficiency (WUEl), as estimated by the analysis of carbon isotopic discrimination. The WUEl results were supported by the physiological and anatomical results, which included improved photosynthetic rate, decreased transpiration rate, and stomatal density. The transgenic lines have significantly more dry-biomass as compared to the wild type. Since the overexpression of PdERECTA can strongly enhance the water use efficiency in transgenic Arabidopsis plants, PdERECTA could potentially be used in transgenic breeding to improve the water use efficiency.     

Heterozygote deficiency,population substructure and their implications in DNA fingerprinting

Summary Substructured populations exhibit an overall deficiency of heterozygosity whose proportional magnitude depends on the nature of substructuring, i.e., the number of subpopulations (s), their time of divergence (t) from the ancestral population, and the rate of gene flow amongst them (m). Since apparent heterozygote deficiency could be caused by many factors other than population substructuring, one must examine the nature of substructuring that could produce the observed extent of heterozygote deficiency, in order to infer the substructuring from an observed heterozygote deficiency. Using the equivalence of proportional heterozygote deficiency and the coefficient of gene differentiation (G _ST), we can generate isolines of G _ST as functions of s, t (in units of 2N _e generations, N _e being the effective population size) and m. Analytical results suggest that large G _ST values cannot be reached by substructuring alone, unless the number of subpopulations are large and they remain isolated over a long period of time. Application of the theory to population data on six variable number of tandem repeats (VNTR) loci in US Caucasians and US Blacks demonstrates that the observed heterozygote deficiencies at these loci cannot be explained by substructuring within these populations alone. This is so because such large values of G _ST (3%–10%) would require an absence of gene exchange between the subpopulations and a divergence time from each other of at least 25000 years ago, neither of which is compatible with the demography and ethnohistory of US Caucasians and Blacks. In contrast, the inability to detect extreme-sized alleles and/or incomplete resolution of nearly similar-sized alleles following Southern gel electrophoresis could easily explain the observed heterozygote deficiencies. The implications of these results are discussed in the context of the forensic use of DNA-typing data, and justify the employment of population genetic principles in forensic genetics.     

土壤水分梯度对灰胡杨光合作用与抗逆性的影响

以塔里木盆地珍稀渐危种灰胡杨(Populus pruinosa Schrenk)幼苗为材料,采用盆栽方法研究土壤水分梯度对灰胡杨光合特征及抗逆性的影响。结果表明:(1)灰胡杨净光合速率(P_n)、蒸腾速率、气孔导度、胞间CO_2浓度和光能利用率均随土壤水分递减而降低,重度干旱比适宜水分依次降低了35.53%、25.32%、48.18%、15.62%和40.92%;而光合午休程度则明显增强,P_n下降主要是由非气孔因素限制造成。轻度干旱能够提高灰胡杨水分利用效率(WUE)3.05%,维持相对较高的P_n和WUE。(2)随土壤水分递降,灰胡杨光照生态幅缩窄,CO_2补偿点升高,RuBP再生受限,光与CO_2利用效率、Rubisco活性和光合效率降低。与适宜水分相比,中度与重度干旱下最大净光合速率(P_(nmax))、表观量子效率、光饱和点、羧化效率、光合能力(A_(max))、光呼吸速率、最大羧化效率、最大电子传递速率和磷酸丙糖利用率均显著降低(P0.05),其中P_(nmax)、A_(max)和生化参数分别降低了42.65%、38.26%、57.10%;63.01%、65.88%、73.43%。(3)土壤干旱显著降低了灰胡杨的枝水势和光合色素含量(P0.01),并且改变了光系统反应中心色素的组成比例,膜脂过氧化程度显著增强(P0.01)。灰胡杨主要通过积累大量脯氨酸和可溶性蛋白质参与渗透调节来减轻土壤干旱对光合机构的损伤。重度干旱对灰胡杨叶片光合系统造成了不可逆的伤害,严重抑制了其正常生长和光合作用。综上所述,塔里木干旱荒漠区灰胡杨生长适宜的土壤相对含水量为60%—65%符合极端干旱区植被恢复与高效节水的管理原则。     

不同平茬年限人工柠条林光合特性及土壤水分的响应变化

平茬是荒漠草原老化人工柠条林营林抚育的重要措施,为系统认识柠条平茬后连续的生理与生态响应过程及其变化规律,该研究设置对比观测样地,以未平茬柠条(WPC)为对照,以平茬后连续生长1～5年(PC1～PC5)的柠条为处理,对各样地柠条净光合速率、蒸腾速率、气孔导度、胞间CO2浓度、水分利用效率等光合生理特征及其土壤含水量分布的影响进行测定分析。结果表明:(1)平茬处理对柠条生理特性的影响因平茬年限的增加而异,其中PC1和PC2柠条的净光合速率和蒸腾速率较WPC略有提高,PC1柠条处于补偿生长的活跃期,水分利用效率明显高于其他平茬处理,PC2柠条的水分利用效率开始下降;PC3和PC4的柠条蒸腾速率、净光合速率和气孔导度显著上升,且PC4处理下达到最大值,相应水分利用效率也逐步回升;PC5的柠条几乎不存在补偿性生长,净光合速率、蒸腾速率和水分利用效率开始回落,逐渐接近WPC;平茬措施对PC1与PC5柠条胞间CO2浓度大小的影响较大。(2)PC1的土壤水分含量在0～100cm土层因受冠层截留大幅减小的影响而低于其他年限平茬处理;PC2的土壤水分略有改善,PC3、PC4的土壤含水量显著提高,PC5的土壤水分状况则逐渐接近于WPC。(3)随平茬年限的增加,柠条光合特性与土壤含水量间存在一定的动态互馈关系,其中PC1的土壤水分略有下降,柠条生长减缓;PC2土壤含水量逐步恢复;PC3土壤含水量增长幅度开始下降,柠条的各项生理指标上升;PC4柠条的光合生理指标、土壤含水量都达到了最高值;PC5柠条的各项指标开始下降。研究发现,PC4处理是柠条光合生理和土壤水分响应变化的拐点,可参考作为平茬柠条优化管理的一个时间节点。     

Photorespiration and photoprotection of grapevine (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L. cv. Cabernet Sauvignon) under water stress

In order to investigate the photoprotective function of photorespiration in grapevine under water stress, potted grapevines (Vitis vinifera L. cv. Cabernet Sauvignon) were randomly divided into three uniform groups for well-watered [watered every morning to keep the relative water content (RWC) of soil over 70 %], water-stress adapted (drought-adapted at 30 % relative soil water content for 30 days), and water stress without adaptation treatment (water-stressed to 30 % relative soil water content for 3 days). Net assimilation rate (A _N), stomatal conductance (g _s), substomatal CO₂ concentration (C _i), transpiration rate (E), actual photochemical efficiency of PSII (Φ_PSII), and maximum photochemical efficiency of PSII (F_v/F_m) were recorded by combining measurements of gas exchange and chlorophyll fluorescence. Gross photorespiration (P_r), photosynthetic electron partitioning (J_C/J_T), photochemical quenching coefficient (qP), and non-photochemical quenching (NPQ) were also calculated. The ratio of net assimilation rate to transpiration rate (A _N/E) was used as an indicator of water use efficiency (WUE). A _N, apparent P_r, Φ_PSII, F_v/F_m, qp, and g _s decreased, NPQ increased, and gross P_r sustained at a high level under water stress. This suggests that both photorespiration and energy dissipation play important roles in protecting photosynthetic apparatus against photoinhibition. C _i in water-stressed plants without adaptation treatment increased, which indicates the leaves suffered a non-stomatal limitation, while the water-stress adaped plants only suffered a stomatal limitation indicated by low C _i.     

Nitrate and ammonium absorption by plants growing at a sufficient or insufficient level of phosphorus in nutrient solutions

Summary Absorption of nitrate and ammonium was studied in water culture experiments with 4 to 6 weeks old plants of barley (Hordeum vulgare L.), buckwheat (Fagopyrum esculentum L. Moench) and rape (Brassica napus L.). The plants were grown in a complete nutrient solution with nitrate (5.7±0.2 mM) or nitrate (5.6±0.2 mM) + ammonium (0.04±0.02 mM). The pH of the nutrient solution was kept at 5.0 using a pH-stat. It was found that phosphorus deficiency reduced the rate of nitrate uptake by 58±3% when nitrate was the sole N source and by 83±1% when both nitrate and ammonium were present. The reduction occurred even before growth was significantly impeded by P deficiency. The inhibition of the uptake of ammonium was less,i.e. ammonium constituted 10±1% of the total N uptake in the P sufficient plants and 30±5% in the P deficient plants. The reduction of nitrate absorption greatly decreased the difference between the uptake of anions and cations. It is suggested that P deficiency reduced the assimilation of NO ₃ ^– into the proteins, which might cause a negative feedback on NO ₃ ^– influx and/or stimulate NO ₃ ^– efflux.     

Leaf anatomy and photosynthetic carbon metabolic characteristics in <Emphasis Type="Italic">Phragmites communis</Emphasis> in different soil water availability

To investigate the variations of anatomical and photosynthetic carbon metabolic characteristics within one species in response to increasing soil water stress, leaf anatomical characteristics, gas exchange and the activity of key enzymes in photosynthesis and photorespiration were compared in different ecotypes of Phragmites communis growing in an oasis-desert transitional zone (ODTZ) from swamp habitat (plot 1–3) via heavy salt meadow (plot 4–7) and light salt meadow habitat (plot 8–9) to dune habitat (plot 10–13) in Northwest China. The results showed that interveinal distance (ID) decreased with increasing water stress except that in plots of dune reed (DR). Vein mean diameter (VMD) in plot 10, 11 and 12 of the DR was significantly larger than that in other ecotypes. Leaf specific porosity (LSP) enhanced from plot 4 to plot 13 from heave salt meadow reed (HSMR) to light salt meadow reed (LSMR) and to DR. Chlorophyll fluorescence in bundle sheath cells were microscopically found in four ecotypes, especially significantly in the DR. Net CO₂ assimilation rate (A _n) dropped rapidly from the swamp reed (SR) to the HSMR and then increased progressively from the LSMR to the DR. Stomatal conductance (g _s) decreased and the water use efficiency (WUE) rose from the wet to the dry ecotypes. Sensitivity of g _s to intercellular CO₂ concentration (C _i) increased, but glycolate oxidase (GO) activity gradually reduced with increasing soil water deficiency. The RuBPCase activity did not reduce in four ecotypes even in DR, but, the PEPCase and NAD-ME activities as well as the ratio of PEPCase/RuBPCase were gradually enhanced with increasing soil water stress. We concluded that anatomical and photosynthetic carbon assimilating characteristics in P. communis were developing to the direction of C₄ metabolism in response to the increasing drought stress in desert areas. The DR enduring severe water stress had more C₄ like photosynthetic features than the HSMR and LSMR as well as SR, according to significantly increased VMD and LSP and higher g _s sensitivity to C _i as well as higher PEPCase activity and lower GO activity in the DR.