Differences In Dry Matter Accumulation Research Articles

Relationship between dry matter accumulation and maize yield in Southwest China

AbstractTo explore the differences in dry matter accumulation and yield of maize varieties having different nitrogen‐use efficiencies in Southwest China, a field experiment was conducted in Yongchuan, Chongqing, and Deyang, Sichuan, from 2019 to 2020. Two varieties, the nitrogen‐efficient Zhenghong 311 (ZH 311) and the nitrogen‐inefficient Xianyu 508 (XY 508), were tested across four nitrogen levels (0–360 kg ha−1). The results showed that compared to XY 508, ZH 311 exhibited a significantly higher accumulation of dry matter at various stages and periods, particularly in the roots during the R6 stage, and in the stem sheaths and leaves throughout all stages. Furthermore, the number of kernel rows, number of kernels per row, number of kernels per ear, and grain yield were significantly higher for ZH 311 than XY 508, whereas the 100‐grain weight was significantly lower for ZH 311 than XY 508. The yield difference between the two varieties was the largest when the nitrogen application rate was 240 kg ha−1. The yield performance of ZH 311 was always better than that of XY 508, and less nitrogen was needed to obtain the best yield. The accumulation of maize dry matter had a highly significant effect on the number of kernel rows, kernels per row, and kernels per ear, and grain yield. The direct effect of the number of kernels per ear on grain yield was very low. However, it affected grain yield through the number of kernel rows and kernels per row. The dry matter accumulation of V6−V12 and R3−R6 contributed the most to grain yield, while in vegetative organs, the effect of leaf dry matter accumulation and yield was the greatest. This investigation will provide insights into factors affecting variations in maize yield under low nitrogen conditions and offer guidance for N‐fertilizer management strategies.

Differences in dry matter production and grain yield of maize (Zea mays L.) cultivars with contrasting nitrogen efficiency

ABSTRACT We aimed to investigate the differences in dry matter accumulation (DMA), distribution, remobilisation, and yield of maize cultivars with contrasting nitrogen efficiency responses to nitrogen application rates. Nitrogen fertiliser increased DMA, crop growth rate (CGR), redistribution of pre-silking dry matter, and accumulation of post-silking dry matter while reducing the root/shoot biomass ratio to substantially increase biomass yield and final maize grain yield. Higher final theoretical biomass yield, maximum increasing rate (MIR), and average increasing rate, later days to MIR, longer duration of rapid growth period, higher ratio of vegetative organs, and rational dry matter distribution aboveground and belowground contribute to higher DMA and CGR in the later growth stage, and higher assimilated dry matter into grain and biomass yield to finally obtain higher grain yield for N-efficient maize cultivar. The N-efficient cultivar had obvious advantages on grain yield compared with N-inefficient cultivar caused by higher dry matter average increasing rate and biomass and kernels per ear, while the advantages increased first, then decreased with higher N rates, and the highest value was observed at 247.5 kg N ha−1. Therefore, selecting N-efficient maize improves maize yield per unit area while reducing N fertiliser supply, especially at low N application rates.

Effects of soil potassium levels on dry matter and nutrient accumulation and distribution in cotton

BackgroundPotassium (K) is an essential nutrient for plant growth and development. However, plant fertilization ignoring the soil K level is very likely to cause excessive fertilizer use, and further arouse a series of side effects. This study investigated the response of cotton growth to different soil K levels and the uptake of major nutrients, aiming to evaluate the appropriate K supply level for cotton growth. Using a random block design with 6 soil K levels, we conducted 18 micro-zones field experiments over two continuous years. The soil available K concentration of each treatment was K1 (99.77–100.90 mg·kg−1), K2 (110.90–111.26 mg·kg−1), K3 (123.48–128.88 mg·kg−1), K4 (140.13–145.10 mg·kg−1), K5 (154.43–155.38 mg·kg−1), and K6 (165.77–168.75 mg·kg−1). Cotton nutrient contents, soil nutrient contents, accumulation and distribution of dry matter in cotton were determined, and the relationships between K content in soil and plants and dry matter accumulation were analyzed.ResultsThe soil K content had a significantly positive relationship with dry matter and K accumulation in cotton plants. There were significant differences in dry matter accumulation, single-plant seed cotton yield, mineral nutrient uptake and the proportion of K accumulation in reproductive organs among different soil K levels. The results showed that there was significant difference between K4 and lower K level treatments (K1 and K2), but no significant difference between K4 and higher K level treatments (K5 and K6) in dry matter, single-plant seed cotton yield, or accumulation, distribution and seed cotton production efficiency of N, P and K.ConclusionThe soil K level of K4 was able to provide sufficient K for cotton growth in our experiment. Therefore, when the soil K level reached 140.13 mg·kg−1, further increasing the soil K concentration no longer had a significant positive effect on cotton growth.

Differences in Dry Matter Accumulation and Distribution Patterns between Pre-Elite Seed and Certified Seed of Virus-Free Potato

Virus-free seed potatoes are generally divided into pre-elite seeds and certified seeds. To study the differences in dry matter accumulation and distribution between pre-elite seeds and certified seeds through a field randomized block two-factor experiment, pre-elite seeds and certified seeds of four varieties were selected to explore the differences in growth characteristics between the two levels of virus-free potatoes and to find a way to improve potato seed expansion efficiency. The results showed that the growth process of pre-elite seeds was slower and the growth period was longer than certified seeds. The dry matter accumulation of pre-elite seeds in various organs was lower than in certified seeds, and the distribution ratio in the roots and stems of each variety was also lower than the certified seed, while there was no significant difference in the leaf and tuber distribution ratio. The average dry matter accumulation rate in both pre-elite and certified seeds was sorted by size of tubers > leaves > stems > roots; however, it was significantly lower in pre-elite seeds than in certified seeds. Tuber fresh weight, tuber volume, tuber number, and the theoretical yield of certified seeds were higher than those of pre-elite seeds. Experiments have shown that appropriately prolonging the harvest time of virus-free potatoes, especially pre-elite seeds, and increasing the proportion of dry matter allocated to roots and stems by pre-elite seeds in the early growth stages can effectively increase yield.

Effects of Nitrogen Application in Recovery Period after Different High Temperature Stress on Plant Growth of Greenhouse Tomato at Flowering and Fruiting Stages

High temperatures have become a severe factor limiting growth and yield for tomatoes (Lycopersicon esculentum Mill.) due to unfavorable, above-optimum temperatures. Temperature and nitrogen application were the main regulatory factors in tomato plant cultivation. This research was undertaken to evaluate the effects of nitrogen application and high temperature on tomato morphology, dry matter accumulation and distribution, root vitality and nitrogen content of the above ground. Tomato variety “Jinfen No. 1” was planted and exposed to 4 day/night temperature levels (25 °C/15 °C as control CKT; 30 °C/20 °C, lightly high-temperature LHT; 35 °C/25 °C, moderate high-temperature MHT; 40 °C/30 °C, severe high temperature SHT) for 7 days after five nitrogen supply levels (N1–N5: 0, 1.3, 1.95, 2.6 and 3.75 g/plant, respectively; 2.6 g/plant is the recommended nitrogen-application rate, as control CKTN4). Within conditions, there was an extremely significant difference (p < 0.01) in all tomato plant parameters and an extremely significant interaction (p < 0.01) between high temperatures and nitrogen supply levels, except for plant height sampling on the 1st day in the recovery period. Dry matter accumulation decreased, and the accumulation rate slowed down. Dry matter accumulation under low nitrogen treatment was higher than in high nitrogen treatment. The proportion of dry matter in leaves decreased, the proportion of dry matter in stems increased and the difference in dry matter accumulation and proportion of dry matter between different nitrogen treatments decreased. Under LHT, the root activity of the tomato was increased under all nitrogen levels, while under MHT and SHT, high nitrogen and low nitrogen supply significantly inhibited root activity. Lightly high-temperature stress can increase root activity, and LHTN4 can increase by 5.15% compared with CKTN4. Appropriate nitrogen application can alleviate the damage caused by high-temperature stress on tomato plants and enhance the resistance of tomato plants, while excessive nitrogen application will aggravate the damage degree of tomato plants. In this study, the optimal nitrogen application rates under CKT-SHT treatment were 2.6, 2.6, 1.95 and 1.3 g/plant, respectively.

Artificial Grassland Had Higher Water Use Efficiency in Year with Less Precipitation in the Agro-Pastoral Ecotone.

Improving plant water use efficiency is a key strategy for the utilization of regional limited water resources as well as the sustainable development of agriculture industry. To investigate the effects of different land use types on plant water use efficiency and their mechanisms, a randomized block experiment was designed in the agro-pastoral ecotone of northern China during 2020-2021. The differences in dry matter accumulation, evapotranspiration, soil physical and chemical properties, soil water storage and water use efficiency and their relationships among cropland, natural grassland and artificial grassland were studied. The results show that: In 2020, the dry matter accumulation and water use efficiency of cropland were significantly higher than those of artificial and natural grassland. In 2021, dry matter accumulation and water use efficiency of artificial grassland increased significantly from 364.79 g·m-2 and 24.92 kg·ha-1·mm-1 to 1037.14 g·m-2 and 50.82 kg·ha-1·mm-1, respectively, which were significantly higher than cropland and natural grassland. The evapotranspiration of three land use types showed an increasing trend in two years. The main reason affecting the difference of water use efficiency was that land use type affected soil moisture and soil nutrients, and then changed the dry matter accumulation and evapotranspiration of plants. During the study period, the water use efficiency of artificial grassland was higher in years with less precipitation. Therefore, expanding the planted area of artificial grassland may be one of the effective ways to promote the full utilization of regional water resources.

Effects of tillage and sowing practices on plant growth, soil nutrient uptake and utilization of wheat after rice

From 2016 to 2018, a field trial on three tillage and sowing practices, deep rotary tillage before sowing (DRT), shallow rotary tillage with simultaneous sowing (SRT), and strip tillage under no tillage conditions along with sowing (NT), was conducted to evaluate shoot growth, soil nutrient uptake, and utilization of wheat (Triticum aestivum) after rice (Oryza sativa) in Guanghan, Sichuan Province, China. Compared with DRT, both SRT and NT improved tillering capacity and fertile shoot rate. In 2016-2017, grain yield did not differ among the treatments, whereas in 2017-2018, NT had significantly higher grain yield (10.9%) than DRT. Furthermore, the diffe-rence in dry matter accumulation among the treatments mainly occurred prior to wheat jointing. Total nitrogen uptake of plants was higher by 9.9% in NT than in DRT, whereas nitrogen harvest index was higher in DRT than in NT. Total phosphorus uptake was not different among the treatments. Total potassium uptake was higher in NT plants than in DRT plants. Overall, the results showed that compared with the traditional tillage practice (i.e., DRT), strip tillage practice along with sowing (i.e., NT) is an effective method for increasing grain yield and soil nutrient uptake for wheat after rice.

Elevated temperature differently affects growth, photosynthetic capacity, nutrient absorption and leaf ultrastructure of Abies faxoniana and Picea purpurea under intra- and interspecific competition.

There is a limited understanding of the impacts of global warming on intra- and interspecific plant competition. Resolving this knowledge gap is important for predicting the potential influence of global warming on forests, particularly on high-altitude trees, which are more sensitive to warming. In the present study, effects of intra- and interspecific competition on plant growth and associated physiological, structural and chemical traits were investigated in Abies faxoniana and Picea purpurea seedlings under control (ambient temperature) and elevated temperature (ET, 2°C above ambient temperature) conditions for 2years. We found that A. faxoniana and P. purpurea grown under intra- and interspecific competition showed significant differences in dry matter accumulation (DMA), photosynthetic capacity, nutrient absorption, non-structural carbohydrate (NSC) contents and leaf ultrastructure under ET conditions. ET increased leaf, stem and root DMA of both conifers under both competition patterns. Moreover, under ET and interspecific competition, P. purpurea had overall superior competitive capacity characterized by higher organ (leaf, stem and root) and total DMA, height growth rate, net photosynthetic rate, specific leaf area, water use efficiency (δ13C), leaf and root N and NSC concentrations and greater plasticity for absorption of different soil N forms. Thus, the growth of P. purpurea benefitted from the presence of A. faxoniana under ET. Our results demonstrated that ET significantly affects the asymmetric competition patterns in subalpine conifer species. Potential alteration of plant competitive interactions by global warming can influence the composition, structure and functioning of subalpine coniferous forests.

秸秆还田配施不同比例化肥对晚稻产量及土壤养分的影响

Straw is rich in organic carbon,nitrogen( N),phosphorus( P),potassium( K),silicon( Si) and other nutrients that can improve physical,chemical and biological properties,increase crop yield,and lower fertilizer costs.Straw is mainly composed of cellulose,hemicellulose and lignin,and the C /N ratio is generally about 60—80; straw is therefore not easily decomposed by microorganisms in soil. Straw also needs to absorb a certain amount of N,for which it competes with crops,affecting seedling growth. Returning straw that contains a certain proportion of fertilizer N and P can mediate the soil C /N ratio,accelerate straw decomposition,and relieve the competition for inorganic nitrogen from microorganisms during the decomposition process. To explore the decomposition patterns of straw,we designed an experiment in Jiangxi to examine changes in dry matter production,soil properties,and biological processes in response toreturning straw. The amount of crushed straw used( 3000 kg /hm2) was determined by an examination of the effects of different amounts of returning straw on early rice. We researched the effects of returning straw containing different ratios of fertilizer on rice yield,dry matter accumulation and distribution,and soil fertility. We used a single application of straw as a control. Other treatments were SN1( 3000 kg/hm2 of crushed straw + 150 kg /hm2N),SN2( 3000 kg/hm2 of crushed straw+ 225 kg /hm2N),SP1( 3000 kg/hm2 of crushed straw + 75 kg /hm2P2O5),SP2( 3000 kg/hm2 of crushed straw + 112. 5kg / hm2P2O5),SNP1( 3000 kg/hm2 of crushed straw + 150 kg /hm2 N + 75 kg /hm2P2O5),SNP2( 3000 kg/hm2 of crushed straw + 225 kg /hm2 N + 112. 5 kg /hm2P2O5),SNPK1( 3000 kg/hm2 of crushed straw + 150 kg /hm2 N + 75 kg /hm2P2O5+ 37. 5 kg /hm2K2O),SNPK2( 3000 kg/hm2 of crushed straw + 225 kg /hm2 N + 112. 5 kg /hm2P2O5+ 56. 3 kg /hm2K2O). The results demonstrate the following:( 1) Compared with the control,the returning straw with low levels of N,P,and K significantly increase the grains per spike,1000-grain weight,seed-setting rate,filled degree of grain and overall crop yield at rates of 9. 32%,4. 28%,13. 70%,2. 74% and 26. 38%,respectively.( 2) The differences in dry matter accumulation between different growth periods are significant. Dry matter accumulation is greatest in the tilling to heading period and the filling to maturity period in all treatment groups.. The following proportion of total dry matter accumulation occurred in those two periods combined: 78. 61%,79. 22%,81. 97%,77. 95%,77. 27%,78. 13%,78. 20%,79.08%,and 78. 47% in the control group,SN1,SN2,SP1,SP2,SNP1,SNP2,SNPK1 and SNPK2,respectively. The heading to filling period is a stage of rapid accumulation of material,but because of its short duration,dry matter accumulation and the ratio of accumulation to the total amount of dry matter was lower than in the other growth periods.With growth,the ratio of stem-sheath length to total plant length continuously decreased from a range of 66. 68% —77. 00%in the booting stage to a range of 25. 97% —34. 79% in the maturity period. In addition,in the SNPK1 treatment,the ratio of leaf length to the total plant length reduced from a range of 23. 00% —33. 32% in the booting stage to a range of 7.41% —21. 03% in the maturity period. The dry weight ratio of the stem-sheath to the whole plant in the booting stage,heading stage,and at maturity was significantly higher in the treatment groups than in the control group,and was highest in the SNPK1 treatment. The dry weight ratio of the leaf to the whole plant is opposite; the ratio is highest in the control group.( 3) Compared with the control group,in the treatment groups,the pH increased by 1. 97% —4. 33%,organic carbon content increased by 3. 76% —25. 05%,total nitrogen content increased by 14. 75% —45. 90%,alkaline hydrolysis nitrogen content increased by 3. 49% —39. 90%,total phosphorus content increased by 10. 00% —55. 00%,available phosphorus content increased by 10. 45% —50. 88%,total potassium content increased by 18. 27% —100%,and available potassium content increased by 9. 39% —79. 72%; the C /N ratio decreased by 6. 02% —23. 59%. These results demonstrate that returning straw that contains fertilizer improves rice yield and dry matter accumulation rates; this translates to a higher potential yield of rice crops,and an increase in the level of soil nutrients. The combined effect of returning rice straw to fields with low levels of N,P,and K is significant. This study will provide a theoretical basis for the use of straw to increase soil fertility in southern regions of China,where rice farming is abundant.

Ratoon sugarcane yield integrated drip-irrigation and nitrogen fertilization

The aim of this study was to compare the use of water and nitrogen on ratoon sugarcane during irrigated and rain-fed conditions, and to assess the production potential of stalks and sugar with different rates of N-fertilizer on the subsurface drip-irrigated management. The experimental design was a randomized block with four replications for each experiment and treatments: (T1) irrigated, 0kg N ha-1; (T2) irrigated, 70kg N ha-1; (T3) irrigated, 140kg N ha-1; (T4) irrigated, 210kg N ha-1; (T5) not irrigated, 0kg N ha-1, and (T6) not irrigated, 140kg N ha-1. Biometric, technological, dry matter and yield variables were analyzed among the treatments. The irrigation system together with the application of N-fertilizer at 140kg ha-1 presented significant differences in dry matter accumulation of shoots, and for the production of stalks and sugar, respectively 94, 105 and 106%, higher when compared to the not irrigated, without N-fertilizer (T5). There was a positive and synergistic effect of irrigation with N-fertilizer on the productivity of stalks and sugar. Ratoon sugarcane irrigated with subsurface dripping had the highest yield (22Mg ha-1 of sugar) with the dosage of 140kg ha-1 N.

Cowpea (Vigna unguiculata L. Walp) response to phosphorus fertilizer under two tillage and mulch treatments

The response of cowpea to four rates of phosphorus (P) fertilizer (0, 15, 30 and 45kgPha−1) on an Ultisol in south-eastern Nigeria was evaluated under two tillage and two mulch treatments. Tilled plots produced plants with significantly larger leaf area indices (2.82–4.05) than the untilled plots (2.11–3.22), while significant differences in dry matter accumulation occurred when plots were mulched, tilled plot values ranged from 3.83 to 5.53t/ha while the untilled plots were between 2.77 and 3.97t/ha. Plants in mulched plots were 39–80% and 20–62% higher in grain yield and dry matter accumulation, respectively, compared to the un-mulched plots. Yield response to phosphorus levels on each tillage–mulch combination was significant for linear and parabolic responses. Maximum yields occurred at 34, 37, 35, and 33kgPha−1 on the tilled–mulched (TM), tilled–un-mulched (TU), untilled–mulched (UM) and untilled–un-mulched (UU) plots, respectively. Dry matter response to P level was of a quadratic polynomial form and indicated apparent maximum accumulation (at flowering) at 30kgha−1 rate under the tillage mulch treatments. Apparent maximum accumulation of dry matter was however at 45kgha−1P rate for the TM treatment. Phosphorus use efficiency (grain yield per P applied) decreased in the order TM (72.4)>UM (66.6)>TU (48.9)>UU (36.4), where the figures in parenthesis represent phosphorus use efficiency (kgkg−1). The rate of change in available P in mulched plots increased faster compared to the un-mulched plots, with the rate in UM plots being significantly faster than in the other plots at the ninth week. Tissue P did not vary in plants following the tillage–mulch treatment. The results also indicated that the tilled treatments (TM and TU) gave 12.3–34.9% comparatively higher gross margin (profit) when compared to their untilled equivalents (UM and UU), however when the profits were considered against the investment costs, the untilled treatments (UM and UU) gave higher returns per unit investment (189.0–588,800).

Structure and biological activities of lipochitooligosaccharide nodulation signals produced by Bradyrhizobium japonicum USDA 138 under saline and osmotic stress

The establishment of a symbiotic interaction involves a signal exchange between the host legume (flavonoids) and the nitrogen-fixing rhizobia (nodulation factors (NFs)). Likewise, abiotic stress conditions, such as salinity and drought, strongly reduce the nodulation process, possibly affecting also the signal exchange. In this work we characterized the structure and biological activity of NFs produced by Bradyrhizobium japonicum USDA 138 under control, salt, and osmotic stress conditions. This strain is the most widely used in Argentine soybean culture; under control conditions, it produces a mixture of four types of NFs (V(C16:0,MeFuc), V(C18:1,MeFuc), IV(C18:1), and V(C18:1,Ac,MeFuc)). Interestingly, under stress conditions, this strain produces new types of NFs, one common for both stress conditions (V(C16:1,MeFuc)) and another one only present under salt stress (IV(C18:1,MeFuc)). All mixtures of NFs, extracted from control, salt, and osmotic stress conditions, showed biological activity in soybean plants, such as root hair deformation, and the radical application of purified NFs induced systemic differences in dry matter accumulation. The inoculation of soybean with genistein-induced bacteria cultured under both control and stress conditions had a positive effect on the number of nodules formed and in some cases on dry matter accumulation. These responses are not related to changes in chlorophyll fluorescence or greenness index.

Growth and nutrient uptake of Citrus rootstock varieties as affected poultry manure and NPK fertilizer in Ibadan, Southwestern Nigeria

Screen house experiment was conducted to determine the optimum rate of organic, inorganic and organo-mineral fertilizers that would enhance the growth and nutrient uptake of citrus rootstock seedlings. Two rootstock varieties [Cleopatra mandarin (Citrus reticulata Blanco) and Rough lemon (Citrus jambhiri Lush)] and ten fertilizer rates [0, 3, 6 and 9 t/ha poultry manure (PM), 0.2, 0.3, and 0.4 t/ha NPK 15-15-15 (NPK), 1.5 t/ha PM+0.2 t/ha NPK, 3 t/ha PM+0.15 t/ha and 4.5 t/ha PM+0.1 t/ha NPK] serve as main and sub-plot treatments respectively in split plot experimental design. Results obtained showed that seedlings grown with 9 t/ha PM and 0.2 t/ha NPK had significantly (p= 0.05) higher plant height, number of leaves, stem diameter and nutrient uptake as compared to other fertilizer treatments throughout the period of investigation. Rough lemon seedlings had significantly higher number of leaves and number of branches compared to Cleopatra mandarin during the period of study. There were no significant differences in dry matter accumulation between the two rootstock types. Since plant height and stem diameter determine the quality of rootstock seedlings, poultry manure at 9 t/ha and NPK fertilizer at 0.2 t/ha are therefore recommended for propagation of citrus seedlings in the screen house.Key words: Spices, Prevalence, Supply, Usage, Profitability, Constraints.

Genotypic Differences in Dry Matter Accumulation, Nitrogen Use Efficiency and Harvest Index in Recombinant Inbred Lines of Rice under Hydroponic Culture

To examine the possibility of breeding high-yielding cultivars with high nitrogen use efficiency for dry matter accumulation (NUEd) and to provide simple criteria for the selecting and breeding high-yielding cultivars with high NUEd as well as useful information for the mapping of quantitative trait loci (QTL) controlling NUEd, we cultured recombinant inbred lines (RILs) of rice hydroponically in 2000 and 2001. RILs with a higher grain yield tended to show greater total dry matter accumulation (TDMA) and higher harvest index (HI), while increasing TDMA resulted in a decrease in HI. The contribution ratio of the TDMA to grain yield (2000 : 67.3%, 2001 : 68.2%) was higher than that of HI in both 2000 and 2001. Even at the same high-yielding level, there was a significant difference in the TDMA and HI values. In both years, the contribution ratios of NUEd and total nitrogen absorption (NTA) to TDMA were about 62.0 and 38.0%, respectively. The contribution ratio of the NUEd to grain yield was higher than those of the NTA and HI in both 2000 (41.6%) and 2001 (42.9%). These results suggested that the high-yielding rice plants generally displayed high TDMA and HI values. Further increase in rice grain yield should be based on the further increase in TDMA than in HI, and to increase TDMA leading to a high grain yield, the emphasis also should be put on improving NUEd in RILs.

Relationship between net photosynthesis and leaf respiration in Mediterranean evergreen species

The relationship between net photosynthetic (P N) and leaf respiration (R) rates of Quercus ilex, Phillyrea latifolia, Myrtus communis, Arbutus unedo, and Cistus incanus was monitored in the period February 2006 to February 2007. The species investigated had low R and P N during winter, increasing from March to May, when mean air temperature reached 19.2 °C. During the favourable period, C. incanus and A. unedo had a higher mean P N (16.4±2.4 µmol m−2 s−1) than P. latifolia, Q. ilex, and M. communis (10.0±1.3 µmol m−2 s−1). The highest R (1.89±0.30 µmol m−2 s−1, mean of the species), associated to a significant P N decrease (62 % of the maximum, mean value of the species), was measured in July (mean R/P N ratio 0.447±0.091). Q10, indicating the respiration sensitivity to short-term temperature increase, was in the range 1.49 to 2.21. Global change might modify R/P N determining differences in dry matter accumulation among the species, and Q. ilex and P. latifolia might be the most favoured species by their ability to maintain sufficiently higher P N and lower R during stress periods.

Physiological and morphological variations of Picea asperata populations originating from different altitudes in the mountains of southwestern China

Population differences in dry matter accumulation and allocation, conifer leaf nitrogen status, stomata parameters and water use efficiency were studied in a 7-year-old Picea asperata Mast. plantation that contains seven populations grown from seed collected from different altitudes in the mountains of southwestern China. In our study, we measured dry matter accumulation (DMA), total projected leaf area (LA), specific projected leaf area (SLA), root/shoot ratio (RS), root mass/projected leaf area ratio (R/LA), projected leaf area/stem cross-sectional area ratio (LA/SA), leaf stomatal density (SD), stomatal length (SL) and total stomatal length (TSL), nitrogen content per unit leaf mass (N mass) and nitrogen content per unit projected leaf area (N area), and carbon isotope composition ( δ 13C). Significant differences in these properties among the populations were detected, but these morphological and physiological responses to altitudinal gradients of origins varied non-linearly with increasing altitude. We found that seed source near 2950 m altitude was likely an optimum zone for P. asperata; growth was most vigorous at this altitude, and with increasing altitudinal distance from this optimum the growth decrease. In addition, seedling early growth, including DMA and LA, negatively correlated with RS, R/LA, N mass, N area and δ 13C, and positively correlated with SLA, LA/SA, SD, SL and TSL. Our results provided strong evidence that variations in these physiological and morphological properties of P. asperata populations reflected genetic adaptations to native habitats. These differences may be used as criteria for genotype selection in the mountains of southwestern China.

Impact of altered gibberellin metabolism on biomass accumulation, lignin biosynthesis, and photosynthesis in transgenic tobacco plants.

Gibberellins (GAs) are involved in regulation of many aspects during plant development. To investigate the impact of altered GA levels on plant growth and metabolism, transgenic tobacco (Nicotiana tabacum) plants have been engineered to express either a GA20-oxidase (AtGA20-ox) or a GA2-oxidase (AtGA2-ox) gene from Arabidopsis under control of the cauliflower mosaic virus 35S promoter. Resulting plants were characterized by elongated or stunted shoot growth, respectively, indicating changes in the content of bioactive GAs. In accordance with the effect on plant growth, biomass production was increased or decreased in AtGA20-ox or AtGA2-ox plants, respectively, and was found to be positively correlated with the rate of photosynthesis as determined at the whole plant level. Differences in dry matter accumulation were most likely due to changes in lignin deposition as indicated by histochemical staining and quantitative measurements. Altered lignification of transgenic plants was paralleled by up- or down-regulation of the expression of lignin biosynthetic genes. Short-term GA3 feeding of excised petioles induced lignin formation in the absence of a transcriptional activation of pathway-specific genes. Thus, short-term GA treatment mediates lignin deposition most likely by polymerization of preformed monomers, whereas long-term effects on lignification involve elevated production of precursors by transcriptional stimulation of the biosynthetic pathway. Interestingly, analysis of stem cross sections revealed a differential effect of GA on the formation of xylem and pith cells. The number of lignified vessels was increased in AtGA20-ox plants pointing to a stimulation of xylem formation while the number of pith cells declined indicating a negative regulation.

Population differences in physiological and morphological adaptations of Populus davidiana seedlings in response to progressive drought stress

Population differences in dry matter accumulation and allocation, gas exchange, abscisic acid content and water use efficiency of Populus davidiana seedlings were measured after exposure to well-watered and progressive drought stress treatments. Three populations used were form dry, middle and wet climate regions, respectively. Significant differences in height growth (Ht), total biomass (Tb), total leaf area (La), root/shoot ratio (Rs), specific leaf area (Sla), net photosynthesis ( A), transpiration ( E) and instantaneous water use efficiency (WUE i) between the populations were detected under two watering regimes; population differences in abscisic acid content (ABA) and carbon isotope composition ( δ 13 C ) were also detected under progressive drought stress treatment, but these differences were not significant under well-watered treatment. Compared with the wet climate population, the dry climate population had lower Ht, Tb, La, Sla, A and E, and higher Rs and WUE i. On the other hand, the dry climate population also exhibited higher ABA and δ 13 C as effected by drought stress than the wet climate population. These morphological and physiological adaptations to water availability showed that the different populations may employ different survival strategies under drought stress at the initial phase of seedling growth and establishment. The wet climate population possesses a prodigal water use strategy and quick growth, while the dry climate population exhibits a conservative water use strategies and slow growth. These differences in drought responses may be used as criteria for genotype selection in different climate regions.

Differences in drought responses of three contrasting Eucalyptus microtheca F. Muell. populations

Changes in dry matter accumulation and allocation, leaf stomatal properties and some aspects of leaf water relations of three contrasting Eucalyptus microtheca F. Muell. populations were recorded after exposure to drought stress. The populations used were from West Kimberleys (northwestern Australia), Central Australia and Walgett (southeastern Australia). In the controlled environment study there were three watering regimes which were watered to 100, 50 and 25% field capacity, respectively. Significant differences in dry matter accumulation and allocation, leaf guard cell length, the minimum daily leaf water potential, carbon isotope composition (described as water-use efficiency) and abscisic acid (ABA) concentration were detected among populations. Compared with the southeastern population, under water deficit the northwestern and central populations had lower biomass production and higher root/shoot ratio, foliage area/stem cross-sectional area ratio and specific leaf area density. The northwestern and central populations also exhibited higher minimum daily water potentials, water-use efficiencies and ABA accumulation as effected by drought than the southeastern population. These morphological and physiological responses to water availability showed that the different populations may employ different survival strategies under drought stress at the initial phase of seedling growth and establishment. The southeastern population possesses a prodigal water-use strategy and quick growth, while the northwestern and central populations exhibit conservative water-use strategies and slow growth. These differences in drought responses maybe used as criteria for genotype selection in arid and semi-arid regions.

Importance of Canopy Attributes in Determining Dry Matter Accumulation of Pigeonpea under Contrasting Moisture Regimes

Variability in the yield of extra‐short‐duration (ESD) pigeonpea [Cajanus cajan (L.) Huth.] genotypes in drought environments is related to variation in crop growth rate (CGR) and total dry matter (TDM) production. Our investigation was aimed at assessing the importance of canopy attributes in determining the growth of ESD pigeonpea under contrasting moisture regimes. Using two automated rain‐out shelters (ROS), six genotypes were grown under well watered conditions or with water deficit imposed from flowering until maturity. Water deficit significantly decreased the cumulative intercepted photosynthetically active radiation (CIR). The relationship between biomass accumulation and CIR was linear and water deficit affected the slope of the relationship (i.e., radiation use efficiency, RUE) (b = 1.92 g MJ−1 for well watered vs. 1.43 g MJ−1 for water deficit). Genotypes differed in RUE under well watered (1.70 to 2.19 g MJ−1) and moisture deficit (1.30 to 1.66 g MJ−1) conditions. Genotypic variation in canopy attributes was significant. Leaf area duration (LAD) significantly correlated with CGR only under well watered conditions. Cumulative intercepted radiation and RUE accounted for nearly 99% of the genotypic variation in CGR under both moisture regimes, of which RUE alone contributed nearly 90%. Variation among genotypes in CIR alone did not explain the differences in dry matter accumulation under either moisture regime. Only RUE explained more than 90% of the genotypic variation in CGR and 70% in TDM under both moisture regimes. The results indicated that RUE is critical in determining pigeonpea productivity under well watered and moisture‐deficit regimes.