Relative Shoot Biomass Research Articles

Revisiting the relationship between nitrogen nutrition index and yield across major species

Crop nitrogen (N) fertilization diagnoses via the N nutrition index (NNI)-yield relationship have been tested for several crop species, but a cross-species comparison of that relationship has not been performed yet. This study aimed to perform a cross-species comparison of the relationship between NNI and yield with emphasis on the yield sensitivity to N deficiency, slope of the models. Additionally, we conducted an evaluation to determine the best NNI sampling moment to predict relative yield, with focus on major grain crops. Based on a recently published global dataset to parametrize critical dilution curves, we calculated integrated NNI, instantaneous NNI, relative yield, and relative shoot biomass for annual ryegrass, tall fescue, maize, potato, rice, and wheat. We obtained 238 observations to fit integrated NNI-relative yield linear mixed-effects models and 1606 observations to fit instantaneous NNI-relative yield models. Subsequently, we performed a sensitivity analysis to determine the best NNI sampling moment to predict relative yield, with focus on major grain crops (maize, rice, and wheat). Our results show that there was low inter-species variation of sensitivity to N deficiency, i.e., the slope of the relationship between relative yield and integrated NNI. For grain crops, instantaneous NNI around anthesis demonstrated a better predictive capability for relative yield, outperforming other vegetative stages. This finding contributed to improving the understanding of the association between relative yield and NNI with implications for breeding programs, nutrient management practices, and crop modelling. Most importantly, this study is a contribution to improving the N nutrition diagnosis for several crop species, by using an integral, comparative approach.

Shallower Root Spatial Distribution Induced by Phosphorus Deficiency Contributes to Topsoil Foraging and Low Phosphorus Adaption in Sugarcane (Saccharum officinarum L.).

Low phosphorus (P) availability in acid soils is one of the main limiting factors in sugarcane (Saccharum officinarum L.) production. Reconstruction of the root system architecture (RSA) is a vital mechanism for crop low P adaption, while the RSA of sugarcane has not been studied in detail because of its complex root system. In this study, reconstruction of the RSA and its relationship with P acquisition were investigated in a P-efficient sugarcane genotype ROC22 (R22) and two P-inefficient genotypes Yunzhe 03-103 (YZ) and Japan 2 (JP). An efficient dynamic observation room was developed to monitor the spatiotemporal alternation of sugarcane root length density (RLD) and root distribution in soil with heterogeneous P locations. The sugarcane RSA was reconstructed under P deficiency, and R22 had an earlier response than YZ and JP and presented an obvious feature of root shallowness. Compared with the normal P condition, the shallow RLD was increased by 112% in R22 under P deficiency while decreased by 26% in YZ and not modified in JP. Meanwhile, R22 exhibited a shallower root distribution than YZ and JP under P deficiency, supported by 51 and 24% greater shallow RLD, and 96 and 67% greater shallow root weight, respectively. The ratio of shallow RLD to total RLD in R22 was 91% greater than YZ, and the ratio of shallow root weight to total root weight in R22 was greater than that of YZ and JP by 94 and 30%, respectively. As a result, R22 had a higher shoot P accumulation than YZ and JP, which thereby increased the relative leaf sheath inorganic P concentration (RLPC) by 47 and 56%, relative shoot biomass (RSB) by 36 and 33%, and relative cane weight (RCW) by 31 and 36%, compared with YZ and JP under P deficiency, respectively. We verified the reliability and efficiency of a dynamic observation room and demonstrated that a shallower root distribution contributed to improving topsoil foraging, P acquisition, and low P adaption under P deficiency in sugarcane. Therefore, a shallower root distribution merits consideration as an evaluation trait for breeding P efficient sugarcane genotypes and genetic improvement.

Critical plant phosphorus for winter wheat assessed from long-term field experiments

Optimizing the use of phosphorus (P) fertilizers is essential considering the environmental issues linked to over fertilization and the limited rock phosphate reserve. Diagnosing the crop P status by calculating a phosphorus nutrition index (PNI) based on the plant critical P concentration (Pc) could help determine the minimum amount of P fertilizer to ensure maximum crop yield. This study investigated (i) the effect of P fertilization on winter wheat (Triticum hybernum L.) shoot biomass and grain yield after several decades of different annual P fertilization rates, (ii) the stability over several site-years of the Pc expressed either as a function of shoot biomass or shoot nitrogen (N) concentration, and (iii) the possibility of using the PNI or the shoot N-to-Pc ratio as nutritional indicators to diagnose P deficiency and predict the expected response to P fertilization. Shoot biomass and its P and N concentrations were measured weekly at five site-years along with grain yield after several decades of P fertilization treatments that ranged between 0 and 5/3 of the theoretical P crop uptake. The P fertilization did not affect the grain yield, but it generally increased shoot biomass especially at the CD 27- -37 developmental stages. The Pc expressed either as a function of shoot biomass or shoot N concentration differed among site-years and this was attributed to differences in crop N status. When N was not deficient, we developed a Pc dilution curve as a function of shoot biomass (SB) (4.56 × SB−0.279) along with a linear relationship (Pc = 1.10 + 0.061 × N) and a power function (Pc = 0.34 × N0.632) between Pc and shoot N concentration. The N-to-Pc ratio was related to shoot biomass accumulation according to a power function, but the relationship also differed among site-years. The relative shoot biomass responded positively to the PNI up to different thresholds for limiting and non-limiting N conditions. The relative grain yield, however, was not related to the PNI. The PNI, based on the Pc dilution curve, has potential as a nutritional indicator to diagnose P deficiency and the expected response to P fertilization, but more research is needed to clarify the effect of N deficiencies on the Pc dilution curve.

Comparative Study of the Effects of Salinity on Growth, Gas Exchange, N Accumulation and Stable Isotope Signatures of Forage Oat (Avena sativa L.) Genotypes.

Identifying suitable salt stress-tolerant phenotypes based on their agronomic and physiological traits remains a herculean task in forage-type oat (Avena sativa L.) breeding. This study examined the responses of six forage-type oat cultivars under four levels of saline stress over the vegetative growth cycle. Crop growth, water status-related traits and nitrogen status-related traits were analyzed in different plant parts to evaluate effective approaches for identifying salt tolerance. Plant biomass, height, tiller number and culm thickness changed substantially during salinity, but they were not precise enough for use in estimating genotypic salinity tolerance during long-term stress. Genotypes bearing larger numbers of tillers showed greater sensitivity to salinity due to its effects on biomass loss. Tolerant genotypes exhibited higher relative shoot biomass together with higher water use efficiency. The concentrations of Na+, K+ and their ratio, combined with the δ13C in shoots and roots were effective indicators for estimating tolerant genotypes through better water maintenance. N concentrations of shoots were the most efficient for evaluating genotypic tolerance. Low nitrate reductase (NR) and glutamine synthetase (GS) activity might be key factors limiting N accumulation. Chlorophyll (Chl) content and net photosynthetic rate, as well as stomatal conductance and evaporation, were useful for identifying salinity tolerance physiological mechanisms, but the effectiveness was low for genotypic tolerance testing for forage type oats due to the interaction between genotypes and salinity levels. The selection of high salinity-tolerant genotypes should focus on genotypes with photosynthetic resilience to salt, followed by high N metabolism (higher NR and GS activities) to ensure accumulation of more N in the shoot dry matter.

Diversity of Drought Tolerance in the Genus Vigna.

Wild relatives of crop plants are thought as reservoir of prominent genetic resources for abiotic stress tolerance. However, insufficient information on genetic variation and phenotypic traits restricts their use for crop breeding. This study focused on wild species of genus Vigna (family Fabaceae) originated from highly humid to arid regions. To clarify the diversity of drought tolerance during the vegetative stage, 69 accessions, including 15 domesticated, and 54 wild accessions, were evaluated under two drought conditions of non-terminal and terminal stresses. In the non-terminal drought condition, the plants were grown in pipes of different heights where surface soil water content decreased faster in pipes with greater height. Relative shoot biomass was used for tolerance evaluation and we identified 19 drought tolerant accessions. Almost of them were wild accessions showing higher relative shoot biomass than that in the domesticated accessions. Domesticated species were mostly classified as drought susceptible but could be improved using tolerant conspecific wild ancestors with cross-compatibility. The tolerance was related with higher plant water status presumably due to small water consumption. However, the variation of drought tolerance could not be explained by simple tolerance factor alone, and other tolerance mechanisms such as deep rooting and increasing in root biomass were found in the tolerant accessions. In the terminal drought condition, the plants were grown in small pots, and the watering was stopped to expose them extreme and rapid soil water scarcity. The tolerance was evaluated as the number of days until wilting. However, the accessions found to be tolerant in the pot experiment were not the same as those in the pipe experiment. In this condition, plant water status was not related with the length of days to wilting. This indicates that different mechanisms are necessary for adaptation to each of the non-terminal and terminal drought conditions. Many accessions were tolerant to one of the conditions, although we identified that some accessions showed tolerance in both experiments. The great diversity in drought tolerance in the genus Vigna might serve to both improve crop drought tolerance and understand the mechanisms of adaptation in drought-prone environments.

Identification of a maize (Zea mays L.) inbred line adapted to low‐P conditions via analyses of phosphorus utilization, root acidification, and calcium influx

AbstractPhosphorus (P) fertilizers are essential for achieving high crop productivity, but declining soil P reserves and cost of fertilizers suggest that improving crop varieties for improved use efficiency of P be important for sustainability. To explore the possibility of selecting crops suitable for low P conditions, two maize (Zea mays L.) inbred lines, i.e., W22 and W23 were compared for growth, root morphology, and electrophysiological parameters, under hydroponic conditions with either insoluble P source (LP) or soluble P source (HP) in a factorial completely randomized design. Relative shoot biomass of W23 was significantly (38%) greater than that of W22 with LP, while relative root biomass of the two inbred lines did not differ. With LP, the P stress factor was the lowest (25%) and P dissolution in hydroponic solution was the greatest for W23. Root electrophysiological analysis revealed that W23 had 89% greater H+ efflux and 225% greater Ca2+ influx than W22 with LP. The distant elongation zone (DEZ) of W23 root was significantly longer and more shoot‐ward than W22 with LP. Thus, W23, having significantly greater relative shoot biomass, lower P stress factor, greater P dissolution, greater H+ efflux and Ca2+ influx, longer and more shoot‐ward DEZ, was better adapted to low‐P condition compared to W22. In the future, the W23 inbred line can be used for developing low‐P stress resistant varieties to utilize native insoluble soil P efficiently or to produce commercially acceptable yields using lower rates of soluble P fertilizers.

Diversity and Evolution of Salt Tolerance in the Genus Vigna.

Breeding salt tolerant plants is difficult without utilizing a diversity of wild crop relatives. Since the genus Vigna (family Fabaceae) is comprised of many wild relatives adapted to various environmental conditions, we evaluated the salt tolerance of 69 accessions of this genus, including that of wild and domesticated accessions originating from Asia, Africa, Oceania, and South America. We grew plants under 50 mM and 200 mM NaCl for two weeks and then measured the biomass, relative quantum yield of photosystem II, leaf Na+ concentrations, and leaf K+ concentrations. The accessions were clustered into four groups: the most tolerant, tolerant, moderately susceptible, and susceptible. From the most tolerant group, we selected six accessions, all of which were wild accessions adapted to coastal environments, as promising sources of salt tolerance because of their consistently high relative shoot biomass and relative quantum yield. Interestingly, variations in leaf Na+ concentration were observed between the accessions in the most tolerant group, suggesting different mechanisms were responsible for their salt tolerance. Phylogenetic analysis with nuclear DNA sequences revealed that salt tolerance had evolved independently at least four times in the genus Vigna, within a relatively short period. The findings suggested that simple genetic changes in a few genes might have greatly affected salt tolerances. The elucidation of genetic mechanisms of salt tolerances in the selected accessions may contribute to improving the poor salt tolerance in legume crops.

Susceptibility of Highbush Blueberry Cultivars to Phytophthora Root Rot

Phytophthora cinnamomi Rands is a ubiquitous soilborne pathogen associated with root rot in many woody perennial plant species, including highbush blueberry (Vaccinium corymbosum). To identify genotypes with resistance to the pathogen, cultivars and advanced selections of highbush blueberry were grown in a greenhouse and either inoculated or not with propagules of P. cinnamomi. Two experiments were conducted, including one with 10 commercially established cultivars and another with seven newly released cultivars, three commercially established cultivars, and three advanced selections of highbush blueberry. Pathogen resistance was based on the shoot and root dry biomass of the inoculated plants relative to the noninoculated plants within each genotype, as well as on the percentage of root infection among the genotypes. Resistant genotypes included four commercially established cultivars, Aurora, Legacy, Liberty, and Reka, and two new cultivars, Overtime and Clockwork. When these genotypes were inoculated, average relative shoot biomass was ≥60% of that of the noninoculated plants, whereas relative root biomass was ≥40%. ‘Star’, as well as two advanced selections (an early- and a late-season type) may also have some degree of resistance, but further investigation is needed. Relative shoot biomass of the susceptible genotypes, on the other hand, ranged from 19% to 53% and relative root biomass ranged from 11% to 26%. The susceptible genotypes included ‘Bluetta’, ‘Bluecrop’, ‘Bluegold’, ‘Blue Ribbon’, ‘Cargo’, ‘Draper’, ‘Duke’, ‘Elliott’, ‘Last Call’, ‘Top Shelf’, and ‘Ventura’. These cultivars are not recommended at sites with conditions conducive to root rot, such as those with clay soils and/or poor drainage.

Counteractive biomass allocation responses to drought and damage in the perennial herb Convolvulus demissus

AbstractHerbivory and water shortage are key ecological factors affecting plant performance. While plant compensatory responses to herbivory include reallocation of biomass from below‐ground to above‐ground structures, plant responses to reduced soil moisture involve increased biomass allocation to roots and a reduction in the number and size of leaves. In a greenhouse study we evaluated the effects of experimental drought and leaf damage on biomass allocation in Convolvulus demissus (Convolvulaceae), a perennial herb distributed in central Chile, where it experiences summer drought typical of Mediterranean ecosystems and defoliation by leaf beetles and livestock. The number of leaves and internode length were unaffected by the experimental treatments. The rest of plant traits showed interaction of effects. We detected that drought counteracted some plant responses to damage. Thus, only in the control watering environment was it observed that damaged plants produced more stems, even after correcting for main stem length (index of architecture). In the cases of shoot : root ratio, relative shoot biomass and relative root biomass we found that the damage treatment counteracted plant responses to drought. Thus, while undamaged plants under water shortage showed a significant increase in root relative biomass and a significant reduction in both shoot : root ratio and relative shoot biomass, none of these responses to drought was observed in damaged plants. Total plant biomass increased in response to simulated herbivory, apparently due to greater shoot size, and in response to drought, presumably due to greater root size. However, damaged plants under experimental drought had the same total biomass as control plants. Overall, our results showed counteractive biomass allocation responses to drought and damage in C. demissus. Further research must address the fitness consequences under field conditions of the patterns found. This would be of particular importance because both current and expected climatic trends for central Chile indicate increased aridity.

Differential Salinity Tolerance among Oryza glaberrima, Oryza sativa and Their Interspecies Including NERICA

Salinity tolerance has been extensively studied in Oryza sativa, but little is known about the salt tolerance levels in Oryza glaberrima and the interspecific progenies including New Rice for Africa (NERICA). In this study, the salinity tolerance of the three cultivated rice species, O. glaberrima (54 genotypes), the interspecific progenies (21) including NERICA (7) and O. sativa (41) mainly grown in West Africa were examined comparatively. At 10 days after sowing (DAS) 80 mM NaCl was added to the culture solution, and the plants were grown for 10 more d. The ratio of shoot biomass in the 80 mM NaCl solution to that in the control was significantly higher in the interspecific progenies than in the other two species, and the relative root biomass was significantly lower in O. glaberrima than in the others. The vegetative growth of six genotypes including the salt tolerant Pokkali, and NERICA4 and its parents were evaluated further in pot experiments irrigated with 80 mM NaCl solution from 22 to 52 d after sowing. At 30 d of the salt stress, CG14 and Mala noir IV (O. glaberrima) were killed by salt, while WAB56-104 and NERICA4 survived; Pokkali maintained the highest relative shoot biomass growth at all sampling times of 10 d intervals. These results indicate that O. glaberrima is relatively weaker to NaCl salinity, while the interspecific progenies are fairly tolerant during the seedling stage, and that the relatively high salt stress tolerance of NERICA4 is derived from the O. sativa parent, WAB56-104.

Genotypic differences and some associated plant traits in potassium internal use efficiency of lowland rice (Oryza sativaL.)

As potassium (K) deficiency in paddy soils is becoming one of the limiting factors for increasing rice yield in Asia, it is important to identify genotypic differences and exploit genetic potential for K use efficiency in lowland rice. Successful identification of K-efficient genotypes and genetic improvement largely depend on development of accurate and feasible screening parameters and methods. In this study, over 134 rice (Oryza sativa L.) genotypes were tested under nutrient solution and field conditions at low and adequate K levels to examine genotypic differences in K internal use efficiency (KIUE) and identify the associated plant traits. Marked differences in K internal use efficiency for biomass production (KIUE-B) and for grain production (KIUE-G) were observed among the rice genotypes. The KIUE-B at the seedling stage (g DW g−1 K taken up) differed sixfold among the 134 rice genotypes under low K. A positive and close correlation was observed between the relative shoot and root dry matter yields, relative root K accumulation and the KIUE-B at the seedling stage, respectively. However, a negative and significant correlation was found between the KIUE-B and the relative K concentrations in shoots and roots, and the relative K accumulation in shoots, respectively. The results from the two years of field experiments showed that rice genotypes with greater KIUE-B at the seedling stage had higher KIUE-B at the tillering stage and higher KIUE-G at physiological maturity. Both KIUE-B at the tillering stage and KIUE-G at physiological maturity were closely and positively correlated with the relative shoot dry matter yield in shoots at the tillering stage and harvest index under low K, and had a highly significant and negative correlation with the shoot K concentration and accumulation at low K among the nine rice genotypes. Therefore, the K internal use efficiency could be used as an index for selecting K-efficient genotypes. The relative shoot biomass, relative root length, K concentration and accumulation in shoots as well as harvest index are among the most important plant traits for identifying K-efficient genotypes in lowland rice.