Verification of water-use efficiency estimates via carbon isotope discrimination in potato under varying nutrient statuses and CO2 conditions.

Elevated CO2 (eCO2 ) has the potential to increase plant biomass while decreasing water demand due to enhanced water-use efficiency (WUE), which interacts with nutritional status. Carbon isotope discrimination (Δ13 C) has been shown to be a valid proxy for estimating WUE; however, its validity is uncertain for plants in an environment where the interaction between CO2 and nutrition strongly affects WUE. Using a single potato cultivar (Irish Cobbler), we examined its validity through three independent trials with varying levels of P, N, or K (Trial P, N, and K, respectively) in growth chambers at two CO2 concentrations. WUE at the plant level varied with CO2 conditions and nutrient supply rates. Plant biomass was positively regressed against WUE in Trials P and K, and water use in Trial N. WUE was negatively regressed against Δ13 C across various nutrient supply rates within each CO2 environment. However, the relationship between WUE and Δ13 C was altered with CO2 enrichment by elevating the intercept along the y-axis (WUE) without affecting the slope, implying the involvement of isotopic discrimination in respiration or photorespiration. These results suggest that Δ13 C can be used to estimate WUE across various nutrient statuses, not only at the current CO2 but also at eCO2 when the comparisons are made within each CO2 condition.

Revisiting Why Plants Become N Deficient Under Elevated CO2: Importance to Meet N Demand Regardless of the Fed-Form.

An increase in plant biomass under elevated CO2 (eCO2) is usually lower than expected. N-deficiency induced by eCO2 is often considered to be a reason for this. Several hypotheses explain the induced N-deficiency: (1) eCO2 inhibits nitrate assimilation, (2) eCO2 lowers nitrate acquisition due to reduced transpiration, or (3) eCO2 reduces plant N concentration with increased biomass. We tested them using C3 (wheat, rice, and potato) and C4 plants (guinea grass, and Amaranthus) grown in chambers at 400 (ambient CO2, aCO2) or 800 (eCO2) µL L-1 CO2. In most species, we could not confirm hypothesis (1) with the measurements of plant nitrate accumulation in each organ. The exception was rice showing a slight inhibition of nitrate assimilation at eCO2, but the biomass was similar between the nitrate and urea-fed plants. Contrary to hypothesis (2), eCO2 did not decrease plant nitrate acquisition despite reduced transpiration because of enhanced nitrate acquisition per unit transpiration in all species. Comparing to aCO2, eCO2 remarkably enhanced water-use efficiency, especially in C3 plants, decreasing water demand for CO2 acquisition. As our results supported hypothesis (3) without any exception, we then examined if lowered N concentration at eCO2 indeed limits the growth using C3 wheat and C4 guinea grass under various levels of nitrate-N supply. While eCO2 significantly increased relative growth rate (RGR) in wheat but not in guinea grass, each species increased RGR with higher N supply and then reached a maximum as no longer N was limited. To achieve the maximum RGR, wheat required a 1.3-fold N supply at eCO2 than aCO2 with 2.2-fold biomass. However, the N requirement by guinea grass was less affected by the eCO2 treatment. The results reveal that accelerated RGR by eCO2 could create a demand for more N, especially in the leaf sheath rather than the leaf blade in wheat, causing N-limitation unless the additional N was supplied. We concluded that eCO2 amplifies N-limitation due to accelerated growth rate rather than inhibited nitrate assimilation or acquisition. Our results suggest that plant growth under higher CO2 will become more dependent on N but less dependent on water to acquire both CO2 and N.

Quantifying Phosphorus and Water Demand to Attain Maximum Growth of Solanum tuberosum in a CO2-Enriched Environment.

Growth promotion by ambient CO2 enrichment may be advantageous for crop growth but this may be influenced by soil nutrient availability. Therefore, we quantified potato (Solanum tuberosum L.) growth responses to phosphorus (P) supply under ambient (a[CO2]) and elevated (doubled) CO2 concentration (e[CO2]). A pot experiment was conducted in controlled-environment chambers with a[CO2] and e[CO2] combined with six P supply rates. We obtained response curves of biomass against P supply rates under a[CO2] and e[CO2] (R2 = 0.996 and R2 = 0.992, respectively). A strong interaction between [CO2] and P was found. Overall, e[CO2] enhanced maximum biomass accumulation (1.5-fold) and water-use efficiency (WUE) (1.5-fold), but not total water use. To reach these maxima, minimum P supply rate at both [CO2] conditions was similar. Foliar critical P concentration (i.e., minimum [P] to reach 90% of maximum growth) was also similar at nearly 110 mg P m-2. Doubling [CO2] did not increase P and water demand of potato plants, thus enabling the promotion of maximum growth without additional P or water supply, but via a significant increase in WUE (9.6 g biomass kg-1 water transpired), presumably owing to the interaction between CO2 and P.

Stomatal density of cowpea correlates with carbon isotope discrimination in different phosphorus, water and CO2 environments.

* Stomatal formation is affected by a plant's external environment, with long-distance signaling from mature to young leaves seemingly involved. However, it is still unclear what is responsible for this signal. To address this question, the relationship between carbon isotope discrimination (Delta) and stomatal density was examined in cowpea (Vigna sinensis). * Plants were grown under various environments that combined different amounts of soil phosphorus (P), soil water, and atmospheric CO(2). At harvest, stomatal density was measured in the youngest fully expanded leaf. The (13)C : (12)C ratio was measured in a young leaf to determine the Delta in mature leaves. * Results indicated that stomatal density is affected by P as well as by amounts of water and CO(2). However, stomatal responses to water and CO(2) were complex because of strong interactions with P. This suggests that the responses are relative, depending on some internal factor being affected by each external variable. Despite such complicated responses, a linear correlation was found between stomatal density and Delta across all environments examined. * It is proposed that the Delta value is a good surrogate for the long-term mean of the intercellular (C(i)) to the atmospheric (C(a)) CO(2) concentration ratio (C(i) : C(a)) and may be useful in understanding stomatal formation beyond complicated interactions.

Draft Genome Sequence of Burkholderia vietnamiensis Strain RS1, a Nitrogen-Fixing Endophyte Isolated from Sweet Potato.

Burkholderia vietnamiensis strain RS1 is an endophytic bacterium with nitrogen-fixing ability that was isolated from tuberous roots of sweet potato. Here, we present its draft genome of 6,542,727 bases that contains a cluster of genes associated with nitrogen fixation. This genome sequence will provide important insights into the plant growth-promoting potential of endophytic bacteria.

Varietal differences in the growth responses of rice to an arbuscular mycorrhizal fungus under natural upland conditions.

Seedlings of three rice (Oryza sativa L.) varieties (one indica, ARC5955; and two japonica, Nipponbare and Koshihikari) with or without pre-colonization by the arbuscular mycorrhizal fungus Funneliformis mosseae were transplanted into an upland field and grown to maturity. Pre-colonization had no effect on the yield of Nipponbare or Koshihikari. However, pre-colonized ARC5955 exhibited a strong tendency toward increased yield, which was accompanied by increases in the percentage of ripened grain and the 1000-grain weight. The rice roots were also colonized by indigenous arbuscular mycorrhizal fungi in the field, but these had only limited effects on shoot biomass and grain yields. We speculate that F. mosseae may have exhibited priority effects, allowing it to dominate the rice roots. There was no significant difference in the contents of most mineral elements in the shoots of pre-colonized ARC5955 at harvest, indicating that some other factor is responsible for the observed yield increase.

Complete Genome Sequence of Kosakonia sacchari Strain BO-1, an Endophytic Diazotroph Isolated from a Sweet Potato.

The complete genome sequence of the endophytic diazotroph Kosakonia sacchari, isolated from a sweet potato, was analyzed. The 4,902,106-bp genome with 53.7% G+C content comprises 4,638 open reading frames, including nif genes, 84 tRNAs, and seven complete rRNAs in a circular chromosome.

Heterogeneity in spatial P-distribution and foraging capability by Zea mays: effects of patch size and barriers to restrict root proliferation within a patch.

BACKGROUND AND AIMS: Localized proliferation of roots in nutrient-enriched patches seems to be an adaptive response in many plants, but its function is still debatable. To understand the efficiency and limitation of foraging behaviour, the impact of patch size and the presence or absence of a barrier to root proliferation within phosphorus (P)-enriched patches was examined. METHODS: In pots filled with P-poor soil, six treatments of heterogeneous P supply were prepared: three patch sizes with or without a root barrier between patches. In addition, a homogeneous P supply treatment was also prepared. Irrespective of these treatments, each pot received the same total amount of P. Maize (Zea mays) was grown in each pot for 45 d in a greenhouse. KEY RESULTS: P content and biomass were greatest in plants grown in the largest patch due to successful root proliferation, and were higher in the presence of a root barrier. Interestingly, plants preferentially developed adventitious nodal roots projecting from the stem into the P-enriched soil, particularly in the largest patch with a root barrier. Removal of the barrier reduced the P-uptake capacity per unit root surface area or volume in P-enriched patches, revealing that the P-uptake capacity per root can be suppressed even in P-rich soil if other portions on the root axis encounter P-poor conditions. CONCLUSIONS: The results suggest that the efficiency of root morphological plasticity is largely determined by the size of the P-enriched patch. Furthermore, the results imply a novel aspect of P-uptake physiology that roots in heterogeneous P cannot demonstrate their potential capacity, as would be observed in roots encountering P continuously; this effect is probably mediated by an internal root factor.

Regulation of rhizosphere acidification by photosynthetic activity in cowpea (Vigna unguiculata L. walp.) seedlings.

In contrast to cereals or other crops, legumes are known to acidify the rhizosphere even when supplied with nitrates. This phenomenon has been attributed to N2 fixation allowing excess uptake of cations over anions; however, as we have found previously, the exposure of the shoot to illumination can cause rhizosphere acidification in the absence of N2 fixation in cowpea (Vigna unguiculata L. Walp). In this study, we examined whether the light-induced acidification can relate to photosynthetic activity and corresponding alterations in cation-anion uptake ratios. The changes of rhizosphere pH along the root axis were visualized using a pH indicator agar gel. The intensity of pH changes (alkalization/acidification) in the rhizosphere was expressed in proton fluxes, which were obtained by processing the images of the pH indicator agar gel. The uptake of cations and anions was measured in nutrient solution. The rhizosphere was alkalinized in the dark but acidified with exposure of the shoots to light. The extent of light-induced acidification was increased with leaf size and intensity of illumination on the shoot, and completely stopped with the application of photosynthesis inhibitor. Although the uptake of cations was significantly lower than that of anions, the rhizosphere was acidified by light exposure. Proton pump inhibitors N,N'-dicyclohexyl carbodimide and vanadate could not stop the light-induced acidification. The results indicate that light-induced acidification in cowpea seedlings is regulated by photosynthetic activity, but is not due to excess uptake of cations.