小麦/玉米苗期磷累积量对介质供磷水平反应的差异

小麦和玉米苗期是磷素营养的关键期和敏感期,研究两种作物苗期对介质供磷反应,可为合理施用磷肥提供参考.试验设缺磷对照、低磷胁迫、中等磷胁迫和正常供磷(P2O5含量分别为0、0.05 mmol·L-1、0.3 mmol·L-1和0.5 mmol·L-1) 4种磷水平,选取小麦"小偃22号"、"兰考4号"和玉米"屯玉65号"、"户单4号"为指标作物,用营养液培养法研究小麦、玉米苗期磷累积量对介质不同供磷水平的反应差异.结果表明,不同介质供磷水平下,两种作物苗期磷累积量显著不同且因作物类型、基因型、器官及测定时期不同而异.总体而言,介质供磷后,苗期早期生长阶段(出苗后25 d以前),小麦的介质最佳供磷水平较玉米高;苗期后期(出苗后40～50 d),小麦和玉米最佳供磷水平一致.如果以低磷胁迫作为对比进行分析,玉米苗期整株磷累积量对介质供磷的敏感性比小麦强;从不同基因型来看:"兰考4号"对介质供磷的敏感性强于"小偃22号","屯玉65号"和"户单4号"基本一致.缺磷条件下小麦较玉米磷效率高,供磷条件下玉米较小麦高;但不同基因型间规律性较差.     

Modulation of plant root traits by nitrogen and phosphate: transporters,long-distance signaling proteins and peptides,and potential artificial traps

As sessile organisms, plants rely on their roots for anchorage and uptake of water and nutrients. Plant root is an organ showing extensive morphological and metabolic plasticity in response to diverse environmental stimuli including nitrogen (N) and phosphorus (P) nutrition/stresses. N and P are two essential macronutrients serving as not only cell structural components but also local and systemic signals triggering root acclimatory responses. Here, we mainly focused on the current advances on root responses to N and P nutrition/stresses regarding transporters as well as long-distance mobile proteins and peptides, which largely represent local and systemic regulators, respectively. Moreover, we exemplified some of the potential pitfalls in experimental design, which has been routinely adopted for decades. These commonly accepted methods may help researchers gain fundamental mechanistic insights into plant intrinsic responses, yet the output might lack strong relevance to the real situation in the context of natural and agricultural ecosystems. On this basis, we further discuss the established—and yet to be validated—improvements in experimental design, aiming at interpreting the data obtained under laboratory conditions in a more practical view.     

固氮肺炎克氏杆菌的产酸和解磷能力

本文报道了549、258属于肺炎克氏杆菌的这一类联合固氮细菌具有产酸解磷的能力.549在培养过程中能产生多种有机酸成分,使无机磷的有效性提高.它还能利用卵磷脂这种有机磷作为自己的磷源,在其培养过程中产酸量有一定限度,达到一定酸度时,培养环境中的酸基本上就不再增加,维持在一个相对稳定的水平.549、258产酸解磷的结果能够改善植物的磷素营养,从非豆科植物根际联合固氮的研究角度考虑,可以认为产酸的联合固氮细菌具有固氮和解磷的双重性.     

家蚕滞育卵中辅酶Ⅰ和辅酶Ⅱ的含量变化

利用苹果酸脱氢酶(MDH)和柠檬酸合酶(CS)串联反应以及葡萄糖-6-磷酸脱氢酶(G6PDH)催化葡萄糖-6-磷酸(G-6-P)脱氢反应,分别测定了家蚕滞育发动、即时浸酸和低温冷藏处理蚕卵辅酶Ⅰ(NAD+)和辅酶Ⅱ(NADP+)的含量。滞育发动时蚕卵NAD+含量显著下降,而即时浸酸和低温冷藏处理使蚕卵NAD+含量显著提高。蚕卵中的NADP+在滞育发动前大量积累,滞育发动时下降,即时浸酸处理后NADP+含量显著提高,在低温冷藏早期其含量进一步提高,低温冷藏处理后期又显著下降。分析上述结果认为,家蚕滞育卵中NAD+和NADP+含量的变化分别与呼吸耗氧量和糖元-山梨醇相互转化密切相关。     

白云石粉对皖南酸性红黄壤磷组分及磷有效性的影响

在施用P肥的基础上配合使用白云石粉,用酸性土壤无机P分级方法测定皖南红黄壤各形态P的含量。结果表明:使用P肥能明显提高土壤全P、无机P和土壤速效P含量;土壤速效P与无机P各组分的相关性以Al-P最好,Fe-P、O-P次之,Ca-P最差。施用白云石粉,当季土壤Ca-P含量及其在无机P中所占的比例明显提高,Al-P的形成受到抑制,但随着时间的推移,却更有利于有效性较高的Al-P含量的增加。     

Oxygen isotope ratios of plant available phosphate in lowland tropical forest soils

Phosphorus (P) cycles rapidly in lowland tropical forest soils, but the process have been proven difficult to quantify. Recently it was demonstrated that valuable data on soil P transformations can be derived from the natural abundance of stable oxygen isotopes in phosphate (δ¹⁸O_P). Here, we measured the δ¹⁸O_P of soils that had received long-term nutrient additions (P, nitrogen, and potassium) or litter manipulations in lowland tropical forest in Panama and performed controlled incubations of fresh soils amended with a single pulse of P. To detect whether δ¹⁸O_P values measured in the incubations apply also for soils in the field, we examined the δ¹⁸O_P values after rewetting dry soils. In the incubations, resin-P δ¹⁸O_P values converged to ∼3.5‰ above the expected isotopic equilibrium with soil water. This contrasts with extra-tropical soils in which the δ¹⁸O_P of resin-P matches the expected equilibrium with soil water. Identical above-equilibrium resin-P δ¹⁸O_P values were also found in field soils that did not receive P additions or extra litter. We suggest that the 3.5‰ above-equilibrium δ¹⁸O_P values reflect a steady state between microbial uptake of phosphate (which enriches the remaining phosphate with the heavier isotopologues) and the release of isotopically equilibrated cell internal phosphate back to the soil. We also found that soil nutrient status affected the microbial turnover rate because in soils that had received chronic P addition, the original δ¹⁸O_P signature of the fertilizer was preserved for at least eight weeks, indicating that the off-equilibrium δ¹⁸O_P values produced during microbial phosphate turnover was not imprinted in these soils. Overall, our results demonstrate that ongoing microbial turnover of phosphate mediates its biological availability in lowland tropical soils.     

Utilization of Sparingly Soluble Phosphate by Red Clover in Association with Glomus mosseae and Bacillus megaterium

A pot experiment was conducted to investigate the mobilization of sparingly soluble inorganic and organic sources of phosphorus (P) by red clover (Trifolium pratense L.) whose roots were colonized by the arbuscular mycorrhizal (AM) fungus Glomus mosseae and in association with the phosphate-solubilizing (PS) bacterium Bacillus megaterium ACCC10010. Phosphate-solubilizing bacteria and rock phosphate had a synergistic effect on the colonization of plant roots by the AM fungus. There was a positive interaction between the PS bacterium and the AM fungus in mobilization of rock phosphate, leading to improved plant P nutrition. In dual inoculation with the AM fungus and the PS bacterium, the main contribution to plant P nutrition was made by the AM fungus. Application of P to the low P soil increased phosphatase activity in the rhizosphere. Alkaline phosphatase activity was significantly promoted by inoculation with either the PS bacterium or the AM fungus.     

Comparative evaluation of Ca chloride and Ca phosphate for extractable sulfur in soils with a wide range in pH

Deficiency of sulfur (S) is becoming widespread in the rainfed systems of India, and there is increasing need for diagnosing the deficiency. Calcium chloride and Ca phosphate are commonly used for extracting available S in soils. Because of cost and the ease of availability locally, we prefer using Ca chloride as an extractant over Ca phosphate, for extracting available S. However, there is paucity of data on the comparative evaluation of the two extractants to extract available S, especially in soils having a wide range in natural pH (from acidic to alkaline range). It is recognized that soil pH plays a dominant role in the adsorption–desorption and extractability of sulfate‐S in soils. We compared the extraction of S by Ca chloride and Ca phosphate in 86 Indian soils having a wide range in pH (4.5 to 10.6). Sulfur in the extracts was determined by ICP‐AES. Considering all the 86 soil samples tested, there was an excellent agreement between the values of extractable S determined by using the two extractants (r = 0.96, p < 0.001). However, the correlation coefficient (r) between the values of extractable S by the two reagents, although highly significant, varied among the groups of soil samples according to the range in soil pH. The highest correlation coefficient (r = 0.99, p < 0.0001, n = 17) was found for soils with pH in the alkaline range (8.5–10.6), and the lowest correlation coefficient (r = 0.71, p < 0.0001, n = 58) was obtained with a set of soil samples with pH in the acidic range (4.5–6.5). For soil samples having pH in the near‐neutral range (6.7–7.3), an excellent agreement was observed (r = 0.93, p < 0.0001, n =11) between the extractable‐S values obtained by the two extractants. While Ca phosphate extracted higher amount of S compared to Ca chloride in soil samples with pH in the acidic range, the two extractants were equally effective for soil samples with pH in the neutral or alkaline range. Our results suggest that for most of the soils in the semiarid tropical regions, which have pH in the neutral to alkaline range, Ca chloride can replace Ca phosphate as an extractant for removing available S in such soils.