The imbalance between nitrogen (N) and phosphorus (P) deposition may shift temperate ecosystems from N- to P-limitation. However, it is unclear how the imbalanced N : P input affects the strategies of plants to acquire P and, therefore, the growth of plants and the competition among species. We conducted a 4-yr N-addition experiment in young and mature larch (Larix principis-rupprechtii) stands. Plant growth and P acquisition strategies were assessed for larch and understorey vegetation. N addition stimulated the aboveground productivity of understorey vegetation in the young stand and larch in the mature stand, with other species unaffected. The competitive advantages of understorey vegetation in the young stand and larch in the mature stand were associated with their high stoichiometric homoeostasis. To maintain the N : P homoeostasis of these species, an increase in phosphatase activity but not P resorption efficiency increased the supply of P. Additionally, N addition accelerated P mineralization by decreasing the fungal-to-bacterial ratios and improved uptake of soil P by increasing the arbuscular mycorrhizas-to-ectomycorrhizas ratios. Our results suggest that plants with high stoichiometric homoeostasis could better cope with N deposition-induced P-deficiency. Although P resorption efficiency showed little plasticity in response, plants activated a variety of P-acquisition pathways to alleviate the P-deficiency caused by N deposition.

The origin of angiosperms has been a long-standing botanical debate. The great diversity of angiosperms in the Early Cretaceous makes the Jurassic a promising period in which to anticipate the origins of the angiosperms. Here, based on observations of 264 specimens of 198 individual flowers preserved on 34 slabs in various states and orientations, from the South Xiangshan Formation (Early Jurassic) of China, we describe a fossil flower, Nanjinganthus dendrostyla gen. et sp. nov.. The large number of specimens and various preservations allow for an evidence-based reconstruction of the flower. From the evidence of the combination of an invaginated receptacle and ovarian roof, we infer that the seeds of Nanjinganthus were completely enclosed. Evidence of an actinomorphic flower with a dendroid style, cup-form receptacle, and angiospermy, is consistent with Nanjinganthus being a bona fide angiosperm from the Jurassic, an inference that we hope will re-invigorate research into angiosperm origins.

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Flower, enclosed ovule and tetrasporangiate anther are three major characters distinguishing angiosperms from other seed plants. Morphologically, typical flowers are characterised by an organisation with gynoecium and androecium surrounded by corolla and calyx. Theoretically, flowers are derived from their counterparts in ancient ancestral gymnosperms. However, as for when, how and from which groups, there is no consensus among botanists yet. Although angiosperm-like pollen and angiosperms have been claimed in the Triassic and Jurassic, typical flowers with the aforesaid three key characters are still missing in the pre-Cretaceous age, making many interpretations of flower evolution tentative. Thus searching for flower in the pre-Cretaceous has been a tantalising task for palaeobotanists for a long time. Here, we report a typical flower, Euanthus panii gen. et sp. nov., from the Middle–Late Jurassic of Liaoning, China. Euanthus has sepals, petals, androecium with tetrasporangiate dithecate anthers and gynoecium with enclosed ovules, organised just like in perfect flowers of extant angiosperms. The discovery of Euanthus implies that typical angiosperm flowers have already been in place in the Jurassic, and provides a new insight unavailable otherwise for the evolution of flowers.

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Abstract. Interest in nitrogen inputs via atmospheric deposition to agricultural ecosystems has increased recently, especially on the North China Plain because of extremely intensive agricultural systems and rapid urbanization in this region. Nitrogen deposition may make a significant contribution to crop N requirements but may also impose a considerable nutrient burden on the environment in general. We quantified total N deposition at two locations, Dongbeiwang near Beijing and Quzhou in Hebei province, over a two-year period from 2005 to 2007 using an 15 N tracer method, the integrated total N input (ITNI) system. Total airborne N inputs to a maize-wheat rotation system at both locations ranged from 99 to 117 kg NÁha À1 Áyr À1, with higher N deposition during the maize season (57-66 kg N/ha) than the wheat season (42-51 kg N/ha). Plant available N from deposition for maize and wheat was about 52 kg NÁha À1 Áyr À1 , accounting for 50% of the total N deposition or 31% of total N uptake by the two crop species. In addition, a correction factor was derived for the maize season to adjust values obtained from small pots (0.057 m 2 ) compared with field trays (0.98 m 2 ) because of higher plant density in the pots. The results indicate that atmospheric N deposition is a very important N input and must be taken into account when calculating nutrient budgets in very intensively managed agricultural ecosystems.