In order to investigate the effects of homogeneous and localized supply of different nitrogen forms (nitrate, NO 3 − vs ammonium, NH 4 + ) on the growth of tomato seedlings, root morphology and six cytokinin (CTK) fractions in xylem sap were analyzed. Whole roots were supplied with different ratios of NO 3 − to NH 4 + (100:0, as 100-0NA; 75:25, as 75-25NA; 50:50, as 50-50NA) under homogeneous supply. In split-root experiments, three treatments were compared: a sole NO 3 − supply (N|N), a spatially separated supply of NO 3 − and NH 4 + (N|A), and a spatially separated supply of NO 3 − and a mixture of NO 3 − and NH 4 + nutrition at a ratio of 75:25 (N|AN). All concentrations of total N were set at 5 mM. The results showed that (1) homogeneous 75% NO 3 − plus 25% NH 4 + supply to the whole root zone led to maximum shoot and root dry matter (DM), root surface area (RS) and root volume (RV). The spatially separated supply of NO 3 − and NH 4 + (N|A) resulted in a contrasting effect on root morphology: in comparison to N|N, root DM in the NO 3 − -containing pot was increased by 50% whereas it was depressed by 50% in the NH 4 + -containing pot. The 75% NO 3 − plus 25%NH 4 + supply in the split-root experiment led to no significant effects either on shoot DM and root DM, or on RS and RV when compared to N|N. (2) The presence of NH 4 + in the external medium led to a significantly reduced total xylem-CTK concentration, and a close negative correlation was found between xylem NH 4 + and total CTK concentration irrespective of culture mode. A relatively high level of zeatin riboside (ZR) was maintained both in 75-25NA and N|A treatments. It was concluded that, in addition to the percentage of NH 4 + to NO 3 − in the nutrient solution, whether NH 4 + was supplied to the whole root system or to only part of the root system was also an important factor affecting plant growth. The fact that the 75-25NA and N|A treatments resulted in optimal growth of tomato seedlings might be attributed to the higher ZR concentration in xylem.

No abstract

Two new genera and new species, Peregrinpachymeridium comitcola gen. et sp. nov. and Corollpachymeridium heteroneurus gen. et sp. nov., of fossil Pachymeridiidae are described and illustrated from the Middle Jurassic Jiulongshan Formation in Daohugou Village, Shantou Township, Ningcheng County, Inner Mongolia Autonomous Region, China. We summarized all fossil genera of pachymeridiids found in China and set up a key to these 7 genera and 7 species. In addition, we hypothesize the significance of a rare, well-preserved, unusual bug fossil showing a male and a female together with their abdomen terminalia facing each other and their heads in the opposite direction.

No abstract

Aims Microorganisms play a crucial role in the litter decomposition process in terrestrial ecosystems. Understanding the independent and interactive relationship between fine root decomposition and bacteria community related to substrate characteristics can help to predict the consequences of changes on ecosystem function. Therefore, the aim of this study was to identify fine roots' influences on rhizosphere microbial structure and diversity. Methods The decomposition of root litters of four dominant tree species of Mount Taishan (Robinia pseudoacacia (RP), Quercus acutissima (QA), Pinus tabulaeformis (PT) and Pinus densiflora (PD)) was tested in a Yaoxiang Forest Farm. Using Illumina high-throughput sequencing of 16S rRNA genes, bacterial community composition was determined. Composition, diversity and relative abundance of bacteria were calculated for per fine root litter. Important findings (1) Fine root litter decomposition differed significantly among different root types. There was no difference in decomposition rate between broad-leaved species and conifer species. In all species, fine roots of RP and QA were more strongly decomposed than that of PT and PD, and these differences were significant (RP > QA > PT > PD). (2) The number of observed species, operational taxonomic units, Ace index and phylogenetic diversity in broad-leaved species were significantly lower than that in coniferous species. Bacterial