Conflicting traffic: characterization of the hazards of birds flying across an airport runway

Bird–aircraft collisions cost millions of dollars to aviation globally and cause deaths. We designed and tested a protocol to study the hazards to aircraft from birds flying across runways where aircraft rotate and climb during take‐off. We recorded birds and flight height of birds flying across runway 03L at OR Tambo International Airport, South Africa. A total of 7,938 birds of pigeon size or larger crossed a 400 m length of runway during 14 h and 15 min, a rate of 8.8 birds per minute; there were 200 aircraft taking off during this period. The biggest bird–aircraft collision hazard is posed by African Sacred Ibis and Grey‐headed Gull. Respectively, these species contribute a mean of 111 kg per 10 min and 47.2 kg per 10 min biomass flying across the runway. We identify possible management options to reduce the hazard of bird–aircraft collisions. Our survey protocol and data treatment is easy to use, will add additional and important definition to existing activities to reduce bird–aircraft collisions and can provide comparable hazard information to aerodrome authorities and pilots.     

Surface N balances and reactive N loss to the environment from global intensive agricultural production systems for the period 1970-2030

Data for the historical years 1970 and 1995 and the FAO-Agriculture Towards 2030 projection are used to calculate N inputs (N fertilizer, animal manure, biological N fixation and atmospheric deposition) and the N export from the field in harvested crops and grass and grass consumption by grazing animals. In most industrialized countries we see a gradual increase of the overall N recovery of the intensive agricultural production systems over the whole 1970-2030 period. In contrast, low N input systems in many developing countries sustained low crop yields for many years but at the cost of soil fertility by depleting soil nutrient pools. In most developing countries the N recovery will increase in the coming decades by increasing efficiencies of N use in both crop and livestock production systems. The surface balance surplus of N is lost from the agricultural system via different pathways, including NH3 volatilization, denitrification,N2O and NO emissions, and nitrate leaching from the root zone. Global NH3-N emissions from fertilizer and animal manure application and stored manure increased from 18 to 34 Tg.yr-1 between 1970 and 1995, and will further increase to 44 Tg.yr-1 in 2030. Similar developments are seen for N2O-N (2.0 Tg.yr-1 in 1970, 2.7 Tg.yr-1 in 1995 and 3.5 Tg.yr-1 in 2030) and NO-N emissions (1.1 Tg.yr-1 in 1970, 1.5 Tg-yr-1 in 1995 and 2.0 Tg.yr-1 in 2030).     

Comparison of the evolutionary dynamics of symbiotic and housekeeping loci: a case for the genetic coherence of rhizobial lineages

In prokaryotes, lateral gene transfer across chromosomal lineages may be mediated by plasmids, phages, transposable elements, and other accessory DNA elements. However, the importance of such transfer and the evolutionary forces that may restrict gene exchange remain largely unexplored in native settings. In this study, tests of phylogenetic congruence are employed to explore the range of horizontal transfer of symbiotic (sym) loci among distinct chromosomal lineages of native rhizobia, the nitrogen-fixing symbiont of legumes. Rhizobial strains isolated from nodules of several host plant genera were sequenced at three loci: symbiotic nodulation genes (nodB and nodC), the chromosomal housekeeping locus glutamine synthetase II (GSII), and a portion of the 16S rRNA gene. Molecular phylogenetic analysis shows that each locus generally subdivides strains into the same major groups, which correspond to the genera Rhizobium, Sinorhizobium, and Mesorhizobium. This broad phylogenetic congruence indicates a lack of lateral transfer across major chromosomal subdivisions, and it contrasts with previous studies of agricultural populations showing broad transfer of sym loci across divergent chromosomal lineages. A general correspondence of the three rhizobial genera with major legume groups suggests that host plant associations may be important in the differentiation of rhizobial nod and chromosomal loci and may restrict lateral transfer among strains. The second major result is a significant incongruence of nod and GSII phylogenies within rhizobial subdivisions, which strongly suggests horizontal transfer of nod genes among congenerics. This combined evidence for lateral gene transfer within, but not between, genetic subdivisions supports the view that rhizobial genera are "reproductively isolated" and diverge independently. Differences across rhizobial genera in the specificity of host associations imply that the evolutionary dynamics of the symbiosis vary considerably across lineages in native settings.      

Phosphorus in agricultural soils: drivers of its distribution at the global scale

Phosphorus (P) availability in soils limits crop yields in many regions of the World, while excess of soil P triggers aquatic eutrophication in other regions. Numerous processes drive the global spatial distribution of P in agricultural soils, but their relative roles remain unclear. Here, we combined several global data sets describing these drivers with a soil P dynamics model to simulate the distribution of P in agricultural soils and to assess the contributions of the different drivers at the global scale. We analysed both the labile inorganic P (P_ILAB), a proxy of the pool involved in plant nutrition and the total soil P (P_TOT). We found that the soil biogeochemical background corresponding to P inherited from natural soils at the conversion to agriculture (BIOG) and farming practices (FARM) were the main drivers of the spatial variability in cropland soil P content but that their contribution varied between P_TOT vs. P_ILAB. When the spatial variability was computed between grid cells at half‐degree resolution, we found that almost all of the P_TOT spatial variability could be explained by BIOG, while BIOG and FARM explained 38% and 63% of P_ILAB spatial variability, respectively. Our work also showed that the driver contribution was sensitive to the spatial scale characterizing the variability (grid cell vs. continent) and to the region of interest (global vs. tropics for instance). In particular, the heterogeneity of farming practices between continents was large enough to make FARM contribute to the variability in P_TOT at that scale. We thus demonstrated how the different drivers were combined to explain the global distribution of agricultural soil P. Our study is also a promising approach to investigate the potential effect of P as a limiting factor for agroecosystems at the global scale.