Partitioning of above and below ground costs during phosphate stress in Medicago truncatula

Phosphate (P) availability for plant uptake can limit the yield of natural and agricultural systems. Under P limited conditions, the P-requirement of symbiotic nodules of legumes may exacerbate the P stress of host plants. Adaptations to survive under P stress may vary between different functioning tissues. This study investigated the physiological adaptations to P stress in above and below ground organs of nodulated Medicago truncatula Gaertner. Seedlings were inoculated with Sinorhizobium meliloti in quartz sand and fed nutrient solution with either 0.01?mM or 0.5?mM P concentrations. P-stressed nodulated plants showed compromised photosynthetic responses. Alternative growth allocation during stressed conditions was observed between different organs. The concentration of inorganic P, carbon, and nitrogen were lower during stressed conditions. The above ground tissues scavenged P and lowered their dependence on adenosine-triphosphate required for metabolism. Whereas the below ground tissues recycled phosphate from phosphate monoesters in the cell.     

Responses of Lolium spp. to glufosinate ammonium application at different temperatures

An experiment to investigate why glufosinate ammonium control of Lolium spp. is more effective at cooler temperatures than warmer temperatures was conducted at Welgevallen Experimental Farm, Stellenbosch University. Wild Lolium spp. was grown at 10/15, 15/20, 20/25 and 25/30°C (night and day) temperature regimes and treated with glufosinate ammonium at 0, 300, 600, 900 and 1,200 g a.i./ha, 6 weeks after planting. Control of Lolium spp. decreased with increasing temperature. Results from elemental analysis, scanning electron microscopy (SEM), fluorescence imaging and gas chromatography–mass spectrometry (GCMS) investigations allude to calcium accumulation, cuticle thickness and plant phenolic compounds playing roles in the response of Lolium spp. to this herbicide. Increased cuticle thickness and calcium accumulation as temperatures increase indicate promotion of plant defence mechanisms through increased phenolic compound production, which is induced by herbicide stress, hence resulting in poor control of Lolium spp. under warmer temperatures.     

Forest proximity rather than local forest cover affects bee diversity and coffee pollination services

Context

As agricultural demands for land continues to expand, strategies are urgently needed to balance agricultural production with biodiversity conservation and ecosystem service provision in agricultural landscapes.

Objectives

We used a factorial landscape design to assess the relative contributions of forest proximity and local forest cover to bee diversity and the provision of coffee pollination services.

Methods

We quantified bee diversity and fruit set in 24 sun-grown coffee fields in Southeast Region of Brazil that were selected following a factorial sampling design to test the independent effects of local forest cover (in a radius of 400 m) and proximity to forest fragments. To assess the impact of landscape simplification, we also evaluated local coffee cover.

Results

Bee richness and abundance were higher in the proximity of forest fragments, but only bee abundance decreased when the coffee cover dominated the surrounding landscapes. Coffee fruit set was 16% higher overall with bee visitations compared with bee exclusion and increased to 20% when coffee bushes were near forest fragments, and the coffee cover was low. Surprisingly, local forest cover did not affect the bee community or coffee fruit set.

Conclusion

Our results provide clear evidence that the proximity of coffee crops to forest fragments can affect the abundance and richness of bees visiting the coffee flowers and thereby facilitate the provision of pollination services. The positive association between forest proximity and fruit set reinforces the importance of natural vegetation in enhancing bee diversity and, therefore, in the provision of pollination services. The negative effect of coffee cover on fruit set at the local scale suggests that the service demand can surpass the capacity of pollinators to provide it. These effects were independent of the local forest cover, although all studied landscapes had more than 20% remaining forest cover (within a 2 km radius), which is considered the extinction threshold for Atlantic Forest species. Interspersion of forest fragments and coffee plantations in regions with more than 20% of forest cover left could thus be a useful landscape management target for facilitating pollinator flows to coffee crops and thus for increasing coffee yields.