Opposing effects of different soil organic matter fractions on crop yields

Soil organic matter is critical to sustainable agriculture because it provides nutrients to crops as it decomposes and increases nutrient- and water-holding capacity when built up. Fast- and slow-cycling fractions of soil organic matter can have different impacts on crop production because fast-cycling fractions rapidly release nutrients for short-term plant growth and slow-cycling fractions bind nutrients that mineralize slowly and build up water-holding capacity. We explored the controls on these fractions in a tropical agroecosystem and their relationship to crop yields. We performed physical fractionation of soil organic matter from 48 farms and plots in western Kenya. We found that fast-cycling, particulate organic matter was positively related to crop yields, but did not have a strong effect, while slower-cycling, mineral-associated organic matter was negatively related to yields. Our finding that slower-cycling organic matter was negatively related to yield points to a need to revise the view that stabilization of organic matter positively impacts food security. Our results support a new paradigm that different soil organic matter fractions are controlled by different mechanisms, potentially leading to different relationships with management outcomes, like crop yield. Effectively managing soils for sustainable agriculture requires quantifying the effects of specific organic matter fractions on these outcomes.

Physical and genetic interaction of filamin with presenilin in Drosophila

Presenilins were first identified as causative factors in early onset, familial Alzheimer's Disease (FAD). They are predicted to encode a highly conserved novel family of eight transmembrane domain proteins with a large hydrophilic loop between TM6 and TM7 that is the site of numerous FAD mutations. Here, we show that the loop region of Drosophila and human presenilins interacts with the C-terminal domain of Drosophila filamin. Furthermore, we show that Drosophila has at least two major filamin forms generated by alternative splicing from a gene that maps to position 89E10-89F4 on chromosome 3. The longest form is enriched in the central nervous system and ovaries, shares 41.7% overall amino acid identity with human filamin (ABP-280) and contains an N-terminal actin-binding domain. The shorter form is broadly expressed and encodes an alternatively spliced form of the protein lacking the actin-binding domain. Finally, we show that presenilin and filamin are expressed in overlapping patterns in Drosophila and that dominant adult phenotypes produced by overexpression of presenilin can be suppressed by overexpression of filamin in the same tissue. Taken together, these results suggest that presenilin and filamin functionally interact during development.