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Title:   Author  item
                                            BOWLES, TIMOTHY - University Of Californiaitem
                                            HOLLANDER, ALLAN - University Of Californiaitem
                                            Steenwerth, Kerriitem
                                            JACKSON, LOUISE - University Of California
  Submitted to: PLOS ONE
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 6/8/2015
                                    Publication  Date: 6/29/2015
                                    Citation: Bowles, T.M., Hollander, A.D., Steenwerth, K.L., Jackson, L.E. 2015. Tightly-coupled plant-soil nitrogen cycling: Implications for multiple ecosystem services on organic farms across an intensively managed agricultural landscape. PLoS One. 10(6):e0131888 doi: 10.1371/journal.pone.0131888.Interpretive Summary:
                                Technical Abstract: Variability among farms across an agricultural landscape may reveal diverse biophysical
contexts and experiences that show innovations and insights to improve nitrogen (N) cycling and yields, and thus the potential for multiple ecosystem services. In order to assess potential tradeoffs between yields and tightly-coupled plant-soil-microbial N cycling, which increases soil N cycling and the potential for soil N retention, biogeochemical indicators and a novel tool based on root gene expression were studied across 13 organic fields growing Roma-type tomatoes in the Sacramento Valley of California. The fields spanned a three-fold gradient of total soil carbon (C) and differed in management practices and markets (fresh market vs. processing) but had similar soil texture and parent material. Overall, organic tomato yields were comparable to the
county average (86.1 Mg ha-1), which includes mostly conventional production. Several fields with tomato yields above the county average showed evidence of tightly-coupled N cycling, based on biogeochemical indicators reflecting high soil organic matter quantity and quality, high soil biological activity, low soil inorganic N pools, and plant indicators showing adequate plant N. Elevated expression of a key gene involved in root N assimilation, cytosolic glutamine synthetase GTS1, in these fields confirmed that plant N assimilation was high even when inorganic N pools were low. Fields with tightly-coupled N cycling, however, had slightly lower yields than fields with higher soil inorganic N pools (mean yields of 97.4 vs. 112.3 Mg ha-1 and mean soil NO3-N at midseason of 3.1 vs. 23.0 μg -N g-1, respectively, for the two groups of field). These results indicate a tradeoff between maximizing yield (a provisioning service), soil N cycling (a supporting service) and the potential for N retention (a regulating service) in this landscape. Overall, the landscape analysis provided the variation necessary to evaluate potential indicators of N cycling and showed how organic production can be competitive with conventional production in an intensively-managed, highly-productive landscape. Engaging with growers and facilitating information exchange via the participatory approach set the stage for individualized strategies to move toward more tightly-coupled N cycling.


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