The Journal of Ecology editors are delighted to announce that Sandra Lavorel is our Eminent Ecologist for 2017. In recognition of her work, we have asked Sandra to select 10 of her most influential Journal of Ecology papers to make up a special virtual issue.
The third group of papers stems from my ongoing research aiming to understand mechanisms underpinning plant functional effects, and specifically on nutrient cycling in grasslands.
Following the “Holy Grail” hypothesis of functional response-effects overlaps (Lavorel & Garnier 2002), the two papers published from our research in mountain grasslands investigated how changes in plant traits in response to management translate into effects on nutrient cycling.
In the first paper, we investigated during Matt Robson’s postdoc contrasts in inorganic nitrogen pools and fluxes across soil conditions associated with historical land use and current management types in French subalpine grasslands (Robson et al. 2010). This study aimed to understand the processes through which soil nitrogen pools are depleted under extensive management.
Using 15N labelling we were able to trace plant and microbial nitrogen uptake and to relate these changing pool sizes across grassland types. Overall we demonstrated under two historical land-use conditions slower N cycling and greater retention with decreasing management intensity. This was the result of decreased plant N uptake and nitrate and to a lesser extent ammonium fluxes, while microbial N uptake appeared stable. Shifts to greater microbial C:N also suggested a shift to fungal dominated soil microbial communities.
I am particularly fond of the final synthesis figure (Figure 5) of the paper which facilitates an integrated understanding of how plant and microbial nitrogen pools and fluxes change with management extensification and associated increase in the grass:forb ratio. One step further, this pictures patterns in response to the shift during extensification from more exploitative to conservative species – though the latter known from our earlier investigations (Quétier et al. 2007) was not analysed explicitly in that particular paper. This is indeed what we investigated subsequently in the paper by Grigulis et al. (2013).
In this paper, using field measurements across three upland sites (in France, Austria and the UK) we aimed to identify the combined contributions of plant and microbial traits to ecosystem processes associated with nitrogen cycling. Given cascading impacts from soil abiotic conditions to plant and microbial traits, and to nutrient cycling (Lavorel et al. 2013) we expected that fast nutrient cycling in more intensively managed, and thus more fertile grasslands could be linked to more exploitative plant communities and associated bacteria-dominated soil microbial communities with faster activities, and conversely in more extensively managed grasslands.
While this was essentially confirmed, we also discovered a switch from more intense plant-centred processes (e.g. primary productivity) and thus greater control by plant traits in more intensively managed grasslands to predominant microbe-controlled soil processes (e.g. nitrogen retention) in extensively managed grasslands. Also while this analysis focused on easily measurable aboveground traits, further detailed analysis of the soil microbial community structure revealed the importance of considering root traits for microbe-controlled soil processes (Legay et al. 2014).
You can read Sandra’s virtual issue on the journal website, or view the individual papers below.