Stoichiometric N:P flexibility and mycorrhizal symbiosis favour plant resistance against drought

Abstract

Summary Drought induces changes in the nitrogen (N) and phosphorus (P) cycle but most plant species have limited flexibility to take up nutrients under such variable or unbalanced N and P availability. Both the degree of flexibility in plant N:P ratio and of root symbiosis with arbuscular mycorrhizal fungi might control plant resistance to drought‐induced changes in nutrient availability, but this has not been directly tested. Here, we examined the role of plant N:P stoichiometric status and mycorrhizal symbiosis in the drought‐resistance of dominant and subordinate species in a semi‐natural grassland. We reduced water availability using rainout shelters (control vs. drought) and measured how plant biomass responded for the dominant and subordinate species. We then selected a dominant (Paspalum dilatatum) and a subordinate species (Cynodon dactylon), for which we investigated the N:P stoichiometric status, mycorrhizal root colonization and water‐use efficiency. The biomass of all dominant plant species, but not subordinate species, decreased under drought. Drought increased soil available nitrogen, and thus increased soil N:P ratio, due to decreasing plant N uptake. The dominant P. dilatatum showed a high degree of plant N:P homeostasis and a considerable reduction in biomass under drought. At the opposite, the more flexible subordinate species C. dactylon increased its N uptake and water‐use efficiency, apparently due to stronger symbiosis with mycorrhizae, and maintained its biomass. Synthesis. We conclude that the maintenance of N:P homeostasis in dominant species, possibly because of a large root nutrient foraging capacity, becomes inefficient when water stress limits N mobility in the soil. By contrast, we demonstrate that higher stoichiometric N:P flexibility coupled with stronger mutualistic association with mycorrhizae allow subordinate species to better withstand drought perturbations. Using a stoichiometric approach in a field experiment, our study provides for the first time clear and novel understandings of the mechanisms involved in drought‐resistance within the plant‐mycorrhizae‐soil system.

Plant diversity maintains long‐term ecosystem productivity under frequent drought by increasing short‐term variation

“…, Mariotte et al. ). For instance, there are a growing number of studies that have shown that drought reduces the mobility of soil nutrients, litter decomposition, and the activity of soil microbes (Durand et al.…”

Global leaf nitrogen and phosphorus stoichiometry and their scaling exponent

“…For example, the length of the growing season, and thus leaf longevity tend to decrease from the tropics to boreal regions, resulting in higher leaf growth rates and higher P demands, particularly in the growing season, with increasing latitude [41,46]. Furthermore, soil P availability relative to N availability tends to increase with increasing latitude or from the humid to arid regions, resulting in decreasing leaf N:P ratios [10,31,32,47]. These trends help to explain why the numerical values of the N vs. P scaling exponent decline from the tropics to higher latitudes for each of the major plant functional groups.…”

Influence of aridity and salinity on plant nutrients scales up from species to community level in a desert ecosystem

“…Both nutrients are recycled via the decomposition of soil organic matter 17 . Although soil nutrients and microbiota are the main drivers of leaf nutrient concentrations 21, 22 , other soil properties and processes (for example, soil moisture and soil salt content) also determine the availability of nutrients to plants 23–25 . A recent study showed that variation in soil characteristics had more profound immediate effects on plant stoichiometry than did climate at the regional scale 26 .…”