DOI: 10.5061/dryad.66t1g1k5f
title: Reduced seed set under water deficit is driven mainly by reduced flower numbers and not by changes in flower visitations and pollination

description: Water deficit can alter floral traits with cascading effects on
 flower-visitor interactions and plant fitness. Water stress induction can
 diminish productivity, directly resulting in lower flower production and
 consequently seed set. Changes in floral traits, such as floral scent or
 reward amount, may in turn alter pollinator visitations and behavior and
 consequently can reduce pollination services resulting in lower
 reproduction output. However, the relative contribution of this indirect
 in comparison to the direct effects of changes in seed set are not fully
 understood. We manipulated water availability using rain-out shelters in a
 field experiment and measured effects on floral scent bouquet, morphology,
 phenology, flower-visitor interactions, pollination, and seed set. Plant
 individuals of Sinapis arvensis (Brassicaceae) were randomly assigned to
 one of three treatments: mean precipitation (= control), reduced mean
 precipitation, or drought period treatment. Our results show that
 decreasing water availability lowers the number of flowers and seed set.
 This indicates a direct link between water stress and seed set, as seed
 mass increases with increasing flower number. The indirect link of water
 stress via floral traits, pollinator visits, and pollination has weaker
 effects on seed set. However, floral traits remain relatively stable under
 decreased water availability, whereas plant growth and flower abundance
 decrease, potentially in order to allow investment in more resources in
 fewer flowers to maintain pollination success. Thus, plants are able to
 compensate for water stress and can maintain floral trait expression, such
 as a stable scent emission and bouquet, to retain pollinator attraction.
 These findings indicate that the direct link from water stress to seed set
 has a stronger impact on plants' reproductive success than the
 indirect link through altered floral trait expression and pollinator
 visits in a generalist plant species.
description: - manipulation of water availability on wild mustard (Sinapis
 arvensis) using rain-out shelters - 3 treatments:
 well-watered, reduced watered, drought period; stem water potential was
 measured to conform plant's water stress and was used as the linear
 variable for further statistical analysis -
 "Foral_traits"-file: following parameters were measured once in three
 freshly open flowers per plant from a low, middle, and high position to
 avoid position and age effects: stamen, style, and calyx length, petal
 length and width, flower display size, and nectar volume. On two flowers
 per plant, we collected one anther each in order to count pollen grains by
 means of a microscope (after 3 weeks under treatment). For pollen and
 nectar collection, nearly open flowers were covered with mesh bags the day
 before collection in order to prevent access by flower visitors. The
 inflorescence size (greatest expansion) was measured once on five
 inflorescences per plant. Floral height (height of the highest flower) was
 measured weekly with a folding yardstick; means values were included in
 the data file and were used for statistical
 analyses - "Int_data"- file:
 plant-animal interactions were observed: each plant individual was
 observed daily; the number of visits by arthropods was recorded; the
 number of visits per day and per flower was calculated and used for
 further statistical analyses -
 "Scent_data"-filechemical (= floral scent) data were analyzed
 using a thermal desorption system coupled with a GC-MS; compounds were
 analyzed and identified using GCMSsolution package; compounds in flowers
 were compared with those found on blank controls; the amount of compounds
 was estimated by comparing peak areas with area of a standard (Octadecane
 C18); absolute compound amounts included in the data file
 - "Loggerdata"-file: raw data obtained from data
 loggers that were placed under each shelter; measured temperature and
 relative air humidity; one logger was placed next to the shelters and
 recorded temperature, relative air humidity, wind speed, photosynthetic
 active radiation PAR and air pressure -
 "Soil_humi_temp"-file: raw data of weekly measured soil humidity
 and soil temperature next to each plant individual using avolumetrix water
 content sensor (Hydrosense II, Campbell Scientific) and a simple
 thermometer (DET3R, Voltcraft) -
 "Plant_list"-file:  file with individual plant
 information
description: Data are saved in a common data exchange format ".csv."
 Statistical anlyses were made with open source software R
 studio.