Yield benefits of additional pollination to faba bean vary with cultivar, scale, yield parameter and experimental method

Abstract

The benefits of insect pollination to crop yield are used to justify management decisions across agricultural landscapes but current methods for assessing these benefits may underestimate the importance of context. We quantify how the effects of simulated insect pollination vary between five faba bean cultivars, and to what extent this changes between years, scales, yield parameters, and experimental methods. We do this by measuring responses to standardised hand pollination treatments in controlled experiments in flight cages and in the field. Pollination treatments generally improved yield, but in some cases yield was lower with additional pollination. Pollination dependence varied with cultivar, ranging from 58% (loss in yield mass per plant without pollination) in one cultivar, to a lower yield with pollination in another (−51%). Pollination dependence also varied between flight cage and field experiments (−10 to 37% in the same cultivar and year), year (4 to 33%; same cultivar and yield parameter), and yield parameter (−4 to 46%; same cultivar and year). This variability highlights that to be robust, assessments of pollination benefits need to focus upon marketable crop outputs at a whole-plant or larger scale while including and accounting for the effects of different years, sites, methodologies and cultivars.The contribution of insect pollinators to crop yield has been used to support conservation measures 1 , provide cost-effective agronomic advice 2 , and to support agricultural policies at a national level 3 . Globally, benefits of insect pollination to food production are estimated to be worth $235-577 billion per year 1 . This value is based upon estimates of the "pollinator dependence" of each crop; the proportion of harvestable yield that depends on animal mediated pollination, or how much yield is lost in absence of such pollination.Recent studies have begun to show that the pollinator dependence of a crop is not fixed and that it interacts with other biological factors (soil quality and predation by pests 4-6 ) or agronomic inputs (fertilizer, agrochemicals and water 7-11 ), see review 12 .Pollinator dependence can also vary with crop cultivar, for example in apples 13 and oilseed rape 14 . Understanding pollinator dependence on a per-cultivar basis could enable crop producers to secure production as pollination services become less predictable 15,16 following shifts in pollinator populations through time 17,18 . In the short term, producers in landscapes with low levels of semi-natural habitat and pollination service capacity 19 may benefit from use of low-dependent cultivars, though this needs to be considered alongside other agronomic attributes (e.g. yield potential, disease resistance).Quantifying variation in pollinator dependence between cultivars has rarely been the primary aim of experiments. Without standardised experimentation it is difficult to identify those cultivars with high or low pollination dependence; as above, each study that estimates the yield benefits of pollination does so...

Quantifying crop pollinator dependence and its heterogeneity using multi‐level meta‐analysis

“…Authors calculating the economic value of biotic pollination commonly account for differences between crop species (Aizen et al, 2009), but there is a clear need to consider differences within crop species (e.g. Bishop et al, 2020; Klatt et al, 2014) when placing economic values on pollination services and/or planning policies and agronomic management. Plant genotype is something that growers can control by choosing to grow a certain cultivar.…”

“…We only included publications in our meta‐analysis if they compared yield production between plants receiving a pollination treatment and plants that did not receive a pollination treatment. We only included publications that presented yield using at least one of four metrics most likely to correspond to economically relevant yield—yield mass, bean number, pod number or bean number per pod (Bishop et al, 2020). Several publications reported yield using other metrics that do not translate to economically relevant yield production, these were not included in the meta‐analysis but are summarised in Table .…”

Shortening the generation cycle in faba bean (Vicia faba) by application of cytokinin and cold stress to assist speed breeding

“…The level of autofertility, defined as the ability of a plant to set seed without disturbance of the flowers (Drayner, 1956), should be also taken into account when seed setting in faba bean is considered. Genetic diversity for autofertility has been reported in faba bean germplasm, and higher levels of autofertility were reported in hybrid faba bean plants (Bishop et al., 2020).…”

Scales matter: Maximising the effectiveness of interventions for pollinators and pollination

“…Effective local, national and international PES schemes have been developed for services such as water quality (Martin-Ortega et al 2013) and carbon capture (Balvanera et al 2012) but not for pollination at present. However, effective PES schemes typically require payments by results, which in the case of pollination requires dedicated methods of assessment (Garratt et al 2019) and can vary due to interactions between the plant and other growing conditions such as soil quality (Bishop et al 2020).…”