UC Berkeley UC Berkeley Previously Published Works Title Interacting effects of pollination, water and nutrients on fruit tree performance. Permalink https://escholarship.org/uc/item/56k3s617 Journal Plant biology (Stuttgart, Germany), 17(1) ISSN 1435-8603 Authors Klein, A-M Hendrix, SD Clough, Y et al. Publication Date 2015 DOI 10.1111/plb.12180 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Plant Biology ISSN 1435-8603 RESEARCH PAPER Interacting effects of pollination, water and nutrients on fruit tree performance A.-M. Klein1,2, S. D. Hendrix3, Y. Clough4, A. Scofield5 & C. Kremen6 1 Institute of Earth and Environmental Sciences, University of Freiburg, Freiburg, Germany 2 Institute of Ecology, Leuphana University, Germany 3 Department of Biology, University of Iowa, Iowa City, USA 4 Agroecology, Georg-August University, Gottingen,€ Germany 5 Scofield Almond Farms, Dunnigan, CA, USA 6 Environmental Sciences Policy and Management, University of California, Berkeley, USA Keywords ABSTRACT Almond; foliage; fruit tree; leaf loss; plant resource limitation; pollination–resource Pollination is critical to fruit production, but the interactions of pollination with interactions; Prunus dulcis. plant resources on a plant’s reproductive and vegetative features are largely over- looked. We examined the influences of pollination, irrigation and fertilisation on the Correspondence performance of almond, Prunus dulcis, in northern California. We used a full-factorial A.-M. Klein, Chair of Nature Conservation design to test for the effects of pollination limitation on fruit production and foliage and Landscape Ecology variables of whole trees experiencing four resource treatments: (i) normal water and Institute of Earth and Environmental Sciences nutrients, (ii) reduced water, (iii) no nutrients, and (iv) reduced water and no nutri- University of Freiburg ents. In each of these combinations, we applied three pollination treatments: hand- Tennenbacher Straße 4, 79106 Freiburg, cross pollination, open-pollination and pollinator exclusion. Pollination strongly Germany. affected yield even under reduced water and no nutrient applications. Hand-cross pol- E-mail: [email protected]. lination resulted in over 50% fruit set with small kernels, while open-pollinated flow- de ers showed over 30% fruit set with moderate-sized kernels. Pollinator-excluded flowers had a maximum fruit set of 5%, with big and heavy kernels. Reduced water Editor interacted with the open- and hand-cross pollination treatments, reducing yield more N. Vereecken than in the pollinator exclusion treatment. The number of kernels negatively influ- enced the number of leaves, and reduced water and no nutrient applications inter- Received: 28 June 2013; Accepted: 5 February acted with the pollination treatments. Overall, our results indicate that the influences 2014 of pollination on fruit tree yield interact with the plant availability of nutrients and doi:10.1111/plb.12180 water and that excess pollination can reduce fruit quality and the production of leaves for photosynthesis. Such information is critical to understand how pollination influ- ences fruit tree performance. emphasis on the role of pollination in determining yield has INTRODUCTION been criticised on the basis that it does not account for possible There is strong evidence that the majority of wild and culti- post-pollination processes affecting the amount and quality of vated plant species benefit from or rely entirely on the trans- fruit maturation (Niesenbaum 1993; Bos et al. 2007; Ghazoul portation of pollen grains by bees, other insects, birds and 2007). For example, water and nutrient limitation can strongly mammals (Burd 1994; Klein et al. 2007; Ollerton et al. 2011). affect early fruit abortion (Pıas & Guitian 2006) and variation Furthermore, at the within-plant or whole plant scales, many in losses to pests and diseases may ultimately be more impor- crops exhibit decreased crop production in response to tant than pollination in determining realized yields (Brown & decreases in the number and types of pollinator (e.g. Ricketts McNeil 2006). Furthermore, the interactions between pollina- 2004; Klein 2009; Carvalheiro et al. 2010; Garibaldi et al. 2013), tion and post-pollination processes are rarely considered for and these results have been extrapolated to field and landscape wild plants (Bierzychudek 1981; Casper & Niesenbaum 1993; scales (Ricketts et al. 2004), as well as regional (Morandin & Niesenbaum 1993) and are almost unstudied in crop plants Winston 2006) and global scales (Klein et al. 2007; Garibaldi (Bos et al. 2007; but see Groeneveld et al. 2010). et al. 2013; Kennedy et al. 2013). In natural populations, polli- Given widespread concerns about colony losses of Apis mel- nation may also strongly limit reproduction, particularly in lifera L., a major crop pollinator worldwide (Neumann & Car- fragmented landscapes (Aquilar et al. 2006; Slagle & Hendrix reck 2010; Ellis 2012), as well as evidence for declines of other 2009). pollinators at landscape and regional scales (Potts et al. 2010), While pollination clearly affects reproductive yields of many a greater understanding of the importance of pollination pro- wild and crop plants (Klein et al. 2007; Ollerton et al. 2011), cesses for reproduction and yield is critically needed. the degree to which it regulates yield in real-world cropping To date, studies of pollination limitation in tree crops have systems is debated (Ghazoul 2007; Kremen et al. 2008). The examined only a subset of flowers per plant or invoke Plant Biology 17 (2015) 201–208 © 2014 German Botanical Society and The Royal Botanical Society of the Netherlands 201 Interaction of pollination and plant resources Klein, Hendrix, Clough, Scofield & Kremen pollinator limitation without supplementary hand-cross polli- Experimental site nation of the flowers (see studies cited in the review of Klein et al. 2007). Instead, yields should be analysed at the whole The experiment was carried out from January to August plant scale to avoid the confounding effects of resource alloca- 2008. The site was located in the Sacramento Valley, the tion among individual flowers or branches (Zimmerman & northern portion of California’s agriculturally intensive Cen- Pyke 1988; Knight et al. 2006; Wesselingh 2007). Thus, experi- tral Valley, in Colusa County, near the border with Yolo ments are needed that compare hand-pollinated yields to those County (122º201.925″W, 38º55019.372″N, World Geodetic Sys- in which pollinators are totally excluded (Kearns & Inouye tem 1984). Colusa County produces around 5% of Califor- 1993), with and without resource applications. Furthermore, nia’s marketable almonds. Precipitation in this area is low, high fruit yield may come at the expense of the trees’ vegetative with an annual amount of 268.7 mm (Lapham et al. 1907; performance, such as quantity of foliage. The indirect influ- WRCC 2010). Rainfall occurs primarily from October ences of pollination in combination with plant resource varia- through May, with a peak in January; no precipitation typi- tion on vegetative features of crops such as leaf quality and cally occurs from June to September. We selected young, pro- quantity is not yet investigated. ductive trees for this experiment, because kernel quantity and Commercial almond production is an excellent model sys- quality of the whole tree can be measured, and accumulated tem for testing effects of pollination on crop production and resources are limited in smaller trees (Morgan et al. 2006). foliage variables in different water and nutrient applications The 3.2-ha study site consisted of Nonpareil trees that were because results are likely to be applicable to many fruiting grafted onto peach rootstock [Prunus persica (L.) Batsch] in trees, such as apples, cherries, pears, peaches and plums, all 2005 and were planted in 2006 (third leaf planting). The trees with main varieties depending on insect pollination. Almond were approximately 1.75-m tall and had not been harvested trees are generally considered to be drought-tolerant (Torreci- prior to this study. The trees were planted 4-m apart within llas et al. 1996), but growers are highly dependent on irriga- rows and 6.4 m between rows. tion and nutrient inputs to produce high yields of top quality Several ‘polleniser’ varieties compatible with Nonpareil were (Castel & Fereres 1982; Micke 1996). Moreover, almond pro- available in surrounding orchards located 100–300 m away duction in California is highly dependent on honeybee man- from the experimental trees. These included a 16-year-old, 4.7- agement to set a commercial crop, but declines in honeybee ha orchard with Mission and Carrion varieties and a 13-year- colonies and an increase in production acreage have resulted old orchard with Nonpareil and Wood Colony. Honeybee in honeybees becoming a limiting resource for almond in the hives were placed in the orchards surrounding the experimen- USA (Thorp 1996; Kremen et al. 2008; Neumann & Carreck tal study site. The eight hives closest to the experimental trees 2010; Ellis 2012). Furthermore, California, as one of the larg- were 300–350 m away and were part of the commercial pollina- est irrigated agricultural areas in the world, is facing water tion management system used by the grower. Padre pollen was shortages, and almond growers may be forced to reduce their placed every second day at 10:00 and 14:00 h at the nest annual water use (Blake 2008). Almond was